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Hivisibility
05-05-2011, 12:19 PM
I have come to the conclusion I am more at home riding with them and find them better all round, wonder why this is so?

mickv
05-05-2011, 12:25 PM
I have come to the conclusion I am more at home riding with them and find them better all round, wonder why this is so?

I love the conventional Showas on my RMX. Beautifully plush! apparently the RM version was even better.

rabskyline
05-05-2011, 12:27 PM
are USD forks a gimick ?

rideo
05-05-2011, 12:40 PM
I love the ones on my xr4, i just wish they had 300mm of travel in them.

dwb79
05-05-2011, 01:33 PM
Conventional forks are great for trail riding.

On USD forks, when hitting a bump, the outer fork tube bends backwards just below the lower triple clamp. The inner fork bush then has to try and go around this corner and of course this then provides a resisitance to movement.

Conventional forks feel smoother because they dont have to deal with this. Instead the chrome tube, held in the triple clamps, bends just below the lower clamp. This does not effect the movement because the fork bushes dont travel up that far.

I love the conventional Showas on my RMX. Beautifully plush! apparently the RM version was even better.

The RM forks from the late 90's (97 & 98 I think) were conventionals so they were nice and smooth yet they were twin chambers. Many people have retro fitted these forks to many different bikes.

Nutty
05-05-2011, 03:55 PM
The RM forks from the late 90's (97 & 98 I think) were conventionals so they were nice and smooth yet they were twin chambers. Many people have retro fitted these forks to many different bikes.

Geez, you must be young Dave, by 1990 NO Jap mxers had conventional forks. Gee, Robbie had factory USDs on his KX80 in 1990!

I think the last Kwacka that had conventionals was the '89s. I know that the Americans got USDs on KXs a year after us. The last conventionals on KXs were either 48s or 50s and they were awesome, as were 50mm Magnums if you could stop them blowing seals. I like big conventionals with a fork brace, that makes them steer.

Tman
05-05-2011, 04:09 PM
I had conventional forks on my 99 KTM and when I bought the 05 I hated it!

It took me a while playing with the clickers and I reckon the standard spring rates on the conventional forks handled my weight better too.

I agree the conventional forks were plush and the issue of blowing seals well, wasnt an issue.

Didnt Old Mr Ballard fit a set to a WR250 off a TTR for comps a while back?

fetid_swamp
05-05-2011, 04:16 PM
have to check my old adbeez but along with the rmx didnt some ktm's swap back to conventionals for a year or two after having usd's? memory fading....

Nutty
05-05-2011, 04:25 PM
have to check my old adbeez but along with the rmx didnt some ktm's swap back to conventionals for a year or two after having usd's? memory fading....

The EXCs didn't, maybe with the EGSs or MXers Swampy, the SXs first had USD in '86 from memory, the year they also picked up a digital ignition and double discs.

brendo_83
05-05-2011, 04:34 PM
Geez, you must be young Dave, by 1990 NO Jap mxers had conventional forks. Gee, Robbie had factory USDs on his KX80 in 1990!

I think the last Kwacka that had conventionals was the '89s. I know that the Americans got USDs on KXs a year after us. The last conventionals on KXs were either 48s or 50s and they were awesome, as were 50mm Magnums if you could stop them blowing seals. I like big conventionals with a fork brace, that makes them steer.

I'm almost positive that the RM's switched back to conventional forks for a couple of years in the late 90's

Hivisibility
05-05-2011, 04:41 PM
Ok what preempted this was as DBW suggested, was the plushness of conventional forks in my dotage is unparrarelled by any upside downers I have yet tried.

My roadie has conventional, yet my previous 4 had upside downers, and yet it has the nicest most predictable front end with terrific feedback at all speeds and in all weather, compliant yet soaks up shoves in the road with aplomb and a surety my GSXR could only dream of.

This got me thinking why?

then I thought to my current YZ as oppossed to my older RMs... same thing from a riders perspective.

We'll be stuffed suspension is not my strong suit, so here we are....

OH and NP, I am almost positive the RM250s from maybe '96-98 went to conventional for a few markets... but could be wrong, might be oldtimers

robo67
05-05-2011, 04:41 PM
i will give Dave the benefit of doubt on this one as a slip of the mind or type error....

I would say 1998 was the last of the conventials for the RM and i reckon i am right...

see even i did it's something about the numbers


1988

Chewy
05-05-2011, 04:47 PM
Dwb is right there were a couple of years of RM with conventionals, 97 and 98

robo67
05-05-2011, 04:54 PM
Dwb is right there were a couple of years of RM with conventionals, 97 and 98
1997
http://p1.bikepics.com/pics/2010%5C01%5C18%5Cbikepics-1879772-800.jpg
1998
http://liveimages.bikesales.com.au/bikesales/general/content/gc5583908807792022306.jpg

OK EVERY ONE BACK ON TOPIC HIVIS WANTS ANSWERS
ps i reckon it was 96-97-98 conventials

Arj
05-05-2011, 05:01 PM
Mmm some 48 right side up forks wouldnt go astray me thinks.My 93 kdx200 forks were absolutly plush beyond belief ^nwrt

Simon_R
05-05-2011, 05:11 PM
a mate just put a set of late 90 conventional forks off a rm250 on his 2009ktm 200. I had a quick ride of it on the weekend and it was certaintly plusher at trail speed. It was too wet to really find out at higher speed around an enduro test.

He bought the whole front end including wheel and made up some sleeves to fit in the original ktm clamps.

Spac
05-05-2011, 05:15 PM
A set of good conventionals are better for most riders most of the time - they can flex more without binding, so the exact set-up matters less and they're less fatiguing.
Having said that, a fast guy punting hard will benefit from the extra rigidity of a set of USDs.

A bit of history:
KTM went to USDs in the mid 1980s (from 1983 on some models, IIRC) with 40mm WP 4054s. The tests of the day raved about their rigidity, but also overlooked a shocking midstroke spike that nobody seems able to tune out, even now. I assume the spike is a product of the lower legs flexing and binding in the bushes.

In 1989, the Japanese pretty universally went to 41mm USDs on the adult MX bikes. The exceptions were the CR125 (Showa 43mm), RM125 (KYB 46mm) and the US-market KXes (KYB 46mm). The CR forks are still a very good fork, even by modern standards. The 46s are an exceptionally good fork, even by modern standards.
The flip side is that those early jap USDs are among the worst forks ever made, even after revalving and respringing. The Showas on the 1990 and 91 CRs are genuinely appalling forks, and probably represent the worst forks ever fitted to a serious dirt bike since the 1970s...

Nonetheless, they perservered with the USDs, progressively increasing the lower tube diameter, while building more flex into the upper leg - all in an attempt to move the flex away from the bushes.

In the mid 1990s, the Marzocchi brought out the 45mm Magnum RWUs and they were easily the best performing fork available. This started a trend back toward RWUs, which included a few years of RMs, Huskies and KTMs.
Without exception, these last era of serious RWUs were the best performing production forks at the time, and had bike testers questioning why we'd embraced USDs in the first place.
AFAIK, the RM Showas were the first commonly available dual-chamber fork.

Since then, the pendulum has swung back to USDs. Notably, it took KTM several years to get their early '00s USD forks working anywhere near as well as the last of their 50mm "Extreme" RWUs.
I think USDs are here to stay, as the physical size required to get the desired stiffness pretty much mandates USDs. Add in the problem of big diameter forks blowing seals as was previously mentioned and its another nail in the RWU coffin.

So... What this all means is that lots of us see RWUs on soft-core bikes like TTRs and DRZs, and assume they're only suitable for soft-core bikes/riding. This is simply not true - as the Ballards TTR-fork onto WRF conversion demonstrates.

Von
05-05-2011, 05:52 PM
USD forks, like the PDS, are really a marketing decision not an engineering one.
Try selling a bike with RSU forks and watch the group think of the magazine journalists discredit the idea. I would like to see RSU or USD offered as options. Build your own bike, if you like.

Can I interest anyone in some near new 49mm DRZ400 forks ?

And the latest marketing exercise is closed chamber V open chamber. If it sells bike why not.

mickv
05-05-2011, 09:41 PM
1997
http://p1.bikepics.com/pics/2010%5C01%5C18%5Cbikepics-1879772-800.jpg
1998
http://liveimages.bikesales.com.au/bikesales/general/content/gc5583908807792022306.jpg

OK EVERY ONE BACK ON TOPIC HIVIS WANTS ANSWERS
ps i reckon it was 96-97-98 conventials

good god were they the worst pics of RMs you could find? WHAT HAVE YOU GOT AGAINST SUZUKIS!!!

http://i8.photobucket.com/albums/a26/MNM96/Picture478.jpg
http://i8.photobucket.com/albums/a26/MNM96/Picture479.jpg

from this (http://www.dirtbikeworld.net/forum/showthread.php?t=48504) thread

I also think your right about the yr models as the 96 was the first of the new model.

NSE.ONE
05-05-2011, 09:59 PM
Yep those RM/RMX forks were nice.
Also 97 Kato 360 ran conventional zokes. Damping in one leg and compression on the other.

robo67
05-05-2011, 10:14 PM
good god were they the worst pics of RMs you could find? WHAT HAVE YOU GOT AGAINST SUZUKIS!!!

I also think your right about the yr models as the 96 was the first of the new model.


yeah i didn't really give a shit what they looked like long as they had the right forks....


nothing against zuks

Mikey
05-05-2011, 10:52 PM
I always get annoyed at having to have USD forks coz I thought RSU's can be just as good for trail riding and don't blow fork seals.

But maybe as you say, RSU's can't get the stiffness without 'going big' and thus then being prone to doing fork seals themselves then that makes me feel a bit better.

No longer annoyed - thanks...

Spac
05-05-2011, 11:11 PM
The lack of stiffness is a big part of their goodness - at least for trail-riders.

WRT fork seal life, if you had a pair of RWUs and a pair of USDs in the same diameter, then the RWU's seals will last longer (assuming no design faults in either fork).

Nutty
06-05-2011, 12:07 AM
A set of good conventionals are better for most riders most of the time - they can flex more without binding, so the exact set-up matters less and they're less fatiguing.
Having said that, a fast guy punting hard will benefit from the extra rigidity of a set of USDs.

A bit of history:.....................etc


Good write up Nath, cheers.

I do remember the RMs going back now, I rode a RMX once with that fork. They were great to change fork seals, you could do it through the bottom of the fork without disassembly.

A lot of you blokes disagree but I wouldn't give two bob for a RWU fork. I am quite prepared to re-valve for a month to get rid of a mid-stroke spike rather than put up with flexy steering. I hate that. Climbing out of ruts etc.

I have a sneaky feeling that you lot are seeing the past through rose coloured glasses, if RWUs offered any tangible benefit, works bikes would have them.

No-one, from Enzo down, is experimenting with them. Trail hacks use them because of this ($$$$$), not for any engineering ideal.

Re: Ballard using them, Geoff could go that quick with the forks welded up, not a great indicator.

megsy
06-05-2011, 12:23 AM
Re: Ballard using them, Geoff could go that quick with the forks welded up, not a great indicator.


Apparently GB used the RWU forks at the SA round of the AORC's because of all the sand here in SA.

Ahh the only thing I like better on a bike more than RWU forks is snailcam chain adjusters, Should be on all bikes!:D


Cheers

Hivisibility
06-05-2011, 12:30 AM
I mean it's a different priority, but i recently rode a ducati M across the same road I ride my VTR everyday, same lines same speeds, the ducati, headshook and deflected like a bitch on the edge of the tar shoves that i pick my lines through to maintain corner speed. Yes I can feel more flex in my showas, but in this case I reckon it's a desirable to not transfer the hit to the frame (such as it is on the honda) and meanwhile the forks action on the showa is light years better in terms of little undulations.

Now i owned a 90 and a 91 CR250 and they WERE bad, nightmares in fact, would slam you around, but a mates ridgy didge RMX250 seems to be more comfortable than my KYBs even AFTER g2s and all that by Paul Baerick. althought to be fair i don't dare push the RMX like mine as it's owner is a fastidious and a good bloke whom I respect heaps. just your average trailspeed seems much nicer on little to medium stuff.

sounds like i need a new look at my KYBs......
but still on the roadies seems so much better

v8r
06-05-2011, 01:10 AM
Apparently GB used the RWU forks at the SA round of the AORC's because of all the sand here in SA.

Ahh the only thing I like better on a bike more than RWU forks is snailcam chain adjusters, Should be on all bikes!:D


Cheers

Good old ttr250, has both :)

mickv
06-05-2011, 10:06 AM
Good write up Nath, cheers.

I do remember the RMs going back now, I rode a RMX once with that fork. They were great to change fork seals, you could do it through the bottom of the fork without disassembly.

A lot of you blokes disagree but I wouldn't give two bob for a RWU fork. I am quite prepared to re-valve for a month to get rid of a mid-stroke spike rather than put up with flexy steering. I hate that. Climbing out of ruts etc.

I have a sneaky feeling that you lot are seeing the past through rose coloured glasses, if RWUs offered any tangible benefit, works bikes would have them.

No-one, from Enzo down, is experimenting with them. Trail hacks use them because of this ($$$$$), not for any engineering ideal.

Re: Ballard using them, Geoff could go that quick with the forks welded up, not a great indicator.

Perspective again? We're mostly trailriders not works bike riders. Obviously works riders need the rigidity of USD, trailriders not so much. Do you think if similar time and effort were put into RWUs that they have put into usds that we might have a better trailrider fork anyway? That is not taking into account money through sales perception (to the market) out of the equation, which is what i believe killed the RM RWU fork trial.

I'd say my Honda's forks are as good as my RMX's forks even though the CRF has been setup for a 70kgs rider and my RMX was setup for me at 90kgs. Having said that i don't push them all that hard.

mickv
06-05-2011, 10:07 AM
Ahh the only thing I like better on a bike more than RWU forks is snailcam chain adjusters, Should be on all bikes!:D


Cheers

yeah I'm not sure why they went to the complicated setup they have now, i friggen hate it.

Spac
06-05-2011, 10:41 AM
I don?t need rose colored glasses to remember the late 80s and early 90s - I'm still living there!
Seriously, my 88 KX125's forks are great (43mm cartridge Kayaba). I rate them well ahead of 95% of the current forks I've used, even though there are times where they're less precise. The same-age KDX forks that are on my KX5, and the forks on my 86 KX are vastly inferior - there was only a brief period when RWUs got the good technology.

Despite my ~95kgs, and not total novice status, I don?t appreciate the extra rigidity of USDs as much as I appreciate the extra compliance of a good set of RWUs.
I have no doubt that a pro level rider would say the opposite.

Ballard's speed on the TTR forks is one thing, but what's really significant is that he performed the conversion in the first place.

Nutty
06-05-2011, 03:09 PM
I mean it's a different priority, but i recently rode a ducati M across the same road I ride my VTR everyday, same lines same speeds, the ducati, headshook and deflected like a bitch on the edge of the tar shoves that i pick my lines through to maintain corner speed. Yes I can feel more flex in my showas, but in this case I reckon it's a desirable to not transfer the hit to the frame (such as it is on the honda) and meanwhile the forks action on the showa is light years better in terms of little undulations.


That comparison would really only be vaild if the same bike was used and the forks re-valved/swapped out. Having owned a VTR and ridden heaps of Ms from 400s up they are quite different chassis. BTW my VTR had USDs Bruce

Perspective again? We're mostly trailriders not works bike riders. Obviously works riders need the rigidity of USD, trailriders not so much. Do you think if similar time and effort were put into RWUs that they have put into usds that we might have a better trailrider fork anyway? That is not taking into account money through sales perception (to the market) out of the equation, which is what i believe killed the RM RWU fork trial.

Sure Mick, and the last RWUs had a superb action. I'm no pro rider just a mid-pace clubman, personal preference but I cant stand steering flex. I think the industry has come to the conclusion that the steering rigidity gains outweigh the slightly better action. Even with non-OEM super rigid triples, the latest USDs have a superb action. The marketing battle was fought long ago, now that RWUs have died out I don't think it's a factor.

I don't appreciate the extra rigidity of USDs as much as I appreciate the extra compliance of a good set of RWUs.
I have no doubt that a pro level rider would say the opposite.

Fair enough, there's a crossover point where the steering rigidity becomes the deal clincher then. I can fully appreciate that.

CentralCoastWaz
06-05-2011, 03:19 PM
The whole theory behind going to upside down forks in the first place is unsprung weight. Simple. It is THE reason, SFA to do with rigidity. It's technology that has filtered it's way down from development in all forms of motorsport. They turned the forks upside down to get the heavier part of the fork sprung. The lighter the mass which is unsprung (eg, wheel, caliper, disc, rim, hub) (eg, bouncing up and down with every rock/bump/rut/root) the better. Same reason GP teams went to a single sided swingarm. I think flex plays a role and the development of lighter stronger materials has changed development yet again allowing them to return back to a more rigid type swingarm without getting the weight....getting back to forks, it's all about the unsprung weight. To say that particular models had awesome "plush" cartridge type forks is correct but I'm not so sure it's got much to do with which way up they bolt the forks in the bike. It's the valving and oil weight/quantity. I had nice plush RMX's with RWU forks and I also had an RMX, about 92 from memory with USD forks and they where super plush as well. You can take any upside down fork and make it plush if that's what you want and vice versa with conventionals. Some enduro model manufacturers and teams went back to conventionals for reliability, getting the more sensitive component of the fork back up and out of harms way, not to go back to a plush fork.

CentralCoastWaz
06-05-2011, 03:28 PM
Ahh the only thing I like better on a bike more than RWU forks is snailcam chain adjusters, Should be on all bikes!:DCheers

I'm hearing that! My 99'RMX 250 had snail cams, grease nipples in all the suspension linkage and right way up forks. Great trailbike. I miss it....at times.

Spac
06-05-2011, 03:35 PM
Single sided swingarms were primarily about fast wheel swaps for endurance racers, with a bit of marketing thrown in. A double sided swing arm will always be stiffer and/or lighter than a single sided one (assuming comparable materials and design effort, of course).
Good engineering applied to a flawed concept can hide it quite well, but its still a flawed concept.

Back in the day, USDs were marketed as being about both rigidity and less unsprung weight.
The original Simons USDs in particular made real effort to minimise unsprung weight. But it became less and less of a marketing feature as the years went by.

bluerider
06-05-2011, 06:35 PM
Ballard went back to USD forks on his WR for one of the races this year, apparently he wished he hadnt and the TTR forks went back on.

The 45 Zoch Magnum's I was running at Finke each year on my 2-smoke's, then my WR400 were awesome, so compliant and great feed back in the high speed square edge stuff... gave you the kind of confidence to just pin it and not worry.

Would like to try them against the newer KYB SSS TC forks (setup for desert) on the YZ250 back to back with the Magnums and see if what i remember is still true. Got the 45 magnums still, just need the YZ250 to go with em ;)

Hivisibility
06-05-2011, 06:57 PM
That comparison would really only be vaild if the same bike was used and the forks re-valved/swapped out. Having owned a VTR and ridden heaps of Ms from 400s up they are quite different chassis. BTW my VTR had USDs Bruce



.

was that a swap or did you have an SP NP?

yes i agree it is only a really valid back to back with same bike etc, but I have got a little feel for what's going on underneath me, and while i did feel the rear of the M900 was a little soft, and the weight mass is hgher (along with rider position) there was really more of a deflection through the fork transmitted into the headstem, you can feel it at the bars.
I am not arguing that Conventional are suoerior in all ways, but just the conventional seem to inspire more confidence in me, mind you on a dirtbike i still ride the rear and brake turn so in many ways am coming to the conclusion my muslce memory movements on a bike and body english is still languishing back in the 80s, and i am who i am that way, so I'm gunna now wonder it a true full floater would feel as good to ME as my linkaged Yamaha, (anyone got a '82-86 Rm I could try spare?...;)

I suppose while i posted this in the tech section it is also an individual preference thing, I do find USDs lack a little feedback in comparison for ME, I like my tyres to stick and some of the stuff above them to flex...maybe that's it....

well i do ride in a loose drift style,, so maybe a loose bike beneath me is the key to reigniting my biking nirvana...

Von
06-05-2011, 07:28 PM
The 45 Zoch Magnum's I was running at Finke each year on my 2-smoke's, then my WR400 were awesome, so compliant and great feed back in the high speed square edge stuff... gave you the kind of confidence to just pin it and not worry.



I still have my set. I run them on the XR400. IMO best fork ever, but for some poor quality control in manufacturing. These came standard on the 410 husky a few years back. These forks made the XR forks look really bad.

Nutty
06-05-2011, 07:59 PM
The whole theory behind going to upside down forks in the first place is unsprung weight. Simple. It is THE reason, SFA to do with rigidity.

Sounds convincing Waz, except....on a USD, the heaviest part of any fork, the chromed steel slider is unsprung. Added to that, on OC Kayabas the cartridge is unsprung also. On a RWU fork the heaviest part of the fork is sprung. On both styles the spring is 50:50. I've been working on bikes for 30 years and can't recall a RWU with higher unsprung weight than a USD.

Now for rigidity, on a late series RWU the overlap between inner and outer slide metals is under 100mm at full extension, on a current USD it's over 200mm! Thats a fair rigidity gain right there. USDs were all about steering rigidity as I re-call......

was that a swap or did you have an SP NP?

Stock red 99 model with Staintunes and Ohlins F&R. The best road bike I ever had.

Hivisibility
06-05-2011, 08:08 PM
Stock red 99 model with Staintunes and Ohlins F&R. The best road bike I ever had.

'03 stock chassis, RWU 41mm showa.... agreed most fun and forgiving roadbike i have ever owned, not a manic hyped steriod mount, but a deceptively fast easy going girl with the heart of Pharlap.....

sure it was USDs on yours NP, some blokes swap them out, but AFAIK all VTR1000s were 41mm RWU.

Just to throw a bit of history, the first telescopic forks were usd.......

Nutty
06-05-2011, 08:21 PM
'03 stock chassis, RWU 41mm showa.... agreed most fun and forgiving roadbike i have ever owned, not a manic hyped steriod mount, but a deceptively fast easy going girl with the heart of Pharlap.....

sure it was USDs on yours NP, some blokes swap them out, but AFAIK all VTR1000s were 41mm RWU.

Just to throw a bit of history, the first telescopic forks were usd.......

Yep, the bike had Ohlins F&R in SP2 front triples. Josh Brookes located the bike for me, someone at Honda owned it. RED1 will probably know who owned it.

Bathy
07-05-2011, 08:54 AM
This thread reminds me of Qwerty.
Are you him Hivis?

Bushmechanic
07-05-2011, 10:47 AM
just weighed up some 48mm USD WPs

lower chromed leg 1.5kgs

upper alloy tube 1kg

Allwys thought the RWU forks had lower unsprung weight but needed to check, the axle lugs will add a bit but not 500gm per leg.

the OC forks have a higher unsprung weight than the Tcs becasue the entire catridge is bolted to the bottom of the fork in the OCs, the TCs have the cartridge "upside down" inside them

all things being equal RWU twin chambers should have the lowest unsprung weight.

I think there are so many variables you can't really say all USD's are better for XYZ and all RWU are better for other stuff, both can be made to work very well for whatever you want them to do,

if you had RWUs with 48mm chrome bits they should have very similar deflection / ridgidtity to 48mm USDs but without the binding

What i'd like to see are 52mm RWUps or USDS with nicasil plated aluminium tubes 4mm thick and outer tubes (usually alloy) with very thin anodised alloy for the wear surface wrapped in 4mm of Carbon fibre

Keg
07-05-2011, 11:03 AM
I bolted my forks RWU and now the wheel hits me in the face. Talk about deflection!

dwb79
07-05-2011, 12:11 PM
I bolted my forks RWU and now the wheel hits me in the face. Talk about deflection!

Ha !!!

You're all missing the most important feature of the right way up forks... Forget flex... forget longer lasting seals...

They turn better in ruts. Picture this. Your smashing along your favourite track and then you wash off some speed before pitching it into that big sweeping rut.

Just when you think you are running too hot and begin to push wide towards the big old gum tree... the massive underhang grabs the inside of the rut and pulls you back in tight keeping you in the rut and on your line.

It's just like having seperate hand brakes in a rally car!

dwb79
07-05-2011, 12:20 PM
all things being equal RWU twin chambers should have the lowest unsprung weight.

Another vote for the twin chamber, right way up forks on the late 90's Suzukis?

Geez, you must be young Dave, by 1990 NO Jap mxers had conventional forks. Gee, Robbie had factory USDs on his KX80 in 1990!

i will give Dave the benefit of doubt on this one as a slip of the mind or type error....


Cough, cough...sniff, sniff... I believe someone owes me an apology ;ug2

It could go like this
"David, we're awfully sorry. Please except our humble offering of endless rums as a gesture of our apology. We were wrong and you were right. We will never question you again...until next time you're wrong!"

Hivisibility
07-05-2011, 12:55 PM
This thread reminds me of Qwerty.
Are you him Hivis?

You know it Big fella, you know it.....^lol


nah I'm sick of bouncing, wanna float again...

oldboy
07-05-2011, 04:40 PM
You know it Big fella, you know it.....^lol


nah I'm sick of bouncing, wanna float again...

Hivis, the forks on my '99 wr400 and '01yz250wr were both crap,even after being resprung and revalved. However the forks on my '06 yz450f are pretty bloody good, in the bush,on the mx track,even at the dirt track goin sideways.And they are STOCK.
Maybe try a ride on a newer YZ. A set of the new CC Kayabas might be just the ticket for your YZ250wr.

Hivisibility
07-05-2011, 05:31 PM
Hivis, the forks on my '99 wr400 and '01yz250wr were both crap,even after being resprung and revalved. However the forks on my '06 yz450f are pretty bloody good, in the bush,on the mx track,even at the dirt track goin sideways.And they are STOCK.
Maybe try a ride on a newer YZ. A set of the new CC Kayabas might be just the ticket for your YZ250wr.

ta Oldboy, I have ridden a few YZs with the SSS KYBs, and they are indeed light years ahead at speed and when riding aggro, but am yet to try a set that has been revalves for the bush, I know the yanks do it all the time, so could be a goer.

bluerider
07-05-2011, 05:58 PM
ta Oldboy, I have ridden a few YZs with the SSS KYBs, and they are indeed light years ahead at speed and when riding aggro, but am yet to try a set that has been revalves for the bush, I know the yanks do it all the time, so could be a goer.

Ridden a Alloy frame YZ with the newer KYB SSS forks, revalved by frank Pons for the bush... very nice fork and bloody good in the rocks/roots/square edge for a TC fork on a 2-smoke. Prob be even better on the steel frame YZ :tick

Bushmechanic
07-05-2011, 06:11 PM
I bolted my forks RWU and now the wheel hits me in the face. Talk about deflection!

:D :cheers

the britten didn't even have forks, I reckon that would be worth a go too

ktm400
07-05-2011, 07:09 PM
I bolted my forks RWU and now the wheel hits me in the face. Talk about deflection!

LOL funny stuff..

Nutty
07-05-2011, 08:19 PM
Geez, you must be young Dave, by 1990 NO Jap mxers had conventional forks.
I think the last Kwacka that had conventionals was the '89s. I know that the Americans got USDs on KXs a year after us.

All that WAS correct, I just forgot about Suzuki's attempt to revive them...I'm old OK?

Cough, cough...sniff, sniff... I believe someone owes me an apology ;ug2

It could go like this
"David, we're awfully sorry. Please except our humble offering of endless rums as a gesture of our apology. We were wrong and you were right. We will never question you again...until next time you're wrong!"

"David, we're awfully sorry. Please except our humble offering of endless rums as a gesture of our apology. We were wrong and you were right. We will never question you again...until next time you're wrong!":D

Here's your endless rums, enjoy...:bourb:bourb:bourb:bourb

asa572
07-05-2011, 08:52 PM
The EXCs didn't, maybe with the EGSs or MXers Swampy, the SXs first had USD in '86 from memory, the year they also picked up a digital ignition and double discs.

Yes they did!

Bathy
07-05-2011, 09:06 PM
IMO USD's need to be on a perimeter frame.

what's the point of a more rigid fork if the frame can't hold it straight?

#39
07-05-2011, 09:35 PM
When I first did Finke in 2003, Stephen Greenfield bolted conventional forks, (Reiger, I think..) into his CRF450R.
He swore by them and said they handled much better for Finke than any USD's.

The RM's that went back to the conventional forks were reputed to handle better than any of the other brands with USD's, but succumbed to marketting pressure. It just isn't "cool" to run conventional forks.

Hivisibility
07-05-2011, 09:44 PM
:D :cheers

the britten didn't even have forks, I reckon that would be worth a go too

I'd sell my soul for a Britten V, I'd sell Rabs into white slavery for a ride on one.....

I reckon I'm gunna disagree on that one Bathy, there has to be some flex in the frame or cornering gets a it wild, and the perimeter frame with the direct line from steering to swingarm pivot has to be of a mterial that allows flex, however as some prototype bikes have shown, one of the better setups has very minimal frame, instead use the set of beefed up engine casings as the integral strength of the overall chassis.
Honda and yamaha have both made some bikes that have had too little flex, and apparently were dogs to ride.

bluerider
07-05-2011, 09:51 PM
When I first did Finke in 2003, Stephen Greenfield bolted conventional forks, (Reiger, I think..) into his CRF450R.
He swore by them and said they handled much better for Finke than any USD's.


They were Marzocchi Magnum 45's, same fork i used on my YZ's. Reiger was the popular shock of choice at the time, which i had a couple of... nice shock :tick

Those boys have got the right settings now for the newer stuff after alot of testing, but back in the late 90's/early 2000's, the Zoch magnum/reiger combo was the go.

Nutty
07-05-2011, 10:05 PM
Yes they did!

Do you have pics Asa? I recall the EXCs going straight from Magnums(1999) to WP USDs (2000) and never going back.

EDIT: Ooopps, my apologies Asa. The EGS/EXC did go to USDs in the late 80s and then went back to RWUs

That was back in the days when KTM was an enduro bike maker and made sure the off-roaders had the same technology as the MX bikes.
Something they need to look back on.......

Bathy
07-05-2011, 10:28 PM
I reckon I'm gunna disagree on that one Bathy, there has to be some flex in the frame or cornering gets a it wild, and the perimeter frame with the direct line from steering to swingarm pivot has to be of a mterial that allows flex, however as some prototype bikes have shown, one of the better setups has very minimal frame, instead use the set of beefed up engine casings as the integral strength of the overall chassis.
Honda and yamaha have both made some bikes that have had too little flex, and apparently were dogs to ride.

You can disagree all you like Hivis,

single backbone frames have too much flex. period.

if i ride a bike and feel the frame twisting and/or flexing,

then stiffer/stronger forks aren't going to help make the steering any more precise :D

BTW I wasn't suggesting a 100% rigid frame,
I know better than to question the millions of $$$ being spent in R&D on chassis design and dyanmics ^lol

Hivisibility
08-05-2011, 12:34 AM
You can disagree all you like Hivis,

single backbone frames have too much flex. period.

if i ride a bike and feel the frame twisting and/or flexing,

then stiffer/stronger forks aren't going to help make the steering any more precise :D

BTW I wasn't suggesting a 100% rigid frame,
I know better than to question the millions of $$$ being spent in R&D on chassis design and dyanmics ^lol

Ok gotchya now Bathy, same tact different words, agreed.

I am a particular fan on roadies of a minimalist frame setup, frame can be used to mount steering head to engine, would like to see similar setup tried on dirtbike..

Funnily enough it was the boutique frame makers who did perimeter frames first and straightlined the pivot areas, then the big blokes took note..
And Yamaha was first to mass produce across the roadbike range, but Zook amd Kwaka did it early on the dirtbikes, and zook has traditionally been the overall handling kings..

Nutty
08-05-2011, 07:26 AM
You can disagree all you like Hivis, single backbone frames have too much flex. Period.

If I ride a bike and feel the frame twisting and/or flexing, then stiffer/stronger forks aren't going to help make the steering any more precise :D

BTW I wasn't suggesting a 100% rigid frame,
I know better than to question the millions of $$$ being spent in R&D on chassis design and dyanmics ^lol

Ok gotchya now Bathy, same tact different words, agreed.

I am a particular fan on roadies of a minimalist frame setup, frame can be used to mount steering head to engine, would like to see similar setup tried on dirtbike.

You two blokes are both correct!

Head set flex which alters rake angle is best to be totally eliminated, as Bathy says. Bruce is correct in that the factories actually build lateral flex into a chassis.

Compare the first alloy CR (97 250) to todays CRF, todays perimeter rails are 1/3 the size. Lateral flex increases cornering grip.

You blokes will remember how the first alloy perimeter frame 500GP bikes used to flex OK then violently unload like a spring coming out of a corner. The problem wasn't the flex, it was the rate of the 'elastic return' as chassis builders call it.

Think of a modern Ducati trellis frame, there's nothing to it laterally, but it looks like the Harbour Bridge, longitudinally.

The original discussion was about fork flex, namely the axle staying parallel to the handlebar, both of which are independent to, and not affected by, chassis flex. It's this steering flex that USDs cure as riders want the wheel to go where the bar is pointing.

p.s. Does anyone remember the 'gull wing' bottom triples that were brought in to give RWUs more overlap and thereby improve steering rigidity?

Bushmechanic
08-05-2011, 11:16 AM
the perimiter frame design is heavier than the single spar upper so there had better be something good about it!

from playing with my frames more stiffer = more better in all directions but you do have to valve to suit

it is easier and much lighter to make a single spar upper stiffer for steering head flex but the torsional and lateral stiffness is higher with the perimiter design

IMHO going from one to the other (same forks) it feels like the perimiter design steers more precisely, stiffening further makes it even more precise, the main difference is the torsional stiffness

Hivisibility
08-05-2011, 12:12 PM
the perimiter frame design is heavier than the single spar upper so there had better be something good about it!

from playing with my frames more stiffer = more better in all directions but you do have to valve to suit

it is easier and much lighter to make a single spar upper stiffer for steering head flex but the torsional and lateral stiffness is higher with the perimiter design

IMHO going from one to the other (same forks) it feels like the perimiter design steers more precisely, stiffening further makes it even more precise, the main difference is the torsional stiffness

Bushy I've always meant to ask you, your mods to the frames is it specifcally for sandy riding?
IE: the terrian is soft so the bike can be hard?

NP I've never seen any "gullwing" triples personally, but i will goggle them so I can google some.

Edit: Ok googled have seen them heaps of times on various roadbikes, in fact my RZs had them.. just hadn't given them a name....

Bushmechanic
09-05-2011, 10:27 AM
yes most of my riding is in deep soft sand. there are limestone rocky sections and roots hidden in the sand that really define what im on about. you can't see all of them so you can't prepare for the impact or choose a path based on what you see so a lot of the time you get caught out by a sudden heap of sharp unpredictable impacts

I find if the chassis flexes more it becomes unsettled by the rocks/roots more because the returning flex is undamped and uncontrolled

its easy to say the alloy chonda built back in the 90s was too stiff but how do we really know? we can't unless someone takes a grinder to one and makes the frame flex more

the thing is if you change things other than the frame stiffness like the weight distribution or the cog position or the rake angle or the amount of trail or the geometric progression of the shock geometry you change the percieved stiffness of the whole bike.. without changing the stiffness of the frame at all, it does play a part but it is a very small part of the whole picture and stiffer = more predictable and not nescesarily harsh.... provided the boingers are set up to suit.

something on flex related to this topic :D ... if you rake out the forks more the forks tubes have to flex more, the older bikes with RWUs mostly had more rake than the bikes of today more rake = more deflection.

Nutty
09-05-2011, 12:39 PM
its easy to say the alloy honda built back in the 90s was too stiff but how do we really know?

The subsequent 15 years have seen the Honda side spars decrease in section volume by at least half, every pro tester of the day said they were too stiff, Service Honda found they were too stiff to work with a 500 2T motor and went to the 250F chassis. Numerous tests were done at the time and from then on, alloy frames were modified to give them steel frame like flex characteristics. Pretty much a given that I'm prepared to accept.

If you rake out the forks more the forks tubes have to flex more, the older bikes with RWUs mostly had more rake than the bikes of today more rake = more deflection.

As rake angle comes back closer to zero, tube flex increases, same as when you rake it out. Obviously, there is a point of minimum outer tube flex within chassis design. This is why rake adjustments to chassis over the alloy frame years only ever amount to 1/2 degree here and there.

Spac
09-05-2011, 01:09 PM
Kawasaki was the main advocate of the gullwing lower triples. Oddly enough, they also tended to have more fork leg hanging below the axle than other brands.

KTM... WP USDs as an option from 1983. Then a few years of either/or, depending on what Bert Flood got out of the factory.
Generally speaking, Enduro bikes had Marzocchi RWUs while MXers had USD White Powers. The rare MXC (enduro/MX hybrid like a Husky XC or TXC) had RWU 'Zokis.

By 1987, all models coming to Australia had the WP USDs. These were progressively updated (2-way adjustment, different upper legs, etc) until they were replaced by the RWUs in 1996.
I think that in the second half of the 90s, they used 45mm Marzocchi, 50mm Marzocchi and 50mm WP, depending on the year, and model of bike.
Until some time in the 90s, the enduro bikes were called "GS" (Gelandar Sport - just like Maico- but I'm sure my spelling is wrong), and the motocross bikes were MX, rather than SX.

Yes, I am a pedant. :)

Bushmechanic
09-05-2011, 04:07 PM
The subsequent 15 years have seen the Honda side spars decrease in section volume by at least half, every pro tester of the day said they were too stiff, Service Honda found they were too stiff to work with a 500 2T motor and went to the 250F chassis. Numerous tests were done at the time and from then on, alloy frames were modified to give them steel frame like flex characteristics. Pretty much a given that I'm prepared to accept.



As rake angle comes back closer to zero, tube flex increases, same as when you rake it out. Obviously, there is a point of minimum outer tube flex within chassis design. This is why rake adjustments to chassis over the alloy frame years only ever amount to 1/2 degree here and there.

depends if you're braking or not? when I change the rake on my frame to steeper, the bike flexes less as a whole system, a more raked out design has more leverage over the steering head and fork tubes becasue the front wheel is further away from the steering head. so the more raked out the bike the stiffer the frame needs to be.

as you know Nutty a material can only take a certain amount of cycles at a given deflection before it fails from fatigue, people like Tom and I who make stuff every day cant see why people place so much importance on flex, a frame simply cannot flex more than a few % at any given point or it will fail early, if it flexes too much it creates other issues with handling. IMHO if a bike is harsh you just need to valve it properly not blame the frame, but each to their own the day i find out im wrong and have made my frames too stiff I'll bring this thread back up and let you know :cheers

an interesting story about fatigue Airbus had to reject a proposal by the japs to use the new 380 as an island hopping comuter fitted out with standing room only cubicles simply beacause the fatigue life of the plane is designed with long haul flights in mind, it can take a lot of cycles at a small deflection (flying) but the landing/takeoff loading and deflection shortens the life so much the plane would be stuffed after a few months.

Nutty
09-05-2011, 04:47 PM
depends if you're braking or not? when I change the rake on my frame to steeper, the bike flexes less as a whole system, a more raked out design has more leverage over the steering head and fork tubes becasue the front wheel is further away from the steering head. so the more raked out the bike the stiffer the frame needs to be..

Both correct in theory. :tick

With dynamic deflection there is a sweet spot, with static loads, as you say, rake angle increases headset deflection. The primary reason KTM give for not having gone to alloy frames is that they cant build the appropriate flex into the frames for the same weight.

Re: V8 supercars (and Tommy might elaborate here) there is a constant engineering aim of removing all chassis flex so that 100% of the vehicle set-up is down to the suspension. BUT, whenever it rains, (i.e. the grip level becomes unpredictable and variable) the older, more flexible chassis come into their own and often win.

I don't pretend to be an expert re: motorcycle chassis design but everything I've read talks about engineering controlled flex into a chassis.
Specifically, damping loads put into a chassis unload with almost no losses, damping loads put into suspension create losses i.e. heat. The bike that creates less heat can put more energy into going faster. If you Google 'lateral suspension' it should come up. That's the topic name it's under in the trade course.

Spac
09-05-2011, 07:16 PM
Anyone who has ridden a 97 CR250 understands why flex is good.
Apparently the early VORs ride beautifully because they have flex built in.
This is the same debate that was had in the MTB world over a decade ago. For a hundred years, road cyclists worshipped stiffness as it transmitted more of the rider's relatively meagre power output into toward motion. This approach was maintained in the early years of MTBs, until everyone worked out that some flex made you faster on the dirt.
The advent of full suspension MTBs changed the parameters, but only after the point about rigidity had been made.

I agree with KTM's approach. Aluminium dirt bike and MTB frames are about ease of manufacturing and marketing.

Tom68
09-05-2011, 09:26 PM
I want to ride a '97 CR250.

Spac
09-05-2011, 09:33 PM
No you don?t. ^lol

Tom68
09-05-2011, 09:58 PM
No you don?t. ^lol

I can't feel the 37mm forks flex on my XR, I can feel suspension that's undersprung or overdamped, steering rake and trail don't concern me, it's just a different feel, although headshake isn't a nice feeling.

I do like to go fast on bikes that aren't supposed to be any good (perspective, I am a trail hack) so a '97 Honda does appeal.

Gear box ratios, bottoming resistance, seat height and cost are my main criteria.

Spac
09-05-2011, 10:56 PM
Yeah... let us know how you go with that...:laughing-

I get what you mean, but I still reckon you'll be unimpressed. They're fundamentally good bikes with a strong motor and good brakes and all the rest (as you'd expect of a MXer of the age), but they're just like riding a piece of railway track.
Remember that they were the bikes that got McGrath off Hondas...

Bushmechanic
10-05-2011, 04:04 PM
Hey Nutty Im no expert on frames either, all I know is so far with my stuff the stiffer the better. what ive noted isn't theory but 100% real world testing and I'm not doing it to sell bikes

a perimiter frame by design is stiffer than a single spar upper, laterally and in torsion then the factories add cylinder head stays and those horseshoe stays around the front of the engine to make it even stiffer again so I think they've found the same thing as me in general.

I couldn't be bothered to FEA my frame Vs a "new" alloy frame but the new alloy frames bolted up with the cylinder head stays and the horseshoes between the radiators may well actually be stiffer than mine.

I want to ride a '97 CR250.

I have, IMHO the boingers and the head angle suck

if you took the shock and forks of the 97 cr250 and put them on a "modern" 2012 alloy frame then changed the geometry to be the same as the 97 frame it will still suck.

im not saying the flex isn't deliberate just that its overall effect is very very overrated. factories can use it as a marketing tool becasue it is the one part of a bike that 99% of riders will never ever experiment with.

everyone can do an experiment, if you have them remove the head stays from the bike and see what happens

Interestingly regarding the "new" ktm frames that are supposed to have more flex, there are a lot of posts on KTM talk recently about people with the old RFS frames re-welding and stiffening the steering head and upper spar and also machining the cylinder head to add a head stay.