Steering Geometry .... Has anyone tried this one yet!



45 replies to this topic
  • WR400_Jay

Posted June 15, 2000 - 03:55 PM

#21

Motogreg thanks for the steering geometry lesson. I have a much better understanding of what is going on now. If I were to use the Scotts clamps or make my own do you think, since the 00' WR has already been moved 5mm, that the extra 5mm would be over kill. The bike is super stable and I don't think a twichy front end is going to be a problem. I'm wondering what would be best. I still ride about 30-40% motocross :) with the bike and don't want to be switching clamps alot. Thanks for the info guys

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00'WR400 75'Yamaha 250 enduro
White e-Series S-bend 12 discs, Yz timed, rejetted to Clark specs, throttle stop cut, lid removed, Topar Racing top clamp, Tag Metals T2 bars, Scotts damper, Devol disc guard and frame guards, lights removed, Cr routed Fastline brakeline, Acerbis Rally pro hand guards fastened to the top clamp, Gel grips Live in Southwest Ohio

  • mcarp

Posted June 15, 2000 - 05:29 PM

#22

Hey Jay, that DR seemed to turned pretty well. :)

Seriously, I thought your bike already turned really well for a WR. I did notice your handlebars seem exceptionally narrow (maybe 30-31"?) and needed more physical input than mine at 31.5", yet that input produces quicker steering, or at least it felt that way in the short amount of time I rode it. (Jay has YZ timing, I have WR-same '00 and tank). What about a little wider bars for more leverage (or will that throw off the ergos?) :D. Did you think my bike felt weird with wider bars? And do you agree the input feels harder on your WR, yet that input produces better results? Of course that pesky DR may have thrown me off for the day,
Have you shortened the chain yet? What about running small amts of fuel to keep the forward momentum down? That only works on the track, though. :D

BTW, your bike rocked, I think YZ timing is going to be in my near future.

  • Taffy

Posted June 24, 2000 - 01:53 PM

#23

Jay, i think your WR2000 would handle really well the only difference you would find would be a bike that gets slightly more out of line under hard braking & oddly enough under hard acceleration.

in & out the corners it should be a better bike. i feel the word we're looking for here is optimum...

the optimum wheelbase is probably 1-2" inches shorter-especially on the tighter stuff. up to this optimum point you will gain by having a more nimble bike.

at the end of the day how hard are you riding it to justify spending this money?

all the equipment & goodies i get for my bike is transferrable to the 2000 & now more especially the 2001WR now that i've seen the basic spec of it.

your 5mm less offset scotts triple clamps will allow you to get the bars right forward, improving your cornering, you've also saved on not buying the adjusters to make your pro tapers fit. you can also put the bike back to standard at the end & flog them. if it were unstable-your all set up for the damper! (correct spelling)

Bargain!

  • WR400_Jay

Posted June 25, 2000 - 05:00 PM

#24

Taffy do you think shortening the wheelbase would achieve almost the same effect. I'm still running the stock 14/50 gearing. I'm going make the taller bar saddles this week to raise the bars up so I can raise the forks tubes this week.

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00'WR400 75'Yamaha 250 enduro
White e-Series S-bend 12 discs, Yz timed, rejetted to Clark specs, throttle stop cut, lid removed, Topar Racing top clamp, Tag Metals T2 bars, Scotts damper, Devol disc guard and frame guards, lights removed, Cr routed Fastline brakeline, Acerbis Rally pro hand guards fastened to the top clamp, Gel grips Live in Southwest Ohio

  • Taffy

Posted June 26, 2000 - 03:51 AM

#25

jay. let's just get the offset thing sorted in our minds first. sit on your bike & look at your triple clamps. if you draw a line straight across the middle of the top of the fork adjuster screws & then drew a parallel line that passed through the post hole where your tank breather pipe goes down you will find that this is a gap i call the offset.

yamaha, as i understand it, only makes this one offset set of TC's on any model so far. scotts made a set where the fork holes were machined 5mm nearer you the rider thus reducing the offset by 5mm & of course, as an aside, the wheelbase by the same amount.

i don't believe you should look any further than these mods. you can raise the forks if you need to after all this has been done.

other posts in the past have said how good the scotts TC's are. i can't see how you are going to enter the unstable zone doing this & now i notice you've got the damper already well.....!!!

moving the forks around in the clamps is a cheap (free) & simple mod that anyone can try. buying the right goodies is the way to go. Jay, looking at the goodies on your bike (lucky git!) you can afford it.

maybe given some of this info someone else could put their ten pence worth in?

has anyone taken their scotts TC's from their old 98 or 99 model & tried them on this years?

  • WR400_Jay

Posted June 26, 2000 - 02:12 PM

#26

Taffy I have a pretty good understanding now and I'm going make taller bar risers so I can raise the fork tubes this week. I'll do the adjustments and let you know how much better it gets this weekend. I'm still curious how well the Scotts clamps work on a 00' WR4. I might make a custom set :) if I'm not happy how it turns. I'll let you know. Thanks! :D

------------------
00'WR400 75'Yamaha 250 enduro
White e-Series S-bend 12 discs, Yz timed, rejetted to Clark specs, throttle stop cut, lid removed, Topar Racing top clamp, Tag Metals T2 bars, Scotts damper, Devol disc guard and frame guards, lights removed, Cr routed Fastline brakeline, Acerbis Rally pro hand guards fastened to the top clamp, Gel grips Live in Southwest Ohio

  • MotoGreg

Posted June 26, 2000 - 05:28 PM

#27

jay. let's just get the offset thing sorted in our minds first. sit on your bike & look at your triple clamps. if you draw a line straight across the middle of the top of the fork adjuster screws & then drew a parallel line that passed through the post hole where your tank breather pipe goes down you will find that this is a gap i call the offset.
yamaha, as i understand it, only makes this one offset set of TC's on any model so far. scotts made a set where the fork holes were machined 5mm nearer you the rider thus reducing the offset by 5mm & of course, as an aside, the wheelbase by the same amount


Ya, that's a good easy way to explain it. One thing though, while yes shortening the wheelbase 5mm will help slighty, that's just a side benefit, the changing of the trail is the big benefit. Also, I wouldn't try it on the '00, you may be pushing it too far. Also to clarify earlier when I said I run my forks 13mm up... That is 13mm to the top edge of the fork cap, or 10mm to the top of the actual fork tube itself. Any higher than that and I started to get a front end tucking and rear end loss of traction while hard on the gas coming out of tight MX corners.


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'99 WR400
'92 GSXR 7/11
Visit my photo album AT YOUR OWN RISK!! My photo album
Anyone here a sportbike fan also? Then visit us here at www.insanespeed.com

  • Ken

Posted June 26, 2000 - 06:49 PM

#28

MotoGreg:

I thought your explaination of rake angle and trail was very good, however I do have one question. I think I understood you to say that the result was an increase in the distance between the line through the steering head and a vertical line through the front wheel axle. If this is true, that is an increase in the trail measuremnet, right? I was under the opinion that an increase in trail resulted in a slower steering response.

Ken

  • MotoGreg

Posted June 26, 2000 - 09:53 PM

#29

Ken,

Less offset = more trail = quicker steering. Less trail makes the front wheel more self centering and stable.

Don't ask me how it works, it's too confusing, but if you want to see a pic, go here and scroll down a little.

------------------
'99 WR400
'92 GSXR 7/11
Visit my photo album AT YOUR OWN RISK!! My photo album
Anyone here a sportbike fan also? Then visit us here at www.insanespeed.com

  • WR400_Jay

Posted June 27, 2000 - 04:28 PM

#30

Motogreg thanks for the cool link. I marked the link and copied it to my tech file.

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  • Ken

Posted June 27, 2000 - 04:55 PM

#31

MotoGreg,

I agree right up to the point that more trail = quicker steering.

Check out:
http://www.activebik...spot/gspot.html

about the 6th paragraph down
http://www.kennedysc...r.com/rake.html
http://www.ctv.es/US...nce/BALANCE.htm

If I understand correctly, more trail = slower steering response. Maybe Scott's improvement is coming from shortened wheel base? If nothing else, the third link has some really good tech info. Back one page in that site, it's got another menu with more.

Ken

  • MotoGreg

Posted June 27, 2000 - 07:57 PM

#32

Ken,

Ok, now I'm really confused. One of your links clearly says more trail = more stable. I talked to two friends just now, one a roadracer and the other a flat track racer and they both said the opposite was true, just like I always thought was true. Also, remember when you were a kid and you turned your handlebars/forks around backwards on your bmx bike so that it put the front wheel back a lot further how twitchy it made it?

Now you've got me thinking more about it and what the actual changes are. If Yamaha just pulled the headtube back in relation to the rest of the frame then they just shortened the wheelbase 5mm and didn't change the trail at all. Scotts claims that their clamps "duplicate Yamaha's change to the '00 model". Well the Scotts clamps change the wheelbase 5mm but also change the trail a lot which is something that Yamaha DID NOT change by moving the head tube. I was checking out some adjustable clamps for streetbikes and found that 1mm-5mm is the range, so that means that 5mm is the maximum adjustment which seems like it would make a HUGE difference. So what's the deal, did Scott's just think about moving the wheelbase 5mm shorter and not even realise that in the process they made such a big change to the trail? Is it the way I thought it was and the more trail they created made it more nimble like they were trying to acheive? Is it the way your link suggests (more trail=more stable) and in the process of trying to duplicate Yamaha's '00 change (more nimble) they actually made it a lot slower/heavier steering? Now I'm so confused I don't know which way is up :)

To me, 5mm of wheelbase is a very small change. I shortened mine 16mm by removing one chain link and it didn't cost me a dime let alone $350 for clamps. You could change the wheelbase 5mm by just adding a couple of teeth to the rear sprocket! By changing the fork offset 5mm Scotts did a lot more than just shorten the wheelbase, they changed the trail drastically. Did they plan this? Did they just think they would change the wheelbase and not even realise what they were doing to the trail? And the main question at this point.. did their increase in trail make it more stable/heavy steering or quicker/more nimble steering???

------------------
'99 WR400
'92 GSXR 7/11
Visit my photo album AT YOUR OWN RISK!! My photo album
Anyone here a sportbike fan also? Then visit us here at www.insanespeed.com

  • Taffy

Posted June 27, 2000 - 10:21 PM

#33

this is fun!

scotts knew exactly what they were doing. you ask the right questions you'll get a straight answer-first rule of racing/tuning. to my mind the bike is a tad too long & yes changing the TC's isn't the way to do it. shortening the frame is. but seeing's how were not changing the frame l-a-d-s are w-e lets look at the other improvements we can make.

changing your TC's will help you as you drop into a corner, the wheel won't tuck under as much, you won't have to push/ pull the bars so hard. the loss for this gain is a slightly naughty bike on flat out climbs, braking & hard second gear acceleration. it's a trade off. deal with A & see what happens, you have a steering damper already.

but troops, this is a web site, someone somewhere has got a set of scotts (5mm less offset TC's) & tried them on this years bike. who is he? step forward that man & tell us.

  • WR400_Jay

Posted June 28, 2000 - 03:12 PM

#34

Hey Taffy do you do any road racing?

------------------
00'WR400 75'Yamaha 250 enduro
White e-Series S-bend 12 discs, Yz timed, rejetted to Clark specs, throttle stop cut, lid removed, Topar Racing top clamp, Tag Metals T2 bars, Scotts damper, Devol disc guard and frame guards, lights removed, Cr routed Fastline brakeline, Acerbis Rally pro hand guards fastened to the top clamp, Gel grips Live in Southwest Ohio

  • MotoGreg

Posted June 28, 2000 - 04:03 PM

#35

Taffy, you are saying that the loss of offset, that gives us more trail makes the bike quicker steering with a little headshake on acceleration? That is what I've been thinking all along however the new evidence that Ken provided says that more trail gives you more stability with heavier steering. According to Ken's chassis links we need more offset, not less...

------------------
'99 WR400
'92 GSXR 7/11
Visit my photo album AT YOUR OWN RISK!! My photo album
Anyone here a sportbike fan also? Then visit us here at www.insanespeed.com

  • Taffy

Posted June 28, 2000 - 09:52 PM

#36

yes i was a road racer- for 13 years & i was always flat broke, so i did all my own tuning & preparation. Ducati Pantah F2 in a harris (eventually), i've somehow accumalated 4/5 dukes & loads of chassis'. i was always sorting problems for the TT circuit & Ireland.

if anyone can remember the early Pantahs they had a kicked out 30% head angle & a huge 35mm offset. we couldn't change the head angle but we could put 900ss yokes on with about 25mm & it made a reasonable difference. where? it didn't flop into corners & slow switchbacks became easier.

i have deliberately only mentioned offset & how it would feel, surely that's the bottom line? & roadracers don't have a front spindle 1" infront of the forks either!

here's one i hope will make us all smile. the reason that streetbikes don't have more than 5mm of adjustment in the adjustable clamps is coz you'd trap your thumbs against the tank!!!

now looking at your questions. i shall call it head angle coz that's what i was brought up on.

kicked out head angle (Hardly's)=stable in a straight line,usually accompanied by large offset-why not, we're not going anywhere in a hurry are we! notice how they flop from lock to lock at standstill-they almost fall, imagine that at slow speed in the car park.

speedway bikes=steep headangle unstable in a straight line,usually next to no offset for instant cornering adjustments.

trail/head angle (for these purposes-no offset headraces or TC's please)is generally straight line & bump stability & offset is coming into & out of corners. if i remember rightly our problem was in the corners.

why did i say previously "slight loss of straight line stability"-we'll if nothing else, to cover myself. the 5mm increase in trail is bearly noticeable as a %. now look at the 5mm you've taken from your clamps (ala scotts)-big % change. knocking 5mm off a 57" wheelbase won't make any difference to straightline stability- look at 5mm as a % of 57"!!!

thats why two of us have used the words "as an aside"

so you see head angle & offset are different & affect you in different area's. in this case we can make an impact in one area & barely touch the other. as my other posts indicate though, quick = twitchy-so can you cope? well yes if you have a scotts damper!

  • Taffy

Posted June 29, 2000 - 03:27 AM

#37

looking at previous posts & to clear a point up.

Motogreg you nearly had the whole picture in your last post & only whatever is on ken's site has rocked your boat.

trail is changed (lets say in this case shortened) two ways. the first is by steepening the head angle this makes the bike twitchy etc etc.ala speedway.

the second is by increasing the offset which this time makes it a little more stable! so you see talking about trail is both twitchy & stable. look at the head angle as the the dollars & the offset as the dimes, huge differences at the headstock-little changes at the offset.

now my bottom line. yes folks we're paid by the word!

john, matt & clark have said quite catagorically on this page that the scotts short TC's work. the difference between their bike & yours with the SSTC's fitted would be the shorter 5mm of wheelbase (Y2K model). in clarkes case because he has the back wheel wedged so far forward they are probably the same wheelbase.

the difference therefore comes down to 1/2-1pc difference in weight distribution. nothing is it. so, who's putting the SSTC's on this years?

[This message has been edited by Taffy (edited 06-29-2000).]

  • MotoGreg

Posted June 29, 2000 - 08:00 AM

#38

Man Taffy I sure do have a hard time following your posts.. Sounds like you have experimented with some stuff but you have a hard time putting that into writting that I can follow. You agreed that 5mm of wheelbase isn't a drop in the bucket but 5mm of fork offset is a big change. The main thing that confuses me about your posts is you keep bringing head angle (rake) into the picture. For the sake of simplicity, since Yamaha didn't change the rake and neither can we, can we try to determine what changing ONLY the fork offset will do?

I have just one simple little basic question...
I want quick light nimble steering, I am not worried about the tradeoff being a loss of stability and being twichy. All I want to know is do I need less offset like I previously thought and like the Scotts clamps will give me or do I need more offset like most of the links in Ken's posts suggest? I don't want to factor in rake and other variables that won't change, I just want to know about trail only.

PS- A Harris Duke must've been a pretty cool bike, I had a Spondon swingarm on my last bike.

------------------
'99 WR400
'92 GSXR 7/11
Visit my photo album AT YOUR OWN RISK!! My photo album
Anyone here a sportbike fan also? Then visit us here at www.insanespeed.com

  • Taffy

Posted June 29, 2000 - 10:10 AM

#39

motogreg
like i said, three other guys say the SSTC's are brill, do it to your bike & whats the difference between your bike & say, clarks with his rear wheel shoved right forward.

greg don't worry that you don't understand me-no one else does either!!! just read about it, go away, talk, sit next to your bike & put your thumb ahead of your right eye a few times.

  • Scott_F

Posted June 29, 2000 - 04:07 PM

#40

I'm jumping in a bit late here, but I will try to shed some new light on the topic. I have always been under the impression that more trail (less offset) equals more stability. One thing to consider is as rake increases, and offset remains the same, trail will increase. That's why choppers don't turn.

I just called Scott's Performance, and I couldn't get a satisfactory answer, and they said to call back on Wednesday when Scott returns. So, if someone will remind me, I will call and speak to Scott Forward and ask him questions about offset.

I could also call John at Applied.




 
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