R1 yokes

[SDN]

I am wondering if my 98 -00 yokes have slowed the steering of my TRX as I now have to use a lot more input to get it to corner, having said that I have not been out on proper warm roads with my new tyres scrubbed in!

A couple of questions what sort of effect will the reduction in trail from 30 - 25mm have in the real world?

How low can I drop the front end and will it compensate, allready have raised rear and YZF750 rear wheel

Does anyone know what R1 yokes have 30mm of trail with identical fork diameters to 98-00 R1

[Mincehead]

A reduction in trail should quicken the steering:

http://en.wikipedia.org/wiki/Bicycle_an ... e_geometry

http://www.vtwo.demon.co.uk/firestorm/steering.htm

I`ve had a lower billet alloy yoke made to allow my R1 forks to be utilised in my TRX, the best option really as Colin my pal and precision engineer has made them identical in every way to a stock TRX from a steering geometry point of view.
The top yoke is a modified billet R1 yoke (streetfighter conversion Lucas brand) I found for little money on Evilbay.

[SDN]

Thanks Mince - interesting. So decrease in trail from 30 -25mm should quicken steering if I have got this correct?

[Mincehead]

Indeed, and the wheelbase will be slightly shorter accordingly. By the way rake and trail for R1`s through model types / years can be found in the table on this Wiki page SDN:


http://en.wikipedia.org/wiki/Yamaha_YZF-R1

[fung]

just thinking that if you have the front forks set with too much spring preload in relation to the rear, it will require more "muscle" to turn in.
Cheers
Fung

[phuk72]

there's also the effet of having proper damping / springs in the front end which will make turn in feel slower

[Kayla]

A common 'fix' for early R1s pushing wide in corners is to use later (02-on) yokes, but they're pretty hard to find and quite pricey when you do. The later R1 had less offset than the early ones, so more trail in essence, but the 5mm shorter wheelbase makes up for the increased trail.

What's the offset on the yokes you have, 35mm? You'll have increased the TRX wheel base by 5mm if so.

The early R1s also had odd forks, they had more negative travel than most forks do/did. Yam's thinking was that it'd help the R1 track the road better, but a side effect was that the forks tend to extend through corners and push the bike wide. The shorter (later, less offset) yokes correct this by changing the way the forks are loaded ever so slightly. I think another 'fix' is to have the stanchions shortened and the negative travel corrected to a more typical amount.

You can't make a blanket statement like 'decreasing trail improves turn in' because you have to take everything into account- the original wheelbase, rake and offset. If you decrease the trail without changing with the rake angle or the attitude of the bike, you must by definition also increase the fork offset and therefore the wheelbase.

Oh, and check your tyre pressures

[B-art]

As
far is may knowledge goes, working in the motorcycle industry and working for 4 years for Hyperpro, next things is what I learned the influence bike handling .

For this discussion
-Tire with
-Wheel base
-Head stock angle
-Trail

Wider tires make the bike steer slower (190 turns in slower than a 170 rear tire)

Longer wheelbase makes for slower steering.

Wider Head stock angle makes for slower steering.

Longer trail makes for slower steering.


In frame design Wheelbase, Headstock Angle and Trail are chosen (engineered)
With the offset (distance between forelegs and head stock) theTrail can be manipulated.
Less Offset mans more Trail, More offset means Less Trail.

In Your case.
Changing to a R1 fork makes the front lower, changing the headstock angle (If you did like Mincehead the trail changed minimum).
Changing the yokes to one with less offset means Trail will get longer. The change in wheelbase has less effect ( as we all know when wee adjust our chain (i.e. lengthening wheel base)
Changing the rear to a wider one (YZF) will slower steering.


I do not know what the size of the fork of the 99 R1 is.
But as I am working on getting an R1 2003 fork in I have bought 2 Top Yoke by mistake 1 different years
Thing is their off set is different (measured center to center)
25mm for the 2007-2008 model RN19
30mm for the 2004-2006 model RN12

And although the newer ones has radial brakes both tope yokes are fitting
And the lower one of the 2004-2006 also fits the forks.

I do not know if this will fit your fork situation.

---

Just to try some thing simple.
You can put the fork through the Jokes 3 to 5mm at the time and take it for a spin
I would not go beyond 15 mm as the front wheel could get in contact with the radiator.

B-art

[SDN]

Checked the offset, my R1 forks do have more offset than my TRX items so probably with the bigger 180 rear tyre this is making it slower to turn in.

[Stankflapper]

Interesting read this, and it seems fitting a different front end to the TRX then poses a whole new range of "sorting problems" to make it handle. I am curious to know how hard it would be to just really "Up spec" the original?

[Mincehead]

The way to go is not skimp on it and have yokes made to the same offset as the originals but large enough to take the R1 / 6, GSXR upgrade USD fork legs Stank.
That`s the way I`ve chosen to go.

[Kayla]

Interesting read this, and it seems fitting a different front end to the TRX then poses a whole new range of "sorting problems" to make it handle. I am curious to know how hard it would be to just really "Up spec" the original?

The simplest swap in terms of geometry would be to use the later YZF750 or a Thunderace front end, the offsets are the same so won't affect the trail or wheelbase. Or if you can find them just bung a pair of Thundercat forks in the standard yokes

[SDN]

What is the diameter of YZF 750 forks and will I have to weld up the steering stem?

[Kayla]

What is the diameter of YZF 750 forks and will I have to weld up the steering stem?

The diameter of the fork tops is 50mm but I don't know what the lower diameter is (it's probably 54mm). You don't need to weld the stem up either, it's a straight swap with the TRX one.

[Mincehead]

Yep 50 / 54mm.