The TRX900 Project kicks off

[coxylaad]

y'know something, I looked at that picture and thought the rear swingarm looked quite compressed.

Its mid corner, and I am not on the brakes as the front forks aren't compressing down. I wonder if the rear spring is too soft for my fat ass.

[coxylaad]

Cobber - was your opinion that it was the damping or the spring rate?

[cobbadiggabuddyblooo]

Std trx spring rate is for around a 75kg rider and an R6 spring rate a little heavier for around 80kg's.
Set your static sag to start and write down your current rebound/compression settings and use that as a base point.
Then work on getting your rebound set then deal with compression and then see how it comes up.
Pre loading the spring further via the spring adjuster only allows for more initial weight (if your a fat bastard) to be applied to the spring before it starts to compress further but after initial weight begins to compress the spring it is still only compressing at a rate set for a 75-80kg rider.
Loading more of that energy to be absorbed by the tyre walls so again creating another weak point to aid in loss of traction.

Spring rate for your weight really should be one of the first adjustments made to your bike.

You can gain so much just from having your suspension set for your weight to start otherwise your really chasing your tail and trying to find a compromise which more than likely will have other consequences involved from this action.
Preloading your std spring further to deal with extra weight over the std spring rate will deal with getting your static sag sort of set in a static situation but the consequence of this once you begin to actual change from statically sitting on the bike to riding is it's working for a 75-80kg rider and compressing at a faster rate than optimum for a fatter arse.

Hope that sort of makes sense to you Coxylaad

[coxylaad]

I have done all the sag setup stuff. The shock is setup as best as it can be.

[dandywarhol]

The drive sprocket centre is higher than the swingarm centre so in effect the chain will pull the rear down in squat as said in a previous post. I think this is better than the opposite as in theory it will help traction.

If the rear spring is too weak for the rider's weight then this will accentuate the problem. If it's a stock TDM unit then you can fit a washer onto the top shock mount to lengthen the unit a few mms. I also agree the chain looks too tight, especially as it'll be tighter yet when the swingarm is at it's "longest" when the gearbox sprox, s/arm pivot and rear wheel centre are all in line

[cobbadiggabuddyblooo]

Not possible with a Trx set up as the sub frame has a yoke already Inplace unlike the TDM and yzf set up. shame as a much preferred way to get a little more ride height than dogbones

[coxylaad]

I checked last night, my dog bones are the stock length, so no issues there. I noticed that the preload setting is 1 notch off max. Its all pointing to a weak spring.

[dandywarhol]

I was getting myself confuse there cobra - thinking it was a TDM900 shock for some reason - Altzheimers setting in fast!

[cobbadiggabuddyblooo]

yer i know that feeling if I could remember what it feels like tho:lol: h

[dandywarhol]

There's appreciably less squat in a previous photo - with all the weight going to the rear.................... You could try shorter dog bones to raise the rear and "stiffen" the spring rate

Did you set up the sag/ride height with you on board?

[coxylaad]

good spot Al. dont know what is going on there as I have changed nothing mechanically on the bike in between the 2 photos.

Only thing i can think is that I am going over the crest of the mountain so the weight could have been thrown upwards?

check this one out:



and the squat is back. Maybe its just the camera angle

[cobbadiggabuddyblooo]

If it's not a std trx swing arm, check the length between the swing arm pivot and dog bone pivot on the swing arm.
This should be 160mm and thats a std length used on just about most of the yamaha 750-1000 motorcycles including the trx.
Measure from centre of your swing arm pivot to the centre of the rear axle and see if you fall within a couple of mm's to the centre of the TRX specs.
Changing gearing alone on a std TRX can make an easy 5% difference in your set up.
If the swing arm measurement is longer you can increase that % even further due to leverage factor and if an incorrect spring rate is inplace all these variables begin to add up.
If running a R6 shocky, here is a good explanation from Ohlins on how your slow/fast compression influence your set up.
All of these factors make up the ratio,dog bone length,and damping set up on your rising rate suspension. You will normally find in a set up like this the further the suspension rises the stiffer it becomes.

Maybe throw it out to a few forum members to get a couple of lengths to compare to yours.

OHLINS manual..

The low speed compression adjuster affects ride height, smoothness over small bumps and grip. The high speed compression adjuster affects stability, firmness in depressions and fast corners.

If the motorcycle has a low riding position, the low speed compression should be increased. Turn clockwise four steps and test run again. If this was too much then turn back two steps (counter clockwise). If it feels unsmooth over small continuous bumps or has bad grip, the low speed compression should be decreased. Turn counter clockwise four steps. Test run and make any necessary correction in two steps at the time.

If the motorcycle feels unstable in fast corners and has a tendency to bottom easily in depressions and chicanes, the high speed compression should be increased. Turn clockwise six steps and test run again. If this was too much then turn back three steps (counter clockwise). If it feels harsh and too rigid or has a tendency to hop during braking, the high speed compression should be decreased. Turn counter clockwise six steps. Test run and make any necessary correction in three steps at the time.

When you have sufficient feel of the motorcycle you can make further fine adjustments. It is feeling and experience that counts.

NOTE!
Ensure that the springs are properly pre-loaded before attempting to make any adjustments. A simple rule is that increased pre-load of the spring should be followed by an increase of rebound damping by two steps.

When you feel that you have achieved an improvement, go back to where you started and check once more. Be observant of other relevant factors such as tyres, temperature, etc. Test run to make sure whether further fine adjustment should be made.

Another common rule of thumb..
If the slow/fast adjusters are not withing 3-4 clicks either side from each other, when set up there is a good chance your spring rate may need to be changed..

I can remember when Quan-time fitted a R1 swing arm a number of years ago and being longer than the std trx swing arm, he worked out all the rising rate equations to build the correct linkage,relay arm lengths and shapes to make his work.

[dandywarhol]

Interesting read cobba - I found the same article when looking at info for my Ohlins 46HRCLS, which unfortunately dosn't have separate low/high speed compression damping

I'm interested in your comment about gearing affecting the setup by around 5% - is that because a larger rear sprocket applies more leverage to the rear axle, effectively pulling the axle up towards the seat?

If the two pics were taken on the same day and the chain hadn't been adjusted then there looks like being quite a difference in distance between the swingarm pivot and the gearbox sprocket with the 900 engine on board, as the tightest point would be when the gearbox centre/swingarm pivot and rear axle centre are all in the same plane.

[coxylaad]

check this out:

http://www.peterwilemanphotography.com/ ... il/3393080

this is me between sunny in and sunny out I think, on the gas, compressed. I am not sure what is going on. I would like to think it was just a case of fitting shorter dogbones to lift the back end up but I have heard the rumours that shorter dogbones muck up the rising rate characteristics of the suspension travel.

[coxylaad]

on a side note:

http://www.peterwilemanphotography.com/ ... il/3393078

I might not have a clue what I am doing but I look the part