Yamaha TRX850 Enthusiasts Forum

Hi there this may seem a bit of an odd request as your all here modding trx's butt

I ride a 95 fzr 4jh customed and tweaked to high hell
2 months ago I literally snapped my rear shock in half and as the 4jh model might as well be non existent here in the uk ive opted for a trx rear shock now that ive finally got my greasy mitts on one.

Its the same dimensions as my fzr stock rear shock apart from the top mount which ive custom fabricated
So bar the settings which are obviously the fact its gassed and oiled for a trx. Its a straight swap

Upon riding it though the spring does feel very very stiff
As in it soaks up the sharp bumps fine but I can't seem to physically bounce the rear and I get no sag from grabbing the throttle
Is the stock spring oversprung on the trx when stock?
If it is then I'm going to build a custom linkage and lose all the preload

I just thought id be better off asking the opinion of the trx community on this subject

In case youd like the information my bike is 190kg wet and I'm another 95kg on top
The shock ive got is from a 96 trx850 it supposedly only done 15000 miles but its absolutely mint all the paintwork is intact with no rust anywhere only a little road grime which was cleaned off the bottom mount

Any help would be most appreciated
-James

the std TRX spring rate is suited for a 76kg rider but the weight of a TRX is around the 207kg mark std..

Hm so I should be expecting a less static sag which I thought would be the case anyway

So my question still stands as does a stock trx feel oversprung on the rear?
Do the majority of trx riders end up using the stock with a lower preload?

I would bump mine down but itd mess my geometry right up on the fzr as the rest of the bikes still got its 18 months of adjustments on it that rely on the high preload to keep the height balance and id rather not go backwards with those to try and go forwards

howdy mate
perhaps check the shocks compression and rebound damping is not wound up full
then maybe soften both ends to keep your balance
what tyre pressures are you running ??
cheers
fung

I get no sag from grabbing the throttle

You shouldn't get any sag from grabbing the throttle and hard acceleration. The back end should actually lift up if anything.

its true

Yep, general opinion is the standard trx rear shock is too hard for the bike

coxylaad wrote:

I get no sag from grabbing the throttle

You shouldn't get any sag from grabbing the throttle and hard acceleration. The back end should actually lift up if anything.

its true

Is the gearbox sporcket higher than the wingarm pivot coxxy?

Thats a good point. although I am fairly certain most bikes are designed that way. plus its not so much whether the sprocket is higher, it also depends on the natural angle of the swingarm. it can be higher and still have the same effect yes?

If the s/arm pivot is lower than the g/box sprocket centre then under acceleration the taught chain will try to bring the s/arm up and effectively make the bike squat for better grip. Old Be-ems did the opposite - the rear end jacked up under acceleration but as there wasn't much power it didn't really have much effect.

The TRX linkage/bell crank is different to the 4JH linkage. Does your bike have shorter dogbones fitted to raise the rear?

Most (all?) bikes have an element of anti-squat built in to the geometry- as the bike accelerates the chain will tend to pull the swingarm down which is what counteracts the 'squat' felt (which is actually weight transfer from front to rear, not the action of the chain on the rear sprocket).

If you have too-short dogbones fitted, the action of the rear wheel trying to move through its arc will tend to pull the linkage through its length (ie front to rear) rather than transmit the load through the shock. The shock will 'feel' stiffer because you need a larger force than standard to provide the necessary component 'up' through the shock to get it to deflect.

what she said

Maybe I didn't explain too well - i didn't mean to imply the chain actually pull the back into a squat. I was trying to explain how the position of the swing arm pivot relative to the gearbox output shaft will have an effect on the bikes geometry under acceleration.
Wot she said

sounds like you have problems with both shocks , are you sure the shock is the problem, are all the linkages and whatnot moving through their range nice and free (without any shocky in place)

cobbadiggabuddyblooo wrote:the std TRX spring rate is suited for a 76kg rider but the weight of a TRX is around the 207kg mark std..

No wonder I've always enjoyed the TRX ride. I weigh 76kg. How lucky.

dandywarhol wrote:Maybe I didn't explain too well - i didn't mean to imply the chain actually pull the back into a squat. I was trying to explain how the position of the swing arm pivot relative to the gearbox output shaft will have an effect on the bikes geometry under acceleration.
Wot she said

Yeah I think thats what I said