Yamaha TRX850 Enthusiasts Forum

Does anyone know the length of a front spring for a std trx fork???.. Possibly on your replacement springs they have given these specs either on the box or paperwork that comes with it???? I have found the free length of 381mm (limit) in the workshop manual which is the threshold when it should be replaced but not the actual length of a std trx spring to start with. Any help would be greatly appreciated.. I have worked out the spring rate of .9kg/mm needed just need a length now... cheers cobbadig

Mate,

Dunno spring length soz, but just a pointer: the standard springs fit in with a spacer tube at the top (prolly about 70-100mm?) whereas replacement ohlins springs for instance are this much longer than the stock ones, so do away with the spacer.

Leads me to think how critical is spring length? As long as they are longer than standard, the spacer can be trimmed to suit, or a new one made up.

Of course, you need to know the length of the standard spring first...................


Dave

Can measure my import jobs hiding in the garage if you want.

Dave E

Any help appeciated cheers....

ones in the box I have are only 341mm long??? Hope there not too short...

A ph call to the shop i was told just to use a spacer to fill the gap if there is one there????? to me there would be a minimum length.... Standard .. for a reason.. would not this affect the absorbsion of the compression of the spring and bottoming out ???? Also durability and fade??? Maybe not so noticible if just a touring bike but I'm tuning this bike to work to thresholds so I'm sure these things would play some sort of part.. new spring length 341mm ... free spring length from manual..381mm... does this mean I'll only get 9/10ths of the travell before bottoming out in the front end... or am I putting too much into this????

The standard spring is, as you'll know if you've had the forks apart, under pressure i.e. you have to press on the fork top/damper rod to get it to thread into the fork tube, and ohlins springs are longer, as I said.

The yamaha tollerance figure is probably the limit for when it will not be under pressure any more, or has been compressed so often it's fecked.

So length shouldn't be too vital (thats what I tell the ladees anyhoo! ) as a fixed rate spring (as apposed to a rising rate spring like Hagon ones) regardless of length, IIRC, doesn't need more force to compress it more i.e. you apply x kg of pressure and it compresses y amount and thats true all the way until it will compress no more.

Your forks should never really bottom out ever, but isn't this governed by how nuch of the fork leg will slip inside the fork bottom, not by when the spring is fully compressed?

But at 341? hmm...........that could be a bit short??

However, I could be taking a load of bollox as usual.

Ok my 1995 Japanese spec import springs are 395 mm, the Euro ones were shorter, and had a gap, but I didnt put a spacer in and the Euro ones are still better.

Dave E

still have the shorted ones around to measure by any chance???

They are in the forks!!

Dave E

395 mm compared to 341mm thats 54mm over 2" does that sound about right from memory??? Maybe the longer spring was a progressive type ??? with no spacer would effect preload upon spring so spring rate comes into play... the shorter spring heavier oviously???

The Japanese springs are softer, bottom out very easily and shake the fillings out of your head!! The European ones are much better, at least I have some suspension now when braking hard! The compression on the Euro spec ones was harder whilst trying to compress by hand than the Japanese ones. Hope that helps. Re size, I think from memory that they were a good half inch shorter. They came from Youngy's garage lol, but then he did have a few TRX bits laying around

Dave E

Cutting a standard spring and replacing the length with a spacer of the same length will make the suspension rate stiffer.

Well same on mine 395mm ... But front forks have been supplied from a wreckers after righting off the front end 18mths previously. First thing I noticed was how spungy the replacement forks where compared to the originals even with new oil. Noticed tho in the manual it states once forks exceed measurement of 381mm so I ask..As the fork springs wear do they actually expand when no longer under compression? I have fitted the new springs and cut the spacer to the 395mm length and have found this gave me an unladen sag of 12mm and laden of 20mm... Makes me think if I take 15mm off the spacer to bring me down to a spring length of 380mm(just under the threshold of 381mm) weather this will bring me into the all thresholds.. 25-30mm unladen sag, 35-40mm laden sag.., under free length 380mm.. and still no preload at all on springs with all 8 lines showing.. common sense says it should ... Couldn't help myself tho and had to go for a ride as is and what a difference already.. now it really accentuates how bad the rear end is ... Will trim it up and see how things go...

Here cobba,this may help you get your head around how springs work in relation to their rate,lenghts and wire guages:

http://www.moto-racing.co.uk/Guides/Lin ... ssive.html

And Hooke`s Law:

http://en.wikipedia.org/wiki/Hooke%27s_law