Ty175 Forks

[andy.t]

Does anyone have an opinion on what is the best height to set the fork tubes above the top yoke,mine are set flush at the moment,20mm has been advised in the Haynes book.Also what is the best fork oil grade to use.

Regards.

Edited January 11, 2007 by Andy.T

[lewisblack]

I think it depends on what rear shocks you are using. Standard TY rear shocks you want 15mm-20mm of the forks above the yolks (yoke's ??). I have just put some Betor shocks on mine which are about 25mm longer than standard and then you want the top of the folks level with the yolks.

[feetupfun]

The steering angle on the standard Ty175 is not as steep as most bikes from the same era. If you raise the rear with stiffer springs, more preload or longer shockies, the steering angle improves towards the ideal. If you then slide the forks down in the clamps, the steering angle will move back towards standard, but will improve the ground clearance.

A negative with sliding the forks lower is that it makes the front end even more flexy in rocks.

Going the other way (lowering the front), there is a limit created by the clearance between the front mudguard and the lower fork clamp. This limit is just a bit past when 20mm of tube protrudes above the top clamp.

If you are serious about improving the front end, consider fitting the forks and clamps from a Ty250 twinshock. It is a bolt in job and improves the front end quite a bit, especially if you ride big obstacles or are over 80kg. In that case, the tubes are fitted flush with the top clamp and this puts the bike height at the front the same as with the TY175 forks with 20mm protruding.

With either set of forks, you really need to set it up to suit yourself. I have found that it is far more important on TYs to get the oil level set exactly right than what oil weight I use. They have seriously poor damping if the level is even slightly too low. I find 10, 15 and 20 wt all work OK with the correct level.

[spinner]

I agree TY250 forks are a great improvement over the stock forks!

Another side effect that I bike tends to climb hills better, a little more weight on the front end is a good thing on a TY175

[andy.t]

Thanks for all your comments so far,would love to fit the TY250 forks but finding some decent ones is another thing,so I changed the oil on mine for now which doesnt seem to have made any difference.How can you tell if the damping is good,when you give my forks a push down they spring back up just as fast and stop at the end of travel,maybe recoil a fraction down again,so is that good?....anyone got any forks they dont want!

Regards Andy.

[feetupfun]

Here are the basics for setting up forks of the twinshock era:

Spring preload

Fork spring preload should be set ideally to give static sag of 40% to 60% of travel with you standing on the bike pegs with no weight on the bars. It is adjusted by adding or removing spacers above the springs. TY175 standard has a tubular steel spacer about 70mm long. If you add too much preload, the springs will coil-bind (which limits travel and may kink the springs)

Oil level

Fork oil level should be approx 125mm from top of tubes with springs removed and forks fully bottomed. The resistance to bottoming can be increased by using a higher level of oil. Too much oil volume and you will limit the travel. Too little oil and the damping holes will be exposed to air at the top of the stroke.

Oil viscosity

Start with 15wt oil. Heavier oil will increase resistance to bottoming out on sudden impacts but will be of little benefit during sustained heavy braking (on a steep descent). Heavier oil also produces a more dead feeling front end which makes hopping the front harder work than it normally is on a twinshock bike.

With a bike the age of your TY175, it is entirely possible that there have been modifications made which are causing your forks to feel weird. I have tried many modifications to TY175 forks (wide range of oil type, different springs, air caps, a great range of preload adjustment) over the years and finally ended up with them completely standard as being the best performance. The next change was to fit TY250 forks which made it just how I wanted it all along.

If you are in doubt about what trials bike forks should feel like to ride with and even just to push down on, try someone elses similar bike for comparison. If still in doubt, compare what your forks look like disassembled with a set you know to be standard.