jc2

2 Questions: How far can you safely bore a TY175 (beyong 68mm) without resleeving? Does anybody know what size bore the Majesty website 200 kit uses?

That would be true to some extent, but its not dependant on runout in the yokes. The rising/lowering of the steering head is a result of both/either rake & offset. Thinking of best/worst-case scenario, if you have zero rake you'd have no rising/lowering of the steering head. But there would be no diff whether the offset is obtained with raked out yokes or in the triples/sliders. One would think that the sideways movement in the steering head (which is more a function of offset/trail) would upset balance more than the rise/fall of the steering head, which already changes with suspension/surface undulations.

Agreed. But the runout is usually only about 1.5deg. If that were the main reason its used, they'd surely use nearly straight-across triples w offset-axle sliders &/or considerable runout in the triples.

Yeh Dave, that was the "exception" I referred to above. Its just elaborating the general with some specifics.

Thanks guys but it hasn't really got to the bottom of it. I understand all yr saying, Feetup, but w one exception all those things can be achieved with offset-axle forks/sliders which have the same total offset/trail, & as you know, many bikes have both offset axle sliders & non-parallel triples, eg, SherpaT, KT, RL, Cota etc. So there must be some other reason why manufacturers use it, which I suspect is the main reason. TrilasRfun, thats the sort of thing I've heard/read claimed before, but I don't see how & I've never seen it adequately explained despite having searched fairly widely. eg Foale & Willoughby say very little in their classic book on frame design (which has considerable content on steering). I can see what yr saying that the forklegs are not vert or backwards at full lock with runout yokes, but don't see that that makes any diff for the better. Steering geometry is a function of steering axis angle (ie rake) & total offset - however that total offset is achieved. The angle of the forklegs doesn't provide rake. It all gets a bit confusing (to me at least) on tight turning, but in the worst case scenario, on full lock, assuming the bike itself remains verticle, the rake becomes camber on the front wheel & there is no rake, & with any offset at all (however it is achieved), we actually have negative trail. Seems to me thats why any bike feels much less stable the closer you get to full lock, and with runout on the yokes it makes for more negative trail & therefore a worse scenario! (it seems to me) In fact, its usually improved/cured by providing more (+ve) trail. The only advantage I can see of runout on the yokes is that as the front suspension compresses, you lose less trail than with parallel triples. ie you don't lose as much of the centring effect so the bike is more stable under suspension compression than with parallel triples. But perhaps I've got it all wrong.

Most twinshock trials bikes have non-parrellel triple clamps, with the forks kicked out about 1.5degrees more than the steering stem rake. Can anybody tell me what the advantage is of this set-up (over parrallel triples)? I've read that they're supposed to be better at/near full-lock, but I don't know if thats correct or why/why-not. Can anyone enlighten us?

TY 250 rear hub is same as TY175, but uses sproket with diff offset (& probably diff # of teeth) Are TYoffroad building the stroker kit now or still developing it?

There are 4 different sets of crankcases, each with diff engine mounts & diff non-interchangeable clutch covers: 1) DT1/2/3, YZ A/B, 2) DT A/B (& perhaps C) 3) TY 4) DT D etc (eng mounts are close to DT A/B but slightly diff DT A/B/C/D cases are about 1" longer than TY cases, so its not a straight forward engine transplant, but I did read of somebody (foolishly, IMHO) putting a DT400 engine in a TY in USA (where else?) I think. TY stud spacing on barrel & head is same as DT250 A/B/C/D, & interchange, but diff porting, Comp Ratio Some internal cluth/primary gear/g'box parts exchange, but not all. IIRC TY A & DT A use keyed primary gear; B/C/D models for ea use splines (or vice versa) DT C/D gears were diff (wider) to DT A/B IIRC but not sure if the whole set will interchange. Don't know if shifting forks & drums are diff/same

Anyone know how close the new MATY frames are to production? When they might be available?

Does anybody have the specs for the standard Mini Majesty? eg Wheelbase, Ground clearence, seat height etc

Sam, how did you clean out the mid-section?

I've done a bit of research on this. As I suspected, it seems its all to do with chain-pull torque/effect under power, which extends the rear suspension & stiffens it up, making it less supple over undulations potentially causing loss of grip. A longer swingarm reduces that effect so potentially offers more grip - most noticeable under acceleration/full power on rough ground. It also means less tendency to wheelstand, since it reduces the effect of raising centre of gravity from the extended suspension. And it means more power is available for drive since less is lost extending the swingarm & raising the C of G. This of course is what Vesty was after when he modified his Bul in the early 80's. I hasten to add that a longer swingarm is not the only thing that affects chain-pull effect on grip & Vesty's bike used several mods to achieve his aim.

I recently scored a 75 247 Cota. Any tips for set-up & improvements?

Interesting comments but too many are off the track. Perhaps I didn't state clearly in the original post what I meant. I'm not referring to extending a swingarm on an existing design. That obviously affects wheelbase, weight distribution & sometimes suspension travel all of which are going to affect grip. I mean, all other things being equal - weight distribution, wheelbase, power characteristics, wheel travel, damping & spring rates - why is a longer swingarm design said to give more grip? I've heard/read it repeatedly applied to trials bikes, MX bikes & motoGP bikes, but perhaps no more so than regarding trials bikes which are my main interest now. Can anyone shed light on it?

Can anyone tell me the theory/reasons why longer swingarms are said to give more grip?

I think you nailed it MRB. On a little more research it seems the change in pivot point actually happened from the M80 to M91 models - it just didn't make the brochures till the M124 models. (The same happened w the pursang brochures when they shortened the wheelbase on the M103 Mk6 but the brochures didn't change till the M135 Mk8) The spanish on the SherpaT (M124/5) brochure I believe can be translated: "thanks to a small advance in the fork" (meaning rear fork, ie swingarm)

Thanks for your responses guys. If anybody's got any more input, I'm still listening

Gents, I've noticed on the bultaco brochures (on Todotrial website) that the model series 124 & 150 have 1315mm wheelbase listed as opposed to 1330mm for earlier Sherpas. Can anybody tell me: 1) is that true - ie did they really have shorter wheelbase? 2) if so what was changed from previous models (M91, M80 etc)? Was it shorter swingarm, steeper rake, less offset on the triple-clamps or what? There is a bit of an explanation on todotrial, but its in spanish & I can't read spanish & it doesn't make any sense attempting to translate with my spanish dictionary or with google translation. Can anyone translate: "gracias a un menor avance de horquilla" Any help greatly appreciated

Hi Gents, New chum here. More or less new to trials. Was into MX back in the day, then VMX. Needing something a little more sedate lately but no less interesting. Have background in spanish bikes, but Feetupfun recently gave me a taste of a range of twinshock trials bikes incl TYs & KT. Loved every minute of it. Thanks Dave, yr a great ambassador for the sport!