michaelmoore Posted March 18, 2008 Report Share Posted March 18, 2008 This didn't seem obviously vintage/twin-shock/modern so I'm posting it in the general section. In another thread Tony Down said about footpeg location "from my own personal preferences I have found the ideal to be 37.5 inches from from wheel spindle to center of rest and 12 inches high." "12 inches high" would seem to presume that the footpegs are not hanging below the engine/bash plate. I'm presuming the footpegs on Tony's bikes are about 1" deep so that would imply an 11" ground clearance. I've seen a number of posts where people have commented that a particular bike had the footrests too high, as in 14, 15" or so. The center of gravity is going to be affected by jacking the engine up quite differently if you are looking at a modern 4T (YZF Yamaha 250 engine is 54.5 lbf with levers, carb and ignition), vintage 2T (my KT250 is 10 lbf more than that) or period thumper (a B50/TT500 etc are in the 90-95lbf range and my G80CS Matchy seems quite a lump). Does clubman trials, even with modern bikes, really need more than about 11" of ground clearance? Jack the engine up, jack the footpegs up to match, raise the rider. And in my case the rider with full gear is an easy 200 lbf which seems like it would make a pretty substantial change vs raising a 55 or 65 lbf engine up an inch. A sideview photo of my stock but for somewhat longer rear dampers KT250 http://www.eurospares.com/graphics/trials/...tsideview1a.jpg shows the engine above a line drawn through the axles, which should be about 13" or so based on the unmounted new Michelins I've got in the garage (presuming they are actually round and not greatly flattened at the contact patch when installed but without a rider). The stock-position footpegs are probably 1.5" above that line. If you've got a taller obstacle, don't you just wheelie a little higher and hold the front wheel up a little longer before/while hitting it so you don't high-center? I can recall reading "back in the day" negative comments about "top hamper" and that makes sense to me. Trials bikes can obviously benefit from a certain minimum ground clearance, but when does it get excessive? Since I've just cut the bottom out of the KT frame I may as well reposition the pegs too. Making them as low as possible seems worthwhile. Lowering the engine and the pegs another inch or two might also be worthwhile. Once the welder is on, why hold back? cheers, Michael Quote Link to comment Share on other sites More sharing options...
swooshdave Posted March 18, 2008 Report Share Posted March 18, 2008 I think that with the newer bikes you can get away with more ground clearance because of the extreme suspension travel, something the old bikes don't have. Are you factoring that in? Sag and overall travel? Quote Link to comment Share on other sites More sharing options...
michaelmoore Posted March 18, 2008 Author Report Share Posted March 18, 2008 How much extra travel do the new bikes have? A new Scorpa is shown on RYP as 165mm rear which is 6.5" or 2.5 more than vintage allows and front travel of 177mm/6.96" which is the same as many vintage bikes. 315mm/12.4" is the ground clearance. That's about the same ground clearance (or less) than my KT seems to have. While rear travel on the Scorpa is +50% over the KT250, 4" to 6.5" is not quite the same as going from 4" to 12" as VMX did. RYP doesn't give foot peg height for that bike. I didn't spot a nice full-side view type of photo to see where the footpeg height was compared to the bash plate. I don't think we want to have the footpegs lower than the bash plate level. It seems like having them as low as possible with that constraining point would be good. If that is the case, then the modern bikes would be shooting for a similar point as a vintage mount. If modern bikes can get away with 12.4" of ground clearance (which with their somewhat greater rear travel may mean the minimum GC is actually lower than a vintage bike) then perhaps there is no reason to go beyond about 12" on a 7"F/4"R vintage bike. And since the vintage bikes aren't going to be seeing modern obstacles, maybe 10-11" is all that is really needed, and the engine/rider can be lowered that much. cheers, Michael Quote Link to comment Share on other sites More sharing options...
Guest majestyman340 Posted March 18, 2008 Report Share Posted March 18, 2008 How much extra travel do the new bikes have? A new Scorpa is shown on RYP as 165mm rear which is 6.5" or 2.5 more than vintage allows and front travel of 177mm/6.96" which is the same as many vintage bikes. 315mm/12.4" is the ground clearance. That's about the same ground clearance (or less) than my KT seems to have. While rear travel on the Scorpa is +50% over the KT250, 4" to 6.5" is not quite the same as going from 4" to 12" as VMX did.RYP doesn't give foot peg height for that bike. I didn't spot a nice full-side view type of photo to see where the footpeg height was compared to the bash plate. I don't think we want to have the footpegs lower than the bash plate level. It seems like having them as low as possible with that constraining point would be good. If that is the case, then the modern bikes would be shooting for a similar point as a vintage mount. If modern bikes can get away with 12.4" of ground clearance (which with their somewhat greater rear travel may mean the minimum GC is actually lower than a vintage bike) then perhaps there is no reason to go beyond about 12" on a 7"F/4"R vintage bike. And since the vintage bikes aren't going to be seeing modern obstacles, maybe 10-11" is all that is really needed, and the engine/rider can be lowered that much. cheers, Michael Here in the UK many "classic" type events also include classes for modern bikes, and are marked out accordingly.....................many older riders such as myself, would welcome a return to the very much easier sort of vintage events, that allow riders of rigid machines to have a good days sport. Quote Link to comment Share on other sites More sharing options...
chewy Posted March 20, 2008 Report Share Posted March 20, 2008 Had to catch my interest with this one I manufacture footrests for trials bikes and was the first to recognise the importance of this. Clearly you want all the ground clearance you can get and it is also obvious that if it made life easier we would all be walking around on stilts so you want your body mass interacting with the bike at maximum leverage; as low as possible. Clearly this is going to be a compromise and several other factors are involved. One thing for sure is that everyone in trials is an expert on such matters and in my experience over last 15 years of design and manufacture is that there are nearly as many opinions as riders. Most of the top riders can ride anything well and it is an easy connection to make between what they use and what is the best; generally speaking bikes and after market bits are popularised by a mixture of good design and good margins but mostly by evolution and feedback from the buying public. Going back to original hypothesis; imagine putting your engine in a rucksack and hanging it around your upper body and then walking up or down a section on 12" stilts whilst holding a broomstick in your hands. Quite ridiculous isn't it. You don't need to be Einstien (or Newton) to rationalise these ergonomic relationships it should help to reach the best compromise for you. Quote Link to comment Share on other sites More sharing options...
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