bigwig Posted December 8, 2004 Report Share Posted December 8, 2004 At last ,someone talking sense Social Climber understands and the Big Bang engine theory. According to nearly everone else on this line what you need for realy good grip is amulti cylinder two stroke. Quote Link to comment Share on other sites More sharing options...
downunder Posted December 8, 2004 Report Share Posted December 8, 2004 Lets face it............. If you learnt to ride in the good ole days you soon figured out that 2 strokes were peaky and had a powerband that let rip when it pleased itsself. The loping ole 4 strokes used a wasted stroke to act as a flywheel to carry momentum. In recent years (post YZ's) 2 strokes were fitted with heavy and even double flywheel to give more torque and a long exhaust with no chamber to tame the savage beasts. Now we are entering a new era (ummm since 1972???) where exhaust emissions govern what is manufactured. All the same, a 4 stroke was more subtle than a 2 stroke and power to ground has generally been the 4's domain. When it comes to traction we need to remember thrust v mass is the main factor (Danny Pedrosa). A 2 stroke always offererd a weight advantage over a 4 stroke in the past, thus potentially more traction when in the right state of tune but less efficent on fuel and emissions. Now we have 4 stroke motors that match 2's in weight together with engine management systems that smooth out power curves and get the best traction. 2 stroke v 4 stroke is a thing of the soon to be past. Get a grip on the throttle and learn to ride what we all have to live with, love them or not. Downunder Quote Link to comment Share on other sites More sharing options...
titanium Posted December 8, 2004 Report Share Posted December 8, 2004 Where we ride, many times we must scale large, slippery rocks. With a 2 stroke, the strategy is to hit the rock hard at the bottom with lots of rpm, shut off and let the motor "wind down" as you progress up the rock. This provides a good amount of traction. With 4 stroke engine braking, how would a rider get this affect riding a 4 stroke? Quote Link to comment Share on other sites More sharing options...
jrsunt Posted December 8, 2004 Report Share Posted December 8, 2004 same applies for the 4rt, big handfull in the bottom and let the momentum carry you over the rest, using throttle against engine braking to govern how much momentum you need. It just takes time to adjust. Quote Link to comment Share on other sites More sharing options...
social climber Posted December 8, 2004 Report Share Posted December 8, 2004 The thread was about traction, not engine braking, though to be honest I think that the extra engine braking of a 4T could be useful on slippery declines too..... By the way, I'm not knocking 2strokes v 4strokes, just stating the physics of the argument.... Quote Link to comment Share on other sites More sharing options...
woody Posted December 8, 2004 Report Share Posted December 8, 2004 The thread was about traction, not engine braking, though to be honest I think that the extra engine braking of a 4T could be useful on slippery declines too..... If you ever get to ride a 4-stroke enduro bike down a snotty Welsh hill you may change your thoughts on that as the back overtakes the front....... In the dry it's useful, in the wet it is a clutch in and brakes job. I'm still of the opinion that you can't categorically state which is best for grip, 2 or 4-stroke. Regardless of the physics theory and mathematical equations it comes down to the type of engine and bike and the conditions being ridden. I've owned a YZ426 and a WR426 Yam. The YZ has such quick power off the throttle it was impossible to feed power in gently in slippy woods. It would just spin up and step the back out. The WR is more gentle so power can be fed in a bit slower with less spin. Still a handful though. Mates 2-stroke 300 KTM is very soft so doesn't spin up and finds grip much more easily. All three make about the same horsepower but the Yams have a much quicker delivery. Technically I can't even begin to explain how that works....... Quote Link to comment Share on other sites More sharing options...
the artist formerly known as ish Posted December 8, 2004 Report Share Posted December 8, 2004 Quote Link to comment Share on other sites More sharing options...
dgshannon Posted December 8, 2004 Report Share Posted December 8, 2004 At the root of the 2-stroke vs 4-stroke debate is the impression that a 2-stroke fires on every revolution and a 4-stroke fires on every other revolution. In principle, this is correct and a 2-stroke does in fact "fire". But, the fireing of the sparkplug is not the issue. The characteristics the engine displays depends on what is currently in the cylinder to be burned, once that sparkplug "fires". The physics of 2-stroke operation, especially in the low rpm range we often use in trials, dicates that there is not a fresh charge of air and fuel in the cylinder for every stroke, even if the sparkplug does fire. At low rpm, there is another cycle going on. Right after the engine fires off a good full charge in the cylinder, the next cycle will not be a full fresh charge. Portions of the previously burnt charge will not be fully exhausted, plus a portion will be pulled backward into the cylinder from the exhaust header. Reed valves help with this, but don't eliminate it at low rpm. This next contaminated charge, does not burn as well and will actually exhuast some unburned content. The unburned content now becomes a portion of what is drawn back into the cylinder, and improves the burn of the next engine cycle. This inconsistant content of air and fuel in the cylinder is why you 2-stroke has the characteristic pop at idle which sounds like the engine is almost misfiring. It is not "misfireing", but "mischarging" or "misburning". This inconsistancy power output, which occurs with each cycle of the engine at low rpm, does not lend itself to providing smooth linear grip in situations where traction is at a premium. The 4-stroke, even though firing on every other cycle, is much smoother and linear because it has valves which make each fresh charge of fuel and air very consistant, and has a heavier flywheel to dampen the power pulse, and carry the engine through the non-firing exhaust and intake cycle. Once you ride one of the modern 4-stroke trials bikes across something like an off-camber uphill turn you will quickly realize the advantage of the different type of power and traction, even if you don't understand it. Quote Link to comment Share on other sites More sharing options...
stevel Posted December 10, 2004 Report Share Posted December 10, 2004 BillyT, I like your comment regarding writing to help each other not to belittle each other-- wasn't that what you did to me when I commented on the revs of a trials bike. Don't dish it out if you can't take it pal!! PS According to the report in the TMX today the Mont ticks over at 1800 revs Appology accepted!! Quote Link to comment Share on other sites More sharing options...
billyt Posted December 10, 2004 Author Report Share Posted December 10, 2004 (edited) stevel My comment on your topic was about your statement regarding the rpms. It was a question or query as to were you got this idle number from. At no point did I knock or belitle you. You are the one taking it all out of context! I quote: "To stevel A trials bike idles at around 300 rpm and up so were do you get 1500 RPM from?" That is a question pure and simple, and not a statement.......... Nowhere in my post did I say you where talking a lot of tosh as was said to us when were discussing the 4t traction. I am still confused regarding the 1800 rpm at idle. When one says "it ticks over at 1800 RPM" that refers to its idle speed. I think or I hope semantics is at play here? I am waiting on my 4RT coming and when it does I will tach the rpms at idle and post accordingly. Idling at 1800rpm seems very high, but untill I get my bike I can not say for sure. I can how ever say that my Beta and Scorp's idled anywhere from 300 > 500 rpm. Hell even a car idles at around 900>1100 rpm. BillyT Edited December 10, 2004 by BillyT Quote Link to comment Share on other sites More sharing options...
munch Posted December 11, 2004 Report Share Posted December 11, 2004 billy i have my 4rt and idle speed is 1800rpm. it is high i know but thats what honda say! Quote Link to comment Share on other sites More sharing options...
jaylael Posted December 11, 2004 Report Share Posted December 11, 2004 "Once you ride one of the modern 4-stroke trials bikes across something like an off-camber uphill turn" Rode one of the works Hondas handed over in 1976 by Bob Nickelson of Team Honda. It was one of the long stroke RTL 300's. That bike would grip! I hope the new Mont. is like that bike. That thing was sweet. The new YZ/CR type 4 strokes are fast, quck revving with no flywheelmass and super short stroke. ALL WRONG for normal use by mortal humans except in full on motocross racing. Honda had it right with the old RTL 300 long stroke. Oh, and brilliant post mr. Shannon! Quote Link to comment Share on other sites More sharing options...
toofasttim Posted December 11, 2004 Report Share Posted December 11, 2004 This next contaminated charge, does not burn as well and will actually exhuast some unburned content. And that gentleman, is why two strokes are not popular with the bunny huggers! Quote Link to comment Share on other sites More sharing options...
charliechitlins Posted December 11, 2004 Report Share Posted December 11, 2004 Wake up and smell the pre-mix. You guys are all missing the point. The math is incredibly simple. If a 2-stroke costs around $5k, and a 4-stroke costs around $6k, the 4-stroke is a better deal. The 2-stroke would be $2.5k-per-stroke, and the 4-stroke is only $1.5k. Quote Link to comment Share on other sites More sharing options...
toofasttim Posted December 11, 2004 Report Share Posted December 11, 2004 Wake up and smell the pre-mix.You guys are all missing the point. The math is incredibly simple. If a 2-stroke costs around $5k, and a 4-stroke costs around $6k, the 4-stroke is a better deal. The 2-stroke would be $2.5k-per-stroke, and the 4-stroke is only $1.5k. Charlie, have you been reading Kevin Cameron? Mo'sikle (to fall into the vernacular) engines are way more expensive than car engines 'cause they gotta look good. You gotta look at it bhp per pounds man..then trials bikes are waaay expensive. BTW for the uninitiated, Kevin Cameron is an ex-GP mechanic who wrenched for many of the US greats and is a really good journalist and used to contribute to "Cycle" and still contributes to "Cycle World". He has a remarkable ability to take a really complex engineering problem and express it concisely in laymans language. Quote Link to comment Share on other sites More sharing options...
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