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Radical new bike design
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Posted by: Casper250
I've been thinking about this since i saw the cannondale bike come out.
For aurgument sake, lets say that we turned the motor on a bike around, such that the cylender was in the rear and the transmission was in front. You could put the airbox where the gas tank is and the gas tank could go under the seat where the airbox was like on that new Rev bike. In doing this,
1. you could have a perfectly strait shot at the motor with the carburator,
2.you could flatten out the seat up front because there wont be a big gas tank,
3.the radiators could be mounted lower on the bike because there is no exhaust pipe,
4. The center of gravity would be lowered and more centralized because of moving the gas tank and moving the cylender tward the middle of the bike, this would as make the bike faster to turn,
5. You could have some kind of ram air induction to the airbox,
The only thing i would see as a problem is a 2-stroke exhaust out the back. You would need a linkless side mounted shock and route the exhaust up the back like a ducati sport bike. A 4 stroke exhaust should be a little easier.
Just a thought.....
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faster till the fear of death is outweighed by the thrill of speed...
http://members.tripod.com/casper_12300/
Posted by: KnobShredder
i think the rear exiting exhaust design is beautiful, and can be made functional with 2strokers or 4 - it's so much more streamlined, instead of wrapping it around the engine. i also am a big fan of single sided swingarms with same-side sprocket/brakes, but from what i hear from streetbikes like Ducati and Aprilia they are heavier than conventional. i hope to someday see a version on dirtbikes. i've been thinking of a design for single-sided front suspension - i know some bmx bicycles have them. as far as ram-air, would a dirtbike attain speeds where you would notice a difference?
Posted by: Norm
Casper,
Cool idea. There's one drawback with this layout that I think should be considered, though. If you turn the engine around, your countershaft sprocket will be near the front of the bike. You'll have to run a chain all the way up there to transfer power to the rear tire. I imagine this would be a pain in the butt to work out. Perhaps even more important would be the problems associated with chain torque on the rear suspension. It's common practice to put the countershaft sprocket as close as possible to the swingarm pivot to minimize the effects of chain torque on the rear suspension. If you move the two points farther apart, it seems like you're asking for trouble in this area. Just my two pennies.
Norm
Posted by: MikeT
I'd bet there is an easy fix for that. The CS sprocket could just be placed in the back with a new case design.
Posted by: marcusgunby
i think there would be a few problems with this.
1 the carb angle still would not be in the centreline.
3 lower rads mean more roost damage.
4 honda tried a really low centre of gravity in 92 and it has undesirable affects(i think u=instability was one)
5 ram air ony gives a couple of HP at 180mph.
Posted by: Casper250
The carb should have a strait shot if it's used in a twin spar frame like a KX or a CR.
The low center of gravity was just a thought because the new Rev bike was touting the lowest center of gravity in their design.
Even if the low center of gravity is not to desirable, having most of th weight in the center of the bike is desirable to maiking it a fast turner.
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faster till the fear of death is outweighed by the thrill of speed...
http://members.tripod.com/casper_12300/
Posted by: cujet
Actually, I am surprised that Yamaha did not make a straight shot carb setup on the new 4 strokes. I'll bet there is some HP there.
Chris
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94 Husky 360 2 stroke, Street legal,(gotta clear my throat now)! Ported engine, FMF pipe, kehin PWK carb, full knobbies, Pro Action Showa suspension, Pro tapers. 50HP
Posted by: MACE
I'll keep the exhaust in front, thanks.
I'm a big fan of the downdraft (downdraught for Marcus http://dirtrider.net/ubb2/wink.gif ) carbs and tank under seat. Just look at any modern sport street bike for the blueprint.
I think you need to keep the heavy engine forward to keep adequate weight on the front wheel. This is a constant problem on v-twin sportbikes - wheelies.
I can't imagine why we would not want a low CG. The bike rolls about the CG so it should trasition faster with a low CG with everything else equal. I suppose you could transition so fast you unload the tire contact patches but the only reason you don't do that with a high CG is because you CAN'T transition that fast....
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MACE
One night I was layin' down,
I heard mama 'n papa talkin'
I heard papa tell mama, "you let that boy MOTO,
it's in him, and it got to come out..."
Posted by: OldassKDX
I'm pretty sure that dirt bikes rarely see speeds where the ram effect of the air would be significant. They do however see all sorts of debris and water, which would turn the bike into a very exotic and expensive piece of junk very quickly.
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Posted by: mxneagle
I've heard that the exhaust out the back of the bike is somewhat of a problem for cannondale. I'm not too sure about exhaust design for 4 bangers but I think you do need some length for low end torque
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Posted by: Casper250
Ok, for the ram air, there might not be enough speed for a suffiecient amount of pressure to be built up for a noticiable difference but i would think that it would still be better then the way it is now. There are all these mods that people do to get more air into the airbox. I would think that it would be easier to get air to the airbox if it were flowing in the same direction as the carb flows instead of having to make an 180 degree turn.
For the exhaust, i'm not to sure what you can do for 2-strokes, but i think a 4 stroke there might be a way to snake the pipe around to get the desired length.
And the tranny problem i think i got something for that. Like mike T said, we can put some intermediate gears from the front to the normal spot. You could change your final drive ratio bye changing the intermadiate gears instead of the chain and sprockets....
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faster till the fear of death is outweighed by the thrill of speed...
http://members.tripod.com/casper_12300/
Posted by: HiG4s
A couple of thoughts, if the carb has a straight shot, it will be more likly to injest water, or be hit by roost and develop a hole in the filter system which would allow in dirt. Notice Cannodale's intake is behind the number plate. I'm not sure just how much difference, if any would make. It also appears from the photos of the Cannondale I've seen, there is no way to take the head off without pulling the enging from the frame. This could be a major concern to a 2-stroke racer.
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Posted by: Casper250
Picture your entire gas tank as it is right now on your bike as an airbox, now put a coke can sized vent right where your gas cap is. Now make a cover so it's not just an open hole. On the bottom make an opening like the one at the bottom of airboxes. This wont be directly hit by roost and even if water got in, it would drain out the bottom like normal.
I think the c-dale bike has a problem with space up fron but if the motor was positioned backwards, it would allow you to have an airbox there.
I'm starting to see holes in my design.....
One of my assumtions was that having the cylender tward the rear, it would allow for a 50/50 weight distribution but it seems that this is not a desireable trait with the need for more wieght on the front tire for traction.
Does anyone know what the weight distribution on a dirtbike is?
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faster till the fear of death is outweighed by the thrill of speed...
http://members.tripod.com/casper_12300/
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