How come the manufacturers can build a street bike like zx10 R1 etc with 180hp and it lasts with very little maintenance , but they cant build a 250 mx bike with 35 hp and make it as reliable ???
How come the manufacturers can build a street bike like zx10 R1 etc with 180hp and it lasts with very little maintenance , but they cant build a 250 mx bike with 35 hp and make it as reliable ???
That's a good question...Most of those bikes are sold to people that use them for weekend cruising around town and see very little race track usage....If your rode those bikes at full throttle like most mx bikes are subjected to you would need much quicker service intervals but still not at the levels needed on dirtbikes because mx bikes are subject to so much more stress than a road race engine would get even at racing speeds....
For the street rider there is no need to ever exceed 4 or 5k rpm to reach the speed limit on those bikes and they may see only the occasional full throttle blast....those bikes can do over 100 mph in 1rst gear and can reach the speed limit easily at low rpm levels.
Another reason is the dirt is alot harder on a motor than the traction found on a street...Overrevving, jumping, landing, engine load is totally different.....Not to mention the amount of dirt that may find it's way into the motor when you're blasting full throttle on a loamy track that's throwing up lots of dust that's being sucked into the airbox.
I don't know this for sure but there may be a quality gap between dirtbikes and streetbikes as well because of liability issues and warranties ect....Perhaps the engine components are more durable...I don't think a manufacturer would want a bike they sold to have an engine lockup on the highway if ya know what I mean.
Street machines aren't engineered to weigh 200 pounds. The low weight of the MX thumpers has to come from somewhere, and in the quest to make the thumpers as light as a two-stroke, you can only take so much weight from the frame, plastics, etc...the heaviest component of a thumper is the engine. The lighter they try to make the various engine components, the more fragile they become, and the shorter their life is going to be.
Still doesnt add up as a 1000 cc street bike weights only 170 kg with 180 hp and has 4 cylinders , fairing , lights , flickers , starter , battery and more .
That 180 hp street engine isn't ridden at 12,000 rpm for the majority of it's run time. More like 4000-8000 rpm most of the time. If you rode your street machine at full throttle and redline from the time you started it until you shut it down, every time you rode it, you would wear that engine out pretty damn fast too.
The 4 cylinder, 1 liter street bike motor can have more radical cam timing and a more agressive, high rpm oriented intake system than the 250cc single. Basically, the big bike's extra displacement provides the necessary low end grunt, and they can tune for top end HP.
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