2006 yzf 250 top speed
- Thread starter 11brianm
- Start date
flyingfuzzball
Member
- May 10, 2007
- 957
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why do you want to go 100mph on a dirtbike? think about it. your bike isnt made to go that fast.
- Aug 2, 2000
- 13,504
- 19
point-one-five past Ludicrous speed
Ahhh, the Gixxer engine would be the only peice capable of 200. I went 85 on an XL600 once, the front fender was sooooo close to being sucked into the tire it was crazy. The difference between 70 and 85 is huuuuge. A dirt bike has no business goin that fast!
11brianm said:
If you can stopping sniffing glue long enough to look at it logically, you'll see that your bike can't go 85 now and isn't likely to ever go 100mph.
Gearing is really pretty simple if you take a step back and look at what is actually happening. Basically gearing just provides a way to reduce the rear wheel speed in relationship to the crankshaft speed. By reducing the rear wheel speed the gearing provides a mechanical advantage. The greater the speed reduction the greater the mechanical advantage.
The total speed reduction comes from three separate speed reductions. You have the Primary reduction which comes from the connection between the crankshaft and the clutch outer hub. If you look in the engine on most modern bikes you'll see they are connected directly together with straight or helical cut gears using a small gear on the crank and a large gear on the clutch. Some older designs used a small primary chain between these two gears. Vintage racers can no doubt tell you lots of horror stories about primary chains that have failed. On the 1998 YZ400 the crank gear has 21 teeth and the clutch gear has 62 teeth , for a primary reduction of 2.952 :1 (62 / 21 = 2.952) . Other dirt bikes will have similar ratios. The 1972 Hodaka Super Rat 100 uses a primary ratio of 3.71:1, while the dual sport Wombat of the same year uses a ratio of 2.75:1 . Street bikes tend to use much lower primary ratios (below 2.0 :1) to provide a higher top speed . Because the crank sprocket (drive sprocket) is smaller than the clutch sprocket the crank will turn more rpm than the clutch when they are connected together. So in the case of the YZ400, the crank will turn 2.952 rpm for each complete revolution of the clutch.
Once the clutch is turning it will transfer it's rotation to the counter shaft. There are two shafts in the transmission , the main shaft that is connected to the clutch inner basket. This is our second speed reduction. This transmission (or internal) speed reduction is variable depending on the gear that is selected. In this case the main shaft is the smaller or "drive" gear while the counter shaft has the larger or "driven" gear . The YZ400's first gear has a 14 tooth gear on the main shaft and a 27 tooth gear on the counter shaft for a 1.929 :1 ratio (27 / 14 = 1.929) . So now the main shaft is turning 1.929 rpm for each full rotation of the counter shaft. We have the counter shaft turning now, so if we hang a small sprocket on the end of it, loop a length of chain around it and connect it to a large sprocket on our rear wheel we can provide one more speed reduction that we'll call the secondary or Final reduction. If we use the YZ one more time we end up with a 14 tooth counter shaft sprocket or "drive" sprocket, working with a 49 tooth rear or "driven" sprocket, for a final reduction of 3.500 : 1 (49/14 = 3.500 ) . Now that we know all the individual speed reductions between the crank and the rear wheel we can figure out the Total reduction with some simple math .
Primary ratio * Internal ratio * Final ratio = Total reduction (ratio)
For the 98 YZ400 with stock sprockets in first gear that works out to : 2.952 * 1.929 * 3.500 = 19.930 ( Total reduction) Which means the crank will turn 19.930 rpm for each rotation of the rear wheel when the bike is in first gear. Now if we plug in your WR & YZ426 numbers for first gear we can see what changes we need to make. If we assume the WR and the 426 has the same Primary reduction as the 98 YZ400 (not sure if this is the case) the numbers look like this For the WR400 with 14/49 sprockets and a first gear ratio of 2.4126 we get : 2.952 * 2.416 * 3.500 = 24.962 ( Total reduction) For the YZ426 with 14/49 sprockets and a first gear ratio of 1.846 we get : 2.952 * 1.846 * 3.500 = 19.072 ( Total reduction) So the first two speed reductions on our virtual WR400 are 23.6 % lower than the YZ426. Now we know that we can't easily change the primary or the internal reductions, all we have left is the final drive ratio. If we use the first two ratios as a constant for each bike, figuring the gearing is just a matter of juggling the sprocket numbers: WR400 first gear constant : 2.952 * 2.416 = 7.132 YZ426 first gear constant : 2.952 * 1.846 = 5.449 Now we can use these constants to determine what final drive ratio we need. WR400 Total reduction / YZ426 constant = Final drive reduction we need 24.962 / 5.449 = 4.581 Now all we have to do is find a sprocket combination that provides close to 4.581 : 1 ratio . 55/12 gives us a ratio of 4.583, and 55/13 is 4.23 :1 . These are pretty low ratios, and I don't know if a 55 would even fit on the YZ.
So to get as close as possible to the WR you'll need to verify the primary ratio on the WR400 and the YZ426 and plug the numbers in to the original equation: Primary reduction (ratio) * Internal reduction (ratio) * Final reduction (ratio) = Total reduction (ratio) You can use this simple formula to determine the top speed of a bike as well. If we plug the fifth gear ratio (0.952) into the equation we get 2.952 * 0.952 * 3.500 = 9.836 (Total reduction) . If the YZ400 peaks at 11,000 rpm then we are reducing the rear wheel speed to : peak rpm / total reduction = rear wheel rpm or 11000 / 9.836 = 1118 rpm
Now we can figure out how far the bike went in one minute Using the equation rear tire circumference (inches) * rear wheel rpm = inches traveled / min we come up with 84 * 1118 = 93912 inches traveled in one minute. If we convert that to feet we get : 93912 / 12 = 7826 feet traveled in one minute.
Then converting that to miles/min gives us - 7826 / 5280 = 1.482 miles / min If the YZ400 has sufficient torque to turn 11,000 in fifth gear and we do the final conversion to miles per hour we get 1.482 * 60 or 88.93 mph.
Of course wind resistance will into play and it you won't see that speed.
In short, get a calculator and a CLUE. :coocoo:
If he dropped it from a helicopter, from high enough, it will go over 100mph? But, it would take a lot of suspension work! Fantastic reading Rich!
11brianm said:
Two things are infinite: the universe and human stupidity; and I'm not sure about the universe.
- Albert Einstein
11brianm said:
Unlike you, I know exactly how much power you can make with a 250F, and how much power it takes to move a motorcycle down the road. Like Al said, human stupidity is truly an inexhaustible resource. Especially in this thread. :rotfl:
11brianm said:
Only because we all know it's not possible..
If you would have read what Rich posted, you'd understand that it doesn't matter how big you bore it, what fuel you run, how it's jetted.
It's gearing.
We already know you run a 52 rear. It wouldn't take long with a calculator to figure out your top speed based on your gearing...
And I am almost certain you have stock gears in the engine and trans..
So.. what's your front sprocket? I'll do the calculation..
