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Discussion Starter · #1 ·
hey i was looking around and i saw a 250r motor that has a little over 75 hp. how fast do u think it would go ahha. i never seen a motor like this and it just amazed me.
 

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fast in what way, top speed? it all has to do with gearing and tire size
 

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not very fast! LOL I have a 370 pro cross cylinder that makes 77.5 hp at the rear wheels on a very conservitive dyno. We run 22 in tall tires and are going to a 16-36 gearing from a 14/37. We dont run for top speed, but... with what my motor makes by writes using a gearing calc in 6th gear with a 14/37 at 8750 rpm would be 92 MPH...now, not every motor can run like that! so i ran the numbers on like a stock 250R with a pipe maybe with the stock gearing and what a 250 stocker would run rpm wise, with 18 in tires, and came up with 62 MPH in sixth gear...
 

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top speed

19-6-10 front
18-10-8 back

and stock gearing
With stock gearing and 18" tires a 75hp bike would be no faster in top speed than a near stock bike. The engine can only spin so fast. You need tall gearing (and the HP to pull it) in order to go fast.
 

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Discussion Starter · #6 ·
well the motor description says its good for mx, drags. really all around use. what would be a good gearing to get the most out of it for mx
 

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depends on whole built the motor, whhat pipe, carb, head design, compression, weight, tires, swingarm, etc etc etc etc etc....LOL it needs to be geared to YOU! Just do some testing
 
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