# Gearing calculator

9 replies to this topic
• # TexN343

Posted February 25, 2006 - 11:05 PM

Can anyone tell my how I could figure out the top speed with different size sprockets? I just want to experiment with top speed and what sprockets I can keep or will have to buy. This is for my 04 yz450f

• # Fizz

Posted February 26, 2006 - 02:41 AM

well, if you know the current top speed, all you have to know is the difference between the new and old gearing ...

(old gear)/(new gear)*old top speed = new top speed
like this;
(49/14)/(52/14)*110=103.6

• # old man dan

Posted February 26, 2006 - 02:38 PM

Ithink Renthal has a good ratio calculator on their website and of course the last answer is also correct. Obviously your bike has to be able to pull whatever gearing you decide to try. Top speed is limited more by aerodynamics after a certain speed.

• # kid on a 426

Posted February 26, 2006 - 08:06 PM

could you post a shortcut for the renthal gear calculator

• # 450_rider

Posted February 26, 2006 - 08:47 PM

http://www.renthal.com/hard.asp#
Just go down to Ratio charts

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• # TexN343

Posted February 27, 2006 - 10:47 AM

OK I think I figured this out right so I posting it for you guys to check. I think stock was 15 50 and top speed 70? so (50/15)/(52/13)*70= 58.3 which sounds about right with what I have rode. So if I change my 13 to a 16 if it fits I will be about 71mph. Plz correct any mistakes.

• # grayracer513

Posted February 27, 2006 - 11:55 AM

(RPM/(PR*TR*FR))*(πWD/63360)*60=speed in gear

PR=primary gear ratio
TR= transmission ratio of the gear in question, be it top gear, or any intermediate ratio.
FR=final ratio (sprockets)
WD=Wheel Diameter (measure distance from axle to ground with rider onboard and multiply by 2 for effective diameter)
π=pi (3.1416)

Primary ratio will be in your manual

Divide the driven gear by the drivinng gear to get the trans ratio.

Divide the rear sprocket teeth by the front to get the final drive ratio.

This will not compensate for tire slippage.

• # mikedabike

Posted February 27, 2006 - 03:42 PM

I have an excel spreadsheet I got from some of the sportbike guys that I have the 04 450 numbers plugged into that seems pretty good. You can just plug in different numbers and it does the calculations for you. If any one wants it shoot me your email and I will send it.

• # grayracer513

Posted February 27, 2006 - 04:47 PM

I used the formula above to create an Excel sheet. Substitute cell references for the variables and then just plug in new numbers. The cell containing the formula will yield the answer. Easy.

• # 02YZ426

Posted February 27, 2006 - 05:19 PM

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