Engine output shaft ratio?

Randy Mckee · Posted: Thu Jan 03, 2013 6:31 pm Post subject:

Might need to account for the difference in powerband and useful top end for various motors. ICC's (KZ) tend to rev much higher than a stock honda; 12700 rpm used for gearing a stock honda will have to be converted to around 14,000 to 15,500 for most ICC's to arrive at the right gear for the fastest straight. Just another wrench to throw at the problem.

Are you creating a spreadsheet to calc some of this? I have a couple spreadsheets from John Denman (I think?) that take care of most of this trickery and allows comparing several gear sets at once.
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#123 TonyKart - S4 Stock Honda

Benn Herr · Joined: 18 Jul 2001 Posts: 1579

Each shifter engine out there can have a different primary and top gear ratio. Some people run the CR125 with the 5 speed still in it. Yamaha, Kawasaki, the Italians, etc... each have a little bit different internal gearing. Our CR250 run 5 speeds plus our top rpm is a lot lower then the 125 boys. It's fun when somebody comes by looking for help with their gearing and ask what you're running!

Here is part of the chart we use. It's the ratio we run on our shortest track (1.25 miles). I generally gear for a certain top speed and let the lower ratios take care of the corners. It's quite a change from the Mac days when you geared to get off the corner and then let the engine scream for the top end.

Engine Axle Drive Ratio
23.00 26.00 1.13

Gear RPM Ratio Input Output RPM after Shift MPH at Shift
1st 10000 1.800 15 27 ~ 54.10
2nd 10000 1.471 17 25 8169.93 66.22
3rd 10000 1.211 19 23 8231.58 80.45
4th 10000 1.000 21 21 8260.87 97.38
5th 10000 0.870 23 20 8695.65 111.99
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Chris Reinhardt · Posted: Thu Jan 03, 2013 7:49 pm Post subject:

That would also depend on the optimum RPM operating range.
You'll find out quickly, what works for one guy/motor, won't necessarily work for another....

CR
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al nunley · Joined: 13 Nov 2006 Posts: 3033

Benn Herr · Joined: 18 Jul 2001 Posts: 1579

2002 CR250 on a Sprinter or a Superkart, the gearing is about the same.

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Come see our Superkart Build Off @
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