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straight cut gears


mx1986

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Other way around

 

This is the way we figure our gearing changes, especially when we do a primary ratio change.

 

The stock ratio was mentioned 2.86 & a 2.68 ratio. That's a change of .18 gearing difference. Now a 17 front sprocket was mentioned, but no  front (comparison) & no rear was, but we'll use a 16/41 = 2.56 ratio rounded down. So, let's take a 1 tooth front sprocket change like mentioned, 17/41 = 2.41 ratio. One tooth is .15 difference, That's a pretty good comparison.

 

The one tooth comparison doesn't work the same when getting to the bigger front/smaller rear sprockets. Let's take the 17/41. 2.41 ratio & a 18/41 = 2.28 ratio rounded up. That's a difference of .13, so, it starts to become bigger difference. 

 

This is what we prefer to do & gives the exact math for the gearing change. This really helps when you have a known baseline gearing set-up. Then you want to change the primary gear, but can work with other scenarios also.

 

We just did this drill for our DMX for a starting baseline. Our old primary 1/4 mile set-up was a 17/36, 2.12 ratio with a 2.86 primary. We take the sprocket ratio & add it to the primary ratio, 2.12 + 2.86 = 4.98 ratio. That gives us a known MPH at a certain rpm with our tires & our overall combination. 

 

Now, we changed our primary ratio on our DMX to a 2.54, add that to our known combo 2.54 + 2.12 = 4.66 ratio. We used a gearing/mph calculator to figure the mph for a given rpm. It gives us around 12 mph more that the old set-up, but at a lower rpm. It puts us close to what we are trying to run & will fine tuned from there.

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when comparing overall gear ration wouldnt you multiply the primary x the sprocket ratio rather than add them together?

 

I stand corrected, you are right. The last 2 paragraphs are incorrect. You multiply the primary ratio x the sprocket ratio.

 

Plus, you can throw in the transmission ratio also for whatever gear is being used.

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  • 4 months later...

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