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General Category >> Rubber Side Down! >> You are gearing this final drive wrong
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Message started by Surviving Philly on 11/10/24 at 12:52:00

Title: You are gearing this final drive wrong
Post by Surviving Philly on 11/10/24 at 12:52:00

Alright. Let's get controversial here.

I think our machine performance exactly perfect with shorter gearing. I just did a chain conversion, with a 15t front and 48 rear, giving a ratio of roughly 3.2 over the stock 2.9-3.0.

I can't tell you how good it feels..... My God. I couldn't imagine going for taller gearing. It's not a highway rider in my book, it wants to rip. And rip it does

. https://photos.app.goo.gl/DHneBZTcKT7Sw1eb6

Title: Re: You are gearing this final drive wrong
Post by JOG on 11/10/24 at 13:58:56

That looks great.. I hope you cover the front sprocket.

Title: Re: You are gearing this final drive wrong
Post by ThumperPaul on 11/12/24 at 05:24:14

Brap, Brap, Brap, Brap, Brapppppppppp! I bet it is pretty fun running it up and down the gearbox! Will the engine braking take you from 60-0 in 5th in 120 feet without touching the brake? (Joking exaggeration)

Can you still hit 75mph? Hey, you might even be able to hit the redline in 5th with that setup! I wonder how much gas mileage is impacted.

I think you nailed it with “controversial”. The taller gear camp wanting lower RPMs at highway speed in top gear.

Nice job on the conversion! If you decide you want to tinker with it, you have fairly simple swap options.

Unrelated - how’s the clutch holding up? What does it think about the chain/sprocket conversion?

Title: Re: You are gearing this final drive wrong
Post by Surviving Philly on 11/12/24 at 11:33:49

I can still hit 75 definitely -- I think 80-85 comfortably but I ditched the speedo so I'm basing this off of feel. The most surprising thing is how much torque I have in the higher gears. Stock gearing felt like there wasn't much to give from 4-5th, whereas I am now comfortably switching gears with some OOMF left if I'm caught off guard in a higher gear.

About the clutch it seems totally fine. I've done a couple long hauls since replacing the Barnett kit and so far, so good. I still suspect the Barnett pack was eating that plate, as silly as it sounds. This caltrec kit is presumably Chinese junk but it was about 40 bucks vs $100+ with barnette or stock.

Title: Re: You are gearing this final drive wrong
Post by ThumperPaul on 11/12/24 at 13:44:33

Here’s a pretty cool sprocket calculator that shows the changes in torque and top speed. There are more elaborate calculators, but I like this one for simplicity.

https://sprocketcalculator.com/

The stock belt drive final drive is 68T/23T = 2.96 (as you vaguely noted).

I figured you could still hit 75 (kinda joking). Top speed for stock is pretty well tested around 93-95. I’ve had the S40s I’ve owned up to about 85. That was fast enough before thing’s seemingly might want to vibrate apart. They all still had a little bit left, so 93 seems doable with the right conditions.

Yeah, 4th and 5th is where I’d expect you to notice the most difference. You actually still have some real torque to use with the lower gearing. While the calculator suggests about an 8% reduction in top speed with the lower gearing, I doubt it’s that big a reduction since you can probably get higher rpms in 4th and 5th with the lower gearing. The calculator rather falsely assumes you can hit the redline before lowering the gear ratio.

Title: Re: You are gearing this final drive wrong
Post by ohiomoto on 11/12/24 at 16:54:43

Sounds fun! It might be a perfect match for this motor's limited power.