Corbin's Treehouse - Corbin Dunn, Santa Cruz, CA
Plug Bug

Final drive ratio in an electric conversion car

So, I’m getting a new transmission for my VW bug (number 3), and probably buying it from What drive ratio should I get? They can do a few different options.

My bug is/was currently running the stock stuff for a 69 bug:

Screen Shot 2014-09-04 at 6.10.30 PM.png

I have 165R15 coker tires, and the diameter was calculated via: &

The ratios I got from the VW manual, and the screen shot is from my Numbers spreadsheet (email me and I’ll send it to you).

Here are my current speeds for a given RPM and a given gear. Max motor RPM is around 5000 (maybe 5500, but that is pushing it), so I have to shift before then. I don’t use first; it is pointless (I have enough torque to not need it), too jerky, and would have to quickly shift.

Screen Shot 2014-09-04 at 6.12.07 PM.png

I always start in 2nd, shift into 3rd at about 40mph, and 4th at 65mph; this keeps me under the 5,000 RPM limit. I have a top speed of a bit under 100mph, based on the RPM.

So, the diff ratio is 4.375 (also called 4.38); also known as the “ring and pinion” gear ratio. What if I get a freeway flyer 3.88 ring and pinion? Dropping that into my spread sheet gives

Screen Shot 2014-09-04 at 6.19.11 PM.png

So, if I did this, I would: start in 2nd, shift to 3rd at about 45 mph, and shift into 4th at about 75 mph. I rarely go 75 mph; the car starts to shake a bit at high speeds, and it just isn’t designed to do that. The lower ratio would probably make the car less torquey, so I’ll stick with the standard ratio.

(c) 2008-2017 Corbin Dunn

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