7 replies to this topic

[Mini1275buggy]

How much difference would a lower drop gear ratio make (1:1 to 1.136:1)?
Thanks.

[Cooperman]

It would lower the final gear ratio by a factor of 0.96. So a 4.133 FDR would become 4.30.
The ability to change the transfer gear ratio is really for racing where the car needs to be geared to just reach max. revs at the braking point at the end of the longest straight is important. Changing the transfer gears can be done without taking the engine out so it's easier than changing the diff.
They are of no practical use on a road car.

[Mini1275buggy]

Thanks for the reply, I have a buggy with the 1275 engine and big quad wheels so i am trying to get the lowest FDR possible.

[Cooperman]

I think the lowest Mini FDR you can get is about 4.6:1. 1.1:1 drop gears would lower this a bit more. I hope that'll be enough for your big diameter wheels.

[Mini1275buggy]

Is it possible to alternatively just get/make a very low first gear?

[Cooperman]

That would be mega-expensive and there would be a big gap between 1st & 2nd. Be cheaper to get much lower transfer gears specially made then you could choose the ratio. You need to speak to whoever machines the straight-cut drop gears for the likes of Mini Spares, but I don't know who does it these days.
A 4.6:1 FDR is very low and would probably suit up to a 15" wheel depending on tyre width and profile. What is the rolling radius of your tyres?

[Mini1275buggy]

The diameter is 25 inch and the circumference is 2m.

[Cooperman]

That makes the rolling radius 12.5" in straight geometrical terms. A 10" with 165/70 tyres has a rolling radius of 9.54.
In terms of final drive ratio, your with a 4.66:1 FDR is like a 10" wheel one with a 3.54:1 FDR, or 3.89:1 if you also fit 1.1:1 drop gears. That should not be too bad in terms of gearing overall.