901 Gearbox ratio calculator

[Chuff]

Hi All,

New here, but thought that I would attempt a contribution. Attached is a gearbox ratio calculator I wrote before rebuilding my gearbox.
Should be easy enough to use, basically anything with a grey background and blue text can be changed.

The bar chart tries to give an idea of whether you remain within the powerband after a change. If the blue bar is above the green bar you are good. Obviously this is more important in the higher ratios and with peaky engines.

Feel free to distribute, but please don't make any changes.

Hope some of you find this useful.

Andrew

[SWBS]

Very nifty, Andrew..give me a couple of days and I'll have it figured out. I have a '68S which was delivered new in Frankfort and is geared quite tall. Is there a method of calculation which will ball-park the actual gearing in my 901with the known factors being tire diameter and speed in gears vs RPM? Or, do I need to determine the diff ratio to make the calculation?

Thanks,
Jim

[jhora]

Andrew,

Thanks this is very nice and I like the graphs...

john

[Chuff]

Hi Jim,

Ideally one should have the diff ratio, however, I seem to remember that there are only 2 common diff ratios for the 901. (Any experts out there, feel free to correct me on this!)
If it were up to me, I would use first gear to have a stab at calculating diff ratio, simply because there are only 5 potential ratios (A,AA,B,C,D) for 1st, and it is unlikely to be C or D.
Hopefully you can find a fit for your 1st amongst the 2 diff ratios and 3 possible gear ratios.

Saying all that, I hazarded a guess at what was in my box, and got it totally wrong.
The only way to be sure is to take things apart.

Andrew

[SWBS]

The only way to be sure is to take things apart.
Andrew

Thanks, Andrew:

Once winter departs, I'll team up with my mathematical son and we'll see what we can determine....just to satisfy my curiosity!

Jim