Author Topic: Sidecar Racing Ratios  (Read 285 times)

Offline Lightningpower

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Sidecar Racing Ratios
« on: 20.11. 2015 00:30 »
I'm looking for some wisdom. Of all the gearboxes BSA offered for the A7/A10, which would be the most desirable to use in a sidecar outfit?
1953 Star Twin - Racing
1956 Road Rocket
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Offline Rocket Racer

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Re: Sidecar Racing Ratios
« Reply #1 on: 18.12. 2015 03:24 »
how bigs the sidecar and how heavy the contents  *eek* or for that matter how steep are the hills or big the straights...

The STD box has a very low first, a big gap between 2nd and 3rd, then a close 3rd and 4th.
These are typically fine with the right gearing although the gap between 2 and 3 can be annoying.

I'm in the process of fitting an SC which makes all the ratios the same, eg if I change at 6500, I will be at 5000 in the next gear right throughout the box, so I can change based on revs, whereas with a STD box the rev changes are not consistent.

Also what tyre/wheel sizes are you using. Will pay to stick with what you've got and do the maths based on your wheel circumference to work out your top/cruising speeds. The issue is typically more what sprockets to run rather than what box.

Unfaired my a10 runs into a wind wall with 2 onboard at around 145kph. So I gear to be doing 7500 rpm at that speed and my acceleration in first will lift the front end.

The question then becomes what speed do you expect to hold and what rev's are you prepared to spin at. The higher they are the quicker the bike will get there, but will be less relaxed. If you gear too high to hold 3rd and 4th up the hills you're then back way down to 2nd which should really just be your intersections gear ratio .

I hope that helps
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