Gearing for SQ4

[Peter.smith]

Hi, I have a 1953 Mk1 square four which runs with a GB gearbox. The bike is running well but seems to run out of puff around 55-60 mph. I have a 19t front sprocket and a 47t rear sprocket, which I think is standard. Is there a 17 or 18 tooth sprocket to replace the original. Any suggestions would be greatly appreciated. The bike could be geared for a sidecar but I am not sure. Thanks Peter Smith.

[simon.holyfield]

You need to be looking at the engine sprocket. Conventionally, we change the engine sprocket to change the gearing, not the gearbox sprocket. This is because the speedo drive is from the gearbox not from one of the wheels so we don't want to change the gearbox sprocket or the rear wheel sprocket, otherwise the speedo will be inaccurate.

I have a 25 tooth engine sprocket on my Mark 1 and it goes very well. It's quite likely that you have less teeth than this!

[Simon.Gardiner]

To lower the revs at any given speed a 'front sprocket' needs to be bigger rather than smaller...
As advised above, Ariels changed the gearing (on all 4-stroke models) by changing the engine sprocket, and those are where the available alternatives are most easily located. (OK, except for a year or two of Huntmasters that had a smaller clutch sprocket. Maybe make that 99.9% of 4-stroke models! )

SG