Rear axle

[BSAA10Richard]

I am a bit confused after reading posts on the forum about different rear axles, I have an early 1953 series 11 convertible same rear axle as a mm series, I have a 948cc engine mated to the original 803cc gearbox, top speed is about 50mph but the engine is reving it's heart out, it has a 5.375 rear axle, will 4.55 axle be okay with the 948 engine and will it increase top speed and be comfortable with gradients etc

[philthehill]

The 4.55 ratio will give you a slightly lower top speed with higher revs. The lower 4.55 gearing will be better on gradients though.

[BSAA10Richard]

Sorry philthehill I said I was confused, the axle fitted to the car at the moment is an 8/43 which apparently is a 5.375:1 the one I have to replace it is a 9/41 which is 4.55:1 I believe this is now correct, so if reading the previous post if the 4.22 gives a higher ratio than the 4.55 then the 4.55:1 should give a higher ratio than the 5.375, if this is correct will the 948cc (rebuilt) engine cope with the higher ratio

[philthehill]

Confused - happens to the best of us.
The 948cc engine will easily cope with the 4.55 ratio rear axle. A better top speed, better fuel economy and a less stressful cruising speed. You may have to change the speedo assy or speedo drive ratio to get the speedometer back to reading right.

[BSAA10Richard]

Thank you, the speedo is already way out so I have fitted a GPS speedo just in case I end up going too fast in a 30 zone I did contact a repair firm they needed me to measure the distance 6 wheel revolutions travelled and needed £170 to do the recalibration etc. hence the GPS

[Edward1949]

Confused - happens to the best of us.
The 948cc engine will easily cope with the 4.55 ratio rear axle. A better top speed, better fuel economy and a less stressful cruising speed. You may have to change the speedo assy or speedo drive ratio to get the speedometer back to reading right.

Agreed. And I've even heard of 4.22 axles being fitted to 948cc cars with satisfactory results. Much quieter high speed cruising, better fuel economy, and arguably a more usable (faster) third gear ratio. And the low first gear on Minors means it'll easily cope with higher-geared standing starts.

[BSAA10Richard]

well the 4.55 axle is now fitted and what a difference to the car so much better