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Altering ratios on 6 speed box


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The box design means that 6 is direct through the box, 1:1 ratio, I think the only option is to go for a higher diff. It seems counter intuitive that the 5 speed box which has an overdriven 0.82:1 fifth speed also has a higher diff (3.62) and the 6 speed which has a 1:1 top gear has a lower diff (3.92:1) . Not that sensible on a road car, but maybe justifiable on a track focussed car.


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Damn. This is all really confusing. I thought that the BMW sourced diffs came with a final drive ratio of 3.62. I didn't know that the gearbox you specify at purchase makes Caterham provide you with a diff with a different ratio. I've just ordered a new Caterham with 5-speeder and plan to try for 6 months before swapping (maybe) to a 6-speed one. This now means that the diff ratio needs changing too according to Oily I think?

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My SLR had a 3.62 dif and 6 speed gear box and would give 144 mph at the 8,000 rpm in 6th on ACB10s. Entirely theoretical as I could not get to 8,000 in 6th.

I have a good spread sheet if you want to see what diff you have and what difference changing the diff or the tyre size would make. If anybody would like a copy just blatmail me your email.

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