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Changing tyre sizes on e.g. GP cars.

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#1 Spa65

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Posted 02 July 2013 - 21:44

I remember about 1964 that F1 tyres shrank in diameter from (I think) 15 ins. to 13 ins. Also I remember reading recently that about 1965 some of the Indy Offy powered cars changed tyre sizes from 17Ins. down to 15 ins.

I also saw a picture once of a Lotus 25 at Spa sitting on some jig, without wheels, as it was being converted to run on the smaller tyres.

Presumably in each case the car bottom would effectively be lowered by an inch by the tyre switch, so they would have fitted different suspension to bring the ride height back to where it was before.

If that is the case then the drive shafts would then be an inch out of alignment (vertically) with the centre of the drive wheels. Is that how they ran? Did nobody bother about the misalignment because there was so much allowable suspension movement anyway in these days? Wouldn't power be reduced slightly through a misaligned drive shaft?

Something I've been curious about since the 60s and now I guess someone will tell me.


#2 Greg Locock

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Posted 02 July 2013 - 23:30

Hookes joints in particular, and CV joints in general, are incredibly efficient. In fact trying to measure their efficiency is rather difficult. The fundamental reason is that the internal velocities are very low, and forces are reacted by rolling elements.