901 ratios

[Mike M]

Hi all... I have noticed that a few guys know a lot about 901 gear ratios etc. My question is this..I have a 901/07 trans. I am running
225 50/15 tires on the rear of my 69S. At about 70 mph, the engine is turning about 4100 rpm. Does this sound right? I am assuming that nobody has changed gears over the years,so 5th gear should be 29:23. Is this correct?
Thanks

[andyjboy]

Mike, I think that a 1969 S fitted with the original sized 185/70 tyres would be doing about 86mph at 4100rpm in 5th gear - the engine speed at 70mph being approx 3400rpm.

The overall diameter of your 225/50 tyres is about 5% smaller than the original tyres which will lower your gearing & affect your speedo reading - but I would not have thought that it would make this much difference. Chances are that your speedo is under-reading (in addition to the effect of the tyres).

Andy Boyle (UK)
'69 911E