Bullwinkle wrote:
>
> Andrew:
>
> Your best bet to determine the ratio is to jack up one wheel, put the
> car in nuetral, and count the turns of the wheel versus the propellor
> shaft.
>
> I have a TD with a 4.875:1 rear axle ratio and speedometer gears which I
> fitted. It has 165SR15 radials which at the time I thought came closest
> to the original diameter cross ply tires. 3,800 RPM gives 60 MPH.
>
> Verify the cars MPH by using a watch and the mile counters on a road.
>
> <<<snip>>>
> 1. I've always thought the ratios ABSURDLY fast and many people have
> said "oh, that's just the old MGs!"
> but I am not foreign to old foreign cars.
> <<<snip>>>
> Correct
>
> <<<Snip>>>
> 2. I'd like to go to a more leisurely ratio but don't know what I'm at
> right now!
> <<<snip>>>
> Without some engine improvesments, the 4.875:1 is about optimum. It's a
> compromise between acceleration, car speed, and engine RPMs.
>
> <<<snip>>>
> 2. I am quite a serious rallyist (see
> www.musketeerracing.com) and we're quite serious about
> distances - I am likely to put a Halda or Aifab or
> Langwell in this car for vintage TSD rallies and
> calibrate it to a rolling distance, but I'd sure like
> to figure out if there's something in the drive ratio
> affecting the standard odo.
> <<<snip>>>
> All TF speedometers are the same regardless of the ratio. There were
> 5.125:1 and 4.555:1 ratios optional. When using different rear axle
> ratios the speedometer gears in the transmission where changed.
>
> The TD-TF 4.555 ratio is very hard to find. However it is possible to
> fit a 4.555 or a 4.3 from an MGA. The 4.555:1 MGA is sometimes hard to
> find, but the standard 1500 MGA gearing of 4.3:1 is much easier. These
> gears are not a drop in, but require carefull and professional fitting.
> BUT, you should have more power than what was provided in the original
> spec 1250 cc engine. You can easily over gear these small engines so it
> becomes difficult to climb hills or pull against a strong headwind. You
> don't want to wind up being late at a checkpoint for a Time Speed
> Distance rally because you couldn't achieve a set speed.
>
> Blake
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