In a message dated 1/29/98 3:47:34 AM Eastern Standard Time,
jworthy@pcug.org.au writes:
> Does anyone out there have any details regarding the gearing of a TR6 circa
> 1972 with o/d on 2, 3 and 4th? This beast of mine is a US delivery carb
> version converted to RHD. It runs Pirelli P400s at 185/65 HR 15 with a
> rolling circumference of approx. 1.885m (or for you imperialists arouns
> 6'2"). I suspect this low profile undergears this car quite substabtially.
> I read some where where the geraing is supposed to be arouns 41.7 Km/1000
> or, once again 25.9 m/1000. i suspect I am getting around 36Km/1000 or
> 22.4m/1000.
John,
Per the '71 TR6 owner's manual, 1000 RPM in fourth should be 20.74 MPH. You
can figure the speed at 1000 RPM yourself for any size tire, using a very
simple formula:
(Tire Diameter X 2.975)/(axle ratio X gear ratio)
To find the tire diameter, divide the tire size by 25.4, multiply that by the
aspect ratio, multiply again by two, and then add the wheel diameter to the
results.
For a 185/65 15, the equation would be:
((185/25.4) X 0.65 X 2) + 15 = 24.46
Plugging that into the speed/rpm formula above, we get:
(24.46 X 2.975)/(3.7 X 1) = 19.67 (for fourth gear)
(24.46 X 2.975)/(3.7 X .8) = 24.58 (for OD)
One thing to keep in mind -- tire sizes, as given by the manufacturer, are
seldom very accurate. It's best if you can measure the diameter yourself.
Dan Masters,
Alcoa, TN
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
http://www.sky.net/~boballen/mg/Masters/
'74 MGBGT---3000mile/year driver, original condition, slated for a V8 soon!
'68 MGBGT---organ donor for the '74(2 night stop-over-$
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