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MG MGB Technical - Rear end ratio question

Hey folks, some years ago I changed the rear end gears in my TD for a taller ratio. It transformed the car! Question: Is it possible to do the same thing in a '73B to lower the RPM's at cruise? Seems a simpler answer than an O/D tranny. Thanks, Tom
Tom

The only factory gears that were higher than the standard B were used in the C and B automatic though I belive that the V8 was also higher. They are in large demand and are hard to come by. To my knowledge, no one makes the gears in the aftermarket that you are looking for. RAY
RAY

Tom,

You can get some help if you want to go to 15-inch wheels. If you combine them with tall tires, you can pick up 5 or 12 % higher gearing, depending upon your starting point.

I recently took off some 175-65-14 and replaced them with 165-SR-15 (SR = 82). Mathematically that is nearly a 12% gain.

If you want to crunch the numbers, it goes like this:

Diameter 1 = (175 x 0.65 x 2 / 25.4) + 14 = 23.0 inches
Diameter 2 = (165 x 0.82 x 2 / 25.4) + 15 = 25.7 inches

((25.7 / 23.0) – 1) x 100 = 11.7% increase in gearing

Substitute your numbers and see what you can do. It made my gearing bearable, but I also have overdrive.

I don't think you can get the "SR" ratio tires anymore, but Kuhmo makes the Power Star 758 in a 165/80/15 for about $45. I have never owned any, but it is probably what I will get when I wear out or get scared of my old Michelins.

If you have disc wheels, you might find that some of the Saab 900 wheels from the 1980s will fit. I don't know about the offset, but I'm sure someone else does. If you have wires, I guess you have to get new or maybe some used Healey/Jag wheels.

Charley
C R Huff

This thread was discussed between 10/04/2009 and 11/04/2009

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