Join Date: Nov 2000
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As you increase the diameter of the tire, it increases the leverage against drivetrain works to propel the vehicle. Imagine if I took away your first gear, when you tried to pull away from a stop you would find the vehicle resisted it more than ever. You would have to give it more gas, slip the clutch more, and it would pull away much slower. That is what bigger tires do to you. Every gear will now seem higher, and rpms will be lower than they were before at a given speed in that gear. 5th gear, if you have it, may be unusable. Now if you compensate by putting in a higher numerical gear set in both axles you can compensate for the loss in torque at the wheel. This will fix that problem, but you still have more torque on the axles themselves, and they will break easier.
As for speedometer compensation, that is a small gear in the transfer case or transmission that spins the speedometer shaft. If you put on different size tires, such as larger tires, your wheels turn less revolutions per mile, and you need a different gear to compensate to make the speedo accurate. That is cheap and easy to do. The regearing of the axles is more involved and expensive, but worth it.