how to change the gear ratios on a BMW?

Answer 1

Best thing to do is check with your local chapter of BMWCCA assuming you're in the United States, for a mechanic that specializes in modifying gearing.

Dinan (http://www.dinanbmw.com) and several other aftermarket tuners and installers may have the savvy to switch ratios, but they'll undoubtedly question your logic. Dealerships can probably handle this type of request.

BMW has a tradition of motorsports and racing, and they put all their expertise into making each car ideally balanced for its intended purpose.

If you're motivated to do this, I suggest bouncing the idea around in a BMW forum like m5board.com or bimmerfest.com.

Answer 2

Changing gear ratio is a very technical issue that involves changing either/or the differential to axel ratio, or installing a different transmission that has different gear to cluster gear ratio. If you are talking about a front wheel drive vehicle, then you must find what is on the market for your transaxle. If you are talking about a rear wheel drive, then you must change the ring and pinion gears inside your differential. One basic and easy way to do this is by finding a different ratio set up that will work with your engine. The best advice anyone could give you is to contact BMW and inquire about what is on the market for what you wish to accomplish. If you are trying to lower the ration for racing applications, then you are going to find it tuff going. A lot of 4 cylinder engines have lower gearing than a 6 cylinder would, so that might be an idea. I'm sure BMW has a performance division that can point you in the right direction, with what you have in mind. One easy and inexpensive way to get lower is to install a much shorter tire and wheel. Tall tire and wheel for top end, and short tire and wheel for drag racing. You can lower the ratio just by going to a short wheel and tire, but you also will have to deal with other issues such as a speedometer that is off by quite a bit. This is a good question, and not knowing what is on the market for the BMW, it makes it hard to say. BMW is not known for racing, but if you contact the factory, someone can tell you where to go for these parts.
Glad to help you, Good Luck!!!

Answer 3

The easiest way is to go to a junkyard and just buy a differential with the gear ratio that you are looking for. There are about 4 or 5 of them I thnk.