[J Persons]

To compute what speedometer gears you need -

Driven gear tooth count = Drive gear tooth count X Axle ratio X Tire revs per mile, divided by 1000

All T5 and Tremac trans have a replaceable drive gear. But it's a PITA to get to, the tailshaft housing requires removal to get to the gear. The good news is: Aftermarket T5 and Tremacs use a 7 tooth drive and don't normally require replacement. Most '90 through '95 OEM T5's use a 8 tooth gear, and it should be replaced with a 7 tooth drive gear.

There is a chart in most all Ford motorsport catalogs that list all the available drive and driven gears and what rear ratios they apply to.

Don't be tempted to use a 23 tooth driven gear to get the correct reading. These are not Ford spec gears, the pitch is wrong and sooner or later they will fail.