scottybaccus

Unless you are aimed at drag racing often, no more than 3.50ish

Norm Peterson

With the overdrive 5th gear being about 0.68, top gear with the 3.73's ends up being pretty close to having a T10/Toploader four speed with a 2.56 axle. That's tall enough, unless you're really going for the last mpg and have specifically tuned for low end and midrange. With 3.55's, your T10/TL equivalent drops to 2.41.


I'd call the typical choice between 3.5/3.55 and 3.73/3.80 as coming down to your tire size. With a 27" tall tire, go with the 3.73. With tires more like 25.5" tall, the 3.55's will be fine. Either of those combinations will give you about 63 mph @ 6000 rpm in 2nd, and a 2500 rpm cruise in 5th will put you just above 75 mph.

Typical, meaning the choice you make as long as there aren't any odd requirements involving the ability to hit a particular speed in a specific gear in order to avoid an "unnecessary" upshift or upshift/downshift sequence. Autocrossing comes to mind, where you'd like to be able to stay in 2nd gear on most of the faster courses you encounter. In that case, you might well end up outside the 3.5 - 3.8 range on the low side, just as you might end up above it for the dragstrip. IOW, build the car with some detailed thought toward its expected use and don't be afraid to run a few numbers.


Norm

tx65coupe

I have 3.50 gears with a T5 and think it works out perfectly. My tires are about 25.5 inches tall. I wouldn't want 3.73, it would make 1st gear fairly useless.

Norm Peterson

There's enough wider of a jump from 1st to 2nd in the Tremecs that 1st is kind of a granny gear anyway. If you gear the axle tall enough to make 1st truly useful, that'll put 5th up where you either won't use it at all or you'll feel like you'll have to downshift back to 4th every time you encounter a hill on the Interstate.

The sweet spot for a street driven car with a Tremec 5-speed seems to be when you can hit low 60's in 2nd at 6000 rpm. That also puts 1500 rpm in 2nd at about 15 mph, which is about as slow as you're likely to be driving once you get it rolling.


Norm

MustangBradley

I agree with Norm. My 5th (with a 3.50) is rarely used around town since it is just above idle at 45mph. That is why I said if I could do it over, I'd go with the 3.73. On the highway though, the 3.50 is great. Those members who said the 3.50 and 3.73 are not much different have made a good point, but there is a enough of a change to notice.