supernova the wheel has nothing to do with the ratio. you will only need the final diameter of the tire you have currently and the final that you want to be at. then you divide them by the original gear that you have and the answer will be close to the gear you need

ex lets say you have a 205-75r15 and want to go to a 31x10.5r15. a 205 is about 28 inches tall
your original gear is a 3.42 and you need to know what to get

3.42/28= .122
.122*31= 3.782 the closest common gear to that would be a 3.73

 

Are you looking to keep the final drive ratio the same?, or just to change the speedometer drive/driven gear combo to reflect the change in tire circumference to keep the speedo accurate?( Always preferable to find a driven gear as close as possible without changing the drive gear on the output shaft). The other option is see if you can find a speedometer shop and have the original one recalibrated.Those are getting harder and harder to find these days.

 

Im trying to ensure my speedo odo readings are accurate. thats really the concern. You guys are really helpful thanks.

 

Post scrpt : i would like to know if i can put a corvette automatic in the van with out having to worry too much. Would I have to change the rear as well??
I was thinking of doing that whol IRS thing later on anyway.

 

what model? They have used a myriad of automatics over the years in corvettes from the 4L60E, 700R4, the TH350 and TH400 and I believe the Aluminum powerglide as well.

 

i dont know the model name but i think the newest version of the transmission is actually in the rear of the vehicle and driven by a torque tube

 

The 4L65E (I imagine that's what you're talking about) would be a significant upgrade however there are a few things that would be required.
A)A controller box for the electronic transmission or a manual valve body
B)the bellhousing to let you connect it. 96+ should work for this.
C)not sure on the converter but you would likely need that
D)the output shaft may be a different length. I Know that the C4 Corvettes used a different output shaft length than the standard 4L60E/700R4 did.

I am wanting to say that the trans also mounts 1" further back but could be wrong on that. If I were going to the trouble I'd do a 4L80E from a truck or get an 88-93 700R4 and put it in instead. Even for the price of parts to make the 4L65E work you would probably be able to put one in that would be significantly stronger than stock and have it be a bolt-in swap. The other option is if you're changing engines to use a computer that supports the transmission, such as a Vortec engine or an LS1 based engine. Then it becomes a lot simpler to do.

 

With a late model transmission, you have the speedometer cable... or lack thereof... to worry about as well.You'd have to go with an electronic speedometer,all the newer vehicles run the speedo off the VSS, not a cable.Some of the aftermarket electronic speedometers can be calibrated, however, so if you're changing tire sizes or rear-end ratios, it makes it easier.

 

OOOOOOH this sounds too rich ofr my blood right now. I wanted to drop a vette L98 in because I cant foot the bill on that LS block and I wanted to know what tranny to put in. The computer mods and all that extra fab is somehitng i cant entertain any longer because i cant pour the money into it. I wanted to know I guess the lesser of the expensive mods. I want mor power but im not in a world chagning modification budgt right now.
Sorry for the late reply but I have had lots of work hours lateley.