Correct gear ratio for tire size.

[drumnerd33]

The reason i went with this tire size is the availability of the tire, the other sizes are really rare and cant really find a good choice in tires.

[drumnerd33]

I'm not sure if the speedo works out 100% on an Aspire trans in a Festy. Logic says it will, but Im not sure math works out between the tooth count on the speedo cable gear that slips in the tranny and the Festy speedometer. I seem to recall there was something odd about the speedometer drive gears between the two versions. I could be dead wrong....there are several people on here that have messed with it and can tell you for sure.
Regardless, the steeper final drive on the Aspire works great to gain back the applied torque lost by running taller tires. I believe the guys running the G25 from an EGT or Capri get like a 4.11 final drive. Some on here have done some cool stuff with swapping internal gears and other stuff.

I already confirmed the aspire speedo gear because the tab broke off of my festy one when i removed my engine for my build... i needed a new one and read on people arguing wether the aspire one works or not... so i finally just went to the yard and pulled out a aspire mtx speedo gear and its identical, as in same shape, same, size, and exact same tooth count. So with the math on the 2 different tire diameters showing i would need to increase my gear ratio to 4.06 the aspire diff is 4.058 thats really close and i know for a fact that the gear calculator im using works cuz i used it to figure my gears when i built my rock crawler.

[blkfordsedan]

Stock Festy 145/80R12 dia = 21.2"
175/50R13 dia = 19.9" this is why your Festy will feel "zippier" with these 13"alternative wheel/tires. http://chadconway.pbworks.com/w/page...re%20Breakdown




Drummer your 185/60R14 specs out @ 22.7" dia . From personal expierence running a Festy tranny in my Aspire's for @ 65,000 miles the max dia I can run is @ 22.6"-22.7".
When I went taller it was just to sluggish on the highway. With 175/64R14 23" dia Blizzacks's the Festy 5spd in my Aspire was just to tall for comfort. My mileage suffered badly(I'm sure some of it was tire drag and the very heavy BMW wheels) but it still was over geared.
My normal "Cruise" speed and commute is 75mph with some very large hills (no CO mountains but Large hills).I drive 102 miles everyday,and with stock Aspire 175/70R13 dia 22.6" tires its just enough motor to feel comfortable. But if I get days with big head winds pulling some of these hills gets annoying in 5th. I would really like to try my Blizzacks with STEEL wheels but I still think its just too tall of a tire for my combo.
So with all that said, for ME a tire that's @ 22.6" dia on my Aspire with a Festy tranny is pretty much maxed out. And @ 75 mph I'm @ 3100 RPM btw. So in a lighter Festy this tire dia should work pretty good with a healthy strong engine.
I'm going to try to get some Honda 15" steel wheels and run 195/50R15 22.7" dia rubber this summer on this Aspire. Also very important to note is that "Printed" tire specs are meaningless! The actual tire specs can vary widely from manufacturer. I worked for Goodyear as a tire salesman so I know this for fact. We would see this ALL the time,so a WISE person will actually measure his overall tire dia. And not just assume its what its supposed to be....
And Drummer how did you get a 14" to fit on your stock hub? Or did you finally pull the trigger and do the Aspire swap? The 14" wheels are hard to get a good tire dia for our MTX cars, the 13" size is easier to find more selection. The 175/70R13 is basically the Aspire size and its still 1.4" larger dia than a stock Festy.

You are correct, the 175/50-13 is actually shorter (not the same as) than the 145-12 and waaay shorter than the 155-12.
youre also correct on the printed tire specs. Many people use the tire size to calculate RPM at a given speed. This will get you close, but the accurate way is to just use the manufacturers published "revs per mile". This takes into account sidewall flex and tread distortion...and can vary greatly from what you calculate. Using the manufacturers rev/mile, I can adjust the electric speedometer in my F250 to be dead-on accurate using a paper clip, jumper wire and the trip odometer reset button on the dash. It takes less than a minute, but you can only do it like 7 times on the same gauge cluster. An accurate speedometer is important when the PCM uses it to control transmission shift points!

[drumnerd33]

I didnt know you could adjust the electric ones... thats cool