Speedo gear

[JeffN]

Anyone ever change their speedo gear in their trans? Are they available? I want to go to a pre 97 tire size and want the correct input to the speedo from the diameter change. thanks

The speedo gears were the same for all SVX's. Subaru compensated for the 97's different tire size by reprogramming the ECU.



Dave

[alltrac]

Originally posted by red95svx
The speedo gears were the same for all SVX's. Subaru compensated for the 97's different tire size by reprogramming the ECU.


Dave

I found this tire calculator someone tell me if I put a 97 ecu in my 96 will I have a higher top speed? with my stock 225-50-16 tires.

[lee]

Originally posted by alltrac


I found this tire calculator someone tell me if I put a 97 ecu in my 96 will I have a higher top speed? with my stock 225-50-16 tires.

the top speed is horsepower/drag limited. A change of 1.8% difference in tire height will not have a measurable effect on top speed. Going from a 215/55 to a 225/16 will yield a tiny bit more acceleration due to the reduced tire diameter, but even this is probably a value that would be two or more decimal places difference in the 1/4 mile (my guess anyway). Said another way going from a 215/55 to a 225/50 is the same as changing from the stock 3.545 gearing to a 3.607 and keeping the same tire - not much change.

[JeffN]

How'd you get those #'s?

Embarrass me if you will. My calc's are:

225x2x.5=225mm/25.4=8.86".

215x2x.55=236.5mm/9.31".

8.86/9.31=0.95 or about 5% change in diameter.

9.31-8.86=0.45"x3.17=1.43"/revolution. So what the hell am I saying? I think it's a 5% change in circumference so 60mph on the speedo is a real 57mph. Maybe my long division became wrong division somewhere.

[lee]

Originally posted by JeffN
How'd you get those #'s?

I measured a ratio of wheel/tire diameters (and I think you forgot to include the wheel).

using your numbers 8.86+16=24.86, and 9.31+16=25.31 and 25.31/24.86=1.018 or .018 increase, which when multiplied by 100 yields 1.8% over a 1 to 1 ratio.

if you want to do it in circumference then the numbers top & bottom get multiplied by pi each to yield 79.51/78.10=1.018.

At any rate, the top speed is not attained at redline in high gear, the car can't push hard enough. The R&T coverage of the SVX shows top speed obtained at slightly less than 5K rpm in top gear before the car runs out of steam.

[JeffN]

Yep, and the piddling diference in the speedo/odo pales compared to driving it which it's all about.