Here's the deal, I got a free set of nearly new tires to put on my Z28, but the new tires are a different size (I think they're the Iroc size, 220/60 15 while I have 215/65 15's) anyway I want to keep the speedo accurate, and according to a program that someone made here thats floating around, I can keep the same drive gear while switching to the 38T Blue driven gear. The program says the part number is 1359272, while the FAQ here says a 38T blue gear is 25513045, and I just got off the phone w/ dealer parts and they gave me the number 25522483. Does anyone know why I'm getting 3 different numbers?? Thanks!

------------------
85 Z28- 350, Comp 262, Edelbrock Performer intake, Edelbrock 600 cfm carb and Edelbrock cat back, Summit headers and vette servo
-JVC, Eclipse, Pioneer, MTX, Phoenix Gold, Planet Audio

 

1359272 is for cable driven speedometers. 25513045 is for electronic ones.

 

"iroc size" would be a 16" wheel. 245-50-R16. All the 15" wheel cars that i'm aware of got the 215-65's. And for the record, there is no such size as a 220-60-r15. Do you mean 225?

all these sizes would require no speed re-calibration. The difference in diameter is very small.

235-60-R15
255-55-R15
275-50-R15 (probably fit on back)

and a 225-60-r16 will only have about a 3.5% speedo error. I wouldn't bother messing with the speedo gears for such a small difference.