The 82 TA that I recently bought came with 215/70/14's and I'd like to change over to 15's. I'm not sure what size tire I want to run but I do know I want to go with the 15 in rims. My question is how do I adjust the speedometer so it will be accurate? Thanks

 

I believe that if you go to 15" rims and use a lower profile tire your speedometer should be close to accurate. Try to maintain the same wheel/tire height that you have with the 14"s and the tall tires you have on them.
As for adjusting the speedometer I have no idea. My speedo is out of action completely so I use my GPS for now. You can use a GPS to compare your speedometer once you change over to 15"s.

 

If you can keep the circumference of the tire the same then you won't have to do anything with the speedo gears - use a tire calculator.

If you have to change the gears, there is a tech article that explains what to do and what you need.

 

I had thought about running 15's with a smaller tire to keep from having to change anything for now. I'll go read that article so I don't mess anything up if I do decide to change the gears. Thanks for the info

 

you are over complicating this. All that matters is the height of the tire, stock is around 25.7". So regardless of the wheel, use a tire that is that height and all will be well.

 

If you know the original tire size, you can calculate the height of them like this...

215mm (tire width) x 70% (aspect ratio) = sidewall height of 150.5mm

150.5 x 2 (total of sidewall height) = 301mm

14" rim = (14" x 25.4mm) = 355.6mm diameter.

355.6mm (rim) + 301mm (sidewall) = 656.6mm

656.6mm / 25.4mm (1 inch)= 25.8" overall ht.

So, Just look for a 15" tire that is the same ht (or as close as possible) as the original tires, and the correct width for whatever width 15" rims you plan to use. Or you could just go to www.tirerack.com and look at the specs for a tire that size and it will tell you the dimensions too...Just depends on if you WANT to go with a different tire height for some reason, or the same ht as original.

Just FYI... My car came with 15s originally on it. p215/65-r15=26.03" tall.

John C.

 

Thanks for all the help. I've got to get the car running before I get tires anyway so I've got plenty to think about now.