After a lot of searching, I have found no post that corrects speedo inaccuracy in 2nd gen minis, especially the nearly 10% error with 175/65r/15 tires. If you have experience and/or input, the main thread is in the tires&wheels forum: https://www.northamericanmotoring.co...y-w-tires.html

I don't mean to replicate posts between the two forums, but I know that some folks only check a particular forum and the speedo error is mostly a 2nd generation issue (this group).

I'm hoping that if we put our heads and experiences together, 2nd gen owners needing new tires can substantially improve their speedo accuracy.

Thanks
Dave

 

Not sure if you've seen this yet but it's a good tool for what you are trying to accomplish.

http://www.miata.net/garage/tirecalc.html

 

and some more.....
http://www.1010tires.com/TireSizeCalculator.asp

http://www.tiresizecalculator.info/

 

I don't know if this will work on all cars but on the s2000 people use this yellow box product when they get different gears installed and it recalibrates the speedometer.

http://www.ricks2k.com/products/yellowbox.php

 

Thanks for the "yellow box" link. I read over the installation sheet and it seems possible that the box could work in a Mini (emphasis on possible). The box is a really simple 4 wire installation: power/ground/speedo-in/speedo-out. The owner just increases or decreases the gain in the speedo signal to correct as necessary. The problem is that 2nd gen Minis are electrically, quite challenging and seemingly simple changes tend not to work and void the warranty - from what I've been told.

Tire calculators don't seem to work. In the most extreme case, tires that the calculator shows to only be 3% different from my stock setup are "right on" in MPH readings while my, any many other "just-a-coopers", are off almost 10%. I'm really looking for anyone with a 15" tire on a 2nd gen with an accurate speedo - I/we want that tire.

 

Newt's Advanced Tire Expert Speedo Fix (for Less):
1. Look at speedo number.
2. Subtract 3mph if under 65.
3. Subtract 4mph if over 65.
4. That's your speed.
5. lol

 

If your off by 10% there is really something wrong with your speedo I'd get that fixed by the dealer, it certainly not something you should just be correcting with a tire change. A change of 1-2% should be max. when changing tire sizes.