Well the time has come that i replace the current stock tires on my 9" wide aftermarket rims with proper sized ones which means i will most likely be getting some 265/35's or 275/35's. My question is how much can i expect these tires to throw off my speedometer by?

Thanks in advanced

 

http://www.miata.net/garage/tirecalc.html
275 would be closer

 

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

 

 

lolol. i just looked at that. you barely beat me to it. no replies as i was copying and pasting it.

 

the correct od of the stock tire is 25.9 "

go from that.. width sidwall and rim diameter have nothing to do with it.

you just have to look at the outside diameter of the tire at 25.9" and you are fine.

beers

 

http://wheelsmaster.com/rt_specs.jsp

Give this a bash, slightly different than the miata one (gives offset calc etc...)

 

ok so if the stock setup is 25.9 and the calculator shows me at 25.6 with the 275/35 combo will that be a difference of like 1/2 a mph? or will it not even be noticeable.

O and by the way i feel like a idiot because i was using the search button and reading through threads and couldnt find anything but now that i type in "tire size calculator" i find a ridiculous amount lol

 

25.6 is going to be about 4 mph slow.

this is from real world experience and gps..

beers

 

https://www.rx8club.com/showpost.php...4&postcount=11

 

beers

 

Ok so if my speedo says 55 really im going 51? or 59?

 

51mph. I was only 2-3mph off between 65-85mph with my 275's. Now with my 265's I'm about 4-5mph off. I use my GPS to validate that.

 

Ok thanks for the help. So at lower speeds will it be off more? Or is 4 mph about the highest its going to be off? And is it possible to get the speedo corrected through a justifiable way without spending a substantial amount of money to do so?

 

It's off by a percentage of your speed, so the faster you go = the more mph it's off.

 

Check the link at miata.net... I just ran through it for my tires. It will explain the mph difference (at 60mph); It is a percent difference, not a constant number

 

255/40 Toyo T1R's are 25.9" overall diameter when mounted on a 9" wheel. They will fit on a 9" wheel better than a 275/35 also.

 

so your saying if i get a 255/40 my speedo will basically be the same and the tires will actually fit the rim better?

 

Yea pretty much.

 

Yup.

 

LOL, so if it wasnt off by a %%% then it being 4 mph slower means that sitting at rest the speedo would have to read 4.... but what if it read 0? are you going backwards?