speedo recalibration for 18" wheels?

[Rio]

What has to be done to recailbrate the speedometer with 18" wheels? Seems quite a few people on here are running 18s, but I have never seen anyone say anything about the speedo recal.........?:shrug:

 

[Wilson & Co]

there are several tire size guides out there I have found useful. They will tell you how "off" your speedo will be. I myself don't even bother with correcting it since it is minimal.

Here you go.
http://www.miata.net/garage/tirecalc.html

enjoy

 

[bigboye]

If use the correct tire size you don't have to worry about it. The fact is that 275/40/17 in other brands are sometimes different sizes and of in rev. per mile. If you are using 18x9 wheel a 275/35/18 is the correct tire size. I'm using a 275/40/18 and that wrong, mine is off by like 3.9% if my speedo reads 60mph I'm realy going 62.3mph.Thats cool with me for every 1000miles that I put on my car I realy drive 1039 miles. If I ever trade I will have less miles on the car. Not worth the money to fix right now for me. However if you are using tire that is to small you rill put more miles on your car than you accualy travel. Hope this helps.

 

[coleman]

do a couple :burnout: & you'll be right on again :lol1:

 

[FKing1]

I went to 295/35/18 rears and my speedo is off 1.8%. At 60 am going 61. Not enough to bother with. There was a chart someone posted a while back with various %'s for diff tire sizes. Maybe they will read this and re-post.
Fred K.