[tw0scoops123]

If I got some 18" deepdish bullits, would I need to recalibrate my computer?

 

[99vert]

Depends on the size of the tire. If you get a tire with the same outside diameter as what is currently used, there is no need to change anything. They do make one, although I forget the exact size. It's a little wider, with a lower aspect ratio than the stock 17" tire, but the outside diameter is virtually identical.

 

[tw0scoops123]

Right now I have the stock 17" Pirelli's. Does Pirelli make the same tire that would fit 18"ers?

 

[Guest]

IF you change the overall height of your rubber diameter from stock, your speedometer will be off.

In that case, a tuner will make adjustments.

 

[99vert]

Stock tire is 235/55 ZR17, outside diameter is 27.1 inches with 768 revolutions per mile. Pirelli makes a 285/40 ZR18 (same series as stock tires) with an outside diamter of 27.0 inches and 771 revolutions per mile. As far as the computer tuner goes, does anyone know how fine the adjustment is for tire size?

 

[tw0scoops123]

Would a Ford dealer re-tune the car?

 

[Guest]

Most FORD dealers will not mess with any aftermarket re-tunes unless they are the ones selling/ doing the mod.

From 27.0 to 27.1, the differences are negligible and I wouldn't worry. I don't think the tuners go to that small of increments.

 

[KiLLeR_WoMBaT]

I have 255/45R18's Toyos all the way around on mine and there is no recalibrations needed. The total diameter is off barely which makes my speedometer read less than 1% higher than actual speed. No big deal. There is this website that will put your wheels and tires up showing what diameter, and the percent it will change your speedo...sorry don't know the link; but all is not lost! I did get the link from this forum, so do a search and you should come up with it.

 

[tw0scoops123]

I have 255/45R18's Toyos all the way around on mine and there is no recalibrations needed. The total diameter is off barely which makes my speedometer read less than 1% higher than actual speed. No big deal. There is this website that will put your wheels and tires up showing what diameter, and the percent it will change your speedo...sorry don't know the link; but all is not lost! I did get the link from this forum, so do a search and you should come up with it.

Cool, I'll try and look for it.

 

[tw0scoops123]

http://www.angelfire.com/fl/procrastination/rear.html

and

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

 

[pcfrisch]

Would a Ford dealer re-tune the car?

Since the 06's now have the 18" option, I don't see why that would be a big deal.

 

[tw0scoops123]

On that one tire size website, I plugged the tires sizes and this is what I came up with:

Stock tires: 235/55ZR17 Performance all-season
New Tires: 255/45ZR18

"Speedometer reading with non-stock tire is 0.5% too fast. When your speedo reads 60 mph, your actually traveling 59.7 mph."

Stock Tire
Sidewall: 5.1 in
Radius: 13.6 in
Diameter: 27.2 in
Circumf: 85.4 in
Revs/min: 742

New Tire
Sidewall: 4.5 in
Radius: 13.5 in
Diameter: 27.0 in
Circumf: 84.9 in
Revs/min: 746