Hi
I just bought a new 2001 supercab xlt 4x4, the tires are P235/70R16SL BSW all season tires. they look really small and out of place, i was thinking of putting on P255 all terrain tires but i'm not sure if they'll fit the stock 16" polished alluminum wheels, i know this will throw off my speedometer but i'll get that adjusted, I have 3 questions will i have to buy a new rim? will this tire adjustment screw up anything more in a mechanicall sense? and will this affect the warranty. Thanks

Jason, calgary alberta

 

You can easily go to a 265/75/16 on the stock rim if you want. It'll change the speedo, BUT, since the height of this tire is the same as the optional 265/70/17, Ford "should" be able to re-cal your computer for this tire size.

 

check out this link

http://www.tirerack.com/tires/surveyresults/orat.jsp

 

Great link! I love tirerack. Got my last three sets of tires from them.

Natty

 

MORE INFO.

235/75-16= 29.9" OD & 265/75-16= 31.6 OD
Speedometer reading with non stock tire is 1.3% too fast. When your speed-o reads 60mph, you are actually traveling 59.2 mph…NO BIG DEAL.


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

 

I don't think that just taking the percentage of the tire height difference is enough to correct the speedo. Mine was off 5%, and I swapped the exact same tire combo.

What you really need to do is find a long stretch of highway. Zero out your trip meter (or just note the exact mileage, including the 1/10) as you pass a mile post. Keep passing mile posts until your trip meter is off by exactly 1/10. Going to a taller tire, you should be 1/10 'lower' then the number to mile posts you passed.

In my case, I would pass by only two mile posts, but my trip meter would say I only went 1 and 9/10's miles. So I was losing 1/10 mile for every two miles traveled. Or, one mile for every 20 actual miles traveled. 20 goes into 100 five times, so that's where I got the 5% figure from. I may actually be wrong on my formulas, but I'm not claiming to be a math professor by any means.

This is just what worked FOR ME. Your mileage may vary!

 

I used a GPS to check my speed-o out. I was .2 mph slow. Don't forget your Speed-O has a plus/minus tolerance build in.


Check the numbers yorself @ http://www.miata.net/garage/tirecalc.html

 

Can't argue with that! Well, just sounds like differences in years and what controls the speedo/odo.

Mine being a '97 uses an actual gear on the tranny. Had to swap it out to one with one less tooth for my speedo/odo to correct.

I guess the thing to do is swap the tires and just see what happens with your individual rig.