I have the stk 19 Prem wheels on the car still, 19/ 8.5 rims.
Iike the wheels but I think they really need wider tires so looking for some recomendations also my friend says just put a wider tire on the rear ?
The current tires are 245-45-19.

 

get some sticky 275s on the back

 

That's not to wide for a 8.5 width rim ?

 

I think the 8.5 can only take up to a 255 if you want to be safe.

When I replace my tires on my CS I'll be getting 255 probably.

 

The issue with those cars that come with the 245/45/19 tires is there aren't any wider tires in the same height, or at least very few, so putting another size on screws the speedometer up and the transmission if you have an automatic.

May not make a lot of difference, just something to be aware of.

Of course if it's tuned then those issues can be adjusted for in the tune.

 

So if I go with the 255/40 and I do have a automatic I may have a problem with the tranny ? I'm not concerned with the spedo.

 

no, 255-40/19 are closer to the stock GT 18's anyway, they're actually taller.

235-50-18 = 27.1"
245-45-19 = 27.6
255-40-19 = 27.2

the only reason they use 45 series on the 19's is for the DOT 1653 lb max load rating, which is well over what you need for a 3500-3600 lb car








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The shift and converter lockup parameters will be off slightly.

Now, you could possibly have the dealer reflash the pcm with a oem tune compatible with the shorter tire, just another thing to pay for though.

 

you won't have any problems what so ever with 255/40's, Ford doesn't program the EEC any differently on cars with 19's or 18's

 

Of course they do, they have a different program for every combination, they have to to keep those issues I stated accounted for.

 

Any one else ?

 

guess i wrote that wrong but the tire sizes are set in ranges, the dif is only 1.4%, the speedometer isn't that accurate. even a police certified speedo isn't that accurate. the tolerance on a std one can be as high as ±10%.

you'll get an error of over 1.4% on any car on a daily basis due to tire diameter variations like wear, temperature, pressure, vehicle load etc













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lol.. guess Curt an I are the only ones up

 

Your speedo should be the same if all you do is put some wider rubber in the rear. I wouldn't go more than 255 though with the 8.5 rim.

 

What does 255 equate to in inches? He would be going from an 8.5" tire width to .....??

 

I hope they will not look taller then what I have now ?

 

It would be approximately 10" wide. There is 25.4mm per inch so just over 10" wide. Keep in mind Ford uses a 255 tire on the OEM V6 PP wheel which is also only 8.5" wide. A 255 will be OK on a 8.5" rim width but it won't be optimal, you would want a 9" rim.

Dave

 

I too am thinking about getting 255-40-19 tires on my factory 19x8.5" wheels. The speedometer issue doesn't bother me, but the transmission one does. Will changing tire size really cause problems with an automatic?

 

It could affect shift points on a auto, on a manual it won't be any real issue.

Dave

 

With an 8.5" rim width? Terrible advise, for a 275mm tire 9" minimum but in reality it needs a 9.5" rim to support the sidewall properly.