Larger Tires on Original Rims
- Thread starter eurolux
- Start date
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Love the tires, have to go and check the size for you when I get home. They do ride a bit on the noisey side but man they are beasts in the snow.
WhooptyWagon
New Member
Anyone know if 285/70/17 would be an issue on the factory rim?
BigOleFordFan
Well-Known Member
Depends on the rims, cause there are limits to how wide or narrow the tires can be to ensure a positive, safe, & reliable seal around the edge of the tire.......
If you look up the tires you are considering online, most them should show you the size ranges that were spec'd from the factory, and if you stray to far from that, then you will be risking blowouts, sidewall bead failures, and/or constant leaks.
Plus, most tire shops with any amount of common sense (not the gung-ho/giga-mod places) won't install tires that are wider or narrower than recommended, cause they would be liable for any issues that might arise as a result...
MesaGuy
Well-Known Member
@eurolux with a small bump to 285 75 16 (or 285 16) from stock 255 70 16, you will get about 9% MPG on mileage, if you drive with a light foot, max improvement. (That's math). In reality, more like 8%. You lose some torque doing this, so if you are towing, I don't recommend. Also, unless you go to the dealer and have the speedo adjusted for the new tiresize, you will end up with speedometer error. (It will also be a 9% error, so at 60mph, you are actually doing 65mph, at 80mph on speedo, you are doing 87mph). But it just daily or occasional local "chores" driving, should be fine. You pick up more in highway than in city. You can get an idea using this https://tiresize.com/calculator/ calculator. Divide the original revs/mile by the new revs/mi, and you will get a number like 1.091, which is a 9% increase in mpg (max), and a 9% speedo error, guaranteed.
Some independent Ford shops can adjust the tiresize on the speedo, most tire shops cannot, some wheel shop can. It requires the Ford ICS software, and a real VCM (or very good copy), or the high end shop 3rd party brands, but even most of those won't reprogram the speedo.
On a 1st Gen, you need a VCM2, and the ICS software, most after market, and Forescan (cheapy low end ICS-like replacement) cannot do the tiresize change. (It can on some of the later models, but not 1st gens, '97-2002).
Some independent Ford shops can adjust the tiresize on the speedo, most tire shops cannot, some wheel shop can. It requires the Ford ICS software, and a real VCM (or very good copy), or the high end shop 3rd party brands, but even most of those won't reprogram the speedo.
On a 1st Gen, you need a VCM2, and the ICS software, most after market, and Forescan (cheapy low end ICS-like replacement) cannot do the tiresize change. (It can on some of the later models, but not 1st gens, '97-2002).
MesaGuy
Well-Known Member
Also, since I don't trust most dealers to do anything correctly, you need to capture a bunch of data on you vehicle before the tiresize change, since the ICS software is not awesome. You need to go look at your backend differential ratio tag, and write that down, the tire size, the calculated circumferance (see the tire calculator), the transmission type, 2WD or 4x4, engine size. Those all have to be "reentered" in the proper screen, and they don't auto-populate with "what you have now". In theory, when you are paying the independent shop ($75) [I had it done 5 years ago for $50] they should crawl under and find your tag, and the bits, but they are not usually that sharp on this type of thing, and NEITHER ARE the dealers. (Doing yours, often the 1st or 2nd time for any given mechanic), in your year.
If they enter any of that wrong, you will get a worse speedo error than you had before you went there and changed the tire size. If it is 265 75 16's, I might just leave it, but then you are only getting half the bump, about 4.5-5%, so from an MPG perspective, not really worth it. Expy 4x4 transmission is forgiving. The 2WD 70R is less forgiving, so the torque and speedo errors can have an effect on shift (but usually do not.)
If they enter any of that wrong, you will get a worse speedo error than you had before you went there and changed the tire size. If it is 265 75 16's, I might just leave it, but then you are only getting half the bump, about 4.5-5%, so from an MPG perspective, not really worth it. Expy 4x4 transmission is forgiving. The 2WD 70R is less forgiving, so the torque and speedo errors can have an effect on shift (but usually do not.)
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