Tire size

ford
excursion

#1

I have a 2005 Excursion, 2WD, Diesel. It has the stock factory rims/wheels(rims) and I HATE the way they look. It is a 16 inch rim with 265/75/16 tires. I would like to buy new rims that are 18 or 20 inch to raise the truck a little and for a different look. How will a larger rim and tire affect my speedometer, performance and safety. THX


#2

You can check out larger rims on tirerack.com with tires that won’t require any modifications. If you’re wanting to go with larger overall diameter tires, you’ll lose acceleration, you’ll need to recalibrate your speedometer, and you’ll need to make sure the tires have adequate load capacity, and that no rubbing occurs.


#3

Larger diameter rims will have no affect on your speedo. as long as you match over all outside diameter and use tires within recommended width specs for your car, and rims have appropriate design and off set to fit.
But, it may handle a little better ,depending upon tires and the sacrifice of ride, loss of cushion will increased tire rim damage potential. Obviously, you’re not using it off road as you compromise it’s ability to do so with larger rims. it’s just for looks right ?
Example; 265/65-17 is very close in outside diameter to 265/70-16 and can be used interchangeably.


#4

OK, THX


#5

With 18 and 20 inch wheels, your vehicle will ride like a fork-lift and pot-holes easily destroy both the tires and wheels. Remember, only YOU care what your wheels look like…You also limit your choice of tires and double the price you will pay for them…But if you have $1000-$1500 you don’t know what to do with, go for it…


#6

They’ll probably be a small detriment to your acceleration and fuel economy, since they’ll probably be more massive. And that’s ROTATING mass (the worst kind to increase) farther from the center of the wheel than before (which means it’s harder to turn), and it’s unsprung (the more unsprung mass you have…that is mass that is not cushioned by the suspension…the worse your ride quality will be all else being equal). Also, the shorter sidewalls on the tires mean more impact and vibration will be transmitted to your truck.

Going to 18s probably wouldn’t be really serious, but 20s might. Regardless, this will do absolutely nothing but bad things to the performance of your car. The only practical reasons to go with larger wheels are:
to make room for larger brakes
to reduce sidewall flex to improve cornering (this is in sports cars with rock-hard suspensions, where no one cares if the car punches them in the spine on every bump, and you probably won’t notice any difference in your truck, BTW)

A larger rim won’t affect your speedometer if the total diameter of the tire is the same. If the tire is larger, too, then your speedometer will read low (since your wheels will be turning fewer times per unit of distance, and your speed is taken from one of the rotating parts on your drivetrain).

It will also act kind of like taller gears, and might give you slightly better highway fuel economy, but this will almost definitely be canceled out by the extra fuel you burn just to get the larger wheels turning in the first place.

Assuming the tire still clears your wheel wells, and the wheel clears your brakes, it probably doesn’t affect safety. If you get larger diameter tires, you may raise the center of gravity a bit, but not by a whole lot without lifting it up. That would make it easier to roll the truck.

Oh, and your new tires will probably be more expensive than your old ones. Maybe a lot more expensive.

Basically, there are a whole lot of cons, and only one pro (that you think it looks cool).

If you’re still determined to do this, and Tirerack doesn’t tell you what you need to know (say you want to buy something they don’t sell, or some tire/wheel combination they don’t sell or something) you can use this to find out if it will come out to the same size:
http://www.miata.net/garage/tirecalc.html

Yeah, it’s a Miata site, but the calculator is adjustable for any wheel and tire.


#7

Let’s say you’re going to do it regardless…do it sanely, and consider this way
To put this in perspective 265/75- tire rim combination, is very truck like. To seemingly contradict what I’ve said earlier, a move to 17" and maybe 70 profile or 18" with 65 profile IS NOT an extreme. It is 2wd, and not intended for off road and though some “air volume” will be lost, it should be acceptable.
Use the 65 ratio to 265 width, to find a maximum “safe” rim…To go below 65 in a truck, would compromise the safe load carrying capacity over rough roads too much I feel.

The potential for safer handling within reason, may be an excuse for better looks and $$$$ on rims; I could justify that approach. After all, it’s a flatlander 2wd with mostly on road use potential.
adding stats
Specification Sidewall Radius Diameter Circumference Revolutions Speedometer Odometer Difference
265/75-16 7.8" 15.8" 31.6" 99.4" 637/mi 60MPH 10000mi N/A
265/70-17 7.3" 15.8" 31.6" 99.3" 638/mi 60MPH 10014mi -0.1%
265/65-18 6.8" 15.8" 31.6" 99.2" 639/mi 60MPH 10027mi -0.3%

You can see the 18" staying with the 65% ratio would work fine. The alloys on many SUVs come that way. You will be giving up some of the load capacity as your diesel tire size combi. seems to have been designed for.

Best of luck