18" Rims & 17" Spare. Problem?

I bought a little red Altima Coupe last Friday and decided that I wanted bigger wheels so I had the dealer install some chromed 18" Rims with Toyo’s. (my daughter says it’s a PHAT ride) :cool:

They of course did nothing about the 17" donut spare (I traded in my 17’s, they are gone). I could possibly find an 18" donut spare off of a Maxima SE but was wondering if I needed to. What would happen if I ran the 17" donut for a couple of miles? Would it damage the differential gears? I’ve driven on a flat/rim before and that didn’t seem to damage the car (just embarrassing). What if I drove with the 17" for 50 miles, would that be worse than a couple of blocks?

The first thing to consider is, is the total wheel diameter different? One would assume when you upgraded wheels, you got lower profile tires to keep the overall diameter the same. If so, then no problems.

Second thing is, does your Altima have a limited slip differential? If not (and I’ll bet it likely doesn’t), then no problem driving with unequal-sized wheels, although that could result in some instability in handling. But then, when you’re driving on a limited spare, you’re supposed to be driving cautiously anyhow…

If you do have a limited slip and the tire diameters are different, then you could potentially cause a problem - I doubt it would do much, but it is a risk. If you’re really concerned, you could do a double-swap - if one of the drive wheels has a flat, move a tire from the other (un-driven) wheels onto that one, and put the spare on the undriven wheels. That’s what they say to do on my Mustang, for example. Royal pain in the ass…

Presumably, the tire shop did proper plus-sizing. That is, they upgraded the wheels to 18" (0.5 inch larger radius than a 17"), but also fitted tires with shorter sidewalls (0.5" shorter) to make the overall radius, and thus the overall rolling circumference, the same.

In other words, the outside edge of the wheel/tire combo is the same distance from the hub. But more of that space is now taken up by the wheel, and less by the tire.

In that case, using the factory spare tire will be no different than it would have been with your old wheels. If it’s a full size spare, it’ll roll just like your 18’s. If it’s a compact spare, it’ll still be just as undersized as it used to be. Compact spares (donuts) are often smaller in overall circumference than normal wheels. That’s why it’s important that they’re mounted to the rear axle on a front wheel drive car.

If you drive slowly and not too far the differential should take it. However, the pinion not intednded for continuous, high speed use.

You can always take the extra time to put the spare on the front. In case a rear tire goes this will mean changing two wheels. And your steering will be kind of funny. You might put your spare on the front as a trial and see what happens.

Altimas are front wheel drive. So the compact spare should always be on the rear, as I mentioned in my earlier post. But the point is that if the OP got a proper wheel upgrade, the rules concerning use of the spare don’t change.

And if he didn’t got a proper plus-size, then he’s got other problems. Like an incorrect speedometer and odometer.

I went outside and checked and they put on 245/45R18 tires. the originals were 215/55R17’s. The stealership installed them, so I guess I just trusted that they knew what they were doing. Can anyone tell by the given info if the circumference is the same? I guess I could go out and actually measure my spare, but that so defeats the fun of asking other people. That and I might actually re-learn something as well about tire numbering. :slight_smile: I’m thinking the first three numbers are width, the last is obviously the inner diameter, so the second set must be the :confused: I guess what I’m getting at is can I calculate the outer diameter of the two tires given these numbers?

You can calculate it yourself.

The 245/45 means the width of the tire is 245 mm and the sidewall height is 45% of that, or 110 mm (4.34 in). Add that to the radius of your rim (9 in) and you get 13.34 inches.

For the 17", 215/55 => sidewall height of 4.66 in + radius of 8.5" yields 13.16.

The new tires are 1.3% bigger in circumference than your old ones, which is generally considered an acceptable tolerance.

A cool online calculator can be found here…lets you compare old and new easily side by side.

I very seriously doubt that your spare will cause you any problems. Some cars with mechanical AWD setups are very picky about tire sizes (to the point if you have new tires on the front and old tires on the rear, you can do damage) but other than that, I don’t see a problem
One word of caution: Look at the sidewall of the spare, the inflation pressures and speed limits may well be different than your standard tires. Some space saver spares use very high pressures, like 60PSI. Many have a speed limit printed on the side like 50, or 60 MPH. These are temporary spares and not designed to go blasting down the highway at 85 MPH.

Thanks Areodave. I also checked the spare and it is a T135/90R16, which works out to a 12.78" Radius. So it’s about 4% smaller than the new tires. Guess I’ll take Ricks advice and not take them up to 135 mph with the spare. Not that I did that last weekend. :rolleyes: