Different rim sizes

[Legopez]

Hello, my Grandsons girlfriend had three different tire sizes on her car, the front had two totally different tires sizes, I understand that that is not good, so I took her to get a new set of tires. The tires are 17", but when I looked at her spare it was 16". I would think it would be really not good, to put it on if she got a flat, but I really don't know what would happen, as I am not a car expert. I haven't been able to find anything online about anyone doing this. Just curious what issues this would cause.

 

[Letfreedomring]

Hello, my Grandsons girlfriend had three different tire sizes on her car, the front had two totally different tires sizes, I understand that that is not good, so I took her to get a new set of tires. The tires are 17", but when I looked at her spare it was 16". I would think it would be really not good, to put it on if she got a flat, but I really don't know what would happen, as I am not a car expert. I haven't been able to find anything online about anyone doing this. Just curious what issues this would cause.

It doesn't really come into play unless they install a big brake system or drop spindle or other non oem parts and equipment. As long as the smaller rim spare has a larger series sidewall ie. if spare was a 75 series tire and other flat tire was a 60 series. More than likely the od of both will be very close. To double check, tirerack.com and discount tire usually have a calculator on their website for upsizing and downsizing tires.

 

[918evo]

Hello, my Grandsons girlfriend had three different tire sizes on her car, the front had two totally different tires sizes, I understand that that is not good, so I took her to get a new set of tires. The tires are 17", but when I looked at her spare it was 16". I would think it would be really not good, to put it on if she got a flat, but I really don't know what would happen, as I am not a car expert. I haven't been able to find anything online about anyone doing this. Just curious what issues this would cause.

There should be a sticker in the driver's door jamb that has the correct tire sizes for the front, rear, and spare. Not uncommon to see a smaller rim on a spare but with a taller sidewall to make the overall diameter the same. It is important to have to same size as what is listed so you don't run into fitment issues with brake calipers or spindles as letfreedomring explained.

 

[gl55]

It's not the wheel size that matters it's the tire size. The over all tire height. You can have two different wheel diameters with different size tires that have the same overall tire height. If the difference is too much it can upset systems like traction control or ABS brakes because a wheel might be turning at a different rpm than the others. On rear wheel drive vehicles with limited slip differentials different tire sizes on the rear axle could damage the limited slip components. Enter the tire size on the car and the tire size on the spare in this calculator and see how much difference the dire diameter is.
https://www.calculator.net/tire-size-calculator.html