Mismatched, over-sized tires

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It's a bit hill-billy of me but here's what I have running through my mind...
Years ago I bought a set of 255/60R19 tires for my '10 X6, not realizing that they are a full 2" larger in diameter than the 255/50R19 and won't clear the front suspension. The shop said they couldn't be returned (because one was mounted) without paying some absurd shipping and return fee, like $450. So the tires have been sitting in storage.

Fast forward to today:
My son has a '14 X5xDrive35i in need of tires soon. The car is a bit a rough from teenage driving misadventures but mechanically sound.
I could have the 255/60's mounted on the rear, giving his car a 2" "rake". He's not completely against it, given the economics of the situation.

Aside from aesthetics, is there any reason not to do this? Will the headlights self level enough to compensate? Presumably the air suspension will also self adjust?

Thanks!

[Cranswick852]

Might be OK if the X5 is a 2-wheel drive S Drive (not sure, check with someone) but a definite NO if it's a 4-wheel drive X Drive - you'll screw your transfer case which is very intolerant of different wheel circumferences front back

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Ah! Thanks!

[1norseman]

You mentioned it was a xDrive35i, so its an AWD. You have to have very similar circumference of tires front and back, as mentioned above or you will mess up the transfer case.

Also, if you have the self leveling xenon headlights, they won't adjust just because of bigger tires at the rear, since adjustment is based on measuring the suspension arms geometry.
Same goes for the rear airbags. Airbags are there to keep the axle in the same position, not let vehicle sag. It won't sense that you put bigger tires on the rear.

The auto adjustment of headlights and airbags is affected by things like adding weight in the back. Additional weight changes the geometry of the arms, and sensors will send the data to computer to adjust headlights. There is a sensor on the front "axle", and a sensor on the rear "axle" giving the computer the data. Weight will also tell the computer to let air compressor pump up the airbags, until it senses the rear "axle" is back to normal position, doesn't sag.


When it comes to the 255/60R19 tires...
This might not be possible, but would 30mm spacers allow you to clear the part of front suspension that curves over the tire? If factory 19" wheels, they usually look quite sunken in without spacers, so even with 30mm spacers, they might not stick out that far. If you had the flares, it would probably not stick out at all.

But spacers could lead to other issues like not being able to turn the steering wheel all the way though.

Only way to find out, is to buy a set of spacers, mount one of the current tires/wheels, and see how much clearance you gain. If it looks like enough in all directions, mount one of the 255/60R19 tires on a wheel and try again.

If it works, your kid will gain a bit more ground clearance and be ready for the MI winter time. He will also think he's driving slower than he actually is, which increases the chance of getting a ticket. (unless you find someone who knows how to code the vehicle to adjust for bigger tires)

[Thumbs]

Great info, thank you for taking the time!

The spacer idea is one I considered too but the factory 19" wheels on stock tires look like they overlap the suspension member by about 40mm. That's a lot of tire sticking out of the wheel well if I use spacers.

Fortunately there are several newer vehicles using that tire size so perhaps the market for them will improve and they can be sold.

Best,
Randy

Originally Posted by 1norseman

When it comes to the 255/60R19 tires...
This might not be possible, but would 30mm spacers allow you to clear the part of front suspension that curves over the tire? If factory 19" wheels, they usually look quite sunken in without spacers, so even with 30mm spacers, they might not stick out that far. If you had the flares, it would probably not stick out at all.

But spacers could lead to other issues like not being able to turn the steering wheel all the way though.

Only way to find out, is to buy a set of spacers, mount one of the current tires/wheels, and see how much clearance you gain. If it looks like enough in all directions, mount one of the 255/60R19 tires on a wheel and try again.

If it works, your kid will gain a bit more ground clearance and be ready for the MI winter time. He will also think he's driving slower than he actually is, which increases the chance of getting a ticket. (unless you find someone who knows how to code the vehicle to adjust for bigger tires)