Tires replace all 4 or are just 2 OK?

[JCL]

Originally Posted by FSETH

If you are only replacing a pair of tires, they should be placed on the rear axle. New tires go on back.

Why? If I was only doing two tires, I would put them on the front, for improved steering, braking, and handling. Rear tires are just along for the ride compared to the work the fronts do, unless one is driving a dragster.

[FSETH]

Originally Posted by JCL

Why? If I was only doing two tires, I would put them on the front, for improved steering, braking, and handling. Rear tires are just along for the ride compared to the work the fronts do, unless one is driving a dragster.

I used to think that as well, but the Tire Rack, Michelin, Toyo, Goodyear, etc. all recommend putting the new rubber on the rear axle if you are only replacing two tires. Apparently, they feel that especially in adverse/wet conditions it is easier for most drivers to control and compensate for understeer than it is to control oversteer. Vehicles with new tires on the front axle and older tires on the rear are more likely to oversteer, causing the rear to break loose.

[omodos]

Originally Posted by JCL

The only thing that matters for the transfer case is the rolling diameter. If it is too much of a difference, then yes it can affect the transfer case.

BMW recommends up to 7 psi different front to rear, depending on expected load, so they obviously expect some difference in rolling diameter.

Sorry to revive an old post but been reading what does matter is also tread depth?not just rolling diameter, if you had mismatched tires like I do...varying tread patterns all round, you reckon drivetrain/transfer case failure is something that is imminent and would be immediate or would I get some sort of warning....?

[wpoll]

Originally Posted by omodos

Sorry to revive an old post but been reading what does matter is also tread depth?not just rolling diameter, if you had mismatched tires like I do...varying tread patterns all round, you reckon drivetrain/transfer case failure is something that is imminent and would be immediate or would I get some sort of warning....?

There is no sudden failure - but the clutch packs in the transfer case could wear out prematurely, as they have to slip a lot to allow for the different tyre rolling circumferences.

In extreme cases you will get ABS/DCS errors....

[andrewwynn]

Originally Posted by FSETH

I used to think that as well, but the Tire Rack, Michelin, Toyo, Goodyear, etc. all recommend putting the new rubber on the rear axle if you are only replacing two tires. Apparently, they feel that especially in adverse/wet conditions it is easier for most drivers to control and compensate for understeer than it is to control oversteer. Vehicles with new tires on the front axle and older tires on the rear are more likely to oversteer, causing the rear to break loose.

By 'they' the meaning is really: "laws of physics". The car will act like a plum bob when one axle has better tires. You get to decide which axle is the string and which is the weight.

By putting the new tires in the front makes the string the front and the back the weight, and will spin the back side right around in a lot of circumstances.

Depending on how much different the wear on the tires, the DSC should be able to compensate but I'm ok with the following 'the law' (of physics). though once the tires are worn a bit, i will move some 8/32 to the front when 6/32 is what is on the front to get them to wear more evenly. Usually if they are on the order of 2 to 3 32nd apart they will wear down almost exactly the same.

[andrewwynn]

Originally Posted by omodos

Sorry to revive an old post but been reading what does matter is also tread depth?not just rolling diameter, if you had mismatched tires like I do...varying tread patterns all round, you reckon drivetrain/transfer case failure is something that is imminent and would be immediate or would I get some sort of warning....?

Just normal driving around curves will cause enough difference front to back that will likely be more than any tread wear difference. BMW specs a pretty generous 3% i believe allowance front to back rolling circumference difference.

[omodos]

Originally Posted by andrewwynn

Just normal driving around curves will cause enough difference front to back that will likely be more than any tread wear difference. BMW specs a pretty generous 3% i believe allowance front to back rolling circumference difference.

Pretty sure saw it at being like 1% somewhere (not sure someone can chime in?), and having said that no idea how my X has suffered as over the years have often seen the tires wear at differing rates (despite all 4 being the same brand age type etc)


PS just had all four tires replaced same size brand tread etc up front and rear, I didnt get an alignment as had this done soon after my suspension work was done 10 days ago...since then those tires are long gone...do i need to get one done again? someone posted a detailed DIY of how to check if one needs an alignment with the use of threads and pieces of wood etc...who was the poster?

[andrewwynn]

That poster was me. You wrap a string tight around wheels front to back at the center top to bottom then put a 1/16" spacer under the string at the front side of the tire at the fattest point. Usually it will only stay on it's own at the front wheel. The idea is the front of each tire is 1/16" closer to the car's centerline and then string helps you confirm. You push the string out with the spacer and the back of the front wheel should just barely touch the string. At the back wheel only the back should touch and at the front there should be a 1/16" gap.

You have to steer the string around any tall raised letters on the tire etc. Also the trig was worked out with 23-24" across the high spot of the sidewall. Even much larger than normal tires would only slightly change the math.



The tires are supposed to be toe In about 0.15°. 1/16 over 24" is almost spot on perfect.

[omodos]

Originally Posted by andrewwynn

That poster was me. You wrap a string tight around wheels front to back at the center top to bottom then put a 1/16" spacer under the string at the front side of the tire at the fattest point. Usually it will only stay on it's own at the front wheel. The idea is the front of each tire is 1/16" closer to the car's centerline and then string helps you confirm. You push the string out with the spacer and the back of the front wheel should just barely touch the string. At the back wheel only the back should touch and at the front there should be a 1/16" gap.

You have to steer the string around any tall raised letters on the tire etc. Also the trig was worked out with 23-24" across the high spot of the sidewall. Even much larger than normal tires would only slightly change the math.



The tires are supposed to be toe In about 0.15°. 1/16 over 24" is almost spot on perfect.

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