[Maina]

Does anybody know if using 225/45r17 winter tires would do any damage to the transfer case/ transmission. That was the winter set up on my 1 series and there is a considerable tread left so I want to use them before switching to 235/60/17. Any thoughts/suggestions are welcome.

[TEF]

Per an on-line tire/wheel comparer, you're speedometer would be affected:

"When speedometer reads 60mph (96.6km/h) actual speed will be 53.3mph (85.8km/h): 11.2% slower." Assuming, however, you have the same sized tires on all corners, it's not clear if that would hurt your drive line."

Another consideration might be the load rating of your old winter tires. They appear to be designed for a lighter vehicle.

[Maina]

The load rating is fine I checked previously and the difference in speed is okay since I always speed so I might drive drive with the speed limit for once , but I just don't want to do some damage that I will regret later on while not spending $800-$900 on new tires for a year or two.

[TEF]

The load index for 245/45-17 ranges from 91 and 94 while the 235/60-17 ranges from 100 and 102. Therefore, the former is designed to support loads from 1356-1477 lbs versus the latter's 1764-1874 lbs. That's a significant difference. Are you sure that one can be substituted for the other?

[02420X3]

My '11 35i came with 18" tires, and the 28i in that year came with 17" tires by default. Many people switched to narrower 17" tires for winter tires. The two potential issues - speedometer reading and load/speed rating have already been mentioned. Dropping from 18" to 17" isn't one of them.

[TEF]

There is no problem switching from 18" to 17" tire/wheel combination. However, there are two considerations: that the 17" set has the same load rating and the overall diameter of both sets are relatively the same. For example, if one changes out 245/50-18 summer tires with 225/60-17 winter ones, then all is fine - load ratings and diameters are the same. Also, the winter set, will be narrower as preferred for snow. But 225/45-17 tires are not even close to 245/60-17 tires in either diameter or load rating. One can ignore the speedometer error, but a tire of insufficient load rating may be unsafe, as the X3 is too heavy for the smaller tires.

[Maina]

Originally Posted by TEF

The load index for 245/45-17 ranges from 91 and 94 while the 235/60-17 ranges from 100 and 102. Therefore, the former is designed to support loads from 1356-1477 lbs versus the latter's 1764-1874 lbs. That's a significant difference. Are you sure that one can be substituted for the other?

You are correct however I recently read in another topic that since the SAV is about 4300 pounds I assume fully optioned, each corner only has to take about 1075 lbs therefore I have a lot of room left to carry people and stuff. Around 1100-1600 extra pounds or so.

[MichiganMike]

Originally Posted by Maina

You are correct however I recently read in another topic that since the SAV is about 4300 pounds I assume fully optioned, each corner only has to take about 1075 lbs therefore I have a lot of room left to carry people and stuff. Around 1100-1600 extra pounds or so.

Your calculation appears to assume a static load with equal weight distribution on each tire. However, dynamic loading on each tire may vary substantially when going around curves or over bumps or when braking. Using tires with a lower than recommended load rating may reduce your safety margin and in an extreme situation might make the tire more prone to sudden failure.

Also, consider the following information from Tire Rack that the carrying capacity of some tires is reduced to 91% of the load indicated on the sidewall if used on a SUV:
"P-metric tires used on passenger cars and station wagons are rated to carry 100% of the load indicated on the tire's sidewall (or listed for the tire in industry load/inflation charts). However, if the same P-metric tires are used on light trucks, (pickup trucks and sport utility vehicles for example), their carrying capacity is reduced to 91% of the load indicated on the tire's sidewall. This reduction in load results in causing light truck vehicle manufacturers to select proportionately larger P-metric sized tires for their vehicles to help offset the forces and loads resulting from a light truck's higher center of gravity and increased possibility of being occasionally "overloaded."

https://www.tirerack.com/tires/tiret...jsp?techid=195

[Roundown]

Originally Posted by MichiganMike

Your calculation appears to assume a static load with equal weight distribution on each tire. However, dynamic loading on each tire may vary substantially when going around curves or over bumps or when braking. Using tires with a lower than recommended load rating may reduce your safety margin and in an extreme situation might make the tire more prone to sudden failure.

Also, consider the following information from Tire Rack that the carrying capacity of some tires is reduced to 91% of the load indicated on the sidewall if used on a SUV:
"P-metric tires used on passenger cars and station wagons are rated to carry 100% of the load indicated on the tire's sidewall (or listed for the tire in industry load/inflation charts). However, if the same P-metric tires are used on light trucks, (pickup trucks and sport utility vehicles for example), their carrying capacity is reduced to 91% of the load indicated on the tire's sidewall. This reduction in load results in causing light truck vehicle manufacturers to select proportionately larger P-metric sized tires for their vehicles to help offset the forces and loads resulting from a light truck's higher center of gravity and increased possibility of being occasionally "overloaded."

https://www.tirerack.com/tires/tiret...jsp?techid=195

This is good advice.

[Maina]

Alright so I guess using the current winter tires is a no go. How about placing 265/60-18 on the current wheels, would this be stressing the transfer case too much? I want to do some cheating and get an inch and a half of extra of ground clearance. Thanks for the replies guys!