[Seattle135is]

I picked up a 340 X-Drive - I have a set of 788M's from my M2 after I upgraded the M2 to 763M's.
So, I want to install the 19" 788M's on my 340 - any advice on this setup with H&R Sport springs? Any potential issues to the X-drive?
TiA

[alohasurftoad]

https://f30.bimmerpost.com/forums/sh...&postcount=136

any potential issues for x-drive transfer case is be caused by the difference in front and rear tire diameters and not the wheels themselves. ideally you want the front and rear tire diameter to be equal as possible up to a difference limit of around 1%.

for the 788, 235/40/19(26.4"), 265/35/19(26.3"), 0.4% difference, like Haddock! on 437m(same specs as 788), in the post above. sorry, his is F36, let me find a lowered f30 w/437m and 235/40, 265/35.

[Seattle135is]

Originally Posted by alohasurftoad

https://f30.bimmerpost.com/forums/sh...;postcount=136

any potential issues for x-drive transfer case is be caused by the difference in front and rear tire diameters and not the wheels themselves. ideally you want the front and rear tire diameter to be equal as possible up to a difference limit of around 1%.

for the 788, 235/40/19(26.4"), 265/35/19(26.3"), 0.4% difference, like Haddock! on 437m(same specs as 788), in the post above. sorry, his is F36, let me find a lowered f30 w/437m and 235/40, 265/35.

Originally Posted by alohasurftoad

https://f30.bimmerpost.com/forums/sh...;postcount=136

any potential issues for x-drive transfer case is be caused by the difference in front and rear tire diameters and not the wheels themselves. ideally you want the front and rear tire diameter to be equal as possible up to a difference limit of around 1%.

for the 788, 235/40/19(26.4"), 265/35/19(26.3"), 0.4% difference, like Haddock! on 437m(same specs as 788), in the post above. sorry, his is F36, let me find a lowered f30 w/437m and 235/40, 265/35.

Thank you so much for this info - how did you get the size in inches? 26.4 and 26.3?

[alohasurftoad]

Originally Posted by Seattle335

Thank you so much for this info - how did you get the size in inches? 26.4 and 26.3?

I use www.tiresize.com and it suffices for the most part, however TR lists the exact tire specs for brand/model/size on a given rim width for higher accuracy. nominally same sized tires usually differ slightly.

[Seattle135is]

Originally Posted by alohasurftoad

I use www.tiresize.com and it suffices for the most part, however TR lists the exact tire specs for brand/model/size on a given rim width for higher accuracy. nominally same sized tires usually differ slightly.

Thanks again - I hope to reciprocate with a knowledge share sometime...

[Seattle135is]

Originally Posted by alohasurftoad

I use www.tiresize.com and it suffices for the most part, however TR lists the exact tire specs for brand/model/size on a given rim width for higher accuracy. nominally same sized tires usually differ slightly.

So, I physically checked the 788's - 245/35/19 and 265/35/19 so, this will not work...

[alohasurftoad]

Originally Posted by Seattle335

So, I physically checked the 788's - 245/35/19 and 265/35/19 so, this will not work...

oh yes, the original size tires on the M2 will not work on x-drive. which is why i recommended 235/40, 265/35

[Seattle135is]

Originally Posted by alohasurftoad

oh yes, the original size tires on the M2 will not work on x-drive. which is why i recommended 235/40, 265/35

So, I can get hold of 2 new MPS 255/35 for front and keep the 265/35 at the rear - the diff is 1.14% - do you think it would be an issue?

[alohasurftoad]

Originally Posted by Seattle335

So, I can get hold of 2 new MPS 255/35 for front and keep the 265/35 at the rear - the diff is 1.14% - do you think it would be an issue?

i have seen some with as high as 1.2% say it worked on their x-drive while others say they've had problems.

my own personal thought is...255/35/19(26.03"=661.1mm) sits squarely on 9" front wheel, while 265/35/19(26.30"=668.1mm) is a very mild stretch on the 10" wide rear. as you stretch a tire its overall diameter will reduce as more stretch is applied. since 265/35/19 is a very mild stretch on 10", lets say the overall tire diameter reduces 2mm(1mm radius) with the mild stretch, making the total diameter 666.1mm=26.22". the new difference between front and rear would be 0.75%, making it a much more suitable number for x-drive. the question is, is the mild stretch reducing the diameter how i think it is, or not...

disclaimer...same sized tires of different brands and models vary greatly. the numbers i'm using is straight mathematical calcs. results will vary greatly in the real world.

would you "take one for the team" and give it a try?

[Seattle135is]

Originally Posted by alohasurftoad

i have seen some with as high as 1.2% say it worked on their x-drive while others say they've had problems.

my own personal thought is...255/35/19(26.03"=661.1mm) sits squarely on 9" front wheel, while 265/35/19(26.30"=668.1mm) is a very mild stretch on the 10" wide rear. as you stretch a tire its overall diameter will reduce as more stretch is applied. since 265/35/19 is a very mild stretch on 10", lets say the overall tire diameter reduces 2mm(1mm radius) with the mild stretch, making the total diameter 666.1mm=26.22". the new difference between front and rear would be 0.75%, making it a much more suitable number for x-drive. the question is, is the mild stretch reducing the diameter how i think it is, or not...

disclaimer...same sized tires of different brands and models vary greatly. the numbers i'm using is straight mathematical calcs. results will vary greatly in the real world.

would you "take one for the team" and give it a try?

Haha - I definitely will take 'one for the team' - one other item of note is the fronts are brand new while the rears have abt 8k miles on them, which will also be an advantage. Let's see if I can wrangle this into my schedule this weekend.
Once again, thanks for the knowledge share...

[alohasurftoad]

Nice. Yup, the 8k mile rear will help your cause.

IF(big if) you have time to measure the front and rear tire circumference, we can get accurate actual tire diameters.

I know how things go and usually end up getting things installed as quick as possible and regret not weighing or measuring stuff for comparison, afterwards.