Sponsored by The Tire Rack

[bennye90]

I am currently running

225/40/18 - 8" width
255/35/18 - 8.5" width

One tire is blown from a pothole and looking for new set since I have xdrive. Square tires seems more feasible than a staggered.

Can I run 225/40/18 on a 8.5" wheel? Will it stretch? If it stretches what % difference in rolling diameter will I achieve?

[Antetokounmpo]

They will certainly fit, it will look a little stretched though. The difference in rolling diameter will be negligible.

[Volasko]

The have a wheel calculator for that exact question.

His specific question can't really be answered by the calculator though...

[bennye90]

Originally Posted by Volasko

The have a wheel calculator for that exact question.

Yeah I did my prior research and using https://www.rimsntires.com/specspro.jsp

Looking into buying Continental DWS06 225/40/18 and they fit 7.5-9" rim size widths with the common size of being a 8" fit. So I felt being the middle width between the two extremes makes it work. Did some forum lurking and talked to the technician I ordered the tire from as well as tirerack, they all said it is OK. Just do not know about the stretch calculation.

Will post an update when tires come in and are mounted and driven.

[Asonchadwick]

I went square and run 245/40/18 now on my 335d with the sport suspension. I was on factory staggered rims now on 8 inch wide all the way around. I got this size because i wanted the continental pure contacts as they are the best handling longest lasting best in wet all season tire. Also they have a very wide footprint at like 9.1 on an 8.5 inch rim. On an 8 inch i am not real sure but its the widest for this type of tire.

They ride good, handle well and handle standing water pretty damn good at high speed. With a 70,000 mile treadware i am pretty pleased.

I would have liked 8.5 inch rims but the voxx rims i got only came in the 8 inch. Honeslty i cant tell any difference but i think i could go 5mm spacer in the rear and be better. Voxx has some new flow formed rims the leggerro for like $140 each at discount tire. Still make in china though but it ticks all the boxes. Light weight, looks great, hub centric and bmw center caps fit.

Hope this was helpful

Originally Posted by Tucson335d

I went square and run 245/40/18 now on my 335d with the sport suspension. I was on factory staggered rims now on 8 inch wide all the way around.

Pics?

Yeah, OP you could go with 245/40 as well...just saw you have an xi. That would help to fill the wheel gap quite nicely.

[spac3]

Originally Posted by Tucson335d

I went square and run 245/40/18 now on my 335d with the sport suspension. I was on factory staggered rims now on 8 inch wide all the way around. I got this size because i wanted the continental pure contacts as they are the best handling longest lasting best in wet all season tire. Also they have a very wide footprint at like 9.1 on an 8.5 inch rim. On an 8 inch i am not real sure but its the widest for this type of tire.

They ride good, handle well and handle standing water pretty damn good at high speed. With a 70,000 mile treadware i am pretty pleased.

I would have liked 8.5 inch rims but the voxx rims i got only came in the 8 inch. Honeslty i cant tell any difference but i think i could go 5mm spacer in the rear and be better. Voxx has some new flow formed rims the leggerro for like $140 each at discount tire. Still make in china though but it ticks all the boxes. Light weight, looks great, hub centric and bmw center caps fit.

Hope this was helpful

No issues at full steering lock or when hitting bump stop?

What tires did you get and whats your offset? I've heard people have struggled to run 245/40R18s on sport/msport cars in the past http://www.e90post.com/forums/showthread.php?t=1241610

Originally Posted by spac3

What tires did you get and whats your offset? I've heard people have struggled to run 245/40R18s on sport/msport cars in the past http://www.e90post.com/forums/showthread.php?t=1241610

See sig. Running this setup on "D8" springs up front and no issues...it does rub on the fender liner *just slightly* on full lock, only in reverse though.

[rothwem]

Lets do some math, it'll be fun. We can solve this with the Pythagorean theorem.

The sidewall height is 90mm, which is 225*0.40.

A 8.5" wheel is 1/4" per side wider, which is ~6mm.

Now we'll make a triangle. The sidewall is the hypotenuse, and the bottom leg is the width. Since the Pythagorean theorem says that A^2+B^2=C^2, and C=90, and A=6, C^2-A^2=90^2-6^2=8100-36, which equals 8064, which is B^2. The square root of 8064 is 89.7998mm.

So, mounted on an 8.5" rim instead of an 8" rim, your side wall will be 0.2mm shorter, meaning your overall diameter will be 0.4mm smaller. Since the original diameter is 637.2mm, your tires will now be 0.06% shorter. The tolerance for xDrive cars is 1%. That calc is also assuming that the tread of the tire is perfectly rigid side to side, and perfectly flexible front to back, which it isn't. So in reality, it'll be even less difference since the tread will bend a bit.

To conclude, you've got nothing to worry about. It will look a little more stretched though, so you can always buy two rears or two fronts to even out the look if you'd like.

[RLe92335]

Originally Posted by rothwem

Lets do some math, it'll be fun. We can solve this with the Pythagorean theorem.

The sidewall height is 90mm, which is 225*0.40.

A 8.5" wheel is 1/4" per side wider, which is ~6mm.

Now we'll make a triangle. The sidewall is the hypotenuse, and the bottom leg is the width. Since the Pythagorean theorem says that A^2+B^2=C^2, and C=90, and A=6, C^2-A^2=90^2-6^2=8100-36, which equals 8064, which is B^2. The square root of 8064 is 89.7998mm.

So, mounted on an 8.5" rim instead of an 8" rim, your side wall will be 0.2mm shorter, meaning your overall diameter will be 0.4mm smaller. Since the original diameter is 637.2mm, your tires will now be 0.06% shorter. The tolerance for xDrive cars is 1%. That calc is also assuming that the tread of the tire is perfectly rigid side to side, and perfectly flexible front to back, which it isn't. So in reality, it'll be even less difference since the tread will bend a bit.

To conclude, you've got nothing to worry about. It will look a little more stretched though, so you can always buy two rears or two fronts to even out the look if you'd like.

bravooo

[Banana Clipper]

If you're going Conti's I have a pair(two tires) of DWS06's in 245/40/18 that have 300(three hundred) mile on them, probably less.

I literally took them off cause I didnt like the way they looked on my car. I'd sell em to you $250 shipped... could help offset your total cost.

[bennye90]

Originally Posted by Banana Clipper

If you're going Conti's I have a pair(two tires) of DWS06's in 245/40/18 that have 300(three hundred) mile on them, probably less.

I literally took them off cause I didnt like the way they looked on my car. I'd sell em to you $250 shipped... could help offset your total cost.

Thanks but I already ordered from warehouse + I get warranty etc through continental + tire store for flats, rotatations etc.

Also I am from Canada as well, ended up getting the DWS06 for $160CDN/tire

[Banana Clipper]

Originally Posted by bennye90

Thanks but I already ordered from warehouse + I get warranty etc through continental + tire store for flats, rotatations etc.

Also I am from Canada as well, ended up getting the DWS06 for $160CDN/tire

Damn... I paid like $1100usd for a full set of DWS06's installed with warranty... FML

Good deal dude...lucky

[Asonchadwick]

Apparently my pics cant be resized. Does this site only allow lower res pics?

I dont even know how to upload them here couldnt find a tutorial

[Asonchadwick]

I click on the paperclip nect to the smilys and it does absolutely nothing.

[Asonchadwick]

Ok finally figured it out. Apparently this site wont let you add pics from google chrome mobile i had to switch to desktop site and then really crop my pic down to get it to fit. There is my car and the el cheapo voxx wheels 8 inch wide with 245/40/18 and a 40 offset front.

[Asonchadwick]

And this is the same just in the rear. I think i want to add a wheel spacer to push it out but looks are deceiving as i doubt i could get 5mm out before i touch the wheel well.