Need Help with this setup

[The M Law]

Hey guys I have a an E46 M3 and have wheels on the way. Been contemplating, switching the the Z4 M Coupe. I ordered wheels for the M3. Down to the point will these wheels fit fine on the Z4M, sorry I don't know much about wheels specs.

19x9.5 +31 front. running fk452 245/35/19
19x11 +25 Rear. running fk452 275/35/19

any help will be greatly appreciated as this will decide if I make the switch over to the Z4 M Coupe. I'm really hoping it doesn't have issues, I don't mind rolling the fenders if I end up dropping it. Thanks guy.

[nekky]

Gonna need more support here, but I have a similar setup in 18" going onto an E86 M. Front should be perfect, rear is what I'm wondering about too.

[The M Law]

Yea there's a guy with 19x11 rear but his offset is different... So i'm really wondering about mine... Just waiting on anybody with experience on here.


http://www.zpost.com/forums/showthread.php?t=542295

^^If its fits anything like this guys M coupe... I will hands down start looking for an M coupe to buy after selling my M3.

[Finnegan]

"Fits" and "fits perfect" isn't the same as "handles well" or "retains good handling characteristics". Lower offsets on the front are going going to throw off the scrub radius. That means they affect the car's handling by making it worse.

The front offset on the M is +42. The engineers didn't select that offset based solely on what would fit or looks but as part of the overall suspension design. Bottom line, the closer a wheel setup sticks to that number the better.

See this post. The discussion above and below it discuss these factors in more detail, along with explanations of scrub radius, handling, and things that can/cannot be done to offset (pun intended) the problems with using offsets not designed for the suspension.

[gcochard]

Originally Posted by Finnegan

"Fits" and "fits perfect" isn't the same as "handles well" or "retains good handling characteristics". Lower offsets on the front are going going to throw off the scrub radius. That means they affect the car's handling by making it worse.

The front offset on the M is +42. The engineers didn't select that offset based solely on what would fit or looks but as part of the overall suspension design. Bottom line, the closer a wheel setup sticks to that number the better.

See this post. The discussion above and below it discuss these factors in more detail, along with explanations of scrub radius, handling, and things that can/cannot be done to offset (pun intended) the problems with using offsets not designed for the suspension.

If I go from the stock 18x8 +42 to a 18x9 +42 will it negatively affect performance?

[Finnegan]

Originally Posted by cliffhopper

If I go from the stock 18x8 +42 to a 18x9 +42 will it negatively affect performance?

No, it's going to keep the stock suspension geometry for scrub radius. The offset is exactly the same. It's going to equally wider than stock on both sides 13mm wider inside 13mm outside. To see how the size and offset works, an offset calculator is a great tool. These wheels should work nicely.

The tire (depending on size, and to some degree shape e.g. squarish, roundish) that cuts down a bit on clearance, but IIRC folks are running 245/40s on this size wheel, it might just need a bit more negative camber than stock to not rub. But I would check before going further (IDK about you, but I don't have this stuff memorized ).

Apologies if this is obvious, but tires are the next consideration for fit. A 225/45 tire (stock), with a measured rim of 7.5", has a section width of 8.9" inches. Add ~2/10 of an inch for the stock 8" rim, and that's around 9.1" with stock tires/wheels. (You can find all this info @TireRack.) A 245/40 tire, with a measured rim width of 8.5" has a section width of 9.8", so with the 9" wheel that probably a hair more than 10" wide. Folks running 245s on the 8" stock wheels end up with a section width of around 9.6", on a 8.5" wheel it's about 9.8".

If you wanted to a test fit experiment you could find the center point on your current tire's width, put a the 5" mark of a ruler on that center spot, and see what the clearance looks like. Since you're not changing offset from stock, the "middle" would be in exactly the same spot with the new wheel/tire. Actual results will vary a bit due to tire sidewall construction and so forth, but you could see if it's in right the ballpark.

This is why the "will 245s fit" question needs to incorporate wheel size and wheel offset into the "fit" equation. It's also why as tire size get appreciably wider offsets usually have to change as the strut clearance becomes more and more of an issue. And then we're into trade offs between more rubber on the road vs. scrub radius and other suspension configuration parameters, camber washers to offset offset changes, and other "voodoo magic" as the The Hack likes to call it.

[gcochard]

Originally Posted by Finnegan

No, it's going to keep the stock suspension geometry for scrub radius. The offset is exactly the same. It's going to equally wider than stock on both sides 13mm wider inside 13mm outside. To see how the size and offset works, an offset calculator is a great tool. These wheels should work nicely.

The tire (depending on size, and to some degree shape e.g. squarish, roundish) that cuts down a bit on clearance, but IIRC folks are running 245/40s on this size wheel, it might just need a bit more negative camber than stock to not rub. But I would check before going further (IDK about you, but I don't have this stuff memorized ).

Apologies if this is obvious, but tires are the next consideration for fit. A 225/45 tire (stock), with a measured rim of 7.5", has a section width of 8.9" inches. Add ~2/10 of an inch for the stock 8" rim, and that's around 9.1" with stock tires/wheels. (You can find all this info @TireRack.) A 245/40 tire, with a measured rim width of 8.5" has a section width of 9.8", so with the 9" wheel that probably a hair more than 10" wide. Folks running 245s on the 8" stock wheels end up with a section width of around 9.6", on a 8.5" wheel it's about 9.8".

If you wanted to a test fit experiment you could find the center point on your current tire's width, put a the 5" mark of a ruler on that center spot, and see what the clearance looks like. Since you're not changing offset from stock, the "middle" would be in exactly the same spot with the new wheel/tire. Actual results will vary a bit due to tire sidewall construction and so forth, but you could see if it's in right the ballpark.

This is why the "will 245s fit" question needs to incorporate wheel size and wheel offset into the "fit" equation. It's also why as tire size get appreciably wider offsets usually have to change as the strut clearance becomes more and more of an issue. And then we're into trade offs between more rubber on the road vs. scrub radius and other suspension configuration parameters, camber washers to offset offset changes, and other "voodoo magic" as the The Hack likes to call it.

I'm actually just looking for lighter rims but I can't find any in stock width for a decent (under 300/rim) price, the 245/275 setup seems like overkill to me right now. Is 225 too narrow for a 9 inch rim?

[Finnegan]

Originally Posted by cliffhopper

I'm actually just looking for lighter rims but I can't find any in stock width for a decent (under 300/rim) price, the 245/275 setup seems like overkill to me right now. Is 225 too narrow for a 9 inch rim?

Yes. I wouldn't run a 225/45 size tire on that width. Max recommended is 8.5". (225/40s would work with that 9" rim, but those are almost 3.5% different from stock radius). Plus it's going to give what, IMO, is that nasty stretched tire look.

What about 235/40 front and 265/35 stay within the 3% radius change from stock and stock stagger? 235/40 is going to work okay with the 9" rim, although 8.5" would be better (and lighter). Trick is finding a light rim, decent price, and good offset.

What's the goal here Cliffhopper? Application? (Street, track, Autox, mixed use, ????)

[gcochard]

Originally Posted by Finnegan

Yes. I wouldn't run a 225/45 size tire on that width. Max recommended is 8.5". (225/40s would work with that 9" rim, but those are almost 3.5% different from stock radius). Plus it's going to give what, IMO, is that nasty stretched tire look.

What about 235/40 front and 265/35 stay within the 3% radius change from stock and stock stagger? 235/40 is going to work okay with the 9" rim, although 8.5" would be better (and lighter). Trick is finding a light rim, decent price, and good offset.

What's the goal here Cliffhopper? Application? (Street, track, Autox, mixed use, ????)

Autocross and street. 235 definitely sounds better than 245, but my overall goal is the lightest rim/tire within a reasonable budget. Maybe I can find flow-formed 18x8s somewhere...

[Finnegan]

Originally Posted by cliffhopper

Autocross and street. 235 definitely sounds better than 245, but my overall goal is the lightest rim/tire within a reasonable budget. Maybe I can find flow-formed 18x8s somewhere...

Well, post up if you find something that meets those goals! The other thing (no personal experience with this) is that some folks report a lot less steering feel with super-wide front wheel/tire combos. My suspicion is that's it's more to do the less than optimal offset required to run larger wheels and rubber. The Hack's experience and tire temp results with same size tires and different wheel offsets sort of point in that direction.

[The HACK]

Originally Posted by cliffhopper

If I go from the stock 18x8 +42 to a 18x9 +42 will it negatively affect performance?

Problem with that size, IMO, would be clearance. I don't think a 18" x 9" with 42mm offset will clear the inner strut.

Just a hunch.