[The Godfather]

Hello all. new to the forum and Xdrives but not to BMW's. I know at this point is like beating a dead horse but as you all know all cases vary when you get into specifics as such.

So I placed my 99 Firebird new set of MRR wheels and Continental Extremes tires on the F30 M xdrive. All fit perfect after adding a 3mm spacer in the back to clear the M calipers. Drove it for a bit but something feels off. A bit of hesitation on accelerating at any speed.

Fronts 245/35/19. 8.5 wide
Rears 295/30/19. 9.5 wide

My question is, what is my percentage on the above set up? Do I just change the rears to a 275/30/19 and be ok or will I have others concerns to look out for?

I saw on another thread someone stating NOT to go with the 35 F / 30 R profile. Any reason for this?

Thanks
First Thread.

[1QuikWS6]

I have been running 245/35-19 Frt & 275/30-19 RR tires on same width wheels as yours, on my 435iX, for years with no problems - they are within the 1% difference suggested

[Genieman]

Originally Posted by The Godfather

Hello all. new to the forum and Xdrives but not to BMW's. I know at this point is like beating a dead horse but as you all know all cases vary when you get into specifics as such.

So I placed my 99 Firebird new set of MRR wheels and Continental Extremes tires on the F30 M xdrive. All fit perfect after adding a 3mm spacer in the back to clear the M calipers. Drove it for a bit but something feels off. A bit of hesitation on accelerating at any speed.

Fronts 245/35/19. 8.5 wide
Rears 295/30/19. 9.5 wide

My question is, what is my percentage on the above set up? Do I just change the rears to a 275/30/19 and be ok or will I have others concerns to look out for?

I saw on another thread someone stating NOT to go with the 35 F / 30 R profile. Any reason for this?

Thanks
First Thread.

they say that the overall diameter shouldn't be more than 1% off for xdrive since it will mess with traction control but in your case it's 0.84% which isn't over 1% so that shouldn't be a problem.

In theory 285 (instead of 295s) in the rears would be even closer to the fronts, but you don't necessarily want to spend that much money on tires to realize it was something else... might wanna get it checked out to make sure it isn't something else....

[The Godfather]

Originally Posted by Genieman

they say that the overall diameter shouldn't be more than 1% off for xdrive since it will mess with traction control but in your case it's 0.84% which isn't over 1% so that shouldn't be a problem.

In theory 285 (instead of 295s) in the rears would be even closer to the fronts, but you don't necessarily want to spend that much money on tires to realize it was something else... might wanna get it checked out to make sure it isn't something else....

Car runs great with the stock M wheels it came with. F 225/40/19 and R 255/35/19

So you are telling me that 285's would be a better choice instead of the 275's?

I have to learn how to calculate this crap. I can't find the calculator I ran into earlier on a thread.

[OddlyCalm]

Originally Posted by The Godfather

Car runs great with the stock M wheels it came with. F 225/40/19 and R 255/35/19

So you are telling me that 285's would be a better choice instead of the 275's?

I have to learn how to calculate this crap. I can't find the calculator I ran into earlier on a thread.

https://tiresize.com/calculator/

[alohasurftoad]

Originally Posted by 1QuikWS6

I have been running 245/35-19 Frt & 275/30-19 RR tires on same width wheels as yours, on my 435iX, for years with no problems - they are within the 1% difference suggested

actually...245/35/19, 275/30/19 is 1.2% however if it's been working for you maybe we should note that as the max difference for x-drive.

[The Godfather]

So this is what came up when I placed my actual numbers.

Size 1: 245/35/19 Front

Size 2: 295/30/19 Rear

Scale / Size 1 / Size 2

Diameter / 25.8" / 26" / +0.8%

Width / 9.6" / 11.6" / +20.8%

SideWall / 3.4" / 3.5" / +2.9%

Circum. / 80.9" / 81.5" / +0.8%

Revs/Mile / 784 / 777 / -7



Correct me if I'm wrong but it seems like this should work just fine. Am I missing something?

[Ultimateone]

Can you post pics of the 295 on the 9.5" wheel

[1QuikWS6]

actually...245/35/19, 275/30/19 is 1.2% however if it's been working for you maybe we should note that as the max difference for x-drive.

With rounding off it's more like 1%, but anywho, here is formula for anyone wanting to figure it out

245/35-19 = 25.8 Dia (V1)
275/30-19 = 25.5 Dia (V2)

https://tiresize.com/calculator/

Percent Diff:

(V1-V2)
------------ X 100 = 1.16959% difference - rounding ~1%
(V1+V2)/2

Doesn't matter which diameter value you put in for V1 or V2 answer will be the same

I don't think .2% has any effect (and I guess not since the car is fine)

https://www.calculatorsoup.com/calcu...calculator.php


And yes, a 285/30-19 tire would have been better @ 25.7 Dia for a 0.38835% difference ~ .4, plus Revs/Mi would be = @ 784, but at the time that I needed the tires that size was out of stock in the MPS A/S +3's

I run that staggered setup only in summer months here in PA so roughly 7 months. Rest of the year I run square setup with OEM size Blizzaks on factory 400M wheels

Come next time I get tires I will go for the 285's in the rear

[alohasurftoad]

Originally Posted by The Godfather

So this is what came up when I placed my actual numbers.
Size 1: 245/35/19 Front
Size 2: 295/30/19 Rear
Scale / Size 1 / Size 2
Diameter / 25.8" / 26" / +0.8%
Width / 9.6" / 11.6" / +20.8%
SideWall / 3.4" / 3.5" / +2.9%
Circum. / 80.9" / 81.5" / +0.8%
Revs/Mile / 784 / 777 / -7
Correct me if I'm wrong but it seems like this should work just fine. Am I missing something?

0.8% should work. 285/30 would make it even closer at 0.4%. this is a pure guess but i'm thinking even though the diameters are ok(=difference in tirespeeds between the front and rear=ok), the transfer case may be detecting a difference in rolling resistance (fronts have less grip than the rear) due to the contact area difference and the transfer case is trying to adjust. this is pure speculation, though.

[The Godfather]

Fellas thanks for chimming in.

That's what I was thinking, it should be ok. unless their calculator is off. Like swapping wheels from a domestic to a import. LoL

I'll post a couple of picture in a minute, Just got home.

[The Godfather]

It's not bad at all. However I think I'm going to add a 5mm spacer up front to equalize the stance a bit with the rear.

[03redtypes]

Originally Posted by alohasurftoad

actually...245/35/19, 275/30/19 is 1.2% however if it's been working for you maybe we should note that as the max difference for x-drive.

Given this is 1.2% if I run a 245/35/20 and a 275/30/20 it’s showing -1.1% this theoretically should be okay?

[McQueen2014]

Originally Posted by 03redtypes

Given this is 1.2% if I run a 245/35/20 and a 275/30/20 it’s showing -1.1% this theoretically should be okay?

It's all fun and games until your front differential packs it in and BMW blames the stagger (even <1.2% differences). There are a few stories/claims of that happening around here so you play at your own risk.

[Spielzeugauto]

245/35 and 285/30 would indeed be perfect. But even then they could still blame you.
I would definitely not show up at the dealer wearing your current stagger.

[5mall5nail5]

The other, other problem is your Firebird bolt pattern is 5 x 4-3/4". BMW is 5x120mm. This means your bolt pattern is 5 x 120.65 on the GM wheels... be careful these don't actually fit. Also you will want hubcentric spacers which you're going to have a hell of a time making in the 3 - 5mm range.

[Littlebear]

Originally Posted by 5mall5nail5

The other, other problem is your Firebird bolt pattern is 5 x 4-3/4". BMW is 5x120mm. This means your bolt pattern is 5 x 120.65 on the GM wheels... be careful these don't actually fit. Also you will want hubcentric spacers which you're going to have a hell of a time making in the 3 - 5mm range.

I think the "hub" size is the same, BMW & some GM, so no hubcentric spacers should be needed (but pls check this).
I ran Enkies with the GM bolt pattern for a few years on my E46, no prob (looked great!). The vendor said others do this too. YMMV!

Murf

[5mall5nail5]

Originally Posted by Littlebear

I think the "hub" size is the same, BMW & some GM, so no hubcentric spacers should be needed (but pls check this).
I ran Enkies with the GM bolt pattern for a few years on my E46, no prob (looked great!). The vendor said others do this too. YMMV!

Murf

Lot of people do it - the problem is it literally bends the lug bolts.

I run GM wheels on my race car that use shank lug nuts (stud conversion). I had to make hubcentric rings (not the same hub size) and then machine the wheels because it was literally bending the wheel studs out which caused false torque readings.

[the dope steez]

Another thing to keep in mind re: tire sizing is that OEM staggered sizes aren't perfectly the same rolling diameter either, the fronts are slightly larger than the rears. I believe this is why the car will tolerate 245/35/19 front and 275/30/19 rear even though a 235/35/19 front gives a 0% difference.

I run the aforementioned setup and even though the fronts are 1.2% bigger I haven't had any issues for about 20,000 miles

[Littlebear]

Originally Posted by 5mall5nail5

... I had to make hubcentric rings (not the same hub size)...

I think some GM cars had the same hubcentric size as BMW, maybe the Camaro & Firebird, but I don't remember (which is why I asked OP to check). They will have the slightly-off bolt pattern you mention, though.

Murf