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      10-30-2012, 12:34 AM   #1
edx1
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323 wheels and different front/rear widths question

I was digging through some option codes for the xdrive35 and noticed that the 323 wheel option actually had 18x8.0 (225/45 R18) front and 18x9.0 (255/40 R18) rear. This fact isn't mentioned (that I could see) on the bmw website or configuation tool.

First thing is don't see why they would do this on an xdrive. On a RWD only car I could see larger rear wheels for drive grip but what does wider rear wheels do to help an AWD?

I've also been reading threads where they say (for xi models) don't do this because it causes problems with the dsc and early failures with the awd components. I would think it would cause the same problems on an xdrive as well.

Could someone enlighten me on what's going on?

And are the actual wheels different dimensions? One is a /40 and the other is a /45 which also confuses me on why they'd do that.

Last, I live where it snows, often I have to drive a mile in 4"-8" of snow a couple times a winter and there are practically no options for winter runflats (I think there was 1 and it had only 3 very bad reviews on tire rack). I guess I could get different wheels for winter that had more common width (and same front/rear maybe?) sizes but I need to know if the fronts and rear actually have the same outside tire diameter (/40 vs /45 on r18) and if their wheels are the same dimensions, minus the widths.

Thanks.
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      10-30-2012, 02:26 AM   #2
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I have got the 322 wheels which are also staggered (different width front and rear).

The main difference is that visually the wider rears give a more aggressive stance looking from the rear. The rear wheels on X1 is quite close to the rear bumper so the difference visually is more pronounced than say a 3 series.

I don't think it would make any difference to a AWD. Firstly the difference in profile 40 at the back vs 45 at the front means that both front and rear tyres have the same total diameter once mounted (more or less - 0.45x225 = 101.25, 0.4x255 = 102, so overall difference in diameter is just 0.75 x 2 = 1.5mm).

Secondly BMW uses open diffs for its x drive system with a wet multi plate clutch to split the torque so really it should make no difference what wheel sizes either axles are driving.

The actual 323 wheels won't be the same dimension - the rears will be wider but the diameter should be the same.

The difference in tyre profile is to compensate for the difference in tyre width. Profile is just a percentage of the actual tyre width.
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      10-30-2012, 06:45 AM   #3
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I am new here. Just order my X1 with the M sport option, which comes with the staggered 355M wheels.

Even with the xDrive, I think the staggered wheels will help a little bit on acceleration and cornering. Don't forget AWD can't defy physics, when you accelerate, the momentum of the car will shift to the rear. At the same time, the BMW xDrive will transfer most of its torque to the rear axle (behaving just like an RWD in this case). During cornering too, the Performance Control will also kick in and put more power to the outer rear wheel too.

I agree, most of it is just for the look.

Last edited by dchao; 10-30-2012 at 11:37 AM.
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      10-30-2012, 09:05 AM   #4
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Unlike most AWD systems, the BMW X1 M-sport has an 80:20 ratio between rear/front for "sports" driving. In light of that, the staggered tires make more sense than for your typical 50:50 (or 60:40 front:rear) AWD system.
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      10-30-2012, 11:43 AM   #5
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That makes sense for the most part, but since the front is a /45, why didn't they do 255/45/R18 on the rear instead of 255/40/R18?

The 1.5mm difference is right near 2/32" which is maximum difference similar (audi, merc, etc) recommend for their awd cars which already kind of puts you at the border doesn't it? Or has BMW said for sure that any tread depth difference between from and rear is fine? It can't mess with traction control or anything else if they rotate at difference rates?

I did some reading up on staggered and it sounds like cars with staggered understeer, so I just want to verify that the better term for wider rear tires is that 'the rear tires don't slide out as much' since they are what changed and are wider(better grip)? Is it actually better or safer to not have staggered for the whole '50/50 balance' of a bmw so it's more predictable and controllable in fast cornering?

I'm also reading that tire warranty becomes very complicated with staggered. Michelin it sounds like only gives you half the tread wear warranty if you have staggered tires. Something about 'you could have got more miles if you could rotate them all around equally'. Also some people mention tire manufacturers won't give you their tread wear warranty unless all 4 tires are at 2/32 wear (kind of low for safety imo) but with wider rears, do they wear faster or slower? I would expect slower but what I've read makes it appear they wear faster but I never could find information about non rwd only cars.

I think for winter though I'll just get a new 4 wheel and tire set of 225/45/r18 all around. Also who knows how this will play with tread wear warranty if I'm not keeping the same wheels on year round, guess I have to hope that noting mileage when they're changed is good enough...

Anyway, I like the wheels and the idea of better performance/safety when driving around corners but I wonder if going with the 323 staggered is actually a bad idea?
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      10-30-2012, 12:01 PM   #6
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Quote:
Originally Posted by edx1 View Post
That makes sense for the most part, but since the front is a /45, why didn't they do 255/45/R18 on the rear instead of 255/40/R18?
As jctg has explained:

(more or less - 0.45x225 = 101.25, 0.4x255 = 102, so overall difference in diameter is just 0.75 x 2 = 1.5mm).

101.25mm and 102mm are the height of the sidewall for the front and rear tires. The difference is negligible due to difference in tread wear and tire pressure.

Now that the rims are the same at 18" front and rear. Plus the same height of the rubber. The result is that, the chassis will sit level to the ground, instead of tilting forward.

Understeering has more to do with the fact it is a front-engine car. If you have a rear-engine 911, then it will be more prone to over steering. Like I said, if you have the Performance Control, then the xDrive will add a little bit of over-steering to correct the inherited under-steering the car has.

The only cons with staggered wheels is that you can't rotate your tires to get better milage out of them. So in the long run it will cost you more. On the other hand, it will definitely improve the handling and stability of your car, thinner front tires also makes steering lighter, useful for the hydraulic steering we have on xDrive.

Last edited by dchao; 10-30-2012 at 12:24 PM.
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      10-30-2012, 12:07 PM   #7
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Quote:
Originally Posted by edx1 View Post
since the front is a /45, why didn't they do 255/45/R18 on the rear instead of 255/40/R18?
The simple answer is tire diameter. 255/40/18's will have a diameter that is just a bit larger than the 225/45 fronts. 255/45/18's, on the other hand, are more than an inch larger in overall diameter.

Staggered wheels do tend to make vehicles understeer a bit more. But understeer is safe for less skilled drivers, and since the X1 will rarely be tracked it's probably a non-issue for most customers. Plus, there's no denying there is a cosmetic benefit to staggered setups.

I use the staggered 18" OEM setup for fair weather, but just changed to a squared 17" setup for winter.
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      10-30-2012, 12:39 PM   #8
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Quote:
Originally Posted by HottRodW View Post
but just changed to a squared 17" setup for winter.
Of course, staggered wheels are totally wasted in the snow.
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      10-30-2012, 05:34 PM   #9
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edx1

I suggest you google and find out exactly what the tyre sizes mean.

http://www.gonebush.org/t213-tyre-si...d-letters-mean

Don't worry about understeer. That is just wannabe racers talking you have been reading. Seriously unless you track the car (or autocross in the US) it won't make a difference. On the road you should be nowhere near the limit of the car for that to be a factor.

And even if it is understeer is safer/more predictable/more controllable than oversteer.
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      10-30-2012, 10:03 PM   #10
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Quote:
Originally Posted by HottRodW View Post
Staggered wheels do tend to make vehicles understeer a bit more. But understeer is safe for less skilled drivers, and since the X1 will rarely be tracked it's probably a non-issue for most customers. Plus, there's no denying there is a cosmetic benefit to staggered setups.
There is another benefit. Acceleration shifts the pressure to the rear wheels, and because of the 20:80 ratio making it closer to rear wheel drive than standard AWD, increasing the rear tyre width nets you more grip during acceleration.
It might presumably also help with drifting, but I don't think the X1 would be a suitable vehicle for that.
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      10-31-2012, 12:02 AM   #11
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Okay, this all makes sense. I wasn't getting that the profile was a % of the width.

I'll start my hunt/research to figure out what options there may be for tread wear warranty with staggered. So far it doesn't look good though. If anyone has experience with staggered and treat warranty let us know too.

Staggered does seem like a good thing for performance at least, but I tried google again tonight to find comments about if fronts or rears wear quicker for an staggered AWD car with no luck.

Last edited by edx1; 10-31-2012 at 12:07 AM.
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      10-31-2012, 04:47 AM   #12
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LOL all you guys' argument about weight transfer M sports sending more torque to the rear and so on are just argument for wider tires being better. When the weight does transfer to the back on a RWD or mostly-RWD car, then the width of the fronts does not matter and has no influence on the grip in the back.

I personally did find the X1 to feel a little bit under-tired in the front and too much under steer for MY taste (your mileage and taste may vary). It was very obvious on the track, but also on the road in some occasions. But obviously no-one will argue that under steer is not safer for most people most of the time, and that said there is still a lot of grip available in the front and you have to be having fun in the twisties to start feeling that under steer.

I would probably (when it's time to change the front tires) look at what it possible to go one size wider in the front, it would still be a staggered setup though because there is a lot of difference in width between those fronts and the backs.

Which brings us back to the reason BMW went with this 225/255 choice in the first place: looks only? 225 not enough in the back?
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      10-31-2012, 06:22 AM   #13
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Do you have the Dynamic Performance Control Option on the car?

I can't argue with you, because I've just ordered my car. But according to the BMW brochure, DPC can rotate the outside rear wheel faster than the inside wheel in hard cornering, thus reduce understeering and improving cornering speed.

If you have DPC, do you think it has helped in reducing the under steering?

IMO, the biggest benefit from the wider rear tires is the straight line performance. Specially on slippery or wet pavement.
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      10-31-2012, 08:07 AM   #14
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Another thing to keep in mind,is the x1 is not full time awd. The rear wheels get all the power unless slipping is detected, then power is is split between front and rear. So yes having a staggered setup would help handling. And no as long as the tire profiles are the same front a rear, then you wont have speedo or wheel speed sensor issues.

here is some math I have done

actual speed when speedo shows 60 mph
235/40/19 = -2.1% tire speed - 61.3mph
235/35/19 = +1.5% tire speed - 59.1mph
225/40/19 = -.90% tire speed - 60.6mph
245/35/19 = +.4% tire speed - 59.8mph
255/35/19 = -.7% tire speed - 60.4mph
265/30/19 = +2.3% tire speed - 58.6mph

So you see the staggered size that bmw recommends (F 225/40/19 R 255/35/19) will not affect your speedo or wheel speed sensors. Rim size for these tires should be no larger than 8.5" up front, and you should be able to up to 9" in the rear without issue. Always make sure to check with tire manf. for recommended wheel sizes for your specific tire.
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      10-31-2012, 12:37 PM   #15
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Yes you can feel the DSC do its job but when that happens you are already sliding/understeering.
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      11-06-2012, 11:54 AM   #16
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I spent the last few nights digging through forums about staggered setups on non X1's and it's been interesting.

A lot of it seems to come down to preference and driving style. Many people who've owned M3's, M5's and other high performance BMW's that came with staggered often are changed to square setups by people who run track. Apparently even with rwd cars having staggered causes too much understeer for the best times.

Some common points for staggered are:
* Often found on performance rwd cars with enough HP that it's easy to spin the rear out and crash so the manufacturers put bigger tires on the back to lessen the chance of people oversteering without the skill to correct from it.
* Staggered is easy to correct from problems when cornering too fast, just let off the gas.
* Most all cars, including BMW's, are setup already with understeer so adding more isn't a good idea.
* Many people say if you like cornering then staggered will let you down for enjoyment.
* Tread warranty is half or not honored at all for rear wheels on a staggered setup.
* Hard to find tires for some staggered (X1's 323 option isn't too bad though)
* If running staggered and you want a neutral performing car you need to add sway bars to counter the extra understeer.
* Staggered "looks" more aggressive and sells.
* Several models of xi's (540, 740) have come with staggered and it's a mixed bag of nuts if it will cause differentials to go bad early. Seems like people say it's bad if the xi didn't have it as an option and okay if it did even though the cars differentials and computers are similar).
* The ABS and traction control shouldn't get confused if the wheels sizes are within about 3% of the same circumference as this is what some xi models came with.

For me I've decided to stick with the standard xDrive35 wheels. I think I'll like the handling better and that staggered is mainly for looks and marketing which isn't the reason I'm getting a BMW -- I want safety and a bit of performance fun and looks comes last (aka wheels). I did like the fact though that the 323 wheels were different in terms of official BMW looks but it's almost too loud I think for a BMW of my liking. I think I would be completely on the fence though for wheel choice if the 323 style was offered in a non staggered option. I will be buying a separate winter wheel set so maybe I'll put the winters on the stock wheels and maybe watch for the 323 or other style of BMW wheels with some more character to pop up on closeout somewhere.

A final note, after my research I do side with the group that a staggered wheel option on cars and especially an AWD is more of a move by manufacturers to offer a "performance" marketing point as it's a $0 cost option on the 35 and it doesn't do much, if anything or possible reverse, for handling performance and it's not like you put down 11's on an X1 automatic anyway to warrant more rear traction, I think? Some people jokingly say staggered options are there so people who want performance car but don't know what they're doing can buy a less performancing and more safe car yet think it's better because it "looks" like it.

I found a site that showed all wheels BMW had ever made. It's pretty obvious that BMW has been trying their hand in wheels that are more loud, and I actually would say the 323 wheel is possibly their most aggressive looking wheel design yet. There are some 4xx wheels though found on the X5 that are pretty aggressive as well.

It's too bad that BMW doesn't allow you to order any wheel style that fits the X1 and let people have a wider selection for their preferences in both handling and looks. I don't think having a check box for "staggered wheels" would add too much buyer confusion. I'd more likely opt for the 323 wheels if they were not staggered, and it was out of luck I noticed they were staggered while digging through third party xDrive35 docs since it's not stated anywhere on the BMW website. I'm sure there will be a number of buyers who regret the 323 option when it comes time to rotate or buy new summer or buy new winter tires.

Last edited by edx1; 11-06-2012 at 12:00 PM.
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      11-06-2012, 12:14 PM   #17
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The 323 is unique design and a great looking wheel. Although you may have to order them staggered as a factory option, you can still outfit your car with them in a squared setup. Just purchase all four from the aftermarket in the 8" width. It will cost more than buying upgrade option, but then you can have the looks and the handling traits you're looking for.
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