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First generation BMW X1 availbe as a X1 28i with either sDrive (RWD) or xDrive (AWD) or the US exclusive I6 N55 powered X1 35i xDrive.

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Old 10-22-2018, 01:07 PM
wvadam wvadam is offline
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Xdrive - which tires wear more front vs back?

Time to put snows on soon an 2 tires have a slightly better tread than the other 2. The question is which wheels I should put the better tires on now, knowing that I want them to wear more evenly and not have two even more worn tires next season.

Looking for other peoples experience with tire wear with awd. If this was a full time fwd with the rear only engaged when the front sllips like most awd's are these days it would be a no brainer to put the best tread at the front but I have been told we have 60/40 split torque which makes this not so simple.
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Old 10-22-2018, 01:19 PM
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It is 40 - 60. The rear axle is always powered. Front is controlled.
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Old 10-22-2018, 01:29 PM
rice_rocket88 rice_rocket88 is offline
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Go measure your tires, whichever one is lower... put the one with more meat on it since those are the ones that wear faster My wife has the 16 X1 and I just measured it.. the fronts were 6/32 and the rears are 8/32 with 23K miles on the car.
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Old 10-22-2018, 01:40 PM
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Fronts steer and brake with weight transfer forward during breaking and traction on TC command. Rears only traction and lightly brake proportional to weight transfer forward.

As to torque distribution; Torque applied MINUS torque resisted must equal zero, otherwise the tire slips. Torque distribution is normal weight force transfer under acceleration.
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Old 10-22-2018, 01:49 PM
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Originally Posted by wvadam View Post
Time to put snows on soon an 2 tires have a slightly better tread than the other 2. The question is which wheels I should put the better tires on now, knowing that I want them to wear more evenly and not have two even more worn tires next season.



Looking for other peoples experience with tire wear with awd. If this was a full time fwd with the rear only engaged when the front sllips like most awd's are these days it would be a no brainer to put the best tread at the front but I have been told we have 60/40 split torque which makes this not so simple.


Suggest you install on the Front and use MICHELIN X-ICE XI3 XL. Maybe better to get 4 news at once. $174.45 per tire.

The front control your directionality and more prone to slipping and losing control if your tires suck.


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Old 10-22-2018, 01:54 PM
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The front control your directionality and more prone to slipping and losing control if your tires suck.
Thatís called understeer, and that wasnít the question, was it?
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Old 10-22-2018, 02:17 PM
wvadam wvadam is offline
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I am definitely measuring them this year when I put them on, recording it, and doing the same in the spring to see what wore more. I purchased a tire depth gauge off ebay for about $20. I think I will put the better treads on the back because of the comment about about the rear wheels being driven all the time.

My summer tire setup is staggered with 255/40/18's in the rear so there isn't even a choice about what tires to put where. The stock pirelli run flats wore down way too fast for my liking but at least wore evenly across the tread. I replaced my front summer pirelli run flats with the new longer lasting compound tires pirelli s7 or whatever they are but wear rating of 500 vs. 260 stock. So far no issues performance wise with one year on them, it seems foolish on a daily driver type car to not put the 500 wear rating tires on it although people will say 260 is better performance on the track etc but I don't want to buy new tires every 2 years either.

My winter pirelli sotozero's are being replaced with non-runflat blizzaks mainly due to the extreme high cost of pirelli run flats and I found a deal on some nearly new blizzaks locally. I just wasn't sure to put the 2 better ones on the front or rear.
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Old 10-22-2018, 04:20 PM
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Instead of a permanent torque split (which is featured in earlier systems), xDrive provides variable torque split between the front and rear axles through the use of a multi-plate wet clutch located in the gearbox on the output to the front drive shaft. This setup allows xDrive to modulate the torque split between the front and the rear axles, which is normally split at 40:60 ratio, respectively. If wheel slip is detected by the ABS/DSC system, xDrive can redistribute up to 100% of the engine power to the front or rear axle.[2] The wet clutch is applied through a high speed electric servo motor turning a cam-shaped actuator disc. As the rear drive shaft is hard-coupled to the transmission output, full torque transfer to the front axle can only be achieved if the rear wheels have no traction and are both slipping.

xDrive is connected to the ABS and DSC systems. In the case that wheelspin or directional instability still occurs while xDrive is or has been modulating the torque split, DSC will brake independent wheels to regain traction and improve directional stability without driver intervention.

The front and rear differentials in xDrive vehicles are typically an open differential design, thus relying on brake application by the DSC system to transfer power from the slipping wheel to the wheel with traction.

A variation on the xDrive system is present in the 2015 BMW X1 (F48), which is based on a front-wheel drive design with a transversely-mounted engine. In the FWD-derived xDrive variant, the front wheels receive 100% of the torque when the xDrive clutch is open, giving it a front bias instead of the usual xDrive rear bias.[3]




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Old 10-22-2018, 06:00 PM
Autoputzer Autoputzer is online now
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For RWD-platform based xDrives, the rears will wear faster, and can also wear differently. How about some data?

Frau Putzer's G01 X3 30i xDrive has about 6k miles on it now. I expect the OE non-RFT, all-season tires (option code 25X) to last past 50k miles. So, I set up a rotation schedule so each tire will be in each corner twice in 52.5k miles. New tires usually wear faster than old tires. So, I make the first rotation stint half the miles of the subsequent rotation stint. So, I rotated the tires at about 3.5k miles. I measure the tread depths right before I do a rotation. I use that data to calculate the wear patterns, and from them identify alignment and improper inflation issues. I maintain the same tire pressures over an entire rotation stint to get enough measurable wear to establish wear vs. tire pressure trends. Based on the trend, I adjust the pressures if necessary for the next rotation stint.

Here's the tread depth data after the first 3.5k miles on the X3. The rears wore about 50% more than the front. My pressures during that stint were two PSI over the door jamb decal pressures (as measured with my dial tire pressure gauge at the morning low temperatures). I got some increased wear in the center of each tire, meaning that I need to lower the pressures. The wear was so small that it was close to the resolution of my measurement (about 1/4 of no 32nd inch). The next stint will be 7k miles, and the wear/measurement resolution will be higher and make for more accurate trend detection.

Yeah, I've gone off the deep end with my "tire hyper-management." My friends call me "The Tire Whisperer." But, I've got more than 70k miles out of all-season tires on multiple cars, and I get 40k miles out of high-performance tires.
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Old 10-22-2018, 07:37 PM
wvadam wvadam is offline
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"As the rear drive shaft is hard-coupled to the transmission output, full torque transfer to the front axle can only be achieved if the rear wheels have no traction and are both slipping"

Basically, Xdrive is RWD with an electronic clutch / transfercase that turns the Front drive train on and off and can vary torque applied to the front axle by varying the amount of slip occurring in the transfercase clutch. This is not ideal because of the wear on the clutch and is only used during specific traction loss events.

Electronic stability control and traction control work in conjuction with Xdrive but also perform the same functions in non-Xdrive vehicles. I am just talking about the power train for now.

Older AWD systems used a center differential in addition to a front and rear differential which allowed for different speeds of the front and rear axle while providing equal torque to all wheels all the time. The major problem was that when one wheel slipped and for example only 5 lbs of force could be transmitted to that wheel, then only 5 lbs of force could be transmitted to each remaining wheel as well because the differentials allowed for equal force transmitted to all wheels regardless of wheel speed.

Even older systems lock all 4 wheels to the same rotational speed without differential action and this is where I think the concept used to market all wheel drive is misleading. Even in the oldest system of having all 4 wheels locked, you could say that "the system automatically transfers 100% of the torque to the wheel(s) with traction" because obviously the only place force can be applied is to a wheel with traction, while the others simply rotate without transmitting a force.

In regards to Xdrive in everyday driving such as a long highway trip, I have yet to see a viable mechanism (other than the audi crown gear which is a completely different discussion) that can transmit the coveted 40/60 torque split without wheel slippage and or transfercase clutch slippage. I bring up highway because imagine all 4 wheels are travelling at exactly the same speed as on a highway they would be. In order for variable torque to occur, the transfercase clutch has to slip. In order for the transfercase clutch to slip, the front and rear axles must be moving at different speeds, which they are not in the highway scenario.
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Old 10-22-2018, 08:33 PM
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Quote:
Originally Posted by wvadam View Post
In regards to Xdrive in everyday driving such as a long highway trip, I have yet to see a viable mechanism (other than the audi crown gear which is a completely different discussion) that can transmit the coveted 40/60 torque split without wheel slippage and or transfercase clutch slippage. I bring up highway because imagine all 4 wheels are travelling at exactly the same speed as on a highway they would be. In order for variable torque to occur, the transfercase clutch has to slip. In order for the transfercase clutch to slip, the front and rear axles must be moving at different speeds, which they are not in the highway scenario.
The term for "older awd" with 3 differentials is 4wd. Those are the real off road cars.

I think the 40/60 ratio comes with a completely engaged, non-sliding clutch. And the weight transfer during acceleration is the one that tilts the 50/50 to the rear. But that's just a guess.
It turns to 20/80 in curves during normal condition to have some more sporty feeling.

The clutch may slide on the highway as well if your tire tread is very different.
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Old 10-22-2018, 08:54 PM
wvadam wvadam is offline
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Originally Posted by Autoputzer View Post
For RWD-platform based xDrives, the rears will wear faster, and can also wear differently. How about some data?

Frau Putzer's G01 X3 30i xDrive has about 6k miles on it now. I expect the OE non-RFT, all-season tires (option code 25X) to last past 50k miles. So, I set up a rotation schedule so each tire will be in each corner twice in 52.5k miles. New tires usually wear faster than old tires. So, I make the first rotation stint half the miles of the subsequent rotation stint. So, I rotated the tires at about 3.5k miles. I measure the tread depths right before I do a rotation. I use that data to calculate the wear patterns, and from them identify alignment and improper inflation issues. I maintain the same tire pressures over an entire rotation stint to get enough measurable wear to establish wear vs. tire pressure trends. Based on the trend, I adjust the pressures if necessary for the next rotation stint.

Here's the tread depth data after the first 3.5k miles on the X3. The rears wore about 50% more than the front. My pressures during that stint were two PSI over the door jamb decal pressures (as measured with my dial tire pressure gauge at the morning low temperatures). I got some increased wear in the center of each tire, meaning that I need to lower the pressures. The wear was so small that it was close to the resolution of my measurement (about 1/4 of no 32nd inch). The next stint will be 7k miles, and the wear/measurement resolution will be higher and make for more accurate trend detection.

Yeah, I've gone off the deep end with my "tire hyper-management." My friends call me "The Tire Whisperer." But, I've got more than 70k miles out of all-season tires on multiple cars, and I get 40k miles out of high-performance tires.
Thank you Autoputzer, that is far more detailed data than I expected to find here by a long shot. The rear wearing faster scenario seems like solid science now.
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Old 10-23-2018, 08:10 AM
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Originally Posted by wvadam View Post
Thank you Autoputzer, that is far more detailed data than I expected to find here by a long shot. The rear wearing faster scenario seems like solid science now.
You're welcome.

My RWD 535i's rear wear is about twice that of the front. My FWD Chevy Cobalt SS's front wear is about 2.5 times that of the rear. But, I absolutely flog the nose-heavy Cobalt SS, shod with Conti' DW high performance tires. If I don't get the car sliding some when I go out to lunch, I consider it an unsuccessful outing.
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Old 10-25-2018, 09:24 AM
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TL;DR.
My X1's rear wears faster than the fronts.
When it comes to rotation.... It's hip to be square.
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Old 10-25-2018, 04:28 PM
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My X1 OEM tires wore evenly, but do mostly highway driving. (Also very little ECO Pro mode) I was anal about keeping tire pressure as spec from the door sticker and owners manual.
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Old 10-26-2018, 06:20 PM
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2013 x1 msport n55 staggered setup. Rears most definitely wear faster. I read somewhere online that the msport tune on xdrive tries to closely mimic a rear wheel drive car. The same article said the torque bias was 80/20 on msport and 60/40 on non msport ... 80 to the rear. 100k on the car 3rd set rear tires. I just put BFG comp 2 a/s on a week ago.
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Old 10-26-2018, 09:07 PM
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2013 x1 msport n55 staggered setup. Rears most definitely wear faster. I read somewhere online that the msport tune on xdrive tries to closely mimic a rear wheel drive car. The same article said the torque bias was 80/20 on msport and 60/40 on non msport ... 80 to the rear. 100k on the car 3rd set rear tires. I just put BFG comp 2 a/s on a week ago.
But the 40:60 ratio is not fixed, and the computers can send 100% of the torque to either the front or the rear axles via an electrically operated centre clutch. Imagine a hillstart with both rear wheels on ice and fronts on tarmac and youíll see why thatís important.
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Old 10-31-2018, 11:03 PM
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But the 40:60 ratio is not fixed, and the computers can send 100% of the torque to either the front or the rear axles via an electrically operated centre clutch. Imagine a hillstart with both rear wheels on ice and fronts on tarmac and youíll see why thatís important.
We already covered that the rear wheels are driven all the time because they are hard coupled to the transmission. It is not possible to turn them off, it is only possible for the transfercase to activate the front axle.

Regarding the hillstart with the rears on ice, it isnt a question of seeing why it is or isn't important. It is that those rear wheels are driven fulltime regardless of traction on them and cannot be de-coupled by the computer so it is not really true about the computer being able to send up to 100% to the front or rear because the front tires cannot be powered without the rears also being powered at the same time. This is why this generation of X1 wears out the rear tires more as observed.
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Old 11-01-2018, 08:37 AM
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so it is not really true about the computer being able to send up to 100% to the front or rear because the front tires cannot be powered without the rears also being powered at the same time.
Mathematically not 100% but 99% on front when the rears are on ice. 1% of torque spent on spinning the rears.
If the rear tires have some grip, then the torque distribution can't be 100/0 you are right.
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Old 11-01-2018, 10:06 AM
wvadam wvadam is offline
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Mathematically not 100% but 99% on front when the rears are on ice. 1% of torque spent on spinning the rears.
If the rear tires have some grip, then the torque distribution can't be 100/0 you are right.
Yes that's a good analysis as well. We can also consider this when thinking about how much the absolute minimum percentage is:

I don't want to look up a lot of exact figures right now but lets say your car with you and a passenger in it weights 4000 lbs evenly distributed at 1000 lbs per wheel. Your car is stuck in the snow somewhere or on ice or whatever you want to imagine. The wheel has 1000 lbs force acting downward on it and tires designed to have some grip on ice and snow expecially true if you have snow tires like I would expect most people who spend the money on BMW's also spend some money and get good tires to get maximum performance from awd in winter. So if you get out of your car now and try and turn that tire by hand, how much force will you have to apply to rotate the tire or spin it? will you be able to turn it at all? it is not likely and it is not just due to the friction between the tire and the ground but also the rolling resistance of the tire itself, the energy needed to deform the tire where it makes the flat patch on the ground, and the resistance in the vehicle drive train as the wheel bearing also has 1000 lbs acting on it and you are also applying a force to turn the drive shaft and differential gears. Anyways its just something to think about.

What I really wish BMW had is something similar to the hill descent control button where it uses the brakes to apply even pressure on all wheels going down a hill. I wish there was a button you could press when you were stuck in the snow that would apply the brakes in such a way that all the tires would rotate slowly and evenly like in a 4-wheel locked setup to get out of a ditch/driveway etc. All the videos I looked up on youtube with people stuck show the awd systems alternating power from one wheel to the next. One wheel slips the brakes then the next wheel slips then brakes and it keeps going on like this.
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Old 11-01-2018, 10:41 AM
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Yes that's a good analysis as well. We can also consider this when thinking about how much the absolute minimum percentage is:

I don't want to look up a lot of exact figures right now but lets say your car with you and a passenger in it weights 4000 lbs evenly distributed at 1000 lbs per wheel. Your car is stuck in the snow somewhere or on ice or whatever you want to imagine. The wheel has 1000 lbs force acting downward on it and tires designed to have some grip on ice and snow expecially true if you have snow tires like I would expect most people who spend the money on BMW's also spend some money and get good tires to get maximum performance from awd in winter. So if you get out of your car now and try and turn that tire by hand, how much force will you have to apply to rotate the tire or spin it? will you be able to turn it at all? it is not likely and it is not just due to the friction between the tire and the ground but also the rolling resistance of the tire itself, the energy needed to deform the tire where it makes the flat patch on the ground, and the resistance in the vehicle drive train as the wheel bearing also has 1000 lbs acting on it and you are also applying a force to turn the drive shaft and differential gears. Anyways its just something to think about.

What I really wish BMW had is something similar to the hill descent control button where it uses the brakes to apply even pressure on all wheels going down a hill. I wish there was a button you could press when you were stuck in the snow that would apply the brakes in such a way that all the tires would rotate slowly and evenly like in a 4-wheel locked setup to get out of a ditch/driveway etc. All the videos I looked up on youtube with people stuck show the awd systems alternating power from one wheel to the next. One wheel slips the brakes then the next wheel slips then brakes and it keeps going on like this.
Good points.
We should add the drivetrain losses and the rubber deformation. So my next guess is 95/5
Drivetrain losses are max 5% in total, and we only need the rear end.
And the "spinning it by human power" comparison is not that accurate because once it is spinning, it is a lot easier to keep it spinning then making it spin the first time. One horsepower is about 5 people at peak combined. (put a horse and a human next to each other and compare, haha) Ok just kidding. When I measured my cycling power it was around 120W. 1 hp is something 746W.

Keep in mind that these apply to any AWD and 4WD system. Even the 4WD will rotate the rear tires versus the front wheel drive car with 100/0 setup that pulls the rear end.


"All the videos I looked up on youtube with people stuck show the awd systems alternating power from one wheel to the next. One wheel slips the brakes then the next wheel slips then brakes and it keeps going on like this."

Does that apply to newer systems too? This is just the matter of how fast the system can react. This is going to be solved since the communication and the computing speed keeps increasing with newer models.
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