Tire size programming, Please Help!
 

Does anyone know if it is possible to update the ECU to a different tire size. Installed New tires on MY 07 Sport pack and now getting an intermittent driveline noise at various RPMs and road speeds especially during cornering. Switched to Pirelli P-Zero Nero MS 245/45 18 front, 275/40/18 Rear. The tire diameter is 3% shorter than with stock tires and I'm sure the driveline noise is caused by Computer Thinking that I have taller tires. It is a weird noise that sounds like when the stability control kicks in. No dashboard lights though.

I go into more detail about this in my Bimmerfest thread. Here is a link

http://www.bimmerfest.com/forums/sho...d.php?t=188710

Any thoughts?

:wavey::xoutpost::wavey:

don't you set the neutral tire pressure by holding down the tpm button?

tire pressure?, yes. Tire Size? no.

wheres the sound coming from...from outside like from the tires or inside the X3 like when u push the lever to signal...it has the clicking sound?

The sound is coming from the differential, transfer case area a bit to the rear of the car. And it is definitely computer related. Meaning the car is telling the DSG or X-Drive to do something. I just don't know what it is telling it.

From the looks of your sig you have different wheels on. Which tire combination are you running.

actually those are the rims i want on my x3. I currently dont have a pic of my x3 so im using that for now...

I went from 17" to 19" and no problem. Nowhere in the manual does it say to reprogram anything other than reset the tire pressure monitor system.

Which tire size 19" did you switch to.

007,
I've re-read your initial post on BimmerFest a couple of times and here's
my 2Cts:
-yes, different tires and different size tires can give considerable variance
in "feel", road noise, handling, turn-in responsiveness, etc.

But, I think the drivetrain/gear whine noise is coincidental, unrelated or,
is tire noise with that specific fitment and/or something else is amiss.

-the tire size rolling diameter "difference" is nil, for practical purposes,imo.

I've gone from punky-azz little 15s to Plus1 ++ 16s on my wife's crappy
Honda CR-V, with no problems; I've gone from oem 18s to big 132 staggered
19s on our X with no problems.

It seems like you are hunting for a problem or overly concerned about
the potential speedo diff: it is no biggie. As for "reprogramming/reclibrating"
the electronics, I must be missing something.

Slap on the tires, in the sizes within reason, you like, and go drive and
enjoy your X.
GL,mD

From your Bimmerfest post:

"The Kumhos are 27.3" OD front and 27" OD rear. Could not find Revolutions per mile on this tire anywhere in the specs. The whine sounds like gear whine, short duration for a few seconds at a time and could be present at any given time and speed. Just from standstill or going 65 on the highway."

I'm no tire specialist nor XDrive expert but I think this might have been the problem. As the tires are not the same diameter it may be having an affect in the XDrive system because even going in a straight line the front and rear sets would be rotating at different rates (or Revolutions/Mile) all the time.

You also stated that when you put on identical Michlins the problem went away.

Maybe a BMW mechanic familiar with the XDrive system (say at your dealer) might be able to verify if that's the problem.

I took that into consideration when buying Pirellis. The 245/45/18 front, 275/40/18 rears are identical 26.7" in diameter and identical 780.4 revolutions per mile. Still the intermittent X-drive problem (noise) persists. All I can think of is that the tires are rotation at slightly higher rpm. About 2.7% higher that the car thinks they should be rotating.

The point I don't get is the assumption that the car thinks the tires should be going a certain rotational speed. The only way the car knows how fast the tires are going is by the wheel speed sensors. It doesn't have another reference signal, relating engine speed to true ground speed. There is usually a torque converter in the equation, so it isn't possible to just compare engine speed to driveline speed. You could have an issue with the torque converter locking up, separate from any problem in the transfer case.

The speed difference between different tires could absolutely cause a problem in the transfer case. I know of no factory or dealer programming for that, but I don't work for the factory or a dealer, so maybe it has just never come up.

I don't think the small differences you are quoting front/rear for rotational speed should cause a problem. You are assuming that the actual rolling diameter is as published by the tire manufacturers, and that may not be a good assumption.

If you want to check, it is very easy to drop the tires on one axle by 5 psi, test drive the car, then put those tires back to spec and drop the tire pressure on the other axle by 5 psi. Don't drive right to the handling limits when doing this, but see if the noise is gone in a straight line. You can easily achieve a different effective rolling diameter just by adjusting tire pressures. If the noise is worse in one direction, and goes away in the other direction, you have found the source of the problem.

It might just be me, but I would just put the stock tires back on and enjoy the car.

[quote=JCL]The point I don't get is the assumption that the car thinks the tires should be going a certain rotational speed. The only way the car knows how fast the tires are going is by the wheel speed sensors. It doesn't have another reference signal, relating engine speed to true ground speed. There is usually a torque converter in the equation, so it isn't possible to just compare engine speed to driveline speed. You could have an issue with the torque converter locking up, separate from any problem in the transfer case.quote]

There are accelerometers in the transmission that always know actual vehicle speed. When the abs sensor detects wheel speed that does not correspond to actual vehicle speed it goes into default. That is the only explanation I can come up with.

Sorry, I don't agree. Accelerometers measure acceleration, not speed. As I understand it, the ABS system works by comparing wheel speed sensors to each other, not to a reference signal.

Did you try changing the tire pressures either front or back to see if you could reproduce the noise, or alternatively, eliminate it?

Don't mean to give you a lesson in high school physics but velocity/time = acceleration.

Didn't try doing that yet. Thought about doing that already. Will try as the weather permits. But in reality probably impossible to match front to rear without measuring. Also the tires I have on now, Pirelli Pzero Nero MS are identical diameter and also identical Revolutions per mile specifications front to rear.

:rofl: :rofl:
Don't mean to give you a lesson in automotive mechanics and engineering, but since you asked for it....If you want to measure the speed of a rotating shaft with an accelerometer you will have to mount the accelerometer on the rotating component. How will you then take the signal off of it? Yes, you can get a wireless accelerometer, but that would be silly. The speed of a rotational shaft will best be measured with an optical or magnetic pickup that counts revolutions (revolutions/time is proportional to velocity). The neat thing about this method is that the sensor is mounted in a fixed position, and wiring isn't complicated by the rotating shaft.

This isn't about physics, or design. It is about automotive diagnosis and repair. The best and most suitable diagnostic aid you have available is a tire pressure gauge.

Cheers

:confused:

This is really all new stuff, for me...:rofl:

I feel like a caveman that just walked into a
college level cosmology class.

DoubleOhSeven, I'm with JCL: I think you are slightly
misinterpreting what your car "does", where it gets
the speed info from, and wringing your hands about
a situ that is not really tire size related.
But, that's just me.

Hope ya'll get it solved.
Good Luck, mD

Your aspect ratios are fine. There are x3's that come out of the factory with 17's and the sport with 18's and others with staggered set ups , in essence +1 . Ecu has nothing to do with figuring out your tire size unless the rolling diameter is completely off, which in turn would trigger the ABS light to turn on . I am confused with your assumption that the ECU is the caused of your driveline noise .

http://www.miata.net/garage/tirecalcold.html

Did you change just the tires or did you buy a new set of wheels and tires? if so , changed back to OE's see if you get the same " driveline noise"....I think you are just getting tire noise. Dont know about the new pirellis , but they are known for tire noise. Had them years back and disliked them for that reason.

Not sure if you read my original post. Here it goes again.

>>>I Got an 07 sport pack and was looking to improve the handling and the look of the car. So I decided to get the 06 staggered 192M wheel option by purchasing two 18x9" rims for the rear. As some of you know in 07 they killed the 18" staggered wheel option and replaced it with a 19" staggered option. I didn't want to have 19s on my car and needed all season tires so I ordered it from the factory standard with 18x8" 192M wheels and 235/50 18 AS tires all around. Stock tires were Michelin Pilot HX MXM4 235/50 18 all around. Ride comfort with stock tires was OK even with the sport pack but handling is only so so. With noticeable body roll and a bit of unresponsiveness.


Since then I've tried three sets of tires on it. Reading great reviews from tirerack I ordered Kumho Ecsta ASX in 235/50 18 front and 255/45 18 rear per 06 Specs. Installed the tires and was very disappointed in them. The ride went to crap. Absolutely unbearable. Very harsh riding tire, Very noisy. Handling better but with such bad ride that becomes irrelevant. Also a weird driveline wine at certain engine speeds and gears and got Automatic Transmission shifting problems. The whine is not related to balancing. I thought it might be due to slightly shorter overall diameter of the tires. The stockers 235/50 18 Michelins are 27.5" OD (overall diameter) and 759 revolutions per mile. The Kumhos are 27.3" OD front and 27" OD rear. Could not find Revolutions per mile on this tire anywhere in the specs. The whine sounds like gear whine, short duration for a few seconds at a time and could be present at any given time and speed. Just from standstill or going 65 on the highway.

At first I thought it was the tires so I got a set of Michelin Pilot Sport AS in the same 235 front 255 rear sizes. After mounting them on the car the whine went away completely. The ride improved but still harsher than Pilot HX. A bit too harsh for my taste. Much quieter than Kumhos and possibly even quieter than stockers on the highway but not over bumps and expansion joints. Handling is fantastic. Feels like a different car. Response is immediate with absolute absence of body roll. What I hate about this tire is the width of the rear 255/45 18 tires. I don't know what Michelin was thinking but they decided to make 235/50 18 and 255/45 18 dimensionally identical. Meaning they are the same width. It looks weird on a 9" wide rim and looks too skinny in the back. Really kills the staggered look. They are both 27.2" OD and 762 revs per mile. Very close to stock (759 revs per mile). Less than 1/3 of a percent deviation from stock OD. Since the whine disappeared I thought to myself maybe it was the difference in diameters of the Kumhos 27.3" front, 27" rear or even a problem with the tires themselves.

Back to Michelin Pilot Sport AS. Unhappy mostly with the look of the rear tires and after getting a few complaints from rear seat passengers about ride quality I went on a new tire search. Now looking for identical or very close diameter front to rears and the ultimate in width rear tire. I came up with Pirelli P-Zero Nero MS in 245/45 18 front and 275/40 18 rear. Specs say these tires will work fine on 18x8 and 18x9 wheels respectively. They are 26.7", 26.6" OD and 780, 782 revolutions per mile front/rear. They are within 2% of the stock diameter. And I thought to myself a worn stock tire would be close to the diameter of these. So I got the tires. Which, mind you was not an easy thing to do. The 275/40 18 is on national back order. No one had these tires. Had to get them shipped from Pirelli directly after a few favors. Got them installed. From the rear the car looks fantastic. This is what the sport pack X3 should look like. Very meaty and mean look to it, though the tires seem to fill the wheel well a little less due to the smaller diameter. Driving impressions: The tire is supremely quiet. Quieter than Pilot Sport AS or the Stock Pilot HX tires. Comfort is better than Pilot Sport but maybe not as forgiving and Pilot HX. After all this is a Z rated tire and the stockers are H rated. Handling is great though responsiveness not as sharp as Pilot Sport AS. Possibly due to the wider 275 tire on the same 9" rim as the 255 Pilot Sport AS. On the Negative Side. The driveline/gear whine is back. Also the AT shifting problems are back. I think the speedometer is way off now by as much as 10MPH at 60. However I wasn't able to verify this. Maybe they are just so quiet that I think I'm going slower. After all 2% difference in size should yield only about 1.5 MPH difference going 60. Now I know for certain that changing tire size will cause all sorts of computer related problems even if it is only a very minor change.

Here is my dilemma. Can the computer be reprogrammed to compensate for tire size? Spoke to a few dealers they tell me, NO, only the factory can do that. Kind of hard to imagine the dealer can't reprogram for tire size. It is very simple to do even with basic hypertech programmer on almost all GM cars. Why would BMW only reserve that for the factory? If I'm not able to get the car reprogramed I will probably have to put my stock 235/50 18 Pilot HX MXM4 tires back on. That would be a shame, not to be able to keep the best tires for the car after spending all this money just because of dealer incompetency in reprogramming the ECU.

Anyone know how to reprogram the ECU for tire size?

I will post pictures of Michelin Pilot Sport AS and Pirelli P-Zero Nero On my car shortly.<<<

Here is a copy of my post from bimmerfest.

Didn't really get a chance to take some meaningful pics of the Pirelli P-Zero Nero MS because of the recent weather but here are some pics in the meantime.

I got some comparison shots for you of the Michelin Pilot Sport AS and Pirelli P-Zero Nero MS.
Pirelli P-Zero Nero MS is in the pictures with snow. Look at the width of the rear tire This is what the Sport Pac X3 should have looked like from the factory.

Look at this picture. Can you tell which one is 255/45 18 and which one is 235/50 18. The only visible difference is wider shoulder blocks on the 255 tire which is on the right. This is my main gripe with Michelin Pilot Sport AS. As you can see from the below pictures the Tire is actually stretching outward to fit on the 18x9 rear rim.

http://www.designwholesale.com/bmw/x3pics/tires/mfr.jpg

http://www.designwholesale.com/bmw/x...ires/mside.jpg

http://www.designwholesale.com/bmw/x...res/mside2.jpg

http://www.designwholesale.com/bmw/x...ires/mrear.jpg

http://www.designwholesale.com/bmw/x...res/mrear2.jpg

http://www.designwholesale.com/bmw/x...ires/prear.jpg

http://www.designwholesale.com/bmw/x...res/prear2.jpg

http://www.designwholesale.com/bmw/x...ires/pside.jpg

James Bond , oh I mean 007x3. now I know what you are after. you are trying to make the x3 look like a X5. mean and meaty.. Your Tires sizes could be over kill, you may end up messing up your transfer case.
I would revert back to the normal set up, plus it might interfere with the manufacturers warranty and in case your transfer case starts to act up which could be SOONER than you think BMW will not cover.

I tried to walk away, really I did. Sorry this is so long. I suspect that ol' MD will stick with it.

The transmission does not have accelerometers that know what vehicle speed is. I tried to explain that nicely. If you continue to believe that such parts exist, please provide a parts reference. You have now introduced the concepts of vehicle pitch but that is a different issue, that is related to the DSC control over brakes, and to a lesser extent, throttle.

The rotating shaft I refer to is the output shaft of the transmission. It is how the transmission calculates the vehicle speed. The counter calculates an expected vehicle speed from an assumed final drive ratio. It isn't complicated, it has been working that way since the forties at least (that is the oldest car I have worked on with a speedometer cable driven from the transmission output shaft). In that sense, yes, there is a different speed calculation than the ABS wheel sensors. My point that there isn't a different measurement is that the output shaft of the transmission is directly related to the wheel speed sensor (by the final drive ratio). They don't vary, they are directly proportional. Apart from the output shaft of the transmission, and the related wheel speed sensor, there is no built in speed sensor on the car.

Let's continue with your theoretical approach to vehicle speed calculation. You are saying that every time the car speeds up or slows down, the computer inputs that acceleration, calculates it over time, and comes up with a calculated speed over the ground. The car must also then filter out the forward acceleration from the three axes of acceleration it is measuring, and compute the resulting forward vector. Incredible. Just think of the error that must be introduced after a several hour drive (since the car has no way of self-correcting this acceleration/time calculation). The whole concept is mind-boggling.

We could do an easy test here. You could drive your car off a cliff. As you plummetted towards the ground, take your foot off the gas, and check your speedometer. If I am right, the speedometer will be zero. If you are right your speedometer will function as an airspeed indicator, indicating your velocity up to terminal velocity. If you want to reduce the damage potential then you can skip the cliff-jumping part. Just spin your tires in the snow. You won't go forward. Using accelerometers, the speedometer would show zero. I suspect you will find that spinning tires results in a rising speedometer reading. Let's just assume that if the transmission knows vehicle speed then that is what it is indicating on the speedometer.

I may not have worked on a modern BMW/ZF/GM automatic transmission, but I do know the inside of C3, C4 and C6 Ford transmissions, Chrysler Torqueflite 727s, and various GM models. I also know that ABS systems use an algorithm that takes inputs from four wheel speed sensors and computes a resultant average that is then compared to the delta at each wheel. It does not use a calculated wheel speed from the transmission output shaft because that is less accurate.

If you want to get back to the issue of when the transmission goes into lockup, then yes, it happens at a certain speed. That speed comes from the rotational velocity of the output shaft. We have now come full circle. Lockup doesn't relate to vehicle speed over the ground (true distance covered) as much as it relates to fluid pressure in a circuit inside the transmission valve body.

This combination of auto repair and physics discussion is lots of fun, but I don't think you are any closer to figuring out why you have a noise under your X3. Hopefully, though, you now know how the vehicle systems interact a little more.

Cheers

JCL

JCL,
Very well written, as per your usual efforts! :thumbup:

You may be howling at the moon, however...

DblOh is on a mission; I suspect a bum tire or two
in his current batch, or was that the problem batch(es)?
I took notes and still couldn't keep the "tire test" straight.

I did not know that XDrive, transfer cases, diffs, and trannies
were so "smart"?! :rolleyes: :rofl:
BR,mD

Wait a minute, I never said the speedometer is reading the transmission accelerometers output. This is your deductive reasoning at work. I wish it did. That would make things a whole lot easier and eliminate tire error. As far as computing vehicle speed with accelerometers, It isn't as complicated as you think. A $200 Gtech-pro does it with great degree of accuracy www.gtechpro.com/

I will get back to you with schematics of AT if I'm able to find what I'm looking for.

You are right, it is my deductive reasoning. I pointed out that if the transmission had accelerometers that knew the vehicle speed, it may as well tell the speedometer so they could both benefit.

I am aware of the device. It is reasonably accurate over a quarter mile. Then it must be reset.

Let me know if you find a Gtech inside your transmission.

Here is the link for the transmission speed sensor. It is item 4. There are two of them. Looks a lot like a magnetic pickup. It counts the revolutions of a shaft, and converts that into a rotational velocity. That shaft speed converts to a vehicle speed via the final drive ratio and tire diameter. Not sure of your model, but this is for the latest 3.0 X3 they had.

http://www.realoem.com/bmw/showparts...97&hg=24&fg=15

Again, I never said it didn't have a speed sensor. All I'm stating is that the ECU that is controlling Transmission, X-drive, DSC has accelerometers that tell it actual vehicle speed, lateral acceleration, yaw and pitch among other things. In fact the GM 6L50 transmission in the 07 X3 has Performance Algorithm Shifting, a transmission algorithm that looks at lateral acceleration from accelerometers, throttle, and vehicle deceleration activity to determine if the vehicle is being driven in a sporty manner. If the algorithm recognizes these conditions, it can force downshifts and hold lower gears for optimized vehicle performance.