07-31-2019, 12:29 PM | #1 |
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Running 275/35/22 and 315/30/22 - Stumbling on hard acceleration
Hi all
So I'm running the Atturo AZ850 in 275/35/22 and 315/30/22 like a few others on the forum here. However, I noticed stumbling at WOT. I saw the posts on transfer case / ignition related stumbling. I swapped out back to the OEM wheels/tires and the stumbling "seems" to have gone away for the most part. I don't have enough time on the OEM combo yet but of the times I have gone WOT it seems to have smoothed out - maybe a super slight stumble but not 100% sure yet. Anyone else have this occur when running this size of 22s? |
07-31-2019, 04:09 PM | #2 |
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Can't understand why different tires would cause an engine stumble.....
Unless it has something to do with the tire diameter difference. The 22's are 29.6 inch diameter and the stockers (assuming 20's) are 28.7 inch in diameter. 18's and 19's are slightly taller. Is the car sensing the difference and retarding the timing thinking it's encountering a problem? |
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07-31-2019, 04:20 PM | #3 |
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The overall diameter is slightly larger than OEM. And I know that there is slight difference between front and rear with this setup. However, it is a small difference and seeing as how many on the forum here have run this size I assumed it was within BMW tolerance. My fear is that this is causing the transfer case to think there is slip on hard acceleration and then kicking in traction control systems causing the stumbling. What's worse is that if that is actually true then I cannot imagine this sizing to work in the long term for the transfer case.
Having said all that though... oddly enough I cannot find anyone on the forum complaining about these symptoms when running these sizes. |
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08-01-2019, 12:50 PM | #8 |
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What is "star marked"?
The 22s are the same set up a number of others are running on here. The Atturo AZ850s. On page one right now there is a dedicated link with feedback from others running these in 22s and that exact size. |
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08-01-2019, 06:12 PM | #9 | |
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Size tolerance means nothing when there is uneven wear - are your atturos new? Basically if one of your tire is more worn, the 2-3% size difference between axles might end up being 3-4% just because of the wear. I had similar issues on my 750. If you have a 2014-15, I wouldn't advise going down this road.
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08-01-2019, 10:03 PM | #10 | |
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The tires are nowhere near 2-3% difference front and rear with this set up. Front comes in at 29.58" overall diameter and rear comes in at 29.44" overall diameter. We're talking 0.14" difference front to rear. Plus not to mention there are many who are running this setup on the forums. This whole thing has me puzzled. How come you mentioned 2014-15 model years specifically and left out the 2016-18 years? Last edited by sam01; 08-01-2019 at 10:09 PM.. |
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08-01-2019, 10:08 PM | #11 |
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Update: took the X5 for a run around the freeway today. I can definitely confirm no stumbling on the OEM rims/tires.
Guess, I'll put the 22s back on this weekend and try them again. Maybe by some sliver of a chance the stumbling was intermittent and happened to go away at the same time I swapped the OEM rims back on? |
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08-01-2019, 10:24 PM | #12 | |
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08-01-2019, 11:53 PM | #13 | |
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08-17-2019, 04:37 PM | #15 |
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I haven't been able to figure it out yet. So far the theory is that it could be linked to a muffler delete and that the ECU isn't compensating enough under the load of WOT. Perhaps when I put the OEM wheels back on the weight difference/reduced load makes the stumbling less harsh. But today I finally got around to putting the 22s back on and noticed it was about the same as the OEM wheels now. OEM wheels ended up with slight stumble but definitely less harsh. Maybe it is because the muffler delete needs a tune to run smooth. Not completely sure at all but just a guess at this point.
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09-09-2019, 05:25 PM | #16 |
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Update: Been running on the 22s for some time now. It seemed to be running a little smoother and I got comfortable with the size difference between front and rear since the OEM 21" setup from BMW actually has larger front to rear differences than this 22" setup.
Anyways, it was running better for a while. Under certain throttle positions there was a bit of stumble. Then last week the stumble started to come back. A few days ago the drivetrain malfunction light came on and the car was stumbling very hard. Even at idle it was missing and was actually causing the car to rock. This actually came as a relief since it then ruled out transfer case issues since it was missing at idle. BMW had the vehicle today and the light wasn't on but they traced the light to cylinder 3. During a test drive the tech was able to reproduce the stumble and has now replaced coil and plug for cylinder 3. I haven't picked up the car yet but will give another update once I get the car back and drive it around. |
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09-10-2019, 02:10 PM | #17 |
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How's the car running now, since you got it back with the new plug and coil? Reading through the thread, my hunch was that the timing of the stumble was just a coincidence and not connected to the tire swap in any way. Hope you got it straightened out.
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09-10-2019, 05:03 PM | #18 |
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The car is running better for sure. I'm not sure if it was just in my head but perhaps there's still a tiny bit of stumbling? I only had time for a short drive home. I don't drive it everyday so once I get a chance to really get on it I'll come back for another update. However, if it helps I don't expect there to be any remaining issue (pretty sure if I felt something it was just in my head).
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09-10-2019, 07:05 PM | #19 |
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Ive put in bigger wheels on all my cars never had an issue like what you're having. I highly doubt its the wheels. Im running 22s pretty much since I bought my X5 with ZERO issues.
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09-18-2019, 12:57 PM | #21 |
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Update
Runs smooth now. No issues. It was an ignition problem but didn't throw codes until it failed hard enough to cause the car to rock during idle. Under full throttle it failed (without code) to the point where it felt like someone was stepping on the brakes during acceleration. Once the coil and plug was replaced it ran smooth again. |
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