Working the tire problem

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bwilson4web

Well-known member
Joined
Apr 30, 2016
Messages
805
Location
Huntsville, AL
Hi,

A couple of weeks ago, I went in for a recall and we got this on the drive-in, tire checker:
tires_010.jpg

Now this was not enough to replace the 13k service mile tires. However, I met the technician outside and he said the tires are 'OK' but I was concerned. So I did a tire tread temperature test.

I took a small tripod and mounted a IR thermometer on it and configured the iPhone to record a video of the readings. Then on a cool day, 65F (18C), I drove 10 miles (16 km) at 75 mph (120 kph). I stopped and video recorded the tread temperatures:
tires_020.jpg

  • -1.0 degrees is the normal camber spec and I had a 4-wheel alignment in December when the motor mount bolt broke.
  • The nner tread is 2F (1C) warmer than the outer tread - this is the profile of too much camber and/or possibly toe (unlikely)
  • 3d tread is noticeably cooler - I run maximum side-wall pressure, 51 psi, and this suggests the 3d tread may be stiff and off loaded by higher pressure on the side treads. This merits investigation.
So this morning, I dropped the car off with instructions to take 0.5 to 1.0 degrees of camber off. So if already at -1.0 degrees, it should come back at 0 to -0.5 degrees. Then I can replicate the tire tread temperature test and see if we are getting something more even.

I'll then start with 51 psi, measure, and then reduce by 5 psi until reaching 35 psi (yes, this is low for the rear tires.) The goal is to see if between changing the rear camber and pressure we can get even heating across all four treads.

Bob Wilson
 
I'm quite interested in your findings. I'm confused by your data, though. In your plot, are the X-axis units the tread bands with 1 being the outermost tread band? Is the plot of data for all 4 tires or only multiple measurements for a single tire? Did you notice any temperature difference between the front and rear tires?

I would be interested in setting the front toe as close to 0º as the spec allows as well as minimizing camber at the rear. I inflate the rear tires to the sidewall maximum pressure of 51 psi with the front tires at 43 psi to maintain the recommended inflation pressure difference. I haven't driven far enough to notice any tire wear patterns, but I will almost certainly experience similar wear patterns as most i3 owners due to the shallow inner treads and the negative rear camber.
 
In your plot, are the X-axis units the tread bands with 1 being the outermost tread band?
You are correct. The "1" is the outer tread and "4" is the inner.

Is the plot of data for all 4 tires or only multiple measurements for a single tire?
Just the driver side, rear tire. In a proper study, I would do all four tires but this was to get some initial results. After the adjustments are made, I'll replicate the study against all four tires. This will also help identify any frame alignment issues.

My particular car came off lease without the tire 'goop' kit and maintenance showing a wheel replaced. This suggests something bad may have happened that was not part of the other records. But one problem at a time. <GRINS>

Did you notice any temperature difference between the front and rear tires?
I only measured one tire, driver side, rear. However, I got a call from the technician and he reported "-1.5 degrees" on one tire and "-1.27 degrees" on the other rear tire. Since the standard is "-1.0 degrees", something was obviously wrong.

My plan is to get everything balanced as best we are able. Then run the tires down until the next groove approaches the threshold and replace the tires. Then I'll do another set of four-wheel, temperature metrics and call it a day.

When done, I'll have all tires loading all treads equally with even temperature spread:
  • optimum camber and toe settings
  • optimum tire pressure

Doesn't everyone want this?

Bob Wilson
 
Alignment can certainly affect tire wear, but it also has an effect on the stability and traction the car has, especially in a dynamic situation (say turns when the suspension may be nearer one limit). What is probably missing from your results are the handling and traction components of changing the basic alignment specs.

FWIW, unless you load the vehicle onto the alignment machine in the prescribed manner, the numbers you record may or may not be correct..
 
jadnashuanh said:
FWIW, unless you load the vehicle onto the alignment machine in the prescribed manner, the numbers you record may or may not be correct..
I wonder how accurate and precise an alignment measurement is. I believe that BMW states alignment measurements to the nearest 1'. Is a typical alignment machine capable of that level of accuracy and precision? When one bounces the car on its suspension, does it settle exactly the same every time, or if not, how much does this affect an alignment measurement? In other words, if an alignment is performed, the car is driven around the block and then back into the alignment machine, how much would the alignment measurements differ?
 
Ok, we have a fix and diagnosis:
tires_040.jpg

The clue is both of the right tires show excessive toe out. I was asked about whether or not I'd hit something and thinking about it, the light came on.

Here is the culprit:
tires_060.jpg

There are two accesses to my neighborhood and this one has those 'split' speed bumps. The gap is designed so firetrucks and ambulances can enter and leave easily. But it temped me to have the 'driver' wheels go through the gap and the passenger side tires took the bump. It also put a torque on the car that probably moved the rear camber too far negative.

I still need to replicate the tread temperature tests but at least now we have a clue about the problem.

Bob Wilson
 
bwilson4web said:
Here is the culprit:
If that's the culprit, then the i3's suspension is so fragile that all sorts of road irregularities are liable to change the alignment. I know of an i3 owner who is trying to get BMW to buy back his i3 because he claims that it has been incapable of maintaining its alignment resulting is severely irregularly worn tires that haven't lasted longer than 8k miles. I hope that this isn't true and that your misalignment is due to something else.
 
Hi,

I re-ran the temperature profile after the alignment and was disturbed by the data:
tires_200.jpg

  • Remapped the treads so -4 is outer driver tread and 4 is outer passenger tread
  • Driver side looks good but the passenger side still shows excessive negative camber
Now my protocol was to use the recorded IR value starting with the passenger side and then going to the driver side. So in theory, the driver side had more time to cool off. So I repeated the test, starting with the driver side tire:
tires_210.jpg

Now I trust the earlier reading, the driver side camber is OK. But the passenger side, camber remains off.

On Tuesday, I'll resubscribe to the Tech Info service and download the alignment procedure. I have the option of using shims but I will need the torque setting for the bolts. But the procedure may show me how to adjust the camber link to achieve perfection. I'm convinced if I want perfect alignment, I will have to do it myself.

I've also ordered a bubble camber gauge as well as a FLIR attachment for my iPhone 5s. The bubble camber gauge will let me quickly measure the static value once I measure the driveway angle. The FLIR will give me a single image of the temperature profile without having to do the MPEG playback and recording the values in a spreadsheet.

I'll also download the instructions on how to drain and replace the transaxle oil. I'll also pickup the electrical schematic in preparation for a powered set of trailer lights. The training materials are OK but I need a proper 12V bus bar and the turn, running, and stop light taps.

Bob Wilson
 
I snagged a FLIR (Forward Looking InfraRed) camera for my iPhone. After running 14 miles at 70 mph:
tires_500_010.jpg

This AFTER getting a four-wheel alignment and still too much negative camber.

It looks like we have these options:
  • self-alignment - read the repair manual and/or insert shims to reduce the negative camber
  • reverse tires - unmount and remount so the outside tread is now in inside
  • both - equalize the wear and leave the wheels ready for the next tires when these wear out

Bob Wilson
 
bwilson4web said:
This AFTER getting a four-wheel alignment and still too much negative camber.
Might the deeper outside tread depth disperse the heat better than the shallower inside tread depth? Rubber is probably not a very good heat conductor, but with the tread not being uniform in depth or style across the width of the tread, I wonder what effect that might have.

bwilson4web said:
reverse tires - unmount and remount so the outside tread is now in inside
The tires definitely have designated inside and outside surfaces for some reason, so flipping those around might have some negative effects.
 
The tires definitely have designated inside and outside surfaces for some reason, so flipping those around might have some negative effects.
Usually the reason has to do with tread design. The treads are designed to "squeeze" or "push" water out as they roll forward. If you reverse the tires, water is pushed inward and the car is more prone to hydroplaning. I suppose it would be a non issue if you never drove in the rain :) At least that's my understanding.
 
I got a FLIR and took photos after a +10 mile run at 70 mph that I am still learning how to use. These were taken at night in a parking lot lit by yellow, sodium vapor lights. Also, I didn't use my tripod setup to fix the distance and orientation. Taking photos, I notice that some orientations seemed to washout the image. I suspect it was from the parking lot lights. Next time, I'll use an unlit parking spot and the tripod.
tires_620.jpg

  • Passenger side front - a 7F temperature difference, the excessive negative camber is a problem.
  • Driver side front - shows the flaring that I suspect is from the lights but the negative camber is evident and a problem.

tires_630.jpg

  • Driver side rear - looks reasonable but I'd like to retest.
  • Passenger side rear - negative camber is excessive.
I've now have a bubble, camber gauge and two lift pucks. Once I get the driveway surveyed for a flat place, I can raise the car; remove the wheels and; check the camber with the bubble gauge. This will give empirical data for the camber adjustments.

Bob Wilson
 
What sort of bubble gauge do you have, Bob?

Wheel aligners have bubble gauges too, but they are only used to get things roughly in spec, then they use the more accurate wheel alignment measurement devices to finish the job.

Have you measured the camber of the roads you are driving on? There is often more road camber on the passenger side than the drivers side, but it does depend on the road.
 
I33t said:
What sort of bubble gauge do you have, Bob?
tires_640.jpg

This was just a quick test to see if I could get a credible reading through the spokes of the wheel. Tomorrow I need to find a level spot on the driveway. Then I'll see if I can get the car raised on two identical floor jacks holding the front with the tires off. I'll use this to inspect the links and compare to the training sketches.
I33t said:
Wheel aligners have bubble gauges too, but they are only used to get things roughly in spec, then they use the more accurate wheel alignment measurement devices to finish the job.
This is something that still has me pissed. My usual tire store won't touch the BMW i3 and they didn't even have metrics for the 2017 Prius Prime. As for the dealers . . . sorry I'll have to revert to some early Ango-Saxton terms used in Marine bootcamp. What should be a fairly easy task, they make way too difficult.
I33t said:
Have you measured the camber of the roads you are driving on? There is often more road camber on the passenger side than the drivers side, but it does depend on the road.
I'm using a stretch of Interstate highway and the term we use is 'crown' that is used to promote water runoff. But I'm not going by just the temperature profile. My initial test with the bubble gauge confirms the values the dealer report shows after their last effort to do a 4-wheel alignment.

My goal is to reduce the negative camber from -1.5 to -0.5 degrees. My past Prius practice has shown this typically evens the wear. I also need to do a tire pressure vs temperature distribution study. I know, one change at a time but I really don't like how the inner tire groove has lost depth. Something isn't right and we have enough other reports that suggests these tires are NOT lasting as long as I want.

Bob Wilson
 
Good on you Bob!

What you need is a wheel aligner who knows his stuff, even if his aligner machine doesn't have any official specifications.

I haven't taken the i3 in yet, but an offroad 4wd was having issues after the manufacturer 'did' the alignment. I took it into the place and he set it up well resolving the problems from the 'official' specs.
 
I swapped my wheels/tires for their winter set yesterday, and it was obvious that the inner area of the tread is wearing quite a bit more than the outer edges on my car. I've booked a 4-wheel alignment for it and will ask them what the before and after numbers look like and get back.
 
A week or so ago, I mentioned having to replace the passenger-side, rear tire after a sidewall puncture from road debris. This was back in http://www.mybmwi3.com/forum/viewtopic.php?f=10&t=4624&p=39919&hilit=rear+tire+sidewall#p39919. So I took photos:
tire_200.jpg
tire_210.jpg


I didn't notice the mounted tread pattern is different. IMHO the right tire, the replacement from last year, looks more correct to handle water. However, these are the same tread. I need to research but I would expect the curved part of a tread should lead so the water is pumped to the side.

It is the shallow, inner tread wear that still bothers me. The left tire has 20k service miles and the right tire estimated 3-5k service miles.

Bob Wilson
 
bwilson4web said:
I didn't notice the mounted tread pattern is different. IMHO the right tire, the replacement from last year, looks more correct to handle water. However, these are the same tread. I need to research but I would expect the curved part of a tread should lead so the water is pumped to the side.
I noticed this when we first bought our BEV in 2014. The tread is asymmetric which must make it behave differently when mounted on left vs. right sides as you have noted. Seems like right and left side tires should have been manufactured, but we have what we have.

bwilson4web said:
It is the shallow, inner tread wear that still bothers me.
That bothers me as well. When combined with the negative camber of the rear suspension, the inner tread wears out faster than the outer tread which seems like a waste. I believe that you tried to have the rear camber set to the minimum negative amount in the alignment spec to minimize this problem, but with the shallower inner tread seems destined to wear out first.
 
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