BMW Tyre Wear: What’s Really Happening?

[HighlandPete]

There is so much to discuss here, with all the recent severe inner tyre wear and cracked rims on the latest 3-series cars, particularly the 19†run-flat shod wheels.

 

I have my own opinions, but would welcome discussion.

 

I’ll start a bit further back in time. My last BMW was an E39 540i touring, running M-Tech suspension and fitted with Style 32, 17†rims, unusual for a touring, had a staggered setup 8â€/9†x 17†rims running 235/45 & 255/40 tyres. Tyre wear was very good on the rear with self levelling air suspension, but took accurate pressure settings to balance the wear across the tyre and the dreaded inner edge wear. I’d get about 20k miles from Dunlop SP 2000E’s and would be down to about 3mm across the tyres with the inner edges just 'almost' knocked off. The rear 32’s were ET26, and running 18.7mm more offset inside, than standard 8†rims for the rear.

 

Now I’m running (from new) an E91 330d SE touring, on standard suspension, running standard 225/45 R17 all corners, style 160 with Bridgestone Potenza RE050A (ll) run-flats. The picture shows wear at 15k miles.

 

 

I’ve a second OEM wheel set, style 161, 8â€/8.5†with normal rubber, for reasons we can imagine, but that’s another discussion. Now the offset for the 8.5†rear is ET37, giving 9.35 mm more offset inside. The wear on the 225/40 R17 Goodyear’s is for 20k miles.

 

 

Try and get your heads around the different wear patterns. Both sets have been on and off the car over the past 35k miles, all on the same geometry, driving the same sort of roads and driving style.

 

You’ll note the Bridgestone’s wear towards the outside, but also has the inner ‘camber wear’. The inner and taper wear were there from early on. Note the tyre at 8 – 9k miles.

 

 

Tyre pressure is critical to get the wear balance right, not to lose the tyres too early. The Goodyear’s were very even across the tyre, as can be seen, just starting to lose the inner edge. (Left side of the picture). What is going on here, geometry? Is it in the tyres? Or is there much more to it... how we corner for example?

 

I’d welcome any comments on this, before we look at the rapid wear on some models today. Much more to say, but trying to keep it limited to start with.

 

HighlandPete

[CIH]

I don't quite follow. Different cars with different wheels and different wear. WHat's your point exactly ?

[HighlandPete]

I don't quite follow. Different cars with different wheels and different wear. WHat's your point exactly ?

 

Sorry if it is not clear.

 

Pictures are from same car, same axle, same geometry, over same 'mixed' period of 35k miles. Why would one wear flat, the other taper across the tyre? Engineering logic says the wider tyre will show more wear. Or we are seeing our dear old 'Run-Flat' exhibiting another strange feature. I'm hoping to take this thread further, into why the very severe wear occurs with the current run-flats and normal rubber. If there is no logic to the problem posed, I can understand why some have the opinion there is no logic to the severe wear patterns.

 

I'm hoping Tony will have some comment.

 

HighlandPete

[Tony]

The problem as i see it is the lack of deformity in the RFT -V- the OEM rear camber position. There is no specific geometry positions for the RFT although i feel in time there will be, i no longer set the BMW on RFT's to the stock suggestion.

 

Camber has many duties and forces but as an angle it conically deforms the tyres sidewall allowing compression and maintaining the contact patch during the suspensions articulation (bump/ droop). The RFT tyre cannot deform so the weight distribution cannot be shared evenly during the tyres dynamic gains on bump.

 

The problem is not confined to the rear but historically the rear would have more negative camber, particularly on the sports suspension so the rate of wear at the rear is the most alarming.

 

Other evidence of the RFT's lack of deformity is found from the volume of complaints with rear wheels cracking

 

As an engineer you would know it takes a huge amount of energy to crack an alloy albeit light weight and this is being done through the tyre.

[HighlandPete]

Thanks for replying. I think we are very much on the same lines, but do you reckon a lot of users are running too low a pressure for how they drive? One reason I say this, is my own experinece with the run-flat fronts. I ended up in discussions with BMW and Bridgstone and I increased the front pressure by 0.2 - 0.3 bar just to try and halt the stepped outer wear and severe 'heel and toe' wear, which came on at an amazing rate.

 

 

I ended up putting together a paper trying to understand the reasons why, which in some ways has merit for rear wear as well, but do wonder if the lateral forces in cornering deform the tyre in a strange way, more readily than normal rubber. Say turning right, the load transfer and lateral force to the inner NS rear tyre, deforms the shoulder more violently. The front 'stepping' problem illustrates the carcass has a weak crossover from wall to crown.

 

I hope you follow the diagrams, without me supplying all the reasoning.

 

Conventional tyre, inflated to correct pressure

 

 

Conventional tyre, coping with camber and cornering

 

 

Run-flat tyre, inflated to correct cold setting pressure

 

 

Run-flat tyre, only works well with reduced camber

 

 

Run-flat tyre, low setting pressure, or not reaching working pressure (slower than normal rubber, even worse in the wet)

 

 

Run-flat tyre, low pressure, or not reaching working presure, NOT coping with camber/cornering demands

 

 

Run-flat tyre, shows resulting stepped front wear, similar issue could exist for rear inner wear.

 

 

One stange thing, some users who have changed to normal rubber, say the rear inner wear can be even faster than run-flats. Can't get my head around that from my experience, are we back to tyre pressure being too low?

 

HighlandPete

[Tony]

From the last image displayed it's quite visible the wear is lateral so not camber related.... The other images offering lateral inertia deformity or lat acc deformity would be amplified/ belayed by pressure manipulation but this is fools gold in my opinion.

 

I wrote a white paper on "heel and toe" wear some years back relating to the Nissan 350z problems, by arbitration it was concluded the reason was geometric not pneumatic or suspension related (revised suspension).

 

I feel it's evident that the "transported" geometric positions for the BMW chassis running RFT's has not taken into account the tyres lack of deformity which of course maintains weight distribution during the suspensions articulation and geometric gains, the lack of deformity will not allow the weight migration witnessed at the contact patch by normal tyres.

 

The wear pattern is consistent with a deep negative camber confining the area to around 10% of the tyres total width, what is also evident is a "apparent" collapsed shoulder support between the armoured sidewall and tread area, this boundary seems to be a communication point between the load and slip angle or in the RFT's lack of slip angle.

[HighlandPete]

Tony

 

Following you... so you reckon tyres pressure is only likely to be a small part of the issue.

 

So looking at my rear tyre, below, you'd say it's defined, or appears as camber wear? At least increasing the pressure did allow it to balance out the wear, to get the tread down reasonably well for a sensible mileage. When you look at my Goodyear F1 GS-D3 in the first post, you wouldn't say camber wear was an issue for that tyre, shows how the same camber settings translate totally different with run-flats.

 

 

Can you imagine how the poor guy felt with this tyre? Certainly not what I'd expect from the negative camber settings BMW dial in. I set up a solid model this morning, using CAD, trying to get the shapes a tyre will make on contact at 1.5 degrees negative camber. A 255 section tyre at 1.5 degrees has just under 6mm vertical difference side to side. All this accelerated edge wear certainly looks like the RFT constuction. Surely BMW and companies like Bridgestone had this wear show up in development.

 

 

In the next illustration I do believe the wear rate of the section marked A, is increased due to the sidewall stiffness not allowing a balanced flex. As it wears the degradation of the communication point makes for a weaker structure, which in turn allows an even faster acceleration of wear, and so on.

 

 

I take it you are not a 'fan' of run-flats.

 

Peter

[Tony]

Not every owner suffers the same problems so in essence the general public are the guinea pigs via complaints inciting revisions. This situation is not uncommon over the marques.

 

It's clear to calibrators like me that the static camber position is wrong for most owners, so for my understanding of the calibration problem has lead to a new rear calibration setup.

[HighlandPete]

Not every owner suffers the same problems so in essence the general public are the guinea pigs via complaints inciting revisions. This situation is not uncommon over the marques.

 

It's clear to calibrators like me that the static camber position is wrong for most owners, so for my understanding of the calibration problem has lead to a new rear calibration setup.

 

I totally agree that we are the quinea pigs, have been since the introduction of run-flats. Almost pushed me to move from the marque. But pleased I moved to normal rubber and fitted different dampers, to get the ride quality back to a real BMW feel.

 

The issue with different owners getting different issues, indicates to me something I've believed from early experience trying run-flat shod models, the working parameters are much tighter on the run-flats and show extremes so much more rapidly.

 

I'll give you a couple of examples. I've found that the run-flats take longer to warm up and therefore don't get to a workable pressure on a lot of the trips we do. I documented my findings when I had the wear, takes at least 12 miles to get about 0.2 bar increase when the ambient temperature is around the 8-degree mark. Typically 0.3 bar over a shorter distance, at higher temperatures and in dry conditions.

 

I live in the West Highlands and when the temperature is around 7- 8 degrees, when it rains there is snowfall on the mountains above us. So drive the Glen and get rain, you get 'water cooled' tyres within seconds, the drive quality deteriorates to such a degree, it is like a different car as you drive. We all know the weird characteristics the run-flats give us anyway, once off of smooth hardtop.

 

I still believe a lot of premature wear is down to low tyre pressure, short trips accelerate the strange wear, paricularly on the shoulders, many of us find that this is so. I've always found that BMW placard pressures have been pretty good, but on the run-flats at least an extra 0.2 bar is needed just to make them work and wear more evenly. And that is driving moderately.

 

This is a Conti on the NS front of a 320d. Included a lot of short trips and the owner was watching tyre pressures closely. Owner changed to the same Conti tyre in non run-flat form and no more strange wear. No change of geometry either.

 

 

Drive an 18" or 19" wheel set hard, I can see why there are severe wear issues. Just can't understand how BMW could have got it so wrong.

 

HighlandPete

[djwozza]

I really just get the idea that run-flats have many more cons the pro's, & am wondering why there is

such pressure behind them becoming the standard ? Also if you get a puncture they are fit for scrap ?

[HighlandPete]

I really just get the idea that run-flats have many more cons the pro's, & am wondering why there is

such pressure behind them becoming the standard ? Also if you get a puncture they are fit for scrap ?

 

Worse for me is no spare in the boot. I'm often away from home, remote parts of the Highlands when there is no support, if I had a major issue. I put a spare wheel in the boot space.

 

I've had most issues, wear, ride quality and poor driving dynamics. I really think the run-flats were not developed enough before letting them loose on the public. It was bad enough trying to select a model, suspension and wheel specification that even worked up here. I took delivery on a warm May day and we went into a good summer in 2006, so didn't get a lot of the strange behaviour until the weather cooled a bit. Then the car's behaviour deteriorated. Soon realised why choosing the car was so hard. We'd test driven several run-flat shod cars through the winter and had no thoughts on temperature being a trigger for much of the bad dynamics. Looking back, One demo 3-series M-sport car was ready to go over the hedge, but the day was very cold, so no wonder the 'Brickstones' were doing their worst.

 

Now of course we have all the wear issues and the cracking rims, I do wonder if BMW wish they hadn't been so fast into the market.

 

I'm very interested in the Bridgestone 3G (3rd generation) tyres, due in the UK soon I believe. I've offered to test a set for Bridgestone, up here in the Highlands, put them through their paces. But another learning curve ahead I imagine.

 

HighlandPete

[Tony]

All previous attempts at runflats by various manufacturers over the years have failed, since these are to be mandatory in the States it seems this time we are the one's who need to adapt.

[CIH]

I really just get the idea that run-flats have many more cons the pro's, & am wondering why there is

such pressure behind them becoming the standard ? Also if you get a puncture they are fit for scrap ?

 

Manufacturers have been trying to do way with spare wheels for years. And yeah, puncture = scrap.

Just as bad is most people seem to be ignorant of the old 50/50 rule (50 miles @ 50mph max) which, more or less, still applies. Even today I had a dude who'd been driving on a puncture for literally 6 months or so.

[HighlandPete]

All previous attempts at runflats by various manufacturers over the years have failed, since these are to be mandatory in the States it seems this time we are the one's who need to adapt.

 

Not sure BMW haven't failed, not an unblemished start. I've read a couple of road tests on the latest 316d ES and an X1. Both testers commented on the improved ride quality. On examination, as base models, they have normal rubber fitted. Improved dynamics in one stroke!

 

You mention we are the ones who need to adapt. I believe the manufacturers need to take the public with them, not have a botched start and blame the customers, as they seem to be doing.

 

One major problem I have found keeps coming up in discussions and also from your industry, is the way TPMS/TPWS is interpreted by the customer. BTW, I notice BMW have moved to the description, UK: Run Flat Indicator, USA: Flat Tire Monitor.

 

BMW actually published this statement.

 

Tyre maintenance:

 

A general misconception is that one doesn't need to check Runflat tyre pressures since the vehicle is equipped with a Runflat indicator (RPA System). The purpose of this system is however to give advanced warning that one of the tyres is losing tyre pressure by measuring the relative wheel speed of each tyre. If pressures are not checked regularly, Runflat tyres lose pressure like normal tyres without the system picking up any relative difference in wheel speed. Thus the extended running of Runflat tyres in this sort of under-inflated condition will negatively impact the Runflat range should you lose pressure completely.

 

For this reason, BMW recommends that tyre pressures should be checked on a regular basis, i.e. at least twice a month as well as before setting out on any long journey.

 

Very importantly, it should be noted that the RPA system must be initialised whenever the pressures are adjusted. This is a very quick and easy operation that is also clearly described in the owner's manual.

 

It is another reason BMW are blaming customers for the strange/accelerated wear. They know lots of users are not checking tyre pressures and/or wear, believing they will be 'told' when to. I was reading of a run-flat 'blow out' and then saw the pictures, clearly the tyre had been run low for a long time and the walls just gave up and disintegrated. Another had the warning flash up, and in 5-miles at 50mph, the whole tyre fell apart. No one will convince me that tyre was running full pressure, to within a few miles of the failure.

 

Again what a lot don't realise is the pressure differential before the warning is triggered. BMW publish about 30% for the indirect TPWS. Plus how many users know if all tyres are going down, the system is flawed anyway. No wonder the States are using direct TPMS.

 

There will be a need for a lot more education on what run-flats are really about, also how tyre/wheel choice is even more critical if we want decent drives, IMO.

 

'Minefield' comes to mind...

 

HighlandPete

[Tony]

My statement "we need to adapt" is aimed at my industry where the need to realise the BMW sport settings and RFT's don't go. RFT's are here to stay so it's up to pioneers like us to identify the problem and allow owners to pursue an alternative outcome other than rapid tyre wear.

[HighlandPete]

My statement "we need to adapt" is aimed at my industry where the need to realise the BMW sport settings and RFT's don't go. RFT's are here to stay so it's up to pioneers like us to identify the problem and allow owners to pursue an alternative outcome other than rapid tyre wear.

 

Ah, see what you mean, think owners will have to adapt a bit as well, we do have this notion that the manufacturers know what they are doing. The franchised dealers are in between a rock and a hard place when it comes to moving off BMW policy/spec, even if a decent technician knows more needs to be done to get a proper solutuon. Too easy to say "in spec and you need new tyres".

 

Do you get a chance to put your views and experience across to the makers, when you find working solutions? Or do you just sort the individual customer and leave the bigger issues alone?

 

HighlandPete

[Tony]

Good question....

 

It's more a situation of filtration and authorization. When we offer a solution the clubs and forums buzz, over time the manufacturers become aware of our solution but our position doesn't have the authority to command they adapt to our findings, which is all kind of odd since we have the authority to act as arbitrators between major manufacturers and the owner?