Z3 Rear Alignment - help please

[mktommo]

I recently put a new set of tyres on my Z3 (Avons for £70 each) and then took the car for a four wheel alignment.

The old tyres had plenty of tread but were a real mismatch of types, etc that I inherited. Importantly they were wearing unevenly on the inside of the rears in particular.

The alignment place told me that it is not possible to adjust the rear set (I'd heard this before but not really paid any attention). Attached is the readout which I only partially understand.

My question is - what might be causing the rear to be so out and what if anything can you do about it?

Thanks in advance

Paul

 

[Cooper]

The rear is not adjustable. If it is out it could be because...... bushes are worn, car is lowered, or the trailing arm has been damaged. I will try to get the allowable specs and post.

 

[Grumps]

Z3 is renowned for this, so not unusual. If the car is lowered it will be considerably worse.

 

[mrscalex]

Was the garage concerned about the set-up of the rear? Did they say it was definitely out?

My perception is BMW set the rear geometry up on many of their cars for road holding knowing full well the tyres will go in the inside first.

Of course the danger is when you check a tyre you don't always look closely enough at the inside edge. So as well as being expensive it can be downright dangerous if it goes through to the cords when you are looking at the 3-5mm on the outside and in the middle. Just google 5GT or 5 Gran Turismo if you want to know all about how serious that can get.

My brother's 1 Series has just done the same. And in fairness my Seat Alhambra did it even after a £100 4-wheel alignment.

 

[mktommo]

Thanks for the answers so far. It is lowered and I suspected that that might be part of the problem. I'm spending quite a bit of money slowly making the car mechanically very good so happy to spend a little more to rectify through amended suspension parts. I'll see what other answers come out but if not will take it to my friendly local BMW specialist and see what they offer. If it means I chew through rears at a more aggressive rate in the meantime it won't be the end of the world.........

 

[mrscalex]

I'd do the sums before spending money purely to correct the tyre wear problem. It's annoying but it's something you may choose to live with.

Assumptions:

• 8mm tread on new tyre
• 2mm legal limit
• Therefore 6mm useful tread
• 18,000 mile full tyre life. Therefore 3,000 miles per mm
• The inside of the tyre wears out while the rest of the tyre still has 4mm left
• Therefore 4mm used and 2mm has been wasted
• So your tyre has only done 12,000 miles instead of the 18,000 expected
• Therefore you will be buying 3 tyres for every 2 you should need (50% increase)

Analysis:

• Calculate what your lifetime tyre spend will be on the car and evaluate the wear issue as costing 50% of this
• See whether paying for the wear issue is cheaper than the corrective action.

Example:

• Plan to do 18,000 miles pa for 4 years
• 72,000 miles total
• 8 rear tyres required at normal 18,000 per tyre
• 12 rear tyres required at premature wear 12,000 per tyre
• £80 per tyre
• 4x £80 = £320 required to address wear issue.

If you start replacing suspension you will quickly go beyond the £320. And many of us just have our Z3s as second cars and will never do that sort of mileage. Hence why plenty of people just take it on the chin.

However! If you are using the tyre wear issue to indicate there is something wrong with the car and if it could affect handling without rectification then obviously prioritise fixing this above saving money

 

[Mnbrennan]

I'd argue it's the bushes causing the issue, exacerbated by it being lowered

 

[the Nefyn cat]

Sorted mine using https://balancemotorsport.co.uk/whi...control-arm-lower-inner-outer-bmw-z3-roadster bushes. Bit of a faff, but certainly got rid of the excessive camber.

 

[t-tony]

You can minimize tyre wear by fitting directional tyres which you can swap side to side to even out the wear factor, something I did on my Z3. If it's still wearing it's original bushes they're bound to be past their best too.

Tony.

 

[GazHyde]

I'd argue it's the bushes causing the issue, exacerbated by it being lowered

Totally agree, the beam bushes in most Z3's are likely passed it now. It's not a difficult job to check the the rear beam bushes. If you don't have access to a ramp take the arch liners off then put a crowbar between the bottom of the bush and the metal plate and push down to see how much play there is.

This picture give you the idea though.

 

[mktommo]

I'd do the sums before spending money purely to correct the tyre wear problem. It's annoying but it's something you may choose to live with.

Assumptions:

• 8mm tread on new tyre
• 2mm legal limit
• Therefore 6mm useful tread
• 18,000 mile full tyre life. Therefore 3,000 miles per mm
• The inside of the tyre wears out while the rest of the tyre still has 4mm left
• Therefore 4mm used and 2mm has been wasted
• So your tyre has only done 12,000 miles instead of the 18,000 expected
• Therefore you will be buying 3 tyres for every 2 you should need (50% increase)

Analysis:

• Calculate what your lifetime tyre spend will be on the car and evaluate the wear issue as costing 50% of this
• See whether paying for the wear issue is cheaper than the corrective action.

Example:

• Plan to do 18,000 miles pa for 4 years
• 72,000 miles total
• 8 rear tyres required at normal 18,000 per tyre
• 12 rear tyres required at premature wear 12,000 per tyre
• £80 per tyre
• 4x £80 = £320 required to address wear issue.

If you start replacing suspension you will quickly go beyond the £320. And many of us just have our Z3s as second cars and will never do that sort of mileage. Hence why plenty of people just take it on the chin.

However! If you are using the tyre wear issue to indicate there is something wrong with the car and if it could affect handling without rectification then obviously prioritise fixing this above saving money

Thanks @mrscalex - I intend to keep the car into old age (mine and its) but will only do 2-3k per year. Getting it fixed is more of an OCD thing but I do like the economics of tyre wear that you suggested. It passed an MOT (with flying colours) since being lowered so now worries on safety, etc.

I'm due to start spending money on aesthetics (paintwork, alloy refurb principally) in the winter but will do some further investigation on this with my friendly expert here in Milton Keynes.

 

[5harp3y]

Just swap the tyres side to side when the wear gets close.

Lowered z3s are always going to wear the inside edge.