What are my wheels worth?

[Ed.Straker]

Edit to add - looks like the largest wheel Mercedes offered on a c class of a similar year was an 18". Audi offered a 19" wheel on the A4, but that ran a relatively chunky 255/35/R19 tyre, whereas BMWs were on 255/30/R19.

The profile "number" is slightly irrelevant, as it is the percentage of the overall width of the tyre. Therefore on a 326 front with a 225mm width tyre, the 30 is 30% of 225 (67.5mm), whereas the rears being 255, it's 30% of that (76.5mm). So it can't be related to the thin profile, otherwise the fronts would suffer more? It has to be to do with the width of the wheel itself which makes sense as there is more unsupported structure.

Not quite correct..on the E89 the fronts are one click up on profile size eg 35 front / 30 rear so the ‘meat’ is the sane height...there may be some logic to the width but 8j vs 8.5j doesn’t really sound much of an issue...I’ve heard as many fronts crack as rears, certainly on MBs and Audis..

[Pondrew]

Not quite correct..on the E89 the fronts are one click up on profile size eg 35 front / 30 rear so the ‘meat’ is the sane height.

Fair play (I didn't check) Probably just down to manufacturers sourcing their wheels from "Franz's cheap wheels of Munich", who have cnc milling machines set with a given program running 24/7 and getting 30 euros a piece for them.

[Smartbear]

Not quite correct..on the E89 the fronts are one click up on profile size eg 35 front / 30 rear so the ‘meat’ is the sane height.

Fair play (I didn't check) Probably just down to manufacturers sourcing their wheels from "Franz's cheap wheels of Munich", who have cnc milling machines set with a given program running 24/7 and getting 30 euros a piece for them.

That covers bmw for charging £650 for a rear wheel then
Rob

[R.E92]

With cast wheels you have a choice between heavy and weak. If they are small wheels with a decent amount of tyre then weakness isn't as much of a problem but the lightweight cast BMW wheels with run flat tyres are a bit of a disaster on British roads. After-market wheels mostly fix that with extra weight, any set of £600 alloys is going to be crap if it's gravity of low pressure cast, they might not crack as easily but they'll add a load of unsprung weight.

There's some decent flow formed wheels around which reduce the weight for a little extra monkey but nothing really comes close to getting a proper set of forged wheels. The downside of those is usually that they cost £3-4k per set. Luckily BMW make forged wheels for their high-end cars which people like to remove and sell off cheap. The 437M is a good example as they cost about the same as some lead circles from CMWheels but are forged and fit the Z4 perfectly.

[Pondrew]

I just checked mine, just to be sure

Some stupid f*cker has put the WRONG size tyres on the rears of mine!

I have 225/35/19 88Y Bridgestone Potenzas on the front and 255/35/19 92Y same on the rears! That means the rolling radius is way out between front and rear (nearly 10mm). Circumference difference is 65mm front to back.

[R.E92]

Not quite correct..on the E89 the fronts are one click up on profile size eg 35 front / 30 rear so the ‘meat’ is the sane height.

Fair play (I didn't check) Probably just down to manufacturers sourcing their wheels from "Franz's cheap wheels of Munich", who have cnc milling machines set with a given program running 24/7 and getting 30 euros a piece for them.

The problem is that they aren't CNC milled, rather just molten alloy poured into a mould.

[mr wilks]

I just checked mine, just to be sure

Some stupid f*cker has put the WRONG size tyres on the rears of mine!

I have 225/35/19 88Y Bridgestone Potenzas on the front and 255/35/19 92Y same on the rears! That means the rolling radius is way out between front and rear (nearly 10mm). Circumference difference is 65mm front to back.

Why is it "wrong " ?
Bmw no longer fit 255 30 19 tyres so perhaps they realised they were pretty much alone amongst the other German manufacturers fitting 255 30 19 to a 9j rim .
You clearly haven't felt any noticeable impairment to handling ( why would you ) & another benefit along with comfort & wheel protection is the speedo will now be more accurate .

[Pondrew]

Why is it "wrong " ?
Bmw no longer fit 255 30 19 tyres so perhaps they realised they were pretty much alone amongst the other German manufacturers fitting 255 30 19 to a 9j rim .
You clearly haven't felt any noticeable impairment to handling ( why would you ) & another benefit along with comfort & wheel protection is the speedo will now be more accurate .

I thought the circumference of the front and rear axles should be (pretty much) the same

[SV8Predator]

another benefit along with comfort & wheel protection is the speedo will now be more accurate .

The higher rolling radius from factory spec makes the speedo more accurate? Explain!

[True-Blue]

another benefit along with comfort & wheel protection is the speedo will now be more accurate .

The higher rolling radius from factory spec makes the speedo more accurate? Explain!

Nearly all factory speedo’s over-read.... tell you you are going faster than you actually are, increasing the wheel/tire circumference over stock will counteract this

[Danglesberries]

ALL speedo's over-read, it's a law requirement in the UK.

[Nictrix]

Why is it "wrong " ?
Bmw no longer fit 255 30 19 tyres so perhaps they realised they were pretty much alone amongst the other German manufacturers fitting 255 30 19 to a 9j rim .
You clearly haven't felt any noticeable impairment to handling ( why would you ) & another benefit along with comfort & wheel protection is the speedo will now be more accurate .

I thought the circumference of the front and rear axles should be (pretty much) the same

More important for 4 wheel drive systems

[Ed.Straker]

Why is it "wrong " ?
Bmw no longer fit 255 30 19 tyres so perhaps they realised they were pretty much alone amongst the other German manufacturers fitting 255 30 19 to a 9j rim .
You clearly haven't felt any noticeable impairment to handling ( why would you ) & another benefit along with comfort & wheel protection is the speedo will now be more accurate .

I thought the circumference of the front and rear axles should be (pretty much) the same

The primary issue is the stability control system..bmw call theirs DSC?

The system needs to know to a very high degree of accuracy what the absolute and relative speeds are of each of the 4 wheels.

Other sensors are required but fir this discussion they are not relevant.

Speed is calculated based on the abs sensor rings on each wheel being counted.

Then the ES computer then uses these rotations multiplied by the rolling diameter of each wheel to calculate absolute speed and relative speed of each wheel.

ES computers assumes that the wheel diameters are constants..it looks like the E89 assumes each corner has an identical rolling radius.

However there is no reason why different sizes front and rear rolling radius cannot be used providing the ES computer knows that.

For the E89 the DCS ‘how it works’ stated that each wheel should be with 1.5%

So by exceeding these parameters it’s probable that the ES system will not work as intended at certain events.

[Scooba_Steve]

ALL speedo's over-read, it's a law requirement in the UK.

It's not a requirement to over-read; rather not under-read and an allowance above:

The Motor Vehicles (Approval) Regulations 1996
SCHEDULE 2
19 Speedometers
1. The vehicle shall be fitted with a speedometer capable of indicating speed in mph at all speeds mph. up the maximum design speed of the vehicle.

2. For all true speeds up to the maximum design speed of the vehicle, the true speed shall not exceed the indicated speed.

3. For all true speeds of between 25 mph and 70 mph (or the maximum design speed if lower), the difference between the indicated speed and the true speed shall not exceed—

V / 10 + 6.25mph

where

V=the true speed of the vehicle in mph.

[Danglesberries]

Not a single speedo reading in a vehicle gives an exact speed. They are deliberately set to over read. Lorries are governed by a maximum of 56mph. Try following one on the motorway and your speedo will read between 59 and 60 mph. The true speed you are doing is 56mph as the lorry s driving (generally) at the very maximum permitted.