E86 Z4C: Question for tyre beards!

[Vroomer]

I need new rear tyres on my E86 Z4C and the current ones are 255/35R18 90W (Runflats).

The tyre co says they can't get 90W but can supply 94Y and they are better tyres.

Are they right and what's the difference?

thanks for your help.

[mmm-five]

The load rating (90/94) or speed code (Y/W) does not mean 'better' - it just means that they can tyre a higher weight, at a higher speed, for longer (on a test rig of course).

You'll need to provide the specific brand/model of tyre for a good comparison - for example a Bridgestone RF of the same age/rating as a Michelin RF may perform much worse.

So everything else being equal, the same tyre with just those 2 code differences may be better for speed/load - but may have a stiffer sidewall and increase NVH.

The consensus on the Z4-Forum however, is to ditch the runflats completely (plus the OE Bridgestones are absolutely awful) - in fact BMW didn't supply the Z4M didn't with runflats as they weren't 'good enough' at the time - although runflat technology has moved on in 12 years.

So either go for a good run-flat, or a mid-range non-RF.

[Vroomer]

Many thanks for the response. You are clearly an expert!

The fronts are nearly new, so I won't be ditching the runflats.

The make is Bridgestone Potenza.

If I take the 'Y' tyres for the back will it cause any problem given I've got 'W' tyres on the front?

[mmm-five]

Vroomer said:

If I take the 'Y' tyres for the back will it cause any problem given I've got 'W' tyres on the front?

Shouldn't cause a problem at all, but I can't see why they can't supply the matching/correct load/speed rating - it's not as if it's a rare size/tyre.

[E-bmw]

Vroomer said:

The fronts are nearly new, so I won't be ditching the runflats.

The make is Bridgestone Potenza.

That is a shame, they are diabolical tyres, especially in runflat guise.

[Mr Tidy]

My Z4C is still on Bridgestone run-flats, and I don't like them - but they still have loads of tread!

I ran my 123d and my current E91 325i on Pirelli run-flats and they are much better.

I'd either look for a better brand of run-flat, or bite the bullet and change all 4 for non-RFTs.