BMW 330d tyre size?

[sorted]

Me again on this BMW, looking get some rear tyres per MOT advisory.
But looking around the car I see it has different sizes! Fronts are 255/40 x 19 and rears 255/35 x 19. Is this normal on these and if not, which should I replace the rears with? Gut says match the fronts but wanted to check if there is a reason!

Thanks

[Noberator]

This tyre set up is common on high performance motors. Using different tyre sizes on the front and rear axle is done for several reasons including improving the car's handling, traction and overall performance. By using a staggered fitment the car can have better grip stability, and balance. This will help performance and handling as it will allow your car to grip the tarmac easier resulting in better acceleration and even breaking.

Check your user manual or have a word with your tyre place if changing to one size will affect the stability of the car at high speed and would it affect the speedo reading at all.

I could be wrong hence checking your user manual or even better check with your local BMW dealer as I would have thought the tyre set up would be front 255/35 x 19 and 225/40/19 on the rear hence me asking you to check with BMW or your tyre professional .

[valhalla]

I was thinking about this whilst you were typing Noberator !!

I'm sure that the way round that sorted has it might be correct, just from an Engineering perspective. The taller section on the front tyres would ensure that the sidewalls flexed more, and therefore the car would tend to understeer in-extremis on bends. This is safer than having the back-end let-go on this sort of suspension, which can emulate the old swing-axle designs if provoked.

All this pales into insignificance if the current tyres are mixed makes/models front and back already! The best solution is always to have identical tyres (except for the sizing differences) and wear-rates on the front and back, as that will match what BMW designers had predicted.

Or drive the car slower, and "don't go there" (near the limit)

[Noberator]

valhalla On reflection of my last post I recon you are correct with your analogy of the front under steering and rear stepping out. I've owned a few performance cars in my time but never had one with a staggered fitment they have all have the same size and ratio etc.24V Senator,XR4X4'S 2.9 had two of those, Granada 24V Cosworth, Sierra Cosworth 4x4 and Mondeo ST220 most recent.

I was thinking bigger tyres on the front would mean heavier steering but with PAS it's not going to be that noticeable is it.

[Rhubarb]

Look in your manual, or many search engines with tyre suppliers on the internet. Just type your reg number in and the info comes up.

I expect a different profile has been picked for price purposes.

My 7 series had different profiles but that was because it had 7 inch width on the front and 8 inch on the rear.

[sorted]

Thanks all will do some more checks now I understand more. They are a matching set of Goodyear Eagle run flats just now, only difference is the profile.

I doubt I will be paying for those to replace them. I won’t be pushing it that hard and it does seem most of the forums say moving away from runflats gives a quieter and smoother ride. But I do recognise the power this thing has so won’t be going bottom of the range budgets either!

[remmington]

Apr 14, 2024 12:53:51 GMT 1 Rhubarb said:

Look in your manual, or many search engines with tyre suppliers on the internet. Just type your reg number in and the info comes up.

I expect a different profile has been picked for price purposes.

My 7 series had different profiles but that was because it had 7 inch width on the front and 8 inch on the rear.

Rear wheels are wider on these

[Rhubarb]

Apr 14, 2024 20:51:41 GMT 1 remmington said:

Apr 14, 2024 12:53:51 GMT 1 Rhubarb said:

Look in your manual, or many search engines with tyre suppliers on the internet. Just type your reg number in and the info comes up.

I expect a different profile has been picked for price purposes.

My 7 series had different profiles but that was because it had 7 inch width on the front and 8 inch on the rear.

Rear wheels are wider on these

Doesn't surprise me, that accounts for the difference in profile, but he's saying 255 for width on all four?!

[sorted]

Yep same size rims on all 4 corners, just the profile depth differs. But all the checks I have done confirm this is standard from factory so will keep it that way.

My local tyre guy doing me a great deal on a pair of Pirelli Sports so will get them fitted at weekend.