Another tyre question, advice please

[N11LS_J]

Would you or do you guys run a 90Y rated tyre as opposed to the OEM 96Y on your car?

The replacement tyres are XL rated and are of a brand name, no budgets

[SuprSi]

Hell No. A 90 load rating is only 600KG as opposed to the 710KG of the 96. There would be more than that on the front tyres while stationary and under heavy braking there would be most of the weight on the car on the fronts. The carcass of the tyre will be flexing a lot more than it should be so if you got into tripple digits it will overheat quickly and you risk having a blow out.

It's not worth taking a chance.

[N11LS_J]

That clears that up!

Lol

Cheers for the reply, appreciate your input and yes it makes sense, definitely not worth the risk in that case.

Back on the hunt for a suitable tyre size it is then...

[nij]

That's the main reason I run 265/30/20 94Y (670Kg) tyres, as the correct radius 255/30/20 only comes in 92Y (630Kg). Therefore, I'm only 40Kg less load per corner. It's not ideal, but that's the closes I could find a tyre that fits.

[Covkiller]

Just spoke to Michelin about my Pilot235 30 20 88 Y XL ZR's
A really nice lady said the 560kg load index can be exceeded and will be fine on a RS4 as the tyre is XL rated and will handle the extra load at high speed as its ZR.

[SuprSi]

I believe there's a bit of mis-information there.

I thought ZR is an old category that basically just means over 150, and they split further into the Z/W/Y ratings. You see that part before before the diameter, ie 235/30 ZR 20

XL just means it has a higher load rating, but you still need to go by the load rating not just the fact it says XL.

I think having a lower rating would be ok if you weren't planning on topping your car out for a sustained period. Unless you live next to the autobahn it should be fine I guess.

[Covkiller]

The Michelin Pilot SS are 186Mph rated so I should be ok

[SuprSi]

I agree the Michelins will be fine.

The speed and load ratings aren't set in stone, as your speed increases you have to increase tyre pressures to reduce how much the tyre flexes, but even doing that as you get close to the max speed rating the tyres won't be able to withstand their max load rating. That's why it's good to have some head room.

If you're interested have a read of this:
http://www.tirerack.com/tires/tiretech/ ... ?techid=72

With the info from that article i re-worked their chart for my car, so if i did a sustained autobahn run I'd be running beyond the ratings of my tyres.



Edit: Sorry for spouting all the nerdy tyre stuff, my old man owns a tyre business so I've always had a bit of an interest in it.