Tyre load index basic question

Bromley86

Our car came 2nd hand with 225/45 R17 94W tyres fitted to the front. The manual says that it needs 91W.

As we need to replace the fronts, we'll be practicing a bit of moneysaving by increasing the speed rating to Y (strangely they're cheaper and then, although not vital, they'll match the Ys on the rear wheels).

But I can't find anything about whether sticking to the load index in the manual is advisable. Might there be a good reason for upping it (as there is for the speed rating)? Is it best if the front and rear loads match, as the rears are currently the advised 91?

Thanks.

somech

wont matter if you exceed the load index and or speed rating

vikingaero

The 91 load index is 615kg and the 94 index is 670 kg so I think you're OK. Obviously it would be more dangerous to have a lower index tyre than the recommended. Aftermarket tyres may not be produced in the exact load index to those originally specified.

marlot

As long as the load index is at least equal to the manual you'll be fine. The sidewalls might be slightly stiffer on the 94s, but no sot much that you'd notice.

Bromley86

Thanks guys.

Slight twist. It looks like with the particular tyre that I'm dealing with (ContiSportsContact 3), the 94 is a runflat whereas the 91 isn't.

That means a little more to me that it would have half an hour ago, so I think the key is that the tyre manufacturers say that runflats need tyre pressure monitors as otherwise you'll not notice that you have a flat.

So back down to 91 it is. Nice to have a motive why the last owner might have gone for 94 though.

mikey72

It'll make no difference whether you put on a run flat or not. Worse it'll do is damage both tyres equally if you don't notice, with a pressure monitor you might have saved the run flat.

Bromley86

Seems I need to look into it more then, as I like the thought of paying an extra couple of pounds to avoid a blowout. Thanks mikey72.

mikey72

You still won't avoid the blowout I'm afraid. Usually it means the car can drive a limited amount on the deflated tyre, the interior of the tyre is better equiped to cope with the rim bearing down on it, and won't crack or cut through like a normal tyre.
Both are usually ok to use on a normal rim, but if you aren't aware of the pressure loss you can still damage the tyre.
That said, it will probably drive better with a flat tyre, so you'll get the benefit of that if there is an unexpected pressure loss.
A tyre fitter may refuse to fit the tyre without the pressure system though, as it won't comply to the manufacturers recommended fitting instructions.