Basic tyre load question

[Bromley86]

Likely more of a generic question, but our CLK 320 has 94W on the front and 91Y on the rear. The manual says 91W for both.

We've got to replace the fronts as one has a deep crack in the tread.

Not that it seems to be important, but I'm happy to go with Ys on the front as well. Hell, they're cheaper!

But I'm not sure about the load index. Is there a (good) reason why someone might have fitted 94 instead of 91 to the front? Is best practice to stick with the manual on this one?

Thanks.

EDIT: Think I'm geting there. The tyres are ContiSportsContact 2. I can't find the data for those but, from the Continental site, with the SportsContact 3 the 91 isn't reinforced whereas the 94 is. So perhaps the last owner chose to put runflats on.

From BlackCircles "As with all runflat tyres, Continental SSR tyres may only be fitted to vehicles equipped with a tyre pressure monitoring system and should not be mixed with standard tyres on a vehicle."

So, as we don't have pressure monitoring, it looks like 91 is better. Makes sense?

Edited by Bromley86 on Saturday 22 May 12:35

[mb450]

I didn't think reinforced meant they were necessarily runflats? My rangerover had reinforced tyres but they certainly weren't runflats.

WRT the speed rating, I was told by our local tyre place to check with my insurer if I fit was to fit a differnent speed rating as it might invalidate a claim.

[Bromley86]

Thanks mb450. I was no doubt using "reinforced" incorrectly, but I believe in this case they are runflats. Todays been the first day that I knew runflats existed though, so I'm still catching up .

AFAIK, you can't go wrong if you increase the speed rating (as long as it's the same on at least the other tyre on the same axle, and even then I'm not certain that's essential). But if you lower it below the recommended level, then you might bump into the insurance problems you mention. Any excuse.