C55 - changed to 255 width rears.... Tyre fitter query

[just240]

Hi everyone,

I require a bit of info from any AMG drivers who have 255 section rear tres. Firstly, I'll explain my situation - my c55 needed new rear tyres - I put the car into a national chain tyre fitters & asked them to replace my standard 245/35/18 PIRELLI P-Zero ROSSO tyres with 255/35/18 Pirelli P-zero Rosso's ( i.e exactly the same just a bit wider).
They were also doing a wheel aliment so they had the car for a day. When I picked the car up they informed me that that put 255/35/18 P-Zero tyres on the car that were MO which meant they were the proper Mercedes fit tyres for my car. However, I noticed that the speed index was lower on these standard P-Zero tyres i.e. they were "Y" instead of "(Y)" - I previously know that the brackets mean the tyres are rated for higher speeds & therefore are a higher performance quality. So I disputed this with the garage & they informed me that Mercedes "don't use P-Zero ROSSO'S for any vehicle above 245 section???
So - in short can anyone confirm if they have 255/35/18 tyres or wider fitted with P-Zero ROSSO'S & whether these are standard fit on MB??

Thanks

 

[redbaron]

They are the wrong size. They will not be MB rated.

Your car may well react badly. It might not - as is only a small change. Where does your insurance stand on this?

As for speed rating Y W and Z are all rated to the same speed.

 

[just240]

Thanks for your reply, I have spoken to a few c55 owners who have also increased the rear tyre width from 245 to 255 & there has been No problems. In fact many owners recommend it. The AMG wheels that came with the C55 were also used on the E55 with 255 tyres instead of 245's so no problem there. I can also confirm there is No rubbing or increase in tyre width outside of the wheel arch. The increase in width is actually on the inside of the car & there is plenty of space to accommodate it.
Regarding insurance, I don't think it is of concern as many people argue this is in-fact a safety modification providing the car with more traction?!

Sorry forgot to mention - any speed rating tyre Y,Z,R etc is only rated for speeds UP to 189MPH and any speed rating with "( )" round the rating is for cars that can go beyond 189MPH. Now, I can safely say that I will never be driving my car over 189MPH however, I have original 225/40/18 P-Zero ROSSO tyres on the front of my car that are (Y) rated & the 245/35/18 P-Zero ROSSO's that were taken off my car were also (Y) rated. So, my question is whether the garage are trying to convince me something that is not true i.e. Mercedes don't fit 255 P-Zero ROSSO'S ??

 

[redbaron]

Modern mercedes safety systems are calibrated with regard to tyre diameter etc.

You have changed the rear tyre diameter relative to the front.

W211 E's use 265 not 255.

 

[just240]

Modern mercedes safety systems are calibrated with regard to tyre diameter etc.

You have changed the rear tyre diameter relative to the front.

W211 E's use 265 not 255.

Yes you're quite right! But the CLK55 coup & cab had exactly the same size wheels as C55 & exactly the same front tyres (225/40/18) BUT 255 rears instead (just confirmed in the AMG 55 series original manual).

 

[DSM10000]

Modern mercedes safety systems are calibrated with regard to tyre diameter etc.

You have changed the rear tyre diameter relative to the front.

W211 E's use 265 not 255.

True but only by around 1%, you would get more variation than that as a new tyre wore down so I would imagine that the systems can cope with that degree of difference?

 

[redbaron]

True but only by around 1%, you would get more variation than that as a new tyre wore down so I would imagine that the systems can cope with that degree of difference?

Quite probably.

More likely to end up in a ditch because of P Zero Rosso's inherant wet weather (dis)ability than the ESP going awol... non the less Insurer may class it as a modification.

 

[just240]

All true, but does anyone know if MB fitted P-Zero ROSSO'S to the E55 or CLK55 rear tyres? My C55 did have ROSSO's fitted from factory same as the fronts.

 

[redbaron]

Why does it matter to you? Rosso's are hardly a desirable tyre?

Put some Pilot Sports on there.

 

[just240]

Yes I may end up doing so but I want to check/ confirm what the garage are telling me is true? Have they provided me with a cheaper tyre than the ROSSO's I had ( factory fit) previously? Do MB actually use ROSSO's on rear tyres larger than 245? Am I being fobbed off? Etc etc

 

[redbaron]

They are Y rated. I have never heard of this significant bracket meaning that you refer to?

My last set of 255 Rosso's were not bracketed and were fine at 180mph....

 

[just240]

As taken from Wikipedia.

Speed rating
The speed symbol is made up of a single letter or an A with one number. It indicates the maximum speed at which the tire can carry a load corresponding to its Load Index. [17]
Speed rating[18]
Code mph km/h Code mph km/h
A1 3 5 L 75 120
A2 6 10 M 81 130
A3 9 15 N 87 140
A4 12 20 P 94 150
A5 16 25 Q 100 160
A6 19 30 R 106 170
A7 22 35 S 112 180
A8 25 40 T 118 190
B 31 50 U 124 200
C 37 60 H 130 210
D 40 65 V 149 240
E 43 70 Z over 149 over 240
F 50 80 W 168 270
G 56 90 (W) over 168 over 270
J 62 100 Y 186 300
K 68 110 (Y) over 186 over 300
Prior to 1991, tire speed ratings were shown inside the tire size, before the "R" construction type. The available codes were SR (112 mph, 180 km/h), HR (130 mph, 210 km/h), VR (in excess of 130 mph, 210 km/h).
Tires with a speed rating higher than 186 mph (300 km/h) are indicated by a Y in parentheses.[citation needed] The load rating is often included within the parentheses, e.g. (86Y).
In many countries, the law requires that tires must be specified, and fitted, to exceed the maximum speed of the vehicle they are mounted on, with regards to their speed rating code (except for "Temporary Use" spare tires). In some parts of the European Union, tires that are not fit for a car's or motorcycle's particular maximum speed are illegal to mount. The sole exception are M+S tires, where a warning sticker stating the allowed maximum speed must be placed within clear sight of the driver inside the vehicle. Some manufacturers will install a speed governor if a vehicle is ordered with tires rated below the vehicle's maximum speed.
[edit]

 

[redbaron]

I think [citation needed] is the clue there...

That info is not what is listed on Michelin or Goodyear websites.

ZR is the 186+ rating.

 

[Bobby Dazzler]

There are two P-zero tyres which are supplied in a M0 fitment:
P ZERO ROSSO?, Car tyres, Summer tyres - PIRELLI UK

Of those one is a extra load (Y) designed for heavy cars with low profile tyres, and one is designed of the same load index but on a physically smaller car:
Tyre size: 17, 18 tyres - All about car wheels tyres - PIRELLI - PIRELLI UK
Tyre guide | Auto Express

I'm not a dentist, nor a tyre expert, but either the XL or standard tyre will be fine for a W203, but you may find the reinforcement I'm the XL tyre may lead a less compliant ride givem the weigh of your car.

 

[just240]

Thanks for the info, I guess the (y) bracket or not doesn't really matter however can anyone confirm MB fit 255 Pirelli Rosso's or just standard p-zeros's?

 

[redbaron]

Mainly bridgestones or continentals on most of the 400-500 I have seen handed over.

 

[Bobby Dazzler]

The M0 rating suggests that Mercedes do, have or will fit this tyre in this fitment on a Mercedes car.

255 35 18 are a W204 C-Class fitment:
AMG alloy wheels | Genuine new 18" AMG 7 Spoke | fits Mercedes C Class Saloon W204 | Alloy Wheels Direct Ltd

If I was inclined to dig deeper then I suspect that I would find a larger car with the same fitment but which justifies the XL rating.

 

[Bobby Dazzler]

The M0 rating suggests that Mercedes do, have or will fit this tyre in this fitment on a Mercedes car.

255 35 18 are a W204 C-Class fitment:
AMG alloy wheels | Genuine new 18" AMG 7 Spoke | fits Mercedes C Class Saloon W204 | Alloy Wheels Direct Ltd

If I was inclined to dig deeper then I suspect that I would find a larger car with the same fitment but which justifies the XL rating.

Probably the C207 E-Class Coupe

 

[G.P]

As for speed rating Y W and Z are all rated to the same speed.

ZR is the 186+ rating.

Does that make Z different to ZR???

Put some Pilot Sports on there.

Are you trying to get him to find a ditch...