Lower Tire Ratings - Mercedes Benz SLK Forum

Tires, Wheels, Brakes & Suspension Discussion and information regarding tires, wheels, brakes and suspension.

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#1 Old 2 Weeks Ago
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Lower Tire Ratings

I'm having tires noise in the front. I currently have 225/40RZ/18, Y rating (186mph) , 92 load.

Is it okay to replace them with 225/40R/18, W rating (168 mph), 92 load?
Max speed I drive is 75mph on the highway.
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#2 Old 2 Weeks Ago
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https://www.1010tires.com/Tools/Tire-Size-Calculator
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#3 Old 2 Weeks Ago
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Quote:
Originally Posted by Melania View Post
I'm having tires noise in the front. I currently have 225/40RZ/18, Y rating (186mph) , 92 load.

Is it okay to replace them with 225/40R/18, W rating (168 mph), 92 load?
Max speed I drive is 75mph on the highway.
You should be able to. The numbers are all the same except for the top speed. Be aware that the top speed involves different compounds and belting arrangements. The handling might be a little different if you are a spirited driver. Otherwise you probably will not see a significant difference.
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It doesn't show speed rating?! I already know the tires size.

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Oh okay. I averaged around 23mph city, 30 on the highway so I don't think I'm a spirited driver.

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You should be able to. The numbers are all the same except for the top speed. Be aware that the top speed involves different compounds and belting arrangements. The handling might be a little different if you are a spirited driver. Otherwise you probably will not see a significant difference.
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Quote:
Originally Posted by Melania View Post
It doesn't show speed rating?! I already know the tires size.
it shows what other size tires can fit on your car.
that includes speed rating, etc, no?
isn't that what you are asking?


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#7 Old 2 Weeks Ago
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No it doesn't. I'm asking if I could put 'W' speed rating on my car instead of Y rating which I currently have.

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Originally Posted by jbanks15 View Post
it shows what other size tires can fit on your car.
that includes speed rating, etc, no?
isn't that what you are asking?
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Question

Will your insurance still be valid if you fit tyres that are not recommended by the vehicle manufacturer?
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you can use any letter really just don't exceed the letters speed rating
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Never heard of such thing.
Quote:
Originally Posted by 55russamg View Post
Will your insurance still be valid if you fit tyres that are not recommended by the vehicle manufacturer?
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#11 Old 2 Weeks Ago
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Does anyone know what page in the R172 manual does it says tires size?
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Yes, no insurance problems in the US, most MBs in the US are sold with "H" rated tires (and are limited to 130mph). Don't change the size that will affect dynamics.

Your car is limited to 155mph, so W is perfectly fine.
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I'm agreeing with pretty much every one else here...as long as you don't change tire size, and keep to the speed rating you'll be fine...as noted the cars are electronically limited to 155 mph (at least here in the states)...I'm running Firestone Indys rated to 168...

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#14 Old 2 Weeks Ago
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Quote:
Originally Posted by Johnkat View Post
I'm agreeing with pretty much every one else here...as long as you don't change tire size, and keep to the speed rating you'll be fine...as noted the cars are electronically limited to 155 mph (at least here in the states)...I'm running Firestone Indys rated to 168...

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Unless you have the P 30 option and then the electronic limiter is removed.
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Unless you have the P 30 option and then the electronic limiter is removed.
That only applies to 55s
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#16 Old 2 Weeks Ago
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That only applies to 55s
True. But the previous poster said “the cars“ he was not referring to a specific model.
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Quote:
Originally Posted by Mensra View Post
True. But the previous poster said “the cars“ he was not referring to a specific model.
Melania drives a 2014 SLK 250

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#18 Old 2 Weeks Ago
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Quote:
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Melania drives a 2014 SLK 250

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I stand corrected.
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