Speed ratings on tyres

[HertsBiker]

Anyone got experience of problems when changing tyre speed ratings? It's only just occurred to me that my 2 day old tyres might have to be changed back as they are lower rated. Still faster than the car can go, but I'd sooner not risk insurance problems in the event of a claim. Damn it.

[Dr Mike Oxgreen]

Just phone your insurance company and tell them. They almost certainly won't care.

[scorcher]

Only a problem if the speed rating is lower than the actual speed your car can achieve IMO. I'm sure plenty of cars are fitted with Z, W and Y rated tyres when theres acbsolutely no need and a V rated (or less)would do. Can't see a reason why your insurance co. would find a problem with it either.

[Pontoneer]

The only real problem is where the load ratings may also be lower and unsuitable for the vehicle .

In practice , it is unlikely to make a difference .

[creampuff]

The tyres on your vehicle should be one of the tyres listed in the tyre placard which is visible when you open the drivers door. The placard lists allowable speed and load ratings.

[HertsBiker]

Thanks for your replies.
Load rating is same, speed rating is above vehicle speed.
Insurance said we'll note it down.
Car handbook doesn't say what speed rating, and depending on what year for the same car, it has different ratings.
I needed a chunkier pattern and have got approval!

[HertsBiker]

Just been outside to check that little placard in the door... It only gives a size but no speed rating. So it seems I was worrying over nothing. As long as the speed of the car is less, it's okay.

[creampuff]

As an aside I've rejected and got the tyre fitter (which was a BMW dealer) to change V rated tyres for W rated. The tyres they fitted were not listed on the tyre placard and were rated for less than the maximum speed of the car.

[HertsBiker]

creampuff said:

As an aside I've rejected and got the tyre fitter (which was a BMW dealer) to change V rated tyres for W rated. The tyres they fitted were not listed on the tyre placard and were rated for less than the maximum speed of the car.

Totally understand your actions there. I'd do the same. So your car actually specifies the lot?

[Hooli]

On some cars higher rated tyres are fitted because the stronger structure allows higher cornering loads rather than just a higher top speed.

[untakenname]

Out of interest I just looked up the different speed ratings.

Rating Maximum Speed
Q = 99 mph
S = 112 mph
T =118 mph
U = 124 mph
H = 130 mph
V Above 130 mph (without service description)
V 149 mph (with service description)
Z Above 149 mph
Y = Up to 179 mph
W Up to 197 mph


Surely as the speed limit in this country is 70mph then a 99mph Q rated tyre should do, even on a quick car? If an insurer fails to pay out in the event of an accident that's not caused by speeding stating you need say a Z rated (197mph) tyre aren't the insurers condoning speeding?
A few models of production cars can do over 200mph so what tyre rating do they use?

[Kawasicki]

untakenname said:

A few models of production cars can do over 200mph so what tyre rating do they use?

Tyres are specially tested for the weight and speed of the car and to indicate this situation I've seen a Y inside brackets with the load index. If you intend to travel at high speeds it is smart to get the original tyre spec from your car dealer.

[creampuff]

HertsBiker said:

creampuff said:

As an aside I've rejected and got the tyre fitter (which was a BMW dealer) to change V rated tyres for W rated. The tyres they fitted were not listed on the tyre placard and were rated for less than the maximum speed of the car.

Totally understand your actions there. I'd do the same. So your car actually specifies the lot?

Yes, it specifies everything. Size, speed and load rating. There is a reduced speed rating less than the maximum speed of the car if and only if you have M+S tyres fitted.

With the V rated tyres you are limited to 149mph. Bit of a problem if you are in a bit of a rush for the Eurotunnel back to the UK

[Pontoneer]

creampuff said:

The tyres on your vehicle should be one of the tyres listed in the tyre placard which is visible when you open the drivers door. The placard lists allowable speed and load ratings.

That must depend on which car you have , it certainly is not universal and I have not seen it on any car I have owned .

Mercedes and Volkswagen do have information relating to correct inflation pressures on the inside of the fuel filler flap ( and have had since the mid 1960's ) but information regarding tyre types , ratings and sizes is printed in the owners' handbooks , or available on request at the dealers .

[JM]

untakenname said:

Out of interest I just looked up the different speed ratings.

Rating Maximum Speed
Q = 99 mph
S = 112 mph
T =118 mph
U = 124 mph
H = 130 mph
V Above 130 mph (without service description)
V 149 mph (with service description)
Z Above 149 mph
Y = Up to 179 mph
W Up to 197 mph


Surely as the speed limit in this country is 70mph then a 99mph Q rated tyre should do, even on a quick car? If an insurer fails to pay out in the event of an accident that's not caused by speeding stating you need say a Z rated (197mph) tyre aren't the insurers condoning speeding?
A few models of production cars can do over 200mph so what tyre rating do they use?

Going by your list above, cars with top speeds in excess of 197mph can use V or Z rated tyres.

[Pontoneer]

Hooli said:

On some cars higher rated tyres are fitted because the stronger structure allows higher cornering loads rather than just a higher top speed.

Exactly , the load rating is not just to do with the static weight of the car which sits on each corner , but is also to do with the dynamic loading generated when accelerating , braking and cornering , hence higher performance cars can require a higher load rating and can be at risk if inadequate tyres are fitted , even though the maximum speed for the tyre is never exceeded .

Speed ratings are also relative to time over which a certain speed is maintained : most tyres will safely exceed their specified maximum for a brief period , but cannot sustain higher speeds indefinitely due to heat build up from internal frictions .

[Kawasicki]

Pontoneer said:

Hooli said:

On some cars higher rated tyres are fitted because the stronger structure allows higher cornering loads rather than just a higher top speed.

Exactly , the load rating is not just to do with the static weight of the car which sits on each corner , but is also to do with the dynamic loading generated when accelerating , braking and cornering , hence higher performance cars can require a higher load rating and can be at risk if inadequate tyres are fitted , even though the maximum speed for the tyre is never exceeded .

Are you sure? I've never heard anyone use dynamic loading for tyre sizing calculations.

[Pontoneer]

Yes , speed and load ratings are all interrelated .

This was explained to me by an engineer from one of the tyre manufacturers ( Continental IIRC ) at a road safety event I was involved in .

[lbc]

Dr Mike Oxgreen said:

Just phone your insurance company and tell them. They almost certainly won't care.

This^^

Insurance company will only be interested if tyres are a different size to standard, or fitted on more expensive alloy wheels than standard.

I have asked insurers before, and they are not interested in speed ratings.

If speed rating was an issue, then all winter tyres would be banned!

[H.7]

untakenname said:

Out of interest I just looked up the different speed ratings.

Rating Maximum Speed
Q = 99 mph
S = 112 mph
T =118 mph
U = 124 mph
H = 130 mph
V Above 130 mph (without service description)
V 149 mph (with service description)
Z Above 149 mph
Y = Up to 179 mph
W Up to 197 mph


Surely as the speed limit in this country is 70mph then a 99mph Q rated tyre should do, even on a quick car? If an insurer fails to pay out in the event of an accident that's not caused by speeding stating you need say a Z rated (197mph) tyre aren't the insurers condoning speeding?
A few models of production cars can do over 200mph so what tyre rating do they use?

That table is different from the one on Black Circles web site. Is either correct? I wouldn't trust what just one web site says. From Black Circles:

Speed Rating Mile/Hour Speed Rating Miles/Hour
N 87 U 124
P 93 H 130
Q 99 V 149
R 106 Z 150+
S 112 W 168
T 118 Y 186

Makes sense to me that the speed increases as the rating goes through the alphabet.