Tyre speed ratings
Discussion
Hi,
Would you use a tyre with a marginally lower speed rating than the car was originally designed for?
It's very difficult to get W-rated tyres in 15" sizes now and I'm wondering whether it really would be such a drama to go down to a V-rated tyre, good for a mere 149mph. I've got no intention of doing that sort of speed on the road and I suspect you'd be hard pushed to go that fast on a UK track day?
I realise that might sound like I've answered my own question, but are there any other factors to consider before going down in speed rating?
Chris
Would you use a tyre with a marginally lower speed rating than the car was originally designed for?
It's very difficult to get W-rated tyres in 15" sizes now and I'm wondering whether it really would be such a drama to go down to a V-rated tyre, good for a mere 149mph. I've got no intention of doing that sort of speed on the road and I suspect you'd be hard pushed to go that fast on a UK track day?
I realise that might sound like I've answered my own question, but are there any other factors to consider before going down in speed rating?
Chris
Chris71 said:
Hi,
Would you use a tyre with a marginally lower speed rating than the car was originally designed for?
It's very difficult to get W-rated tyres in 15" sizes now and I'm wondering whether it really would be such a drama to go down to a V-rated tyre, good for a mere 149mph. I've got no intention of doing that sort of speed on the road and I suspect you'd be hard pushed to go that fast on a UK track day?
I realise that might sound like I've answered my own question, but are there any other factors to consider before going down in speed rating?
Chris
I am interested tp hear this as I always go with the correct speed rating, but can never work out why I should...Would you use a tyre with a marginally lower speed rating than the car was originally designed for?
It's very difficult to get W-rated tyres in 15" sizes now and I'm wondering whether it really would be such a drama to go down to a V-rated tyre, good for a mere 149mph. I've got no intention of doing that sort of speed on the road and I suspect you'd be hard pushed to go that fast on a UK track day?
I realise that might sound like I've answered my own question, but are there any other factors to consider before going down in speed rating?
Chris
Is there something like insurance claims that could be affected - I'm assuming the speed rating does not affect the braking ability? I don't know if the tyre is just more reinforced or has a slightly different compound though.
Two things to bear in mind with tyre speed ratings:
1) Speed ratings are about far more than how fast you can drive before they explode. Fitting 116mph rated tyres on a car designed for 149mph rated tyres because you never intend to exceed 115mph does not work. Speed rating takes into account weights, accelerative and braking forces and many other factors when chosen for the car.
2) Your insurance company will probably be quite unhappy about this when you inform them and very unhappy about it if you don't and then make a claim.
Just out of interest, what size are you needing?
1) Speed ratings are about far more than how fast you can drive before they explode. Fitting 116mph rated tyres on a car designed for 149mph rated tyres because you never intend to exceed 115mph does not work. Speed rating takes into account weights, accelerative and braking forces and many other factors when chosen for the car.
2) Your insurance company will probably be quite unhappy about this when you inform them and very unhappy about it if you don't and then make a claim.
Just out of interest, what size are you needing?
If fitting winter tyres, you are usually allowed to drop 1 speed rating, so I'm not sure why it would be an issue if you only drop 1 rating and you stick to UK legal speeds. After all, in choosing the speed rating of the tyre, the manufacturers have to assume it will be used at the max speed the vehicle can achieve, so a big margin of error is built in. The load rating is far more important in day-to-day driving.
BeeRoad said:
Two things to bear in mind with tyre speed ratings:
1) Speed ratings are about far more than how fast you can drive before they explode. Fitting 116mph rated tyres on a car designed for 149mph rated tyres because you never intend to exceed 115mph does not work. Speed rating takes into account weights, accelerative and braking forces and many other factors when chosen for the car.
I can imagine... that's why I asked. 1) Speed ratings are about far more than how fast you can drive before they explode. Fitting 116mph rated tyres on a car designed for 149mph rated tyres because you never intend to exceed 115mph does not work. Speed rating takes into account weights, accelerative and braking forces and many other factors when chosen for the car.
I'm after 205/55 r15 fronts and 225/50 r16 rears. It seems Yokohama S Drives are available in a W rating, but the usual Toyo, Kumho, Dunlop and Michelin contenders stop at V rated.
It's quite a light car in the grand scheme of things (about a ton), but I guess these are hot hatch sizes these days and a 5-litre V8 might have a bit more torque than the carcasses are designed to handle.
Lots of Chimaera/Griffith people are turning to 16" wheels (or larger) for this very reason.
The insurance angle on this is interesting. Id imagine that a large percentage of the older cars on the road have tyres of a lower rating than originally specified.
I'm thinking specifically about owners who use budget tyres , they may have the right size but the rating is likely to be lower.
If it mattered to the insurance companies would there not be a duty of care by the tyre fitters to ensure that the tyres were suitable for the purpose?
I'm thinking specifically about owners who use budget tyres , they may have the right size but the rating is likely to be lower.
If it mattered to the insurance companies would there not be a duty of care by the tyre fitters to ensure that the tyres were suitable for the purpose?
Having experienced first-hand what happens when you exceed a tyre's speed rating, I wouldn't recommend it.
I was driving on a snow tyre at 70mph on a dry motorway. 5 minutes into the journey we started discussing what speed a snow tyre would be rated to. Shortly afterwards it exploded in the most spectacular way a tyre can.
I was driving on a snow tyre at 70mph on a dry motorway. 5 minutes into the journey we started discussing what speed a snow tyre would be rated to. Shortly afterwards it exploded in the most spectacular way a tyre can.
durbster said:
Having experienced first-hand what happens when you exceed a tyre's speed rating, I wouldn't recommend it.
I was driving on a snow tyre at 70mph on a dry motorway. 5 minutes into the journey we started discussing what speed a snow tyre would be rated to. Shortly afterwards it exploded in the most spectacular way a tyre can.
What was the speed rating? Even the cheapest winter tyres these days are usually "T" rated (118mph)I was driving on a snow tyre at 70mph on a dry motorway. 5 minutes into the journey we started discussing what speed a snow tyre would be rated to. Shortly afterwards it exploded in the most spectacular way a tyre can.
durbster said:
Having experienced first-hand what happens when you exceed a tyre's speed rating, I wouldn't recommend it.
I was driving on a snow tyre at 70mph on a dry motorway. 5 minutes into the journey we started discussing what speed a snow tyre would be rated to. Shortly afterwards it exploded in the most spectacular way a tyre can.
True, I've had tyre blowout too (fortunately on a test track) so I can confirm it's not pleasant. Without wishing to be facetious though I am talking about using the very next speed rating down on a similar performance-orientated summer tyre, not switching to a completely different type of tyre. I was driving on a snow tyre at 70mph on a dry motorway. 5 minutes into the journey we started discussing what speed a snow tyre would be rated to. Shortly afterwards it exploded in the most spectacular way a tyre can.
I've also had a play around with the TRC rolling radius calculator and it seems I could get it to within about 6mm of the same dynamic radius if I dropped 5% on the profile and went up to a 16" wheel (still 205mm wide). The question is whether this would adversely affect the sidewall stiffness (logically yes, but I'm told the OEM tyres were much stiffer than things like the Toyo T1-Rs that a lot of people use now...)
Chris71 said:
durbster said:
Having experienced first-hand what happens when you exceed a tyre's speed rating, I wouldn't recommend it.
I was driving on a snow tyre at 70mph on a dry motorway. 5 minutes into the journey we started discussing what speed a snow tyre would be rated to. Shortly afterwards it exploded in the most spectacular way a tyre can.
True, I've had tyre blowout too (fortunately on a test track) so I can confirm it's not pleasant. Without wishing to be facetious though I am talking about using the very next speed rating down on a similar performance-orientated summer tyre, not switching to a completely different type of tyre.I was driving on a snow tyre at 70mph on a dry motorway. 5 minutes into the journey we started discussing what speed a snow tyre would be rated to. Shortly afterwards it exploded in the most spectacular way a tyre can.
Bluebarge said:
What was the speed rating? Even the cheapest winter tyres these days are usually "T" rated (118mph)
Snow tyre - not winter tyre (it even had studs) 
Chris71 said:
Hi,
Would you use a tyre with a marginally lower speed rating than the car was originally designed for?
It's very difficult to get W-rated tyres in 15" sizes now and I'm wondering whether it really would be such a drama to go down to a V-rated tyre, good for a mere 149mph. I've got no intention of doing that sort of speed on the road and I suspect you'd be hard pushed to go that fast on a UK track day?
I realise that might sound like I've answered my own question, but are there any other factors to consider before going down in speed rating?
Chris
Just done this on my Audi, then accidentally found myself doing quite a bit over the speed rating, realised and slowed down, but as long as you don't exceed the speed rating you should be fine, and even if you do, you will probably be ok!!!Would you use a tyre with a marginally lower speed rating than the car was originally designed for?
It's very difficult to get W-rated tyres in 15" sizes now and I'm wondering whether it really would be such a drama to go down to a V-rated tyre, good for a mere 149mph. I've got no intention of doing that sort of speed on the road and I suspect you'd be hard pushed to go that fast on a UK track day?
I realise that might sound like I've answered my own question, but are there any other factors to consider before going down in speed rating?
Chris
Just check the load rating etc is ok, but there shouldn't be any issues!!
durbster said:
Chris71 said:
durbster said:
Having experienced first-hand what happens when you exceed a tyre's speed rating, I wouldn't recommend it.
I was driving on a snow tyre at 70mph on a dry motorway. 5 minutes into the journey we started discussing what speed a snow tyre would be rated to. Shortly afterwards it exploded in the most spectacular way a tyre can.
True, I've had tyre blowout too (fortunately on a test track) so I can confirm it's not pleasant. Without wishing to be facetious though I am talking about using the very next speed rating down on a similar performance-orientated summer tyre, not switching to a completely different type of tyre.I was driving on a snow tyre at 70mph on a dry motorway. 5 minutes into the journey we started discussing what speed a snow tyre would be rated to. Shortly afterwards it exploded in the most spectacular way a tyre can.
Bluebarge said:
What was the speed rating? Even the cheapest winter tyres these days are usually "T" rated (118mph)
Snow tyre - not winter tyre (it even had studs) OP... there must be hundreds of people using a lower speed rated tyre with no problems what so ever. Speed rating is just that. A quick google suggests they are tested for 10 mins or so at maximum speed ( may of changed ).Theres so many combinations of speed ratings and load indexes for thousands of different speed/weight of cars it would be impossible to cover every combination. If you're that worried about it upgrade your wheels to 16s/17s/18s.
BeeRoad said:
Two things to bear in mind with tyre speed ratings:
1) Speed ratings are about far more than how fast you can drive before they explode. Fitting 116mph rated tyres on a car designed for 149mph rated tyres because you never intend to exceed 115mph does not work. Speed rating takes into account weights, accelerative and braking forces and many other factors when chosen for the car.
2) Your insurance company will probably be quite unhappy about this when you inform them and very unhappy about it if you don't and then make a claim.
Just out of interest, what size are you needing?
Are you sure about point 1? Load index covers the weight, and I can't see how you can reliably link a car's top speed (and therefore its tyre rating) to its accelerative capability. If that were the case, there would surely be horsepower ratings? 1) Speed ratings are about far more than how fast you can drive before they explode. Fitting 116mph rated tyres on a car designed for 149mph rated tyres because you never intend to exceed 115mph does not work. Speed rating takes into account weights, accelerative and braking forces and many other factors when chosen for the car.
2) Your insurance company will probably be quite unhappy about this when you inform them and very unhappy about it if you don't and then make a claim.
Just out of interest, what size are you needing?
From my understanding, the tyre rating is literally just the maximum speed that the tyre can sustain for a given period without failing, but if you know better than me I'm happy to concede.
Point 2 is valid though, insurance don't like under-rated tyres, and there could be a legality issue under the construction and use regs.
The Wookie said:
BeeRoad said:
Two things to bear in mind with tyre speed ratings:
1) Speed ratings are about far more than how fast you can drive before they explode. Fitting 116mph rated tyres on a car designed for 149mph rated tyres because you never intend to exceed 115mph does not work. Speed rating takes into account weights, accelerative and braking forces and many other factors when chosen for the car.
2) Your insurance company will probably be quite unhappy about this when you inform them and very unhappy about it if you don't and then make a claim.
Just out of interest, what size are you needing?
Are you sure about point 1? Load index covers the weight, and I can't see how you can reliably link a car's top speed (and therefore its tyre rating) to its accelerative capability. If that were the case, there would surely be horsepower ratings? 1) Speed ratings are about far more than how fast you can drive before they explode. Fitting 116mph rated tyres on a car designed for 149mph rated tyres because you never intend to exceed 115mph does not work. Speed rating takes into account weights, accelerative and braking forces and many other factors when chosen for the car.
2) Your insurance company will probably be quite unhappy about this when you inform them and very unhappy about it if you don't and then make a claim.
Just out of interest, what size are you needing?
From my understanding, the tyre rating is literally just the maximum speed that the tyre can sustain for a given period without failing, but if you know better than me I'm happy to concede.
Point 2 is valid though, insurance don't like under-rated tyres, and there could be a legality issue under the construction and use regs.
Point 2. Its quite common in TVR circles to fit V rated tyres to the front of Griffs and Chims and the insurance companies are fine with it if you ask them first.
I did a lot of research on this lately and it seems that (as usual) we in the UK are unusual in europe that we fall for the "must maintain the speed rating" marketing scam by the tyre manufacturers and fitters. In the rest of europe they buy the speed rating for the fastest they expect to drive - and there's little reason anyone in the UK needs a tyre rated to do 50mph more than the car is capable of - which is often the case.
As for insurance, they will try to protest, but so long as the tyre will pass an MoT then they have no legal standing to refuse a claim unless they proved you were exceeding the speed rating...they can't simply dismiss a claim because of speed rating.
So I would say as long as you are sensible you could evaluate the speed rating used and go down a band.
As for insurance, they will try to protest, but so long as the tyre will pass an MoT then they have no legal standing to refuse a claim unless they proved you were exceeding the speed rating...they can't simply dismiss a claim because of speed rating.
So I would say as long as you are sensible you could evaluate the speed rating used and go down a band.
I run Vs on the front of my Chim for the same reason and the insurance are fine,but the thing to remember in all of this is if you had an accident at say 110mph on an UK motorway on correct rated tyres would the insurance company still payout considering the speed you were going and according to the BIB not in a legal manner,i don't wish to try!
P
P
jvr said:
I run Vs on the front of my Chim for the same reason and the insurance are fine,but the thing to remember in all of this is if you had an accident at say 110mph on an UK motorway on correct rated tyres would the insurance company still payout considering the speed you were going and according to the BIB not in a legal manner,i don't wish to try!
P
True, I guess the problem arises if they're so anal that they try and wriggle out of it in a low speed accident that could be linked to grip. It's not beyond the realms of possibility that a mainstream insurer would try, but I can imagine the specialists might be more realistic.P
Unlike many cars specced with V rated tyres or above mine should genuinely exceed the 149mph rating if I find a long enough runway, but I don't particularly intend to try. If nothing else it feels like it would take off before you got too far into double figures - think I might need to check the splitter.
ETA: Coincidentally, never looked to see what it's on currently. Only bought the car recently and always intended to swap the wheels over.
Edited by Chris71 on Monday 22 November 14:26
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