tin top tyre rating q
02GF74 - 25/2/14 at 08:43 PM
volvo 850 t5 - top speed listed as 149 mph
just checking that speed rating of W (max 168 mph) will be ok?
britishtrident - 25/2/14 at 08:50 PM
quote:
Originally posted by 02GF74
volvo 850 t5 - top speed listed as 149 mph
just checking that speed rating of W (max 168 mph) will be ok?
I think you have answered your own question.
Max speed 147mph so v rating is also OK.
Slimy38 - 25/2/14 at 09:51 PM
I've never understood tyre ratings in terms of their use in the real world. Yes I can understand at type approval time your tyres must exceed the
speed of your car, but in a country that frowns on speeds greater than 70, is it actually necessary to go for the higher rating tyres?
It became apparent to me when searching for high rated winter tyres. I don't even think you can get w rated winter tyres, but even if you can
would you want to do 168mph on snow? So you're forced to put tyres on that are below the rating of your car.
morcus - 25/2/14 at 10:17 PM
same, I had to buy V rated tyres for the Vectra because on paper it was capable of 140mph and thats all they'd let me had and the garage claimed
it was the law. The car never went faster than 80 the entire time I had it.
coyoteboy - 26/2/14 at 04:30 AM
It's an interesting connundrum. It's only ever going to be an issue if your tyres suitability are called into question when you have an
accident, it's not illegal to run lower speed rating (unlike load index) I don't think.
snapper - 26/2/14 at 06:31 AM
You have to understand the whole construction of the tyre and the loads of acceleration, braking & cornering not just the speed rating of the
tyre
As most laws now are European any car could simply drive to Germany and exceed any speed it would have done in the UK
It does worry me that people on this site who are building or driving high performance cars would not have a deeper understanding of tyre ratings
Slimy38 - 26/2/14 at 08:34 AM
quote:
Originally posted by snapper
You have to understand the whole construction of the tyre and the loads of acceleration, braking & cornering not just the speed rating of the
tyre
As most laws now are European any car could simply drive to Germany and exceed any speed it would have done in the UK
It does worry me that people on this site who are building or driving high performance cars would not have a deeper understanding of tyre ratings
I wouldn't necessarily call my tintop high performance! It might have a book top speed of 145mph, but even if it could still get there I
wouldn't want to drive it that fast. And I also don't have enough faith in my own abilities to put it under any sort of stress in
acceleration or braking (and it corners like a blancmange).
I agree with the 'potential' of it going to another country, and if my daily commute included a German Autobahn then yes I'd start
using higher rated tyres. My kit car will probably get higher rated tyres than my tintop, as that is likely to get the sort of use you're
suggesting.
I wouldn't use a tyre with a lower load rating, and I always aim for four of the same tyre, but I've no problem using H rated tyres rather
than the Z that is recommended for my car.
mcerd1 - 26/2/14 at 11:09 AM
the speed ratings themselves aren't that straightforward either - they are only rated to to the quoted max. speed for a limited time (10min) and
I think thats tested at less than full load too
I think that's partly why you get odd cars like my focus's that according to ford need V ratings (for 120 - 125 mph cars), yet the same tyre
size on my mates astra apparently only needs to be an H....
(both 205/55 R15 with a 91 load rating)
obviously you can use a lower rated tyre, but it comes into construction and use regs - which insurance companies will use to avoid paying out 
if you look at what some manufacturers say about speed ratings for winter tyres which are nearly always a lower rated tyre
eg - ford official advice:
"Winter tyres have a lower speed rating than standard summer tyres. However the lower speed rating should be adequate in winter conditions – for
example dropping down from a V rating (max 149 mph) to an H rating (max 131 mph).
While winter tyres should reduce the risk of accident when temperatures drop below 70C, their fitment may be viewed as a modification. They should be
in line with the motor manufacturer’s specification and fitted by a reputable dealer. Although fitment of winter tyres should not affect your
insurance premium, it is best practice to notify your insurance company"
britishtrident - 26/2/14 at 12:15 PM
A speed rating is nothing to do with cornering or acceleration, in fact it use to be the case and may still be in some cases the tyres with a higher
speed rating have less grip than lower speed rated tyres because of the rubber compound used.
Essentially the speed rating is the maximum speed the tyre manufacturer is prepared to certify the tyre will sustain under rated load for the
specified time.
The tyres are tested in a roller machine, when the test rig reaches a. speed that the tyre cannot maintain the first sign of failure is normally large
chunks of tread breaking off from the harder carcase rubber below the tread.
Of course if the tyre is overloaded or under inflated it will overheat and result in a blow out.
[Edited on 26/2/14 by britishtrident]
Slimy38 - 26/2/14 at 02:39 PM
quote:
Originally posted by mcerd1
While winter tyres should reduce the risk of accident when temperatures drop below 70C, their fitment may be viewed as a modification. They should be
in line with the motor manufacturer’s specification and fitted by a reputable dealer. Although fitment of winter tyres should not affect your
insurance premium, it is best practice to notify your insurance company"
A little off topic, but this subject came up last time the snow dropped, and most news reports who interviewed insurance spokespeople said that they
don't consider it a modification. Having said that, you're absolutely right, I do wonder whether they'd change their mind if they had
to payout, particular if it's a rear end because the owner of the winter tyres was able to stop a fair bit quicker than normal.
mcerd1 - 26/2/14 at 03:11 PM
quote:
Originally posted by Slimy38
....Having said that, you're absolutely right, I do wonder whether they'd change their mind if they had to payout, particular if it's a
rear end because the owner of the winter tyres was able to stop a fair bit quicker than normal.
so imagine what they'd say if they found you had the incorrect summer tyres on
[Edited on 26/2/2014 by mcerd1]
morcus - 26/2/14 at 05:24 PM
I thought the modification issue was the wheels?
coyoteboy - 26/2/14 at 05:31 PM
quote:
You have to understand the whole construction of the tyre and the loads of acceleration, braking & cornering not just the speed rating of the tyre
As most laws now are European any car could simply drive to Germany and exceed any speed it would have done in the UK
It does worry me that people on this site who are building or driving high performance cars would not have a deeper understanding of tyre ratings
With respect, I think you're over-egging it a little here. Load index is related to tyre load (including expected impacts, accelerations and
cornering events), and dictates sidewall and ply construction. Speed rating also dictates construction but, as explained above, is simply a speed
which the tyre can sustain for a fixed period without disintegrating. Load index is far closer to what you're worrying about (two tyres with the
same speed rating may have vastly different load ratings) and tyre construction is a different issue again.
Assuming you pick a tyre with the correct (and that can fall in a band) load rating and don't exceed the tyre's speed rating, you will have
no mechanical issues, other than questions from the plod. However, if placing an under-(speed)rated tyre on a car, one might be considered negligent
or responsible if the tyres failed in use at higher speeds.
Whether the load and speed ratings affect grip and/or ride quality is a whole different matter, it's not UNSAFE to use a lower speed rated tyre
at UK legal speeds.
And to be honest, it's hardly surprising most folk don't understand tyre law and construction detail - I've never spoken to a tyre
fitter who agreed with the last over ratings, construction, or knew anything about suspension geometry and its effects, so it's not surprising
Joe Public doesn't either.
[Edited on 26/2/14 by coyoteboy]