Saabscene Saab Forum - Saab Technical Information Resource banner
1 - 10 of 10 Posts

·
Registered
Joined
·
561 Posts
Discussion Starter · #1 ·
I'm sure this has been touched on before, but I can't find it now.
Does anyone have any knowledge or experience about this:-
Can you put a lower speed rating tyre on your car if:-
1 The rated speed is higher than your car's maximum
2 70mph is the fastest your can legally drive in UK anyway.

What is the actually different between an H and V rated tyre of the same type? I know it can run faster safely, but has it got more rubber, more inner steel cords ??
Does a higher speed rating also mean other improved properties too?
 

·
Registered
Joined
·
2,928 Posts
H = not more than 210 kph (~130 mph)
V = not more than 240 kph (~149 mph)

As speed ratings increases, so does the stiffness of the tyre, especially the sidewalls. It's the flexing of the tyre that produces heat and leads to tyre failure. So if you want to go fast (more load cycles per second) you need a stiff tyre that stays cool.

I recently had a discussion with a traffic plod about speed ratings. His view was that as long as the rating was greater than 70 mph and you didn't go faster than 70 mph, you would not be prosecuted (in the UK, obviously!!!!). The problem is with insurance companies saying "not the manufacturers specification" = "no pay out".
 

·
Registered
Joined
·
1,908 Posts
Just to re-iterate Marks last point for sake of importance...:

Technically and legally your insurance won't be valid if you put a lower rated tyre on your car than that specified in the hand book by the manufacturer!

Some tyre fitters won't fit a lower spec tyre than rated by the manufacturer. They claim it is because it's illegal, but I suspect profit margins may have something to do with it as well?!

I would be interested to hear of any cases where an insurer has copped out for this reason - but having to fork out £340 each year for an invalid insurance policy would be rather galling!!


Based on above feedback, instead of a small financial saving, I'd definately opt for not less than the manufacturers spec or 'higher' rated tyres, due to improved safety (i.e. reduced braking distance), irrespective of how fast I drove the car. Having to brake hard can happen to any type of driver, and reduced stopping distance could at least save you your insurance 'excess' and alot of hassle!
 

·
Registered
Joined
·
11,343 Posts
Surely the manufacturer sets a "specifcation" for a reason and not on a whim. Therefore, it is reasonable to conclude that fitting items that do not meet the manufacturer's specifcation are possible to be compromise the ability of the vehicle. Is that fair?
 

·
Registered
Joined
·
1,908 Posts
Agreed.

Which makes me think that speed isn't the only factor which would cause a manufacturer to spec a higher speed rating a step or two higher than a car may even be capable of achieving.

Vehicle weight will obviously have a direct bearing on how stiff/strong the tyres need to be, in order to achieve a specific safe performance level.
 

·
Registered
Joined
·
4,427 Posts
It's all a bit dodgy this. If you fit winter tyres, or even more so if you fit M&S tyres, you're unlikely to match the speed rating, but in current conditions these will surely be a safer proposition than the OEM spec?

The safety aspect is also to do with the Load Index of the tyre - possibly more so than speed rating. When I fitted conti sport contacts to the Barge I accepted that I would have a lower speed rating (V instead of W) but as they were the reinforced variant of the tyre, which only came in a V, I felt it was a better case than getting the W rated regular tyres which experience has shown just aren't up to the stick I give them in a very heavy car.

I can't see an insurer using this argument successfully unless the tyres are so patently unsuitable as to be unsafe - if you put crappy S or T rated remoulds on a powerful car then it's just plain daft, but dropping from V to H or Z to W etc isn't really going to be a genuine safety issue unless you are going to drive at a sustained very high speed.

You could buy a cheapo Z rated tyre which was far less grippy than a decent W. QED.

I've said it before when it comes to the "Safety Police" - we all have to make compromises on our cars at times, you just have to get the best you can afford. If we took NO risks then we'd never venture off the drive.
 

·
Registered
Joined
·
1,411 Posts
Originally posted by Fliptop:
[qb]I can't see an insurer using this argument successfully[/qb][/b]
I don't think it matters much. None of us can afford to sue the insurer to get them to change their mind and pay up.

If you want to use tyres of a lower rating than they're telling you too, then you would be wise to inform them first. It's certainly a notifiable change, and not notifying them will allow them to invalidate your insurance, regardless of whether it's actually safer or not - it's not making an inappropriate change that invalidates it, it's not telling them
 

·
Registered
Joined
·
2,928 Posts
A couple of points.

W and Y speed ratings have superceded the old Z "as fast as you like rating" as follows:

Speed Category "VR" For vehicles having speed capability over 210 Km/h (e.g. 195.50 VR 15)
Speed Category "ZR" For vehicles with a speed capability over 240 Km/h (e.g. 205.40 ZR 17)
Speed Symbol "V" For vehicles with a speed capability not exceeding 240 Km/h (e.g. 225.55 R 15 91V)
Speed Symbol "W" For vehicles having speed capability not exceeding 270 Km/h (e.g. 225.60 R 15 96W)
Speed Symbol "Y" For vehicles having speed capability not exceeding 300 Km/h (e.g. 275.40 R 18 94Y)
ZR+ Speed Symbol "W" Tyres marked with both designations for vehicles with speed capability over 240 Km/h but not exceeding 270 Km/h
ZR+ Speed Symbol "Y" Tyres marked with both designations for vehicles with speed capability over 240 Km/h but not exceeding 300 Km/h

The load rating, eg 91, defines the maximum load that the tyre may carry at its maximum speed.

As for winter tyres, the manufacturers state a winter tyre. For my MY94 car it is 195/65 HR 15, as opposed to the summer options of 205/60 ZR 15 or 205/55 ZR 16. So it is clearly defined. However that was in 1994. Now you can get V rated winter tyres, so I could use 205/55 VR 16 M&S tyres when I go skiing. The original winter tyre size is one size narrower than the summer tyres to allow fitment of snow chains without hitting the wheel arch liners. The whole issue of winter tyres is difficult in the UK as it is unusual and outwith insurers thinking, compared with various Euro lands where it is clealry defined in law, eg in Germany you must have a reminder sticker in front of the driver showing the reduced speed rating. In other countries this is not required as even H rated tyres exceed the motorway speed limit.

Fun isn't it?
 
1 - 10 of 10 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top