Mixing tyre speed ratings

[Patrick Bateman]

Does this make one iota of difference in reality when you're talking about ratings that are way above actual speeds I'm going to travel at?

Currently have Y rated tyres on the car but have a nail in the sidewall of one of the new ones only fitted 2 months ago.

H rated tyres are available now and are cheaper or I can wait on Y ones.

[Dave Hedgehog]

ask your insurance co if it affects the policy

not sure on speed rating but i have been told by an insurance if XL is manufacture spec they must be XL rated

[wpa1975]

Dave Hedgehog said:

ask your insurance co if it affects the policy

not sure on speed rating but i have been told by an insurance if XL is manufacture spec they must be XL rated

Correct, if you had an accident it could get interesting if they are not the correct spec.

[brillomaster]

depends what car it is, i think insurers get funny if the tyre speed rating doesn't cover the top speed of the car. H rated is only good for 130mph.

you can overspec a tyre (ie Y rated tyres on a Micra), but you shouldnt underspec it (ie H rated tyres on a Mclaren)

[donkmeister]

It's an interesting point though... Even an H-rated tyre is rated for 130mph, so for an accident taking place within the UK is it going to be a valid reason for insurers to get sniffy? If you crashed at 130+ they'd be concerned about your driving more than the tyre spec, presumably.

I've had Costco get funny about installing Y-rated tyres on a car that had lesser tyres before... They're odd like that, mind.

[Rich1973]

Insurance companies will get much more sniffy about load rating than speed rating.

[Pica-Pica]

Speed ratings are as much to do about longitudinal and lateral acceleration loading as they are about speed, otherwise we would ALL be driving at a speed rating of T.

Keep to the minimum speed rating as shown on the door label.

Note: a space-saver will often be a T rating, but it has a speed sticker on it too.

[scorcher]

Pica-Pica said:

Speed ratings are as much to do about longitudinal and lateral acceleration loading as they are about speed, otherwise we would ALL be driving at a speed rating of T.

Keep to the minimum speed rating as shown on the door label.

Note: a space-saver will often be a T rating, but it has a speed sticker on it too.

Taken from the Uniroyal website………
How is the speed rating calculated? Speed ratings are based on laboratory tests in which the tyre is run at 6.2 mph steps, in 10 minute increments, until the required speed has been met. To receive its rating it must demonstrate that it can sustain a particular speed when tested with simulated loads.

[Pica-Pica]

scorcher said:

Pica-Pica said:

Speed ratings are as much to do about longitudinal and lateral acceleration loading as they are about speed, otherwise we would ALL be driving at a speed rating of T.

Keep to the minimum speed rating as shown on the door label.

Note: a space-saver will often be a T rating, but it has a speed sticker on it too.

Taken from the Uniroyal website………
How is the speed rating calculated? Speed ratings are based on laboratory tests in which the tyre is run at 6.2 mph steps, in 10 minute increments, until the required speed has been met. To receive its rating it must demonstrate that it can sustain a particular speed when tested with simulated loads.

To repeat, there is more to a speed rating than just speed.
Continental tyres:
‘ In addition to top speed, the letter also provides information about driving comfort, traction, wear and corner stability. Higher index tyres generally offer better grip and braking performance, but may wear out faster and offer lower performance in cold conditions. As a result, V-, Z-, W- and Y- indexed tyres are generally more suitable for sports and high-performance vehicles that operate in warmer climates.

To obtain better tyre performance, you can fit your vehicle with tyres that have a higher speed index. But when you choose a lower index, you automatically reduce the maximum permitted speed of your car to the value specified for that index.’

The AA
‘ But it’s not just about speed. The rating also relates to:
Ride comfort
Tread wear
Traction
Cornering ability’