Query / Advice re: new tyre on Vauxhall Astra

jase1

Most budget tyres are of passable quality -- the press concentrates on the very small number of truly bad tyres on the market.

It wouldn't take much to tighten up the rules either -- the reasonable tyres are typically only a couple of quid more expensive (if they are even any dearer at all) than the bad ones.

sinbad182

AdrianC wrote: »

...until somebody steps out in front of you, and then you find that it just locks up...

I assume you know more on the subject than me so I'll take your word for it, but the way your average motorists drive around town (ie. on autopilot) I cant help but think the tyre wouldnt make any difference in a freak, random occurrence like that. I'd imagine the sophistication of the cars ABS system would probably be more important.

There are some truly, truly horrible "budget" tyres out there - I've lobbed quite a few new and near-new off cars I've bought, transforming the way they drive.

Have to disagree here - again, looking at your average motorist doing a mixture of pootling round town and the odd dual carriagway/motorway, there is no way they are going to notice any difference between tyre brands. I certainly don't, and im a bit more into cars than some. Of course, this will be different for a real motoring enthusiast, or someone with a performance car, or who drives 'progressively'.

As for "reputable source" - you ought to see the Chinese telfon/concrete rubbish (mismatched front/rear) that the main dealer put on my mother's car at service. When they said "new tyres" to her, she assumed they'd be the same brand as OEM. Uh-uh.

I'd have assumed the same too, so thats pretty shoddy practice!

AdrianC

sinbad182 wrote: »

I assume you know more on the subject than me so I'll take your word for it, but the way your average motorists drive around town (ie. on autopilot) I cant help but think the tyre wouldnt make any difference in a freak, random occurrence like that. I'd imagine the sophistication of the cars ABS system would probably be more important.

ABS intervenes when the tyres lock. It releases, then reapplies the brakes. ALL OF THEM. Not just the one wheel that's locked - because that'd quickly see you turning sharp left if just one side was on wet leaves, say. It'll bring the stopping distance down to somewhere around the minimum possible. BUT that minimum possible is governed by the amount of grip available, which - so long as the brakes are good enough to lock the tyres - is entirely governed by the tyres. And it's the tyre with least grip that's the relevant one.

Slam the anchors on on dry tarmac, and the stopping distance is far shorter than on wet tarmac, which is far shorter than on mud or ice. That's obvious, yep? Not because the brakes or the ABS are any different, but solely because the tyres have less grip. Exactly the same when you take some decent tyres off and shove the cheapest rubbish possible on.

http://www.tyreblog.co.uk/2010/information-safety-risks-buying-cheap-budget-tyres-517
Wet stopping distance from 70mph - Best, 60m. Worst, 83m...

23m is one heck of a big difference. Damn near 40%. I wonder what the impact speed would be, if the car on the best tyres had stopped JUST short of the obstacle? Extrapolating the HC stopping distances, probably somewhere around 35-40mph. Ouch.

colino

AdrianC you might want to revisit your belief that ABS releases and reapplies all of the brakes when one stops rotating. Perhaps an early Lada design?

AdrianC

colino wrote: »

AdrianC you might want to revisit your belief that ABS releases and reapplies all of the brakes when one stops rotating. Perhaps an early Lada design?

Go and try it some time. Get the tyres on one side in nice slippy mud, and slam the anchors on.

Rodney_Trotter

AdrianC wrote: »

ABS intervenes when the tyres lock. It releases, then reapplies the brakes. ALL OF THEM. Not just the one wheel that's locked - because that'd quickly see you turning sharp left if just one side was on wet leaves, say. It'll bring the stopping distance down to somewhere around the minimum possible. BUT that minimum possible is governed by the amount of grip available, which - so long as the brakes are good enough to lock the tyres - is entirely governed by the tyres. And it's the tyre with least grip that's the relevant one.

Slam the anchors on on dry tarmac, and the stopping distance is far shorter than on wet tarmac, which is far shorter than on mud or ice. That's obvious, yep? Not because the brakes or the ABS are any different, but solely because the tyres have less grip. Exactly the same when you take some decent tyres off and shove the cheapest rubbish possible on.

http://www.tyreblog.co.uk/2010/information-safety-risks-buying-cheap-budget-tyres-517
Wet stopping distance from 70mph - Best, 60m. Worst, 83m...

23m is one heck of a big difference. Damn near 40%. I wonder what the impact speed would be, if the car on the best tyres had stopped JUST short of the obstacle? Extrapolating the HC stopping distances, probably somewhere around 35-40mph. Ouch.

Are you trying to claim a vehicle on the worst tyres in that test on a wet road would impact at 40mph, having taken your data only from the Highway Code stopping distances?

Rodney_Trotter

AdrianC wrote: »

Go and try it some time. Get the tyres on one side in nice slippy mud, and slam the anchors on.

The side on the slippy mud won't stop as quick. That's a fact.

However it will stop a lot quicker than all four on mud.

You claim braking is only as good as the worst tyre grips but you don't account for the factors of the three better ones.

Rodney_Trotter

Stooby2 wrote: »

It doesn't matter if the tyre sppeds differ, so long as they are able to cope with the speeds the vehicle is capable of. According to the website below, V and W are for 149mph and 168mph respectively, so I'm guessing you're probably going to be ok!

http://www.ctyres.co.uk/tyre_info/Speed_ratings.html

AdrianC read this.

That's the difference in rating the OP asked about and the maximum speed limit is 70.

AdrianC

Rodney_Trotter wrote: »

Are you trying to claim a vehicle on the worst tyres in that test on a wet road would impact at 40mph, having taken your data only from the Highway Code stopping distances?

Did you bother to read the linked article?

charliedog000

Thanks to one and all for your replies.

In the first instance (because I didn't know any better) I was just worried whether having V's on the front and W's on the rear would compromise safety. General consensus of opinion would seem to suggest it would not?

When I'm home tomorrow I'll have a look at the handbook and providing the V and W exceed the minimum stated recommendation then I think I'll put a W on the front and start the merger towards getting all 4 on 205/50/R17 91W

Cheers