Getting to know your tyres

Questions and answers on steering, suspension, bush replacement, wheels, tyres and much more

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Liquid
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Post by Liquid » Sun Dec 10, 2006 1:19 am

118118 wrote:Here's a thought also.

I had to put my old wheels in the loft tonight and I found that cheap tyres are much heavier than good tyres, therefore they can hamper performance on that level also.
I neglected to go into it at this stage, as it could be considered too geeky lol

There is a sizeable difference between budget, mid range and premium tyres where weight and rolling resistance is concerned. Whilst it may not be appreciated by most drivers, these are two hugely important factors.

Naturall, a lighter tyre aids unsprung weight. An budget tyre of a typical size (say 215/45R17) can be upto 2 kilos heavier than a premium tyre. Obviously, that's 8 kilos overall if you don't include the spare. The effort to drive the extra weight of four of these tyres, is quite considerable.

The other factor is rolling resistance. Whilst this is more prevalent in the transport industry, it is still high on the list of priorities for passenger vehicles, due to the need to reduce fuel consumption.
Based on an unaided (undriven) rolling test, one particular tyre managed to gain over an extra 50 metres compared to it's predecessor in a standard run.
Go tell that long tongue liar. Go and tell that midnight rider. Tell the rambler, the gambler, the back biter.
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Post by caboosemoose » Sun Dec 10, 2006 3:56 am

Is it really true that tyour insurance is void if you are using mixed tyres on the same axle?

Personally, although I would not choose to run mixed tyres on a single axle on most occasions, I generally think that the dangers of doing so are usually overstated. If you think about driving in wet or damp conditions, the difference in available grip, side to side, can be hugely variable, regardless of what tyres you are using - much more variable than the relatively small difference in grip and other characteristics that results from using two different tyres on the same axle. Even when road conditions ae dry there are a huge number of factors that can lead to a large grip or stability differential, side to side, even if you are using matched tyres. I think you'd be hard pressed in most circumstances to notice the impact of mixed tyres on your car's stability.

To be clear, I obviously favour using matched tyres and I'm not suggesting that anyone should actually do anything else or saying that Liquid's excellent advice isn't generally worth following. But I personally don't think that mixed tyres are a that big deal in safety terms - the style 32 rims I bought have mixed rear tyres with lots of tread of them, so I am going to run them over the winter and replace them in the spring. I really don't think there's any point in changing them now.

Having said all that, I would probably be a lot less comfortable with running mixed tyres on the front axle...
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amir328i
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Post by amir328i » Sun Dec 10, 2006 12:12 pm

how much does a decent pair of 18" tyres cost? :lol:

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Post by caboosemoose » Sun Dec 10, 2006 1:13 pm

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Post by Raj24v » Sun Dec 17, 2006 10:24 pm

Good read there Liquid, very informative.
I already knew abit about them but the constituents and construction were all new to me.

I think you've got that 'wierd' love for tyres just as I do! :oops: :lol: :wink:
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Post by Liquid » Mon Dec 18, 2006 1:54 am

caboosemoose wrote:Is it really true that tyour insurance is void if you are using mixed tyres on the same axle?

Personally, although I would not choose to run mixed tyres on a single axle on most occasions, I generally think that the dangers of doing so are usually overstated. If you think about driving in wet or damp conditions, the difference in available grip, side to side, can be hugely variable, regardless of what tyres you are using - much more variable than the relatively small difference in grip and other characteristics that results from using two different tyres on the same axle. Even when road conditions ae dry there are a huge number of factors that can lead to a large grip or stability differential, side to side, even if you are using matched tyres. I think you'd be hard pressed in most circumstances to notice the impact of mixed tyres on your car's stability.

To be clear, I obviously favour using matched tyres and I'm not suggesting that anyone should actually do anything else or saying that Liquid's excellent advice isn't generally worth following. But I personally don't think that mixed tyres are a that big deal in safety terms - the style 32 rims I bought have mixed rear tyres with lots of tread of them, so I am going to run them over the winter and replace them in the spring. I really don't think there's any point in changing them now.

Having said all that, I would probably be a lot less comfortable with running mixed tyres on the front axle...
Bit late in responding to this

The bottom line is balance. There will be very few situations where the conditions experienced by the car will be different from one side of the vehicle, to the other.
Maintaining the same tread pattern will minimise the risk of any shortcomings due to the environment. Differing trewad depths are also very important. A difference of 3mm and over between axle pairs have a huge affect on braking ability and water clearance.

Granted with most modern high level cars, on board computers will calculate many variables in order to appropriate the required power to each wheel, so this does minimise the issues to a degree.
It's common sense to a degree, that the same tyres should be worn on each side. Not everyone will notice the difference and not everyone has the capability of pushing their cars to the limits where the differences can be found, but there is irrefutable evidence that matched pairs are far less likely to see you in trouble on the road. These are the findings that our insurance compaines pay a lot attention to.

As far as legalities are concerned, insurance companies will investigate this area thoroughly if an accident is believed to hold the tyres as a contributory factor. Like your yearly premium, every insurer is different. With road safety getting increased funding and public awareness, it will only be a matter of time before some concrete legislation will be passed in favour of these sorts of actions.

As an example, Porsche have a series of tyres that are specific for their cars from all manufacturers. These have the denotion N0, N1, N2 and N3. They have a directive whereby all the four tyres must be exactly the same on their vehicle (save for sizes on wider rears) otherwise their warranty is invalidated.
Imagine how annoying that will be when 6 months after someone buys their 911 Turbo, their N2 tyre pops and all that is available is N3's. That's four new tyres and a light wallet for Mr 911.
Go tell that long tongue liar. Go and tell that midnight rider. Tell the rambler, the gambler, the back biter.
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Post by caboosemoose » Mon Dec 18, 2006 4:12 pm

Liquid wrote:There will be very few situations where the conditions experienced by the car will be different from one side of the vehicle, to the other.
I guess it depends on how you look at it. From my point of view, the available grip on each side will never be exactly the same. And in my opinion it will often be highly variable when you take into account different road surface cambers side to side, maybe a patch of loose material, a damp area and so forth. Likewise, even the slightest bump on one side or the other will mean a big difference in tyre loadings and therefore grip. There are loads of factors that can contribute to a big difference in available grip, side to side.

I'm not tyring to say it's fine to use mixed tyres. I just think that it's a case of it being preferable / optimal to use the same tyre on each side rather than a major safety concern.
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Post by Hookdex » Mon Dec 18, 2006 4:46 pm

Anyone know where i can find out how much PSI i should have in my tyres. My car only came with 17s so now I have 18s i dont know what to put in them.
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Post by amir328i » Mon Dec 18, 2006 11:19 pm

ye same as, i have 18 inch azevs on my car with 225/40/18z written on the tyre, i'm not sure what psi i should keep them on? could any 1 help please? :(
does 32 psi sound right??? :wink:

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Post by Liquid » Mon Dec 18, 2006 11:21 pm

You're both looking at between 36-38 psi
Go tell that long tongue liar. Go and tell that midnight rider. Tell the rambler, the gambler, the back biter.
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amir328i
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Post by amir328i » Mon Dec 18, 2006 11:44 pm

is that 38 psi on all 4 tyres?

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Liquid
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Post by Liquid » Mon Dec 18, 2006 11:45 pm

Providing they are all the same size, yes

The surefire way is checking with cars that have those tyres as an OE fitment (E46 etc)
Go tell that long tongue liar. Go and tell that midnight rider. Tell the rambler, the gambler, the back biter.
Tell 'em that God's gonna cut you down.


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amir328i
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Post by amir328i » Tue Dec 19, 2006 11:26 am

thanks alot for the info liquid :smt023

Hookdex
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Post by Hookdex » Tue Dec 19, 2006 1:16 pm

Liquid wrote:Providing they are all the same size, yes

The surefire way is checking with cars that have those tyres as an OE fitment (E46 etc)
Where might i find this information? Have searched for it and could only find details for 15" e46 wheels. Thanks for your help mate.
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its not big, its not clever, and even if you win you're still retarded.

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Liquid
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Post by Liquid » Tue Dec 19, 2006 2:27 pm

The 330 came on 18's as standard, as did the M3

You need to have exactly the same tyre size and profile as stated in the BMW literature. This information is in the user handbook and the information included is generic, so you will find it in the book from any model
Go tell that long tongue liar. Go and tell that midnight rider. Tell the rambler, the gambler, the back biter.
Tell 'em that God's gonna cut you down.


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