Wheels/alloys/tyre sizes

[kalniel]

Thanks for the replies

ok...from the top:
As the tyre gets widers, you do not get extra grip. Trust me. Extra width does not a grippy tyre make!

Why not? Remember it's not just friction here, we're talking about adhesion - there's chemical bonding between the tyre and the road. A wider contact patch means more hydrogen bonds and more grip.

BUT...with wider tyres you also need to get a lower profile, hence the 75 needs to go down frationally to make sure your speedo reads roughlt right.

Yeah I was looking at that - I could get 185/65 and it's only a difference of 0.7%.

I'd suggest that you are suffering understeer because you wang the steeering wheel around too fast and expect the laws of physics to leave you alone for a split second... It wont happen

MkIV ashtrays (of which my lass Sair has one) have Electronic Power Steering, and it's quite light, and fairly fast. That means you're asking too much of those tryes for the weight of car.

I never wang the steering wheel around thank you The problem is either under acceleration away from a roundabout where the weights transfered away from the front tires (and I'm spending a portion of the grip quota on forward acceleration) and sharp roundabout where you have to make a sharp turning angle and have little room to start a smooth turn which would balance the car better

Also you'd have to try my car.. the steering is far from light - it's the heaviest power steering I've tried, certainly heavier than an R reg mondeo, W fiesa, Volvo V40, 52reg mondeo, vectra etc.

If you are serious about getting more grip, and not about looking cool...

I drive an astra remember. Looking cool is out of the question

get some Yokohama 14" tyres. 185/65 or similar. Your speedo wont be far out (fractions of a mile per hour) and you will die of shock at the grip once warm.

Guess I'm asking for the impossible - more grip, good wear rates and not much reduction in rolling resistance (going from 175 to 185 is likely to only give 1-2% worse fuel consumption).

So I guess the question now is: can I fit 185's on my normal rims? I mean, I'm sure I can but won't that have a detrimental effect because the tyre will be pinching in at the rim?

Wider tyres have a bigger footprint - this reduces the amount of pressure the car's weight puts on the road, which has the effect of increasing the tyre's life as it's not working so hard - regardless of grip, a narrow tyre will work much harder at a given speed than a wider tyre made of the same compound - smaller footprint, more pressure

The force/pressure arguement only takes into account friction, it doesn't allow for chemical adhesion. While the friction of the whole tyre remains mostly similar due to the reduction in force/area, the adhesion increases due to the larger contact area for chemical reaction. Imagine glueing a piece of card down - the larger the area of card that you can glue to the floor the stronger the grip. Or better, imagine glueing a square table leg to the floor - compare glueing the base of the leg so that it's vertical and pulling that. Now consider lying the leg horizontally and glueing the whole side to the floor. When it's on it's size the larger contact area with glue is going to give more grip.

Incidentally trains do use the friction arguement - there's no chemical reaction between steel and iron etc. (that's relavent at least )

edit: I'm currently running 175/70 14inch T michellin energy greenX. Great fuel economy and wear rate granted. I was thinking about getting something like conti premium contact, which I'd have to get in 185/65 anyway.

[kalniel]

Oh.. found a nice page with some useful information here:

http://www.carbibles.com/tyre_bible.html
(which completely blows away my idea of adhesion But also says wider tyres give more grip for other reasons )

[Lowe]

This whole tyre arguement has been done quite a few times. Do a search for it Kalniel.

[Lowe]

Oh.. found a nice page with some useful information here:

http://www.carbibles.com/tyre_bible.html
(which completely blows away my idea of adhesion But also says wider tyres give more grip for other reasons )

Yup, it totally reinforces Zak's point lol.

Like I say - do a search, we've done it a few times.

[5lab]

wider tyres look cooler and last longer.

but they are much more liable to aquaplane

[kalniel]

Aaanyway.. Seems there is a ton of stuff to bear in mind. Looking at some online places it seems my existing rims are 14x5.5, and have an offset of 39. That means I could just swap tyres to 185/65/14 and they'd fit on the same rims (require 5-6.5 rims), or I can look for alloys that match the offset and number of nuts, size up to as much as 19" (would be mad to, I like the current ride thankyou very much!) and just keep the ratios in mind to give the same overall size.

Next question is how much of a weight saving are alloy wheels over standard? I'm guessing that the impact would be negligable over all, this isn't exactly a caterham

[5lab]

alloys on a road car save pretty much nothing - they're not designed to be light, and as they are generally larger, the weight is further from the centre and actually worsens fuel economy (higher rotational force).

i recon you'd be lucky to save more than 100g per wheel without going to something specialist

[Butuz]

Totally depends what alloys your buying. If your talking about a cheapo set of halfords alloys then they are probably heavier, and weaker than the standard steel wheels, if your talking about a set of forged nissan alloys, theyre not only substantially lighter than the steel wheels, theyre 30 times as strong.

Its all up to what you spend really.

Butuz

[kalniel]

Cheers. I certainly don't need anything 30x the strength of steel - I've never even heard of someone breaking a wheel in normal use!

[Rave]

Thanks for the replies
Why not? Remember it's not just friction here, we're talking about adhesion - there's chemical bonding between the tyre and the road. A wider contact patch means more hydrogen bonds and more grip.

You reckon that for the tiny fraction of a second that any given bit of rubber is in contact with the road it's chemically reacting with it? It forms a quick bond, produces some grip, and then reverses said reaction almost instantaneously?

I got an A in A-level Chemistry and that sounds unlikely to me TBH....

[kalniel]

You reckon that for the tiny fraction of a second that any given bit of rubber is in contact with the road it's chemically reacting with it? It forms a quick bond, produces some grip, and then reverses said reaction almost instantaneously?

I got an A in A-level Chemistry and that sounds unlikely to me TBH....

Well it takes a matter of femto seconds to form H-Bonds (millionths of a nanosecond). So, yes Not chemically bonding as in epoxy glue setting, but in terms of forming H-Bonds. Of course I was making lots of assumptions about the chemical make up of rubber and tarmac which I haven't actually bothered to look up

I suspect they're almost certainly non-polar which would largely rule out h-bonding. (I only deal with protein structures myself )