Why do wide tires generate more grip than narrow tires?

[schofei]

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[Frankmd]

I bet it is an interesting read, but dont you think the tone of the article is a little bit too scientific for the average forum visitor? :)

[KiDCoDEa]

and if it is, there is nothing wrong with that. i certainly dont want a forum leveled by lower standards.
thanks for posting a interesting thread.
This pdf doesnt seem public domain though... ;)

[geeman1]

Why do wide tires generate more grip (under dry condition on asphalt) than narrow tires?
Wouldn't the simple answer be: Wider tyre has more area touching the road. More gripping area = more grip.

[Frankmd]

What I ment was that if you just post an article like that without (for example) a summary, you wont get a lot of discussion.

[tristancliffe]

Two things occur:

1. More tyre area = more rubber to bite into the tarmac, and provide longitudinal force, as opposed to simple smooth body mechanics we all did in school.

2. Pressure = Force/Area. For a given force on the tyre (corner weight if you like), the narrower the tyre and hence contact patch, generates more pressure. This pressure is especially good for damp conditions.

So, wide tyres are great in dry conditions, but lose grip much quicker in less than ideal conditions.

I know this is very simplified, but it's the gist of what I always thought was going on...

[KiDCoDEa]

Wouldn't the simple answer be: Wider tyre has more area touching the road. More gripping area = more grip.

that answer could be wrong in many cases therefore it falls short on its universal characteristic.
thing is, keeping it simple as you like, more area, less pressure.
and if youre within material limits, many times larger areas will only slow u down and not develop the needed load in corners for tyres to perform optimally.

[geeman1]

I now actually taked a look at that article and I admit my simple answer was wrong in many cases. I guess there really isn't a simple way to put it :p

[Bob Smith]

Oooh, will read. :)

[Fonnybone]

As far as i know, it can be resumed simply:

Grip raises with load, up to a point. Grip/load is not a linear relationship
Once you overload a tire, it loses most of it's grip and is basically useless.

THIS is the only reason to get wider tires in fact.

In theory, the narrower the tire, the more pressure is applied on the same
square inch, so the more the tire 'digs' to get grip. This is why narrow tires
are preffereable in snow, sand, or any loose surface where the tires NEED
to dig to find a stable surface to apply force to.

A wider tire will tend to float on these surfaces and have a hard tire finding
any grip. Also, wider tires will slow you down because of the increased drag
and the lower pressure per in² means you use less of the potential grip (you
might not be taking advantage of optimal grip). The only valid reason, as far
as i know, to use wider tires is too spread the weight as to prevent overloading
the tires at the limit. This is because as you increase load on a tire, the grip it
can generate also increases (i.e: if you put more weight on the tire, it
can grip more), up to a point (optimal) where grip just falls off and the
tire slides (put simply, the tire overheats). The only way to prevent this
'overheating' is to increase the contact surface, which lowers the pressure
per in² (im not using PSI as not to create confusion btw) giving the tire a
higher 'load capacity' (im vulgarizing for the sake of comprehension here).

Another factor, although related, is tire deformation, as a tire approaches it's
optimal zone, the tire starts deforming and overloading it means it deforms
beyond it's intended shape which also reduces the grip potential of your
tire, not to mention it will be harder to control, and possibly dangerous.
You also risk blowing out the tire, which we all know, will also decrease grip ;)

So, ideally, you want the narrowest possible tires that will NOT 'overheat'
when you push them at their/your limit. Wider is NOT always better ;)
It also costs more money :p

I'm not sure, but i think this is what they refer to as load sensitivity.

Ok, so i can't keep it simple...lol

[tristancliffe]

Don't tell the boy racers that - it'll spoil their myth that wider and stiffer (I'm talking cars here) is ALWAYS better...

[Fonnybone]

Don't tell the boy racers that - it'll spoil their myth that wider and stiffer (I'm talking cars here) is ALWAYS better...

Ya, the myth of wider is better is not totally false. It just choses to ignore
the negative side effects. Wider DOES have more potential grip the way i
understand it.

The myth comes from the theory that the wider the tire, the more headroom
you'll have. In extreme cases, you would never be able to overload or overheat
the tire, heck, it might even barely get up to operating temperature. More
important to some, is you wouldn't be able to go over the tire's limit, so
you'd probably never slide, at all. I can see how having a tire that grips
so much you can never make it break traction sounds like a good thing, but
this isn't exactly true (a VERY light car with VERY wide tires would have very
little surface psi so it might still slide simply because it's tires aren't getting
enough load to do their job). Then, there's the rolling resistance which can
become an important factor which can remove negligeable gains in optimal
grip. In fact, if important enough, the increases drag/resistance could keep
you from even reaching speed where you'd take advantage of the supposed
higher potential grip.

[Shotglass]

This is why narrow tires are preffereable in snow, sand, or any loose surface where the tires NEED to dig to find a stable surface to apply force to.

not true for sand where a narrow tyre will sink in (dakar drivers lower their tyre pressure when the drive in the dunes to get a larger contact patch)
on very loose surface (sand mud etc) you want a very wide soft tyre that act like a shovel so it sinks into the surface a bit and grabs as much mud as it possibly can ... its very obvious when you look at the tyres those icelandic 4x4 racers use

[ayrton senna 87]

in karts in the dry we run 210mm at the rear magnesium cast wheels to stop the tyres overheating, in the wet we run spun aluminium wheels of 175 rear in the wet to get some heat into the tyres. even in the cold we run narrower rims of different materials and manufacturing procceses. naturally in the wet we run like 40psi to get the contact patch very small in the wet and try to make it as wide as we can in the dry. that just proves that wider isnt always best :)

[Fonnybone]

Good point ;) So there it is again, there is no X is better, it's a compromise
between surface pressure and load, you want a tire optimal to both. Sure
makes sense though about the sand, i'd imagine the car would be stuck on it's
belly way before it can find any hard surface by digging...hehe. Still, you
don't see them with 2 foot wide tires...ok so monster trucks do :p

[Shotglass]

Still, you don't see them with 2 foot wide tires...

well rally-raid cars use tyres somwhere in the 1 foot region:
http://www.rsportscars.com/foto/2005geneva/vw_touareg_dakar_01.JPG
and the jeeps in iceland i mentioned above indeed use 2 foot wide tyres:
http://www.4x4iceland.com/ggj/ggj20040718hella1.jpg

[Hyperactive]

Q&A:
http://www.physlink.com/Education/AskExperts/ae200.cfm
(no science stuff there...)

[AndroidXP]

and the jeeps in iceland i mentioned above indeed use 2 foot wide tyres:
http://www.4x4iceland.com/ggj/ggj20040718hella1.jpg
Hahaha, driving on such tyres would extremely suck in LFS. Traction would probably be lower than on Blackwoods ramps (read: none) :D