This is going to be an easy question to all of you racing gurus. I was always wondering why tires on regular road cars are not slick. My background in physics suggests that greater the surface area, the better the grip of the tire to the road. I know that F1 cars use slick tires for better grip. How come regular road cars dont use slicks??

I came up with two possible explanations:

1. When driving in the rain the slicks would "glide" upon the water and provide little friction, whereas the grooves in regular tires would allow the water to be pushed from under the wheel, and still maintain the grip

2. Tire companies want to save money, so they market the grooves on tires as if they actually provide better grip, and that way save on the amount of resin they have to use

Am I even close?

Quote from silver bullet :

This is going to be an easy question to all of you racing gurus. I was always wondering why tires on regular road cars are not slick. My background in physics suggests that greater the surface area, the better the grip of the tire to the road. I know that F1 cars use slick tires for better grip. How come regular road cars dont use slicks??

I came up with two possible explanations:

1. When driving in the rain the slicks would "glide" upon the water and provide little friction, whereas the grooves in regular tires would allow the water to be pushed from under the wheel, and still maintain the grip

2. Tire companies want to save money, so they market the grooves on tires as if they actually provide better grip, and that way save on the amount of resin they have to use

Am I even close?

Answer 1 is correct. The treads guide the water away from the middle of the tyre so that the tyre does not simply aquaplane over the surface of the water.

And on other more slippery but not wet surfaces, like on gravel, slick would be useless.

Don't know the exact reasons but an obvious one would be wet weather which is just a killer on cold slicks. People manage to have silly accidents in the wet with the current tyres so could you imagine people on slicks? I've met people who didn't know there was less grip in the rain :S

Throw in all the various surfaces we come across on the road such a mud, snow and ice it would just be stupid to use slicks. How many people are going to whip out a set of wets that's taking up half the boot and back seats, yet alone jack up each corner to change the wheels.

Another reason could be racing tyres have a temperature band at where they work and most people on the road would never get them up to that temperature.

I doubt slicks would be any cheaper than the current road tyres, especially if you were going to chase after racing ones.

Do remember though that you can buy near slick tyres for road going category races such as hill climbs. They look like a slick but have little cuts in them and are pretty much just road legal.

Thanks for your responses

Im assuming that slicks would be useless on gravel etc. for the same reasons they are worthless in the rain? Would they sort of "glide" on sand/gravel, is that it?

Slick tyres would struggle to get hold of a loose surface, that's why off-road tyres have big knobbles on.

I've driven many hours in the rain on slicks with my kart. It's like being on wet ice.

It's great fun.

speedfreak227

Quote from speedfreak227 :

I've driven many hours in the rain on slicks with my kart. It's like being on wet ice.

It's great fun.

speedfreak227

Is indeed

Although I still remember when I was in Jnr TKM and was the only one on the grid with wets on (had a bad day so thought I'd gamble). It had already been spitting but not wet enough for wets until we just started to get ready to leave and it just started throwing it down, Scottish weather for ya

Anyway one guy was weaving about like crazy on the parade/rolling start lap and ended up having to countersteer which put him into the side of the guy alongside him. Chain reaction sent that guy flying off the track and he hit the MSA clerk of the course and knocked her flat on her face, to make things worse the sudden impact seemed to make the guy hit the throttle harder.

Race was red flagged and unlucky for me everyone changed to wets for the restart

Oh and the clerk of the course was walking wounded the rest of the day, although I wouldn't like to be in the shoes of the guy who caused the accident when she got her hands on him

were i go Karting (Rentals ) they never change from Slicks, heck they advertise "Slick racing in all weathers" - i presumed slicked would make oversteer - all it seems to do is make nice boring understeer!

Your knowledge of physics should suggest that the surface area (commonly called "contact patch") should not matter.

Your knowledge of chemistry, that wonderful subset of physics, should provide the reason for greater surface area being generally better. That is "adhesion and cohesion." The interface between the rubber compound of the tread and the road surface is not simple friction. As a result of all this, tires have a non-linear force/grip curve. Increasing the normal force doesn't increase the maximum grip as much as simple physics would suggest.

The fact that a car can benefit from a larger contact patch inspires engineers to fit the widest feasible tires. The side effect of such a large contact patch is a low aquaplaning speed. NASA developed a rule of thumb formula for aquaplaning speed in standing water: 7.5 times the square root of the tire pressure in psi gives onset of aquaplane in knots. This is for an aircraft tire which has a long/narrow contact patch instead of a short/wide one, although I doubt that makes much difference Ultimately, slicks on cars would aquaplane over standing water at around 50mph. Before the tire gets all the way to the dynamic aquaplaning stage, grip will be dramatically reduced at lower speeds through several mechanisms.

As a result, ways must be found to prevent a "wedge" of water from building up under the face of the tire. That is why your vehicle tires have treads. If you look at a long haul truck, you'll notice the common tread pattern is simple circumferential grooving. These truck tires operate at far higher pressures than car tires, and thus can get away with it.

In situations where the largest contact patch isn't the most important factor, tires are shaped in a round fashion with no tread pattern. No road motorcycle or bicycle should have a tread pattern on the tire, if it does it is only for looks and detracts from performance. Airplane tires are similar. Completely "slick" airplane tires stop airplanes hard even in the wet.

Try driving an old car with bald tires in the rain, it's not fun. I have brand new rain tires on my car, and I've still hydroplaned, it's scary as all hell when you're not expecting it.

While these things are valid for real life I have a question concerning LFS tires and would rather ask it here than create a new thread for it.
When driving long distances where tire wear is noticable, does the grip decrease with the thickness of the pads or is the grip constant (until puncture occures)?

Quote from K.David :

While these things are valid for real life I have a question concerning LFS tires and would rather ask it here than create a new thread for it.
When driving long distances where tire wear is noticable, does the grip decrease with the thickness of the pads or is the grip constant (until puncture occures)?

In LFS, grip with the tires seems to me to be more dependent on temperature rather than wear. I always us R2's no matter what the distance is, in the FZR. For the first 1/3-1/2 of the tire run, the tires heat up and may overheat a bit. They will loose some grip as they pass into the point of heating up too much, but then after that point in a long run, they start to cool back down. Therefore, the grip begins to improve again. I've never really noticed grip changes due to wear, unless you count the temperature changing as a result of wear.

Yes I knew that temperature affects grip very much and I also know about how they cool down when the pads get thinner. Not taking temperature into account (have it say at optimum all the time) you get maximum grip no matter how worn the tire is, right?
I'm attending the Hungarian National League and races are way longer than I have experience in so I need to get to know things

Quote from K.David :

Yes I knew that temperature affects grip very much and I also know about how they cool down when the pads get thinner. Not taking temperature into account (have it say at optimum all the time) you get maximum grip no matter how worn the tire is, right?
I'm attending the Hungarian National League and races are way longer than I have experience in so I need to get to know things

In real life it isn't as simple as LFS. The point at which the tire will have the best (dry) grip is usually achieved by shaving much of the tread off when new, and then heatcycling the tyre X number of times before it ever sees the road.

In general, the less tread depth there is, the greater the dry grip. The problem with this is that most compounds have been seriously damaged by less-than-optimum (and too many) heatcycles by the time the tires get worn that far, not to mention uneven wear. This is why "road" tires used for dry racing should be shaved when new; it actually increases their usable life.

A properly prepared tire with 4/32nds of tread depth will perform better and last longer than the unprepared tire with full depth.

Quote from skiingman :

long.

Congratulations, you managed to make a short explanation take up several paragraphs, and then concluded by telling us that bike tyres with tread are useless. Wait for it to rain, then try to ride a bike around with slicks on.

Quote from spookthehamster :

Congratulations, you managed to make a short explanation take up several paragraphs, and then concluded by telling us that bike tyres with tread are useless. Wait for it to rain, then try to ride a bike around with slicks on.

Actually his point about bicycle tyres stands (for on-road use) - the average road bicycle has about 120psi in those skinny tyres which effectively means it would take approximately 200+ km/h to make that to aquaplane. The training tyres I got on my bike now are basically just very soft compound slicks.

I found his response quite interesting. I know most of it, but I thought he explained it very well, it wasn't too long. Also, I don't see anywhere that would imply he's talking about bike tires...

Quote from 96 GTS :

Also, I don't see anywhere that would imply he's talking about bike tires...

I think skiingman's penultimate post does?

Quote from skiingman :

No road motorcycle or bicycle should have a tread pattern on the tire, if it does it is only for looks and detracts from performance. Airplane tires are similar. Completely "slick" airplane tires stop airplanes hard even in the wet.

Quote from xaotik :

Actually his point about bicycle tyres stands (for on-road use) - the average road bicycle has about 120psi in those skinny tyres which effectively means it would take approximately 200+ km/h to make that to aquaplane.

What pressures do MotoGP bikes run?
Seeing they change tyres when it rains.. ?

edit: Uhm, nm, I just noticed that you were talking about unmotorised bikes.. ^^

I'm not too sure, but I don't think it's over 50 psi (less than that probably as the bikes are pretty light). And they easily do over 200km/h, although aquaplaning occurs at lower speeds for them.

Quote from xaotik :

...120psi in those skinny tyres which effectively means it would take approximately 200+ km/h to make that to aquaplane...

Cyclists of the world, the gauntlet has been thrown down.

Quote from jtr99 :

Cyclists of the world, the gauntlet has been thrown down.

in my experience, 1" slick tires with 100 psi will not hydroplane at any sane speed (though this is not to say that traction isn't reduced in the wet, which it is).

however, with 2" slicks and 50 psi, i've experienced very terrifying hydroplaning at only 35-40 km/h.

Quote from evilgeek :

however, with 2" slicks and 50 psi, i've experienced very terrifying hydroplaning at only 35-40 km/h.

On my commuter I've never noticed a single bit of hydroplaning at those speeds, and I got 2.1" slicks on it - crappy grip because the compound is rather hard, sure, but nothing you wouldn't get from knobby tires. The formula posted above (7.5 * sqrt(pressure) ) shows that it would take about 53 knots - which is approximately 98km/h.

With my roadbike (100-110psi) I've done some 60-70km/h descents on wet road and again the only thing I've noticed was all kinds of interesting wiggling and sliding, but not hydroplaning for sure, the wheels were definetely in contact with the road the whole time (just at varying angles ).

Quote from xaotik :

On my commuter I've never noticed a single bit of hydroplaning at those speeds, and I got 2.1" slicks on it - crappy grip because the compound is rather hard, sure, but nothing you wouldn't get from knobby tires. The formula posted above (7.5 * sqrt(pressure) ) shows that it would take about 53 knots - which is approximately 98km/h.

With my roadbike (100-110psi) I've done some 60-70km/h descents on wet road and again the only thing I've noticed was all kinds of interesting wiggling and sliding, but not hydroplaning for sure, the wheels were definetely in contact with the road the whole time (just at varying angles ).

i think a lot depends on the shape of the casing, and it's affect on contact patch. ie, not all 2" bicycle tires have a round cross section.