Best adhesion - Asphalt or concrete?

[autobonrun]

I know some of you guys regularly push your car to the limit on the track so this is probably obvious to you but I was wondering whether you can push your car harder on say asphalt than a concrete surface before the tire loses grip. What surface do most of the tracks you race use?

[orbmedia]

Tracks I have run on in the NE are mostly asphalt with concrete patches. In general the concrete has more grip. In most cases the concrete will be on the dry line anyway. See the photo showing a concrete patch on Limerock's "Big Bend".

Please note this is a generalization, conditions may vary from racetrack to racetrack and corner to corner depending on a variety of factors including temperature, weather, surface condition, etc.

[1980SC]

All of the racetracks I've run on are asphalt, but with autocrossing, we run at both concrete and asphalt sites. Concrete offers more traction if it's in good shape.

-Rob
1980SC

[Zeke]

Asphalt is made w/ oil. On a hot day it will lose traction. Concrete is more stable to weather variations, the deposits on the surface not withstanding. A green, or washed off, concrete track is inert. However, the tires are not. The relationship of the tires to the environment exclusive of their own subjectivity is arguably the single most vexing aspect in racing.

[ChrisBennet]

Lime Rock's concrete patches seemed a little slipperier in the rain but that may just be because they are on the "dry line" - the oiliest part of the track.
-Chris

[304065]

I would think that concrete would have the higher friction coefficient-- regardless of the material itself, asphalt's prone to having voids in the surface, reducing the total contact area. But would welcome input from a civil engineer on this.

JC- you aint' kiddin' about big bend. I was working flag station 2 with CVR on March 16th and you could hear the tires squealing around both apexes as they transitioned on and off the concrete patches. Very disconcerting feeling and noise. I also saw some of the "C" cars doing very interesting things with the throttle through that corner-- stomping and releasing it-- you could see the front bumper pitch up and down (which isn't easy to do on a prepped "C" car) and hear the exhaust note come and go. Is that the fast technique, are guys throttle-steering through there?

[RarlyL8]

Concrete by a mile, unless wet.

Run your hand across the surface of both. The concrete will tear you up.

The dragstrip in Texas (Motor Speedway I think) has a concrete launch pad. Fastest strip in the country because of it.

[orbmedia]

John,

Hey buddy!

Yes there are some creative things that 911 drivers do to get through Big Bend as fast as possible. What you may have seen is attempts at inducing rotation by throttle lift? I like a double apex line through there, if done well you can catch people there.

[89911]

Most of the concrete on race tracks, especially on the dry line, have been polished from tire travel so much that the concrete is highly polished. I found this out on a wet morning at Laguna Seca. Get on the dry line in the wet and you will be off the track. I would have to say its a toss up. Most of the track lay concrete where asphalt would be tore up from tires.

[KTL]

Asphalt is prone to polishing as well. The bituminous material gets worn off the aggregate and you have a smooth, slippery surface. Polished asphalt would most likely provide a lower grip surface due the to voids as mentioned before, but the voids also provide an area for the tire to dig down into the surface and gather grip against the edges of the voids. So it's probably a toss up like 89911 said.

Asphalt is prone to rutting (if the subbase is unstable or overloaded) and ravelling. Ravelling is when the mix starts to break down and the bituminous material no longer bonds the aggregate pieces together. Becomes a loose, rough surface. Ease of maintenance and construction makes asphalt the popular choice.

Concrete is stronger, but maintenance and intial costs are much more than costs for asphalt construction. If concrete remains crack-free and stable it could be reprofiled/resurfaced with micro-surfacing grinding, but this is really only done on highways to maintain acceptable driveability standards.

Short tracks like Martinsville and Bristol on the NASCAR circuit use concrete and those tracks have tremendous grip (and banking) which eats tires like nobody's business.