THSCC Forums

Knowing that there are different types of asphault (sealed as Greenville || Rockingham, unsealed as Sanford), but which, on average can generate the most lateral load for a tire, or, is it negligible?

I ask as I *thought* that concrete would generate more lateral load, however, I always hear interview's of people on roadcourses complaining that the concrete sections of the turn have less grip that the asphault sections.

Just wondering if anyone had experience/emprical data that could help me out with that. In trying to dial out some of the hack, I need to know which of our surfaces have the most 'grip' (not abrasiveness) in trying to find a good 'overall' camber/alignement setup with my tires.

Thanks, gentlemen.

- dow

First off you make CONCRETE with CEMENT....

There are exotic types of both concrete and asphalt, both with their own set of desireable properties. We will leave those out of the equation.

There are also different compositions of both asphalt and concrete depending upon the aggregate they are made with.

Down east, we have a Coastal Limestone. It features MANY jagged edges but is very fragile and easily fractured (Lower LA Abrasion). Towards the piedmont/mountains, you get into granite. Granite features a much higher LA Abrasion making it grippier and last longer.

Maintence also play a HUGE role in grip. If you allow it to get dirty/sandy grip obviously goes down.

Concrete can also be placed SO well that its almost a "polished" finish (think garage floor). Dont try to divorce abrasiveness from the equation, its a factor of grip.

Amy Mindick works for Martin Marietta, she works with aggregates everyday. Maybe she can chime in, Im no expert.

Dont try and "out dork" yourself, its still comes down to smooth inputs, looking ahead, and a dash of luck

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02 Focus SVT
STF 9

I seem to remember some of the the concrete patches at Summit Point were laid as a strip in three sections. You'd go from asphalt to slippery concrete to sticky concrete to slippery back to asphalt, all on one line in one corner. So it really does depend on a lot more than asphalt vs. concrete.

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Martyn Wheeler
AXing Kit's '05 Mazda 3, #29 HStock
(when The Gonzo Symphonic allows)

Correct. I am just looking to the scope of what we race to play into the small amount of logic I am trying to add.

Thanks Ryan.

- dow

Brian,

In addition to any difference in grip from the surface material, keep in mind the relative amount of and/dirt/gravel that is likely to be on the line. From my experience in 2005, the cleanest and highest traction THSCC surface was Greenville at the hot summer event. Course was clean and was hot enough to allow Miles's Victoracers to get sticky (just before at least one corded). Sanford is almost impossible for many tires. For me it is simply gravel without dirt. L'burg has a lot of high grip concrete (and some with lots of polished stone) BUT it also has lots of dirt and stones and vegetation. Both tend to have low traction starts due to loose stuff at the start line and gravel stuck to sticky tires. The Greenville site used for the NCAC had some very good asphalt. The Virgina Motorsports Park asphalt is about as good as asphalt gets from my experience with many autocross sites over a few decades in the sport.

Keep in mind also that a lot of concrete sites have bumps due to expansion joints, broken areas, etc. which hurt traction and make a stiffly sprung car behave more like a rally car. L'burg certainly has that problem.

Dick

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Dick Rasmussen

FS 50 2018 Mustang GT

Dick,

If you had street tires, Greenville was one of the WORST events for grip Especially Azenis in a 3300 lb car.

I appreciate the input.

- dow

Hey! See my performance at Greenville. 300lbs surely doesn't make that much difference.

[Give a guy a break - how many other 1st class finishes have I had?]



Siimon

Hmmm Having run all of our sites on street tires and R's, I'd rank them the same regardless (highest grip to lowest):

Laurinburg
Danville
Greenville
Sanford

I think that Laurinburg has the most grip of any surface we run by a pretty good margin. I found the new black stuff (is it sealer or just paint?) at Sanford to be super slippery and just adds to the challenges there. Note that this assumes the runs were taken in decent conditions (or hot) on relatively fresh tires. Changing any of the variables tends to jumble things a bit with Greenville perhaps being the most temperature sensitive.

Out of all the sites in North Carolina I've run, I would say the Dixie Classic Fair Grounds that Triad uses is the slickest by far. It was the only site I would always turn the boost down when running my old turbo Miata. After taking a couple of fun runs in a WRX there, I think the AWD guys have a *huge* advantage there.

On a related note, I've always found that as grip increases, the car I'm driving tends to tighten up. I usually wind up making a couple of changes at Laurinburg to loosen up the car to compensate for this. This really showed up in Topeka last year where the car was decent at local sites but wouldn't turn in a 40-acre field on the uber-grippy concrete out there. Of course, it didn't help that the rear sway bar was disconnected but I really didn't notice it much locally and I hadn't run Laurinburg in a while. In fact, the last site I ran before I went out there was Dixie and the car was nearly perfect! Probably a mistake instead of going to the Laurinburg nationals TnT but, hey, I was a rookie...

I don't think you can make a generalization just based on the surface type. For instance, in Toledo, the grip level varies with the direction you are headed! The site is concrete and while it is table-top flat, it constructed of big squares with each having a distinctive grain. If you are going with the grain, the grip is below average and if you are going against the grain, the grip is above average. The real difficulty lies in the fact that the grain of each consecutive square doesn't necessarily lie in the same direction! Even when it does lie in the same direction, if you are turning on it, the grip may pick up or fall depending on your direction of travel. Needless to say, it is one of the most interesting surfaces I've ever raced on. It's too bad it's gone for this year.

There was another concrete site I ran last year in Alabama and I'd put the grip there on par with Sanford. The concrete was relatively smooth and grain-free which I'm sure contributed to its grip level. In addition, there were a few spots where fuel was spilled (it is a heli pad for the military) and they were very slick. I imagine that place would be downright treacherous in the rain! Of course, that is the home site of the SCCAForums wunderkind Cole and his frictionless rollers so that may also play a part in the lack of grip!

Incidentally, I ran the Alabama site prior to Dixie before heading to Topeka and the car was perfect there as well. Live and learn...

Jim

I also heard that thing about the car tightening up as the grip goes up from Tom Hoppe, and experienced it for myself with the STS RS. With spring rate f/r balance that was perfectly neutral at Laurinburg, it was constantly threatening to spin at Sanford. Which made it a lot of fun at both places.

If you want to take anything away from this discussion, Brian, you should take the spring rate f/r balance into consideration when changing surfaces. Not sure if the STi is affected the same way as the RS - maybe DCCD setting will be an easier way of adjusting out the tightness?

I really liked Mr Alien's explanation as I seem to 'learn' better from experience, and reading what he wrote allowed me to pick up some information. As far as site generalization, I agree that broad sweeping generalizations for ANYTHING in life are almost always flawed and useless, but I was just looking for some input (as I believe L'burg to be the grippiest, so I was looking to just some slight understeer there, and hoping that I would have a more neutral car at the other sites).

I could 'try to dial the hack out' with the DCCD, but honestly, on a non-stock car that doesn't have oodles of push, the auto-DCCD >>> 'dialing hack out'. Once you actually have a car that uses ALL of the tire, manual DCCD use is about useless for me, as all it seems to do is help you 'lose' rear grip (from the rear when stock) to keep better balance.The only time I would touch the hack button is at Greenville when I can't generate enough front grip to get the car to turn in, so setting the centre diff open would give me more 'rear push' to get the car to rotate (and throttle manipulation).

I appreciate all the input in the thread as everyone has a different way of looking at things (especially with all the 'different' types of people in the club), and I always seem to get useful information from the very experienced THSCC vets.

So, thanks for some of the reaffirmation, and I will experiment a little to see if I am correct (or not ).

Thanks.

- dow

I really like the way Jim explained everything. I always thought Sanford had good grip then they went and sealed it and it is horribly slick in those spots.

If you want to see an example of AWD having a huge advantage on a slick surface look at the results from the Triad event at Dixie from October. Rankins slaughtered everyone else that can normally keep up with his raw times. They were able to launch the STi at 5k rpm where as I had to launch the Miata at 3k rpm instead of my more abusive launches that I normally do to get the engine speed up.

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2010 Honda Fit Sport
Couple of bicycles

I guess some times you just have to dail the hack up

- dow

That is an option in the STi but it sure won't work in the miata. That day was all about patience or I just played drifter as I slid the tail about and came out of the corners spinning the rear tires and my car only makes about 100 horse at the wheels. There are times I miss AWD and then there are other times I don't. Needless to say that was a day I wish I brought the WRX.

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2010 Honda Fit Sport
Couple of bicycles

This was something that I found very interesting and I was wanting to address this a little more directly.

So, on asphault/pavement/concrete, I think we can all agree that there is generally more grip there (on average) than dirt (no For Oaks references allowed ). However, it has been brought up by some of our more experienced rallyXers that a RWD CAN be driven quite quickly in rally situations as well as a FWD (or close.. MR2 is a great example by one of our best drivers). Can the same (althought stretched) association be made to RWD cars on a slick 'road' surface? While it MAY be easier to drive an AWD car quickly in those instances, can't a well driven patient RWD driver drive their car as quickly as an AWD driver?

It would seem to me from a theoretical POV that, in STU let's say, the RWD/FWD cars are given MORE static grip than their AWD counterparts (275 vs 245). So, it would *seem* that someone driving a 275 tire'd car would have the potential to be faster than a 245 tire'd AWD car. What makes that non-probable from happening (throttle manipulation... ??)?

Just curious as I agree that AWD may be more 'point and shoot', it seems that a well driven/prepared RWD car for that situation should have a slight advantage.

??

Thanks for the intelligent banter!

- dow

That particular course was an STi driver's dream. It had no real flow with several places that went from very slow to very fast. If you had a low-hp car, you had no chance to maintain any momentum to gain an advantage over a high-hp car. The start was basically a drag race to the first turn. I know that even with my meager hp, I was banging off the rev-limiter with my foot to the floor having never lifted from right after the kink in the start. The kink in the start wasn't enough to keep the AWD guys from being hammer down right out of the gate and the STi guys were *well* into 3rd gear by the first turn. PAX was seen huddled in a corner crying like a baby by the first heat.



As usual, the answer is "it depends." On a large course with big sweepers and such, the RWD car would actually have a chance to utilize its advantage for more than a microsecond. However, with a really slick surface and high-hp cars, that is more than nullified by not being able to put any power down even with slightly bigger tires. Ask Adam Breakey how much power he can use at Dixie even with monster r-compound tires. Even with perfect throttle modulation, you are suddenly reducing your effective hp by a *large* factor.

With the exception of the big sweeper at one end of Dixie, it is a classic point and shoot site. At the particular course we had last October there, the big sweeper was taken out of the equation by design. With my old turbo Miata running at 7lbs of boost (~160rwhp), there were 2 spots at that site where I had to lift in the middle of the straights otherwise the rear tires would light up. This wasn't due to surface traction at that point but rather relatively large bumps (one is actually a dip) that run across the racing surface. A stiffly suspended car would literally jump over those spots and that wasn't conducive to putting power down either. The CRX does the same thing but unlike the Miata, it will actually stop spinning the tires after a few feet so no lift is really needed. That’s not to say it wouldn’t surprise me to see the car spit out an axle at some point. Advantage: high-hp AWD.

You really have to run there to appreciate the nuances. With all that said, I still like running the place.

Given a sticky surface, can a high-hp RWD beat a high-hp AWD car? Sure. Heck, given equal cars, I'd pick the RWD car. With respect to STU, can a well-prepped M3 compete with an STi? My guess would be it depends on the course but on paper, I'd still give the advantage to the STi in most cases. Was that helpful? Probably not...

Jim