Q: “I have a series of questions that were triggered by the Tires for Drivers webinar you and Samir Abid did recently. First, what is the grip tendencies of tracks that are super smooth like the newly-paved Watkins Glen compared to a very rough-course surface? The slides in your webinar of the tire on stones vs the smooth surface raised my awareness. My interest is in car setup for each, and a game plan or base line to start with a set up’s. 

 Then:

1. Tire pressures best being lower or higher on a smooth or rough surface?
2. Do tire temps (we use a probe) increase normally or decrease on each of these surfaces? 
3. Which way do dampers get adjusted based on these two surfaces?
4. Is camber increased or decreased based on these surfaces?
5. Is body roll increased or decreased based on these surfaces?”

A: I’m far from an expert of asphalt, but one thing I know for sure is that Watkins Glen is one of, if not the grippiest tracks in North America. I do know that when the Glen was resurfaced, they choose to use a very grippy type of asphalt, so there’s more to it than just how smooth it is. At the opposite end of the grip spectrum is Laguna Seca, one of the least grippy tracks in the world (they’re planning to resurface soon, so that will change). My understanding – from what I’ve seen from staring at different track surfaces during track walks and comparing what I saw to what I felt when driving – is that over time, edges of the aggregate in the asphalt is worn smoother. The Glen has not gotten to that point, although it’s not quite as grippy as it was when they first resurfaced it. While it looks smoother than the rough old pavement on some tracks, when you look closer you’ll see the edges of the stones in the asphalt are actually less smooth – and that’s where part of that grip comes from. The edges of the aggregate is sharp. So, I wouldn’t necessarily relate smooth with more grip. In fact, Laguna Seca is polished smooth, and therefore has less grip. I believe there is also a chemical component to asphalt grip, too, but that’s way beyond my understanding!

1. “Tire pressures best being lower or higher on a smooth or rough surface?”Are you asking about more or less grippy pavement, because as I just said, what appears smooth may not be less grippy – it might be more grippy. So, I’ll try to answer this using “less grip” and “more grip.” Think about what works the tires more – usually the grippy surface. That usually means that the tires will heat up more, and therefore you may have to start with lower cold pressures. Typically, a tire’s optimum grip will come from a certain hot pressure, and that doesn’t matter much whether it’s on a more grippy or less grippy track. How you get to that ideal pressure may change, though! For example, with the same car, we had to start our cold pressures about 1 psi higher at Laguna than we did at the Glen because it was harder to work the tires and get them up to the ideal temperature/pressure on the less grippy surface. Now, if you’re talking about a bumpy track, that’s a different situation. For example, we all know Sebring is very bumpy. The additional flexing of the tires as they pound the bumps builds temperature and pressure, so we started with slightly less pressure to get to the same ideal hot pressure. Again, the goal is to get to the ideal hot pressure, and that doesn’t change much despite the track surface. There can be an exception to what I just said… running a little less hot pressure is a bit like running a softer spring in your suspension (remember what Samir said about the tire being a spring), and that can help generate more grip on a bumpy surface because they soak up the undulations. One more thing to consider: think in terms of extremes… a less grippy track is like a wet track, and what hot pressures do you want then? Sometimes – but not all – you might want slightly less hot pressure to “soften” your overall setup on a less grippy track. If all of this seems a little confusing, that’s okay – it should be, because this is not easy. There’s no blanket statement that anyone can give you for all conditions. One of the things Samir and I tried to emphasize is that you have to test, and experiment. But if you think about what the level of grip is doing to the tires, that usually gives you a direction to start in when experimenting.
2. “Do tire temps (we use a probe) increase normally or decrease on each of these surfaces?”Tire temps typically go up with more grip in the track. Why? Because it’s working the tire harder – the grip allows more load to be generated. Recall the slide in Samir’s presentation where he talked about the 3 ways tire generate grip and temperature. The load through braking, cornering and acceleration is going to work the tires more, building more heat.
3. “Which way do dampers get adjusted based on these two surfaces?”This is an even tougher question because it depends on where you are now with the settings. It’s a bit like the question, “How long is a piece of string?” 🙂 It depends! But start by asking yourself if the track surface is working the tires more or less. That could give you a direction. If you’re on a grippy track, often you can run stiffer springs, anti-roll bars, and dampers because the track will take the extra load. Go the opposite direction, and think about a wet track – you’d likely want to soften your settings, and this could be similar with a low-grip track, and your damper adjustments.
4. “Is camber increased or decreased based on these surfaces?”Same thing: Is the track working the tires more or less? Typically, we’d run more camber at the Glen than at Laguna Seca. The goal is to have as much of the tread surface in contact with the track, and if it’s a high-grip track, there’s going to be more lateral load, and therefore you’ll need more negative camber to counteract it. On a low grip track, you tend to stand the wheels up more straight (less negative camber) to keep the tread surface on the track.
5. “Is body roll increased or decreased based on these surfaces?”The more grip, the more lateral load. Given the same roll stiffness in the car (same springs, anti-roll bars, dampers), there will be more roll on the high-grip track.

Keep in mind that there’s almost always an exception to everything I’ve just said! But what I’ve said should work more often than it won’t. The key in each of your questions is to think about what the tires are doing in relation to the grip level of the track.