NASCAR Race Weekend Central

Tech Talk: Brake Temperature & Bump Stop Shims with Tony Gibson

The No. 41 team driven by Kurt Busch put itself behind the eight ball at Martinsville Speedway thanks to a poor showing by its standards. The entire Stewart-Haas Racing organization struggled all weekend, and it didn’t get any better during the race.

As a result, crew chief Tony Gibson and his team are going to have to be aggressive in their strategies the next two weeks if they want to make it to Homestead-Miami Speedway and compete for the title.

Heading to Texas Motor Speedway, Gibson knows that tires are going to be critical for their success. He speaks repeatedly about tires this weekend for Tech Talk, knowing the history of tires at Texas can end someone’s title hopes in a hurry. He also details the role of bump stop shims in getting the optimum right height and load timing in the suspension.

Mike Neff – To say your race at Martinsville wasn’t what you’d hoped for is probably an understatement. How did you view your weekend in Southern Virginia?

Tony Gibson – No, none of our cars, as a company, ran very well. We ran pretty well at the start. We drove up through there pretty good and I thought we were going to be OK. It was around the third pit stop where we started to lose the handle on it. The track rubbered up and we just went to crap pretty quick. We could just never get the car to hook up. We had those long runs which gave us minimal time to work on it that much.

As a company we just struggled up there for some odd reason. We were hoping to run a solid top 10 and keep ourselves close and just stay out of trouble all day. I think we were running ninth and doing OK, and then it just fell apart there. It wasn’t what we wanted, but we’ll keep our heads up, go to Texas and take two more shots to make something happen. We’ll keep digging.

Neff – It was decidedly warmer during the race this past weekend than it has been in a long time for a Martinsville fall race. Did that hinder your ability to fall back onto your notes since you’ve had that same tire for four years and it has never really put down rubber before?

Gibson – Yeah. I think that is why you didn’t see a lot of cautions. You could actually diamond the track like we used to a long time ago; guys could run a little higher up the track. That seemed to cause it to string out and didn’t result in a lot of cautions. The track was just so different with the heat and everything, and as the day went on it just continued to rubber up more and more, and we seemed to struggle because of it. The setups that we ran very well with the last few times there was definitely not the one to have late in the day. The weather had a lot to do with it, for sure.

Neff – Texas is an aged surface with character that seems to be in your wheelhouse, and tire management is certainly going to be a priority. Does that limit the aggressiveness you can utilize when it comes to camber in your setup, or are you able to be aggressive since everyone is in the same boat?

Gibson – I believe we’ve had some issues at Texas the last few times with this tire. This tire likes really low air pressure to make optimum grip. Unfortunately, when you run low air with the speeds and the loads we run at Texas, it stresses the tire out really bad, and we see a lot of tire problems here because of it.

I don’t think you can get too aggressive on your camber settings and things because it can bite you big and in a hurry; we’ve seen that in the past. The approach you want to take on your camber and air pressure is to not be too aggressive on it, especially in the first couple days. As the race starts and things go along, you can drop air pressure and get more aggressive on it. During the early stages of the race you have to be very careful with tire wear for sure, until the track gets some rubber on it.

Neff – I know everyone talks about air pressure when we talk tires, but in reality, don’t all of the teams use nitrogen in their tires?

Gibson – We do, to try and keep moisture out of the tires. The tires still gain pressure pretty rapidly with the amount of load we push through them. Even with nitrogen in them it still grows pretty fast. You just have to be so careful. You’re trying to be pretty good while you’re holding on for the first five laps, but it is the last 10 laps of the run where you’re trying to make sure you are a little bit better than everyone else and make hay on older tires, because you’ll spend more time on older tires. Getting the pressure low helps the tire keep better grip throughout the run.

Neff – If you compare nitrogen to air what is the difference of growth rate between the two?

Gibson – It will knock it down about a third. The lack of moisture in nitrogen makes the difference. Moisture makes the pressure grow faster, so the lack of it in nitrogen reduces the growth. Even then the build is still really big. We would like to knock a lot more of it out of the tires if we could.

Neff – Johnny Sauter said he had brake fade early in the race at Martinsville. It has been several years since we’ve talked much about brake fade, especially in a Truck race. His crew chief, Mike Beam, explained that the problem they had is that the optimum temperature for their tires is 100 degrees or so on either side of 1,250 degrees. If they get outside of that, the performance degrades rapidly. For you, assuming you have a similar parameter, how do you gauge the openings and fans you’ll utilize to achieve that optimum temperature?

Gibson – It depends on what package you are running. With all of the brake pads that are out there, and the different materials that they use, it varies what temperature a given pad wants for maximum friction grip. Some pads work better at a cooler temp and some work better at a hotter temp; it depends on what combination you’re running. The driver can dictate the temperature by turning his fans off under caution to keep heat in them and things like that. We can also get aggressive with tape on the front end to limit the air going into the ducts. There are some pads that like a lot of heat while others don’t like much heat at all. It is more of a preference for the team when it is all said and done.

Neff – Does your race engineer track ambient temperature and perform a calculation to determine the size of opening you want to leave on your brake ducts?

Gibson – We go off of history for the most part and keep track of what we’re seeing in practice. We keep track of the temperatures when the car comes in, and we know what range we want for our package to work around. We use our fans and tape on the front end. Ambient temperature does come into play, but for the most part we basically tune on it each weekend for what we’re seeing at the time. In traffic you’ll use more than you will when you’re out front. In practice we don’t use as much as we do in the race. We generally go off of past notes more than anything.

Neff – Texas is a pretty high-speed track. You mention that you’re using lower air pressures to get optimum grip. That means you’re going to be lower to the earth at the beginning of each run. As you are shimming your bump stops to set that static height, do you have varying degrees of pliability for the shims that you utilize in order to allow for your suspension to travel a little more once the pressures build?

Gibson – The shims dictate the amount of load that you’re putting through the stop and ultimately where you want the front end to ride. We made several adjustments during the race at Martinsville based off where we thought that load needed to be and based on Kurt’s comments. The shims are pretty much that same for everybody, as far as the material they are constructed from. You aren’t wanting the shim to give as much as you’re trying to load or unload the suspension or change timing of the load through the bump stop with the shims. Some of the shims are aluminum and others are neoprene, but they are strictly to change the load of the stop and the height of the racecar.

Neff – Is it a balancing act by the driver as to how hard he can push it without pulling the tire off of the bead, or is it something you determine from practice to determine how hard he can push the car?

Gibson – A lot of guys will mess with it in practice. Everybody runs by themselves, so the speeds will be way up in practice. We’ll be able to know how aggressive we can be. The tire will give you signs of weakness. When you are starting to harm the tire and do things that can cause a failure, you can see indications of that in practice before it actually happens. We’ll have an idea on what our limits are for how low we can be well before we get into the race.

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