Cup2R Tires Road Atlanta - Managing Pressure at HPDE Track Event

[Bill Pemberton]

What pressure are you starting with?

 

[Egparson202]

What pressure are you starting with?

Depends on the tire and how many laps I’ll be running. In an ideal circumstance, I’ll be able to get up to temp quickly and have a fast setup that lasts a full session. Not easy.

Let's say I’m on Cup2’s. I want hot pressures to be 33. So I’d likely start off at 25. That gets me a fast setup, but it takes a couple laps for the tires to build pressure. If I’m patient, the car is quick until the end. But the first few laps I really have to take it easy or it’s hard on the tires.

I’m hoping to shrink the pressure gain so I can go out closer to the hot pressure, go fast sooner for longer and not hurt the tires.

[I know. All I want is everything. And I want it for free.]

 

[Bill Pemberton]

Sounds to me like you are doing fine and it will often take one or two laps to get to a good temp, but I started at 25-26 lbs when I ran Cup 2s. I do make sure on Lap 1 ( especially when I was running W2W ) to drag the brakes plenty as the heat from the brakes will translate into getting some warmth into the tire early, but honestly if you are running long sessions few tires will stay completely the same during the entire term. That is part of the fun drama of racing, being able to adapt to changing conditions , whether it is the track, the weather , or the tires. I know I found Cup 2s getting greasy toward the end of a session, but then I have seen this with practically every tire I have run on. Sure, some stay more stable for longer periods but some of the ones that see almost no change often are also slow.

I guess I would not be that concerned ,it sounds like you have a decent handle on things, but you also will likely see differences at various tracks. Some heat your tires up faster than others, many heat up one side more than the other due to the number of turns or load and as you noted you just want everything ---- well , you can't have it all, ha, but you are analyzing things to get the best overall usage imho.

 

[Egparson202]

Sounds to me like you are doing fine and it will often take one or two laps to get to a good temp, but I started at 25-26 lbs when I ran Cup 2s. I do make sure on Lap 1 ( especially when I was running W2W ) to drag the brakes plenty as the heat from the brakes will translate into getting some warmth into the tire early, but honestly if you are running long sessions few tires will stay completely the same during the entire term. That is part of the fun drama of racing, being able to adapt to changing conditions , whether it is the track, the weather , or the tires. I know I found Cup 2s getting greasy toward the end of a session, but then I have seen this with practically every tire I have run on. Sure, some stay more stable for longer periods but some of the ones that see almost no change often are also slow.

I guess I would not be that concerned ,it sounds like you have a decent handle on things, but you also will likely see differences at various tracks. Some heat your tires up faster than others, many heat up one side more than the other due to the number of turns or load and as you noted you just want everything ---- well , you can't have it all, ha, but you are analyzing things to get the best overall usage imho.

Thanks, Bill. We do our best.

What hot pressures do you see from 25-26 cold? How long are you staying out?

 

[Bill Pemberton]

I was getting to 34-35 at one track and closer to 33 at another. Usually out 20-25 minutes but I usually have to adjust my line a little towards the end. Keep in mind, regardless if you are watching Nascar or F1, the common phrase is these tires are going away, so yes you are asking for everything , because even purebred race rubber does not stay constant for long periods. The ability to feel the change in your tires, to adjust and find where they seem to work better is one of the things that is fun ( in my mind ) to discover. It is not always very dramatic , but if you find that change in line before others, it gives you an edge and at times it will actually cool your tires down for another run.

You are analyzing and that is a key, but just remember every moment of Max Verstappen whining when he is setting the fastest lap of the race, " These tires be junk, I can't control this crap, what do you expect from me with such schittee rubber?"

 

[blacksheep-1]

So if I have been seeing pressure gains in the 8 lb range, what should I expect from dehumidified air?

Kind of hard to say, what you should see is conistency, You can actually see each specific tire rise the same amount every session. instead of 6 psi one session, 10 the next, or of humidity is a thing, as much as 15 or more psi. So you can expect the same amount of pressure rise in say, the right rear 6 psi every time, same with the rest. (depending on the track, it might not be the same as the RR, it could be more of less, but the same each time)This lets you set the pressure consistently and because air pressure is spring rate, tune the car better.

 

[Egparson202]

Thanks, guys. This is super helpful. Can’t wait to try it out again at VIR in 10 days.

 

[Bill Pemberton]

Post pics, I will be racing vicariously with you since it was 29 degrees when I got up this am, ha. Have fun, Virginia is definitely for Racers!!

 

[blacksheep-1]

Yes, I would like to see the results myself, 200 or whatever TDW tires are not nearly as finnicky as race slicks, but there should be an improvement.
That kind of thing came up this weekend with the Michelin rep, we were wondering why our predicted pressure settings were off, it was because he was using .65 per 10 degrees and I was using .7, so being that close, everything you can do to feed consistency is vital.
FWIW that 24 hour race is going on in Wales, UK shortly and my disabled vet that I mentor is doing tires, they are using a similar tire with a Toyota BRZ based race car. So that is one of the reasons that I'm interested.

 

[Dave_W]

what you should see is conistency

This is the key. You'll be able to set your cold pressures and have confidence that when the tires warm up they'll be at the hot pressures you want.

Once you deal with any water vapor problems and get consistent pressure rises based on temperature, the only way to reduce the pressure rise is to start with hotter tires (if allowed by the rules).

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[Egparson202]

Dangerous question warning…

Because there is more than 1 right answer, and because I’ll have to experiment to find the right answer for me. But I’d appreciate if you all could share your experience with Cup 2’s in terms of what hot pressures you would target with performance being valued slightly more than wear.

 

[blacksheep-1]

I'm no habla on that one

 

[Egparson202]

Off the record? C’mon. Gimme a little something.

 

[stevbd]

Sorry if this is a slight threadjack but does anyone use or recommend an in-car tire pressure monitoring system, maybe something like this?

https://www.amazon.com/Monitoring-%E3%80%90Detached-Installed-Windowshield-Real-Time/dp/B0BJZWR41D/ref=asc_df_B0BJZWR41D/?tag=hyprod-20&linkCode=df0&hvadid=647362046573&hvpos=&hvnetw=g&hvrand=12723292543225115036&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1018127&hvtargid=pla-1972663031274&psc=1

It'd be nice to see what individual tire pressures are doing in real time.

 

[Egparson202]

I know some folks use/trust the OE TPMS. And I know AIM has a Motorsports level product. At this price ($30) you might just take a flyer.

 

[dragoon]

I have found a new to me thread to follow. I have a brand new set of cup2’s that came on the car but not tracked them till I get more camber.

 

[Dave_W]

an in-car tire pressure monitoring system, maybe something like this?

Not sure I'd trust this in a motorsports/HPDE venue (high speeds & curb cutting). It looks like the valve stem cap contains the sensor/sender/battery unit, so it needs to push the Schrader valve in to be able to read the pressure. Which means if the cap loosens, you start losing tire pressure. And the sensor/sender/battery unit in the cap needs to weigh more than a standard cap, which can put more g-load strain on the valve stem at high wheel speeds - probably not a concern with a metal valve stem, though galvanic corrosion may come into play with a metal valve stem. Then again, I like to game out worst-case scenarios. This might be fine.

However, if you already have TPMS sensors installed for the built-in Ford system (and you don't have a built-in PSI readout - my 2013 Boss only says "OK"), you might be able to tap into the CAN-BUS data with something like ForScan on your phone or a tablet and build a real-time dashboard.

 

[stevbd]

Not sure I'd trust this in a motorsports/HPDE venue (high speeds & curb cutting). It looks like the valve stem cap contains the sensor/sender/battery unit, so it needs to push the Schrader valve in to be able to read the pressure. Which means if the cap loosens, you start losing tire pressure. And the sensor/sender/battery unit in the cap needs to weigh more than a standard cap, which can put more g-load strain on the valve stem at high wheel speeds - probably not a concern with a metal valve stem, though galvanic corrosion may come into play with a metal valve stem. Then again, I like to game out worst-case scenarios. This might be fine.

However, if you already have TPMS sensors installed for the built-in Ford system (and you don't have a built-in PSI readout - my 2013 Boss only says "OK"), you might be able to tap into the CAN-BUS data with something like ForScan on your phone or a tablet and build a real-time dashboard.

I removed the oem tpms sensors on my track wheels because the plastic/rubber oem valve stems were breaking under hard track use. Metal stems fixed that problem but now I don't have tpms on track. Similar to you, my 2011 GT tpms doesn't give specific readouts. You make good points about potential problems, although I suppose if I started losing pressure on track at least I would know about it lol.

This system looks pretty cool, check out the video: https://www.racebeat.net/products/tire-temperature-pressure-monitoring-system-ttpms

 

[EF1]

Why didn't you just replace the plastic valve stems with metal and keep your TPMS sensors? That is what I did on my 2011. Yes they don't give actual pressures, just a low warning, but at least it keeps the lights off on the dash.

 

[blacksheep-1]

FWIW, the TPMS sensors are just another tool, all teams take their pressures on.pit road. When you get the read out, or observe the tpms sensor on the readout screen you will see peaks and valleys in the pressures. Say a sweeping right hand corner might see a left side swing of 28 degrees on the straight, 32 under hard braking ( heat) then a slight drop and another raise to 33 before the car goes down the straight and the tire returns to about 26. So, if you observe that, and you want to change it, you have to make the reference and change on pit lane. Even if you have all the star wars crap that can tell you mean and average pressures, you will still need a put lane reference for change.