R888 cold/hot pressures?
- Thread starter mvanbuhl
- Start date
34/30 cold. Shoot for 38-40 hot. It depends on the outside air temp and how hard you drive. The rears heat up more than the fronts. After the first session bleed down the pressure to get around 38-40. I usually run my fronts at 38 and rears 40 hot and adjust from there depending on how the car is behaving that day.
Interesting advice. I'm sure you know there are a lot of "experts" at the track. My last time out, I had a NASA instructor tell me that Advan A048s should be run 30 to 33 psi max hot. Now I am running the R888s since the A048s are no longer available. Wouldn't the pressure recommendations be similar for all R comps?
Was this instructor's advice just way off and I should be at 38 - 40 hot?
Was this instructor's advice just way off and I should be at 38 - 40 hot?
The real truth is you need to get a pyrometer and check the tire temps. The pressure really is a means to an ends as the tire temps are the key. If you are too low a pressure then the tire will roll over on itself and the outside edge temp will go through the roof causing it chunk or even delaminate. If you are running too much pressure than the middle will get too hot. If you go to Toyo's website they for example, give a guideline of a temperature of 160-220F and hot inflation pressure of 32-38 for the R888. The former being more important - temp.
Making a blanket statement that all R comps should be at xx or even all A048s should be xx is blatantly false as it depends on the car, the outside temp, the car setup - including spring rate, sway bar size and camber, etc, track surface and even driving style.
For example, go out on a 55F morning and run those A048s on your NSX at 30psi hot and more than likely you are going to be buying new tires because the outside edge will be gone because they overheated and chucked off.
The real answer is get a pyrometer and check the temps and do what it takes between alignment and tire pressure to get those tires in their optimum temp range.
In my case, for MY car and MY alignment setup, I ran R888s at 38-40 hot. BTW: My Dunlop Z1s are set at the same pressure hot and they are street tires (even though they are close to Rs). This has come from 20+ track days on the Dunlops, a pyrometer and experimenting with different pressures to fine tune my balance.
BTW: I'm a NASA Instructor, as well as PCA Instructor and a few other misc groups too.... and I'm an idiot. But I know better than to make a generalized statement that YYY tire should be run at xx pressure. Hell, I just came back form Mid Ohio where my student was running his Porsche 997S at 48/56 because a Hoosier rep told them a month before in "class" that they should run their street tires 10psi higher than their street settings cold setting. Just looking at the tread you could see that it wasn't even using the outside 1". Then we took temps with a pyrometer and the middle of the tire temps were through the roof.
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Great guidance, thanks!
In defense of this instructor, he did tell me to get a pyrometer, which I did. I don't mean to take this thread too far, but I did collect tire temps from my last track day.
Laguna was the track. Air temp was in the mid to upper 60s. I was running the A048s. My mods are JIC suspension (full stiff front and 8 down from stiff rear), lowered 1.5", Comptech sway bars, and upgraded pads.
Temp readings from outside in:
RR 160/149/150 34psi
LR 165/150/144 34 psi
LF 135/133/132 33 psi
RF 130/125/129 33 psi
It doesn't sound like I am getting the temps up enough for these tires (especially the front). With inside and center temps almost the same, but outside temps higher, does that say anything about the pressure, or is it alignment issues?
I appreciate the advice!
In defense of this instructor, he did tell me to get a pyrometer, which I did. I don't mean to take this thread too far, but I did collect tire temps from my last track day.
Laguna was the track. Air temp was in the mid to upper 60s. I was running the A048s. My mods are JIC suspension (full stiff front and 8 down from stiff rear), lowered 1.5", Comptech sway bars, and upgraded pads.
Temp readings from outside in:
RR 160/149/150 34psi
LR 165/150/144 34 psi
LF 135/133/132 33 psi
RF 130/125/129 33 psi
It doesn't sound like I am getting the temps up enough for these tires (especially the front). With inside and center temps almost the same, but outside temps higher, does that say anything about the pressure, or is it alignment issues?
I appreciate the advice!
It's a combo of alignment and/or pressure. In this case your middle temps are lower than the outside AND your temps are low across the board which is probably not enough pressure vs not enough camber. I would have bumped up the pressure 2 psi all the way around and then checked again after the next session. Then bumped it again 1 psi and checked again to see if it was better or worse.
As well, don't chase temps - I know it's counter to what I'm saying, but the end goal is really a car that handles the way you want it, not perfect temps (if that makes sense). :smile:
Remember you have to take the temps as soon as the car comes off the track or the data won't give you correct info. Checking in the cold pits after you finish lets them cool too much. Stick the pyrometer in a tire when it first gets off the track in the hot pit and just sit there and watch the temps come down.... in 30 seconds it can drop 10+ deg. Even if you run around the car to do all 4, if you check the 1st one again it will be significantly cooler.
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A048 has a very ROUND profile, moreso than the R888 -which is much rounder than the squared carcass NT01.
Because of this, lower pressures can greatly improve the contact patch by 'flattening out' or 'squishing' the round carcass against the ground.
Like others have said, it all depends on many factors ranging from spring/swaybar rate, dampers, tire size, car weight, etc...
Both really low and really high pressures can increase heat in the tire. With both the A048 and R888 i've ran with 30-32psi hot before (starting in the mid to high 20's).
Did you do a cooldown lap? Did you check the temps IMMEDIATELY after you got off the track?
*also make sure to stick the ENTIRE probe (0.5-1.0cm) into the carcass of the tire. Do not worry, you will not pop it.
Because of this, lower pressures can greatly improve the contact patch by 'flattening out' or 'squishing' the round carcass against the ground.
Like others have said, it all depends on many factors ranging from spring/swaybar rate, dampers, tire size, car weight, etc...
Both really low and really high pressures can increase heat in the tire. With both the A048 and R888 i've ran with 30-32psi hot before (starting in the mid to high 20's).
Did you do a cooldown lap? Did you check the temps IMMEDIATELY after you got off the track?
*also make sure to stick the ENTIRE probe (0.5-1.0cm) into the carcass of the tire. Do not worry, you will not pop it.
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Ah, no I did a cool down lap and checked temps back at my parking spot. Yes, I am sticking the entire probe into the tire to take the temp readings.
I guess my real reason for going into such detail is I have always felt my car has too much over steer (I have spun twice under acceleration, but thankfully stayed on the track). I have never felt even a hint of under steer.
I'm sure 90% of the problem is driver and I am working on more seat time. But I assume getting the car set up properly will help me.
I will skip the cool down lap and check temps immediately off the track. Am I targeting 160 to 220 deg with similar temps outside/center/inside? With the R888s, should I start lower (33 hot) and go up if the temp readings aren't good and the "feel" is not good, or start high (40 hot) and go down? Thanks!
I guess my real reason for going into such detail is I have always felt my car has too much over steer (I have spun twice under acceleration, but thankfully stayed on the track). I have never felt even a hint of under steer.
I'm sure 90% of the problem is driver and I am working on more seat time. But I assume getting the car set up properly will help me.
I will skip the cool down lap and check temps immediately off the track. Am I targeting 160 to 220 deg with similar temps outside/center/inside? With the R888s, should I start lower (33 hot) and go up if the temp readings aren't good and the "feel" is not good, or start high (40 hot) and go down? Thanks!
In a perfect world, with a perfect suspension and perfect tire pressure, you would see the same temperature inside, center and outside. BUT we don't live in a perfect world. Looking at the three temperatures, the center of the tire is your 'pressure' temperature. You typically will not see the same temperatures on the edges, but the center will split the difference with the outside edges. Example: if the outside of the tire is 160 degrees and the inside is 140, then theoretically you want the middle to be 150. If your center is higher than 150, then there's too much air and the tire is bowing the center of the tire out, in which case you want to let a little air out. If the center temperature is under 150, then pressure is too low and you'd want to put a little air in. But again, there are a lot of variable at play here including your driving style and alignment. For example: I run 3 deg of camber and lots of front toe, so when my car is going down the straight the inside edge is heating up. So I'm not going to have that 160 150 140 type reading.
Just me personally, I'd start low and go up.
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Tire size front and rear?
Spring rates front and rear? (JIC)
Sway bars front and rear?
Camber and toe front and rear?
Rake (difference in ride height measured at the front jack point on the frame rail relative to the rear jack point)?
Target ~200-210*F. A general rule of thumb is to have a 20*F split from inside to outside with the INSIDE being hotter.
Ex): Outside-Middle-Inside (L) (R) Inside-Middle-Outside =
180-190-200 200-190-180
You want the insides to be hotter than the outside, because the outer edge of the tire cools down on straights while the front stays in contact to the ground, has more load on it, and does not cool down as much as the outer edge (because it's being loaded and used more).
I went from running RA1's for a few years to running three sets of R888's this past year. The R888's were a chore to get dialed in and seemed to hate higher pressures and got really loose when pressures rose. Due to the R888's rounded sidewall, they tend to like a lot of camber and very low pressures on my car (about 4-6lbs lower hot than RA1's). I had the best handling and wear with them at 32lbs hot front and 32lbs hot rear similar to what Billy mentioned. I think he drove my car with this setup.
Anyhow, I've moved on to Nitto NT01's and I'm much happier. They are more predictable and quicker. I run these 36 hot front and 36 hot rear with great success (I'm also running less camber than with the R888's).
Anyhow, I've moved on to Nitto NT01's and I'm much happier. They are more predictable and quicker. I run these 36 hot front and 36 hot rear with great success (I'm also running less camber than with the R888's).
