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Track Day Tire Pressures

Siestarider

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#1
New set BFG Rival S scrubbed and halfway heat cycled, HDPE event this Saturday. Scanned a bunch of forums, seems these particular tires want less hot pressure than I ran in the SC-2's. Maybe as low as 34-36 psi hot is their sweet spot for light cars.

So I figure on dropping pressures at track session by session to maybe as little as 36F and 34R rear hot, no idea where that will leave me on ambient pressures for drive home, probably at least 5 psi less than track hot pressure. Way less than Ford recommends for street.

I am not comfortable running on 10 lbs lower pressures on track based solely on what I find on other forums for other cars tracking Rival S, anyone have some guidance?

Yes, I need a pyrometer and do not have one, I have always just "felt" for even heat across and between tires, looked at wear patterns, and adjusted accordingly.

Thanks
 


Young L

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#2
Not sure about the rivals but I was dropping the factory down 10 -15lbs and wasn't having any issues. Probably wasn't that smart of an idea but meh its all about learning.
 


MPA

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#3
30psi should be fine for the drive home - most cars I've had in the past were only 30psi. The FiST is the first car I've had that had the pressure so high.

I was thinking of dropping to 32.5F/30Rto try and soften up the ride a little
 


OP
S

Siestarider

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Thread Starter #4
Thanks guys, this is my first car with relatively high stock tire pressures. But my first two sets of tires have worn evenly so it must suit the car.

I will start at stock and reduce hot pressures back to stock after each session, maybe last session of day try some 5 psi lower than stock (hot pressure). Drive home is easy, not worried about that part.
 


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#5
Thanks guys, this is my first car with relatively high stock tire pressures. But my first two sets of tires have worn evenly so it must suit the car.

I will start at stock and reduce hot pressures back to stock after each session, maybe last session of day try some 5 psi lower than stock (hot pressure). Drive home is easy, not worried about that part.
I have a set of StarSpecs on mine, I start the track with 35 F and 32 Rear on my first session. My goal is to have the tires up to stock pressures when fully hot. Have not had any problems with grip as of late. My next track day is April 11th, I'll toy with lower pressures and will report back my results.
 


Young L

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#6
I have a set of StarSpecs on mine, I start the track with 35 F and 32 Rear on my first session. My goal is to have the tires up to stock pressures when fully hot. Have not had any problems with grip as of late. My next track day is April 11th, I'll toy with lower pressures and will report back my results.
How have the star specs been holdin up? Are you using them for daily or just track?
 


haste

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#7
Just ordered a set of Direzza ZII Star Spec myself. I will report my results after track days at VIR full in mid-may. I ran the stock tires last year and am expecting a huge difference in performance. I am furiously working on trying to keep the brakes cooler this time around.

I believe my cold tire pressures were too high last year. My tires had marbled to the middle of the tread during each session. They started feeling greasy after 4 laps or so. I think hot pressures were around 43 front/39 rear when starting with 35 front/32 rear. VIR is a fairly smooth track, so I don't think I need that high of a cold pressure.

Unfortunately, I didn't record my tire pressures and temps last year during sessions. I have a laser temp gun this year and hope to report temps all around, including ambient. Each track is different, so it might not be relevant for some drivers.
 


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#8
How have the star specs been holdin up? Are you using them for daily or just track?
They're great tires, I am currently DD'ing them and using them on the track. So far I have about 5 track days on them, will be coming up on my 6th track day on the 11th of April and they seem to be wearing a little faster than I expected. I am down to about 40%-30% life on them with those track days and less than 10,000 commuter miles. The current state that they're in they are HORRIBLE in the rain. I don't feel safe going over 55 mph on the freeway with them, the car hydroplanes/skids back and fourth over bumps in rainy conditions. Ironic because when new they held up perfectly fine in the rain. I won't be getting these again.
 


OP
S

Siestarider

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Thread Starter #9
Interesting and disappointing day at track. Started Rival S's on stock pressures, damp track, 80F ambient. End of first session hot pressures up 8 lbs from 39/36 cold. Started taking out 2 lbs all round, then went to pits during sessions and lowered again. By 4th session I was running 35 F and 32 R hot pressures, ambient was up to 90F. Nothing I did with pressures made a big difference. Handling stayed about the same, well balanced enough to drive long turns with throttle. Turn in began to suffer with lower pressures, and I began to wonder if I needed to add air to get home.

Never got within a second of my pb, set last October on near worn out BFG SC-2's. Seemed once I overdrove these tires during first morning session, could not re-gain grip. Tried alternating cool and hot laps, tried slow warm up, dang its strange.

Just went to garage and checked cold pressure, 29F and 27R.

Data say my best time was run on about 37F and 35R hot temps. But lack of grip persistent all day with max lateral g's below 1. I expected a lot more from the Rival S tires.

Only thing I can think of is maybe when I tried to heat cycle them last week I did not get them hot enough. They got plenty hot today, lol.
 


Pete

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#10
On my track days at Streets of Willow I was using the Re71-r tires. I came to the conclusion that cold tire temps should be at 26F and 28R. When I bought them I had a long conversation with the guy from tire rack about track temps. He suggested in the high 20's which I was skeptical at first. My first track day I did 32f/34r and gradually went down to the 26/28 combo. At my second track event I started with that combo and had perfect grip for 20 minutes at a time. No cool down laps just constant pushing. Only downside is the tires look like they are going to only last 3 track days.
 


Young L

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#11
yea that 25-30 psi range is what I was doing with the factory tires cold and when Id come off track id be right around factory specs again. I try to keep the rears around 35 and the fronts 39 or 40.
 


OP
S

Siestarider

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Thread Starter #12
Left the Rival S on for street use, set cold pressures at 37F 35R. Lots of rain yesterday, have to say the SC-2's were a much better street tire and better on track. Rivals are slippery in wet. They better be really good next track day or they will be replaced. I am hoping my failed attempt to heat cure them before tracking is now remedied by a track day, and they will shock me with gorilla grip next time out.
 


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#14
On my track days at Streets of Willow I was using the Re71-r tires. I came to the conclusion that cold tire temps should be at 26F and 28R. When I bought them I had a long conversation with the guy from tire rack about track temps. He suggested in the high 20's which I was skeptical at first. My first track day I did 32f/34r and gradually went down to the 26/28 combo. At my second track event I started with that combo and had perfect grip for 20 minutes at a time. No cool down laps just constant pushing. Only downside is the tires look like they are going to only last 3 track days.
Pete, I remember meeting you at the Dec. 26 Streets of Willow event and you recommended the 30/30 on my tires. I used it that day and this last track day I had at Thunderhill West, and it's been very good to me. This was running on my Federal Evo 595's. When I change to a higher performing tire, I might have to fiddle around a little more. But this worked for me. Thanks! (I was in the Red FiST that day)
 


meFiSTo

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#15
I very much like the advice of lower cold temps to start (when running ambient air). I think the "ideal" pressure depends a little bit on the tire. That is obvious I guess, but in particular I have been thinking about this question in relation to tires of different sizes.

The stock tires have very short sidewalls and probably work better and are safer with a little higher pressure overall than tires with more sidewall. I think that's why the stock tires have such a high cold street pressure recommendation.

I have have not run this car at the track that much yet and I have different tires dimensions compared with my previous car. That car had 17x7 and 16x7 wheels. I ran 215/45-17 and 215/45-16 Extreme Performance Summer tires or 205/40-17 R-compounds.

i believe the best way to arrive at an "ideal" pressure for any given situation is with a tire temp probe, like this: http://www.summitracing.com/parts/lng-50640?seid=srese1&gclid=CPKP8oPkvMwCFUlufgodd_4KfQn
You want to have as consistent of temps across the tire contact patch as possible and as much surface on the ground as possible, within the design of the tire.

I had one, but then sold it back in 2012 when I thought I was done with this stuff. Stupid.

In general, for my Fi SVT Focus, I landed at about 37-38 PSI hot front and back for the street tires. Depending on the direction of the track and the type of track, that usually meant starting around 30 to 31 PSI in the front (lower on the outside tire) and then 31 to 32 on the rear tires (same approach). That did NOT nail 38. I would invariably come in having run the last few laps of the first session a little greasy. I would let a little air out to get to about 37ish and then run like that and observe my pressures when I came off for subsequent sessions.

Having said that, I added maybe a pound all the way around for shorter sidewall 205/40-17 RA1s and the like, still shooting for about 38 PSI hot at the end of a session.

For my 15x7 and 15x8 wheels and tires (205/50-15 and 225/45-15) on this car, I might take a pound of cold pressure out and see where that lands me. I just monitor how the tires do against the triangular wear-indicators on the top of the sideway. I might get a probe again, but at this point I'm not sure that it's worth the $140 plus. Maybe. However, I'm not racing and I'd just be getting readings to come up with guidelines. I wouldn't probe religiously. I kind of think i have a reasonable guideline already. We'll see. You can kind of tell by how the tires perform during a session.
 


Pete

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#16
Pete, I remember meeting you at the Dec. 26 Streets of Willow event and you recommended the 30/30 on my tires. I used it that day and this last track day I had at Thunderhill West, and it's been very good to me. This was running on my Federal Evo 595's. When I change to a higher performing tire, I might have to fiddle around a little more. But this worked for me. Thanks! (I was in the Red FiST that day)
You are most welcome. If I remember correctly you were pretty much stock on that day running around the track. Good fun the fiesta is. The harder you drive and with different tires and compounds you have to start playing around with the tire pressure. Same goes when you change your suspension as why now I have higher pressure in the rear vs front.
 


OP
S

Siestarider

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Thread Starter #17
Being a data hound, I will obtain a probe type sensor and monitor temps next track day. Mefisto presented an excellent rationale behind the general pressure starting points, but I see no alternative to taking the measurements across each tire. I am just not experienced enough to play with pressures and "feel" on track.

I am still on stock running gear, and until I understand tire temps and pressures, have enough challenge just getting the stock setup to work through tires to track.
 


OP
S

Siestarider

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Thread Starter #19
Laughing. Like I knew my old BFG SC-2's had hardened into roller skates at their last trackday, in spite of wear bars saying they had a little left.

Just ordered Joe's digital tire temp probe, will post anything useful I learn from it. While researching which one to buy, I found you can also buy a durometer to measure hardness, tell you when tires have heat cycled into roller skates.

I doubt the Rival S's I am running now will last long enough to heat cycle out, but it would be interesting to know the relationship between heat cycles and hardness. Just what i need, another tool and set of measurements to record and analyze. Only to learn it probably depends more on which tire you use than anything else
 


OP
S

Siestarider

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Thread Starter #20
Ran Rival S again today at PBIR. Started with cold pressures 35F/32R. Tire temps recorded with Joe's meter (works great) are presented as if looking down on car, three temps per tire. Clockwise track especially hard on front left. First session

188/185/165:155/155/155
150/140/135:133/134/142

Took 1 lb out of left front before second session:

170/165/150:165/160/156
146/139/134:138/136/133

No changes third session, except ambient temps early afternoon went above 90F

170's:160's
150's:150's

Set new PB first session, lowered it third session. Last 3 laps 3rd session all within 0.5 sec of PB and within 0.1 sec of each other. Obviously pretty light traffic.

Hot tire pressures after 3rd session:

45:45
44:43

Its easy to see a little more negative camber left front and rear would be appreciated by the tires. No complaints about grip, very easy to drive plus more seat time accounts for consistency.

I would have kept lowering pressures but the temps across tread looked good to me. Not obviously over or under inflated.

Maybe the 215/45/16 Rival S is just a little too wide for 7" wheels and needs the higher pressures to keep tread flat?

My tracking mentor Nick says suspension is next mod. Need to get enough camber to even up the stress, especially up front. But then may need a little more spring rate in rear.

So, I conclude that testing temps across tread probably saved me going further down with tire pressures and just becoming more confused, like I obviously was the first time I tracked these tires. Still seems like too much pressure but if tires are happy, so am I.
 




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