28psi for me at Sebring in Florida heat
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Would love to see how the new A7 stacks in this list. NASA is calling it a 22 point tire. I heard it has more grip than the A6.
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Originally Posted by k24madness
(Post 1156097)
NASA is calling it a 22 point tire.
Wonder where it'll land officially? |
Originally Posted by billybobster
(Post 1156045)
What's a good cold pressure for the Rivals? I've got a pyrometer so just looking for something in the neighborhood for the first session going out. I saw Emilio said 35psi is their hot happy place on one of his cars. So cold at 30psi?
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Wow, I thought the BFG R1-s getting 15 points was a bit excessive. 22 points? NASA's very subtle way of saying "Don't run this tire!"
What's the Hoosier R7 get? 13? 15? |
Originally Posted by billybobster
(Post 1156045)
What's a good cold pressure for the Rivals? I've got a pyrometer so just looking for something in the neighborhood for the first session going out. I saw Emilio said 35psi is their hot happy place on one of his cars. So cold at 30psi?
15x9 wheels ~2350# w/ driver -2.3 front, -1.9 rear To Leafy's point about water, there is a way to get most of the moisture out that I heard from a local guy. I can't remember it off of the top of my head, but I'm pretty lazy when it comes to setting pressures for the day since I'm pretty slow. My routine is to set the tires all to the same pressure at the beginning of the morning, do my first session, and bleed off pressure until they're all the same hot. I had about 200 street miles on my Rivals (including the 90 mile drive up to VIR) before my first DE this year, and the water vapor had some nasty spikes on a few of the tires. I think it was something like 42-40-39-44, bled it down to 37psi after hopping out of the car and was going to adjust if the car felt loose later on the day. :2cents: |
Originally Posted by Leafy
(Post 1156136)
Starting pressure depends on how hot they're going to get and how much water is in the air inside the tire. Now that I've started mounting my own tires I noticed that if I dont wide the tire lube off the inside of the wheel and tire before I seat the bead that I get huge pressure rises with heat because of all the water.
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Originally Posted by WAM
(Post 1156426)
Not saying you're wrong. You saw what you saw. But some guy ran a pretty well controlled test of pressure build-up vs heat on the internet, and I think his results mirrored the perfect gas law. He was trying to debunk the nitrogen craze which he thought was a $$ scam. His test procedure looked valid to me and did include moisture as a factor.
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Originally Posted by WAM
(Post 1156426)
Not saying you're wrong. You saw what you saw. But some guy ran a pretty well controlled test of pressure build-up vs heat on the internet, and I think his results mirrored the perfect gas law. He was trying to debunk the nitrogen craze which he thought was a $$ scam. His test procedure looked valid to me and did include moisture as a factor.
Just for reference. |
I have 225 Rivals on 9 in wheels. The car w/driver is around 2,500 (OK I'm on a diet). I start cold at 26. Have you checked out the Grassroots tests on the Rivals?
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Originally Posted by Dustin1824
(Post 1156435)
Keep in mind, air coming out of an air compressor is at 100% relative humidity, for the most part.
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Originally Posted by EricJ
(Post 1156436)
I have 225 Rivals on 9 in wheels. The car w/driver is around 2,500 (OK I'm on a diet). I start cold at 26. Have you checked out the Grassroots tests on the Rivals?
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Originally Posted by EricJ
(Post 1156436)
I have 225 Rivals on 9 in wheels. The car w/driver is around 2,500 (OK I'm on a diet). I start cold at 26. Have you checked out the Grassroots tests on the Rivals?
https://grassrootsmotorsports.com/fo...w/63368/page1/ I did check it out before switching from R888's to the Rivals. The "pixie dust, rainbows and unicorn farts" was definitely a positive factor. I think I'll start at 30psi and see where the pyrometer leads me. Or 28. Or 29. Two more questions... - A comment on the review mentioned dropping pressures to get more temp into the tires (if necessary). Anybody with experience on this? - Has anyone tried bumping up the cold pressure in the rain on the Rivals? Towards crowning helps clear water and reduces the contact patch helping get some heat into the tires. I did an A/B test on the R888's during the M@MRLS 2012 April monsoon. One session at 34psi cold - grip was OK but tires got no heat. The next (still bucketing down) at 40psi - noticeably better grip and the tire centers were steaming. |
Originally Posted by billybobster
(Post 1156507)
You mean this?
https://grassrootsmotorsports.com/fo...w/63368/page1/ I did check it out before switching from R888's to the Rivals. The "pixie dust, rainbows and unicorn farts" was definitely a positive factor. I think I'll start at 30psi and see where the pyrometer leads me. Or 28. Or 29. Two more questions... - A comment on the review mentioned dropping pressures to get more temp into the tires (if necessary). Anybody with experience on this? - Has anyone tried bumping up the cold pressure in the rain on the Rivals? Towards crowning helps clear water and reduces the contact patch helping get some heat into the tires. I did an A/B test on the R888's during the M@MRLS 2012 April monsoon. One session at 34psi cold - grip was OK but tires got no heat. The next (still bucketing down) at 40psi - noticeably better grip and the tire centers were steaming. tl;dr : Find a hot pressure that doesn't get your tires greasy, avoid understeer if they get greasy anyway. -Bumping pressure works in the rain for most tires. |
I dump pressure in the rain for more grip.
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let me clarify, I generally increase pressure in the rain to get more heat in the tires (also helps a bit with hydro-planing). I don't know if that leads to more grip, I have maybe 3-4 weekends in the rain.
decreasing pressure ~ more contact patch, so I am sure there is a sweet spot there. Probably depends on the amount of rain/puddling on the track btw. |
Originally Posted by k24madness
(Post 1156460)
Sounds like a good water separator like the body guys use for paint would go a long way to help PSI gain without the expensive Nitrogen gas.
edit: and on the current topic. We run very high pressures in full wet conditions. |
Availability and available gear (regulators etc) control suitability, but scuba air is just as dry as tech Nitrogen.
My small 0.85L 200bar bottle was capable to fill 4 empty 205 to 2 bar. Using a 3L 300 bar bottle now, lasts a whole season for me and my buddies. |
Originally Posted by greddygalant
(Post 1089213)
That's interesting to me I'm almost 3 seconds a lap faster on used SM RA1s vs fresh rivals. Same 205 size on a 15x8. This is around Portland International. I'm trying sm6 takeoffs for this year on a 15x8 again and see where that brings me.
As for required/budget I get free takeoffs all the time so I guess they fit my budget. |
Originally Posted by billybobster
(Post 1156507)
You mean this?
https://grassrootsmotorsports.com/fo...w/63368/page1/ |
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