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· 2JZ NA-T
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7,624 Posts
Discussion Starter · #1 ·
Hey guys, i'll be heading back to the track on the 16th of this month to shoot for 11's after running a 12.011 at 118 last time (which was my first time out).

i know what everyone thinks of it, but regardless, i am running the MT ET' streets in the back ( 26x11.5 i think) and my radial tires up front. last time out there was little to minimal swaying in the rear, and it was far from uncontrollable, especially with me only making 450rwhp @ 16psi.


but anyways, last time bfore i went to the track, i pumped the MT's to 22psi, in between the 9 runs, i dropped the pressure 4 times, and at the end of the night i left with just as much, if not more pressure in them as when i started. I know tires build pressure as you warm them up, but i didnt realize how much....

so here is my question.....

next time out im want to start with 18psi in the rear, and progressivley work my way down to no less than 16, or maybe 15 psi, i dont want to risk running into the wall running only high 11's..... so would dropping the pressure to 14psi and doing a nice long burnout get them back up to 16psi range? is there any good rule of thumb when it comes to things like that?

i know the tires have a lot more grip in them, but im not going down to 12-and 13 psi range to get it, i jsu tneed a little bit more grip to get my 60" down from the 1.8 that it is @ now.


all help is greatly appreciated
 

· Speed Addicted
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857 Posts
I am probably not the right person to get the exact right pressure from considering you are running radials in the front, but I can tell you from experience that it is probably not safe to drop your tire pressure down really low with radials in the front. The car sways bad enough on ET Streets with low tire pressure even with skinnies, and it would be considerably harder to control with radials in the front. I drove to the dyno once with radials up front and ET Streets in the rear (maybe 18 lbs or so in the tires) and the car swayed a lot with every bump in the road or lane change. I guess I'm saying all this so you know to expect the car to be very hard to control if you are going to do this. I think I'd get some skinnies if I were you. I personally don't like wild unpredictable side-to-side rides down the track. LOL The wall doesn't look too great to me. :)
 

· WI-FI FTW, GTFO fuse box!
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9,209 Posts
I would not run the full 1/4. The 1/8 is the only thing that is safe for your setup. Hell, it was still annoying for me to keep it straight in the 1/8 with ET streets our back and radials up front.
Leave the line with 15psi COLD and go down in 1 psi increments.
 

· 2JZ NA-T
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7,624 Posts
Discussion Starter · #4 ·
the swaying really isnt as bad as everyone makes it seem, lol

and i have already taken it down the track, but they had about 19 psi in them.


i did take it out on the highway with 16psi cold, no warm up, and took it to 90 mph in a 1, 2, 3 gear pull, swayed? yes, but it was horrible or scary, but i gues i am used to the car kicking out on me at high speeds, i drive in the rain and on wet roads all the time, which means i break loose at about 90 mph and get a bit sideways.

and the thing about swaying... you dont need correction, maybe just a little bit... the swaying you are feeling is coming from the rear end changing direction, just the sidewalls giving a little bit...meaing what? more then likely the car is still driving straight, so just over come the natural tendency to correct unless it really is heading for the wall, in which case you can just back out of throttle and give up the run
.

but any ways, thanks for hte advice, i'll let youo know what happens this thursday
 

· 2JZ NA-T
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7,624 Posts
Discussion Starter · #6 ·
damn man, thats awesome!

congrats on taht run.

are you running skinnies up front? im going to start at 16 psi and work my way down a bit as i feel comfortable... only thing is that i wont be able to make a lot of passes, my car has a lean issue right now so im not going to beat on it too hard.

do you have some sort of 2step or launch control?
 

· 7M Fanatic
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3,614 Posts
2 thoughts.......

There are tire relief valves available, typicly found in circle track suppier's inventory, for like sprint cars,
that will bleed off air as the tires heat up.

And you might think about picking up a nitrogen tank (like Co2 & nitrous tanks),
with a regulator.

When I was road racing, I only used strait nitrogen in the tires.
It does not expand as much as it heats up.
 

· Premium Member
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7,718 Posts
I figured since Raven didn't answer, I'd give this a bump.

I also wanted to throw out there my experience on ET Streets and radials. It can be a handful if the tire pressures are too low, anything below 13.5psi cold and I usually end up getting out of it on the back half of the 1/4. Anything above that and it is very controllable. For the price of FD wheels and ET Streets, it is well worth being a little on your toes. Too many people say it's such a big deal, and with the price of skinnies, it's no wonder so many guys try it.

As far as hooking for the OP, I usually run at 14psi cold and have no problems. If you are continuing to let pressure out as much as you say, it sounds like you are hot lapping and not giving the tires much of a chance to cool down. You have to understand that cold and hot pressures are very different. Good luck!

Reid
 

· WI-FI FTW, GTFO fuse box!
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9,209 Posts
Auto and 6MT tire pressures cannot be compared to each other 100%, if the same tire is used. If an auto guy tells you what works for him, use it as a REFERENCE only.
 

· 19in 795R HRE's FTW....
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8,015 Posts
Auto and 6MT tire pressures cannot be compared to each other 100%, if the same tire is used. If an auto guy tells you what works for him, use it as a REFERENCE only.
Really? How many passes have you made on slicks with an auto and a manual on various slick tires over the years? Do you have experience with both auto and manual tranny cars on slicks?

I run the exact same pressure in my manual and auto cars on slicks and run the same tires on both. I always start at 11psi and work my way down.
 

· WI-FI FTW, GTFO fuse box!
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9,209 Posts
Good to know! People learn from/like to hear this info. Like I said, it's a reference only. Weight, suspension, setup, etc....
 

· Premium Member
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7,718 Posts
Really? How many passes have you made on slicks with an auto and a manual on various slick tires over the years? Do you have experience with both auto and manual tranny cars on slicks?

I run the exact same pressure in my manual and auto cars on slicks and run the same tires on both. I always start at 11psi and work my way down.
Not minimizing your knowledge in any way, but I really only think this will only apply when comparing a 6spd car to an auto on a trans brake. An auto car that's foot braking is going to launch and squat differently due to the suspension preload. 6spd's and auto trans brakes leave a lot more similarly.

Reid
 
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