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Author Topic:   Air Pressure
LittleJohn0104
Dirt Roller

Total posts: 11
posted July 13, 2004 05:06 PM  
I realize that different tracks use different pressure but I am just starting in this whole racing thing. I wanted some ideas on what kind of pressure to run on a open wheel modified. I have a 3 inch roll out.

x13jc
Dirt Freak

Total posts: 390
posted July 13, 2004 05:55 PM  
10 PSI left, 12 right. (give or take)

de94wcc
Dirt Forum Racer

Total posts: 87
posted July 13, 2004 07:36 PM  
We usually run 14 rf, 12 rr, 10-11 lr, and 9 lf. You see a lot of guys running 6-7 pounds in the lr. I have heard the G-60 tends to "cup" in the middle when you go that low. Try to get your air pressure to where you are using the maximum surface area of the tire and you shouldn't have to adjust. Run your palm across the inside, middle and outside of the tire after the race and you can get a good idea if you are low or high on pressure.

zeroracing
Dirt Forum Champ
Total posts: 1875
posted July 13, 2004 08:24 PM  
i run 8 lf 10 lr 12 rr and 14 rf, keeps it simple for any helpers, start with lf and go around the car just adding 2 to each tire. if the track is rough, i usually know ahead of time(rain..certian tracks..) then i go 8 lf 11 lr 13-14 rr and 15-16 rf.
beadlock on rr only. also adjusting air pressure will mess up your scale numbers, so unless you have changed them at home and see what it does i do not recomend doing it at the track.

good points by de94wcc!

BrianW
Dirt Freak

Total posts: 385
posted July 14, 2004 09:00 AM  
I run really similar pressures to de94wcc

on a heavy track
9.5-10 14.5
10-11 12-12.5

on a slick track the Right side comes down a pound

NJantz
Dirt Forum Champ
Total posts: 755
posted July 14, 2004 01:49 PM  
3" of rollout????? wow, with what kind of tire?

With the IMCA G60 I'll run 8-10 typically and its usually dry slick.
Have tried to 6psi on the RR before. Don't recommend that! You tend to wear out the sidewalls. lol

JMillerJr76
Dirt Maniac

Total posts: 128
posted July 14, 2004 08:34 PM  
We have had 4 inches of stagger, but it came by a complete accident...when we mounted a new tire on the beadlock, we aired it up to 40psi, and forgot about it, it stayed out in the sun for about a week. and when we went to measure it I dropped the air down to 10psi, and it measured to be an 84. I couldnt believe it

LittleJohn0104
Dirt Roller

Total posts: 11
posted July 16, 2004 09:49 PM  
For our rollout we use a 91" on the right rear and an 88" on the left rear. We use a 88 on the left front and a 90 on the right front. Does this sound right? Do you let air out of the left side to put more weight on the left side of the car in order to get more grip on the track? Like I said we are very new to actually racing a car. We have raced four races. And as you guys know at the track every driver has something different to tell you. Most of them answer with, "Put your foot off in it!" Hehehe. Thanks for the advice all.

mod70
unregistered Total posts: 11
posted July 17, 2004 10:22 AM           send a private message to LittleJohn0104   Edit/Delete Message   Reply w/QuoteBBBBBB
LJ0104 - Get your info here, we're not racing against you. Think of air press as adding or removing spring rate to your car. The more air you put in a tire, the higher the spring rate that wheel will have. The higher the spring rate, the more weight that wheel is supporting. Letting air out of a tire can improve grip by making a larger footprint and getting more of the tire's surface area on the track.
By putting more pressure (and thereby adding more stagger) to both right side tires you are adding cross on entry which will loosen up the car going in (RF), and taking cross out which will loosen the car up comming off (RR). Just realize that you generaly will run more pressure on the right side to keep the tires on the rims since they recieve most of the weight while racing.

LittleJohn0104
Dirt Roller

Total posts: 11
posted July 17, 2004 09:27 PM  
Got you mod70. Thanks guys for all the info. Just remember don't leave me behind I don't have all the technical language down yet. Fast learner though. So what does that mean if you get a higher spring rate or that your wheel is supporting more weight? Does that help with handling or loosen the car up? Another thing. I have heard people through around loose, tight, and push. I realize that it is talking about how the car is handling. I believe push is when you go into a turn the car wants to push to the high side instead of turning. What about loose and tight. What "exactly" would these terms mean?

mod70
unregistered Total posts: 11
posted July 17, 2004 09:49 PM           send a private message to LittleJohn0104   Edit/Delete Message   Reply w/QuoteBBBBBB
OK, the eazy terms first; loose refers to the back of the car wanting to pass the front, spinning you out. Tight and push are the same thing, the front won't steer and the car just goes straight. When it's too tight you get to see the wall when you hit it, when it's loose you don't.
When a wheel is supporting more weight it is doing more work. If you want to add cross to the car you have the RF & LR supporting more weight, and if you remove cross you put more weight on the LF & RR. Adding cross will loosen the car entering the corner and tighten it up comming off. Removing cross will do the opposite. So if you add spring rate to the RR (either by air press or a stiffer spring) the car will tighten up as you turn in and loosen up as you get back in the gas.
Don't worry about being confused, it takes a while to get all this stuff right in your head. Visit this site often and read every question, even those about other suspentions and even classes. Ask lots of questions. You'll get it. Good luck!

LittleJohn0104
Dirt Roller

Total posts: 11
posted July 18, 2004 01:05 AM  
Thanks a million to you mod70 and the rest of you for the info. That info on the cross there will help us a ton!

LittleJohn0104
Dirt Roller

Total posts: 11
posted July 19, 2004 05:06 PM  
Okay here is another question. I hear about stagger. What is stagger? Is this the same thing as cross?

xhubby
Dirt Freak

Total posts: 376
posted July 19, 2004 07:49 PM  
Stagger is the difference in the circumference of one tire compared to another with tire pressures set at the psi you want. Example: RR tire measures 85" around at say 12psi. LR tire measures 84" at 8psi. You would have 1" of stagger in the rear. Cross is the total weight of your RF wheel added to your LR wheel as it sets on a set of scales. Hope this helps.

LittleJohn0104
Dirt Roller

Total posts: 11
posted July 20, 2004 07:50 AM  
Yes it does thanks. Another question though. What exactly does more and less stagger do? We call stagger rollout around here. Like I said above we have 3 inches. Is that enough or too much or good?

de94wcc
Dirt Forum Racer

Total posts: 87
posted July 20, 2004 11:25 AM  
Think of stagger like a styrofoam coffee cup laying on its side. If you push it, it will go around in circles. That's what stagger does, keeps your race car going around in circles. The bigger one end is than the other, the tighter the circles will be (i.e. the quicker it will turn). You will have to experiment to find out what the appropriate amount of stagger for your car/driving style is. 3" sounds a little excessive, but that's just to me. If you are loose in the middle of the corner, try taking some stagger out, if you are tight in the middle, try putting more in to help the car rotate. Good luck.

mod70
unregistered Total posts: 87
posted July 20, 2004 11:56 AM           send a private message to de94wcc   Edit/Delete Message   Reply w/QuoteBBBBBB
Just a quick suggestion L J, get yourself a copy of "IMCA Modified Racing Technology" by Steve Smith. It's the first book that I ever read on the subject and it got me a real good base of knowledge. It covers everything from the different types of rear suspentions to front end geometry (bump steer, Ackerman steering, camber, caster, etc.) even driving techniques. It's not the bible of racing by any means, but like I said, it's a real good place to learn. Check your local performance shops to see if they have a copy in stock, if not you can order one through Speedway Motors' race catalog www.speedwaymotors.com 402-323-3200. (less than $20) Keep up the good questions.

LittleJohn0104
Dirt Roller

Total posts: 11
posted July 20, 2004 01:24 PM  
Thanks for the suggestions! I will check that book out as soon as possible. Y'alls information should help me this weekend. Again thanks.

LittleJohn0104
Dirt Roller

Total posts: 11
posted July 21, 2004 01:36 AM  
Another question. When we are talking about modifieds are we all talking about the same class. Because here in MS we have the Southern Modified, an open wheeled car with a rear fin and big tires. We also have the UMP Modifieds, open wheeled car with out a rear fin, less engine ( I think) and street tires. What are most of you in?

mod70
unregistered Total posts: 11
posted July 21, 2004 12:28 PM           send a private message to LittleJohn0104   Edit/Delete Message   Reply w/QuoteBBBBBB
Although there are many different varriations of the "modified", the most common type is the IMCA modified (International Motor Contest Assoc.). I read that there are over 8,000 registered IMCA racers in the US, and that doesn't count all the racers that run an IMCA type mod on non-scantioned tracks that are unregistered. I think most mods are generaly baised on the IMCA rules with some changes made for different scantioning bodies and tracks. Here in the mid-west we follow the IMCA rules pretty closely, the usual changes being in the rear spoiler and tire brand. (IMCA runs McQuerry G-60 American Racers, most commonly changed to Hoosiers) Regardless of the scantioning body, the key to any class of racing is controling weight transfer, and the basics of how you go about doing that is pretty much the same.

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