Air pressure vs track conditions and size.

When is it good to increase PSI? Adversely when is it good to drop PSI. It seems to me the radius of the turns would have some effect. Big radius needs a higher roll speed etc... Likewise the amount of grip available.

just trying to understand more about the tire dynamics.
 

XXX#40

2A supporter
Keep adding air till it loops, then back down 1/2 at a time until it doesn't.
That will be your baseline for that track under those conditions.
 
Keep adding air till it loops, then back down 1/2 at a time until it doesn't.
That will be your baseline for that track under those conditions.
That’s not a bad idea. I should be able to tell pretty quick even if it doesn’t loop. It’s hard for me to measure grip without being on that track. I’m assuming it’ll pick up grip throughout a night.
 

XXX#40

2A supporter
That’s not a bad idea. I should be able to tell pretty quick even if it doesn’t loop. It’s hard for me to measure grip without being on that track. I’m assuming it’ll pick up grip throughout a night.
Depends how the weather is, have seen tracks slow down after dark, and some get really fast.
Watch your tires, the more fuzz, the more bite.
Start putting the stop watch on others in your class, or other classes can also let you know how the track is going
 
We’ve been racing for about 10 races... 14 year old kid that’s a total gear head. He lives at the dirt tracks in our area. However, he’s a little too conservative as a driver. He often cleanly races to the front just to be bullied by the fast kid that spins nightly and pushes kids out of their way.

My comments are “go faster so he can’t touch you”. We need a little more speed and I’m not considering motor.

We got our feet wet on a 1/10th mile dry slick short track. The help I received there was paramount. My guy had us on 2psi/3psi. To me that is crazy but I went with it. Now, we’ve moved up to a 1/7th mile dry slick track. Fundamentally I can’t run 2/3psi. I’ve bumped it from 3/4 then bumped it to 3.4/4.4. The kart looks like it’s on asphalt. He turns, it bites and it goes wherever he wants to put it. However, he simply doesn’t look as fast as the other karts. He regularly turns lap times faster than what the winners are turning.

Then we went to practice at a brand new track. We spent a lot of time at practice. **note** we only have three sets of tires. One 2016 practice set and two 2019 race sets. (I didn’t want to destroy new tires learning resurfacing, stagger, psi, prep etc so we’ve only used three sets10-12 races). At the new track we ran the practice set and lap times 16.5ish, 2nd attempt we ran with better tires with better stagger dropped times down to 16.2ish. Third attempt same results.... 4th attempt we use the same set of tires that we ran 16.5’s with. He goes out against adults and runs a four lap average of 15.5.

I always check psi after a run. His RF was 15.6 psi. I didn’t walk the psi down on that tire by mistake. He was against adults running 15.6psi which probably put his RF stagger around 1.7

This got me to thinking that I need to find the sweet spot on PSI. I know we’ve been low for the 1/7th mile. We last raced at 3.4/4.4. I think I can possibly bump each tire 1.5 and still not be there.

**note** I have four new sets of Burris 33’s ready to go. But, I don’t want to use them until I get this figured out. I’m assuming they will need a slightly different psi.
 
Was that the only one you forgot to drop air on or were they all high? It might be saying you need more cross, he went almost a full second faster when you forgot to let that one down, or maybe the track was getting better we cant tell from the cheap seats.

Set it on the scales with all the air in the RF and see what the numbers are. 2/3psi range is small bull rings or "dirty" tracks that slicks cant get ahold of territory. I would be up in the 5-6 range all around next time at that track, like xxx said keep adding air until its loose.
 
Was that the only one you forgot to drop air on or were they all high? It might be saying you need more cross, he went almost a full second faster when you forgot to let that one down, or maybe the track was getting better we cant tell from the cheap seats.

Set it on the scales with all the air in the RF and see what the numbers are. 2/3psi range is small bull rings or "dirty" tracks that slicks cant get ahold of territory. I would be up in the 5-6 range all around next time at that track, like xxx said keep adding air until its loose.
Yea that was it. Front stagger was about 1.75”.

We’re definitely bumping it up. Not sure to what numbers yet but they’ll be up. We were rained out this week.

possibly he felt better against the adults. 🤷🏻‍♂️ I really don’t know.
 
^ If the carrot runs faster, the rabbit chasing it runs faster as well.

No doubt that your low air psi is hurting you on the bigger track(s.) Typically you're on 5/6 air with 33s as a starting point. I'd suggest starting there, and since you saw a real gain with your psi mistake - add a bit of cross by dropping the RF spindle a washer or two.
New tires will definitely help on low/no bite tracks like we have in the midwest.

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Update here. (Raced the same track Saturday where we had the psi goof)

Talking to others in this region I decided to roll out to practice on 5L/6R PSI.
Out of four laps he had three loops and one turn that looked like a Super Late model.

reminder We’d been running 3.4/4.4

I didn’t want to search for the sweet spot as discussed up top. I knew it would take more time so Saturday we rolled out in our heat race at 4/5. I knew it would be much better than the practice. He proceeded to take his first checkered flag in a kart. Started 5th and passed the field by the end of the 2nd lap. He had four laps of 15.2. The kart looked just hooked to the dirt. Very little sliding.

started #1 Spot for the feature. He lead 7 of 8 laps before getting pushed out of the inside lane. He was faster on straights and considerably slower through the center of the turns. He had four laps where he averages 14.95. So he literally smashed his lap times but the kid in 2nd made the right adjustments cause now he could get to his bumper.

i wanted to bump the psi up to maybe 4.4/5.4 but I didn’t just because is didn’t want to change anything. The next set of tires were nearly indentical but had a little more stagger in the RF.

big improvement this weekend.

now I just need to considered how we can be faster center off. It looked like it was a little tight on exit. I know the driver needed to back up the corner a little and he can’t give me much feedback yet.
 
Without have a tool to measure grip and know for certain I didn’t want to possibly take him out of chance to win. Had he backed the corner up and drove it in deeper he would’ve won as it was. But, he’s learning.

In what cases would a dry slick track “lose” grip in an evening? When does dry slick grip improve?

This track had some moisture to it. Rained all week. They worked the track 24 hours before the event and had it in pretty good shape. Watered it 2 or 3 times during the night. Standing on it it felt soft. Even spongy in some cases.
 

racing promotor

Moderator
Without have a tool to measure grip and know for certain I didn’t want to possibly take him out of chance to win. Had he backed the corner up and drove it in deeper he would’ve won as it was. But, he’s learning.

In what cases would a dry slick track “lose” grip in an evening? When does dry slick grip improve?

This track had some moisture to it. Rained all week. They worked the track 24 hours before the event and had it in pretty good shape. Watered it 2 or 3 times during the night. Standing on it it felt soft. Even spongy in some cases.
You always have a tool to measure grip, monitor times of the faster Sr class drivers 4 classes ahead of you.
Curious were you on a set of your new tires. ?
 
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