Track Tac

Tire Pressure help... I'm wrapped around the axle on this one.

ShialaBEEF

ShialaBEEF

Member
I have a JR1 and JR3 driver. We race primarily Saturday night club (points) races. The track has a Maxxis Tire rule for all classes.

I struggle to confidently make tire pressure decisions at the racetrack. There are so many other variables such as tire prep, durometer reading, track conditions, etc. and I just can't seem to keep it simple or wrap my mind around appropriate psi adjustments. I have simplified by internal and external prep program, and I generally use 3-4 preps from one prep line, with a few other preps on hand in case the track condition or situation calls for it.

In general, we perform well, run with the pack, and have the speed to be in the hunt. Where I am struggling is knowing that 0.1-0.5 psi adjustments can make a huge difference. I use the Maxxis recommended 6 psi on the rights and 5 psi on the left as a starting point. From experience I've found that something close to 6 & 5 works well on a regular Saturday night. If the track grips up fast during the day I've run as much as 8.5 & 7.5 on my JR3 driver's kart and in general I can run 0.5-1 psi more in my JR1 driver's kart. In opposite situations where the track is literally a sponge, the weather is cold, heavy dew sets, or the track lacks grip in general I've run as little as 4 psi and 3 psi.

If anyone has experience they are willing to share on psi starting points and adjustment strategies I'm willing to listen without judgement.
 
you are making the right decisions in my opinion you should be more confident. I tend to start out on a pressure between the two extremes and adjust psi based on what ratio/lap times are telling me. if your motor is over revving I up the pressure and take teeth off until i hit my target. opposite for when the track has no grip. reading the track comes with experience. a lot of races are won by having the confidence to take a chance on what you know to be right while others are hesitant . talk to your prep supplier for scenarios when prep A will allow you to do this and prep B is needed for that. Most i have talked to will give you really good advice if you just ask.
 
You have a better understanding than your giving yourself credit for, however for the softer, wet, lower grip times do not use a full 1 lb split, use straight up air same all 4 tires, and as it starts gripping up transition to 1/2 lb split, then full 1 lb, max air you can get away with will provide roll speed which turns into forward drive, however to much air that it slides you'll never make that up with roll speed, if you miss it by a 1/2 lb your better off being 1/2 lb low than 1/2 lb high, remember more air will build heat quicker.
 
Thanks for the confidence boost. I know I can get it in the ballpark, I just don’t know when to confidently say, for example, 6.2 psi is optimum… i.e. not 6.1, not 6.3.
 
racing promotor said:
You have a better understanding than your giving yourself credit for, however for the softer, wet, lower grip times do not use a full 1 lb split, use straight up air same all 4 tires, and as it starts gripping up transition to 1/2 lb split, then full 1 lb, max air you can get away with will provide roll speed which turns into forward drive, however to much air that it slides you'll never make that up with roll speed, if you miss it by a 1/2 lb your better off being 1/2 lb low than 1/2 lb high, remember more air will build heat quicker.
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This helps a lot! I’ve been toying with the thought of reducing the split. When to do it, why to do it, hence the “wrapped around the axle” thread title 🤦‍♂️
 
J'-remy said:
you are making the right decisions in my opinion you should be more confident. I tend to start out on a pressure between the two extremes and adjust psi based on what ratio/lap times are telling me. if your motor is over revving I up the pressure and take teeth off until i hit my target. opposite for when the track has no grip. reading the track comes with experience. a lot of races are won by having the confidence to take a chance on what you know to be right while others are hesitant . talk to your prep supplier for scenarios when prep A will allow you to do this and prep B is needed for that. Most i have talked to will give you really good advice if you just ask.
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Thanks! There is so much good info in this! On a normal Saturday I know where to begin with the gear and MIGHT go up or down a tooth to keep them in that torque band. When adding air on days when the track is fast I’m also dropping teeth of the axle to prevent them from turning the engine to the moon. I’ll also be sure to ask the mad scientist (prep guy) for an air pressure course 😃 appreciate the advice!
 
I think the biggest thing is just don't overthink tiny corrections like 6.1 vs 6.2 or 6.3. Generally if the air is close on the heat or qualifying, or if you're running multiple classes and think you can get away with it. Test in classes that you KNOW aren't going to hurt. So if you're running 6.2 and you feel like the prep is where it needs to be and finished second. 6.3 isn't going to usually make the difference. You only have so many chances and the conditions week to week, track to track are going to be different. It's all a guess in dirt track racing. There are some pretty educated guesses, but ultimately it's all a guess. There is almost NO WAY to prove you'd have won if you were at 6.3, 6.4, or even 6.5. Too many variables. No reason to get bogged down in the unlimited amount of adjustments you COULD have made.

For what it's worth, I make most of my adjustments in .2 or .5 increments. Depending on how much I expect them to gain. No sense in fighting tenths in air pressure, the gains just aren't there in my opinion.
 
ABR #69 said:
I think the biggest thing is just don't overthink tiny corrections like 6.1 vs 6.2 or 6.3. Generally if the air is close on the heat or qualifying, or if you're running multiple classes and think you can get away with it. Test in classes that you KNOW aren't going to hurt. So if you're running 6.2 and you feel like the prep is where it needs to be and finished second. 6.3 isn't going to usually make the difference. You only have so many chances and the conditions week to week, track to track are going to be different. It's all a guess in dirt track racing. There are some pretty educated guesses, but ultimately it's all a guess. There is almost NO WAY to prove you'd have won if you were at 6.3, 6.4, or even 6.5. Too many variables. No reason to get bogged down in the unlimited amount of adjustments you COULD have made.

For what it's worth, I make most of my adjustments in .2 or .5 increments. Depending on how much I expect them to gain. No sense in fighting tenths in air pressure, the gains just aren't there in my opinion.
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Great input! Thanks! I agree it’s nearly impossible to prove I guessed right with precision lol. Realistically I’m still at the point where if my JR driver overdrives it into the corner then pinches the wheel and brings the back end around they’ll complain about how loose it is. So… yeah 6.1, 6.2, 6.3 are all the same to me right now. I have people that help me at the track and we’ve never had a debate over 0.1 psi. If there was ever such a conversation among the big boys I’d love to be a fly on the wall 😃
 
ShialaBEEF said:
Great input! Thanks! I agree it’s nearly impossible to prove I guessed right with precision lol. Realistically I’m still at the point where if my JR driver overdrives it into the corner then pinches the wheel and brings the back end around they’ll complain about how loose it is. So… yeah 6.1, 6.2, 6.3 are all the same to me right now. I have people that help me at the track and we’ve never had a debate over 0.1 psi. If there was ever such a conversation among the big boys I’d love to be a fly on the wall 😃
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Don't spend any time on .2 or .3 psi change right now, work on your little driver
Smoooooooooth on that wheel. Hit his marks, preach Momentum, Momentum, Momentum, Momentum. Did I say Momentum, once that's fixed then start testing that .2 to .3 adjustment.
 
Also, if you are not running nitrogen, then it is very common to see an increase of way more than .1 or .2 psi pressure as the tire (and air) heats up over a run.
Don't get caught up in splitting hairs. Even the "big boys" look at 1/4 and 1/2 psi changes more often than not.

I've always found myself running more air in my slower classes and putting more bite in the tires so that we don't lose sidebite as we gain roll speed.
You can also run slightly less split to get the left side tires up on air and help on roll speed and not skate so much in the corners with the little guys. Consider their total weight, VCG, and corner entry speed into your chassis set-up and tire program and you can see why this works. FWIW, doing the same thing in an adult class will generally lock him into the racetrack. :)

Like Ken said, Small plate and low HP classes are all about momentum.


-----
🏁Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
33 years of service to the karting industry ~ 1Cor 9:24
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
 
ShialaBEEF said:
I struggle to confidently make tire pressure decisions at the racetrack.
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As others have said your doing just fine with air pressure.

In general the amount of air relates to the amount of grip between your tires and the track.
More grip/More air ............ Less grip/Less air ........... and that's about all there is to it

Weight move to the right in the turn which in general raises grip on the right side so the reason for baseline recommended 6 rights/5 lefts.

The rest is about how much the track varies and how much you alter grip prepping.
You already know if the track increases in grip you go up on the air pressure.

In general you'll roll faster with less grip so long as you have enough grip.

The rest is about driving, seat time, seat time seat time, how you make your chassis and tires work to move weight around and did I mention seat time and your drivers gaining experience with seat time, seat time and more seat time?

With your already stated knowledge of air pressure your way ahead in the game of learning.
 
bottom line if your in the top 5 every week your doing better than most. the best out there miss tires all the time. can't win them all. I'm not advising you to settle for second so don't get me wrong. but you should be proud of what you've accomplished in a short amount of time. I race against people who've been doing this for 15-20 years. agree .1-.2 psi is not a thing to fret over. i shoot for .25-.50 increments. you will not gain any knowledge making micro adjustment its got to be bigger to know what the change does.
 
paulkish said:
As others have said your doing just fine with air pressure.

In general the amount of air relates to the amount of grip between your tires and the track.
More grip/More air ............ Less grip/Less air ........... and that's about all there is to it

Weight move to the right in the turn which in general raises grip on the right side so the reason for baseline recommended 6 rights/5 lefts.

The rest is about how much the track varies and how much you alter grip prepping.
You already know if the track increases in grip you go up on the air pressure.

In general you'll roll faster with less grip so long as you have enough grip.

The rest is about driving, seat time, seat time seat time, how you make your chassis and tires work to move weight around and did I mention seat time and your drivers gaining experience with seat time, seat time and more seat time?

With your already stated knowledge of air pressure your way ahead in the game of learning.
Click to expand...
Thanks @paulkish Yes I'm doing all I can to get these JR drivers the experience and laps required to not only be FAST, but smart, patient, and consistent. We've got a 20 race schedule laid out and have already improved remarkably with just a year under our belt.
 
CarlsonMotorsports said:
Also, if you are not running nitrogen, then it is very common to see an increase of way more than .1 or .2 psi pressure as the tire (and air) heats up over a run.
Don't get caught up in splitting hairs. Even the "big boys" look at 1/4 and 1/2 psi changes more often than not.

I've always found myself running more air in my slower classes and putting more bite in the tires so that we don't lose sidebite as we gain roll speed.
You can also run slightly less split to get the left side tires up on air and help on roll speed and not skate so much in the corners with the little guys. Consider their total weight, VCG, and corner entry speed into your chassis set-up and tire program and you can see why this works. FWIW, doing the same thing in an adult class will generally lock him into the racetrack. :)

Like Ken said, Small plate and low HP classes are all about momentum.


-----
🏁Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
33 years of service to the karting industry ~ 1Cor 9:24
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
Click to expand...
Thanks @CarlsonMotorsports & @racing promotor !!! Yes Momentum is crucial in the restricted classes and I'm trying to coach my JR3 driver to drive it up out of the corner (he arc's it in pretty well and pretty consistent) even when he is traffic or running behind another kart. He learned a valuable lesson a few weeks ago. You can catch someone but if start pulling it down out of the corner and peaking every lap you'll never get by them because you lose MOMENTUM. He had a very experience, smart JR driver in front of him and that kid pretty much put on a master class. They held their line and drove it up out of the corner, didn't pull down whatsoever, kept it wound up, and with my driver pulling down and scrubbing speed he couldn't get to the their bumper. My advice to my boy was in that situation you have to drive your line, keep her wound up, put the pressure on them and let them know you are there (LORD PLEASE DON'T HIT EM) and find a spot on the track where they bobble, or don't have as much grip/pull etc. If you can find that spot where they are prone for mistakes, you know that's where you're going to pass them, just wait for it! ...and other smart drivers will do the same to you, so when someone is on your bumper, keep it wound up! Make less mistakes than other drivers and you'll finish ahead of them. JR3 is a really competitive class with kids that have even more character than they do driving ability. Egos haven't gotten too big yet lol :)
 
J'-remy said:
bottom line if your in the top 5 every week your doing better than most. the best out there miss tires all the time. can't win them all. I'm not advising you to settle for second so don't get me wrong. but you should be proud of what you've accomplished in a short amount of time. I race against people who've been doing this for 15-20 years. agree .1-.2 psi is not a thing to fret over. i shoot for .25-.50 increments. you will not gain any knowledge making micro adjustment its got to be bigger to know what the change does.
Click to expand...
Thanks @"J'-remy !! I'm confident we have a top five kart, even top three kart every week but to be sure we don't cross the finish line in the top 5 every week. I don't want to overinflate my contribution to that, we've had a lot of help :)

@paulkish preached seat time and experience and my son and daughter need a little more to get it to "click" We've set the pole more times than I can count on one hand, but when the green flag drops and the wolfpack starts coming for them they still get nervous and make mistakes. Not huge mistakes lol. We keep it out of the bails and stay pointed the right direction generally. In JR1 the karts space out a little more but on any given night in JR3 there are 5+ karts nose to tail jockeying for position. It's just going to take more time for my JR3 driver to learn to look 2 and 3 karts ahead of him and be ready to react. I'll be sure to report back after we get "the nut that attaches the seat to the steering wheel really tight"

And kudos to you for knowing the best out there miss the tires sometimes. I'd say we've gotten to the point where that's less than 10% of the laps that count for us. A few races ago I knew, and my son knew on the first lap that the tires were off. He spun right in front of me and I called him over. "Look buddy, sorry we missed the tires. Now your goal is to go drive it within it's limits, finish this race and pick up as many spots as possible." (kinda cool caution laps don't count and I can have a quick chat with my boy in a situation like that). He ended up 4th out of 9 or 10 I think. One kart pulled off and a few karts cracked it up with 2 to go and were put to the back and he was able to hold them off for two laps.
 
This might be of some help- (not mine, from Phantom)

𝘼𝙙𝙟𝙪𝙨𝙩𝙞𝙣𝙜 𝘼𝙞𝙧 𝙋𝙧𝙚𝙨𝙨𝙪𝙧𝙚 𝙤𝙣 𝙀𝙖𝙘𝙝 𝙄𝙣𝙙𝙞𝙫𝙞𝙙𝙪𝙖𝙡 𝙏𝙞𝙧𝙚
Adjusting individual tire pressures is a quick & useful tool in fine tuning your kart at the track. You can "customize" each tire's contact patch size & stiffness, along with the kart's cross. Changing the tire's stiffness will also change how the weight is transferred. So, now let's dive into the individual tire pressures...
𝐋𝐅 - The LF is typically the most common corner that you will make individual air pressure adjustments. The main reason for this is to adjust your kart's cross. More pressure will remove cross, and less pressure will add cross. The normal range of adjustment is +/- 1 psi in 1/4 psi increments.
𝐑𝐅 - More psi will stiffen the tire, which causes it to take weight transfer quicker at corner entry. This can add grip at that part of the corner. However, it makes the contact patch smaller which tends to reduce grip. Because these two effects compete against each other it is difficult to predict what will occur. Only testing this yourself will tell you what happens at your track under your conditions. More air in the RF will also add cross. Reducing psi will have the opposite effect(s).
𝐋𝐑 - More air will increase cross. This will also narrow the split between LR & RR. This can help the kart get off the left side tires and help the chassis work. More air in the LR can also decrease the amount of grip that it makes, which can help a push center-off.
𝐑𝐑 - Much like the RF, more air can cause faster weight transfer, but creates a smaller contact patch. Sometimes increased PSI will help the RR plant quicker on entry giving it more grip... but other times the reduced grip can cause the tire to slide. Similar to the RF, the effects vary and you must test them for yourself to figure out what will happen in your environment. Also, more air can sometimes help the kart free up center-off if the RR was being overworked prior to the adjustment.
 
Heading to the track Saturday. It’s going to be a hot one. Thanks everyone for the input. I feel more prepared to make informed decisions and take manageable risks on tire pressures for the kids!
 
A well known fellow member here uses equal air on both the LR and RR. The reason is that statically, most of the weight of the kart is on the left rear, and so that tire is smashed down more than the other 3 tires. That higher air in the left rear improves acceleration. That's what I would do, and just change stagger or grip on the tire to get the same handling. Since the left front does not cause much drag when the air is lower or higher, quick setup adjustments can be made with that tire
 
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