Tips on setting tire pressures?


(Davin Roberts Sturdivant) #1

So, I thought I’d start a thread about people’s thoughts about how to appropriately set tire pressures for dry and wet tires. We know that tires can be use to set when the kart ‘comes in’ and also to help with some minor balance changes. However, I’d love for us to start chatting about tips and tricks that we use to get our karts dialed in.

One thing that I will throw out there is that having a setup journal is really helpful for this sort of thing, because then you can track your tire pressure notes over the course of all of your sessions to notice trending.

Your turn, guys!

(Andre Molina) #2

Set up journal: A good idea.

Wet tires: No idea, I don’t like moist races.

Slicks for New Karters: Pump it up :muscle: 20 PSI cold, take it out for a few laps, warm the tires up good and bring them in hot HOT hot down to between 15-20 PSI. Log starting pressures before you dial it down and try to set a trend. Find a tire pressure that works for you, stick to it, and work on the chassis instead of the tires. If you get to the point where you can’t dial the frame right, then start play with tire pressures. That will take care of the details.

Pro Tip: The thing about atmospheric air is that it’s volume expands and contracts in a non-linear direct relationship with temperature, since air is made up of different molecules with different densities (Nitrogen, Oxygen, Carbon Monoxide/Dioxide, etc.) so it is difficult (but not impossible) for you to nail tire pressures exactly without first warming up the tires.

I haven’t experimented with Nitrogen on karting, bu it works really well on cars and it’s a lot more predictable. Only then you can really say stuff like: “I like 20 PSI warm, I’ve learned that 15 PSI cold at 68 degrees F gives me 20 PSI warm, the track temp today is 70F, so I’ll bring the cold pressures to 14 PSI and I’ll be 95% sure I’ll be racing on 20 PSI tires.”

(Aaron Hachmeister) #3

Oh god that’s so complicated… I just mess around with cold PSI knowing it’s between 10-14. I figure 10 would be the lowest we go, rationalizing if it’s above 90 that’s probably what to go with, and if 14 is the highest it’s probably going to be like 40 degrees out. otherwise I’m just guessing somewhere in between.

Otherwise I tend to stagger my outside rear by .5 PSI due to the added work that it does. I found doing that eliminates the small hopping that happens occasionally

(TJ Koyen) #4

We’ve gotten to the point where we always run pretty much the same pressures since we run MG Yellows/Evincos all the time.

But what I like to do starting on a new tire, is set it at the manufacturer’s specification first. Most brands have a recommended race pressure for each compound. From there, keep dropping pressure until you feel the sidewall begin to flex and fold over. That’s your minimum pressure. To get your maximum pressure, keep going up from that recommended psi until you hit a point where the kart starts to become super loose (tires overheating) after 2 laps. That’s your qualifying pressure.

If it’s colder and lower grip, run closer to your qualifying pressure. If it’s hotter and high grip, run closer to your minimum pressure.

We don’t do a lot as far as staggering pressures, but sometimes if the track is really left or right turn biased we will drop .5 on one side and go from there.

Once you get a feeling for the tires at their lowest and highest workable pressures, you can start to feel how different pressures actually affect the balance of the kart. I’ve always found on a soft tire like MG Yellows, the lower you go the more dig you get in the corner. If you go too lower though, the tire will start to fold over and hop.

Example: MG Yellows run best between 8-10 psi. If you go lower, you risk folding the tire over during hard cornering as the sidewall gives way. We’ve gone to 7.5 when it’s really hot out, but it’s rare. At 10 or higher, you’re starting to overheat the tire really quickly. With higher pressures, the tire starts to bulge and bit and doesn’t bite into the track as much. It skates around on top of the rubber rather than digging into the rubber.

We did the LeCont tire test last year and used this method and were able to dial a completely unknown tire in, in just a few sessions.

(Andre Molina) #5

Pressures set with the tire cold or hot?

(TJ Koyen) #6

Sorry, that’s set cold. I should’ve mentioned that!

(Andre Molina) #7

Sweet! What kind of press. are you seeing coming out hot?

(Davin Roberts Sturdivant) #8

You know, I’ve never really been one to care about hot pressures, only because I only really care about how the kart is handling once it’s out on the track. I’ll look at the tread wear pattern, but that’s it.

I guess that’s because I can’t change what the hot temp raises too once I go out, all I know is if the balance is good or not. It might affect what wheels I use, but that’s it.

(Andre Molina) #9

Honestly, if that’s what you want then you should be looking at hot pressures. Those are the pressures your kart is running at, at that particular track and environmental temp.

Cold temps don’t tell you a story.

(Davin Roberts Sturdivant) #10

I guess, but I guess what I’m saying is that to get to hot pressures, you have to start with cold pressures. If I leave with 8 psi, and I have a good handling kart, after checking the tire wearing, I’ll have a sense of the handling of the kart. Then if I’ll do another session at 10 psi and have a poor handling kart, then I know that I should go out at 8 psi.

I guess that’s why the starting PSI is what I pay more attention to, because they’re what I actually have the ability to change. I just might not be explaining it well.

(Andre Molina) #11

IMO, your first session for the day should always be a dirty, setup session. Go out and focus on setting the tires and the carb for the day.

(TJ Koyen) #12

Really depends on the track, but 11-12ish usually. Tuning to optimize your hot temps and analyzing your hot temps can tell you where the balance of the kart is. The driver should be able to convey that information by just feeling how the kart is on the track, but I’ve found with younger kids or particularly unreliable drivers, I can debunk their bogus handling assessments with tire pressure readings, or especially the tread wear like Davin mentioned. Tread wear will tell you basically everything you need to know about how the tire is working.

When I was driving for Merlin, we had Umberto Merlin himself at a national race one weekend. I was slightly off-pace, didn’t really have a good feel for the kart. He came over, looked at the front tires for about 20 seconds, and said “Zee kart has understeer. Widen front 5 mm.” Did that, picked up 3 tenths.

All he noticed was the graining on the front tires, no black magic or anything. But having that information base in your head helps make quick work of addressing handling maladies.

(Aaron Hachmeister) #13

I’ve never been good at feeling what the tires are doing on the kart. What would the sidewall flexing and folding over feel like?

(TJ Koyen) #14

It’ll be a hopping feeling usually. You’ll feel the outside tire take a “set”, where you feel it dig in initially, and then usually mid-corner when load has reached the maximum, you’ll feel the outside rear get a little soft and noodle-y and the kart will bounce a bit. That’s the tire folding over and rebounding.

(Ty Schlorer) #15

I’ve found that once I set the pressures hot, the next session they’ll come right back to that temp once they heat up. We usually shoot for manufacturer recommendations for pressure to start and then adjust from there.

(Aaron Hachmeister) #16

Any suggestions to start with for Bridgestone YLC’s? I can kinda imagine what you’re thinking about but I’m gonna try testing it on a practice day out at Badger once the track opens up again

(TJ Koyen) #17

13 psi on YLCs and adjust from there.

(Davin Roberts Sturdivant) #18

When you were testing on LeConts, were the the Reds or the Whites? (As I selfishly ask for tips on the Reds :stuck_out_tongue: ) lol

(TJ Koyen) #19

They were whites. Which is softer? At the time I tested them, we heard there was a harder and a softer compound but they never gave us the softer one to try.

The ones we tested were sweet, most durable and consistent tire I’ve ever driven, minus the YDS which isn’t really a tire as much as an actual rock.

(James McMahon) #20

Keep in mind your starting pressures will vary with the weight of your karts VS sidewall stiffness. Enduro tires tend to operate well at higher presssures, softer (compound) you could be running as low as 5 or 8.

One thing with wets is that the higher the average speed, the higher the pressures. This opens the tread up and allows it to disperse more water at higher speeds.