tire pressures

[angus' dad]

we run counter clock-wise at local track. left hand turns. it's a short-technical track, i've been told, compared to others. good lap times are 26 seconds. great - high 25's. 6 turns. about 35 mph top speed. i've been running 15 lbs inside and 14 outside. we're new, and i was told by local kart guru i had it backwards. i switched to 15 inside and 14 outside and it slowed lap times down. the 15, 14 combination i came to by trial and error. should i stick with the higher pressure inside and just get my driver to get used to the difference? and would you suggest a different pressure? some are as high as low 20's and as low as 11's i've been told.

[Garry Lobaugh]

Which compound?
Do your own research.
Pressure should not grow more than 3 lbs after ten laps for a jr driver. That should help you make your decision.

Good record keeping is needed.
In cool temps, higher pressures are fine, in summer you will want to lower. I'd bet you would run higher pressures on the outside of the kart and not the inside. It is important to watch the surface of the tire for overheating, or too cool with pickup of rubber.

Watch the stop watch for each lap, are you fast early and fade later? Those are going to be things we will be teaching at our advanced summer camp in the first week of July, soon to be announced.

[Marc Miller]

To further Garry's comment, you usually want to shoot for even pressure changes to get them equalized. 3 pounds growth is good, but you also want them even left to right.

If you find the kart works best with hot pressures around 18 pounds, then set your pressures and go test. Do a 10 lap session and look at where the best lap times were made (lap 3, 4, 5?). If they didn't come in until lap 8 or 9, then you can stand to raise starting pressures a pound or so. You want them to come in quick, but not fall off and make it hard to drive either. Check pressures right coming off the track and if you a track mostly left handers, that right front might be a pound or two higher than the rest - but the other 3 tires might be fine (for example purposes - hypothetical). Bleed the right front down a pound and let the tires cool. Whatever that cools to should be your starting pressures.

Alo keep in mind that as tires expand and contract as they get hot and cool down, if your track has several proactice sessions and the tires have completely cooled - it is easy to bleed down your tires to lower pressures accidentally. EXAMPLE. Set your pressures to 12 lbs.... run 10 laps, tires come in at 15 lbs. If you go back out on track 20 minutes later and your tires are still warmer than normal, your pressures might be 13.... I leave them there... as if you bleed them down to 12 again, you might actually be starting the pressures lower than 12 when the tires are cooled down completely.

Hope that helps!

[Garry Lobaugh]

Hope that helps? Wow that is a mouth full. It is all good stuff Marc, but this could get really complicated on the internet and all. Let's save something for the hands on experience on the upcoming Summer Camp for Racers and crew chiefs.

[angus' dad]

thanks guys, we're heading back down to practice tomorrow and i'll test some more

[angus' dad]

thanks for the air pressure help! present track record in micro is 25.627, and angus today ran consistent 25.5's, with his best a 25.48. new track record coming at next race!

[Marc Miller]

our pleasure! You can always count on MRP for help.