Trying to gain understanding tire pressure change in middle of race

sekart

New member
I'm trying to understand why (or how) a pressure change caused a severe whole kart hop.


I was in a race this past weekend where it was run in 2 parts. 20 laps counter clockwise, a 5 minute break, and then 20 laps clockwise. Toward the end of the 1st 20 lap segment, the kart seemed like it started developing a slight rear hop. Starting pressure was 12psi. It grew to 14psi in this 20 laps. We decided to drop it 1 pound bringing that down to 13psi. After doing this and the 5 minute break, the kart developed a severe whole kart hop in even the long sweeping turns, binding and bogging down in sharper slower turns. I was 1/2 second off from the first 20 laps to the last 20 laps.

I'm trying to wrap my head around why there was such an extreme effect. The thought was that if some kind of hop was starting to develop as pressure was rising that we could drop pressure to predict this.

Can someone help theorize what went on and how 1lb less could have made such a dramatic change?
 
Usually when I had a hop going up in pressure cured it or more left side %

Running Nitrogen in the tires will keep the pressure more even.
 

paulkish

old fart
Your tires will only increase in pressure not loose pressure unless you have a leak.

The only reason for tires to increase in pressure is because they heat up.

The tire that's used the most or over used the most, will heat up the most.

How much pressure increase you get per how many degrees the tire heats is determined by how much water or water vapor is in your tires. More water/water vapor, more pressure increase.

Your fix if your abusing a tire and causing unusual heating is to change something so you reduce the abuse of your tire.

Water or water vapor in the tires is about how you mount your tires and what you use to fill your tires. Soapy water around the bead may make it easier to mount tires but it leaves water inside your tire. stop it? Though you have to clean it off with gasoline or something else use white lithium grease to get your tires mounted past the bead. No water or water vapor from it and once your tires are on it dries giving off petroleum fumes not water vapor.

Use nitrogen to inflate tires or hydrogen if you want to make your kart lighter. ... :) no water vapor !

And evacuate lowering air pressure inside your tires to lower the boiling point of any water in the tires before filling them.

Some use air which has been put through a machine to take water and water vapor out of the air.

If that doesn't fix it your just out to lunch on the track abusing your tires and you need to bring your numbers and on track problem to us for help. I ain't going to help you all I do is spew my theory but with numbers there are folks on here who know what to do to help you. ... :)
 

Freezeman

Site Supporter
You ran two races in two different directions. I would not think that all 4 tires increased the same amount of PSI. Generally while running clockwise the left side tires build more heat and then when running counter clockwise the right side build more heat. Treating all four tires the same is part of your trouble and expecting your kart to handle your four tires the same in either direction is also troublesome.
 
I have seen this happen a lot, stop lower the pressures, and cant find any performance. In practicing ill try to find the hot air pressures, This hot air pressure runs best.

What happened is, you ran, with air nitrogen or what ever. You pick a starting pressure, to try and hit a Finishing pressure. The thing is , 1 psi at your cold pressure isnt exactly 1 psi on your hot air pressure. So, when you sat for the 5 min, you dropped below your optimum air pressure...

The other thing is you reversed directions. This made a bigger change than you think... Think of driving into a corner. The entry line for you is more or less the same as every one else. The middle and exit, changes in karts, drivers handling the line is more spread out. So when you changed directions your entry is running over the fanned out exit targeting a tight line into the exit, the first 20 lap entry....

So i think a combination of these is what happened.
 
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