Hi Everyone,
Just picked up a go-kart for my son and we’re running an OTK 950 on the Mojo C2 tyres. First few races, I ran with a team just to see how things are done, but I’ve realized I’m not learning anything by letting them do everything, so I decided to take the kart and work on it at home. My only issue is that tyre pressures seem to remain a mystery to me and I can’t figure out how to get them right. On the Rotax website, the optimal tyre pressure for Mojo C2 tyres is 12 psi. I tend to set my pressures at 8/9/10/11 psi with the rears 0.5 psi lower as they tend to come in a little bit higher to get them at 12 psi. The issue is people at the track keep giving conflicting info, as some have said they run higher temps at 15 psi and 8 psi in the exact same session, and I kind of figured out some aren’t being truthful about what they’re running.
One session, I decided to run the pressures extremely low at 8 psi, and he suddenly was doing the league’s race pace time on extremely worn tyres, which was surprising. I tried the same pressure on a different day with the exact same setup but slightly cooler conditions, and he went 1 second slower.
What I want to know is, am I doing the right thing setting my cold temperatures to come in hot at 12 psi, or are there other methods on here that everyone uses to get the right tyre pressure for the current conditions? And is there any conditions where i would run the pressures at 15psi in the dry well above the manufacturers guide?
We’re also running the OTK MXC rims. For some reason, my son doesn’t like driving on the standard OTK rims, as he tends to slide a lot after a few laps.
Others will chime in with more detail… but a good rule of thumb is to shoot for about 2psi increase at the end of a session. You can use that as a baseline.
I look at manufacturer pressures like seat position. They are a recommendation and a starting point. But the conditions and your own driving will influence where you end up.
Hi james, thanks for the reply. So for reference if i set me tyre pressure at 13 and it comes back as 15 thats the correct pressure to be on? Or lets say i set it at 10 but comes back at 11.5 the 13-15 would be the correct pressure to be on?
Apologies if that sounds stupid But I’m just trying to wrap my head around this issue. Its the one area im struggling with, Everything else seems to be straight foward but this just have me confuse.
He is probably sliding on the MXJ because they are aren’t shedding the heat like the MXC. Look at the lap times over a session on the J vs C. The MXJs are better for cooler days as they tend to want to retain the heat.
Your pressure that you set would be different in the MXJ vs MXC for the same conditions.
Hi Mark, so this is where one of my confusion is coming from. On a cooler day would you go higher on pressure on the mxc to mitigate the lost of heat or just run the mxj on a cooler day and set the pressure as i would normally. As james said ideally i would want a rise in 2psi from cold to hot. Would that be the same on the MXJ?
I would never run the Js to be honest. Even when it was cooler I would run the Cs with just more pressure because I prefer the feel of the Cs and they are a better tire to maintain consistent temp and pressure. The Js will build heat faster for sure, but they won’t be as consistent over a longer run.
We do the same for the most part even in cadet. For 98% of situations, it is MXC with adjusted pressures. Like TJ, we almost rarely use the MXJ.
Look at a 12-15 lap run on MXJ and you will probably see a smile shape in lap times. The MXC will stay flat. If you son feels like he has immediate grip when leaving the grid, you have probably gone too high, then the sliding will come too.
In this race, the fourth lap time is slightly higher than it should be due to the pass. Same for the defense and final lap. When looking at any data during a race, there will be a lot more noise to sort through to make sense of the data, so you have to pay attention to the race. Best to get a handle on it during solo practices at first. You will figure out how much to adjust from track temp/ambient changes, etc. When you get comfortable you are in the right window, you can try to adjust where you want your fast lap to be depending on your situation and strategy.
Lap times look extremely consistent. Ill continue to let him run on the MXC, although its getting colder I’ll just compensate by running higher pressures. I have another Question but ill just create another thread.
This right here. It’s unfortunate the rolling chassis essentially comes with scrap metal and you need to go buy MXCs. Just charge me more for the MXCs or cut me a discount for no wheels. They weren’t even worth having around to practice on. When getting a new chassis I would just keep those bad boys in the box unopened and toss them on the shelf to collect dust.
I wouldn’t be locked into chasing an even psi increase of 2psi. This is going to be very track and temperature dependent. Bunch of left handers? Then you’re going to get more heat buildup on the RH side. If you really want hot temp/pressures “equal” then you need to set them equal the second you come off the track hot and allow them to cool. Once cooled note that pressure as your cold settings. You should see each corner is slightly different.
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