You probably won’t build the heat you’re looking for if the track surface is very slippery and poor quality. The tire is never really biting into the track in these conditions, and instead of flexing and generating friction, it sort of just skids across the surface and doesn’t heat up enough. On very low grip surfaces, we have found raising the pressure significantly (sometimes up to 20-25 psi on MG Reds) to generate any form of heat. This is pretty common when a track is new or the surface is fresh, or if the surface is a temporary track/parking lot/street circuit.
Our typical range on MG Reds is about 10-13 psi depending on temperature. If you are struggling to generate the tire temps you’re looking for, I wouldn’t be afraid to pump up above those numbers a bit and see how that changes the temp, and then in turn if that improves the kart or lap time. The stopwatch is the ultimate guiding principle.
Measuring tire temps is interesting but it’s academic and mostly useless but all kart racers go through this tire temp phase, which includes me. The best is to measure tire pressure the same way every time and then during races determine what the tire is doing. Over a period of time, you’ll get a sense of what the right tire pressure is and soon will be agonizing about whether to change tire pressure by a 1/4 psi.
You guys seem like you really want to help out! Here’s another recent example of a recently repaved circuit.
09 Birel R30 w/LO206, Bridgestone YLCs 4.5/7.10 at Whiteland. 42.5% front, 49% cross.
365 lbs, maybe 40-50 laps on them. 12 psi cold.
Feels pretty decent but I’m still kinda new. Finally have the balance where I want it and its working pretty well minus an inside section where it’s sometimes a little flat/tight.
Im no expert, but it looks like those tires had too little air pressure.
They look almost sanded down, as if they weren’t “used” enough or not generating enough heat or grip
I’ll throw some picture up for diagnosis. GoPro Motorplex KA100 Senior MG Reds for reference. Track was pretty green from some recent rain and rental karts going out every other session. Was really struggling for rear grip all day and I think it shows in the tires. I’ve been out of karting for quite some time and really only turned around 100 laps in total at GPM. I haven’t done much chassis tuning just air pressures and sticking with a baseline setup as I gain seat time. I’m sure some over driving isn’t helping, but try as I might I’m stuck around high 52s and not making much progress. Feel like lack of rear grip is holding me back. Air pressure were all over the place while testing, but these are from my last session running around 14 psi hot all around. Cold was 10 lr, 10.5 lf, 10.5 rr, 11 lf. Thanks for the input!
Tires looking like they have the optimal temp/pressure, except for your left front. That one has too much pressure in / is too hot or “overdriven”.
Are you struggling with understeer?
Thank Alex. I would say the kart has plenty of front end grip. I can still point the front end where I want with more steering input, but the rear end stepping out is limiter. GoPro Motorplex is a pretty fast clockwise track so the left front sees alot of G’s and load. To my novice instincts the left rear should see the same/similar wear if it is gripping the track equally as the front.
The reason that the rear may not look the same, is probably because of some sliding or twisting that scrapes the wear pattern of the tire.
Just from looking at the tires, my theory would be understeer. Though your explanation points to oversteer.
(Or the solution to our inconsistent wear pattern problem may just be tire pressure settings🤷♂️)
I’m trying to splice together some GoPro footage of my better laps for others to review. Perhaps the setup and tires pressures are good, just not my driving at this point. I haven’t raced anything recently requiring this much finesse is along time. Just recently jump out of desert racing, which basically amounted to can I get though these whoops or jump without dying? Then your setup is good!
Well… I’ll let the video be the judge of that. I’m open to critique so let me have it. Feel free to have a laugh on my behalf at the end of the video. Thanks!
Driving looks very good. Never been to Gopro but looks like you know it well. Is the kart hopping a bit on the more loaded turns? Its hard to tell if that’s just camera shake or some kinda instability.
Thanks I really only have 100 laps or so at the track. Shows in some of my inconsistency. Fighting some axle hop. I’m roughly 5’10" 190lbs and broad up top so depending on my lean in the turns I feel like I can induce some axle hop. That being said any thoughts on reducing axle hop? Really seems to kill speed mid-corner when it starts to hop.
Not sure. I first encountered this in heavy rental karts. It seems that if you ask too much laterally, load wise, the kart hops. This is compounded by the extra 160lbs or so your typical rental kart carries around.
From a tuning perspective, it might have something to do with you being top heavy, like you say. Someone here probably has ideas for that.
In rentals I have to tune my driving, so the answer was to take a less V or sharp apex. Round it a bit so that peak lateral load is lower.
Driving looks not bad, just a little heavy-footed on the brakes. Too much locking, leading to the kart being crossed up at apex. Combined with your height/weight, you’re just getting the kart too out of shape at max load.
GoPro is a flowing track and really emphasizes getting the kart through each section with minimal input. Really have to finesse the kart into the corners rather than chuck it in hard under braking.
Try being smoother on the brakes first, and then if you want to try a chassis change to smooth it out, widening the rear track or stiffening the axle (tighten third bearing or harder axle) can help settle it down at max load.
Tire wear looks normal, a little feathering on the rears and left front indicates sliding. Rears probably from the lock ups and aggressive brakes, left front probably because it’s a clockwise track. Right front looks perfect.
TJ thanks for the input! I watched your video quite a few times before heading out yesterday to turn laps. Tried to match up break and turn in points to your video. It’s going to take quite some more seat time before I flow that well.
Will a wider track also assist in oversteer? I feel like there is more speed left in the kart, but the lack of rear grip is holding me back.
Next session out I’d like to get a shot of the rear wheels to see if I can catch the rear tires loading and unloading, as well as how much lift I’m getting in the rear.
I’m a learner through data as much as seat time, would anyone be will to share a session from there MyChron so I can compare against? I’d gladly share mine, but I know some people are hesitant.
Again thanks to all for the input!
Especially at a flowing track like GoPro, I find it is pretty common in those fast corners to get oversteer when you’re overloading the outside tire. Often at that track, we are hunting for the fine knife-edge where the kart is neutral in fast corners but not too understeer-y in the hairpin. Wider rear track should settle that down and neutralize the kart in the faster stuff. You can specifically see in your video when the kart reaches max load at apex, you’re fighting it ever so slightly as it tries to kick out.
