7 Reasons You're Slower on New Kart Tires (and How to Tell Which One)

Picture this. You're out there doing some pretty good lap times on used tires. And then you have this shiny new set ready to put on, and you're very excited, because you're like, okay, now I'm going to find at least two or three tenths, I'm going to be the quickest on the track, and I'm going to destroy my competitors that may already have been on new tires.

Then you put the new tires on, and at the end of the session you see your lap time. What the hell? I'm two tenths slower than before, with new tires. How is that possible?

I'm sure it has happened to all of you, including myself, at least once. It's very upsetting and surprising, that's the right word. So here are the seven reasons why it may have happened. Some are driver related. Some are tire related. And some are just conditions related.

1. The track got slower (80% of the time)

Number one is probably the track condition, because at the end of the day the track condition is the most decisive factor. Think about it. If the track suddenly gets super slow for whatever reason, maybe the weather, it picks up a lot of humidity, or somebody went off and brought a lot of dirt and mud onto the racetrack, then all of a sudden the conditions are worse.

Or maybe there have been a few drivers driving with really bad tires, like Maxxis, very hard tires that make the track a bit slower. Say it's a random practice day, it's just you and a bunch of other drivers, and you're on really high quality, very soft tires with a lot of grip, and the other drivers are all of a sudden on very bad grip. You're going to be like, what the hell just happened? Then you realize they layered the track not with real grip but with soap, as I'd say. That layer of rubber is the part nobody talks about when comparing tires.

The track is the most important thing you have to always monitor.

If some drivers showed up with a bunch of really slow tires, it's inevitable the track gets slower, maybe three or four tenths. Even if your new tires make you two or three tenths quicker on paper, the track compensates by becoming much slower, and you don't have much of a chance. You just have to accept that your lap times are going to be slower. So number one, if you get slower on new tires, consider the track conditions, because in about 80% of cases it's the track. The track grip evolution post covers how that shows up in your data.

If it's not the track, you know that because the other drivers are still going fast while you went slower. If the others are fast and you're slow, it can't be the track, because you were driving the same track, unless you were on the dirty side of it, but that's your problem. So if you have worse performance and the others have the same performance, look at the tires.

2. You got a bad set

Many times you pick a wrong set of tires. That happens. Unfortunately it's a bit of a lottery, especially in the wet, when you select rain tires. It's a bit unfair, and one of the problems of our sport. You may do everything well, then you show up, get an unlucky set, and there's not much you can do. You survive, you're a passenger. That's really upsetting.

What you can do is get rid of those tires, go back on the other set and see right away. If all of a sudden you get faster on the older tires, it's 100% the tires. Maybe an unlucky compound, or maybe they're very hard because they were stored somewhere with a lot of heat cycles. If they sat in a warehouse with exposure to light, they'd cycle from hot to cold and back every day. Even a 20 or 30 degree cycle during the day is huge.

The more heat cycles the tire has had, the harder the compound becomes, and that's ultimately not a good thing to have.

So be mindful, it can be just down to the tires. Especially if the tires look blue or purple. If you see that, it's probably because they've been sitting for a very long time, and you were unlucky to pick that set. Replace the set, try another one, and see if the lap times get back to normal. I went deeper on why unused tires get slower in the soft vs hard explainer.

3. The two tires aren't the same size

The third reason is still down to the tires, but it has nothing to do with the compound. It's the shape of the tire. Maybe there are some defects, some blisters, although it's very unusual to have a blister on a new tire, and if so you should definitely return it to the store that sold it.

Something more nuanced: one tire has a circumference of 83 centimeters and the other has 85. One of the two is wrong. Not only does that change the final drive ratio a lot, the bigger circumference is like a smaller sprocket and the smaller one is like a bigger sprocket, more exit and less stop, the same effect as changing your gearing. It also massively unbalances the chassis when the two tires have different circumferences.

I personally hate it. It has a huge effect on the straights and even on the braking. Two asymmetric tires is something you just don't want to have. If it happens, there's not much you can do. You can pump up the smaller tire and try to expand it to the same circumference as the other, but it's probably not going to be good anyway, because tires don't love to be expanded and the tread will suffer. This one is more evident than a compound problem: you can literally see it and feel it when you drive.

It could also be that the tire is unbalanced. That you should fix yourself, by putting some weights on the rims. If the tire is very unbalanced it's not so bad for performance, but it's very bad for drivability, and the driver will struggle with it.

4. Somebody left the wrong pressure in

Number four is whether you got something wrong on your side, in your driving or in your setup. For example, you put the new tires on but for some reason you set a wrong tire pressure. Too high or too low, and I mean really high or really low. Say your hot target is normally 0.90 and you end up at 1.2 bar. Your pressures are way too high, and you won't have the right grip level, except maybe on lap one or two.

Vice versa, if they're way too low, so low it feels like a puncture even though the tires are new, you won't extract lap time either. New tires with the wrong pressure are still not good.

Maybe you were in a hurry and left the pressures at two bar from mounting. Even on new tires you won't extract any performance at all. That has happened in the past to drivers, unfortunately even in my case, in my team. Two mechanics were maybe in a hurry and by mistake forgot to lower the pressures after mounting the new tires on the rims. The driver felt it, came back into the pits, and they lowered the pressures, but by then you've lost the peak of the tire. So that's something you have to look after, and you're responsible for it together with your mechanic. The pressure cheat sheet gives you the targets to check against.

5. Too much grip for your setup

Number five is having too much grip on the kart. Suppose you go on new tires and there are no other problems. The track grip is fine, the pressures are fine, the compound is fine, the circumference is fine, everything. But you still go slower. Maybe the tires you were on weren't that bad, they had one, two, three sessions and they were quite good, and now on new tires you're not much slower, maybe one tenth, or you do the same time.

In that case the only reason may be that the tire had really good grip, but it gave you too much grip for the setup you had. Your setup was so grippy that new tires made it too grippy, and you didn't have performance anymore.

That happens a lot in 60 Mini. Whenever those karts have too much grip they suffer, the engine especially, and the kart is, quote unquote, stuck.

So it happens a lot that when you go on new tires you go slower because you're 100% too high on grip, and you have to release some. Whether that's from the rims, going magnesium, or smaller hubs, a lower center of gravity, more camber, lower tire pressures, a wider rear track, less caster, and so on. There are a bunch of things you could do. It depends on the specific kart balance you have in that moment, we can't generalize too much. But if you have too much grip, you go on new tires and it starts hopping, it starts pushing and you get stuck, you need to release grip. Reduce the contact patch, make the hubs smaller, reduce the center of gravity. Next time you go out on new tires, you'll find the performance back. The mechanism, and the order I change things in, is in kart setup basics.

Remember this rule of thumb, because it's very important. If you feel too good on the used tires, the grip is perfect and you're on rails, then when you go on new tires you'll probably struggle a bit. What's better is that you're sliding a little bit on used tires, so when you go on new tires you're spot on.

You can't have exactly the same setup between used tires and new tires. What works on used tires is a little grippier. On new tires you may want something a bit more slippery.

It's really important, and you have to be mindful about it. If you go slower on new tires, especially in single-speed karts, you probably have to release some grip because you have too much.

6. You didn't adapt your driving

The sixth reason is related to you again, to your driving. You probably didn't adapt your driving, because let's be honest, when you go on new tires you have to take advantage of the extra grip. If you pick up extra grip but you're not using it, and your kart is already on the edge of having too much grip, then you're not going to go faster. You're probably going to go slower, because the kart gets stuck, and if you're not pushing more, it starts to hop. That goes hand in hand with point number seven.

7. You drove under the limit

You probably drove under the limit and didn't use the extra grip the tires gave you. If you really drive under the limit, what's the point of new tires?

New tires are for those who push the limits, who go beyond the slip angle, who use all of the friction circle the tires are giving them in that moment.

You can't expect to go faster if you're driving conservatively, under the limit. New tires reward those who push, who try to carry more speed by braking later, carrying more minimum speed, getting on the gas and carrying a lot of exit speed. Entry, mid, exit, and try to pick up lap time everywhere. Whether you're actually using the grip is exactly what the friction circle shows.

What I notice is that on new tires you don't get a lot of lap time on the braking. You get more in the mid-corner, and on the exits if you need a lot of traction. Mid and exit, that's where you get most of the lap time, and mostly not in the slow corners but in the medium to fast corners. That's where you pick up the most grip, based on my experience. Which is why rolling speed is the thing to watch on a new set.

Investigate it like a detective

So here are seven points I believe are great to have in mind next time you go on new tires. If you still feel you're not fast enough on new tires, pay attention to this checklist. I'm sure it will help you massively in detecting the actual problem. Go from one point to the other, make an investigation almost like a detective, and come up with the reason why it happened. Start from the track, then the set, then the shape, then the pressures, then the grip, and only then look at yourself, which is the same order I use when I'm asking is it me or the kart.

And I'm very confident that if you ask PURPL, it's going to help you a lot to investigate and figure it out. I feel that's going to be your coach, really helping you analyze your data and come up with some useful insights. So let me know how it goes. Sign up to PURPL, you have a free trial to get started, and make sure you check out the six-month training program. I'm sure you'll find lap time there. I'll see you next time.