Ok, many are familiar with all of the cliches and platitudes of, ‘smooth is fast’, ‘sliding is slow’, yadada yadda. And I understand that at the very least, being ‘hooked up’, even if at the higher end of optimal slip angles, is generally accepted at the fastest way to drive, especially for full race distances.
That said…
…am interested in possible exceptions - are there times, whether in qualifying, or just specific-types-of-sections where a LITTLE sliding is not only ‘not-bad’, but is going to be the faster way??
A little sliding that’s controlled can keep the rear tires slipping more freely in the absence of inside rear wheel lift. So a bit of slide in faster corners is pretty common when the kart is handling well, because you aren’t inducing mechanical jacking since you only turn the wheel a tiny bit. The kart doesn’t flex as much in these corners, so the only way to reduce bind on the inside rear wheel is to have a tiny bit of slide in the kart.
Generally, a little slide is okay in faster corners sometimes, but in slower corners is where sliding will hurt you more. As you need the kart to jack weight and unload the inside rear wheel to rotate around a sharper, slower corner, and when you slide and have to countersteer, the inside rear sits down and you scrub speed. Plus, being at low-speed, you don’t have the grunt to pull yourself out of a slide as easily. In a faster corner where you’re revved up, the engine isn’t dragged down by the slide as much.
Here’s a clip of me taking turn 1 at Trackhouse and you can see a tiny bit of slide and correction at apex.
Other than indoors on slick surfaces, I have yet to see a slidy situation that makes sense.
Here’s the exception… it’s just not possible to be gripped on this bottom floor surface. The two turns on the lower level, 180 cutback followed by another 180. You can see that the grip is so low I am “sliding” the back, sorta. But it’s not really a tire smoking kind of drift. I’m trying to stay in slip.
And now I understand why… can’t generate enough lateral load to have lift.
Keep in mind, too, how karts are very unique in the world of four-wheel vehicles. We use absurd amounts of caster to lift the inside rear, but this does the exact opposite if you have opposite lock. As soon as you give it opposite lock, that caster is actively fighting the inside rear from lifting.
Maybe in a hypothetical hop situation, this could be a good thing. Say the track has gripped up but your settings are for low grip, a little oversteer that requires countersteering could reduce excessive lift that leads to hopping.
That makes sense. Also, from looking at Mychron data that included a tire temp channel (believe was distributed with RS Analysis), I noticed that tire temps are far lower in fast corners versus slow corners (counter intuitive, but the lower amount of air flowing in slower corners is the reason why), so in addition to helping out the kart’s rotation there’s an added bonus that your tires will be at the lower end of their temperature range if you decide to let it slip a little in the faster corners.
Actually I have been pondering this too but not insofar as whether it’s ok to slide… what I’ve been thinking about is how much/what kind of tire noises are ok.
Being at the limit is sort of the point and it’s inevitable that you have some chirpiness. But any amount of chirp is the result of tire grab/release. Some of it is fine… presumably the chirpiness that comes from the slip angle is unavoidable.
But chirping can also potentially be the beginning of sliding and it’s unclear to me at what point it’s too much. I am going by feel. I can tell when I break grip, obviously, but what I can’t tell is what going on below a certain point of lateral movement.
Here’s an example of some chirp. I am trying to stay fully gripped up and not lose speed to lateral sliding. I seem to have to have some tire noise. The only way to have none seems to be to drive below the limit of the tire.
Also,bear in mind that this is a smooth and almost polished surface. It’s gonna make more noise than the asphalt tracks which have a deeper "shralp"ing noise as compared to the high pitched squeaks.
The amount of noise you get from your tire is going to vary greatly track to track or day to day too. On very hard tires, you’re going to hear squealing a lot more than a soft tire.
I also just wanted to make a point of mentioning how we are often very focused on the “ideal” way to drive a kart to complete a corner the fastest. But I think something worth noting is that some of the best drivers also might use techniques that wouldn’t be considered “correct” to adjust the kart’s attitude on the fly. It’s one thing to know how to be smooth and hit all your apexes, but another to muscle and drive the kart into submission in a racing situation or to maneuver it in a way that may be beyond the “normal preferred” style. For example if you need to launch a massive curb to set up for a corner, or flick the kart more sideways in the braking zone, or dump a bunch of steering input in if there’s a bump in the track or the corner is off-camber. All that stuff is a little more intangible.
The braking thing is a good example of a technique that makes me scratch my head pretty hard. That is to say, where the real confusion/nuance starts for me is when there’s a sliding technique that seems faster/advantageous, my mind immediately drifts to the idea that it’s still probably bad, because tires.
Honestly, just thinking about it, I think these kind of questions show how valuable extensive racing experience becomes. I have all kinds of questions, ideas, and theories, but I’m sure 3-4 seasons of racing hard at the front of a competitive series would answer all of them, and more, lol.
Being slightly sideways under braking makes the kart artificially wider, and also allows you to slide up into the line a bit and take up more space, so it can serve as a little thing that might give the chasing driver pause if they are thinking about overtaking.
Also, I have no idea on the answer to this, but it certainly feels like the tires have more lateral traction than longitudinal traction, so possibly getting the rear to step out slightly under braking allows you to use some of that lateral grip to slow down the kart faster. Again, that could be totally false, but my butt says it feels that way.
But yes, this is why I always tell drivers to go try a bigger race with higher levels of competition because you will naturally pick up things that the faster guys are doing through watching them and being wheel-to-wheel.
What you feel is backed up by physics, according to the vehicle and tire dynamics books from the big boys. It’s down to the shape of the contact patch - it is generally wider in measurement than it is long, so we generally have more grip laterally than longitudinally.
You can generally get away with sliding on entry, but you lose a lot of time by sliding on exit. This is mostly where the really fast drivers make the difference.
This is especially noticeable in rental karts. Those engines bog down massively when you lose revs, so sliding on corner exit can lose you a lot of time. The fastest drivers in rental kart races have usually mastered this technique and it makes a big difference to a fast driver who might still not metronomically consistent with his inputs over the lap, I have seen “aliens” take pole by huge margins in very closely matched fields, and most of the time they are able to replicate it over an entire race.
On further inspection, you must mean when I point ahead and express "let’s goooooo!"after passing a kart.
I actually racing a couple of the local hot shoes that came over to do some laps. The fella working there introduced us. We are trying to set fastest pace.
That’s not me mocking the lady I just passed but telling the guy not far behind me “never mind the bollocks, let’s goooooo!”.
To riff on this a little more, it is rooted in CG (as well as tire geometry as @1pieceatatime said).
For a kart with no front brakes, the rear tires have to do all the work but have only ~60% of the kart weight on them, and braking causes a forward shift in weight distribution. This means that, for a tire that can grip 2G laterally, max decel is only around 1G or even less. I went through an iterative exercise in Excel a while back to find how much a kart can decel, knowing that the more it decels, the more weight transfers away from the braking tires. It ended up working out really closely to what I saw in my data, which was kinda neat.
This is before accounting for the wide aspect of the rear tires. Similarly, with forward accel, you are pushing all the weight through the rear tires but they don’t have all the weight pushing down on them for grip.
Laterally, the smaller front tires have less weight on them, so the contact patches can be loaded pretty proportionately laterally. Pitching the kart to scrub speed can definitely slow it down faster, but it usually works too well and this is why “sliding is slow” exists as a mantra. You will probably drop too much speed by sliding because you can’t just suddenly stop sliding, but, going back to the hypothetical ideal, it could be possible to brake later if you can scrub off the exact right amount of speed and no more.
So, this is definitely in the category of techniques that I’ve pondered, used, then quit using so much ‘because tires’. I guess that gets to the main questions left in my head - what is the cost for doing this technique (if any), and how much is too much? I don’t feel like I see it used very frequently by top drivers in non-passing/blocking situations so then I kind of think, ‘welp, it must not be that recommendable or else they’d be doing it many places every lap’.
I think it goes back to the inability to just turn it off once you start. If you feel you are over-braking (or simply done with the braking zone), you can just left off the brake pedal. If you tossed the kart to slow down, you can’t just un-toss it midway through when you have scrubbed enough speed. In theory, you could toss it with such precision that it slows the exactly right amount while staying on the intended line, and this would enable you to dive a little deeper before braking, but I don’t see this happening with the precision it needs to be viable.
If you can get the kart slowed down in the shortest distance possible, and have the chassis settled before you go to turn-in, you can kinda do whatever you want in the braking zone, with the caveat always being that too much sliding will flash heat the tire surface and you could prematurely wear the tire or make it drop off.
Also, I’m not saying get the kart completely sideways under-braking; much more subtle than that.
Just watch some KC footage from Orlando, specifically the braking into the tight hairpin off the back straight, and you’ll see some dancing under braking from most of the guys. This is more what I’m talking about.
In general, just watch some of the movements the drivers in X30 are making on the wheel when they launch curbs or enter corners. It isn’t all smoothness all the time.
One theory I’ve been working through is “does turning count as four-wheel brakes”, at least in terms of the front tires creating longitudinal decel. Turning certainly binds the kart up and slows it down, so I feel like some of the slip angle on the front tires must have a significant longitudinal component. This would give you more decel than rear-wheel braking alone, but, like you said above, this is far less slip angle than what I’d call “sliding” like in the original post.
