Hairpin turn in low hp kart

Driving, Data & Fitness.
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I have a problem dealing with hairpin at my local track. I have a feeling I am loosing too much time at it so I decided to ask you guys for a quick advice if you have any.

The reason I am asking you this is that we have very low hp rentals at our track. All I know about the actual line and braking points into the hairpin is quite useless as all I learned about it is mostly referring to much stronger karts.

Here from 1:19 you can see the approach to the hairpin that comes at 1:34. (This is not my footage, line is kinda similar to mine but I will make sure to get my line filmed soon)

I understand how you are meant to drive a hairpin, hard braking, release to rotate, and full throttle as soon as possible, especially at my track, as there is very long straight coming after it (2 full throttle corners before it) but what bothers me the most is that kart really chokes after that braking. Momentum is completely lost. I feel like I could do something with braking or the actual turn in could be different, but I am really not sure.

About what I do. I brake around the start of the apex, as soon as I turn my wheel (just at the end of left apex), I get on power (before the inside apex) and try to hit the inside white line, and clip the apex at the exit.

I just have a feeling that kart revs down too much at the corner so I lose time. If you have any tips, experiences with lower hp rentals I would be really thankful If you can share it with me.

About the kart/s I am driving at the track. They are Rimo Alpha2 karts powered by Honda gx270 engine with only 9hp, with weight of 130kg (full fuel tank).

Links to videos of the telemetry (if that helps, some guys have it in videos, but rarely) here and again, the guy that is one of the fastest and his line through the hairpin here.

I know it probably sounds silly to literally ask you to explain me a single corner of my racetrack, but I find it very difficult to understand it by just 3/4 sessions per month as an amateur driver and being in conditions that can`t give me the seat time frequently enough. Thanks

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Pavle,
I went rental karting yesterday onbthat exact same engine package (outdoor rentals) and was having the same issue at turn 1 NJMP. These 4 strokes really don’t like losing revs!

I only got two sessions in and I am not experienced in 4 stroke. That being said…

I’m not sure about your situation (will look at footage on train) but I noticed that on those types of turns that you’d normally throw yourself into fast and with heavy braking…
I eventually had to brake earlier in the low power kart and start feeding in gas earlier and lighter. Just mashing pedal at apex = farting noises and not much else.

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The super tight 180 at the bottom?
There’s a pretty visible patch of rubber that indicates turn in. Do you see it? This is your backstop. This is what you can lean into to get grip.

I am guessing the turn prior splits you out 1/2-3/4 to edge of track (bottom of pic). Hustle back up to top (left) edge of track.

This appears to be a straight line brake from the top left edge of track. I think what you are going to need to mess with is brake release and how you transition to power here. It’s going to be quick transition but not to full power immediately.

If it was me I’d be playing with "at what speed, when I release these brakes and turn in, will the tires “just” hold in that patch of rubber.

I’d be hunting for a feeling of load that had my tires at the point just before they start making bad noises or hopping as I’m leaning into the turn. This will be pretty close to a spin.

I’m gonna want to feel the front end very loaded up as I am finishing braking. I am going to want to try to time that peak load such that I release brake and get on gas just before the chassis/tires says “enough” and lets go. (Spin).

This brake release allows that weight that has been sent forwards to “flow” freely again and seek escape. If you don’t release brake at this point, you’d feel the kart chatter and hop maybe. You’d also suddenly snap spin.
Basically all that energy you bled off in braking is saying “ok boss where to, what now?”. Release and instability goes away. Turn.

So this is where that transition to gas matters. Try to make that immediate change from release to gas not only fast but subtle. Start feeding in very slightly as you pay attention to how loaded up the left side of your kart is as you enter and go through the turn in to apex. Use that sense of load in the left side to try to determine wether you can be more aggressive adding in throttle.

You are drawing a semi-circle with the left side of your kart. Load it up and dig in. If it holds, try a bit more throttle out earlier.

It could be that in these low power karts, no amount of pedal mashing will help. In other words, transition to throttle might be semi-irrelevant in that the power delivery is so slow that there is not much difference in how you modulate throttle. Then it’s gonna be in the braking. Try to mess with braking with the eye to prioritizing speed at turn in. Maybe brake harder earlier or softer later. Just mess with it until you get an entry to the turn that is very loaded and balanced.

Try not to hit tire barrier too fast as you figure this out :crazy_face:

Edit: I am just a random karter like you so don’t take this as gospel or anything

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Yes, exactly that turn. I must admit, never thought of using google map as a way to scan the lines. Although I generally know the line through it, it just seems weird that kart just loses revs so much through the corner.

Seems like not much can be done to improve except being clean and accurate on braking and turning, as I am pretty much doing the same as you described, maybe just more practice for more consistent line.

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Sorry took a bit to type… see above for more complete thoughts

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I will test out mentioned options in the following days and share the impressions
after the session or two. Thanks a lot for the explanation, really helps me to better understand what I actually do and why is good or bad :hugs:

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Yes the 4 stroke engines seem to be very sensitive to braking. Touch them and there goes the revs.

I think we have some 4 strokers here that might be able to provide some thoughts about how to manage revs. (I hope).

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4 stroke here, hairpin at my local track, leading our series — but new to karting so take with a grain of salt

GET ON THE GAS AS SOON AS POSSIBLE — sooner than feels right. I brake quickly and am back on the gas an instant after I start turn in. I also try to hit an early apex and run WIDE on the turn — basically as little turning input to get through the turn as possible, it’s one of those maintain momentum moments and the earlier you can get on the gas the better

GOOD LUCK, seat time really will pay off

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9

Phew. Thanks for that. So far so good. Worried that might have been too ambitious. I do get the impression given the narrowness of this turn that it’s gonna be instant on but soft.

Also, given joes comment about " get on earlier than you think"…

This would suggest to me that a big part of getting this turn right isn’t going to be in the drama at turn in and apex. It’s gonna be in how and when you decelerate. I’ll bet braking differently is gonna he more important that the turn itself. Try earlier braking.

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“These four strokes don’t like losing revs”
I would have said that an industrial engine 4 / was normally far less affected than ,for example, a 125 kz.
I think the point here is that you have to drive the kart as it is given to you. You cannot alter the gearing or the clutch engagement. ??The operator has probably geared higher than optimum for laptime to extend engine life, and set the clutch to engage at low revs to maximise clutch life.
Given that the track has the one very slow corner in anotherwise fairly fast looking layout it may well be that the revs are unavoidably being pulled down to well below reasonable torque revs, and this is a situation you are stuck with.
Essential here to maintain momentum as much as possible through this corner, possibly try shifting driver weight to the outside to keep the inside rear wheel unloaded?
Just another random EX karter so don’t…

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Can you elaborate? I don’t quite follow.

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The industrial 4 strokes eg. Honda 270 have a much 'flatter 'torque/ revs curve compared with a kz so that these engines will pull well over a fairly wide proportion of their rev range. Max torque around 3000 rpm ,serious drop off under 2000 and over 4000.
I wouldn’t think a commercial rental operator would want to gear for more than 5000 max .which might well bring the revs at that track down to below 2000 if the clutch is engaged.
Imo a 100 cc 2 stroke with direct drive ( no clutch) would struggle even more than the 270 honda round that track due to the apparent variation in top track speed to hairpin speed.
Afterthought:
Don’t rental karts usually run with the engine governor fitted.? which would mean 3,600 rpm. max!

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Ah ok that makes sense. Thank you. So basically, in order to preserve their rental fleet, they are likely compressing the useable range of the engine. Coupled with a turn you can’t gear for… whole lotta nothing.

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Very similar to driving direct drive with a 2 cycle. My technique, the day I learned how to drive a kart, in a turn very similar to what you have, River kart track in Herndon California 1969, was to go “straight” into the turn, breaking as late as possible, start your turn, and get back onto the gas as soon as possible. At the speeds and the horsepower that you’re talking about, you should be able to get back on the gas almost as soon as you start your turn. I set fast time, new track record, that day in Mc 91 and won all 3 heats. The race was called the “Coca-Cola race”. Kind of a big attendance race. Almost a Regional.

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Since it may be impossible to break grip under acceleration alone (I am assuming) I may be wrong about feeding it in. It may be just as effective to go flat as soon as possible in that it’ll take a few for the kart to speed up by which time you are straight. There may not be enough power to even have to worry about little traction loss moments.

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Pavle,
This might be very useful. The karts are very heavy with the extra safety stuff. If they have differentials this doesn’t apply. Try leaning outwards (left) as you turn here. Hang your weight over the planted wheels on left.

Also this thread has some info in it that isn’t exactly to your question but possibly helpful. Accessing peak performance - #9 by speedcraft
It’s not about how to take a turn but rather more about thinking about speed and there’s stuff in there that is directly related to this. Take a good look at the writings of Warren Chamberlin in that thread, he offers some insights that are exceptional.
Another thought: we have a rental kart racer from Holland named Matthijs who likely has rental kart mastery. @Matthijs_Hofman He runs and races a rental kart series.

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Completely truth

This is also one thing I did not really mention at all, but I feel almost no grip loss, no rear end twitching when applying throttle, except in this this corner, where most people actually spin:

Slika

Yes, I read a lot about this and I am really keen on trying this out at the track, will try it out on Thursday, it is really flipping hot right now, some rain should pour on Wednesday, I really want to see the effect. :grimacing::grimacing::grimacing: It should theoretically lift the inside rear wheel and therefore increase kart rotation, right?

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It will in theory allow your inside wheel to stay “up” longer allowing for a free turn. You definitely don’t want the inside wheel coming down as you will bog hard.

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This is familiar. Did you happen to ask on r/karting at one point? I recognize this wacky complex. That’s a funny turn at the end of a fast bit. There’s a series of low speed turns so how fast you go in seems to be less important. It kinda looks like you can karate chop late apex straight down! I exaggerate but I sure would try to see how much I can ignore those bends.

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You might be simply braking/slowing too much. What happens when you carry more entry speed?

Rental karts have a pretty linear torque band, it’s just very low.

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