Corner speed or rotation speed?


(Lee Swindell) #1

Gurus:

Hairpins. One has a choice of approaches:

  1. Optimise corner speed by keeping mass over the rear axle, or

  2. Optimise rotation speed by doing the opposite.

The advantage of:

  1. is you’ve just preserved speed that you don’t have to recover.

  2. Is you’ve changed direction quicker at the expense of speed, which you now want back.

Which one?

Thank you.


(Aaron Hachmeister) #2

In most racing, the first option is ideal. Trying to maintain as much momentum through the turn as possible so that your exit speed is higher.

The one catch is in shifter racing, as far as I’ve seen. While I was at Vegas, I noticed that the KZ drivers almost parked their karts on the apex of the hairpins, rotated the kart, and then hammered the gas out of the turn. They seem to be more focused on rotating quickly and accelerating in as straight of a line as possible rather than carrying all their momentum through the corners.

I do not, however, race shifters, so I could be totally wrong on that part, but in general I’m trying to keep as much speed through a corner as possible rather than optimize my rotational speed.


(Lee Swindell) #3

interesting observation Aaron.

Can anyone explain why this might be?

Front brakes?


(James McMahon) #4

Front brakes and being able to take advantage of the abrupt acceleration you have on hand.

“Square” off the corner and send it on the exit. Arcing corner like you would in a non geared kart won’t allow you take full advantage of the acceleration on offer.

Of course as the turn(s) you are dealing with start to get faster, say gears 4,5,6 then you’re going to use a more conventional line.


(Lee Swindell) #5

So big acceleration positive and negative = optimise rotation speed.

Else, optimise corner speed?


(Mike Clark) #6

To me it can be a bit confusing. I would always say optimize corner EXIT speed. There can be other factors to consider like which facilitates passing/ not getting passed. But the bottom line for me on how to judge it initially is speed (RPM) @ a certain point down the following straight. If it is hard to see, move the judgment point farther down the straight. A segment time would be probably the best method to say what is the fastest. I also tend toward the Method 2 as being riskier in that all the work is very condensed and not spread out.

Lee, how much have you driven in the rain and or very low grip conditions? Or even a mixed track, with wet and dry spots? I ask because I think both can be fun, challenging and make you think about line much differently. Probably my biggest upset was in a practice with a very mixed track. I think I had as much as 7 seconds on some and almost lapped 2nd place before the end of session. I credit it to just spotting where to ask the kart to do work vs where to tread lightly. It is also interesting to see what the other drivers approach something was. I think some guys also just can tell what is dryer vs wet better.


(TJ Koyen) #7

One thing you always need to keep in mind is that a kart NEEDS the inside rear wheel to be unloaded to rotate properly. This is where it differs from conventional “car” driving thinking. All things being equal, yes there are probably a couple different optimal lines from a traction limit perspective. However, bearing in mind the need to keep the inside rear wheel unloaded, a certain line might be beneficial in karting.

As noted above, in something like KZ, you’ve got a different line and driving style than you have in a single-gear class. In KZ with all the power, the gears, and the front brakes, you can very much drive it in deep, sacrifice mid-corner speed, and hammer it out of the corner. In a single-gear kart you’re required to keep the kart’s momentum up, so you’ll need to be more conservative with how you use your traction. To keep the inside rear wheel unloaded, you’ll need to ease the kart into the corner a bit more and get that wheel to carry to the apex. This typically requires a smoother arc and more mid-corner speed. If you go into a corner and put a bunch of wheel in the kart to get it to rotate quickly, 9 times out of 10 you’re going to ‘shock’ the kart into unloading too quickly and upsetting the balance and handling.


(Warren Chamberlain) #8

I think that before you could make a productive decision about which technique(s) to use in the corner, a lot more information is needed about:

The Context

For example is the hairpin at the end of a long straight, or at the beginning of a long strait, or both? What is the angle of the turn (not all ‘hairpins’ are 180 degrees)? What is the radius of the turn (it’s much easier to manage ‘quick’ rotation in a turn with a shorter radius)? What is the camber profile in each phase of the turn? Does the track surface have any characteristics that can/will influence how much speed you can carry through the turn, or how easily you can manage rotation (e.g. concrete patches, polished asphalt, bumps, etc.)?

The Kart

Once you have the context, then consider the strengths and weaknesses of kart you’re driving.

For example, quick rotation would obviously be much easier in a short-wheelbase sprint kart than a long-wheelbase lay-down kart. Regaining speed sacrificed to the cornering gods is much easier in a high HP or multi gear kart than in a lower HP or single gear kart. However, maintaining tire slip angles, temps, and life is much easier in a lower HP kart. Also, if you want to ‘pin’ the front end at the turn in point and quickly rotate the kart around the front end, then that would be much easier in a kart with FWBs.

Your Objective(s)

The last piece of information needed is what objective you’re trying to accomplish in the turn. The obvious answer is lowest time in the turn, and highest speed on the following straight. But what if the hairpin is at the end of the longest strait and leads onto an inconsequentially short straight, or into a turn that requires the kart be placed somewhere other than a typical ‘track-out’ location? You may also need to temper outright performance with tire management. For example, the fastest way through the turn with a shifter kart may be to pin the front end, rotate the kart, and blast out of the turn on the outside rear tire, but will the rear tire survive being used like this for a whole race? Perhaps you might need two cornering strategies (one, a tick slower, that puts more of the burden on the fronts to supplement the Banzai strategy that is fast but uses up the rear tire), then you can cycle through the strategies as needed during the race to manage your position and tire performance so you have rubber left for the end of the race.

Selecting Techniques

I think that once you’ve thought through the Context, Kart, and Objectives, then you would be in a better position to select and assemble techniques to accomplish your objectives, which you could then evaluate using segment times.

One last thing I want to point out; when managing rotation, it’s important to consider where/when rotation occurs in addition to the rate of rotation. Also, when rotating a kart aggressively into a corner, it is as, if not more, important to manage where/when the rotation stops. For example, if you pin the front end, rotate the kart in, and then time getting back to the throttle to check rotation just before, or just when, the kart is tangent to the line you are driving, then the well managed rear slip angles will allow the kart to finish the turn, while the acceleration forces efficiently push thought the kart’s center of mass. If you are late checking the rotation (so the kart is beyond tangent – tail is hanging out), then you will produce excessive rear tire loads/slip angles/heat/usage, and the acceleration forces will inefficiently spill outside of kart’s center of mass, which typically requires steering and throttle modulation to manage.


(Dom Callan) #9

Lee, I am basically a n00b so I don’t have much weight behind my words… That being said, from my first year of racing, corner speed is King.

It’s exponentially harder to throw it in hard and be consistent. Pushing hard into corners increases the likelihood of making a small mistake which negates any benefit. It is fun though. Messing around in turn 7 at e-town (big 180 at end of long straight) I have seen variation from 26-31 mph through turn (slowest speed). The 26-29 mph ones are where I heroically dive into the turn, the 30-31 mph ones are where I try to roll as much speed through apex. The latter is the better result, obvs.


(Lee Swindell) #10

Mike:

Great stuff. One of the guys in my crew makes a habit of observing where on track the limiter cuts in as a guide to how well he’s just driven the previous corner. You’ve said the same here, so maybe I need to get more intentional in that regard. There’s no alternative really, given that you cant capture segment times in hire karts.

Ive had karts in my life for decades, but actually done very little track work - almost all the racing Ive done has been in my mind (although that changing as of a few months ago). I’ve done just enough to know that I revel in wet roads, but can’t yet differentiate areas of low grip v. High. but I’m working on it.

So look out …


(Lee Swindell) #11

Nothing wrong with being a noob Dom. I’m one, as were all the great heroes once.In fact, noob ness lends itself to great discussion places like this because it requires the leaders among us to exercise / challenge their thinking in order to explain a concept. Therefore, I think we’re great.

That variation in corner speeds you’ve measured is interesting. If we put Senna into your kart in the same corner trialling the same techniques, would we measure the same variations in speed? I say yes, but I also suspect a great driver would instinctively settle into a technique that’s some combination of rotation speed and corner speed that us mortals have yet to discover, let alone perfect.

Agree? Or no?


(Dom Callan) #12

Well I’d like to think that someday I’ll he able to be heroic and consistent but for now it’s one or the other.

That being said, it was pointed out to me that I have been experiencing the exact opposite result on the preceding turn at e- town. In the case of t6, the data shows that the turns with the lowest apex speed were the most successful in terms of generating Max speed at end of straight. So in that case, hucking it in works best.


(Mike Clark) #13

Lee,
There are a couple of corners that seem to have multiple lines that work and all come out the same in the end. Some of it is due to bumps.
Funny thing, In cars you look at tach on trackout and/or various points down a straight. It is taught as pretty standard.* No one ever told me to do that in karting. I do think some guys can just tell what is faster by feel. In rental league it is all seat of the pants. So there you get a feel for telling whatever you can based on no tach. You do listen to the engine as a guide and a lot of visual I seem faster here, slower here action.

  • I find it easier to get a rev count farther down the straight. You are less busy and I think get truer read of the exit speed. I do think there are some corner with enough variance that the exit speed alone might not show the best line, due to distance covered in corner.

(Lee Swindell) #14

Warren:

Ok, great points about context because that matters in the real world.

To make it simpler, Let’s retreat into a mathematically perfect track which has a flat surface and simple geometry - no bumps, no camber and constant radius turns.

Let’s put 2 karts - one with a hundred horsepower and 4 wheel brakes, one with ten horsepower and rear wheel brakes, but identical in all other respects - on tyres that supply the same slip angles.

Now lets swap a perfect AI driver between them, and drive that lap in the same conditions.

How would our AI driver’s technique differ in those 2 karts under the conditions above?

Thanks for contributing. Great stuff.

Lee


(Lee Swindell) #15

TJ:

Can you talk more about ‘shocking’ the kart in and out of corners please? What does that look like and why is it bad? I’d have thought that if you can ‘shock’ the inside rear off the deck as quickly as possible, that might be a good thing. No?

One of the guys in my crew told me as long as the inside rear is on the ground, the kart will push. I love that for its simplicity - but do you agree with it? Your thinking seems more analog - the greater the load, the greater the push is how I’m reading you.

The big power / big brake thing confuses me. What I’m hearing is that the greater the acceleration, the straighter the line and the harder the turn. I don’t get this because a kart is a kart: I have one with 92 horsepower, and race one with 13, and they have one thing in common - cornering scrubs speed and you don’t want that, regardless of how quickly you can recover scrubbed speed. 2 guys in one hundred horsepower karts - one throws it around like a sprint car, the other treats every ounce of horsepower as if it were gold. Physics says the second guy will be faster finishing the lap, and much faster finishing the race (I think).

The way I interpret this, the greater the grunt, the lazier the driving. Why should a fast kart be driven any differently from a slow one if the physics is the same?

Or is the physics not the same?

Thanks for joining the conversation.

Lee


(Marin Vujcich) #16

Simple answer is if you have front brakes you cant turn and brake. So to use single gear kart line you would have to brake a lot earlier and roll more. The fastest way is to vee the corner. Drive straight to the apex while braking, that way you can brake to the apex and cover a lot less ground. This will kill the kart for max corner speed, but you have a gearbox and more power to compensate. you can still roll a shifter like a single gear kart, its just not as fast. Simple as that. Hope this helps


(Mike Clark) #17

Lee,
I like your post & approach.
I am a proponent of a new karter driving a kart that really doesn’t work. By that I mean until I drove a kart that didn’t lift (front end settings) and mega-pushed I didn’t get it. Same with axle swap. I was shocked at how I felt the difference immediately at very low speed in both instances. Mini-epiphany for me, mini-epiphany being an oxymoron, but enough to cause epiphora.
In cars I liked to drive with the sway bar off or a dead shock to see what it felt like. The vast contrast in conditions made it easier to see and when you made small adjustments it was easier to see. I use see vs feel because when you drive visually you can see the conditions as easily as feeling them. Seeing being quicker than feeling in car with suspension, but having a feel doesn’t hurt.


(Mike Clark) #18

Good post - should exit speed further up the straight be better if it is faster? IE how do you check what is faster? I know in DD2 it will drift a good way up the straight if you get on it too early, kart not straight, 1 wheel unloaded.


(James McMahon) #19

Sector times and/or top speed like you said.


(TJ Koyen) #20

Good questions Lee. I would tend to agree with your crew member. It’s a little simplistic, but I think it was meant to be.

‘Shocking’ the kart into unloading the inside rear typically puts the kart over the line with regards to traction. It’s simple physics at work; when you put harsh forces through the kart, you’ll get a harsh reaction. Remember that when cornering, the kart is basically teetering on three wheels when all is going well. So essentially, it is a balancing act to keep that that inside rear at a steady rate of unload. When the inside rear wheel lifts, you are reducing your overall rear traction, as now one tire (the outside rear) has to bear all the force you are putting through the rear of the kart. This means there is a very fine line where the traction limit is. When you crank on the wheel to get the inside to lift, 99% of the time you’re going to put the kart past that limit, resulting in some handling malady that most drivers blame on the chassis, when in reality it’s usually their choppy hands making the kart bounce. In my opinion, in single-gear classes driving at 95% is better than driving at 105%. That way, you’re never putting the kart over its limit, so you’re always under control and the kart will be stable and predictable.

When grip is low, in the rain for example, a harsh driving style might be the ONLY way to get the inside rear wheel to lift, as you can’t generate enough force with the tires since traction is so low, so the only way to get lift is to ‘shock’ the kart into lifting the inside rear by yanking the wheel. Even then though, you need to use your right foot to control the kart and keep it from going too far over the limit so you aren’t sliding completely sideways.

As @Marin_Vujcich rightly noted, when talking about KZ driving, you are more looking to chop off the exit of the corner and drive straight from apex off. This is because you have front brakes so you can drive the kart harder and deeper into the corner, and you have 6 gears and 50 hp at your disposal, so rolling with high speed through the center of the corner isn’t important because you can recover your speed so quickly. Plus, with that much power and torque, getting the inside rear wheel up quickly and then having it set back down again before apex is going to give you additional traction to control the rear wheels from spinning as you drive off the corner. That’s specifically why the shifter driving style is different than single-gear. If you were running a higher horsepower single-gear class, you would still see drivers preserving momentum and corner speed mid-corner. Watch any video of the OK class vs. the KZ class and you’ll see noticeable difference in how they are attacking the corners.