high HP, low hp - changes to driving line

two weeks ago my dad and i competed in our first official wheel to wheel racing, running stock honda shifters in the Texas Prokart Challenge Amarillo event.

Wow, what an incredible experience. We were horrible,56 seconds a lap behind the best (now the best there was the #1 guy in the country)

I did a ton to help set up and prep the track which had never had a competition before. THe payoff for this was that I not only got to learn from the pros, when they left they gave me all there race studio data.

One thing that quickly stood out comparing the good drivers to us is they took a very very different line through corners. My dad and I come from autocross, with low HP cars, (miata and s2000). our approach to corners has always been maximize the radius to carry as much speed through the corners as possible. We continued doing this in the karts. The good guys don't. They take a line that basically minimizes the time there off the throttle. they are actually slower when they are turning (and they turn much tighter, and are turning for less time).

Thinking about it, this makes sense. but I have no idea how you envision this type of line. My old version of maximize the radius is easy to see. How do you figure out what the best line is in something that accelerates like a shifter kart?

How about a late apex? Get all your turning done early.

Slow entry, fast exit.

Deceleration is only for the purpose of positioning the car for a fast exit from the curve.

At least that's what I've been taught. Doesn't mean I'm any good at it!! Lol!

I was just reading some different media and whatnot that says hp vs momentum is bullE36 M3.

The fastest line around the track does not matter how much power you have. The ideal line doesn't change.

I can see this when racing chumpcar. Cars have very different power to weight ratios. All of the fast cars carry similar lines through the corner. It doesn't matter if it is a miata, a camaro, or a bmw.

Most karts have a single brake on the rear, and a true 'solid' axle. You have to throw them into corners to get them to turn so you can get back on the power sooner.

red line is an early apex, yellow line is the geometric apex, green line is a late apex. Unlike the image though - the fastest way around may depend on what's coming up next - like an early apex to set up through a combination of corners. Yellow line should be the one that lets you carry the most speed through the corner. Green one allows later braking, a little slower corner speed though.

wvumtnbkr wrote: I was just reading some different media and whatnot that says hp vs momentum is bullE36 M3. The fastest line around the track does not matter how much power you have. The ideal line doesn't change. I can see this when racing chumpcar. Cars have very different power to weight ratios. All of the fast cars carry similar lines through the corner. It doesn't matter if it is a miata, a camaro, or a bmw.

I'm 99% sure that statement is wrong. I'll draw it up and do the math tomorrow. But if you have a car with no acceleration (ultimate momentum car) but very good cornering, than all that matters is increasing the radius. Vs a top fuel dragster that can pull .1 g's in a corner but multiple in a straight line.

icaneat50eggs wrote:

wvumtnbkr wrote: I was just reading some different media and whatnot that says hp vs momentum is bullE36 M3. The fastest line around the track does not matter how much power you have. The ideal line doesn't change. I can see this when racing chumpcar. Cars have very different power to weight ratios. All of the fast cars carry similar lines through the corner. It doesn't matter if it is a miata, a camaro, or a bmw.

I'm 99% sure that statement is wrong. I'll draw it up and do the math tomorrow. But if you have a car with no acceleration (ultimate momentum car) but very good cornering, than all that matters is increasing the radius. Vs a top fuel dragster that can pull .1 g's in a corner but multiple in a straight line.

Maybe if power is the only factor that is changing, then the same line makes sense. Aren't karts hard to trail brake, though? Better to do all your breaking early, then make the shortest corner you can to get back on the gas?

In reply to racerfink:

Leaning to the outside of the corner, while counter-intuitive, lifts the inside tire and can help reduce understeer.

On the racing karts, adding/removing bracing can help tune the chassis along with tire pressures and using the steering for weight jacking. You are a pretty major part of the chassis, so throwing your body around can make a difference.

Stefan wrote: In reply to racerfink: Leaning to the outside of the corner, while counter-intuitive, lifts the inside tire and can help reduce understeer. On the racing karts, adding/removing bracing can help tune the chassis along with tire pressures and using the steering for weight jacking. You are a pretty major part of the chassis, so throwing your body around can make a difference.

this was a major lesson learned, you want as much weight transfer as possible, exactly the opposite of what I was trying to do!

icaneat50eggs wrote:

wvumtnbkr wrote: I was just reading some different media and whatnot that says hp vs momentum is bullE36 M3. The fastest line around the track does not matter how much power you have. The ideal line doesn't change. I can see this when racing chumpcar. Cars have very different power to weight ratios. All of the fast cars carry similar lines through the corner. It doesn't matter if it is a miata, a camaro, or a bmw.

I'm 99% sure that statement is wrong. I'll draw it up and do the math tomorrow. But if you have a car with no acceleration (ultimate momentum car) but very good cornering, than all that matters is increasing the radius. Vs a top fuel dragster that can pull .1 g's in a corner but multiple in a straight line.

If you change the cars ability to handle, then yes, there are different lines through a corner. This has nothing to do with being a momentum car. Every car should be driven as a momentum car.

An ill handling car, or one that doesn't go through corners as fast as it can, is it's own set of problems.

Maybe I am being too specific. The title and first post imply driving a vehicle different because 1 has more power than the other.

In reality, I think you are asking about power and handling.

I believe the line through an I individual corner would not change if you were driving a tag cart or a shifter cart.

Look at the data. Time gained at corner exit is WAY better than time gained at corner entry or even mid corner.

Maximize corner exit.

Late apex ftw.

By no means am I a Kart expert but thanks to friends who have a few KM nationonal championships under their belts I know some.

Kart chassis are such that the very act of turning the steering wheel acts like a weight jacker. What you find with karters who switch to cars is they're set up results in a car that oversteers all the time unless you are quickly rolling into the throttle.

Basically because the karts rotate so rapidly they can take a much shorter route through a corner and because doing things like pushing on the steering wheel with the heal of your palm change the balance you can still get off the corner well.

The net of all of the above is the ability to unwind the wheel early and free up the motor; you can hear who has this down pat by the tone of the motor in slow turns.

I'm someone who uses trail braking to great effect. Many years ago while following a friend and former F125 champ I noticed while trail braking allowed me to carry corner speed but I was getting clobbered on the exit. Whereas he lept forward off the corner I went about 12-18 inches sideways then forward. I'd lose 2-3 feet of almost every corner. Another friend and multi time national champ explained that I need to get back on the power sooner because the chassis doesn't need to be trail braked that much to get it to rotate. The funny thing is my lines where near identical it was the angle of the kart relative to the direction of travel that was different.

I wanted to do this part of my reply separate from the kart part as it addresses the low power high power part;

wvumtnkbr Noted corner exit is what matters; where the power thing starts to really alter lines is really in low power cars. I'm talking cars in the 28-30lbs per horsepower zone. In any corner over 75-80 mph range you have to start worrying about more about corner speed than the exit because the car simply won't accelerate any where near fast enough to take advantage of a proper line. This is most noticeable in big sweepers or other sections where the corner speed is near the top speed.

With all that said most modern cars don't suffer from this; remember we think of them as low power but a Miata is faster down the 1/4 mile than a stock 240Z.

The converse of this would be a big V8 tube frame car with spool rear end; you're likely to drive a different line than a Spec Miata. Again this is a less common situation.

Where I find the approach to differs for power level is high speed vs low speed corners but as mentioned only for the extreme circumstances.

This is how people used to talk about riding 500cc two-stroke GP bikes, which had violent and explosive power delivery. Sail into the corner on brakes, get it almost stopped, get it pointed straight and pull the trigger. The 250s took a completely different line.

In reply to Stefan:

You made be able to shift your weight in a sprint/shifter kart to the side, but an oval kart, you are planted in the seat.

Tom1200 wrote: I wanted to do this part of my reply separate from the kart part as it addresses the low power high power part; wvumtnkbr Noted corner exit is what matters; where the power thing starts to really alter lines is really in low power cars. I'm talking cars in the 28-30lbs per horsepower zone. In any corner over 75-80 mph range you have to start worrying about more about corner speed than the exit because the car simply won't accelerate any where near fast enough to take advantage of a proper line. This is most noticeable in big sweepers or other sections where the corner speed is near the top speed. With all that said most modern cars don't suffer from this; remember we think of them as low power but a Miata is faster down the 1/4 mile than a stock 240Z. The converse of this would be a big V8 tube frame car with spool rear end; you're likely to drive a different line than a Spec Miata. Again this is a less common situation. Where I find the approach to differs for power level is high speed vs low speed corners but as mentioned only for the extreme circumstances.

If you took a high horsepower car that handled well and made your same line, it would be faster than if you did some other line as well. However, that line is NOT the maximum radius.

The maximum radius is a longer distance. The lower speed car will lose more time going a longer distance versus doing the late apex situation.

Ask the pros and see what they say.

Tom1200 wrote: wvumtnkbr Noted corner exit is what matters; where the power thing starts to really alter lines is really in low power cars. I'm talking cars in the 28-30lbs per horsepower zone. In any corner over 75-80 mph range you have to start worrying about more about corner speed than the exit because the car simply won't accelerate any where near fast enough to take advantage of a proper line. This is most noticeable in big sweepers or other sections where the corner speed is near the top speed.

I mostly race lemons in either a 35lbs/whp car or a 41lbs/whp car. Something I read in a book(Bondurant? Smith?) really changed how I drive it. He said, "don't drive to the line, end up on it." With a low HP car you don't end up on the "line" in the fast stuff and sometimes in the slow stuff. When I first started racing I was trying to clip all the apexes and I was tracking out to all the curbing like the fast guys were doing. Why waste time driving out to the line. With our slow pigs I need to get what little power I have down and take the shortest route possible. The cool thing is that I'm full throttle where most other cars are feathering it. More tire than HP is sure is fun.

When working with Toyota, the sensei's always told us to 'speak with data'. Don't rely on what you think. Copy the fast guys line and technique. You see the line, but there must be some subtleties to their technique that might be a challenge to decipher and duplicate.

icaneat50eggs wrote: One thing that quickly stood out comparing the good drivers to us is they took a very very different line through corners. My dad and I come from autocross, with low HP cars, (miata and s2000). our approach to corners has always been maximize the radius to carry as much speed through the corners as possible. We continued doing this in the karts. The good guys don't. They take a line that basically minimizes the time there off the throttle. they are actually slower when they are turning (and they turn much tighter, and are turning for less time).

Then you've been autocrossing wrong. 99% of the time the fastest autocross line is the shortest distance. This is one of the core elements of the Evolution curriculum. My data acquisition with a co-driver in the same car over the last 3 years has substantiated this.

In reply to Ricky Spanish:

Agree. Road courses sacrifice corner speed for straightaway speed, and usually you come out ahead (because - gasp - even road course drivers spend most of their time going straight). In autox, there are no straights, and no high speeds. So minimize time by minimizing distance.

Not like I am any good at taking my own advice though.

I think it's not so much just power, but power vs cornering speed that matters.

The more power you have relative to the speed you can carry through a given corner, the more you want to prioritize getting back on the throttle early. A slightly slower line that gets you back on the throttle sooner might be faster.

On the other hand, cars with high cornering speeds and low power will want to prioritize highest speed through the corner as they can't re-gain speed as quickly.

buzzboy wrote:

Tom1200 wrote: wvumtnkbr Noted corner exit is what matters; where the power thing starts to really alter lines is really in low power cars. I'm talking cars in the 28-30lbs per horsepower zone. In any corner over 75-80 mph range you have to start worrying about more about corner speed than the exit because the car simply won't accelerate any where near fast enough to take advantage of a proper line. This is most noticeable in big sweepers or other sections where the corner speed is near the top speed.

I mostly race lemons in either a 35lbs/whp car or a 41lbs/whp car. Something I read in a book(Bondurant? Smith?) really changed how I drive it. He said, "don't drive to the line, end up on it." With a low HP car you don't end up on the "line" in the fast stuff and sometimes in the slow stuff. When I first started racing I was trying to clip all the apexes and I was tracking out to all the curbing like the fast guys were doing. Why waste time driving out to the line. With our slow pigs I need to get what little power I have down and take the shortest route possible. The cool thing is that I'm full throttle where most other cars are feathering it. More tire than HP is sure is fun.

Just out of curiosity, what are you driving that has a worse power-to-weight ratio than a 1.6 Miata by double?

In reply to oldtin:

You left out how the late apex sets you up for the pass because you carry more speed at the end of the straight, it also sets you up for out braking at the next corner.

z31maniac wrote: Just out of curiosity, what are you driving that has a worse power-to-weight ratio than a 1.6 Miata by double?

Planet Express weighs 3500lbs with a half tank of fuel(11 gallons) and me(145lbs) in the seat. She's sitting at ~85whp.

@ wvumtnbkr we're on the same page I should have clarified my point. In a really gutless car it's often faster to drive along the bottom of corner as pointed out because it's shorter distance (much like autocross) The corner loads are also not high enough that the tighter line bogs the motor down. I certainly would never suggest running the maximum radius.

My 1200 would be a good example; when it had 73whp there were 3 spots on my local track where the car was never going to drift out to the exit curbing. Now with 32whp more that is not the case. My line is now the same one I use in a Spec Miata and the D-Sports racer. There is still one section that semi comes into play; turn 2 is a 180 left that leads onto a 4000ft straight with a 30 degree right (turn 3) that leads into a 50 mph 180 left (turn 4) In a car that travels through turn 3 at less than 100 mph, you stay full right exiting 2, through 3 and into 4. My car now does 106 through 3 and I need to let the car run out about 5ft from the right hand track edge or it will start to scrub speed (100rpms). Now in the D-sports racer you needed to come back nearly full left at turn 3. In a 750hp Viper you needed the full track to negotiate turn 3, obviously going 130+ requires a different line then it does at a 98 mph.

Probably the most glaring example I can use is an H production sprite can negotiate turn 9 at Willow Springs without ever lifting. If it's a moderately tuned sprite, 9 is no longer a decreasing radius turn.

There is a case of extremes because with a few exceptions I teach the same line for most cars. There are the odd cases of reeeeeeealy gutless cars and really heavy cars with loads of power but again most cars don't fit into that category.

Now whoever brought up telemetry is spot on; with all the apps out there it's easy to come up with a basic set up. If you can review your camera footage after each run you can do sector times and view your tach reading (if the tach is visible on screen)

This brings me back to the original topic; part of the reason the front running Karters are front running is they pour through their telemetry after every session. Last year I was privileged to spend some time with one of the factory kart teams at the big international kart meet that takes place here in Vegas. Truly an eye opener, really small things add up quickly.