Cornering line

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gizmo
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Cornering line

Post by gizmo » Thu Jul 30, 2009 9:26 pm

After running a TAG kart this weekend for about 20 minutes, I've begun to wonder if I'm taking the proper line through turns. All of the racing books I've read, along with all of my school experience, has me reaching for a late apex. Granted, this is the line one needs to run when driving a naturally tight racecar, but I seem to begin my turn far later and more abrupt than other competitors.

I've decided to neglect the few karters I've seen drift through turns because I don't believe that technique has any basis outside of karting.

That considered, I've also noticed that I carry much more speed starting mid turn and through the exit apex than the drivers who have been taking that earlier entry I previously mentioned. Albeit, their kart may be setup differently than mine and may be faster kart too and therefore what works best in my kart may not work best in theirs.

I wonder if I'll ever really know whether I'm running as fast as the best of them until I get my own car and find out for myself.

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Re: Cornering line

Post by gizmo » Thu Jul 30, 2009 9:27 pm

I'll post a poorly taken video of the 20 minutes in a few days.

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Re: Cornering line

Post by LHOswald » Fri Jul 31, 2009 12:45 am

aren't you supposed to drive towards an apex thats at the...well apex? not late or early but dot on?
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Re: Cornering line

Post by gizmo » Sat Aug 01, 2009 12:00 am

It's circumstancial, but more often than not, I'd say no.

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Re: Cornering line

Post by ra64t » Sat Aug 01, 2009 1:17 pm

The racing apex is certainly not always at the geometrical apex of a corner. A verity of factors can influence where to apex the corner, including elevation change, camber/banking change, surface changes, sequence of corners before and after, and increasing or decreasing radius of the corner.

If the corner is a perfectly symmetrical 90 degree turn, with none of the other factors listed above, in theory the fastest line should be taking the geometrical apex. An early apex would allow higher entry speed, but kill exit speed as you'd have to tighten your line on exit, very bad. A late apex would mean slower entry speed, but a bigger arc on the exit of the corner. This could be good, but it would only be worth it if you could make up for the lost entry speed from mid corner off. Most basic race theory says most of the time you can't, and the geometrical apex is fastest.

However, this is hardly always the case. In the case of a hairpin, very common in the real world, because the corner is so long it may be possible to make up the entry speed lost in a late apex rather then a long period of constant speed cornering. obviously, how long the strieght is after the corner can influence if you want to go late, and how late. Also, how much power the vehicle has would be a factor. Higher powered cars would make up the lost speed easier. And this doesn't even begin to factor in elevation change, surface change, etc. etc. Or the possibility of double apexing some long corners (treating the corner like two separate corners).

Taking a real world example, lets look at a diagram of the e-town kart track with a racing line drawn in: Image

I believe this line is based on what one would draw in looking at a diagram of the track. turn one is close to a geometrical apex. turn 2 is a double apex due to being 180 degrees +, and late on the second apex to help the entry into 3. 3 is clsoe to a geometrical apex, maybe a little late. 4 is a little late as it's almost a hairpin (180 degrees). 5 is early as its increasing radius (the corner opens up off) and 6 is pretty late as it is slightly deceasing radius, a near hairpin and leading on the a long strieght. 7 and 8 lean late because they are pretty much geometrical true hairpins leading on the straights. 9 is double apex, slightly late as the shape is two sharper corners.

e-town is on a parking lot so elevation change and camber/banking are not really factors. However, surface changes are! This is where it gets even more interesting. Do a google maps search for the track (Raceway Park Dr, Englishtown, NJ 07726) and see the concrete patches in some corners and the real line (dark area in the corners from the tires). Notice the differences between the line on the diagram and the real line. IMO, some corners aren't as late apex as the diagram implies! Consider turns 4 and 7 where the acutal line looks close to a geometrical apex. Both these corners have concrete patches. My theory is on this track, the concrete provides extra grip over the asphalt, so it is faster to turn in a little earlier and get more cornering done on the concrete patch. Consider turn 8, with no concrete patch, and how the line there looks much closer to the diagram.

Generally, I think aiming for a slightly late apex isn't a bad idea, because naturally one is inclined to apex early, and I feel late apexing is better then early. Reviewing the skip barber book, they actually suggest to find the best apex when learning a track, to start with a later apex then you expect, then gradually apex earlier and earlier until you see (through a tach or speedo) or feel that you exit speed is dropping off.
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Re: Cornering line

Post by LHOswald » Sat Aug 01, 2009 4:40 pm

that all makes absolute sense. nonetheless, i now need 2 ibuprofin and a nap. that made my head hurt
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Re: Cornering line

Post by comingbackdown » Mon Aug 03, 2009 1:41 pm

Image

Alright, really shitty MS Paint editing, but from what I've read that wouldn't be a half bad cornering line... Situationally, that is. Problem is, I just drew that crap up in MS Paint, and I can't use paint for beans.
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Re: Cornering line

Post by gizmo » Mon Aug 03, 2009 8:51 pm

What you drew is similar in nature to what I ran there.

The idea of a late apex, for me anyway, is threefold:

1) it allows for all of the braking and steering input to occur before mid corner.
2) it allows for the throttle to be reapplied earlier because of the straighter exit line
3) points one and two effectively elongate the two straightaways connecting that hairpain turn.

Frankly, and I probably speak for myself, but I just can't "feel" another line to run. I feel like, once I turn the wheel, I shouldn't need to slow more before I can feed more wheel into that turn, but instead be carrying turn speed prior to steering input and merely feed steering input accordingly so that the slip angles are built up properly and the suspension stays balanced (load is transferred smoothly). I've drivers like Schumacher (sp?) have made a living turning in earlier and somehow holding the same line at higher speeds despite the earlier entry but I've yet to figure out how they do it when behind the wheel myself.

So, effectively, I threshold brake as close to the turn as possible slowing near turn speed while traveling in a straight line. The remainder of the braking is done while turning, in such a way that a small almost indiscernable push is induced because of the braking, and the steering input is fed in in such a way that the car rolls into the turn. Once I have the front wheels facing somewhat toward exit apex, I roll back onto the throttle so that all traction belongs to cornering, and once the nose is pointed where it has to go I roll back into the the throttle as much as conditions will allow.

To me, that allows what is likely an equally fast lap time, but it seems far easier on the tires (although I have no tire pyrometer readings to back that up). However, I've yet to compete in an event where tires alone decide the race...

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Re: Cornering line

Post by gizmo » Sat Aug 29, 2009 10:27 am

I'm surprised how inactive this part of the forum is.

I've been thinking a lot about my cornering line and what I've learned in books/class and I am convinced, until I get a skilled driver behind the wheel of an indentical car and lose to that driver by more than a few tenths, that I pretty much have a handle on how things are supposed to happen at the envelope.

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Re: Cornering line

Post by LHOswald » Sat Aug 29, 2009 10:42 am

do you think you could come close to a race with gary sheehan with an identical car?
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Re: Cornering line

Post by gizmo » Sat Aug 29, 2009 10:47 am

I'd sure like an opportunity to find out.

Addendum: I mean no disrepect by that. If the question weren't asked, I wouldn't even haved ventured to say or think such a thing. But I believe, based on my experience, that I can run with the big boys; as I think all good drivers have had confidence in themselves throughout history. Although stock car racing is my forte, I do okay for myself turning right and downshifting too.

I feel like Rocky did, in the first move, right about now. If I can go the distance, then I'd be happy.

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Re: Cornering line

Post by ra64t » Sat Aug 29, 2009 1:52 pm

Ok, I propose a standardshift.com racing championship! we'd all meet at a central location and do a race with equal cars/karts.

If only we could find a sponsor to fund everyone a few thousand bucks for it...
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Re: Cornering line

Post by gizmo » Sat Aug 29, 2009 1:54 pm

karting would be a possibility. but like all kart rental shops, unless the karts are very new, the kart equality is dubious. if we could run enough races to force everyone into every other kart, that would technically equalize the field. but it would probably take a while to orchestrate.

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Re: Cornering line

Post by mad_finn » Sat Aug 29, 2009 2:09 pm

ra64t wrote:Ok, I propose a standardshift.com racing championship! we'd all meet at a central location and do a race with equal cars/karts.

If only we could find a sponsor to fund everyone a few thousand bucks for it...
I'd gladly would take the challenge, but the distance is a bit of an issue. planeticets etc... would sipply just cost too much.
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Re: Cornering line

Post by LHOswald » Sat Aug 29, 2009 7:29 pm

yeah we can all just drive our cars there. you'd have to fly and get your car shipped here. that would suck :P
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