Racing line between alternate direction corners

[raymondu999]

Hey folks. I have a question regarding how to drive a circuit; in the straight (however long/short) between two corners who go in different directions.

As an example, Turn 9 Barcelona is a right hander, connected by the straight to the Turn 10 left hander. Or how Turn 7/8 in Sepang is going to the right but Turn 9 is then a left hander. Or how the Ascari chicane exits on the right hand side of the track but drivers have to go left for the Parabolica entry.

Given a racing line usually consists of a wide exit and wide entry at some point, that means that at some point in that straight you have to move across from one side of the track to the other.

When is the optimum time to perform this move?

I read Peter Windsor's blog quite a bit; I love his writing and his style of prose is very "story like" making all the pieces very enjoyable reads with their eloquent wording. However I do know better than to trust him on technical matters; or even factual for that matter. He makes a lot of mistakes in his articles factually; so much so that it's quite dangerous; given that a lot of people are entrusting him to write factual pieces and will trust what he says. (For example he was saying how Vettel's 22.6 lap in Monza was the lap on which he did the Ascari powerslide; when the powerslide happened AFTER the 22.6 lap)

His technical knowledge seems like a lot of guesswork for someone who is not really technically learned (I'm not criticizing him for lack of technical knowledge; I'm criticizing him for including it in his writings; such as he was saying how a car with more downforce will be better able to maximize its use of the option tyres; because the car with less downforce will not have enough downforce to maximize it; which is baloney to me. He also states how this, in reverse, means that the harder a tyre is; it will nullify the differences between aero of different cars as they can't "maximize the use of their downforce" as the tyre doesn't have enough grip to do that.)

Anyways; I digress. He's been saying for quite a while now; that on corners such as I say above; you should keep the car dead straight on these exits (it supposedly "drains the engine of any g load) and will cost you revs. I assume he is talking about the friction acting longitudinally on the car when the frontal tyres have some steering lock applied to them; more commonly known as tyre "scrub" or "drag" I believe. He says that you should keep the car dead straight and accelerate for a bit before you begin to move across.

When I think of it more however, as the car accelerates, there should be more downforce pushing the front tyres into the tarmac; and hence with the same degree of steering lock, there should be more friction produced as such. Which would be affecting the car more, no?

Would it not be better to immediately point the car at the next braking zone, AND THEN go straight from there? I do do some amateur track races and track days; but I'm not a professional racing driver; nor am I schooled in racing lines/techniques. Hence I would like to ask those who are better in the know regarding this.

Or should I just regard this as I do any technical knowledge I find on his site?

Cheers folks

[mep]

I would say on low speeds a F1 has car enough power to overcome some higher tire friction. So you can immediately point the car in the direction you want to go. On the other side you might want to go straight a few meters to keep control of the car. For example on the exit of Ascari you might have half of the car on the curbs. Reducing tire drag becomes more important the higher the speed is for example in high speed corners like Blanchimont in SPA or even the tunnel in Monaco.

[raymondu999]

I get that the car will have enough power to still accelerate given the tyre drag from "reasonable" angles of steering lock. But would it be better to get the car pointed at the next braking zone early on whilst there is less downforce, and hence less tyre drag for any given steering angle, or would it be better off later on?

[mep]

I don't know how downforce will affect the tire drag but it is likely that drag will increase with load. My point is that at high speeds the car gets limited by aerodynamic drag and there is no engine power left to overcome tire drag. So it's better to steer the car early in the right direction.

[raymondu999]

That's what I thought so too; tyre drag increases with the vertical load as normal force increases to the tarmac (with friction being coefficient x normal force) so I was thinking get the damn thing turned first; while the friction and tyre drag is still low. I wonder if someone else has anything to say on this

[godlameroso]

Depends too how fast you're going, F1 cars lack ABS and thus aren't great at heavy breaking from weird angles, so if the straight is short you want to hold a line that will let you brake more or less in a straight line. But on fast corners where you have some leeway, like after the 130R, you want to drift slowly into the line for braking. Remember the less you turn, the faster you go in a straight line. That being said taking the diagonal route across the track is always slower than going straight albeit only slightly. The correct line is the one that maximizes your acceleration towards the finish line, so sometimes you have to be slow in a certain part of the track so you can be faster in another. I say go to formula1.com watch the onboards, and study the lines that they take, how they drift to their braking line. No better way to watch how something is supposed to be done than studying the pro's. That said, watch the onboards on youtube for other race series.[youtube]http://www.youtube.com/watch?v=44tg_MLVCTo[/youtube]

A good example is turns 1, 2 and 3 in China, there are multiple lines you can take, but essentially you want to set up to go flat out out of the continuous left at the end of the sequence. Some people prefer to go a little wide from the long right , so that they can set up a tighter turn 2 and get a better launch out of 3.

[010010011010]

In Monza anyway they keep right for the first half of the straight before the Parabolica to avoid the worst of the bumps in the road. I think it'd be stuff like that that would make the biggest difference to the lines used.

[godlameroso]

In Monza anyway they keep right for the first half of the straight before the Parabolica to avoid the worst of the bumps in the road. I think it'd be stuff like that that would make the biggest difference to the lines used.

Good point, like in Monaco, where instead of going straight on the approach to Mirabeau they go around that huge bump in the middle of the road.

[raymondu999]

I know; but I'm more talking about the best line if the surface were smooth

[Tim.Wright]

This problem a question of path curvature. The tighter the curvature of your trajectory, the more cornering force you need and the less is available for traction.

For this problem, ignoring any road irregularities, you can split it into two cases
1. One grip limited condition (LH corner) followed directly by another (RH corner)
2. One grip limited condition followed by a power limited condition (straight) then another grip limited condition

case one is like les combes in Spa, case two is like the exit of ascari in Monza.

Starting with case 2, you have a long straight following so you want to finish the corner as early as possible so you can use your full longitudinal acceleration capability as early as possible. This means you need to reduce the trajectory curvature to zero as soon as possible. To do this you need to finish the corner with the vehicle parallel to the outside of the track. Even better would be to run very wide at the exit to lower the path trajectory even further. The earlier you reduce the steering angle, the earlier you can get back on 100% throttle.

Once you move from grip limited, to power limited, you can move to the other side of the track without loosing any performance.

For case 1, there is no advantage to this approach because any lowering of the path curvature on the exit of the first turn, will cause an increase in the required curvature at the entry to the next corner. In other words, if you take a wide exit for the first corner, you have made the next corner tighter and therefore slower.

Tim

[raymondu999]

Yes but let's take the Ascari exit. For most cars it's easily flat out anyways; so it's not grip limited for one thing.

Next; again; I repeat. there will be some performance hit by any sort of steering angle. Tyre drag will increase (given that downforce increases) with more speed. So to say that there is no performance hit isn't quite true; and this is kind of the whole point of the argument. Not to mention you would have to put more lock on (a fraction more) as you're traveling to the same point but you've already travelled some distance towards it. If what I'm saying makes sense

[Tim.Wright]

Ok Ascari was a bad example then.

Yes it is true what you say about steering input. Any steering angle of the front wheels will cause a drag force on the vehicle. But still, if you have to move from the right side of the track to the left, its best to do it after you have left the grip limited phase of the corner.

What I meant about loosing performance was probably not clear. Yes, moving from one side of the track to the other will affect your acceleration, but it has to be done. so you are not loosing any overall laptime performance by doing this.

Tim

[mep]

Very good explanation by Tim Wright. In general I agree with it except with one point.

Once you move from grip limited, to power limited, you can move to the other side of the track without loosing any performance.

I think once the car becomes power limited it is to late to change position on track because that is the moment when additional steering drag will cause a drop in velocity. It has to be added that a F1 car will become power limited on fairly high speeds so usually not during a corner but on the end of a long straight. So as soon as the car has left the bend and is stable you can make a small steering adjustment to get it to the other side.

[bill shoe]

I'll use Tim Wright's terminology.

Can I define a case 1.5 situation? This is two grip-limited opposite-direction corners separated by significant longitudinal accel/braking, but the accel itself is still grip limited, not power limited. In other words not a left-right transient where the velocity is roughly constant through the whole process.

An F1 car can always generate higher G-forces in braking than acceleration. What does this imply for the ideal line for case 1.5? I think this means the ideal entry/exit width will not be an even tradeoff. There will be some asymmetry for ideal exit width vs ideal entry width. I'm not sure which way is optimum-- wide exit and tight entry, or the other way around?

[Tim.Wright]

I think once the car becomes power limited it is to late to change position on track because that is the moment when additional steering drag will cause a drop in velocity. It has to be added that a F1 car will become power limited on fairly high speeds so usually not during a corner but on the end of a long straight. So as soon as the car has left the bend and is stable you can make a small steering adjustment to get it to the other side.

The steering input is going to penalise you longitudinally whether its in the corner or on the straight, however its for different reasons. On a straight, yes it takes away from your Ax capability. In a corner, it has the effect of taking away some of your lateral grip capacity which will lower your exit speed. The exit speed is critical because any delta here will cause a continual loss of time for the full duration of the straight.

In practice, I think what we see is the drivers pointing the car at the next turn directly after (maybe 20m or so) after the exit of the grip limited section.

Tim