Steering drag in high speed corners

[Jersey Tom]

Edit - not gonna bother

[Belatti]

Sorry, Im working 14 hours a day in several proyects and all mixed with a race this weekend.. Havent seen enough of the car to answer now, just a speed-time chart and google earth images of the track, will reply soon...

[speedsense]

Some food for thought here:

A month ago I saw data acquisition from a steel frame / 120HP / 550Kg-driver included openwheeler. It called my attention that the car entered a 200m radius corner, pedal to the metal at 210Km/h. Full throttle. The exit speed? 185 Km/h...

The driver barely turned the steering wheel. The tyres are a little bit over sized for that car... from my humble point of view.

Why that much steering drag? I dont know the steering geometry in detail, but the first thing that came to my head was and odd ackerman.

I have some data on something close to this, a FF going through the Kink at Road America, which is just over 200m from entry to exit and is flat out. The Kink is also flat (the road that is) and flat out (all the way through) in a well handling car. Typical size FF tires. 0 ackerman. The car set a track record on this lap, and scrubbed 7.9 mph off the speed of the car in this corner (entry to exit). The car has a little more horse than your car. Before setup changes were made to this car, the scrub was 9.6 mph (still flat out). None of the changes involved steering toe changes...but roll, pitch and ride height as the differences. BTW, the lateral G average is 1.6 for this car, in this corner
I would say that if the tires were larger, that the car scrub would also be greater, as an assumption probably around 10-11 mph as there's just not enough horse available to over come the footprint of the tire, let alone the air drag on the straights, at least at RA.
A 15 mph loss seems a bit much, are you positive that the throttle is absolutely flat and a solid flat line with no waver? A driver lightly holding the throttle against the throttle stop and hitting a bump or curb could end up without full throttle and not know it. IE. Going from 100% to 95% for a brief instant could knock a 100 to 200 rpm out of the car. Seen this happen many times.
Also the driver's use of the steering wheel, even though the steering angle is slight, I've seen many times driver's that have what I call a "nervous" steering wheel, where theres a lot of small movements during cornering and scrubs 1-2 mph just with those movements. The only cure is to slow his hands down.
You could have both going on. If not, you might have some mechanical issues, engine? drive train drag? IMHO..

[DaveW]

Good post, speedsense. For what it's worth, I suspect that speed loss through "flat" corners might be reduced by moving lateral balance away from under-steer.

[speedsense]

Good post, speedsense. For what it's worth, I suspect that speed loss through "flat" corners might be reduced by moving lateral balance away from under-steer.

Yes, though even an over steering car will also lose momentum, especially at the top end of the car's horsepower ability, the loss of grip front or rear will slow the car... In terms of stability, as related to the drivers mind, of the two evils U/S and O/S, in high speed corners such as this, it's more confidence building to have "slight" understeer rather than slight oversteer, as the driver can't and won't go any faster with the slight oversteer. (If the corner isn't flat out already and driver is attempting to find flat out)..

A great analogy on the driver's use of the steering wheel "If you had a car with no brakes, no engine compression (no wings or aero devices as well) and you had to slow down the car for the upcoming corner, what would the driver do to slow down the car?

Answer: Use the steering wheel to scrub the speed off. So anytime you steer the car, you are slowing down the car akin to using the brakes.... understeer is exactly that, too much steering input for too long of a duration. Oversteer is exactly that as well, with the steering correction and the sliding of the rear both slowing the car.

[Ciro Pabón]

Strad, speedsense, scrub and slip are different things.

Scrub radius: related to the distance between the point where suspension steering axis touch the ground and wheel centerline.



Slip angle: difference in lateral and longitudinal velocity "from the point of view" of the tyre.



When you scrub a tyre you can fix it (on some cars with McPhersons: scrub radius will change if you change camber A LOT).

For years cars had positive scrub radius (toward the interior of the car) to make it easier to steer while parking.

Nowadays many have negative scrub radius (to make easier to recover from a flat tyre, most front wheel driven cars have it).

Many racing cars have positive scrub radius since times immemorial: if you get a flat, the steering wheel can move without control, but you feel the road better.

That's why some times people makes mistakes when using wider tyres with non-standard rims: they change the scrub radius without noticing.

So, scrub is scrub and slip is slip.

[Jersey Tom]

Ciro gets it again...

[xpensive]

Ciro gets it again...

How does it feel Ciro, to receive such unconditional approval from the highest of authorities?

[Ciro Pabón]

Engineers recognize no authority


Engineers need no approval

[DaveW]

Strad, speedsense, scrub and slip are different things.

At the risk of raising a proverbial storm in a teacup, Ciro, I (with my non-automotive background) was quite happy with speedsense's use of the word "scrub", as in "scrubbing off speed". I don't think that "slipping off speed" would have quite the same ring to it.

X, be kind... Forgiveness is a virtue. JT, when he chooses to be constructive, is always worth listening to.

My earlier comment about lateral balance was based on the observation that "oval" set-ups often generate transient over-steer in a vehicle. That is a decidedly risky strategy in my view, so it must offer a performance advantage. I concluded that the strategy probably reduced momentum lost when negotiating turns.

[Ciro Pabón]

Sure, Dave, thanks. In this country where I live people do not drink tea, there are no hurricanes nor tornadoes.

Believe me, Tom, Strad, speedsense, X, Dave, you are not wasting your time in this forum. I happily recognize your deep knowledge, wide interests and quick mind, racing experience, sarcastic humour and wisdom (respectively).

For example, a proof of my respect is that I don't make jokes any more about Swedish, Canadians, Britons nor Americans... almost always (except when they dance, of course).

Now, if somebody can put some flesh on the bones of the calculations I made, I would be grateful.

[Sayshina]

Strad, Universally used by drivers, journalists, fans, and perhaps owners. In other words, people who lack any knowledge of what's actually going on. Yes, even most drivers. It's easy to get suckered in by journalists, after all, they're trained to sound like they know what they're talking about. But very few journalism degrees require any math or science above the minimum, which is really just a highschool level.

And you should listen to your average driver try to explain in the pits what he feels when his front suspension is binding up mid corner. He'll use words like "boom" or "pop".

Given this, is there any better way to take the curve?

Probably like a V-shape. Don't steer, steer hard and go out. I mean for this type of full throttle corner
Caito.-

Caito, that's called squaring the corner. It's usually used to correct for some defect, often engine related. If you have say lousy transient response you square the corner up to separate the turning from the accelleration.

There are drivers who naturally tend more toward that or more toward a traditional line, but in my experience it's more something that happens on a subconscious level rather than some decision to do it. You're having some problem through that corner so you square it up. Now you're maybe not as fast as other guys taking a normal line but you're faster than you were and you're fast enough. That's 1 problem you can drop to the bottom of the list and work on later, if you ever run out of other problems.

If you look at formulae where turbo cars are running with atmo cars under equivelance, you'll often see the turbo guys square up a lot of corners. Oh, also, you mostly see it in formulae with an abundance of power.

[speedsense]

Sure, Dave, thanks. In this country where I live people do not drink tea, there are no hurricanes nor tornadoes.

Believe me, Tom, Strad, speedsense, X, Dave, you are not wasting your time in this forum. I happily recognize your deep knowledge, wide interests and quick mind, racing experience, sarcastic humour and wisdom (respectively).

For example, a proof of my respect is that I don't make jokes any more about Swedish, Canadians, Britons nor Americans... almost always (except when they dance, of course).

Now, if somebody can put some flesh on the bones of the calculations I made, I would be grateful.

Ciro, you are very correct to point out my use of slang. My use of the word scrub was to reflect a speed loss which would include kingpin/upright scrub and/or slip angle, aero drag,etc. The list is very long as to causes of the loss of cornering speed, with some items having more impact than others (steering for instance)
Sort of a composite term to include all.

[Belatti]

Still couldn´t be able to measure the car, it has ackerman pretty near to ackerman geometry, so that can be something to work in.

When you speedsense refer to 0 ackerman, you mean parallel?

Thats what I would choose to in a time limited situation. I wont dare to use "anti-ackerman" because of some tight corners...

I will intall a steering position sensor maybe in the next race there, next month. The in-car camera tells me the driver doesnt move the wheel too much as someone suggested.

In this car, average lateral G is arround 1.6 too, but mind the car is capable of 1.8 because its over sized in the tyre department. With this I mean you can go through the corner full throttle even if the car sucks.

The major thing here will be to improve that scrubbing there without sacrifizing in other areas.

[malcolm]

Hang on... LSD was mentioned, but not really commented on (unless I missed it).

So open-diff? Torsen? Clutch-type? Viscous? Welded?