The Theory of Slow Turns

[Doug Landau]

Greets
I've decided that there is a theory of slow turns, in auto racing, and I know what it is, and it should be stated. I realize that it is not exactly a huge advance mathematically, but it is an advance, and very interestingly, i think, it is also the first advance in ther subject since 1959: Piero Taruffi, "The Technique of Motor Racing". In which he draws a rectangle to represent a car in a turn to the right, a dot in the center as the CG, and a right angle made of two vectors representing the braking force and the turning force, and their vector sum, and claims that when their rising vector sum equals the available traction, the car will lose the road, and in that direction.

I am simply adding that one should -keep- the vector sum adding up to 99.9% of available traction, at all times while entering the turn. Coming off the brakes to match the increasing demands on/of/for the available traction from tuning.

www.tinyurl.com/thetheoryofslowturns

-dkl

[John B.]

As I understand the term it refers to cornering with the path of the
car following a arc which is determined by the ability of the tire to
resist slip.

But do racing cars do this? Certainly motorcycles do not and from
memory stock cars do not either.
https://tinyurl.com/y69mh8jf
https://tinyurl.com/2p96jtt2
--
Cheers,

John B.

[Doug Landau]

otr
What term? Slow turn? In auto racing, it's a turn for which one would brake hard and deep into there turn. It is defined in the doc. As are slow and medium. I guess that because there are two things, gas and brakes, there woiujld be four combos, but there is noit much place for them both to be used at the same time, so... three: do nothing, lift, brake. maybe there shoulod be four: nothing, lift, brake before the turn, brasker into ther turn. The important thing is the car's attitude, or situation, do you agree? IOW that the car is under braking at the moment that turning begins.

[Ralph Barone]

You can also achieve this by coming into the turn at the highest speed
possible for the maximum turning radius you can manage, and then as you
scrub off speed in the turn, tighten the turning radius to keep the g force
constant. But most importantly according to Jackie Stewart, is to drive as
smoothly as possible, gently segueing between maximum acceleration, maximum
deceleration and maximum cornering.

[Frank Krygowski]

I think there may be different strategies depending on one's objective. If a person
were riding alone and trying for a record (KOM) on a certain course, I think Ralph's
version might be best. But if one were in a race, the objective is not to be as fast
as possible; it's to be faster than the other guy. In that situation, the best strategy
may be different, because it may include finding a way to get past the other guy,
or prevent the other guy from passing you.

In any case, I remember reading an article in a motorcycle magazine decades
ago, titled something like "A Safer Way to Corner." It argued that for road riding,
most motorcycle riders were better served by riding straighter into the curve
(straighter than a parabolic path, or whatever), braking hard, then accelerating
out in a straighter exit line.

I played around with that strategy a bit, but I was never (and still am not) an
aggressive motorcycle rider.

I'm sure Tom will set us all straight very soon!

- Frank Krygowski

[Catrike Rider]

On Sat, 31 Dec 2022 18:02:41 -0800 (PST), Doug Landau

I've never raced motorcycles or bicycles. The only reference to the
term "slow turn" in racing go carts or cars, which I have done, was
simply to refer to a turn where you had to greatly reduce speed.

I know that one key element in those types of racing is to exit the
turn faster than your opponents. It's also generally considered bad
practice to be braking in the turn, which pitches you forward and
causes a loss of traction in the rear. It's generally assumed fastest
way through a corner involves the hardest braking prior to entering
the turn. Then, do the severest turning when you first enter the
corner later then what would require a perfect arc and with no braking
or accelerating. You would then apply modest acceleration as you
gradually straighten your wheels through the rest of the corner. The
process is called late apex cornering or squaring off the corner. In
the site below, it's applied to motorcycle racing.

https://lifeatlean.com/late-apex-advance-racing-lines/

[Catrike Rider]

As I posted elsewhere, most drivers today take a different route
through a corner..

https://www.apexdyna.nl/en/the-apex-of-max-verstappen

[Catrike Rider]

I agree with Frank, here, as long as the braking is over before
starting the turn.

[Andre Jute]

Taruffi's book is brilliant and is revered by vintage car enthusiasts. But it was written in an era when good electronic calculators were still on the horizon (I fondly remember a statistical calculator of the mid-1970s that could do what million-dollar and some computer couldn't do fifteen years earlier) and part of an engineer's skill (Taruffi had been trained as an industrial engineer) was to simplify matters so that they could be calculated on a slide rule. In addition the presumption was that every effort had already been made to lower the centre of gravity to the roll axis between the axles (achieved on the Jaguar SS100), and that the tyres of the period would be skinny and have low grip (by today's standards). The upshot of the sum of these considerations was that the car would break friction rather easily and would always slide. Today's tyres are wider, of grippier compound and construction, and of course there is ABS (not permitted in all formulae), shorthanded as "anti-skid brakes" that will give a large saloon weighing 5-6000 pounds, and with its CoG raised by lush options, cornering that racing car designers of the Taruffi era never dreamed of. Also, the track of a modern racing car is getting on for twice that of the racing cars Taruffi knew. Taruffi started racing with solid front axles or "independent" suspensions with solid axle geometry plus other dangerous behaviours. Just fitting modern SLA independent front suspension, which makes the spring base equal to the track, and through the lever arm squared principle, when you drop the track to spring base ratio from a typical solid axle's 2.25 to 1 for the independent geometry, you're also multiplying the front roll stiffness by a factor around five, which was the case towards the end of Taruffi's racing career, when he wrote his book.

I think that today, to make a serious advance in Taruffi's rule of thumb calculation, you need many, many more inputs than four, and with the available calculating power, you could handle them in groups without too many shortcuts, assumptions or bodging constants.

Don't expect too many kudos, though. Here
https://www.audio-talk.co.uk/fiultra/KISS%20141%20by%20Andre%20Jute.htm
is a major advance in thermionic tube audio frequency response forecasting that I worked out, which was too complicated for the flame warriors (who all claimed they knew more electronics than I did, of course -- and so they did, except it was all the wrong kind of electronics!) but was nodded through without much discussion by the smartest engineers in tube hi-fi, though I noticed an increase in design commissions coming in after I published it.

***
I don't know much about the theory of two-wheel handling (which doesn't really owe that much to car handling, according to Jobst Brandt, who had a firm grip on the matter) but I found that setting up my touring bike as if it were the 7+litre Ford Galaxy that I used for fast Continental (Europe, not the US) crossings in the 1960s/70s, London to the oval at Nardo in the boot of Italy overnight, with a good deal of understeer, is both safe and pleasing: nothing upsets my bike except "training" roadies getting my way on the downhills; all other disturbances are turned harmless by lifting the bike slightly, putting in pedal power if not already coasting in the overdrive gears of my Rohloff hub gearbox, or gentling the thumb throttle on the electric motor to increase rear wheel grip to tighten the line. Going the other way, as you imply, would make for a very nervy, even dangerous bike, not a pleasure to ride, and not even faster, just permanently dangerous (I tried it and frightened myself shitless).

Andre Jute
Author of DESIGNING AND BUILDING SPECIAL CARS (published by B T Batsford, London 1985 and
Robert Bentley, Boston, 1986).
>

[John B.]

Many years I used to race "jalopies" on both 1/4 and 1/2 mile dirt
tracks. As I remember it the cornering technique was to basically
accelerate through the corners. The rear end would swing out and was
controlled by counter steering and the throttle,, but basically you
controlled the "angle of attack" with the throttle and in an ideal
turn you would complete the turn with the car lined up down the
straight with the throttle wide open.
--
Cheers,

John B.

[Catrike Rider]

On Sun, 01 Jan 2023 19:03:06 +0700, John B. <sloc...@gmail.com>
wrote:

Dirt track racing is an altogether different thing as was the go kart
racing I did back when I was a kid. The go karts had a live axle and I
learned that maintaining rear traction while turning really slowed
down the high reving engines. I could lean forward and take weight off
the back and thus keep the reves up while controlling the rear side
slippage by moving my weight forward and back. Then, to accelerate, I
leaned back and got the forward traction back. I believe the auto dirt
trackers use the throttle to do what I did with my weight.

[AMuzi]

I don't know.

What I do know is that cars, drivers, speed and courses vary.

In a Corvair piloted by me under most conditions it's brake
before and then accelerate through the turn. In a front
wheel drive on the same turn with the same pilot that would
be dangerous if not deadly.

--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971

[Andre Jute]

You should explain to the younger posters that the Corvair's handling (what happens when a car runs out of its natural roadholding) was not electronically moderated, or they might think all rear-drive cars are as safe as a modern Porsche 911. -- AJ
>

[AMuzi]

I don't know 911 handling but the 2d generation Corvairs are
IRS. Early models were not, which is how we lost Ernie Kovacs.

[Tom Kunich]

I road raced motorcycles and the name of the game then was to maintain traction at all times. I mechanic-ed on flat track motorcycles which were dirt tracks and they would slide through corners with the throttle on almost wide open for the entire oval. Bart Markel was especially good at that and he was the factory rider for Harley.

[Frank Krygowski]

On 1/1/2023 11:48 AM, AMuzi wrote:
>
> I don't know 911 handling but the 2d generation Corvairs are IRS. Early
> models were not, which is how we lost Ernie Kovacs.

First generation Corvairs did have IRS, = Independent Rear Suspension.
But it was a simpler variety, simple swing axles.

The swing axle system gave large camber change in relation to wheel
travel, and could cause the outboard rear wheel to tuck under the frame
during hard cornering. The second generation had a much improved version
of IRS.

--
- Frank Krygowski

[AMuzi]

Yes that's a better description THX.