## Will some future tire technology bring back drifting?

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This might help people confused about slip angles and contact patch deflection. From a high level (macroscopic) view of tires, there's two features that are important here: the effective contact patch friction and the carcass/structural stiffness of the tire. While we argue about sliding versus drifting semantics, we should realize that it's possible to create a tire that can exploit sliding around or operating at high slip angles. I like to work in extremes so I'll imagine a tire (just a single tire, no vehicle/suspension) with infinite contact patch friction (we're ignoring all the complex mechanisms that create this friction). Obviously this contact patch will always be in a state of static friction and will never slide. This doesn't mean the tire can produce 'grip' yet. Its structural stiffness will determine how the tire deflects/distorts under the presence of friction forces from the contact patch, and therefore it determines the slip angle that the tire will operate at. If the structural stiffness is zero then there is no grip, the tire will deflect forever and it will not change its overall velocity even though its heading (direction of the wheel plane) is changing resulting in a 'slip angle'. If the structural stiffness is infinite (and we still have infinite patch friction) then there will be no deflection/distortion and a slip angle of zero: the tire velocity matches its heading exactly wherever it points. Similarly, if we have zero contact patch friction then the tire will slide with no deflection (no friction means no deflection/distortion regardless of structural stiffness). There is still a slip angle, according to the definition, since tire velocity will not follow its heading, but there is no grip. On a real tire, these are heavily coupled as high structural stiffness increases the shear stress at the contact patch and reduces patch friction (less static, more sliding). Obviously, a real tire has numerous compromises made, but you get the idea. The concept of a 'cornering stiffness' lumps these two effects together.

Older F1 tires certainly didn't have the levels of contact patch friction we see today: 50 years of chemical and material evolution will do that. Structural stiffness was way lower as well, as there have been significant advances in overall stiffness without harming friction or durability (or any of the other important factors a tire must deal with). So I think it's probably both effects that cause the large yaw and side-slip angles we saw in older racecars, and I also think it's probably pretty tough to the the effects apart from looking at a picture.
GSpeedR
24

Joined: 14 Jul 2011

0
conceptual 'thought experiment'

a railway train has no slip, slide, drift or whatever (because of the flange)

if you replace the train with a 1950s F1 car (but keep the rail wheels flange and suitably fix it to the tyre laterally) the tyre should (as when driving) be distorted according to the cornering force developed
so would have to be angled inward to follow the required line, by (most of) the manufacturers 'slip angle'

the car would (apparently) be (4 wheel) drifting, but there is no slip, slide, or anything but 'apparent' (ie false) slip/drift
so most of the 'slip angle' is caused by tyre distortion (and shouldn't be called 'slip' angle !)

for a 70s tyre the 'false' ie distortion-related apparerent drift would be much less
(more of the apparent drift should in this case be credited to the driver)
Tommy Cookers
98

Joined: 17 Feb 2012

0
Tommy Cookers wrote:conceptual 'thought experiment'

a railway train has no slip, slide, drift or whatever (because of the flange)

Trains have conical wheels (i.e. at the inside the wheel has a larger diameter that at the outside). Also the distance between the flanges on one axis is smaller than the gauge. So in a corner the train slides outwards, making the outer wheel effectively larger than the inner one.

I'm not sure if that affects your thought experiment.
16

Joined: 25 Jul 2012

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I agree that 'slip angle' is a bit of a misnomer and doesn't necessarily indicate that a tire is slipping or distorting, but it is significantly easier to measure slip angle than actual tire deflection. The concept of slip angle seems to describe a lot of things with a convenient parameter.
GSpeedR
24

Joined: 14 Jul 2011

1
It appears that there’s agreement that tail-hung-out racing is unlikely in F-1. It’s just faster to be tidy. Yet on dirt tracks sprint and late models as well as rallies they’re running full opposite lock and driving with the throttle. Would they be faster if they cleaned up their act? Is F-1 racing of years past analogous?
olefud
59

Joined: 12 Mar 2011
Location: Boulder, Colorado USA

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Two concepts

1950s = cross ply

Modern tyres don't allow for 4 wheel drifts as the "normal" way of going around a corner. No slide/drift is the fast way around a corner. Sliding/drifting is slow so, no, we won't see it again in F1.
Just_a_fan
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Joined: 31 Jan 2010

0
As tires become grippier they tend to developing peak grip at lower slip angles. Don't know if this can be explained with theory, but it's consistent with a large amount of test experience. When peak grip occurs at lower slip anges the tires inevitably become easier to drive. This means, somewat unintitively, that quicker tires are easier to drive quickly. I think the difficulty of rain driving is partially explained by wet peak-grip slip angles being larger, or at least larger relative to the grip.

Yes to increasing the slip angles to differentiate the drivers more. Also to make it more interesting for us fans to watch, it would be easier to see and feel what the car is doing. I actually enjoy some Nascar racing, including road courses, because of the larger slip angles.
bill shoe
18

Joined: 19 Nov 2008
Location: Dallas, Texas, USA

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olefud wrote:It appears that there’s agreement that tail-hung-out racing is unlikely in F-1. It’s just faster to be tidy. Yet on dirt tracks sprint and late models as well as rallies they’re running full opposite lock and driving with the throttle. Would they be faster if they cleaned up their act? Is F-1 racing of years past analogous?

Don't think they would be faster like that, no. Completely different animals. For one, there are race series in which there is an aero advantage to running at large yaw angles, whereas I would venture a guess that a F1 aero map of late would generally be poorer with large yaw.

Rally is itself an interesting beast, and RC vehicle dynamics is something I've wanted to dabble in for a while. To wager a big guess I'd stab at saying there are probably advantages to operating at high sideslip angle in certain situations there as well, though not for aero and perhaps more to do with thrust vectoring.

Just_a_fan wrote:Two concepts

1950s = cross ply

Ehhh I wouldn't go that far. Belted vs not belted though, sure.

bill shoe wrote:As tires become grippier they tend to developing peak grip at lower slip angles.

Not necessarily true. Though "grippier" is a big vague of a term, and "grip" is one of my least favorite words in general.

Don't know if this can be explained with theory

It's not so much theory that explains it as design intent.
Grip is a four letter word.

2 is the new #1.
Jersey Tom
127

Joined: 29 May 2006
Location: Huntersville, NC

2
Cars on dirt tracks have no chance of maintaining near-static friction when they go fast around the corners. They will always be in a kinetic friction regime. A high slip angle means the spinning drive tires push the car into the center of the turn so you can go around the turn faster. Again, this wouldn't work with typical pavement and tires in the near-static friction regime because the radial drive force of the spinning tires would take you into the lower-grip kinetic regime, but when a dirt surface already forces you into kinetic friction you might as well optimize that situation by using the drive force to directly accelerate toward the turn center. In theory the optimum slip angle would be a full 90 degrees, but then you would lose forward drive around the turn. You have to drive some angle less than 90 so you have a tangent component that keeps you going through the corner.

This is also true on snow, gravel, or situations like really hard kart tires on polished concrete. Any situation where fast driving puts you into constant kinetic friction.
bill shoe
18

Joined: 19 Nov 2008
Location: Dallas, Texas, USA

0
bill shoe wrote:Cars on dirt tracks have no chance of maintaining near-static friction when they go fast around the corners. They will always be in a kinetic friction regime. A high slip angle means the spinning drive tires push the car into the center of the turn so you can go around the turn faster. Again, this wouldn't work with typical pavement and tires in the near-static friction regime because the radial drive force of the spinning tires would take you into the lower-grip kinetic regime, but when a dirt surface already forces you into kinetic friction you might as well optimize that situation by using the drive force to directly accelerate toward the turn center. In theory the optimum slip angle would be a full 90 degrees, but then you would lose forward drive around the turn. You have to drive some angle less than 90 so you have a tangent component that keeps you going through the corner.

This is also true on snow, gravel, or situations like really hard kart tires on polished concrete. Any situation where fast driving puts you into constant kinetic friction.

This, with JT’s thrust vectoring appears to cover it well. Also, on dirt there also is often a dirt kerf –marbles working for you rather than against you- that provides a bit of added turning thrust.

With the tires, brakes and driving styles of old, F-1 drivers were dealing with low friction tires (rather than grip), throwing the car into a turn to scrub off speed and, for the most part, a fast-into-the-corner-rather-than-out attitude. It was much closer to today’s dirt track racing. Those days are long gone.
olefud
59

Joined: 12 Mar 2011
Location: Boulder, Colorado USA

0
race car designers were trying to un-invent this by the mid 30s, to get the both ends contributing to cornering (4 wheel drift)

postwar ie F1 cars were designed for such (balanced) cornering (eg Ascari won every GP for 2 years this way)
(this was/is harder to drive, (older) drivers didn't like it)

the slightly oversteery car is much easier (than the slightly understeery) to get into a drift early, and more saveable
(important, and why the Maserati 250F and Cooper were liked etc)
steady state cornering was much bigger on circuits then, drifting started early in the (longer) corners
starting the drift before the apex was crucial, oversteer helped this, understeer hindered/prevented this

so F1 was not full of opposite-locking, people just remember it that way because of the big angles (like Historic today)
the non-oversteery cars (were designed to) put more power down at low/medium speeds (like today)
Lotus etc etc won lots of races and made the same (big) angles 12-15 deg generally without opposite lock ( 5"-6" tyres )
Tommy Cookers
98

Joined: 17 Feb 2012

1
I'd like to see photos of what people are envisioning when they talk of vintage cars in a neutral or 4-wheel drift or whatever.

Stuff like this...

...and this...

...are pretty clearly two wheel (rear) sliding around. Looks cool, but generally not fast. Particularly if you have to do some rapid directional change (like a chicane)
Grip is a four letter word.

2 is the new #1.
Jersey Tom
127

Joined: 29 May 2006
Location: Huntersville, NC

0
these are the fun moments that make good pictures, so get published (granted the Maserati was that way as I said before)

'The Racing Driver' by Dennis Jenkinson c1960 has many head-on shots showing understeering, neutral and oversteering drifts in the same place, also some in the Piero Taruffi book (the DJ book has tyre data with 18deg angles I think)
any 50s and skinny-tyre 60s footage will show it all ways

the neutral/slight understeer drift is easy to do, at 90% cornering power up and the front gets lighter and develops a greater slip angle, the back develops a greater slip angle because of the increased tractive force vector, don't move the wheel
I wouldn't want to try it in an oversteery car

why wouldn't the designer want both ends of the car developing high cornering forces ?

PM if you want to ?
Tommy Cookers
98

Joined: 17 Feb 2012

0
Tommy Cookers wrote:why wouldn't the designer want both ends of the car developing high cornering forces ?

The designer of what? Car? Or tire? In either case the intent is to create high cornering forces at both ends of the vehicle, by some balanced metric.
Grip is a four letter word.

2 is the new #1.
Jersey Tom
127

Joined: 29 May 2006
Location: Huntersville, NC

0
I had in mind the car design

(Fangio was using Pirellis, still with a structure of natural fibre ?)
the tyre's job was to be black and round and to keep the tread on

Lotus 18 (F1, F2 and F Junior) won lots of races cornering with the inner front wheel off the ground, designed for understeer

regarding distortion's contribution to drift and /or slip, my experience was with modern (road) tyres 185/55
increased tyre pressures certainly reduced drift/slip (by reducing distortion)
Tommy Cookers
98

Joined: 17 Feb 2012

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