Braking and turning in - Trail Braking

[timbo]

Yes that is true. I wonder if that is hurting some of the more prolific trail brakers

Reportedly it is.

[spacer]

What about the Pirelli's rumoured lack in coping with a combination of lateral and longitudinal grip? Would this make their traction circle more of a traction diamond? Or am I getting things wrong?

[raymondu999]

Spacer kind of along the right lines.

Having said that trail braking works with the front traction circles more. The Pirellis' reported saturation under combined loading happens more at the rear. I've never heard anyone say it of the fronts before

[machin]

But what I'm getting from this discussion here is that I should view the longitudinal and latitudinal friction forces as two separate things. Gotcha.

They are not completely separate, after all there's temperature buildup and both process heat the same tyre.

They're definitely linked; I've never seen any tyre (from road-going, semi-slick or pure slicks) which allows 100% lateral at the same time as 100% longitudinal... granted, as I said in my first post, they're rarely an actual circle... but I've never seen a pointed-corner "traction square" (but happy to be proven wrong if anyone has any contrary data?)

Frame by Frame analysis of schu shows this circle shape in action:-


Its not surprising that the last frame has a lower longitudinal G-force than the blue circle would suggest he should have -he's going slower due to the earlier braking and therefore has less downforce and hence less grip and hence less braking performance....

[strad]

I find it interesting that it does not show any accelerational G forces.

[machin]

It does... but acceleration is small compared to lateral and braking.... lateral and braking are essentially limited by the grip from 4 tyres... acceleration is limited by the engine power/car drag and the grip from 2 tyres -the result is that acceleration is low in comparison to the lateral and braking performance...

Even 0-60mph (~27m/s) in 2 seconds (a very fast time) is <1.4G...

[volarchico]

EDIT: machin's post is better

[hollus]

Don't forget EBDs, specially last year in quali. By being in the throttle as early as possible, even if you would expect to lose lateral grip from the tyres, you win downforce from the exhaust, which likely more than makes up for the lost lateral grip in the lateral acceleration sense, while still allowing you to be on the throttle.
The fastest option with an aggressive EBD might well be to shed more speed in the first part of the corner to be able to get on the throttle (EBDing) earlier.

[Tim.Wright]

Ok now I can see where I (conceptually) went wrong. I was thinking that the source of grip was the tyre, and that produced a friction force in whichever direction. But what I'm getting from this discussion here is that I should view the longitudinal and latitudinal friction forces as two separate things. Gotcha.

No you had it right at the start, the lateral and longitudinal forces are linked. If you add one, you must take away the other like you said in the first post.

The reason it works is that your peak demand for lateral and longitudinal forces occur at different times. Longitudinal force requests are peak in the braking and acceleration phases and the peak lateral forces are at the corner apex where there is no braking/accel.

The combination of the two is where the art of driving is. Theoretically you should be able to achieve practically equal accelerations in all directions, but typically there is not so much combined braking/cornering as accel/cornering because of stability reasons.

tim

[raymondu999]

I get that they're still linked; but I was thinking more along the lines of the grip being just 1 component; which can act in any direction; rather than 2 separate components which combined together in a vector fashion

[Jersey Tom]

I get that they're still linked; but I was thinking more along the lines of the grip being just 1 component; which can act in any direction; rather than 2 separate components which combined together in a vector fashion

There is no difference.

[raymondu999]

JT - let's say you had a fantasy tyre; which had a traction circle; that had a 5G radius all the way around. Ignoring tyre wear/heat/other things; say you were loading the tyre up at the 45 degree point in the circle - yes you're getting 70.7% (sin/cos 45) of maximum long' and lat' load; but surely the end result is still just 5G; in the 45 degree direction; is it not?

So my initial premise of the first post wasn't incorrect at all? You could; in essence; brake at 100% grip in a straight line; then use 100% lateral; to get the same laptime?

[Jersey Tom]

JT - let's say you had a fantasy tyre; which had a traction circle; that had a 5G radius all the way around. Ignoring tyre wear/heat/other things; say you were loading the tyre up at the 45 degree point in the circle - yes you're getting 70.7% (sin/cos 45) of maximum long' and lat' load; but surely the end result is still just 5G; in the 45 degree direction; is it not?

Correct.

So my initial premise of the first post wasn't incorrect at all? You could; in essence; brake at 100% grip in a straight line; then use 100% lateral

I suppose you could attempt such a maneuver, but nobody drives like that. That would entail instantly going from max braking to nothing while immediately doing a "step steer" input with the steering wheel and trying to immediately go from straight ahead to maximum. Would be extremely abrupt and violent, maybe even spin the car out depending on what you're driving.

In either way you're trying to use 100% of the car's capacity, but by trailbraking you can smoothly enter and exit the corner on the arc of the driving line. Going from 100% brake to 100% cornering would result in a different driving line and would be quite difficult to manage, probably quite slow as well.

[timbo]

Going from 100% brake to 100% cornering would result in a different driving line and would be quite difficult to manage, probably quite slow as well.

Yeah, also remember that steering is braking. You'd have to step on the gas to compensate.

[raymondu999]

In either way you're trying to use 100% of the car's capacity, but by trailbraking you can smoothly enter and exit the corner on the arc of the driving line. Going from 100% brake to 100% cornering would result in a different driving line and would be quite difficult to manage, probably quite slow as well.

Yep I know - my question was purely hypothetical. But as I said above though; in 2009; Jenson used to do a mix between the two. He used to brake (probably at what he felt was 100%) then trail brake while he was turning the steering wheel; and once he had the correct amount of steering lock (as he likes to stay with a single steering angle through the whole corner) he would just stay at constant speed; and obviously applying the appropriate amount of throttle too.