Max Rate of Deceleration (units g/sec)

[Larry H]

Does anyone know what the maximum rate of deceleration is for a Formula Ford on Hoosier VFF and/or Toyos?

[stonebridge20]

It depends on the density of the object that you hit.

[TimH]

Ok, here's a partial answer. Bear with me for the length.

When I ran the Crossle' on Toyos a few years back at COTA, I noticed that faster drivers in equivalent cars on Hoosiers were braking at least 50 feet sooner than I was at the end of the back straight, about as pure a flat threshold braking zone as I know. Maybe they weren't using all their braking ability, but I doubt it. They had better corner speeds, no doubt a combination of superior grip and driver skill. So much for comparisons.

Running a math channel on my wheel speed data I get a noisy trace with negative g peaking around 1.2-1.3 in that zone (compared to about the same lateral g in multiple corners). Interestingly, I got consistently better braking at turns 1 (of course, it's uphill) and 11 (I think I recall a slight hump before it dips) with many peaks near negative of 2.0 just before lockup.

Take all that as you will.

[jrh3]

Ok, here's a partial answer. Bear with me for the length.

When I ran the Crossle' on Toyos a few years back at COTA, I noticed that faster drivers in equivalent cars on Hoosiers were braking at least 50 feet sooner than I was at the end of the back straight, about as pure a flat threshold braking zone as I know. Maybe they weren't using all their braking ability, but I doubt it. They had better corner speeds, no doubt a combination of superior grip and driver skill. So much for comparisons.

Running a math channel on my tire speed data I see negative g peaking around 1.2-1.3 in that zone (compared to about the same lateral g in multiple corners). Interestingly, I got consistently better braking at turns 1 (of course, it's uphill) and 11 (I think I recall a slight hump before it dips) with many peaks near negative of 2.0 just before lockup.

Take all that as you will.

Low powered, inertia racing. I bet their right foot was flat on the floor 50+ ft sooner.

[TimH]

Low powered, inertia racing. I bet their right foot was flat on the floor 50+ ft sooner.

Very possible but more likely is that I was over-slowing, so it didn't matter how soon I got to full throttle (often by the apex). They still should have been able to use maximum braking early in the zone but mine was noticeably better there. And their minimum speed was much higher in the esses.

[halcyon]

What question are you ultimately trying to answer?

The answer will be differ based on car (suspension setup, coefficient of drag, etc), weather conditions, track surface (coefficient of friction, elevation change in braking zone), whether you are talking about initial straight line braking vs average rate including trail braking, and many other factors.

[Larry H]

What question are you ultimately trying to answer?

The answer will be differ based on car (suspension setup, coefficient of drag, etc), weather conditions, track surface (coefficient of friction, elevation change in braking zone), whether you are talking about initial straight line braking vs average rate including trail braking, and many other factors.

Condition are straight line braking under good conditions in an FF with treaded tires. No trail braking.

I do know that using the AiM data, the maximum GPS lateral and longitudinal is roughly 1.8 and 1.4 g's respectively for a FF w/ Toyos. At this stage whether its Toyos or Hoosier is not significant. What I'm looking is the maximum slope of the braking acceleration trace to see if I'm in-the-ballpark. At best I see is 1g/sec.

[DaveW]

Condition are straight line braking under good conditions in an FF with treaded tires. No trail braking.

I do know that using the AiM data, the maximum GPS lateral and longitudinal is roughly 1.8 and 1.4 g's respectively for a FF w/ Toyos. At this stage whether its Toyos or Hoosier is not significant. What I'm looking is the maximum slope of the braking acceleration trace to see if I'm in-the-ballpark. At best I see is 1g/sec.

Are you locking (or close to locking) brakes, or are you pad friction (or fluid-pressure) limited? You need to be close to locking on all 4 corners to maximize the tires' potential.

[Larry H]

Are you locking (or close to locking) brakes at all 4 corners, or are you pad friction (or fluid-pressure) limited?

I think I know where the braking threshold is as I've locked the brakes a few times but what I don't from a data perspective is how quickly can I get there.

I did find some other data by a better driver and found rate of braking deceleration to be around 4 g/sec and maybe 5 g/sec. I looked around a bit more and found a best case for me at 3 g/sec. I think the most likely place where this can happen is at the end of straight leading into a slow hairpin type turn.

[TimH]

I see. "Rate of Deceleration." So you're looking at how quickly you can slam on the brakes rather than maximum deceleration. That would take a pretty sensitive right foot to know when to start modulating. It should also be nearly independent of car or tire as long as your hydraulics are reasonably responsive.

[DaveW]

What pads are you using? If the pads don't get to maximum coefficient of friction (too temperature sensitive) until later in the braking zone, that may be your issue. The Carbotech XP20's I use have a high CF and get there almost instantaneously.

[Larry H]

What pads are you using? If the pads don't get to maximum coefficient of friction (too temperature sensitive) until later in the braking zone, that may be your issue. The Carbotech XP20's I use have a high CF and get there almost instantaneously.

Dave, Hmm, never thought it could be a car problem but can't discount it but I think it's a driver problem. Maybe I'm not pressing the brake pedal quick enough.

I was looking at acceleration traces for braking g's and noticed that there was a significant slope to max braking g's. The time to max g's could be as high as 3/4 of a second, which surprised me. The slope is very noticeable when zoomed in. I created a math channel for g-rate (the derivative of g's wrt time) and see some significant differences in g-rate between a better driver and I.

Larry

[DaveW]

I think you'd be surprised how many times a "driver problem" is solved by fixing a car problem.

I've been driving racecars since 1968 and just about every time I thought it was me screwing up it turned out that when I fixed a car issue my problem went away.