noturavgm

Yeah. At one point I was feabily giving chase to a BMWCCA IP class M3 in my not-a-racecar M3 at Lime Rock this spring and actually saw the brake lights flicker off during his 5-4 downshift into Big Bend two laps in a row. I found that surprising.

2BWise

I'd be interested in the data as well. Is the loss in decel caused by the driver coming off the brake as the blip occurs (loss in brake pressure), or is the blip too big and what was drag torque becoming drive torque (- torque to +torque). Plus, how does this compare to what is seen with top pros.

KaiB

Peter may want to answer about the top guys as I still shut my eyes at the scary spots, but mine is caused by an ever so slight release of the brake pedal during the H/T operation - as opposed to constant even pressure when not selecting a lower gear.

ProCoach

Backed up by brake pressure observations that parallel the loss of Long G (decel g), as well as additional cameras trained on the feet of the drivers doing the blipping, it's the "see-saw" effect of the foot COMING OFF the brake pedal when rolling to the right blipping.

Not ALL the way off (like you're Big Bend guy, boo!), but lessening...

The torque change measure could be seen, but without a driveshaft strain gauge, not accurately.

I'm very sold on the inadvertent brake pressure release, partially because it's SO drilled into drivers heads to blip, instead of STAYING steady on the brake, and blip as a secondary priority.

2BWise

That was what I figured. To provide a point of reference to the other scenario I have seen the torque reversal cause decel inconsistencies on vehicles with ABS. Usually, as the clutch is released a temporary increase in drive torque will cause the ABS controller to increase rear brake pressure, but once that torque disappears it immediately drives the rear wheels into slip and then a corresponding reduction in rear brake pressure. That reduction usually causes a dip in the decel trace. It is also possible for it to happen the inverse if the blip doesn't get the revs high enough.

mark kibort

again, it might be a little oversight , but Mikes 1st is almost identical to my first, if you didnt notice. Its not only the gear ratio, but the speed at which you shift out of the gear for which you make the selection. the engine and transmission are a matched pair. so, we both shift out of 1st at near 50mph, regardless of the gear ratio. (im at 6600, he is at near 8,000rpm). the point is, most all vets have this same redline speed in 1st, and are used occasionally for the same purpose. to max hp if you need it. i use 2nd most of the time at turn 11 as you can see, and so does most everyone. 1st , if you need it. and all use 2nd down the corkscrew and turn 11, which are near the same speeds. Some novices will use 3rd down the corkscrew, but most use 2nd.

yes, that car is going a heck of a lot faster down the straight, but in that turn, not a whole lot faster. Everyone puts around turn 11 within a few miles per hour of each other and its basically a drag race out of it.

and by the way, they dont have infinite gear slection in WC. As you can see, he is stuck with near the stock ratios, and runs only 1st through 5th gear, never touching 6th gear. (im assuming it is a 6 speed sequential, if not, its probably the 5 speed sequential, and you are right)
if you go back to when i ran a few WCGT races, the vets had the stock transmissions, and they used 1st on rare occasions too., but certainly 2nd for the turns I mention at laguna. I remember being able to hang in the braking zones and turns with my old bucket, only to get blown out in the straights.

I do remember Mike skeen.. Didint he roll that pontiac on the TV show "set up" and made the comeback to win the show.
he hasn't been racing that long. But, he is doing a fantastic job and getting a TON of experience now driving most everything. Living the dream...

mark kibort

Peter knows better, but I understand his point. But, the quote was that no one uses 1st gear at any track in NA, but i can show not only in the purpose built race car (and by the way, Skeens car's ratio is close to a stock 1st gear, by the way) and many of us racers in the west use 2nd at a lot more than just turn 11 at laguna. He said, only 3 turns in NA, and i can show 3 at just laguna, and 3 at Sears Point.

mark kibort

Ill defer to you opinion here, as i believe your right,constant braking pressure is important for optimizing decel.... but, you know how many drivelines have been lost for not matching the gears to the appropriate RPM. a clutch release when the RPM is not matched can make your constant braking pressure, effectively go haywire, with a rear tire lock, and possibly a broken main driveshaft, that would then see forces much higher than the engine can possibly produce under decel. I think you , of all folks here, know why.

getting back on the sub topic here..... all this talk was from an analogy of a braking and shifting problem, a BMW had going from 4th to 3rd over a hump. he had a grind at the hump, always, but when he shifted before or afterwards, it went away....... I started to mention better RPM matching to lessen burden on sychros that might be the cause, and then the discussion went sideways

I still think my good luck with the gear box synchros (life) has been due to what ive explained here. the dirveshaft is spun up with residual friction from the clutch upon pushing the gears through neutral. basically, its a very very fast double clutch effect, that most racers do, with probably not even knowing it.

ProCoach

Interesting theory.

The most modern cars not only have four wheel speed channels, but also four brake pressures supplied through the CAN.

With the aid of a $700 AiM Solo DL, on a car with those eight channels supplied, you could perhaps correlate those measures, which might affirm your idea. Or not.

Usually, moderations in brake pressure propagated by ABS actuation occur SO fast (and at such a high frequency) that they can't be seen in the end result measure, Long G versus Distance trace. Motorsports ABS is even quicker, better.

Good discussion...

mark kibort

Peter,
WCGT has the Holinger 6 speed gear box.

ratios are fixed for the most part, not "infinite" as you say.

and the gear ratios are very close to stock, which are close to mine (based on MPH in each gear, but I only have 4 usable gears, while the vet has 5 out of 6 for even the fastest tracks.
FROM THE VTS WCGT SHEETS:
The Holinger RD6 TC, or the Xtrac 399, sequential gearbox may be used with the following ratios:
Holinger RD6: 1st – 2.296, 2nd – 1.593, 3rd – 1.230, 4th – 1.000, 5th – 0.843, 6th – 0.745
Xtrac 399 (One final drive, an 11:36, and two sets of gear ratios will be used to come within 1% of VTS
specified ratios due to the difficulty in changing out the final drive.)
Xtrac ratio set #1: 1st – 13:36, 2nd – 16:31, 3rd – 19:28, 4th – 21:25, 5th – 26:27, 6th – 25:23
Xtrac ratio set #2: 1st – 13:38, 2nd – 16:33, 3rd – 18.28, 4th – 22:28, 5th – 21:23, 6th – 23:22
A no-lift shift system may be added with the Holinger or Xtrac gearbox.
Teams using the Tremec close ratio gearbox, the stock M6, or the stock

ProCoach

From the Holinger RD6SS brochure: "All gears are removable from shafts with an
extensive range of ratios available"

Done talking, Mark. Hope your car gets fixed so you can trust the brakes.

mark kibort

yes, the transmission gears are removable, but not in world challenge. they are locked down pretty tight. I thought we were talking about skeens car. either way, 1st gears are used in street racers at laguna's turn 11 sometimes, and 2nd 3 other places and should be.

Thanks for the well wishes....

I think i have enough to go on.

Mark

Matt Romanowski

I don't think it's where 2BWise works, but I know at least one manufacturer uses the Solo DL in evaluating their high performance production cars. It was very interesting to hear how they mixed subjective feel with the objective numbers from the DL.

ProCoach

Interesting. Great endorsement!

Most of the OEM Proving Grounds (as well as many of the US OEM tire manufacturers) use this stuff: http://www.velocitybox.co.uk/index.php/en/products-main

It starts at about $100K per car for the basics...

2BWise

Yes, all 4 wheel speeds are available, but actual pressures are not. If pressure is available on CAN it is a modeled value, that may or may not be accurate.

I agree that the ABS control is quick. 200hz quick, but the limiting factor is the orifice sizing in the valve unit. While the valves might be able to react quick enough the pressure does not and you can see varations in deceleration during that time. One of the other big factors is that the wheel and drive line inertia will affect the response time. What you'd be looking for is a small reduction in deceleration, 20% or less. Generally, as a driver, you won't notice the increase in brake distance as it'll be in the range of a dozen feet, which I would suspect is less than the resolution of most driver's perception in the braking zone (I'm assuming most can perceive a marker change in the 25 ft range based on placement at most tracks).

I'm fortunate enough to use equipment that cost 100x more than that, and it is noticeable in the data traces, but often time the driver does not perceive it. Usually the perception is that there was unusual pedal activity that correlates with a mismatch in drive torque to decel torque, and that the entry speed was a bit higher than desired despite the same brake marker.