Racing Brake Pad / Brake system discussion/questions
#376
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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.
#377
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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.
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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.
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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.
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.
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#380
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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.
#381
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Mark, Mike's WC GT car uses a purpose-built, infinitely variable ratios available, sequential shift, non-synchro racing gearbox.
His first is between your first and second, closer to your second (in case you hadn't noticed, he is going a LOT faster...), so as proper RACING transmission gear selection indicates, he is able to use the lowest gear for the slowest corner and select the highest ratio allowing full use of the engine rev range (plus a tiny margin for the draft) at the vMax on the longest straight.
You and other folks that use street car gearboxes don't have that luxury. You're stuck with what you have. If you get baulked by slower traffic, by all means, use first gear, but detailed analysis will show that is not normally the best way to achieve optimal laps with street car ratios.
I was Mike Skeen's first CI and you, sir, are NO Mike Skeen!![Big Grin](https://rennlist.com/forums/images/smilies/biggrin.gif)
His first is between your first and second, closer to your second (in case you hadn't noticed, he is going a LOT faster...), so as proper RACING transmission gear selection indicates, he is able to use the lowest gear for the slowest corner and select the highest ratio allowing full use of the engine rev range (plus a tiny margin for the draft) at the vMax on the longest straight.
You and other folks that use street car gearboxes don't have that luxury. You're stuck with what you have. If you get baulked by slower traffic, by all means, use first gear, but detailed analysis will show that is not normally the best way to achieve optimal laps with street car ratios.
I was Mike Skeen's first CI and you, sir, are NO Mike Skeen!
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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.
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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...
Last edited by mark kibort; 07-29-2014 at 01:39 PM.
#382
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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.
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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.
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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.
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.
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...
#385
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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
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
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extensive range of ratios available"
Done talking, Mark. Hope your car gets fixed so you can trust the brakes.
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#387
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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
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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...
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...
#389
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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...
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...
#390
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Interesting theory.
The most modern cars not only have four wheel speed channels, but also four brake pressures supplied through the CAN.
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...
The most modern cars not only have four wheel speed channels, but also four brake pressures supplied through the CAN.
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...
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).
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.