mark kibort

if done right, its a real fast way to run up on a H pattern shifter that is going through 2-3 downshifts unnessarily. (you need to do this with sequential gear boxes, but not H boxes patterns) the shifting is done after a trailbrake, if it is done right , you run can brake later and threashold brake better, as the braking forces is more consistant and easier to feel. dont take my word for it, im running almost 2 seconds faster than Andersons Speedvision times at Sears Point (Infinion Raceway) now, with 100less hp. (and the same time as his 1999 appearance at Laguna seca) when i dont do it, im 1-2 seconds slower a lap. trail braking does two things, it allows you to use the brakes later and go into a turn hotter, while the beginning of the turn in earlier bleeds off speed too, compared to a traditional late apex approach. the faster approach also allows for less steering input, better attitude of the car through the turn, slightly slower speed through the turn but a faster exit speed.
many Nascar drivers are doing this on road courses now. they are also finding more consistant braking in gear and changing gears later and faster and at the right time as to not upset the car. Yes, mistakes can be costly as far as time.

its more of a feel and hard to describe, but if you spending time double clutching, you are wasting valuable time.

Mk

Benton

Mark,
Sorry man, I have to disagree. First off, your blipping does not speed up the shafts... you are still using the synchros (If I am understanding you correctly, you are saying this). Secondly, double clutching wastes no time at all (edit: if done quickly and correctly); it is done under braking. It does not interfere with trail braking at all. Trail braking is completely redundant in the double clutch argument (although you argument about trail braking is very correct). Most cars do not need to be double-clutched, but I do it on my 928 just so I won't have to rebuild the tranny anytime soon (it already has 120k). Pros don't double clutch because it is wasted movement and something else to focus on. If they had to, they would and could. I bet that any pro could take their car out, double clutch downshifts, and turn the same times within a 10th of a second. Watch a GT3 cup video and see how fast they shift. They rebuild the gearboxes very often. Just as a reference point, braking 10-20 feet later doesn't save much time... corner entry speed is what is important.

I understand your times are fast, but they are not the ultimate time. I believe that if you could master the standard way of downshifting (which is the way most pros do it), you could probably shave a bit more time since you are currently shifting after turn in. Just IMO. If you can prove me wrong and highlight pros that utilize your technique, then please do... I'll admit I'm wrong.

mark kibort

I understand the layshaft theory. sounds right, but i still wonder if there is any real wear to the change of inertial of that part of the transmission vs the big inertial mass! (ie, the car!) I also agree that a pro could double pump his clutch with the leg that is only doing that too, and just time the gear shift level to do it. dont know if it really helps, as i have been racing traditionally for a while now, and the only gear box that failed was the old 84 style. the 86 and 87s are pretty tough.

One of the things i saw in world challenge is with the guys that were not in the top 10, i seemed to run up on them on the heavy braking zones. I even got a mention on TV about the porsche brakes, when Derrek bell pulled around me, and i ran up on his bumper around turn 11 at laguna, only to be blasted by his hp on the exit down the straight!

Im not loosing any time in this area. in fact, like i said, a few of the nascar guys are doing this as well. its not much different, other than not running throught the gear boxes on approachs to turns. my shifts are smooth, engine revs are matched, and car is never upset.

I think you can see this at 928motorsports.com in the video link area. go to the laguna seca speedWC GT race clip. its a good example lap of this.

http://www.electricsupercharger.com/...stang_pass.mpg

let me know what you think

mk

mark kibort

actually, was just reading a study from data aquisition systems that verified this technique of a later turn in. the old " slow in, fast out" is now a little dated as not they are proving that the faster in, slightly slower through and faster out was resulting in faster lap times.

Ill see if i can find the article. it was pretty telling. There were some trade offs, but overall the faster lap times are what we want. by the way, if you brake 20 feet later, im going to fly right buy on the inside! happens to me with the lighter bmws all the time. ive found ways to even later brake and that seems to be keeping them at bay and turning some faster laps too.

that term "pro" is often over used. At Grand Am cup, the class of car is basically like my 928 prep. only headers and ecu changes for most cars allowed 3000lbs, and DOT tires. the best drivers in the world. BMW M3s, porsche 996s, with the ecu box change to pump the HP up, firebirds, the new 400hp crate engine mustang, etc. top drivers in the world. (ie Auberlin, Said, Marks, Cronin, Hainer, Sofronas, Law, and many more) the BEST time at laguna was 1:39, the top 10 time out of 40 cars was 1:40.xx, a time i do with my 20 year old 928!!! no mods, just headers and some holes in my air box!
In watching the guys (pros) that were not as familar with Laguna, they were tapping the brakes out of turn 9 (corkscrew area) wher anyone that knows the track well, doesnt do. there are lots of "pros" out there, heck, I have a pro license and have 7 professional pro starts, but im not one of best drivers in the world, but i think i do somethings well, and if i had a car that was tuned by "pros" it should make me faster right? (ie wheel work alignment 4 years ago, ride hight adjusted once or twice , shocks at full max, swaybar at full max, used tires, etc) heck, all of those variables added up by general concensus time values, there is 5 seconds a lap to be found!!!! I lost 2-3 when my used tire luck wore out last year including RAmerica and part of this year.

Mk

Dennis K

This discussion is too civil. Let's step it up.

GO FRY ROCKS!!!1!!11!

Just kidding, Mark. Can you tell I just finished reading the supercharger thread?

The guys above have already given the theoretical reasons why to double clutch. I do it mainly because I can. When it's done right, it feels great.

I don't feel like I'm losing a ton of time on the brakes, but I'm not a demon late-braker. The white "PORSCHE" lettering on my Big Reds is still fairly white after 60+ track days. On most heavily tracked cars, the lettering turns to a tan or the Big Reds start looking like Big Browns.

I suppose if I go racing and find myself getting killed in the braking zones, I'll switch. But for now, nothing beats the sound and feel of a properly executed heel-toe-double-clutch-4-3-2 downshift.

I've watched your videos and seen your technique. It is definitely interesting to see the shifts so late after turn-in. I don't get how you're able to control the rear sliding without the gears being engaged and therefore not able to use the throttle to stop the slide. When I trailbrake, the car rotates and I use the throttle to transfer weight back to the rears to catch the slide. I mean the millisecond I'm off the brakes, I'm back on the throttle.

goliver

Cool Video. I had the thing running again and again while working just to hear that glorious sound of your exhaust. Man that thing sounds sweet.

mark kibort

no doubt you will be even faster and will also start cooking the brakes!! my pads go from orange to black in the first session! calipers are black , so who knows, but im crumbling pads (pagid oranges ) in 4 practices and 2 races.

back to the shift, if you notice, im never shifting when there is loading on the car, its right before the turn starts. so, i use the throttle as you say, for keeping the car balanced and near the edge through the turn. its a shift, just after the trail brake and just before the actual turn in where you wouldnt be on the throttle anyway.

Mk

Benton

I agree with all of that. If you aren't trail braking, you aren't fast. SIFO is a good technique to teach newbies.

I don't doubt that you have great car control; I can tell you are a good driver from watching your videos. It's pretty impressive how you correct slides with one hand on the steering wheel (I'm not too good at the one-handed corrections). Just IMO, I think you could even shave a few more tenths if you didn't have a stagnant period where you are shifting gears (even if it is nearly nonexistent).

Edit: Also, I was just using the late braking as a reference for lap times. No doubt, braking later is a key in racing (but not too late--then you understeer on entry and spend the mid-corner shaving off speed) to prevent being passed.

Dennis K

I just watched some laps of yours at Laguna on CD . . . One question: are you heel-toeing?

If you are then I understand what you're doing. You're threshold braking then trailbraking and downshifting during the ending of the traibrake, then getting back on the throttle. The shift happens late at the very end of your braking. You're doing the shift later after max decel, not during like me.

If you're not heel-toeing, well then I'm really confused. It would mean you're completely off throttle and off brake while you downshift. You'd have to do the blip with clutch in so there's no torque (braking or accelerating) being delivered to the wheels. That would seem uncontrollable if the rear is sliding/rotating from trailbraking! Or you let it slide then catch it after the downshift? Or just try not to get it sliding that much?

mark kibort

ive done it both ways, and some turns it pays to not heal toe, depending on the turn 11, seems to be quicker heal toeing, but the times i havent, produced my fastest times. (like that video clip. i remember that lap and i just wanted to get on the inside of Hollfelder in the mustang, but not go crashing into Mike Davis in the saleen. it actually worked out well and after Davis got out of shape to the right of the screen, there was a neutral point where i did a quick blip and actually used 1st gear from 5 to 6600rpm.

actually, i brake and start a trail braking and as the car is slowing i do a quick release of the brake, blip, shift, a little more brake if nessesary and throttle steer out and out of the turn. works very well for the corkscrew, as there is a weightless period just before the plunge where there is no need for throttle or brake, and i grab 2nd if im in a heated battle or hot lap. turn 5, and turn 2 hairpin, same thing. 11 is the only real place where i heal toe for the reasons you mentioned. turn 5 is a very late brake and trailbrake turn in. release, a quck stab of the gas, match the gear and slowly on the gas to the limit of the rear tires . at Thunderhill this works great for the "hill" and turn 9 on the back side, as well as 10. However, the second to the last turn off the straight, heal toe works best as you are coming down from 120mph to 2nd gear, and its a big trail brake turn.

To bad we cant get a $10k motec, and then have a top pro drive our cars to see where else we can gain time and plot out the differences. One of the BMWs i go against, david smith, had Johannis Van Overbeek drive his car at sears. after some review of the times and setting changes, he got his car down to 1:48.5, by the end of the day while Van Overbeek was in the 1:47.5 range. ( i was at the 1:50 flat range in my car with no tuning and similar HP to weight, but heavier by 200lbs. so i think a lot of some of the club guys are driving pretty well, but there is always a second or so when you think you have it all together. I dont know how much time your double clutching is costing you , but i bet you loose it in your first race!! we have very similar cars. (i almost bought your car if it had not been for the Holbert car being available) its got a little more hp than my old 5 liter, and a little less than the holbert car. I think you should finish your cage and start doing some 13/13 racing. try and make the Sears point race with the rest of the 928ers. You dont daily drive you car these days do you?

mk



mk

mark kibort

Dennis,

Here is part of the theory.

on entry to a 90 degree turn, a fast run up, and hard straight brake sets the nose and increases grip, then a trailbrake with a turn in allows the front of the car to be pointed more toward the apex. this all hinges on the techique of driving even faster to the turn and later braking so that after the trail brake, the car is still too fast to apply throttle, BUT, is now neutral (50/50 balance, no gas, no brake) and allows all 4 tires to continue to scrub off speed for a .5 second or so. at this point, a blip and gear change effects nothing, and then after a fration of a second in gear, gas is applied to power out of of the turn.

this works at turns like i mentioned, Laguna's turn 2, 5 and corkscrew, as well as thunderhill's 1, 10?(after kink) 11? (turn after that)

opposing theory would want more braking on approach with gear changes, and then immeadiate throttle after turn in. this follows more closely to the theory of slow in and fast out, but clearly, due to modern data aquisition, and lap times, there is a clear case for faster in , faster through and slightly slower top speed down the following straight. this "rockers" the car's weight more front to rear vs what i have suggested. In my opinion, the less the major transitions, the better the car will feel. you metion that i must be controlling a "slide" , but actually, the car feels firmly planted and no loss of adheasion until the power out and that is slightly on the loose side, proportional to how much i hammer the gas on the exit. I never even get a wiggle unless it at turn 11 at laguna or the exit of 2 at laguna! (and providing the tires are decent)
Ill have to find the article i just read in SCCA mag, or Racer Mag, that talks about this verifying what i have found to help overall lap times.

mk

Dennis K

Very interesting. Thanks for the explanation, I get what you're trying to do.

There's a point on the friction circle during a corner where you don't want any acceleration longitudinally in order to have maximum acceleration laterally. You're achieving this by letting the car roll after you ease off the brakes. During this rolling period you do your downshift.

I've been trying achieve this max lat acceleration point by being on maintenance throttle. If I were to lift, engine braking would kick the rear end out because I already have the lower gear engaged.

The thing I've been working on is getting some slip angle on the rear tires to get them working. After turn-in, I'm keep braking to cause the car to rotate. When the car's starting to rotate, I immediately am back on throttle to slow the rotation and eventually stop it when I get the car pointed where I want it to go. From there on, it's just surfing that curve of lat. vs. long. acceleration on the friction circle by modulating the throttle.

I've described it to people as driving into the corner and "setting off the bomb." I trailbrake the car enough to the break the back end loose (light the fuse). If I don't do anything then the car will spin (bomb goes off). So I either have to countersteer or get back into the throttle to stabilize the rear end (put out the fuse). I hope this makes sense.

I think I saw a similar article to the one you're talking about in Racecar Engineering. It was done by the Mitchell Software people. Check this link out:
Driving Sim software

mark kibort

I truely think that if you are sliding at all, it is killing time. its my opion, but i think by now, ive taken turns as many ways that are possible in a 928. i sometimes use this technique with turns like turn 2 at laguna when my car has been pushing real bad. go like a bangie into the turn, and pitch the car a little, throttle steer and point the car where i want it to go.

we have very similar cars, so it would be interesting to ride with you to see how this is working for you and then go for a ride with me an see if there is any time difference. Ive also run my car with 350lbs extra ballast with POC a few years back. it drove similar, but just felt heavy an harder to stop. time were about 2 seconds slower too. 1:43 vs 1:41. I think i would take the weight over those used hooseirs any day!!!!!

Mk

Dennis K

Dude, you have Laguna wired. I am ~4 seconds behind you at T-hill and Sears but Laguna, there's no way I'm doing a 1:44. My fastest lap there has been a 1:49 and I felt a 1:47 was in reach if I took off the Supertrapp.

Can you come out to Tracquest at T-hill on 8/14 or 8/15? We could swap cars and compare notes . . .

mark kibort

Dennis, went to the link, and their message is on the right track, but still not exactly what im talking about. Actually the article i just read is from Sportcar mag, scca publication verifying what im talking about in general terms. (they dont get into the specifics on gear changes and were power is applied)

Below is a quote from your link and it says that this technique gives up speed while cornering, but gets better exit speed and sector speeds. what im talking about gains entrance and cornering speed, shortens the distance traveled, and gives UP exit speed, HOWEVER, improves overall lap times . There are three techniques evaluated in this particular article. traditional slow in fast out line, inside radius line, and then the trail brake line. the trail brake line produced the fastest lap times, inside radius line (really early apex was still fast, but not as fast) and I suspect, what i do is a combination of all trail brake and traditional depending on the turn. I think this is how you run fastest consistantly. I ran against a inside radius driver for an entire race, and every time we faced each other for a bunch of years. now i know why he was able to fend me off, not only was it a reasonably quickline, but it was defensive by nature. however, he didnt vary his game, and when it came time to get him a traditional, mixed with trailbrake line, gave me a shot at a finish line win, and it worked. havent beat him since, but thats a tire story. we will see Aug 7th at Laguna when we all go at it again and i got some real good used garbage can Hoosiers that should last for laguna and sears in sept.. Then, its back to toyos forever!


MK

From the link Dennis provided:

"The fastest way through a turn is to brake in a straight line, drive an arc of constant radius to the exit, and then accelerate in a straight line. But this line, known as the reference line, is far from the quickest line. By giving up a bit of speed while cornering the driver can accelerate before reaching the exit. This produces a higher exit speed and a quicker sector time. Every known racing driver does this: only mathematicians use the reference line because it is easy to analyze."