TD in DC

Hey, that reminds me . . . I forgot to post the plot of the puckometer, which records magnitude of code brown moments. Here is the plot of steering input and code brown magnitude:


I also managed to get a screenshot of myself at that particular moment. Funny how much helmet distortion I experienced . . . wonder what impact that has on ISAAC and HANS devices . . .

}{arlequin

nice save

Professor Helmüt Tester

Tankslapper: oscillation in the front forks of a motorcycle, due to geometry, weighting and a host of other dynamic conditions. Usually happens as the front end unloads. The 'tankslapper' moniker came from the fact that when this happens, your forearms/elbows whack off the sides of the gas tank rapidly. Can be helped by mechanical dampeners ('steering dampers'), by fiddling with the steering head angle and by having the rider plant his fat *** a little further forward when he decides to crash his bike.

Note my first post's "Joey Dunlop" comment.

For additional reference info, look up "Bray Hill" or "Ago's Leap". Car racers have leeetle teeny tiny *****. IOM racers have huge dangly scabby *****.

TD in DC

I noticed something interesting that I would like to hear your thoughts about. I overlaid the data from my fast lap with the data from my tankslapper on a variable by variable basis.

Here are all of the variables compared one by one. The fast lap is in red . . . the tankslapper is in black.

The funny thing is that my speed was, for the most part, faster in the "fast" lap (although it was a few mph faster when the car broke loose), but both the lateral Gs and vector Gs were higher in the tankslapper lap, despite the fact that the steering inputs were nearly identical in both.

So. . . the difference has to be throttle, which I am pretty sure it was, or it was that I was just so close to the limit that the 1 or 2 mph made the difference.

If I am right about my hunch, it goes to prove what I have been thinking for awhile now . . . there are times when you can really be at the limit going through a turn by braking and then accelerating, and yet the answer to going even faster is to brake even less and go through the corner even faster, because the extra speed can make it easier to balance the car with more subtle inputs (provided that you are subtle enough to pull it off). Interesting (to me at least). Just thinking out loud here . . . and intesested in what you see in the data.

TD in DC

Please let me know if I am thinking about this the right way.

In order to understand what is going on, you have to know what the bus stop looks like: It is a braking zone, that leads to a right, then a left, and then a long sweeping right.

My tankslapper happened at the exit of the bus stop, where I was already starting to turn right for that long sweeping right hander.

I wouldn't pay too much attention to the rpms or the entry. All you are seeing is the blip for the downshift, which went perfectly fine apart from the fact that I apperently stayed on the gas a little after the blip on the tankslapper lap. There was a car right on my *** going in IIRC, and this may have distracted me. But, and this is an important point, the car was actually MORE settled at the entry of the bus stop on the tankslapper lap. How can you tell? Well, in addition to me remembering, you can see that my downshift was actually earlier, and my lat gs going into the busstop were smoother and LOWER (steering was nearly identical).

So, what was the difference? I braked a little more, and was back on full throttle to settle the car. So, there really wasn't a bobble on the way in, and the car felt great on entry.

It started to fall apart after I made the left to get out of the bus stop. You can see from the throttle trace that on both laps, I had to lift a little to get the car to rotate. Well, actually, since I came in faster on the "fast" lap, I didn't really lift because I could not get back on the throttle right away. However, on both laps, I was back to full throttle after the car "made" the left-hander in the bus stop.

Now is when it fell apart, and, as far as I can tell, it is due to one of two things.

First, it could be that, since I was going 2 mph faster when the rear snapped out, I had just pushed a little too hard for conditions.

Second, it could instead be that the car was more balanced when I went in faster and carried my momentum through. On the fast lap, I entered faster, burned off 2 extra mph mid-turn, but was able to be back on the gas and exit with roughly the same speed. My throttle inputs were more progressive and gentle: I waited to get back on full throttle, which meant that I was on maintenance throttle until I got the car rotated. On the tankslapper lap, I braked more, but was back on full throttle immediately, then I had to lift, and then I was back on full throttle immediately, albeit at the exact same point I had been on the fast lap. Perhaps overslowing the car and then speeding back up caused enough extra weight shifts in the car to throw me over the edge. You can see from the lat g charts that I was carrying more lat Gs through the busstop, and then it started increasing towards the exit until it really broke loose. By contrast, the fast lap was a fairly smooth and consistent max G through the corner (a pretty good g at that ).

Thoughts?

ronbo56

You write: "On the tankslapper lap, I braked more, but was back on full throttle immediately, then I had to lift, and then I was back on full throttle immediately, albeit at the exact same point I had been on the fast lap. Perhaps overslowing the car and then speeding back up caused enough extra weight shifts in the car to throw me over the edge."

I would think that almost has to explain it, especially since you were otherwise smooth. My own experience in a 944 (DE not racing) is that braking later and jumping on the throttle is not what these cars like. Instructors keep telling me to get off the brakes and back on the gas ASAP and use the throttle rather than, say, trail braking to rotate the car. The later I brake the worse it gets, and not because I'm at the threshold. Last time I was at the Glen my instructor told that if I wasn't going flat through the bus stop (other than feathering to rotate) I wasn't driving it correctly.

M758

I can't say anything about the Glen and the bus stop, but I will say that in 7 year of driving my 944 I have NEVER used the gas to rotate the car. I use the brakes or throttle lift to rotate the car and the gas to STOP rotating the car. You can throttle steer the car but more gas = more understeer, slight lift to tigthen the line.

As to the reasons for TD's tankslapper.... Hard to say as I just don't know about that corner and I don't believe I have even had a tank slapper in the past 5 years. That it NOT to say I have never gone off track. I just tend to either catch the slide (which I will do quite often) or the car is too far gone and just goes off. I have experineced a reverse tank slapper (tank slapper going backwards), but I don't think tha applies. I did have student experince a tank slapper when I was in the car. I think it occured because the student was too late in correcting the slide and too agressive in the correction. You get behind then the car drives you. I am not cetain this has any bearing on TD's case however.

TD in DC

Oh you can bet the tankslapper part of this was caused by me getting behind the car and then refusing to give up. I was mentally exhausted on the last lap of an extremely tight race (I raced about four or five cars very tightly the entire sprint). I usually catch snap oversteer, but I got just a touch behind this one, but I refused to give up so I got into a tankslapper. I know why the tankslapper part happened. I am more interested in what I did to cause the rear end to snap out in the first place.

M758

I believe this to certain extent. There is one corner at Phoenix International Raceway that is rather challenging. Entry is 100+ MPH and exit speed is 60 mph or so. Corner is decreasing radius and requires good trail braking on the way in. Most of the time you fight understeer. That is unless you over cook it and the oversteer off in to the grass. Basic 944 technique is to trail brake pitch the back end catch it shoot off through the corner. The problem with the lack of really good markers it always seems to be bit of a crap shoot. One thing I noiced was if I slow down a bit too much there is not enough energy in the car for me to pitch it so I can catch just right. I either get lots of understeer to I try to trail brake too much spin. If however I brake just a bit less as begin the major turn in I can get the car rotated just right. So in effect if I go a little faster the car has more momentum that I can used to control the car. Strange yes, but it does seem to support TD's point. I am not sure how it applies to other corners since I have never thought about that while driving.

M758

This may sound strange, but is the rear stepping out a bad thing?

There are many places on the tracks I visit where a slight slide in the rear is not bad thing. You just catch it can go on. My post previous was one example and on that track there is another corner were I touch the brakes to get the rear end to rotate just a bit and then catch the slide with a little countersteer and throttle. So routine that in car video will catch the counter steer lap after lap after lap. My mind infact goes like this.

1) touch the brakes
2) turn the wheel (Turn in) with front end still loaded down from brake touch
3) Turn the wheel (counter steer a bit)
[3.5 car gets a bit loose & rotates]
4) Back on the gas hard
[4.5 car settlsdown and shoots out perfectly for next corner]
5) Straighten then wheel and setup a straight line brake for the next corner.

This corner is easy to catch the slide, but there are others where is more difficult and sometimes I don't catch the slide or to do so in such a way as to lose speed) and then it becomes and issue.

Point is catching a little slide is I feel a part of racing at limit. If you want to be fast there are places the car may slide and issue should not be that you got the car to slide or twich, but problem not saving it.

TD in DC

This type of stepping out was definitely bad. First . . . it was not expected as in I did not do anything to induce the slide intentionally. I was exiting one turn and making the transition to the other. Second, it violently snapped out. Look how much and how quickly I had to open the wheel from the steering plot . . . and it still wasn't quick enough . . . The rear end snapped out bigtime . . . That just isn't very helpful ever . . . A controlled slide is one thing. A snap out is another thing altogether.

ronbo56

I apologize if my meaning was unclear. I simply was commenting that I have been urged to get back on the gas quickly so that I can in fact, as you so ably put it yourself, "use ... throttle lift to rotate the car and the gas to STOP rotating the car." I assure you that I was not saying that I use more throttle to steer the car. I'm not sure that's even possible in a 944 but I certainly don't want to be the one to find out.

TD in DC

If you go in with a high enough entry speed, you will not be able to get back on full throttle right away without spinning on entry . . .

If you look at the fast lap, I couldn't get back on the gas right away . . . and the data says I was at 1.2 or so Gs . . . not much more left I assume . . .

But I hear what you are saying. That's why I am thinking about this . . .

ronbo56

That's true. For a variety of reasons I had decided that I would dedicate this season to outbraking everyone on the track. I learned trail brake rotation at Skippy School and I tried to apply it to my car.

This was, to put it mildly, a bad idea. My instructors (944 veterans all) told me straight up that this isn't the way to get around quickly. My
car throttle steers very well but tends to get light under heavy trail braking. I honestly don't know whether this is a function of my (lack of) technique or something related to the shifting weight within the car. All I can say is that it's very straightforward to use throttle position to get the car around a corner, and that it's far more difficult to come in hot and try to use the brakes to steer.

TD in DC

I do think that coming in "hot" and traibraking into a corner is the fast way around many corners BUT it is not intuitive and it will take a lot of practice to do it correctly.

You MUST go in with a higher entry speed or the braking will cause you to be slow.

I know very, very, very few people who really trailbrake. A ton of people say they do, and then I watch them closely on the track and see their brake lights go off very shortly after turn in.

The only time I have ever seen anybody really trailbraking at a DE was at VIR when there was a pro driver there in a blue 997 GT3 Cup Car . . . his brake lights were illuminated all the way down to the apex, and his entry speeds were incredible.

I can trailbrake well "sometimes" in DEs. I am too scared to do it with traffic in races yet, because I am not yet confident enough in my timing and sense of proper entry speed. But give me time . . .