Larry Herman

Last month I put on a Performance Clinic for our club. It was about how changing your car will affect its performance and how it requires you to adapt as a driver. It was very well receivd. I gave a cut down version to the advanced drivers at our Watkins Glen event, and was subsequently asked to write an even shorter version for our newsletter. I figured that some of you here might be interested in it as well, and so here is the unedited version:

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Performance Clinic (synopsis from the event held on 7/10 at Fabspeed Motorsports)

For the novice and even the intermediate track driver, improving the handling of one’s car is probably the hardest thing to truly understand. What will it do for your car if you were to install R compound tires, stiffer roll bars, stiffer shocks and stiffer springs? How will it affect your car’s personality? What will it mean to you and your abilities as a driver? In the short space provided I will touch on some of the basics.

Larry Herman

The stock car, represented by the green line, has a large, flat plateau of grip. As you stiffen the car through roll bars, shocks and springs, the grip of the car improves and the reaction time to take a set will decrease. Note that the blue line of the modified car (say upsized roll bars, 600/800 lb springs and Bilstein sport shocks on Hoosiers) has a higher level of grip that comes with less steering angle, but also with a smaller window of grip. This car will “feel” much better when driving it below the limit, and will provide greater performance, but it will be harder to find the limit in this car. The racecar (red line) takes that to an even higher level. It has much higher performance, but much quicker to react, a very small window of grip and a very peaky limit.

Starting with the stock Porsche, when you get to the limit of grip the body leans, the tires howl, and the car starts really moving around on its suspension. You get plenty of warning that the car is getting to the limit. And the car has a nice fat window of grip before it starts to fall off the back side. What does that mean? Simply that you have a large margin of steering input, or speed differential to play with before it really is gone. As you can see from the chart, even if you add a little too much steering, you have a window that is almost 2 degrees wide where you will maintain roughly the same amount of grip. As a novice or intermediate driver, this is a good thing to have, as your skills and consistency are still improving and the safety margin that a stock car has will provide an added level of safety and confidence. It may not feel all that secure, but it really is. This is the car to learn on where you can approach the limits carefully.

But everyone wants to go faster, and the first thing is to make the car handle better. I think that you may be starting to understand what will happen. The more you stiffen the car, the flatter the tires will stay on the track, and the more grip that they will produce. This comes at a price, and it is that the window of maximum grip that they produce, though higher, will be smaller, and harder to stay within. You can see that it will take less steering input to produce the same cornering forces, because the car reacts faster. It leans less, and the tires don’t squeal much (if at all). But also realize that you now have less margin for error. So less warning, and smaller window means a car that is harder to find the limit and stay there, so it takes more experience from you as a driver knowing where the limit is and how to not drive right past it.

With the full race car on slicks, the grip levels are very high, but the reactions are really fast, the feedback is subtle, and the window is very small. Unless you are very proficient at sliding your car around, it is a limit that you can very easily overshoot because it is so hard to feel. These cars require years of driving to develop the ability to get the best out of them. They require a level of talent and feel that even a good number of advanced drivers may never acquire.

There are many drivers who will claim that they are going so much faster and how the car is so much safer now that they have upgraded their suspensions, but they are only half right. Those are the drivers represented by the X. They never quite learned where the limit was on a stock car, and so now with their upgraded suspension they are going faster, but are still X away from the much harder to find limit. This means that a mistake will inevitably result in a moment; i.e. a nasty spin or worse. And so it reinforces their inclination to stay a healthy distance from the limit, never really knowing where it is and never learning how to dance at it. At this point the “learning to drive better” pretty much stops, and now it becomes just trying to achieve lower lap times.

So after pounding around a few years in a stock car, what can you do? The answer is to start with small improvements and once you have mastered that, slowly move up the ladder. If you and maybe your favorite instructor feel that it is time, I would suggest starting with stiffer roll bars, and see how that makes the car handle flatter. Once you can drive it with the same confidence you had before, then try going to R compound tires and a full-blown track alignment. Once you feel that you are really on top of this, then you can think about stiffer springs and shocks. Try and resist that temptation to modify your car beyond your skill level. And if you are uncertain as to whether or not you are ready, just hitch a ride with one of the faster instructors who race. You’ll see what I mean about dancing at the limit.

Stay tuned for the next der Gasser where I will explain why the car becomes so much quicker to respond and harder to drive.

beentherebaby

I drive Flat Out. That's me Flat Out... usually 200 mph, at night... in the rain.

Good write-up BTW. You can tell the better drivers by how well they execute turns lap after lap usually with closer to stock suspensions and low HP compared to the straight line rockets. The Instructor-Student video pretty well summed it up when a Ford Focus or Miata driven by a student catches a 200 mph rocket in the twisties and waits for a passing signal.

Paul 996

Very cool. Also, gotta love the pic of Mike doing a faceplant. Heard he drove Flat out at the Glen.

sig_a

Constructive post...thanks.

911SLOW

Very good points and I like the table but there is a flip side.
Best drivers I know started driving with Karts.
Karts would be represented with a line in your table that would be even taller and narrower than the red race car line. That shows that although it might be safer to start with a normal car and move up it doesn’t necessarily mean that if you do the other way you have no chance. It’s just a different approach. Closed tracks offer the safety and instructors the knowledge to learn to drive with ANY car you want. Time it takes depends more on the individuals and methods rather than the car.
If we are talking about driving on the streets I am with you 100%. Bigger safety margins are better for most people and automotive companies seem to agree delivering their cars the way they do.

John

gums

Very insightful post, but I'm not sure I totally agree. In my old GT car (which you remember, Larry) I used to switch between Hoosier R's and Michelin Slicks. The full on slicks afforded more ultimate grip and were faster than the R's, yet were also more forgiving and gave more warning or feedback as they approached limit. They were much easier to go faster with.
Interested in your take on that....

mark kibort

great points and information

Land Jet

Thanks Larry, I'm looking forward to the next part of the series.

M758

In general terms Larry is 100% spot on correct. Even so there will always be contradictions to that for one reason. Larry's curves assume the car is set-up properly. Meaning that it has good balance and odd cornering behavior. Stock the car is probably pretty darn close. However once you start to mod the car it can move off it sweet spot for balance. In fact chassis balance follows a similar type curve where the faster the parts the harder it is to get belance optimum and more important it is do it. So to get the most from race car on Hoosiers vs slicks takes a different set-up. If you just change tires and go the car will not be optmized for at least one tire and possible optimized for neither tire. That is not to say it won't be faster on slicks, but it just may not be as fast as it could be.


Example. I had my 944 spec set-up for an open diff. The car was just about as fast any LSD car overall. Sure in places it was weaker, but the gap was small. I installed and LSD and promptly went no faster. The reason? I have not adjusted the chassis to optimize the advantages of the LSD. So all this car prep improvement stuff should make the car faster, but it must be done right.

Then again that is part of Larry's Follow-up. How modding a car improperly can make it slower.

IPguy

Excellent post Larry!

himself

Great post. Thanks!

-td

DWS964

Thanks for the post, Larry. I am still WAY down on the steep part of the learning curve. And the engineer deep in my soul loves this kind of stuff. I read very similar instruction in the book Speed Secrets by Ross Bentley. Recommend it. I still need the practical application part - seat time. Larry's comments help me with the realization that I need to perhaps slow down on the slippery slope of adding mod's to my car, and just improve the nut that holds down the seat.

Rceron

True or False, can you be smooth with steering inputs (one input toward apex and some post apex unwinding) and still be at max slip angle ? At this point I would imagine you would have to be constantly giving inputs to the steering wheel.

M758

True smoothness is measure by the the chassis and how it moves around in the track. Inputs (steering, brake and throttle) can vary wildly to ensure the car is smoothly flowing around a track.