himself

Without knowing what the corner actually looks like, in a typical you slow speed corner (perhaps a hairpin or decreasing radius corner), you can try to get your rotation done earlier under braking and then get to full throttle at/before the apex. In my guestimate, this will cure 80% of slow speed corner understeer. In other slow corners, just take a slighly later apex. This will cure another 10% of understter. Keep in mind that these corners are (by definition) already slow, so any time you might be losing on entry to get the car rotated earlier will be partially equalized with earlier throttle. By (or right around) track out you will have the same exit speed. So, you might lose a 10th or so under the curve due to overbraking, but at a DE a 10th won't even be noticed.

I strongly recommend your first step to be proper seats and harnesses, which will improve your driving by seconds a lap. At a minimum, get a CG-Lock.

As for when to move from street tires, my general rule of thumb is when you need to drive with opposite lock in 2-3 corners per lap, you are probably OK for R-comps tires. This means you are getting close to driving on slip with street tires, and you could apply those tools to stickier tires. I constantly have to remind folks that correcting the car in a corner does NOT mean you have exceeded the limit of the tires. Many students feel a little loose back end and believe they need to slow down just a bit to stay in control. We call this driving on rails, and this is where most drivers stay throughout their DE career. But if you are not correcting the car almost every corner, you are not driving fast. *note: this is not the same as catching the car due to bad inputs. If you upset the chassis or run over debris, the car will need immediate attention to stay on the track. When you are driving on slip, you are gradually getting to the maximum slip ange for your tires, and the correction is expected.*

Here is a good video I found illustrating the level folks should have before moving off of street tires. [Not me driving] You need volume to hear the tires. There are a number of instances of great skill shown in the video, the ones below are just noteworthy:

• 2:25 - opposite lock in a high speed corner.
  
• 2:48-2:56 you can see and hear that the street tires maintain almost full grip with LOTS of slip angle (compare with 5:46 noted below). With street tires, maximum grip is maintained over a large slip angle allowing you to develop good car control skills [as shown].
  
• 2:48+. Also illustrates one important reason you should NOT shuffle steer. If you need to grab close to 180 degrees of opposite lock, you'll want the steering wheel back to straight quickly to avoid a tank slapper or spin.
  
• By contrast, check out 5:46-ish. This is a section of video illustrating when street tires exceed the maximum grip of the tires. [volumne needed]. That is, you can hear the tires sqealing everywhere, which is what the should do when driving on slip. But at 5:46, you can hear a deeper howl coming from the tires. This is the sound of getting past the limit. You only hear it for a split second and then it goes back to screeching. This is yet another example of how forgiving street tires are and how much grip they actually have. You can go over the limit, correct the car and carry on.

-td

himself

Below is my grip presentation that I posted a while back on a different forum. It addresses some of the myths and issues of driving with R-comps and slicks, and explains some of the terminology involved.

Also, WRT R-comps, most give plenty of audible warnings before braking free. Only slicks have a short window. Toyos [RA1, R888], Nitto [NT-01], MPSCups and Hoosier R-6s all talk to you plenty. [Personally, I've never driving a R-comp that didn't make noise.]

I suppose this is a perfect time to post up a preview of a presentation I've been meaning to finish up on the dynamics of traction to help my students out. It's still a work in progress, but most of the heavy lifting is done. I got assistance on this from Larry Herman, who has a great understanding of these concepts and has worked up similar materials on these points.

Feel free to let me know if you have any questions/comments on this - including if it reads OK, if is too hard to follow, or if anything needs further elaboration.

PRESENTATION ON GRIP
You hear a lot of people talk about the traction circle, grip, slip, under/over the limit, etc. when talking about track driving. Of course, everyone understands that the only thing keeping you on the road is your tires. The simple equation is "more grip equals faster lap times." But many drivers are not getting the full potential out of their tires for their platform. Overlaying comparative data with better drivers in your car is one data point, but you can also get a comparative range for your platform by reviewing data, track records, video, etc. One problem is that are only a few descriptions out there for intermediate and advanced drivers to review to really grasp what is going on with their tires. And those may be too complicated to understand or too simple to be of value.

SLIP ANGLE
The first thing to understand is they way a tire generates force (i.e., grip). When a tire is turned left or right, the rubber at the contact patch deforms and generates force in the direction the wheel is pointed. But, the car doesn’t actually turn the same amount – instead it turns a little less than the wheel is turned. That is, where you point the tire is [generally] always more than the actual path the car takes. For example, if you have your steering wheel turned 10 degrees to the left [which we will assume equates to your tire pointing 10 degrees to the left], your car may actually only turning 4 degrees to the left, thus, you have 6 degrees of slip angle.



Tires generate more force (grip) as more slip angle is added, up to a certain point. That is, a tire only has so much grip.

GRIP
This can be illustrated graphically as shown below. This graph is fairly accurate for all tires [street, R-comp, or slick] but the slip angle will be different.



In this graph, force is shown on the vertical axis. The horizontal axis represents slip. As shown, as slip increases so does grip – but only up to a point. After the tire reaches its maximum grip it starts to taper off. But, contrary to what most believe, no tire just drops completely off. Grip may be substantially reduced, but it never goes to zero. The reason many say the tire just gave out is probably due to one end of the car losing some grip, which unbalances the car and results in a spin. For example, if all of the tires are at 1.0 G, but then the rear tires drop to .8 Gs, you have a car with pretty serious oversteer.

The Yellow line represents something we can refer to as “driving on grip.” It is most often manifested by steering the car with the steering wheel [or front end of the car] only. There are very few corrections at corner entry, mid-corner or corner exit. The car is on rails the entire time. Most people drive on grip and never realize that they are doing it, or that there is more grip to be had.

The Green portion represents “driving on slip.” This is manifested by steering the car with your feet or driving with the back end of the car [not to be confused with turning the car, which is done with the steering wheel]. There are many corrections in a corner with the brake (trail braking), gas (trailing throttle oversteer) and steering wheel (progressive countersteer to counteract excessive mid-corner or exit yaw). The tires have reached their maximum force and it is difficult to balance traction at all 4 corners at the same time. Because this section is so small, it is very difficult to maintain this level of grip in all corners all the time. As a reference point, using trailing throttle oversteer (throttle steering) in some corners is approaching the threshold from yellow into green. Rotating under braking [trail braking] and light countersteering under throttle at corner exit are indicative of actually moving into the green zone. Maximizing grip typically requires balancing the car in each corner by using throttle/brake/steering corrections. Balancing the car should not be confused with “catching” a car in a corner, which is more indicative of rapid traction disparity requiring immediate and quick correction – often referred to as not driving smoothly.

The Red portion represents exceeding the tire’s maximum grip. As shown, the tire still generates substantial grip, but the tire is now at a slip angle that may be chewing away rubber rather than simply turning the car. It is possible to go from the yellow line to the red line almost instantaneously bypassing the green line. Most often, only one end of the car is in the red zone. Without a good skill set, this type of grip disparity often ends in a spin.

As alluded to above, one common misconception is that lifting in a corner automatically pushes the tire into the red section. Although this may be the case, many spins due to lifting in corner are due to excessive grip differential between the front and rear. That is, a driver may be completely in the yellow section [say .8 Gs at all 4 tires] but then lift in a corner. At this point weight is transferred to the front or the car, which may push the front tires to the far end of the green section [say 1.0G] while the rear tires fall to .6G at the same time. At this point, the car has a tendency to oversteer. If the driver does not immediately [and quickly] correct this with countersteer (and gas) the rear tires will continue to add slip angle and ultimately will shoot into the red area.

PRACTICAL EFFECTS
In sum, every tire will have a window where there is maximum grip. However, most never get over the proverbial hump and learn to drive on slip. One reason for this is that many believe that driving on slip is actually driving “over the limit.” When a small correction is needed, they believe they have exceeded the tire’s grip capacity and then drive below that grip level. On the graph, this would actually be crossing the threshold into green, but then pulling back. A car driven at the limit will need correction in almost every corner. Another way to gauge where you are driving is by looking at your lap times. If you are about 2 seconds (or more) slower per lap than the track record for your platform, you are probably not driving on slip. If you are 1 second off pace, you are probably driving on slip most of the time, but not getting everything you can out of the car. [Generally, this equates to time lost on corner entry due to trail braking technique].

DIFFERENT TIRES
The second graph is a generic representation of grip levels between different tire compounds. The black line represents street tires, which typically generate under 1.0 G of force. R-compound tires [e.g., Hoosier R6s, Nitto R888, Toyo RA1, etc] are represented by the blue line and typically generate under 1.2Gs. Slicks, shown in green, generate around 1.4Gs. These numbers may vary based on actual compound.



There are two things to note: (1) each tire has a maximum grip level based on slip angle, and (2) each tire still has a point where driving on slip beings. Interpreting this graph illustrates that street tires have a large margin for error – even when driving on slip. They provide plenty of warning that the car is getting to the limit, and there is a large window of grip before traction starts to fall off on the back side. Put differently, there is a large margin of steering input and speed to play with before grip starts to fade. As shown, even if you add a little too much steering, the slip angle window is almost 2 degrees wide where roughly the same amount of grip is generates.

Many people switch over to R-compound tires before they actually master driving on slip with street tires. Because of this, they do not have those skills to apply when using stickier tires. Although ultimate lap times decrease, there is still much time left on the table. Also, the nature of R-compound tires is that less steering angle is needed to generate maximum force and the window for this force is substantially reduced. There is much less margin for error, so it is harder to get to the maximum and stay there. The actual amount of slip angle varies by tire manufacturer. Driving at the maximum with the lowest slip angle is generally the best.

With slicks, the grip levels are very high and the car’s reactions to input are very fast. Feedback is subtle and the window for maximum grip is very small. Because the window is so small, it is hard to find but easy to overshoot. Driving slicks to their maximum requires a level of talent and feel that most drivers will never acquire.

Conclusion
Driving any car close to its maximum is very difficult and equally rewarding. Pushing towards the evelope is not easy and requires dedication and patience. If you have gotten to a point where your lap times have plateaued but you know that there is more in the car, it may be time to get an advanced instructor in your car to get you over the hump.

himself

Just wait! It'll get worse. Here's where I ended up before I sold my 996 and replaced it with something more appropriate


Track Mods:

• New 3.4L engine
• Upgraded to ROW M030
• Upgraded to PSS9
• GT3 rear sway bar / HR front sway bar
• adjustable drop links
• X51 oil pan
• GT3 lower control arms
• Cobra Imola II Seats (driver and passenger)
• Scroth 6 point harnesses
• 3rd radiator
• GMG roll bar
• Full Ruf body kit
• GT3 brake scoops
• GT3 brake liners
• PFC front 2-piece rotors with PFC-06 pads
• PFC-97 rear pads with stock rotors
• Motul 600 (sometimes Castrol SRF)
• Fabspeed muffler bypass
• BM shortshift
• 1 set: 5-spoke 18" wheels (AM)
• 1 set: turbo twist 18" wheels (AM 8X10)
• 1 set: turbo twist 18" wheels (AM 8.5X10)
• HANS
• Aggressive alignment

There was still more to do, but I gave up on trying to make it a GT3 and just bought a GT3.

If you want any comments on what was done and why, I'm happy to fill you in.

Some really old pics of the car:







-td

Hardback

Very nice. Thx for posting... I'll keep you guys updated with my progression on the track and upcoming mods.

Hardback

Himself, I really appreciate your last post. Great clarification of what different compounds are able to achieve along with their attitudes on track. I know I still have a lot to learn. One day I'll follow in your footsteps and buy a GT3 but for now the 4S is going to be my dual purpose machine. I realize it is not the best platform for track events but man you should see the perma-grin on my face after I log another DE. Truly an addictive and rewarding sport.

Hardback

That Honda is a hand full huh? I did not see the time elapse on the video (using iPad) but watched the driver get a lot of opposite lock input throughout his cornering. Turn in seemed to be a problem as car was plowing. (front wheel drive) Glad I don't have that issue. Must've been quite a ride for you in passenger seat.

ivangene

awesome Tom...

and I have to wonder if Tim was that driver.... he keeps saying his Honda is a POS but he seems to be getting all of the $$$ out of it

great write up, gives me some thinking.... I can definantly say I am NOT in slip - I have my work cut out for me...thanks for the read!

V225

Beautiful car being run like it should be!


But.....
C4s > GT3

Seriously though, I might get another car later on, but I think the C4S is staying forever. It has the looks, and contrary to what people say, it's a really fun track car. As for the mods, I have this 100% surefire way of not spending money on mods.

It's called being broke

ivangene

Hey Varun, we are on the same "mod plan"

Malakas

You bastards - I wish I would not have stumbled on this thread! I love tracking my 4S, but I was thinking of selling it (or trying to sell it) to get a Spec Miata or maybe Exige. I'd prefer something lighter and less forgiving. (ideally with cheaper consumables)

The 4S has been great to start my DE "career" but I feel (perhaps incorrectly) that the AWD and stock setup makes up for a lot of little mistakes. You can be so aggressive with the 4S that Im starting to wonder what would happen if I was man-handling a RWD platform in the same way -- I think its called an "off".

The sounds is incredible (Tubi), and I love nearly everything about the car... I just wonder if I'd learn more with a different platform. (I can say these things now that I have a daily driver)

Nevertheless, after seeing V225's stripped interior with rollbar and seats - Im starting to doubt my choice of getting rid of the car... you jerks.

ivangene

LOL ^^^

yea, sweet looking "strip" I was eyeing that quite a bit myself

himself

Some skills will translate, but not all. Some RWDs are easier to drive than the C4S AWD [think E9X M3], and some AWDs are even easier to drive [think GT-R]. But, some RWD cars are a beast.

Just get a GT3, and you'll have everything you need. Well, except a back seat.

-td

Malakas

A GT3 is definitely in my plans, someday... Two of my buddies here have GT3RS 997.1s - they are just incredible.

Sorry I've taken converstion OT. OP: I have an extra set of solid spokes for the 4S if you need them.

Sneaky Pete

+911 to Himself! Great points and info! Thanks for this.

V225

Thanks! I love the 4S. It does everything really well and I've become so familiar with it over the years. That said though, the Exige is my dream car. I'd say that once you're able to get similar times as a good instructor in your 4S, you might want to consider changing the car. Until then though, have fun. The car can be a total beast if you let it

And a huge thanks to Himself for that article!