Month: July 2015

Left- or Right-Foot Braking?

Left- or Right-Foot Braking — a Matter of Preference

Driving stars discuss braking techniques in this SAFEisFAST video.

If you’re a right-foot braker, I recommend practicing left-foot braking on the street for a few months before you take it to the track.

Obviously, an automatic transmission is ideal for learning subconscious competency in left-foot braking.

However, manual transmission cars can also be used in re-training your brain as long as it is used in corners that require only a minor speed adjustments that don’t require a downshift.

Additionally, if your car is equipped with a dog box transmission that does NOT use synchronizers (meaning you can shift without using the clutch) then you CAN incorporate left-foot braking while driving into the turns.

Incidentally, Michael Schumacher is credited for introducing left-foot braking to Formula One.

Gearbox Dependent

The gas pedal in Beck’s Lister Corvette #007 (a Facebook page opens in new window) has been modified to allow blips for heel-and-toe braking when downshifting using a synchronized gearbox.

However, now that #007 has an EMCO dog box, left-foot braking can be used with the right foot dedicated to the gas pedal…once you go dog, you’ll never go back! 😉

NOTE:  Do NOT ever modify the brake pedal when rearranging pedals to accommodate heel-and-toe down shifting; otherwise, it can turn into heal-and-tow.

Steering Wheel Action – Street Course

In-Car Cameras — Good for Watching Hand Positioning

Watch Tony’s struggle to hold the wheel out of the hairpin in the very last shot of this video…don’t skip ahead, this one’s worth every second.

Ryan’s upper wing on his right hand needs some additional fine tuning, though.  It’s lacking a groove that would make his job a whole lot easier. The current design challenges him outside the home position, and this distraction is costing him since the lower signal-to-noise ratio makes it harder to concentrate on the contact patches’ feel.

Since drivers don’t think about how their hands operate the steering wheel, they operate it in what is called subconscious competent state.

This is why in-car cams are so important.

Tire Sidewall Flex & Relaxation Periods

Relaxation Periods

As a racecar goes from the different loads for a typical corner — acceleration, braking, cornering, acceleration — transition periods occur as the tire’s cords settle down into their tasks at hand.  As the tire transitions to-and-from the various loads, there’s a certain “dwell period” that lies in between these steady-state conditions.

These are typically referred to as “relaxation periods”, since the tire is essentially relaxing in between “jobs”.

Tire Flex

Watch the contact patch at work in this video. Tire flex controlled by pressure/sidewall stiffness is the kart’s suspension, so the behavior you see here is similar to what you’d see in a vintage car today.

Today’s Short Sidewalls — Not as Good as it Looks

20+” rims fill the rotating mass with more metal and tosses a thin rubber band of a tire on top.

Compliance goes away, and unsprung mass goes through the roof.

Sure, cornering stiffness skyrockets and steering response gets noticeably snappy since the relaxation period — time it takes for forces to take a “set” — goes away.

Somewhere in between is where you need to be if you drive on the street.

http://en.wikipedia.org/wiki/Relaxation_length

If you have a FaceBook account, here’s a beautiful example of tire flex in action on a kart:

https://www.facebook.com/KartingEmozioneEPassione/videos/vb.114201065400594/487261031427927/?type=3&theater

Ayrton Senna Footwork

Ayrton Senna at Play in an Acura NSX

Ayrton probably didn’t have a lot of seat-time in this car when this was shot. So, the amount of lock needed to dance it around the corners wasn’t as ingrained as it was in his F1 car.

Based on this footage, I would not design any circumferential wings on his wheel, and would only put them on the backside in the finger area. My Lister’s wheel would have worked nicely for the steering method shown here.

His right-hand home position is ABOVE the horizontal spoke which suggests he was either using the horizontal spoke to pull down, or feeling more at home since he always preferred a higher steering wheel position…or both.

Footwork Analysis

Now, his footwork is very interesting, indeed.

Some might argue that his “tapping” the gas pedal isn’t smooth. However, he was dancing the tires across the very top of the mu-slip-load plot with a VERY small deviation.

This mu-slip-load graph adds a 3rd dimension by incorporating load into the standard mu-slip curve which plots cornering force against slip angle. Luckily, the vertical load vs cornering force plot also follows a bell curve; that is, it builds up and then fades away after a peak.

Handwork Analysis

You’ll notice that his hands were relatively quiet while his foot “Spiked the Friction Circle”, repeatedly. By keeping his hands quiet, he was able to toss load back-to-front with his feet and manipulate only one variable: vertical load.

This is exactly why I stress how important it is to relax your grip on the wheel…his hands showed no signs of stress.

By relaxing your grip, you’re better able to read peak steering resistance with a higher signal-to-noise ratio which corresponds to the peak of the mu-slip curve…simple. So, by constantly relaxing your grip on the wheel, the peak force is easier to feel AND maintain.

Speed Determination

Then, it becomes a simple matter to determine if the trajectory you’re on in the corner for your chosen entry speed is contained enough by the combined cornering forces available from all 4 tires…if not, lift to get the nose to tuck-in/back-out and slow the car down until the available cornering forces keep it on the course.

With the closing speeds and cornering capability that Ayrton was used to in F1, this NSX was a slow-motion ballet to him. So, once he got used to how much cornering and brake force was available, it became child’s play for him to dance it on the edges of the Friction Circle.

Manual Transmission Operation Explained

Racing vs Street Transmissions — or Gearboxes

Dog boxes used in car racing shift lightening fast, and are basically transmissions without synchronizers.

As such, input/output shafts must have matching speeds before the shift can occur…otherwise they grind going in.

Upshifts are “self-matching” since engine speed drops while the clutch is in; however, downshifting requires a technique called double clutching.

Double Clutching

At the Skip Barber Racing School we always instructed students to think of double clutching as: “two shifts in a row, when in neutral, you try to go.”

So, after putting the clutch in, you move the shifter to neutral, and let out the clutch while quickly stepping on the gas pedal to rev the engine.  Then, within a split second, you put the clutch back in, and finish the downshift…all this is done as fast as you can move your left foot.

Dog Boxes on the Street

Motorcycles are good examples of how dog boxes can be used on the street.  However, for street cars, they’re a bit impractical since they usually “clunk” going into first gear, and they can be noisy.

Synchronizers allow the use of helical-cut gears — which run quieter — and match the speeds of input/output shafts.  But, it’s difficult to visualize how it all works…even when holding the parts.

This video animation is superb, and shows you how it all works together.

More Info

For more incredible, straight forward explanations of complex principles in relatively simple terms, be sure to visit:

Learn Engineering’s Website (click)