This weekend, on my way to Lowe's, I got stuck on a highway exit loop. Well, OK, not exactly stuck, as I had driven 10 or 15 miles out of my way to get to it, but stuck in the sense I went around the whole cloverleaf (four ramps) without ever really exiting.

Several times.

:-)

The beauty of a cloverleaf is you can run it more or less perpetually. If you just stay in the exit lane you can loop off going North, which takes you West, then loop off West to go South, then loop off South to go East, then loop off East to go North again, then start all over.

And, unlike most other places where you want to go fast on the street, because you can run the loops more than once you can take a bit of a reconnaissance run the first time to make sure there aren't unsettling bumps or dirt or slippery bits before getting a good run at it.

Although there are a several excellent cloverleafs to choose from around Columbus, this was the one at Routes 270 and 161 in Dublin, my personal favorite. All four of the ramps are smooth, clean, and nicely banked, making for excellent fun.

The key to a fast entrance ramp is throttle control or, more specifically, steering with the throttle.

If you've never tried it, steering with the throttle sounds like a combination of impossible and, well, stupid, but it's not all that hard to do and really makes a difference. Here's how it works:

Imagine that you are driving around a constant-radius circle (say, for instance, an exit ramp) at more or less your car's cornering limit. All four tires are working more or less evenly. Tires get their traction from friction, of course, and the friction is largely a product of how hard they are pressed to the road by your car's weight.

More weight causes more friction which causes more traction. Now, before you get your underwear all up in a ball, yes, I know that heavier cars don't usually handle as well as lighter ones. That's because all the extra weight and all the extra traction is wasted trying to hold more mass on the road. It's a losing proposition.

But that's also why racing cars have wings, spoilers, ground-effects, and all the other shenanigans: Those devices push the car harder down on the track. To the tires it's like having more weight but without the extra mass to have to hold back. So they go faster around the corner.

What's this all have to do with entrance ramps and throttle-steering? I'll tell you. By changing the weight on your front or rear tires you can change the balance of traction and, therefore, the way the car is pointed. How do you do that? With the throttle.

When you accelerate in a straight line, what does the car do? It squats toward the back and lifts the nose. It's putting extra weight on the rear, shifting it off the front. In effect, it's adding friction, traction, to the rear and reducing it in the front.

When you let off the gas, the opposite happens: Weight moves forward, giving more traction in the front and less in the rear.

On the exit ramp, er, imaginary constant-radius corner, lifting or pressing the throttle doesn't really do much of anything unless you're pretty close to the tires' limits. The car just goes a little faster or slower. But when you are near the limit, suddenly the throttle becomes a steering tool.

Running a little too wide and can't get the car to turn in? Lift the throttle a bit and the front end will miraculously turn in. Then get back on the gas to even it out again. Even more gas will get the front to run wider (push, to you NASCAR fans). You can make surprisingly significant course changes without ever moving the steering wheel.

This, then, is the fun of entrance ramps: Using the throttle to hit the perfect line while skittering near the brink of control. It's even more fun when you start to use the "right" line on the ramps, which is probably not the line you normally drive.

We're talking about a 270-degree turn. Most people hug the inside all the way around, especially when they're trying to go fast. And, while that is plenty fun, it's not The Fast Way Around.

The object here, on our imaginary little race track, is to carry as much speed as possible into the turn--in other words, to slow down as late (and as little) as possible--and then to leave with as high an exit speed as possible. That's the object.

Now, if you are driving laps around a circle, there's not a whole lot you can do to adjust your speed. You can try hanging the tail out, maybe, but on the whole, it's just a constant turn and your car will only go so fast.

But an entrance ramp is not a full circle. There are straights on either end. That makes a difference.

The wider the radius of a turn, the faster you can drive it. You already know that. When you drive fast around, say, a 90-degree turn, you can start at the outside, clip the apex on the inside, then exit far to the outside and effectively widen the radius of the turn, making it possible to go through faster than if you'd hugged the inside edge all the way around. By using all the road you come in faster and exit faster, both.

The cool thing is, you can do the same thing on an exit loop. Well, almost.

The Right Way around an entrance loop is this:

• First, carry a little too much speed onto the exit, apexing reasonably early and letting the car drift wide as you ease off the throttle a bit and the car scrubs off a little speed.
• By about a third of the way around the loop you should be near the outside of the road and have given up a little velocity to be able to make this, the tightest part of the turn. Don't go too wide, especially if it's dirty, as this can be slippery on some ramps (do the reconnaissance run).
• A little past halfway around, start your turn-in. The object here is to give up a little speed right here in the middle of the loop to get the car turned in but, as a result of that sacrifice, to flatten out the rest of the turn, allowing you to accelerate harder, earlier, resulting in a higher exit speed. To do the turn-in, use the throttle. Lift off a tad, tighten the line, then roll on the gas and go.

It's a lot of fun. A lot. And a perfect amusement on a beautiful Sunday morning.

1. Alan Schmandt11/17/2004 09:17:12 PM

I was wondering if you could provide a good description on how to perfect the act of heel and toeing?

2. Scott Good11/17/2004 10:36:06 PM
Homepage: http://www.scottgood.com

Hi Alan,

Actually, I can.

Heel-and-toe is the term used for braking and throttle-blipping at the same time. Although there was a time when it probably actually required braking with the ball (toe) of your foot and blipping with the heel, I've done it in a pretty broad range of street and race cars and in modern cars it's really just a matter of using the left and right sides of the right foot.

So, not so much heel-and-toe as interior- to exterior metatarsal, but it doesn't sound nearly as sexy that way.

Before geting to the actual technique, perhaps a bit about why you need it in the first place.

The point of the whole thing is to make downshifts faster and--even more importantly--smoother. On the street it's a nice-to-have skill as it makes your driving smoother, jerking your passengers around less. On the track, it makes a real difference in your ability to go fast.

Imagine you're running down, say, the backstraight at Mid-Ohio. At the end, depending on the car, you're doing somewhere between 110 and 150 or so--5th gear--into a 70 mph, third gear corner.

The object, of course, is to wait as long as possible to brake--to carry all that speed as far as you can--and then to brake as hard as you can for as short a time as you can because, after all, braking does not improve your lap time.

The problem is, when you're braking at the very limit of adhesion, any jerk to the drive wheels will push you over the limit and upset the car. If you push in the clutch, wait until you get near 70 mph, then put it in 3rd gear and let out the clutch, you're going to at least jerk the car if you don't just spin out.

That's because when you let off the gas and put in the clutch the engine drops to idle speed. In my car, 70 mph in 3rd gear is at something like 5,000 RPM. To get the engine from 800 RPM (idle) to 5,000 RPM has to be done by the rear tires stepping up to the plate and basically forcing the transmission and engine to speed up.

But if the rear tires were already at their traction limit because of braking, there is no more friction left for dragging the driveline up to speed. Either (a) you have to brake less or (b) you have to find an alternate means of speeding up the engine. Such as, for instance, the throttle.

Enter heel-and-toe.

If you use the left side of the ball of your foot (the part behind the big toe) on the right side of the brake pedal you can apply plenty of braking pressure but, more importantly, get the right side of your foot over the throttle. By twisting your foot to the right you can blip the throttle with the right side while still braking with the left side. This is the essence of heel-and-toeing.

The subtlety comes in degree and timing. Done right, it truly is a blip, not a press. No different in duration than if you were sitting at a light blipping the throttle. Blip. Blip. Blip. Just about as fast as it takes to say it. A quick press and you're off.

The catch is learning to blip up to the right level of revs, and that's mostly a matter of experience but not as hard as it may seem. The blip starts at just about the same moment you're ready to let the clutch out.

Not when you push it in; when you let it out. You need the revs to still be there when you re-engage the clutch.

What you want to have happen is to have the revs matched well enough as a result of the blip to be able to let the clutch out very quickly. You don't have to eeeaase it out. You just lift your left foot. Quickly. While the blip is still at the right revs.

OK, so how do you learn to do this?

I started by not worrying about the braking. I just started blipping the throttle on downshifts, trying to match up the revs and make the downshifts fast and smooth.

Once I got that working (it's really not that hard), then I added braking. It's a little ironic that heel-and-toeing is actually a lot easier at racing speeds as you're pressing the brake pedal a lot harder, which matches its height up a lot better to the throttle. On the street, where you're not braking nearly so hard, it's a lot more subtle science.

On the other hand, if you can do it consistently and smoothly on the street, it's easy to do on the track.

That's really all there is to it. Brake, blip, de-clutch.

All there is until you're ready to double-clutch in the middle, that is. But that's a story all by itself.

Scott

3. Rock11/19/2004 08:23:43 AM
Homepage: http://www.LotusGeek.com

GEEK ALERT! GEEK ALERT! - While I am not going to ever argue with you about driving (I'm not worthy! ) I do want to add a little bit to the conversation, from the geek perspective...

Cloverleaf ramps are deliberately not circular, not even during the "curvy' part. They are more elliptical. Or, if truth be told, their degree of radius is deliberately not constant. Why not? Scott touched upon it, really.

You have two forces (ok, you have a crapload more forces, but we're keeping it simple) working on your car during a turn. First, as Scott details greatly, you have the coefficient of friction holding the car down to the road. This coefficient of friction is what Scott (and others) are so gamely controlling, keeping the car under that coefficient. Go over it, and you lose traction; stay under, and you look like Andretti (or Scott Good ) going through the corner.

The other force is acceleration - that fun stuff that Scott and others so crave. But in reality you have two types of acceleration working on the car - forward acceleration (provided by the engine, blah blah, blah), and lateral acceleration. Lateral Acceleration is the force that makes you feel that leanleanleanLEANLEAN as you go through the cloverleaf. As you increase forward acceleration, you also increase lateral acceleration; but what many people don't really realize is that if you stay on a constant arc (i.e. one that doesn't change in degree of curvature), you also increase Lateral Acceleration, even if your forward acceleration stays constant. That's why, even when you are holding the gas steady, you continually lean more in a curve. The bad part is that at some point the amount of lateral acceleration can overcome the forward acceleration; and if it overcomes the coefficient of friction you spin out, and if it doesn't, but your center of mass is too high, you will turn over. This is usually bad, and is to be avoided.

Enter the structural engineer. Now, structural engineers (geeky guys from GA Tech who design bridges, roadways, and yes even racetracks) figured this out. They also realized that the average driver probably doesn't understand what's happening, and they would wind up with spun out and overturned vehicles all on their cloverleafs unless they did something about it. So, what they did is that the cloverleaf's degree of arc occasionally flattens out a bit; this flattening out decreases the lateral acceleration, even if the driver maintains a steady foot on the gas. So they "spill off" the excess lateral acceleration to keep normal drivers (like me, not like you, Scott) safe on the road - even when they don't even realize it is happening.

Whew, I feel better. Had to get that off my geeky chest

Rock

4. Scott Good11/19/2004 10:57:17 AM
Homepage: http://www.scottgood.com

Rock,

I want to clear up in my head that you're saying what I think you are. You said, "...if you stay on a constant arc...you also increase Lateral Acceleration, even if your forward acceleration stays constant...." I'm reading that to mean you are, indeed accelerating, that is, speeding up, but at a constant rate (as opposed to maintaining a constant speed which, technically, isn't acceleration).

In that case, you're absolutely right that the lateral forces will continue to build to higher and higher levels as you go faster and faster around the same radius turn. Ultimately, you'll slide off the road, flip the car over, or the scrubbing of your tires will balance out the push of the motor to maintain a constant velocity (and keep you squealing around the turn, no longer accelerating).

I'm even bothering to ask because the rest of what you said later almost sounded like you were talking about the lateral acceleration continuing to increase even if you maintained a constant speed around a constant-radius turn which, of course, won't happen.

The amount of lateral force is a product of speed and radius. When both remain constant, so does the g-force (in which case, I suppose, it's really more correctly a lateral force than lateral acceleration).

You and I had too much Physics in High School, my friend.

Scott

5. Rob09/04/2005 03:28:11 PM

Heh, I ran across your site trying to find a diagram for the proper line on a 270 onramp as I was explaining to a friend how my Ford Focus managed to carry enough speed to surpass a line of Yamaha R series sportbikes that were merging at the same time.
Granted if they knew this I would have been eating humble pie. But as a large portion of motorcyclists never seem to be completely aware of the forces involved in proper riding/driving. They are content with the extent of their knowledge being "If I twist the throttle and lean back my wheel goes into the air" (Which, of course, they did end up doing down the highway)

What an investment, all that power but not the brains to use it.

6. debasish05/30/2009 09:23:11 PM

Mr. Scott Good can u please explain the process of heel_and_toeing with double clutching? also i would be obliged if u cud elaborately clarify what blipping the throttle means?

7. Scott Good05/31/2009 10:16:41 AM
Homepage: http://www.scottgood.com

Heel-and-toe double-clutch downshifting is here: http://www.scottgood.com/jsg/blog.nsf/d6plinks/SGOD-68CJ52

"Blipping the throttle" is a quick poke of the gas pedal to get the engine to rev up momentarily. You don't hold the revs anywhere, you just, well, blip it. It's very quick and then you are right back off again, as quickly as you got on.

In the case of downshifting, blipping the throttle is used to get the engine revs about where they would be at the current speed in the gear you're changing into. In other words, if you're in 4th gear at 3,500 RPM and downshift to 3rd gear, your motor will then be turning at around 5,000 RPM if you continue at the same speed.

However, as soon as you take your foot off the gas and push in the clutch to make the downshift, the engine's revs will drop down to idle. To get the revs back up to 5,000 for 3rd gear you can either (a) slowly let the clutch out and let the driven tires and the entire drivetrain drag the motor back up to speed (which will both unnecessarily wear the clutch and badly upset the car if you're anywhere near its limits or on a slippery surface) or (b) blip the throttle to get the engine to about 5,000 RPMs and let the clutch out quickly.

The latter of these is (a) easier on the car, (b) more fun, and (c) absolutel necessary if you're driving anywhere near the car's limits.