Column: The Momentum Over Horsepower Debate

In reply to ProDarwin :

There isn't an ideal line. Even something simple like changing tires, or adjusting aero on a car will change the fastest line.

Aero makes perfect sense.

Does anyone have a top view that can illustrate how the line would change when you add/remove mechanical grip or horsepower?

In reply to ProDarwin :

You made me do some googling but it seems to have been worth it, take a read through these two blog posts and see what you think.

https://yousuckatracing.wordpress.com/2016/10/16/math-on-the-racing-line-part-1/

https://yousuckatracing.wordpress.com/2016/10/22/math-on-the-racing-line-part-2/

They really highlight how much of a crutch power can be using his hypothetical corner and grip/acceleration levels. The Miata could lose 1.39 seconds in this corner with different lines whereas the Corvette using those same lines could only lose 0.22 seconds from best line to worst. 

ProDarwin I will attempt this without drawings, note that some of this may be peculiar to vintage race cars, specifically to my Datsun on bias ply Hoosiers. I'll use a medium speed 90 degree corner as an example.

80whp Datsun; just shy of the known turn in point I will actually ever so slightly over rotate the car via trail braking, this has a triple effect of shedding that last little bit of speed allowing me to take a slightly tighter line and pick up the throttle earlier.  What you would see if I drew a line would be a 10 degree deviation from straight ahead for the first 1/8th of the corner followed by a 60 degree arc from 1/8th through 3/8ths, by 1/2 I'm fully on the throttle and unwinding the wheel to free up the car the last 20 degrees of corner. In general I end up with a progressive and slight 4 wheel drift on exit.

So while I'm slightly pinching the corner on the entrance I'm also carrying a bit more entrance speed that needs to be scrubbed off (we're taking 1/2- 3/4 mile an hour to be scrubbed off).

By contrast in the Formula 500 I would use a steady arc with the apex at the geometric center.  This is becuase the car is on slicks and it does what you ask it. It also has the ability to spin the tires mid corner so even if you were back to the throttle earlier you couldn't put more power down anyway. The F500 is also much more straightforward to drive. Power wise it keeps up with 450hp to 480hp road cars.

Most of my experience with down force is with my old D-Sports Racer. My previous description of the line used in the Datsun may come into play here. Because the car stuck you could use more aggressive steering inputs; if there was a straight after said 90 degree corner I'd pinch the entrance in order to be opening up the wheel to flatten out the car and get the power down earlier. If the 90 degree corner only had a short chute to the next corner then I'd use a line like the F500. The D-sports would out accelerate Dodge Vipers but because of the down force the line options were pretty limitless. 

The most fun I've had racing is with a near stone stock MGTD. 54 horsepower around 2000 pounds. 
     Honest drafting being pulled along by a MGTC with a supercharger that increased his horsepower  to 70.  But by staying in his draft with the windshield folded down I could go just as fast as he could then my "modern" front suspension allowed me to out corner him only to be repassed on the next straight.  By sand bagging just a little I set him up for a last corner pass and held on to lead at the Checker by 2 inches. 
After the race we laughed and patted each other's back. I didn't stop grinning for the whole day. Everyone else in our group felt the same. 
Please don't tell me you need 700+ horsepower to race.  Maybe your ego does but that's not where the fun is.  

adam525i (Forum Supporter) said:

They really highlight how much of a crutch power can be using his hypothetical corner and grip/acceleration levels. The Miata could lose 1.39 seconds in this corner with different lines whereas the Corvette using those same lines could only lose 0.22 seconds from best line to worst. 

Thanks for those links.  Interesting reading.

Here is how I interpret some of that:  

1) I'm not sure how far out the poster carried that simulation.  IMO, it requires a full circuit for it to be comparable, otherwise time is only 1/2 of the equation.  The Corvette is 0.01 faster on the rally line, however what is the exit speed?  I suspect its slightly faster on the late apex line, meaning unless there is a LH turn immediately approaching, the late apex is truly the faster line.

2) Above said, the late apex line is truly the fastest line for both the momentum car and the horsepower car.  Sure, the horsepower car suffers less when its off line, but its ideal ine is the same line.

For the snow situation, see point #1 above.  Its hard to tell which is faster without an appreciable straight or upcoming turn after the corner.

We've LeMons raced a Volvo 122 with perhaps 110-120 HP in a warm B20, and had a riot.  Our current car has a 350-ish HP big block in a heavier chassis and it's also fun.

Drag racing on the street anymore is pretty much dead.  I realized this last weekend when some CUV (I still don't know what it was, nor do I care) beat me from a stoplight in my ~220 HP Jaguar 3.8s.  Any modern car has too many turbochargers, transmission gears, and variably-timed valves for all but the hottest older iron.  Our LeMons car _might_ have beaten it, but it's a caged, single seat car with no interior, heat, wipers, or glass. 

Real driver skill shows up in the corners.

ProDarwin said:

Keith Tanner said:

That's my point. The reason you're taking different lines is not because one car has more horsepower than another - it means one car has more grip than horsepower. Up the grip on a high power car and you're back to those lines that emphasize corner exit speed instead of corner exit traction. You can have a 400+ hp momentum car, but you're going to have to build the chassis for it.

My 500 hp Miata has been a momentum car or a point and shoot car depending on what I'm running against. 

I'm having trouble following this.

Your 500hp miata - for your fastest lap time there is only one optimized line, right?  (assuming no traffic here)  If you subtracted 250 hp, you would drive a different line to maximize your laptime?

I've always thought of the perfect line as staying relatively constant, just the speed at which you can trace it goes up as you add grip and horsepower.  All cars want to maximize the speed carried through the corner, right?

When I'm chasing a 911 with an LS7 shoved up the rear, I'm struggling to get traction off slow corners by comparison so I'm trying to preserve momentum. So I'm driving the momentum car in this case.

When I'm chasing something with more grip but less horsepower (say, a well set up E36), I'm the one with all the acceleration so in that case I'm driving the point and shoot car. My lines don't change, but my role does.

If you have the ability to put down serious acceleration coming out of a corner, you'll run a different line because it allows you to start to accelerate sooner. Giving up 5 mph mid-corner is worth it if you can add 10 mph to your exit speed, because you get that extra speed allll the way to the next braking zone.

frenchyd said:

Please don't tell me you need 700+ horsepower to race.  Maybe your ego does but that's not where the fun is.  

You do if the guys you're racing have 1000+. That's the same equation you had so much fun with, just scaled up. It adds new corners to the track - you don't understand why the Andretti hairpin at Laguna Seca is called "turn 2" until you have some horsepower and you discover the very exhilarating turn 1 that you thought was the front straight.

I was at the track a few weeks ago with a 90-ish hp Honda. Well, it was 90-ish hp 35 years ago, it may not be now. This is a track where I spend a lot of time in cars with 500 hp. Did I have more fun in the momentum car? Not really. Did I have less fun? Not really. I enjoyed them both, and I don't know which one I'd take to the next track day. The Honda sure left me in better shape, though - I feel pretty battered after dealing with the high power/weight cars.

It's a different skill set to get the most out of it. Not a better skill set (car guys love to pat themselves on the back for having a crap car for some reason), a different one.

Keith Tanner said:

frenchyd said:

Please don't tell me you need 700+ horsepower to race.  Maybe your ego does but that's not where the fun is.  

You do if the guys you're racing have 1000+. That's the same equation you had so much fun with, just scaled up. It adds new corners to the track - you don't understand why the Andretti hairpin at Laguna Seca is called "turn 2" until you have some horsepower and you discover the very exhilarating turn 1 that you thought was the front straight.

That's a very good point.  Back to my own experience, racing at CMP, the "Kink" isn't really anything you worry about with a 100-HP car, you simply mash the go juice pedal all the way from corners 8 to 11.  But when you have enough grunt to be doing north of triple-digit speeds by the Kink, some strategy is required or you'll be sideways, backwards, &/or upside down by the time you get to turn 11. 

People like to make this so complicated, which is easy to do with theory.  Put it this way:  A 3000-ish pound car with 340 HP on 225-width tires and a stick axle will feel pretty sprightly at points (like where you're losing grip trying to power out of turns), and quite competent at times (esses/turns in series).  The same-ish car with similar power and a more modern IRS rear (and way better front geo), but with 315-width tires will be a completely different beast where the old setup found quick limits.  This is where it gets possible to have a 400 HP momentum car.

When the chassis is built to specific power limits (or better still, beyond), confidence is more easily and reasonably found.

More power = more fun, but only when the chassis ability corresponds.

You know what's no fun?  Driving your car with one hand because you have to point-by every other car on track with you.  When I started doing track days, the fields had Miata's, E30s, E36s, air cooled Porsche's (for the big tippers), old Vettes or other generally modest cars.  It was fun because it was possible to pass most cars using your driving skills.

Now, folks show up with McLarens, GTRs, Porsche GT2, GT3, GT4, ZR1 Corvettes, ZL1 Camaros, Shelby Mustangs and full on race cars/trucks from sports cars to NASCAR.  If you are still driving your original "momentum car" you spend your whole track time pointing cars by.  Only the most totally inept driver in one of the above cars might get you a pass, but because you are not allowed to pass in the corners, they can pull away on every strait.  It ruins the day for me.  I need enough power to pass on the strait.  I found that 440rwhp in a C5 was enough.  Made a mistake selling the C5, thought I would track my '13 Carrera S, but I chickened out for fear of damaging the car.  Instead, I bought a momentum car, '96 Mustang GT for $3500.  We shall see if I can have fun being a rolling roadblock.

@Keith Tanner  "car guys love to pat themselves on the back for having a crap car for some reason"  It's that classic case of the wrong side of the tracks versus the townies mentality.

Part of why I like momentum cars is I love dragging a car farther up the order than it has a right to be.

maj75 (Forum Supporter) said:

You know what's no fun?  Driving your car with one hand because you have to point-by every other car on track with you. 

LMAO, ain't that the god's honest truth.  

At the PCA events I do the passing is done on the straights only, so coming off the gas and pointing 3 or 4 cars buy isn't an issue.  At events that have open passing (not a fan of this practice for cars with no safety equipment) that would spoil the fun.

maj75 (Forum Supporter) said:

Now, folks show up with McLarens, GTRs, Porsche GT2, GT3, GT4, ZR1 Corvettes, ZL1 Camaros, Shelby Mustangs and full on race cars/trucks from sports cars to NASCAR.  

What organization do you run with where those are the majority of entrants?

Keith Tanner said:

If you have the ability to put down serious acceleration coming out of a corner, you'll run a different line because it allows you to start to accelerate sooner. Giving up 5 mph mid-corner is worth it if you can add 10 mph to your exit speed, because you get that extra speed allll the way to the next braking zone.

So lower power:grip car has an earlier apex than the higher power:grip car?

I'm not fully understanding how - I might need to do the math on this myself.  As shown in the above links (I have no idea what simulation was used), the low power car is still fastest around the corner on the late apex line.

I haven't followed the links, but the momentum car is going to want to carry as much speed as possible even if it means less traction available to accelerate, because it doesn't need as much traction to accelerate. The point/shoot car (aka higher power/grip ratio) will want to emphasize the ability to get on the power sooner and prioritize grip for acceleration. So yeah, that sounds like a later apex for the high power/grip car.

I went to a track day at Calabogie with an almost stock 1996 Miata on all-seasons. Now that's a momentum car. I did spend the entire day pointing people by because it turns out that people bring the crazy toys to this series of events. Like a Mercedes GT with a mirror wrap. Had fun for the one or two spots where I could make up ground on the GT3s by being a lunatic, but on the next lap they were long gone...

What I took from that simulation is that late apex is faster for everyone that can accelerate. The less that acceleration is a factor (lower power car, faster turn) the less advatage that you gain from a late apex and the closer you should be to a geometric line. 

ProDarwin said:

Keith Tanner said:

If you have the ability to put down serious acceleration coming out of a corner, you'll run a different line because it allows you to start to accelerate sooner. Giving up 5 mph mid-corner is worth it if you can add 10 mph to your exit speed, because you get that extra speed allll the way to the next braking zone.

So lower power:grip car has an earlier apex than the higher power:grip car?

I'm not fully understanding how - I might need to do the math on this myself.  As shown in the above links (I have no idea what simulation was used), the low power car is still fastest around the corner on the late apex line.

Different lines through the corner trade off speed in the corner for time at which you can get on the throttle.  Changing the grip and power level will change the optimal tradeoff as far as lap time is concerned.  Length of the straight that comes after will change it as well, but presumably that's the same for both cars.

As for having fun at the track in a car with no power, this is most commonly an issue when you're in the intermediate groups.  Those often include drivers with a wide variety of skill levels, many of whom haven't gotten the "I want to use all 500 hp down every straight" out of their system yet.  Combine that with limited passing rules and it can make for a very frustrating track day.  This situation is why my Miata got its first turbo. :)

As far as ideal "fun" goes, I find that I really prefer track cars to have fewer than 10 pounds per horsepower.

I've had a Porsche put on its brakes on the back straight at HPR to let me past in a high grip 150 rwhp ND Miata. Lifting off just wasn't getting the job done. It was pretty funny to see the thought process - point by, lift...brake lights. I did thank him later :)

Keith Tanner said:

frenchyd said:

Please don't tell me you need 700+ horsepower to race.  Maybe your ego does but that's not where the fun is.  

You do if the guys you're racing have 1000+. That's the same equation you had so much fun with, just scaled up. It adds new corners to the track - you don't understand why the Andretti hairpin at Laguna Seca is called "turn 2" until you have some horsepower and you discover the very exhilarating turn 1 that you thought was the front straight.

I was at the track a few weeks ago with a 90-ish hp Honda. Well, it was 90-ish hp 35 years ago, it may not be now. This is a track where I spend a lot of time in cars with 500 hp. Did I have more fun in the momentum car? Not really. Did I have less fun? Not really. I enjoyed them both, and I don't know which one I'd take to the next track day. The Honda sure left me in better shape, though - I feel pretty battered after dealing with the high power/weight cars.

It's a different skill set to get the most out of it. Not a better skill set (car guys love to pat themselves on the back for having a crap car for some reason), a different one.

My  Black Jack with 300 horsepower and 2000 pounds could still beat 427 Cobra's.  Aero wise I pushed a lot less air than they did  and I could position myself on the inside of a corner and out brake him from corner entry. 
Once  past, my car got very wide and somehow I was always in front of him under acceleration. When he was nearing his top speed I'd still have a little left since the D type body was really good while the Cobra body shoved a whole lotta air. 
If he'd back off me he could've beat me under acceleration but he couldn't think that way.  He'd follow my taillights into the next corner and when he could stop as quick as I was he'd swerve, get off line and spin out. 
 

The ability to plan your moves quickly is one of the things that can make a slower car beat faster cars. ( that and having your car set up to allow quick changes when they appear. 

Things I've said at a PCA event during the drivers meeting "your car at half throttle out accelerates my car at full throttle"  "please lift aaaaall the way off the throttle"

As for the earlier apex in a low horsepower car this is two fold; the car may not accelerate fast enough that the car drifts all the way out to the exit kerb and so you start unwinding the wheel sooner to free up the car and use all of the road.

Also one is more likely to rely heavily on trail braking and rotating the car more aggressively will allow you to get away with an earlier apex.

In the Datsun I'm actually thrust vectoring i.e. pointing the car to the inside of the apex kerb, by the time the car actually arrives  at the kerb the car has moved over about a foot.

The picture below best illustrates this: note my hand position on the wheel (almost center with my helmet) and the slip angle of the rear tires. Also note that while I'm at the apex I'm already tracking out toward the exit kerb. The Spitfire behind me is on using a more traditional line and driving style.

I've had corners before in low powered cars where I keep moving the apex back further and further until I can finally carry enough speed that the car is going fast enough to track out properly. This is not a problem that my Corvette driving friends have. 

One metric that has been left out (somewhat) is the one that includes style of track.  Some tracks do not really reward horsepower as much as others.  From what I've been told, as an example, Road America has a straight that literally does not end.  From what I've seen, NOLA has something similar, depending on how they've configured it for the day.  From experience, both Laguna Seca and Sonoma can make you feel pretty happy with 350 HP (which is basically low power these days), depending on your skill (and grip) level.  As for my future track, I somewhat fear Road Atlanta, as I'm not sure if my car's brakes are up to task; grip and power will be sufficient, however.

On that note, who here has figured out how to make up time with brakes?  I did a fairly recent ride-along with a friend in a basically stock (Koni struts and track day pads) first-gen RX7 (not remotely poweful), and he did very well in not being passed by far, far faster cars on a track that favored higher horsepower (Thunderhill).  Granted, he would have killed for an LS swap, given less laziness . . .