JackOlsen

Jack667 suggested this could be a thread of its own, and I agree.

My car weighs 2400 pounds, empty, and puts out about 275 hp. In the time trials I compete in, it has to be driven in more of a momentum fashion than the Vettes and Vipers I might be sharing the track with. At my home track, I can clock better times than guys hitting close to 150 mph on the straights, while my car is geared to max out at 136.

On the other hand, if I was on a track filled with just about any model of n/a 4-cylinder or pre-1983 Porsche, I'd enjoy a pretty significant advantage when it comes to overall power-to-weight ratio. The other cars would consider me the big-hp guy in town.

It's all relative, of course. But outside of 996's and Turbos, the 911 seems to me to be a car you've got to keep smooth and fast through the corners if you're going to keep up with the big dogs on track days.

mds

I don't believe there is such a thing. A car is a car and a better driver will drive whatever he or she is in faster through the corners. If you are keeping up with the big dogs then probably if you were in their car you would be faster.

Petevb

I think you’re right in that this is the case of the old adage- it’s all relative. Go to Le Mans and the LMP 2 class are “momentum cars” compared to the LMP 1s.

That said, I’d say the issue comes down to grip vs power. If you’re heavy on grip relative to power you’re a momentum car. This in turn means you’ll take wide, larger radius lines through the turns, which is probably what defines a momentum car. As power increases or grip decreases you’ll sacrifice mid corner speed to get power down sooner, and your wide, smooth lines will disappear.

I’d use the above to argue that a small motored radical could be considered a momentum car where a viper with the same power to weight would be a hp car. But then what do I know?

carreracup21

I think my car at 2700 and 270 hp is right at the borderline. If I maximize mid-corner speed near the limit of grip in 3rd gear or lower, I really can't go flat at the apex without getting loose and scrubbing speed in a slide. If I go in to mid corner just a shade below the max, I can go full on and increase my exit speed vs. the other way. I think if a corner leads to a straight, I'm better off doing the go in slow come out fast method, but if it's a longer turn or sweeper, I'm better off staying fast the whole way through like a momentum car. I guess what I'm saying is you might be better off using either technique to your advantage for the particular situation. Fast corners use a momentum approach , slow corners use your power. I bet some people with experience looking at track data loggers could say more about this stuff. I can only describe the way it feels for me and I'm still trying to learn which way is best.

Bill

Adam Richman

In racing, I refer to a momentum car as one that needs a fast in, fast out corner approach that uses this "momentum" through that process to overtake a better accelerating/faster straighline speed car or put sufficient space between them to keep the faster straightline car from overtaking. Its all completely relative. In an ITS, ITA race, my ITA car is a momentum car. If it were an ITA, SM, ITB rungroup, I would have the point and click car. In each race group, the higher powered cars will highly torque the lower powered guys if they are running the same laptimes because cars of disparate straightline speeds won't be running the same speeds in the turns and its more detrimental (laptime wise) for the car that has less at its disposal for getting down the next straight. Also, as most cars out there are racing someone else in-class, affecting a guy in a lower powered car's cornering speed in essence hurts his race.

Its not about absolute power or absolute weight or number of cylinders or power to weight or whatnot, its about disparate straightline vs. cornering speeds. In a DE environment, again, the momentum car is the one that cannot afford the lead car to park in the turns and still appear to be deserving of a point by. They also have a much smaller window for how much they can slow in a corner and not be harrangued by cars less driven by "momentum" in that environment. But again, all cars are "momentum" cars, I would think we are talking about comparatives here.

RJay

I agree. My 70 3.6RS, at least as its currently configured with 205/245 rubber tends to be at its best when observing the old adage, "Slow in, Fast out". More power than stick. OTOH, the brake locking seems to be a fact of life in this car, as it has so much power and so little front rubber, which means I can gain speed rapidly, but I'm limited in my ability to scrub it off. This forces me to either brake earlier and try to accerelate through the entire corner or try to take the wider line in an effort not to over tax the brakes.

But on the subject of wider versus tighter lines, in watching the ALMS race from LRP yesterday, I was amazed at how tight a line the R8s (and others) were taking through Big Bend. A good instructor friend of mine once remarked that, "there are a million lines through that corner, all of them bad." All my instructors have placed the line (on entry) with the outside wheels on pavement, the inside on concrete. From what I could see the fastest cars had both wheels on the pavement to the inside of the concrete patch. Being a hard core AXer and having done a bunch of Evo schools, while watching I recalled their school on reading the fastest line. They've proven, at least to me, that the tightest line in a 90+ degree corner is always the fastest (its simple physics really), so perhaps as some here have remarked, there really isn't such a thing as a momentum car, there are just different cars with different characteristics, the sum of which force a particular driving technique.

Or prehaps there are no momentum cars, only momentum drivers.

mitch236

I also agree that all cars are momentum cars. It's a case of relativity between two different cars. If I were out against a stock Miata, I would have the power car, and if I were out against a cup car, I would be the momentum car.

Momentum is a misused term like "slow in fast out".

Al P.

Big Bend has a fair ammount of banking and you can run inside the concrete BUT you need to be very carefull on the exit, hold it too long and the track will throw you to the inside tire wall.

JC in NY

I agree with this. All cars are "momentum" cars.

A Viper driven poorly will be a fast car but the driver will just manhandle into the corner, turn it and blast the throttle for a fast exit. However, a pro driver will take that same car and keep the speed up through the turn (just like what you think of as a momentum car) and turn a much faster time.

SundayDriver

My take is this...

All cars are momentum cars. If you give up speed at any point on the track, you lose time or position. However, there are high HP and low HP cars, with low HP cars referred to, by some, as momentum cars.

Now high or low HP has nothing to do with total HP, but the ratio of HP to grip (this was pointed out to me by Brain Till). High HP cars can be poorly driven in a DE environment, or within a race class that has few entries, and it won't be obvious because the lap times look reasonable. In other words, you can drive a TT poorly and turn 1:38 at Willow - all the students turning 1:59 will think you are flying but a competent TT driver will know what you are really doing.

High vs Low HP will sometime need a different line. Later apex may reward the High HP with better exit speed, but this is only sometimes. I have had many high HP students swear they are faster with a bad line. Truth is, it is an excuse for poor technique. But, a place like the exit from the carousel onto the front straight at Mid Ohio (left right combo) does require a different line. Fastest line can not be used by high HP because they must then lift for the final left hander. It is quicker for them to hold the first right hander longer before they release the car so they can stay flat through the final turn. This combo is the main place where lines may differ for low vs high HP.

There are also challenges with ultra low HP cars, like SRF. In those cars, overslowing by ~5 mph at corner entry will penalize you for a long time, as you can not get the apex speed and exit speed back. Other low HP cars can still correct that mistake so there is little penalty. My biggest flaw as a driver is exactly that - In an SRF at a place like Willow, I can loose over 1 second for that mistake. The same error in a DSR (identified and corrected early) costs a small fraction of a second.

Finally, I will share how Brian Till introduced the high/low HP concept. He was leading a track walk at Mid Ohio and said "Low HP car, like a Formula Atlantic, will need to..." That got our attention and he proceeded to explain. Best definition I have ever heard for different lines and what cars are what. That makes a Viper or TT a high HP car (400-600 HP and no better than 1.5 g's plus 3500+ weight), Jack's car is Low HP. My Stohr is usually low HP but in some low speed places it needs a bit of a line compromise for high HP behavior.

SundayDriver

There are so many things going on when you watch other cars, it is hard to generalize.

1. bumps and pavement changes - this can be a big factor for one car and a non issue for another.
2. Aero - My car will pull over 2.5 g's at 130 mph, but only 1.6 at low speeds. What is the fastest line when the cornering capacity is changing? It isn't the fastest geometric line.
3. Defensive lines - in racing, many times you take a line that defends rather than the fastest line.
4. Poor technique - I have seen some poor lines in almost every pro series from some drivers. Just because the driver is paid (a lot in some cases) does not mean they are driving the fastest line all the time. Drivers use their strengths to overcome some weakness'.

I agree 100% with your last comment about momentum drivers.

Jack667

I think that there is some truth to many of the statements here:
- its relative to the cars that you are sharing the track with: "Momentum Car" connotes underpowered, and that would be relative to the other cars.
- to some extent, all cars are momentum cars: any car that gives up speed through a corner will have a hard time getting it back on the straight.
- there's a grip vs power consideration: cars with more grip than power will go relatively faster through corners and slower on the straights, unless they maximize momentum. Then they would be able to compete down the straights based on their faster corner exit speed.
- we should be talking about "momentum drivers". It's the driver that maximizes corner speed, takes advantage of momentum, resulting in faster speeds down the straight and lower lap times.

Here's another way of looking at it:
Maybe the whole thing is only relevant when there is a big disparity in driver ability. Like in the White group of a DE and some Black groups, but fewer Red groups. Almost never in PCA Club Racing, and certainly not in professional racing. Here's the concept - people talk about mometum cars at a DE, like when 944 NA can keep up with much faster cars, like a 993 (in club racing, this would be an "I" car vs a "D" car. The 944 driver conserves momentum, flying through corners and carrying that speed down the straights. He might say that he is driving a momentum car. However, if the 993 driver was any good, there is no way that the 944 could keep up. The 944 would no longer be a momentum car, it would be just slow.

In the end, its probably another one of those things that defies definition.

996racer

I was watching the ALMS race at LRP yesterday also and I too saw the tight line the R8 takes around big bend. At first I thought wow he is taking a different approach than I do, but then I thought that he just might be trying to block another car for passing him. Then I realized it is an R8 and he can do pretty much what he pleases.

carreracup21

I think in racing you are forced to make comprimises between what is the absolute fastest way around the track for your car vs. what technique or line do I have to use to get around someone or to keep from getting passed. That's race craft and that's why someone can lay down some fast lap times in a time trial situation, but not necessarily be fast once the green drops. If we are talking about time trialing only, then the absolute perfect lap by definition could only be done one way. The trick is finding out which way is better for your car for each corner. The fast in wide line momentum approach or the tighter slow in power out approach. In faster corners or corners with extended g - time a momentum approach works best , maximize entry speed. In tighter slower corners you need to give yourself room on the traction circle to get flat before the apex. IMHO.

Bill

M758

A few of you have hit it on the head.

The real definition of momentum is a grip vs hp thing. Lost of grip with modest hp means you get fast lap times by never slowing in the corners. However if you have lots of hp and little grip then you must us the hp to generate speed. Best example are things like GTS Class at Le Mans vs LMP2. GTS cars have something like 500-700hp, but don't have anywhere near as much grip as a 400 hp LMP2 car.



In our world (DE & Club racing) momentum is much different. The reality is that there are two ways to be fast. One is with HP and the other is with driver. Cars like the 944 are momentum cars since in order to appear "fast" on the track the their drivers MUST learn to carry speed in corners. In a 993 for example the same "appearance of speed" can be achieve with the power of the car. Of course if a 993 were driven as hard as the 944 using the same momentum gather in techniques then it would be much faster.

Another example is this...

My Stock 944 Turbo S vs 944 spec race car.

My turbo S on street tires is more of a point and squirt car? Why? Not enough grip from the stock suspensino & street tires. In most evey corner I can overpower the tires with the engine. Thus to be fast I need to adjust my lines with the purpose of maximizing the power. In my 944-spec race car on R-tires it is down 100 hp, but has much more grip than my 944 Turbo. The lines I take with that car are different because I can apply power long before I can in 944 Turbo partily since I have more grip, but also since I have much less power. Thus to be fast and maximize the car I must slow as little as possible as corner exists are often quite easy. More time is to be gained from not slowing down than getting the power down. In the Turbo I need to ensure that I get the power down as the car MUST slow more than my race car. If I add r-tire to the 944 Turbo and do suspension work I am pretty sure I can start to take my momentum line as I do in my 944-spec and achieve much faster lap times.