RR98ITR

Once upon a time I argued that all cars were momentum cars unless the competition wasn't close.

A respected friend told me that the other side of the argument was right. I discounted his opinion.

Over time I've come to appreciate that the penalty for loss of momentum IS greater in a low powered car, and recognized that my earlier argument, whatever the merit, overlooked significant factors.

Scott, who says "that's why they call me a genius"...

Track rat

Quote I heard somewhere..."mistakes in small bore cost more lap time, mistakes in big bore cost more bodywork."

phat-S

If we are at a driver school and we have a big spread of cars out there, Vipers and 993s and what have you, tnord's Spec Miata is by and large the momentum car of the bunch and he pays a much greater price w/ scrubbing speed unnecessarily at trying to overtake other cars out there than the rest of the gang.

In our ECRs where we have SRF (sometimes), ITS, ITA, ITB, ITC, SM, SSB, SSC; my old ITA CRX was at a great disadvantage if an ITS (or even SSB car) car ran ahead, got wide in the turns and used its power down the straights (but in reality, we never had too many issues w/ this - think once in over a dozen races - not suggesting its a problem, just a hypothetical) - you want to get around those guys as quickly as possible so it doesn't determine how you run your race. But we could be the same type of problem to the ITB,C,SM, SSC cars if we ran slower than we should through the turns and used our power down the straights.

But if we are talking about comparing Trans Am cars to Trans Am cars or Spec Miatas to Spec Miatas, how is there any appreciable difference to what is a momentum car per some definition of grip over power or power to weight - everyone's fighting w/ the same sticks. Scrubbed speed is scrubbed speed and to say that the high powered cars are masking mistakes head to head w/ equal cars doesn't make much sense to me. If you guys are right, it makes me wonder why Trans Am was using competition yellows.

Jack Black

It seems like the question of what makes a momentum car is similar to the question of whether a car is traction limited or torque limited in its ability to accelerate. A car that is torque limited could be considered a "momentum car" because any loss of speed can not be regained by engine torque. This would mean that all cars are "momentum cars" at some point, like in high speed corners.

It also seems like the distinction would have a lot to do with the ideal line through a corner. If the ideal line is one that emphasizes maintaining the highest possible average speed through the corner, then it's a momentum car. If the ideal line is one that emphasizes spending as much time accelerating as possible, then it isn't a momentum car. This would again indicate that all cars are "momentum cars" at high enough speeds.

One last way to look at it is power to weight ratio. At low speeds, the ability to accelerate (with sufficient traction) is almost totally determined by power to weight ratio. Thus you would expect a "momentum car" to have a low power to weight ratio. At higher speeds, the ability to accelerate is governed mostly by aerodynamics. So again, the distinction between a "momentum" and "non-momentum" car is diminished at high enough speeds.

asoduk

I've been on both sides of the situation. I learned to drive in a 944 and didn't move up to the 944 turbo until long after I learned all about momentum from a couple SSB miata racers. Now that I am an instructor and ride along in a ton of different cars every weekend it becomes very obvious that every car is a momentum car.
This past weekend I was driving the 944 at beaver run and found that the cars that were faster than me were cornering at about the same speed as me, but had much more straight speed. I also had the opprotunity to drive my student's CTS-V and found that my driving it the momentum way was much faster than his driving it the HP way. Likewise, my student in a WRX knew about momentum and was absolutely flying in HPDE2 compared to even many HPDE3 cars.
So, the conclusion is that all cars require momentum to achieve the best result, but a high HP car can achieve mediocre results by simply making the straights as long as possible.

Grumpy

If two cars have the same time at the same track the one with the slowest MPH on the main straight is the momentum car???

speedengineer

This is a very old thread, but I enjoyed reading it and figured I would bring it back. I have been pondering this very question lately, trying to decide if my S2000 was a momentum car or not. Here are my thoughts:

Some people feel every car is a momentum car, while others do not. I think that while every car requires proper use of momentum to set fast times and be used to its full potential, not every car can be called a momentum car in the sense that we mean it.

To properly drive many low powered cars, you roll back to full throttle very quickly after turn in, often well before the apex. Once at full throttle, the continued acceleration of the car is limited not by traction, but by power. I would call this race car a 'momentum car'

In contrast, a race car with gobs of power must slowly roll to full throttle as they move through the corner. Simply planting the pedal would cause a spin - the vehicle is traction limited throughout most of the corner. It is not a momentum car in the sense we are talking about.

Granted, both types of cars must use momentum to go fast. While botching a corner in a low powered car will more drastically hurt lap times than in a high powered car, both types of cars benefit from conserving momentum. Certainly if you brake more than necessary in a high hp car, or run wide on entry, or miss an apex, etc, you are not getting as fast of lap times as you could. I would argue that the driving line and technique for a spec Miata vs a turbocharged (but otherwise identical) Miata would not be all that different.

solo-x

Momentum car is one that is power limited. IE, you can't turn a better lap without more hp. A non-momentum car is one that is traction limited. IE, you have plenty of power in reserve exiting every corner, but not enough traction to use it all.

pmachan

I drive a GT1 car, I also a couple times a year drive an ITB VW.
My approach is more or less the same, but there are obvious differences in technique to achieve the same result. The ITB car is all about softness, especially on the brakes, must be careful not to overslow, and be even more carefull not to carry too much speed in and start to scrub, kills those VW's!
For me though, trying to carry as much speed in, and through the middle is very important in both cars, as much mid corner speed as possible and still being able to maintain a clean exit is everything. Doesn't matter what you drive.
I believe every car is a momentum car.