power-weight formula ????

[icemang17]

Okay the car I am building for GTS2 just got its official dyno sheets!! Using the "highest of three" run formula listed in the rules my official dyno # is 222.48 (dyno was 203.44hp-241.52 torque)....okay using DOT tires that puts me at a post race weight of 3226lbs.

 

Here is my question...with the +/- 4 dyno forgiveness...does that mean my actual weight is based off of 218.48 dyno # or 3168lbs?

 

I think I am going to have to ballast the car just a tiny bit anyway.....I just need to make sure not to add too much!!

[JSG1901]

The minimum weight you have to meet in after-race technical inspection is based on your dyno results and DOES NOT including the 4hp grace. I round to the nearest tenth, so by my calculation you will need to weigh:

 

((203.4 + 241.5)/2) * 14.5 = 3,226 lbs

 

If you don't make that weight, you are disqualified (we do allow the NASA one-time-per-weekend 5 lb grace, however). Assuming you DO make weight and are sent to the dyno, then the actual dyno results are compared to your actual coming-off-the-track weight. It is here that the 4 hp grace is used but to get here you have to have made weight.

 

So, bottom line, you need to weigh 3,226 lbs.

[icemang17]

The minimum weight you have to meet in after-race technical inspection is based on your dyno results and DOES NOT including the 4hp grace. I round to the nearest tenth, so by my calculation you will need to weigh:

 

((203.4 + 241.5)/2) * 14.5 = 3,226 lbs

 

If you don't make that weight, you are disqualified (we do allow the NASA one-time-per-weekend 5 lb grace, however). Assuming you DO make weight and are sent to the dyno, then the actual dyno results are compared to your actual coming-off-the-track weight. It is here that the 4 hp grace is used but to get here you have to have made weight.

 

So, bottom line, you need to weigh 3,226 lbs.

 

Great info...I will have to look very closely at the dyno-weight #'s and determine the best way to set the car up....I am leaning towards lower power vs more weight....

[JSG1901]

I don't think there is any question about it: If you can get down to the target 14.5:1 ratio both as a powerful heavy car and as a less-powerful lighter car, the lighter car will be faster in the real world.

 

Power-to-weight ratios are all about acceleration. Given identical cars with identical gearing and identical power to weight ratios, they will accelerate substantially the same. There will be a small advantage to the more powerful car in the very fastest parts of the track where aerodynamic drag plays its biggest role and that extra horsepower helps push through the air.

 

So, if you are drag racing or going for a land speed record, go for more power.

 

But if you are road racing, that's the wrong solution. In road racing, acceleration is only one of a broad range of factors used to determine lap times and, I would argue, the least important. That's not to say a car with a much better power-to-weight ratio wouldn't be faster around a track than one with a lot lower power-to-weight ratio. All else being equal, of course it would. But we're talking about cars with similar, if not identical, ratios and in that case the difference in lap times due to acceleration from either configuration is negligible.

 

That's because in addition to acceleration you have to brake, corner, and transition from side to side. In ALL of these cases, more weight is a bad thing. It is harder to stop, it is harder to turn and it is harder to move from side to side. So, every extra pound of mass conspires to make the car slower in each of these situations. While your acceleration in the higher-horsepower car is comparable that of the lower horsepower (and lower weight) car, it is at a disadvantage in the corners and under braking. That also means you come onto the straights marginally slower in the heavier car (and have to make up the difference) and cannot drive as deeply into the corners because (a) you have more mass to slow down and (b) you have to slow down more because you can't go as fast through the corner when you get there.

 

Given the choice, follow the Colin Chapman principle: To go faster, add lightness.

 

But, to be honest, none of this even begins to address the biggest factor in the lap time equation which is the difference driver skill plays in road racing. In drag racing the driver is a small part of the process. He has to have quick reflexes at the light, not spin the tires, and keep it on a straight road. In the grand scheme of things, that's pretty easy unless you're in Top Fuel or one of the completely crazy classes. Drag racing, then, is mostly about equipment and significantly less about driver. It is hard to win a drag race without superior equipment.

 

In road racing, however, we regularly see lesser cars--even cars from lower classes--beating what should be superior cars strictly on the basis of driver skill. This in no way diminishes the discussion above about lightness being a better way to go but, at the end of the day, driver skill is probably the most important of all the controllable factors.

 

IMNSHO.

Edited September 27, 2010 by Guest

[kbrew8991]

it also could boil down to the kinds of tracks you race on in your region - or what track you want to do well at for Nationals if that's a goal. I wouldn't say carte blanche that lower weight is the way to go bar-none. As always - it depends

 

- KB, who has a much better Mid-Ohio car than a Miller car due to the principles he's thinking of when writing the above statement