[roy@gambitmotorsport]

Regarding weight VS handling it seems to me that the concept of "lighter is better" is potentially shallow. From my experience in light and heavier cars, both given appropriately stiff suspensions:

+ Lighter cars are easier to purposely change direction in a corner
- Lighter cars more easily steer off in unintended directions based on the road

+ Lighter cars experience less front/rear weight transition during braking and acceleration
- I guess the negative is if you want that transition more controllable through the pedals

- Heavier cars are harder to "pull back" from a mistake

Any better rules of thumb from seasoned track drivers here? Additionally, it may be expected that .9G in a 2000lb car at a certain radius is not equivalent in speed to .9G in a 3000lb car at the same radius - although this often taken as the "description of handling", the slalom speed tests give a better picture sometimes.

Almost obviously, weight reduction on a front-engine, rear-wheel-drive car will help with drag races, which isn't really what I'm thinking about regarding handling.

[2e9x's]

It all comes down to physics... f=ma (force = mass * acceleration). The more mass you have, the more force you need to achieve the same acceleration (be it forward, lateral, or backward). The heavier the car the more force required to change direction.

Auto-x is the best place to experience the difference. Try this experiment...for an auto-x, try borrowing a Miata (think rent-a-car) and running it. Then jump into something heavier and try the course again. It is amazing how different they feel!

[roy@gambitmotorsport]

Originally Posted by White05X3

It all comes down to physics... f=ma (force = mass * acceleration). The more mass you have, the more force you need to achieve the same acceleration (be it forward, lateral, or backward). The heavier the car the more force required to change direction.

Auto-x is the best place to experience the difference. Try this experiment...for an auto-x, try borrowing a Miata (think rent-a-car) and running it. Then jump into something heavier and try the course again. It is amazing how different they feel!

Sure. I had the chance to feel this between an M-Coupe and an M6 at an Intel/BMW event a few months back. The M-Coupe certainly transitioned faster, but I was kind of left wondering which could take a high-speed constant bend faster (HP aside).

[heavychevy]

Take your car, with a passenger, and drive a few laps on a track, then let the passenger out and drive that same few laps and you'll immediately feel the difference.

Weight/Hp ratio is very valid performance measure. Look at how racing cars are penalized. Adding weight, or hp restrictors. Weight affects cornering speeds, and most of all braking and acclerating.

Now comparing over different lines of vehicles is different because there is a plethora of different things you can do the offset extra weight (suspension, center of gravity, downforce), but you can only cover up so much ofa fat pig.

[2e9x's]

Originally Posted by roy@gambitmotorsport

Sure. I had the chance to feel this between an M-Coupe and an M6 at an Intel/BMW event a few months back. The M-Coupe certainly transitioned faster, but I was kind of left wondering which could take a high-speed constant bend faster (HP aside).

There are so many factors that would go into that other than just weight. Let's assume two identical cars...call them widgit VVF (Very Very Fast)...Physics tells us that is one VVF is 500 lbs heavier than the other one, it would require more force to create the same (lateral) acceleration. Assuming force remained constant (because of same tires, suspension, aerodynamics) and the only difference was mass, acceleration would necessarily suffer. Hence the heavier car would not be able to go around the corner at the same speed.

If I could do math (I can't or I would have been a doctor instead of a lawyer) I could probably reduce this to some numerical values...but I can't. Take a look here and see why...

http://en.wikipedia.org/wiki/Newton's_laws_of_motion

[DrDomer]

Lighter cars tend to have a shorter wheelbase, and some can be "twitchy". So, depending on driver skill level, you may not be as fast in a car that's lighter, just because it's lighter.

White05X3... I would agree it is much more complicated than weight. Friction is obviously extremely important. We assume the track is a constant so, of course suspension and tires obviously have a huge impact. If you have unlimited traction, then weight is less of an issue for cornering but still an issue for acceleration. Unfortunately, traction is not unlimited.

If everything else is constant.. Two Miatas with same suspension, tires, etc... but one is 200lbs lighter, then obviously it should have greater exit speed because it should have less lateral force on the tires.

BTW.. doctors can't really calculate these numbers very well. Even if they aced everything from basic physics to quantum mechanics.

[roy@gambitmotorsport]

Thanks for all of the insights.

Here's an idea, though, what if you had two cars with the same suspension, wheels, and tires (unsprung weight), but the sprung weights were 2000lbs and 3000lbs. They're coming out of the same corner at near traction limits for whichever would take it slower (assuming the 3000lb "hog"). Then, they hit a series of uneven 1/2" to 1" short bumps.

Would the weight of the heavier car help it complete the corner better, steadying the unsprung weight better? Or would the lighter vehicle allow better inputs to the driver for greater correction, carrying off the turn faster?

[S4to335]

I used to play on track with Spec Miata guys with and without passengers...it didnt change their lap speeds that much. Maybe a second slower with a 160-190 lb passenger.

[heavychevy]

Originally Posted by roy@gambitmotorsport

Thanks for all of the insights.

Here's an idea, though, what if you had two cars with the same suspension, wheels, and tires (unsprung weight), but the sprung weights were 2000lbs and 3000lbs. They're coming out of the same corner at near traction limits for whichever would take it slower (assuming the 3000lb "hog"). Then, they hit a series of uneven 1/2" to 1" short bumps.

Would the weight of the heavier car help it complete the corner better, steadying the unsprung weight better? Or would the lighter vehicle allow better inputs to the driver for greater correction, carrying off the turn faster?

Heavier car wont be affected as much by bumps, but the lighter car should still be faster. The bumps will upset both cars. The heavier car will be upset less, but the lighter car will correct faster (but more difficult).

[roy@gambitmotorsport]

Originally Posted by heavychevy

Heavier car wont be affected as much by bumps, but the lighter car should still be faster. The bumps will upset both cars. The heavier car will be upset less, but the lighter car will correct faster (but more difficult).

I hear you. A good driver paying attention can carry the lighter car through faster with corrections. An average driver not paying attention, may actually carry a heavy car through more safely, provided they weren't really at the edge of traction to begin with. I think that's the sense of stability in weight, though not lap times, I've been trying to get straight in my head - thanks!