Why does C5 like gas on exit?
Team Owner
Joined: Mar 1999
Posts: 28,753
Likes: 9
From: San Jose/Bear Valley CA
CA Events Coordinator
Re: Why does C5 like gas on exit? (Pipes)
:lol: thats funny... kind of like driving my electric golf cart... I sneak up on people and they dont know it.. My C5 on the other hand is loud... nice a times and not so nice at others.
VR :cheers:
VR :cheers:
Instructor
Joined: Sep 2003
Posts: 104
Likes: 0
Re: Why does C5 like gas on exit? (BlackZ06)
Jon,
In reference to ...
I agree to a point. You are changing the front tire loading dramatically, which changes the lateral force, BUT other things are going on: under hard acceleration, the limited slip diff tries to assure equal torque to each rear tire which tends to push the car straight ahead in spite of any lateral forces from the front. When you lift, you now have differential action available again, and you have an existing front slip angle (which you determined by the steering angle you cranked in) which, as load increases rapidly, causes lots of lateral force at the front just because of the increase in normal force (load) on the fronts, which could be about 325 lbs. at 1 g longitudinal acceleration. Combining this with the loss of straight line thrust from the "locked" rear end and voila'...spin city!
While the Corvette's limited slip diff may contribute slightly to the fact that the car tends to understeer under hard acceleration, this phenomena will work with any car .... front wheel drive, rear wheel drive (limited slip or standard diff), even 4 wheel drive.
At a car control clinic I've attended, they lay oout the following cones (as seen from above:
+ + + +
+ + + +
+ + + +
+ + + +
The two rows of cones are about 100 feet apart. The driver is asked to get his car driving in a circle so that they can maintain a constant throttle and steering input and the car is driving through the two lanes (the lanes are quite wide) as a part of the circle.
+ + + +
+ + + +
+ +
+ + + +
+ + + +
Now, the two added cones shown above are pointed out to the driver. These cones are outside the circle the driver is following. The driver is informed that they must now drive so that they include the outside cones (effectively driving in an ellipse) WITHOUT CHANGING THE ANGLE OF THE STEERING WHEEL currently used to drive the circle.
Again, front wheel drive, rear wheel drive, whatever, the driver can do what seems to be impossible by using weight transfer to throttle steer the car. As they come through the upper line of cones they have to accelerate to understeer the car. It will "straighten out" somewhat and drive out toward the outer cone on the right. Once they come up to the cone, they come off the accelarator and the car will oversteer around the cone. As the car comes around they get back on the throttle and "steer" the car toward and through the (in my picture) lower row of cones.
OK, when you add throttle to "understeer" the RWD car you are unloading the front due to weight transfer and you are "pushing" the car straight ahead. I'll buy a combination of those. Witha FWD car, acceleration decreases the lateral force (Traction Circle) so understeer occurs.
====================
Also, I'm not following your math. Look at the body movement in a Corvette that is accelerating or cornering hard. It takes hundreds of pounds of force to move the body that much. See how far your front end comes up when you hit the loud pedal and then try lifting the nose that much in your driveway. It is far more than the 60 pounds your math implies. If you look at this picture .....
<img src=" http://www.bearhead.com/IMG_9683.JPG " border=0>
There is no way you can get your Corvette to lean that far over without many hundreds of pounds of force ... A 200 pound driver sitting in the car created no where near the lean you are seeing in this picture. All of that force is going into the tires.
Weight transfer depends ONLY on vehicle weight, acceleration, CG height and either wheelbase for longitudinal transfer or track for lateral transfer. Even if the suspension were bolted solid (kart) the weight transfer is the same.
Body roll of the sprung mass depends on CG height, roll axis height and acceleration and those things (springs and A/R bars) resisting it. Body roll doesn't effect weight transfer. OK, if the CG moves enough there could be a few pounds, but effectively it's negligible in a car. Very tall truck and hay wagons are a different story. If you had VERY soft springs and no A/R bars you could have many degrees of body roll but no more weight transfer.
The C5 has very low roll centers, like a few inches front and a few more rear, so there is maybe a 12 or 14 inch moment arm for body roll. At .9 g that's about 2700 lb-ft acting on the (3000 lb) sprung mass to roll it. Lateral weight transfer at .9 g (3500 lb gross) is a little over 1000 lbs total.
That seems counter-intuitive to some folks.
Have you noticed that if you raise the vehicle's sprung mass (hard to raise the unsprung and still keep the car on the ground) a lot, you get more weight transfer? CG height increase and shorter wheelbase cause that.
How come a Top Fuel dragster doesn't always flip backward at the 4 g launch? With a 25 ft (300 in) wheel base and a 15 inch CG, and a 2200 lb weight, there is about (2200 x 3.0 x 15/300) = 440 lb of weight transfer off the fronts. Cut that wheelbase to 120 inches and the transfer becomes 1100 lbs.
Keep her shiny side up ... and a spell check ... preview function would be GREAT ....
Hey, fun to debate "real world" versus "theory" ... huh ?? :cheers:
Steve
[Modified by BlackZ06, 7:25 AM 2/9/2004]
In reference to ...
I agree to a point. You are changing the front tire loading dramatically, which changes the lateral force, BUT other things are going on: under hard acceleration, the limited slip diff tries to assure equal torque to each rear tire which tends to push the car straight ahead in spite of any lateral forces from the front. When you lift, you now have differential action available again, and you have an existing front slip angle (which you determined by the steering angle you cranked in) which, as load increases rapidly, causes lots of lateral force at the front just because of the increase in normal force (load) on the fronts, which could be about 325 lbs. at 1 g longitudinal acceleration. Combining this with the loss of straight line thrust from the "locked" rear end and voila'...spin city!
While the Corvette's limited slip diff may contribute slightly to the fact that the car tends to understeer under hard acceleration, this phenomena will work with any car .... front wheel drive, rear wheel drive (limited slip or standard diff), even 4 wheel drive.
At a car control clinic I've attended, they lay oout the following cones (as seen from above:
+ + + +
+ + + +
+ + + +
+ + + +
The two rows of cones are about 100 feet apart. The driver is asked to get his car driving in a circle so that they can maintain a constant throttle and steering input and the car is driving through the two lanes (the lanes are quite wide) as a part of the circle.
+ + + +
+ + + +
+ +
+ + + +
+ + + +
Now, the two added cones shown above are pointed out to the driver. These cones are outside the circle the driver is following. The driver is informed that they must now drive so that they include the outside cones (effectively driving in an ellipse) WITHOUT CHANGING THE ANGLE OF THE STEERING WHEEL currently used to drive the circle.
Again, front wheel drive, rear wheel drive, whatever, the driver can do what seems to be impossible by using weight transfer to throttle steer the car. As they come through the upper line of cones they have to accelerate to understeer the car. It will "straighten out" somewhat and drive out toward the outer cone on the right. Once they come up to the cone, they come off the accelarator and the car will oversteer around the cone. As the car comes around they get back on the throttle and "steer" the car toward and through the (in my picture) lower row of cones.
OK, when you add throttle to "understeer" the RWD car you are unloading the front due to weight transfer and you are "pushing" the car straight ahead. I'll buy a combination of those. Witha FWD car, acceleration decreases the lateral force (Traction Circle) so understeer occurs.
====================
Also, I'm not following your math. Look at the body movement in a Corvette that is accelerating or cornering hard. It takes hundreds of pounds of force to move the body that much. See how far your front end comes up when you hit the loud pedal and then try lifting the nose that much in your driveway. It is far more than the 60 pounds your math implies. If you look at this picture .....
<img src=" http://www.bearhead.com/IMG_9683.JPG " border=0>
There is no way you can get your Corvette to lean that far over without many hundreds of pounds of force ... A 200 pound driver sitting in the car created no where near the lean you are seeing in this picture. All of that force is going into the tires.
Weight transfer depends ONLY on vehicle weight, acceleration, CG height and either wheelbase for longitudinal transfer or track for lateral transfer. Even if the suspension were bolted solid (kart) the weight transfer is the same.
Body roll of the sprung mass depends on CG height, roll axis height and acceleration and those things (springs and A/R bars) resisting it. Body roll doesn't effect weight transfer. OK, if the CG moves enough there could be a few pounds, but effectively it's negligible in a car. Very tall truck and hay wagons are a different story. If you had VERY soft springs and no A/R bars you could have many degrees of body roll but no more weight transfer.
The C5 has very low roll centers, like a few inches front and a few more rear, so there is maybe a 12 or 14 inch moment arm for body roll. At .9 g that's about 2700 lb-ft acting on the (3000 lb) sprung mass to roll it. Lateral weight transfer at .9 g (3500 lb gross) is a little over 1000 lbs total.
That seems counter-intuitive to some folks.
Have you noticed that if you raise the vehicle's sprung mass (hard to raise the unsprung and still keep the car on the ground) a lot, you get more weight transfer? CG height increase and shorter wheelbase cause that.
How come a Top Fuel dragster doesn't always flip backward at the 4 g launch? With a 25 ft (300 in) wheel base and a 15 inch CG, and a 2200 lb weight, there is about (2200 x 3.0 x 15/300) = 440 lb of weight transfer off the fronts. Cut that wheelbase to 120 inches and the transfer becomes 1100 lbs.
Keep her shiny side up ... and a spell check ... preview function would be GREAT ....
Hey, fun to debate "real world" versus "theory" ... huh ?? :cheers:
Steve
[Modified by BlackZ06, 7:25 AM 2/9/2004]
Safety Car
Joined: Mar 2002
Posts: 4,928
Likes: 1
Cruise-In V Veteran
St. Jude Donor '09
Re: Why does C5 like gas on exit? (Pipes)
This is a great thread! Fun reading...I need to print it out and take some serious time to read it.
From hands on (non- competition) experience - I'm 48 yrs old - everything I've ever driven likes some throttle input in a turn. This includes my shifterkart. I've always assumed it was due to suspension/chassis loading. In fact things can seem a little scary to me without some throttle input. FWIW.
Thanks for all the Excellent info.
:yesnod:
From hands on (non- competition) experience - I'm 48 yrs old - everything I've ever driven likes some throttle input in a turn. This includes my shifterkart. I've always assumed it was due to suspension/chassis loading. In fact things can seem a little scary to me without some throttle input. FWIW.
Thanks for all the Excellent info.
:yesnod:
Melting Slicks
Joined: Aug 2003
Posts: 2,010
Likes: 1,346
From: Des Plaines, Il
Re: Why does C5 like gas on exit? (binksZ06)
If you want a handle on racing dynamics try reading "Going Faster" by Skip Barber. Aside from how to apex, it goes into detail about weight transfer, the traction circle and how it affects your car.
