Weight Savings? How much can you shed.
03-01-05, 03:24 PM
#26
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Originally Posted by DaleClark
The stock driveshaft is actually INCREDIBLY lightweight for what it is. Going to a carbon fiber driveshaft would be quite costly (like $500-1000) and realistically only save a few pounds - not a lot of bang for the buck there.
Makes more sense on cars with goofy multi-piece driveshafts.
Dale
Makes more sense on cars with goofy multi-piece driveshafts.
Dale
03-01-05, 03:33 PM
#27
RX-7 Bad Ass
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Originally Posted by Gargamel
every lb you take off rotating mass is like taking 7 lbs off the vehicle itself.
http://www.sportcarmotion.com/drivetrain.htm
$842, thank you very much.
Dale
03-01-05, 03:48 PM
#28
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Originally Posted by Gargamel
every lb you take off rotating mass is like taking 7 lbs off the vehicle itself.
03-01-05, 04:28 PM
#29
Originally Posted by Gargamel
every lb you take off rotating mass is like taking 7 lbs off the vehicle itself.
If you don't already have the lightest flywheel you can get I wouldn't spend a cent on a CF driveshaft.
Lightweight wheels would be a better place to save weight.
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03-01-05, 05:09 PM
#30
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Originally Posted by RedR1
Please don't flame as i'm always learning more, but shouldn't we try to get the car at a 50/50 (or as close to) weight balance when moving, therefore try to get a 53% front bias? As the car accelerates wight shifts. . . well im sure you know the physics and what not so theres no need to cover that.
Is your rear weight bias personal prefference? Please shed light if you do not mind.
Is your rear weight bias personal prefference? Please shed light if you do not mind.
Last edited by BATMAN; 03-01-05 at 05:34 PM.
03-01-05, 05:25 PM
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The spare tire in the trunk might seem like dead weight, but average person in this country probably is carrying a spare tire with about the same weight around their middle. So instead losing the tire in your car, get on a scale and look in the mirror. We could also demand that our girlfriends lose a few pounds to help, or maybe just lose the girlfriend, heck who can afford one of those if you drive a Rx-7?
03-01-05, 09:15 PM
#32
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Originally Posted by turbojeff
Depends largely on the diameter of the rotating component. Since the driveshaft is very long and thin the difference rotating interia is significantly below that of a lightweight flywheel.
If you don't already have the lightest flywheel you can get I wouldn't spend a cent on a CF driveshaft.
Lightweight wheels would be a better place to save weight.
If you don't already have the lightest flywheel you can get I wouldn't spend a cent on a CF driveshaft.
Lightweight wheels would be a better place to save weight.
If I went to a 16 lb 18" (don't ask which one) and ran the same tire (roughly 30 lbs for 275), my net reduction in weight would only be 8 lbs or a 15% reduction on each corner. Anyone think that would be significant enough to justify switching wheels?
03-01-05, 09:51 PM
#33
Originally Posted by pianoprodigy
Yep. I think my 24 lb 18s are hurting my performance; however, I'm not sure how much.
If I went to a 16 lb 18" (don't ask which one) and ran the same tire (roughly 30 lbs for 275), my net reduction in weight would only be 8 lbs or a 15% reduction on each corner. Anyone think that would be significant enough to justify switching wheels?
If I went to a 16 lb 18" (don't ask which one) and ran the same tire (roughly 30 lbs for 275), my net reduction in weight would only be 8 lbs or a 15% reduction on each corner. Anyone think that would be significant enough to justify switching wheels?
When I put my stock 16" wheels with race tires on them I can really feel the car is faster than with the 17" Fikses. There is both a significant weight difference and a diameter difference. The rears 17" wheel/tire combo is about 10lbs heavier each and the gearing is effectively ~3% taller IIRC.
03-02-05, 12:24 AM
#34
Super Snuggles
To estimate the difference in performance of a wheel of one diameter vs. one of another diameter, use the formula: I = M (R^2)
I = Inertia
M = Mass
R = Radius
The stock 16x8s are about 15 lbs., give or take.
I = 15 (8^2) = 960
For a 17" wheel not to affect acceleration or braking performance...
960 / (8.5^2) = 13.3 lbs.
For an 18" wheel...
960 / (9^2) = 11.9 lbs.
But how much does the extra inertia of a heavier and larger diameter wheel affect performance? Well, here's what Grassroots Motorsports apparently had to say on the subject...
I = Inertia
M = Mass
R = Radius
The stock 16x8s are about 15 lbs., give or take.
I = 15 (8^2) = 960
For a 17" wheel not to affect acceleration or braking performance...
960 / (8.5^2) = 13.3 lbs.
For an 18" wheel...
960 / (9^2) = 11.9 lbs.
But how much does the extra inertia of a heavier and larger diameter wheel affect performance? Well, here's what Grassroots Motorsports apparently had to say on the subject...
Weight Vs Acceleration.
To find out what a set of lightweight wheels would be worth in terms of speed and elapsed time, 8 pound steel discs were attached to a set of 46 pound wheels and tires in an effort to bring them to the weight (and moment of inertia) of the wheels they were replacing. (note: base line wheels were 17x9, weighing 54 lbs. with tires)
The car was also equipped with removable ballast bolted to the roll cage at about the car’s center of gravity. This meant adding or removing ballast had no effect on the weight transfer or front to rear distribution.
The car was initially ballasted to bring the weight with fuel, driver and wheel discs to 2,000 lbs. Before the second set of runs, the four eight pound steel discs were removed. To keep the car’s weight consistent at 2,000 pounds, 32 pounds of ballast were added.
For the third test, the 32 Lbs of extra ballast were removed giving us a 1,968 lbs. car. For the final test the discs were placed back on the wheels, while more internal ballast was removed until the car matched the times produced by the lightweight wheels.
Our testing revealed a few facts. First, the wheels, even on this somewhat low-powered test car, had a very measurable effect.
Fitting the lightweight wheels and restoring the weight as internal ballast showed that the reduced wheel moment of inertia alone was worth more then half a tenth on the quarter mile. At the end of the quarter mile, this translated into a lead of 6.7 feet over the base like vehicle. Dropping the weight from the car by 32 pounds (1,968 pounds total) while running the lightweight wheels further reduced the elapsed time by a solid tenth, resulting in a 13.1 foot lead over our baseline runs.
Now how much weight would the car have to lose to match the gains seen by just the lightweight wheels? With the wheel discs reinstalled, we had to drop the car’s sprung weight by 60 pounds to match the performance gains seen by losing the 32 pounds of rotating weight.
What we can say here is that weight removed from the wheels as at least a 70% more positive effect on performance than weight removed from the sprung part of the vehicle.
Baseline: heavy wheels, 2,000-pound car
average E.T.:14.7303 sec
average speed:88.98 mph
Light wheels, 2,000 pound car
average E.T. 14.6973 sec
average speed: 89.17 mph
improvements over baseline: 0.051 sec, .019 mph, 6.7 feet
Light wheels, 1,968 pound car
average E.T.: 14.6303 sec
average speed: 89.52 mph
improvement over baseline: 0.1000 sec, 0.54 mph, 13.1 feet.
Heavy wheels, 1,940 pound car
Average E.T: 14.6307
Average speed: 89.65 mph
Improvents over baseline: 0.996 sec., .67 mph, 13.1 feet.
SO, if you increase the size of the wheel, you are in effect increasing the weight of that wheel, unless the wheels are substantually lighter than stock. But the effect is not all that much in the grand scheme of things, unless you are hunting down that last .1 second...
To find out what a set of lightweight wheels would be worth in terms of speed and elapsed time, 8 pound steel discs were attached to a set of 46 pound wheels and tires in an effort to bring them to the weight (and moment of inertia) of the wheels they were replacing. (note: base line wheels were 17x9, weighing 54 lbs. with tires)
The car was also equipped with removable ballast bolted to the roll cage at about the car’s center of gravity. This meant adding or removing ballast had no effect on the weight transfer or front to rear distribution.
The car was initially ballasted to bring the weight with fuel, driver and wheel discs to 2,000 lbs. Before the second set of runs, the four eight pound steel discs were removed. To keep the car’s weight consistent at 2,000 pounds, 32 pounds of ballast were added.
For the third test, the 32 Lbs of extra ballast were removed giving us a 1,968 lbs. car. For the final test the discs were placed back on the wheels, while more internal ballast was removed until the car matched the times produced by the lightweight wheels.
Our testing revealed a few facts. First, the wheels, even on this somewhat low-powered test car, had a very measurable effect.
Fitting the lightweight wheels and restoring the weight as internal ballast showed that the reduced wheel moment of inertia alone was worth more then half a tenth on the quarter mile. At the end of the quarter mile, this translated into a lead of 6.7 feet over the base like vehicle. Dropping the weight from the car by 32 pounds (1,968 pounds total) while running the lightweight wheels further reduced the elapsed time by a solid tenth, resulting in a 13.1 foot lead over our baseline runs.
Now how much weight would the car have to lose to match the gains seen by just the lightweight wheels? With the wheel discs reinstalled, we had to drop the car’s sprung weight by 60 pounds to match the performance gains seen by losing the 32 pounds of rotating weight.
What we can say here is that weight removed from the wheels as at least a 70% more positive effect on performance than weight removed from the sprung part of the vehicle.
Baseline: heavy wheels, 2,000-pound car
average E.T.:14.7303 sec
average speed:88.98 mph
Light wheels, 2,000 pound car
average E.T. 14.6973 sec
average speed: 89.17 mph
improvements over baseline: 0.051 sec, .019 mph, 6.7 feet
Light wheels, 1,968 pound car
average E.T.: 14.6303 sec
average speed: 89.52 mph
improvement over baseline: 0.1000 sec, 0.54 mph, 13.1 feet.
Heavy wheels, 1,940 pound car
Average E.T: 14.6307
Average speed: 89.65 mph
Improvents over baseline: 0.996 sec., .67 mph, 13.1 feet.
SO, if you increase the size of the wheel, you are in effect increasing the weight of that wheel, unless the wheels are substantually lighter than stock. But the effect is not all that much in the grand scheme of things, unless you are hunting down that last .1 second...
03-02-05, 01:19 PM
#36
Originally Posted by Tomarx7
The spare tire in the trunk might seem like dead weight, but average person in this country probably is carrying a spare tire with about the same weight around their middle. So instead losing the tire in your car, get on a scale and look in the mirror. We could also demand that our girlfriends lose a few pounds to help, or maybe just lose the girlfriend, heck who can afford one of those if you drive a Rx-7?
03-02-05, 04:07 PM
#38
FD = Mr. Toad's Wild Ride
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Hmm, the GRM study has me still pondering, does the increase MOI of the wheel have a noticable effect over ballast weight if the car has enough power to be at the limits of traction? Gut feeling, yes -- but it would be nice to see some data from somebody that can actually run consistant drag times (i.e. asking Joe at the strip to take the spinners off his F body and run again probably isn't giving us real results).
09-06-06, 12:44 PM
#39
I know this is an old thread, but I like giving new members a chance to see what sort of things have been discussed already. I weighed my car yesterday, and was very pleased with the results:
Empty: 2691 lbs (without driver or spare tire).
LF: 721, RF: 665 (52% front)
LR: 640, RR: 665 (48% rear)
Loaded: 2861 lbs (with 143lb driver and 27lbs of spare tire & jack).
LF: 767, RF: 672 (50% front)
LR: 709, RR: 713 (50% rear)
Here are the mods that got me there:
Chassis:
1994 Base model, no sunroof, single oil cooler, stock stereo/cassette player and speakers (not the Bose system). The fuel tank was about 40% full, just below half a tank.
Suspension & Wheels:
Avon 245/45R16 tires. Racing Beat front swaybar, Mazdaspeed sway bar mounts, Tripint endlinks. Stock shocks, springs, wheels and rear swaybar.
Engine Bay:
Odyssey PC680 battery, Megan Racing downpipe (Jet-Hot coated). Removed Cruise Control. Everything else is stock including radiator, air pump, AC & power steering, exhaust.
Interior: all stock. Base model has cloth not leather. Autometer boost gauge might weigh 0.5 lbs. I haven't gotten around to removing the cruise control computer, but I doubt it weighs more than a pound.
For comparison, my friend's '86 Mustang LX weighed in around 3100lbs (about a 60/40 balance), and the corner scales showed my weight as being within 3 lbs of what my bathroom scale says so I trust their accuracy.
Someday I might shoot for 2600 lbs, I hope I can get there by removing the AC, PS and air pump, and installing lightweight seats.
-s-
Empty: 2691 lbs (without driver or spare tire).
LF: 721, RF: 665 (52% front)
LR: 640, RR: 665 (48% rear)
Loaded: 2861 lbs (with 143lb driver and 27lbs of spare tire & jack).
LF: 767, RF: 672 (50% front)
LR: 709, RR: 713 (50% rear)
Here are the mods that got me there:
Chassis:
1994 Base model, no sunroof, single oil cooler, stock stereo/cassette player and speakers (not the Bose system). The fuel tank was about 40% full, just below half a tank.
Suspension & Wheels:
Avon 245/45R16 tires. Racing Beat front swaybar, Mazdaspeed sway bar mounts, Tripint endlinks. Stock shocks, springs, wheels and rear swaybar.
Engine Bay:
Odyssey PC680 battery, Megan Racing downpipe (Jet-Hot coated). Removed Cruise Control. Everything else is stock including radiator, air pump, AC & power steering, exhaust.
Interior: all stock. Base model has cloth not leather. Autometer boost gauge might weigh 0.5 lbs. I haven't gotten around to removing the cruise control computer, but I doubt it weighs more than a pound.
For comparison, my friend's '86 Mustang LX weighed in around 3100lbs (about a 60/40 balance), and the corner scales showed my weight as being within 3 lbs of what my bathroom scale says so I trust their accuracy.
Someday I might shoot for 2600 lbs, I hope I can get there by removing the AC, PS and air pump, and installing lightweight seats.
-s-
Last edited by scotty305; 09-06-06 at 12:55 PM.
09-06-06, 10:26 PM
#40
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Originally Posted by RevZempoe
what's the advantage of moving the battery to the back other than engine room? Sorry, i'm new to all of it and I've heard of people doing that. Isn't the best ground the firewall?
12-30-12, 04:25 PM
#41
the fd is a front engine rear drive car. as such, when attempting to lower road race lap times or canyon carve on the street the primary challenge is making the rear end stick from apex out. the more rear weight the better.
the first one on the gas in a corner wins... you can't get on the gas if you have no rear traction.
remember that unlike the front tires, the rear tires not only support roughly half the vehicle weight but drive the car forward.
that's why we run larger rear tires, lower rear air pressure, softer rear bar, softer rear springs and shocks. all to attain more rear grip.
additional vertical load from a greater % of rear weight helps plant the tires.
the front of the vehicle is most important from corner entry to the apex. less weight in front makes it easier for the front tires to change the direction of the car. less front weight equals less mass to change direction. less front weight creates better braking just before corner entry as you can dial in more rear brakes so as not to overload the front tires just before you need them the most at corner entry.
if you are just going to the store 50/50 is excellent. if you use your car more aggressively you want rear weight bias.
howard coleman
the first one on the gas in a corner wins... you can't get on the gas if you have no rear traction.
remember that unlike the front tires, the rear tires not only support roughly half the vehicle weight but drive the car forward.
that's why we run larger rear tires, lower rear air pressure, softer rear bar, softer rear springs and shocks. all to attain more rear grip.
additional vertical load from a greater % of rear weight helps plant the tires.
the front of the vehicle is most important from corner entry to the apex. less weight in front makes it easier for the front tires to change the direction of the car. less front weight equals less mass to change direction. less front weight creates better braking just before corner entry as you can dial in more rear brakes so as not to overload the front tires just before you need them the most at corner entry.
if you are just going to the store 50/50 is excellent. if you use your car more aggressively you want rear weight bias.
howard coleman
Now this is interesting . and if possible if somethings could be elaborated on . for example .
A rear wing , when you are driving it pushes down on the rear , giving it a rear weight bias . which gives you more grip exiting a high speed corner and the likes , BUT
What of a slow speed corner say a 30-40 mph tight corner on a mountain . I know if you have enough angle on a wing it should still push the cars rear enough to give it some rear grip ,
NOW my question is .. if a car has a wing is it ok for the car to have more front bias IE removing the glass windshield , all the plastics , the spare , replacing hte hatch with Lexan , and carbon fiber . Would work towards lightening the car overall but bringing hte weight bias forward .
so what can be done in this situation .
A wing? , But during lower speeds its much less effective .
What abotu reverse rake . from what I've read about corner balancing , you play around with the ride height to disperse the weight evenly . And you do that by lowering said corner . Lower it is the more weight it carries .
So could you lower the rear of hte car to give it more grip out of the corner?
12-30-12, 07:48 PM
#42
tard of teh century
Now this is interesting . and if possible if somethings could be elaborated on . for example .
A rear wing , when you are driving it pushes down on the rear , giving it a rear weight bias . which gives you more grip exiting a high speed corner and the likes , BUT
What of a slow speed corner say a 30-40 mph tight corner on a mountain . I know if you have enough angle on a wing it should still push the cars rear enough to give it some rear grip ,
NOW my question is .. if a car has a wing is it ok for the car to have more front bias IE removing the glass windshield , all the plastics , the spare , replacing hte hatch with Lexan , and carbon fiber . Would work towards lightening the car overall but bringing hte weight bias forward .
so what can be done in this situation .
A wing? , But during lower speeds its much less effective .
What abotu reverse rake . from what I've read about corner balancing , you play around with the ride height to disperse the weight evenly . And you do that by lowering said corner . Lower it is the more weight it carries .
So could you lower the rear of hte car to give it more grip out of the corner?
A rear wing , when you are driving it pushes down on the rear , giving it a rear weight bias . which gives you more grip exiting a high speed corner and the likes , BUT
What of a slow speed corner say a 30-40 mph tight corner on a mountain . I know if you have enough angle on a wing it should still push the cars rear enough to give it some rear grip ,
NOW my question is .. if a car has a wing is it ok for the car to have more front bias IE removing the glass windshield , all the plastics , the spare , replacing hte hatch with Lexan , and carbon fiber . Would work towards lightening the car overall but bringing hte weight bias forward .
so what can be done in this situation .
A wing? , But during lower speeds its much less effective .
What abotu reverse rake . from what I've read about corner balancing , you play around with the ride height to disperse the weight evenly . And you do that by lowering said corner . Lower it is the more weight it carries .
So could you lower the rear of hte car to give it more grip out of the corner?
Whether you need lots of wing or not is track and car dependent. You should prioritize the corners first and then worry about whether high speed, low speed or mid speed corners are most important. Aero balance is used a lot of times to make up for a bad weight balance but as you said, that weight balance will still screw you over at low speeds. Ideally you should shoot for an ideal balance with an ideal aero balance as well but it's rare anybody ever gets to play with ideals. Formula 1 currently is mandated to about a max of 55% rear biased and any team I've seen bring it up in interviews has said that they would prefer more weight on the rear for an ideal balance but they are making do with what they can.
You can always do as the front engine production type GT cars do and move the transmission to the rear.
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