C5 and unsprung weight
02-05-2004, 11:23 AM
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C5 and unsprung weight
....coming from the import world unsprung weight was a major concern. I just got some new wheels n tires and they are slightly heavier then the stockers. However, on this car driving around with them on didnt feel all that different.
Then I was reading another car forum and came across this article from the May 03 issue of Grassroots Motorports. Its called The Weighing Game. I got the highlights of it.
"Crankshaft Dampers:
"That round lump of steel and rubber on the front of your crank is not a harmonic balancer. There's no such thing. You can not balance harmonics. This piece is a crankshaft damper or torsional damper. It is commonly accepted that having the lightest possible damper may not be good for crank life, although it will allow the engine to deliver it's best performance. The reality of the situation though, is that in terms of power, the reverse is almost always true. A modern, quality camshaft profile is based on highly complex mathematical formulate intended to produce a profile that will generate a smooth, minimal-vibration lift curve at the valve. On a 400hp HP 5.0 motor, swapping out the 14-ounce aluminum crank pulley (definately not a stock pulley) for a 15-lb, but highly functional damper increased output by more than 11hp. In addition to less power, the lighter pulley that was removed allwoed the crank to flex as much as 250% more than with the damper. All this flex adds up to broken cranks, especially for inline sixes (BMW reference I'm sure). Okay, to sum up crank dampers, the rule here is simple: forget the weight and just make sure you get one that does what it's suppose to do- dampen. This will allow the car to go faster, longer."
Flywheels:
"The situation on the other end of the crank presents a dramatically different picture. Here we can shed some weight. During the summer of 2002 I spent a week with Fidanza Flywheels, dyno and track testing flwheels of different weights in three different Mustang 5.0 with power ranging from 390hp to 560hp. Out on the drag strip, the lightweight rotating assembly (20lb lighter clutch and flywheel) delivered more than tenth of second reduction in ET and almost 1mph of extra trap speed."
Anyway, I'm wondering what the ill effects of having heavier wheels on my car is for accel, braking and MPG. While .1 and 1 sec ET may win a race, it seems like it is an awefuly small # to be worrying about when it comes to just a day to day driver.
[Modified by eRiCdWoNg, 11:25 AM 2/5/2004]
Then I was reading another car forum and came across this article from the May 03 issue of Grassroots Motorports. Its called The Weighing Game. I got the highlights of it.
"Crankshaft Dampers:
"That round lump of steel and rubber on the front of your crank is not a harmonic balancer. There's no such thing. You can not balance harmonics. This piece is a crankshaft damper or torsional damper. It is commonly accepted that having the lightest possible damper may not be good for crank life, although it will allow the engine to deliver it's best performance. The reality of the situation though, is that in terms of power, the reverse is almost always true. A modern, quality camshaft profile is based on highly complex mathematical formulate intended to produce a profile that will generate a smooth, minimal-vibration lift curve at the valve. On a 400hp HP 5.0 motor, swapping out the 14-ounce aluminum crank pulley (definately not a stock pulley) for a 15-lb, but highly functional damper increased output by more than 11hp. In addition to less power, the lighter pulley that was removed allwoed the crank to flex as much as 250% more than with the damper. All this flex adds up to broken cranks, especially for inline sixes (BMW reference I'm sure). Okay, to sum up crank dampers, the rule here is simple: forget the weight and just make sure you get one that does what it's suppose to do- dampen. This will allow the car to go faster, longer."
Flywheels:
"The situation on the other end of the crank presents a dramatically different picture. Here we can shed some weight. During the summer of 2002 I spent a week with Fidanza Flywheels, dyno and track testing flwheels of different weights in three different Mustang 5.0 with power ranging from 390hp to 560hp. Out on the drag strip, the lightweight rotating assembly (20lb lighter clutch and flywheel) delivered more than tenth of second reduction in ET and almost 1mph of extra trap speed."
Anyway, I'm wondering what the ill effects of having heavier wheels on my car is for accel, braking and MPG. While .1 and 1 sec ET may win a race, it seems like it is an awefuly small # to be worrying about when it comes to just a day to day driver.
[Modified by eRiCdWoNg, 11:25 AM 2/5/2004]
02-05-2004, 03:04 PM
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Re: C5 and unsprung weight (eRiCdWoNg)
When speaking of a daily driver, I doubt you would be able to tell any difference in acceleration, braking or fuel economy with different sets of wheels/tires that were within a couple pounds per wheel of each other. However, these are not the only things adversely affected. The extra unsprung weight also taxes your suspension, forcing the springs and shocks to attempt to control the now heavier wheels as they travel through the normal up/down suspension motions. I'd think you might notice a difference in handling, especially over bumpy surfaces.
02-05-2004, 04:48 PM
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Re: C5 and unsprung weight (Duck916)
Just got an alignment done.... hopefully it holds this time now that I have a non-worn rear right tie rod.
the car does drive better, it drives straight and doesnt pull for a change. Woo hoo. Ther performance issue Im going to have to try to investigate further, my 25 mile commute to school today on the highway it felt pretty good.
the car does drive better, it drives straight and doesnt pull for a change. Woo hoo. Ther performance issue Im going to have to try to investigate further, my 25 mile commute to school today on the highway it felt pretty good.
02-06-2004, 09:49 AM
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Re: C5 and unsprung weight (eRiCdWoNg)
[QUOTEAnyway, I'm wondering what the ill effects of having heavier wheels on my car is for accel, braking and MPG. While .1 and 1 sec ET may win a race, it seems like it is an awefuly small # to be worrying about when it comes to just a day to day driver.
[Modified by eRiCdWoNg, 11:25 AM 2/5/2004][/QUOTE]
You are right! As for rotating inertia (flywheel), remember that the engine is spinning about 10 times as fast as the wheels in first gear, and you don't do much fast acceleraton in 5th or 6th (or 4th in A4). Rotating inertia at engine speed is about 15 times as critical as inertia at wheel speed.
A couple of pounds is a small % of total unsprung weight at each wheel. Some non-EMT tires are that much lighter than the OEM's. If you go to larger dia wheels you move the mass concentration (rim and tire) farther out so that hurts rather than helps. Of course C6 has 18s and 19s.
Alignment and wheel offset is more critical.
[Modified by eRiCdWoNg, 11:25 AM 2/5/2004][/QUOTE]
You are right! As for rotating inertia (flywheel), remember that the engine is spinning about 10 times as fast as the wheels in first gear, and you don't do much fast acceleraton in 5th or 6th (or 4th in A4). Rotating inertia at engine speed is about 15 times as critical as inertia at wheel speed.
A couple of pounds is a small % of total unsprung weight at each wheel. Some non-EMT tires are that much lighter than the OEM's. If you go to larger dia wheels you move the mass concentration (rim and tire) farther out so that hurts rather than helps. Of course C6 has 18s and 19s.
Alignment and wheel offset is more critical.