How much sprung weight is 1lb of unsprung weight equivalent to in terms of speed? I heard the equation once long ago but have since forgotten it...anyone out there remember this?

 

i dont know of an equation because there are so many variables. it would make a lot less of a difference if you have more tourque.

 

Also remember that the location of the weight on the vehicle has a lot to do with it as well.

 

I believe its 10 lbs. 1 unsprung=10 sprung

And every 100lbs you take off is equal to .1 seconds in the quarter.

 

The sprung versus unsprung makes a big difference if it is rotating or just suspension weight. I've heard the 1:10 for rotating weight but would hesitate to quote it myself since I have not seen any good proof of it. Non-rotating unsprung weight has an effect on ride and handling but is just weight as far as acceleration goes.

As far as the 100lbs=.1 sec, that varies too much based on the power to weight you started with. Remember the SCC where they tore apart the Nissan? They dropped several seconds but did not drop 2000lbs off the car.

 

most equations like that only work alright under certain circumstances.. i think SCC took that one to an extreme!

 

My exp with weight vs time.
My EX (2300, no spare, appx) + me 200 = 2500
Stock ZC, 2.4 60, ran a 10.42 in the 1/8
Add in a friend, 150, ran a 10.68
So roughly in the 1/4, 150lb extra weight would make me run about .38 sec slower.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by dmotoguy &raquo;</TD></TR><TR><TD CLASS="quote">most equations like that only work alright under certain circumstances.. i think SCC took that one to an extreme!</TD></TR></TABLE>

That they did they ruined a perfectly good daily driver!

I don't know how much wieght i have taken out of my car but i know it is a lot but i don't have timeslips to show anything just a kill list from the street don't do that anymore but i am trying to get My Si around 2500 with cage and me in it for next season i hope i can do it

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nojoke &raquo;</TD></TR><TR><TD CLASS="quote">
And every 100lbs you take off is equal to .1 seconds in the quarter.</TD></TR></TABLE>

that is not true, there is alot more to it then just dropping 100 lbs and bam your .1 second faster.

 

Maybe I'm being silly (only had 3hrs of sleep), but I don't see how changing sprung and unsprung weight makes a difference in how fast the car is. It will definately make a difference in the suspension and handling, but for straight line driving, shouldn't be a difference (depending on where the weight is located). I know that losing weight makes you faster, but whether you lose 10lbs of sprung or 10lbs of unsprung shouldn't make a difference for straight line driving.

However I would imagine that sprung/unsprung could make a difference in traction...

Now, if you lose rotating mass (i.e. lighter flywheel/clutch, lightweight wheels, etc.), then that will definately make a difference.

 

Can someone explain the difference between sprung and unsprung weight? All weight should be the same as long as it isn't rotating. I worked out the equations to figure out how much rotating weight slows you down compared to fixed weight. There is too many variables involved, size of rotating object, where the weight is located (moment of inertia, most wheels have the weight towards the outside), also, what speed you are accelerating at.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Cyphear &raquo;</TD></TR><TR><TD CLASS="quote">Can someone explain the difference between sprung and unsprung weight?...</TD></TR></TABLE>Unsprung weight is the stuff that has to follow the wheel up & down over bumps. Like the brake calipers, steering knuckles, part of the shocks & control arms.

But if you're talking about acceleration - that's rotating weight. Moment of inertia, like you said. This thread has lots of confusion between those different things... Unsprung weight can influence acceleration by changing how the tires contact, bounce & chatter, but that's another thing.

 

Thanks JimBlake. I wouldn't think unsprung weight would make any difference. Can someone explain why it would?

 

Rotating weight makes the difference. Sounds like you already know what moment of inertia is all about.

I suppose unsprung weight can make a little difference. If the road's not smooth, low unsprung weight might give you better traction because the suspension can follow the bumps easier. Maybe unsprung weight can also influence wheel hop??

 

Thanks Jimblake, heh I have in fact been asking about rotating mass, rather than unsrpung weight....oops, brain fart.....anyways, thanks guys for all the helpful discussion, helped me out quite a bit.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by scorched0 &raquo;</TD></TR><TR><TD CLASS="quote">... heh I have in fact been asking about rotating mass, rather than unsrpung weight...</TD></TR></TABLE>If you do the math, one pound right out at the tread surface is worth 2 pounds of non-rotating mass. As the mass is located closer to the center of the wheel, it approaches the worth of simple non-rotating mass.