View Full Version : Just exactly how much would 100 extra lbs make?

gran racing
07-20-2004, 08:10 PM
With all of this talk of PCAs and car weights, I'm curious how much 100 lbs (and other increments) effects the car's performance. Yes, I totally understand the obvious physics and recognize that weight does impact performance in several area.

For example, people have talked about adding weight to the RX7s to get it into ITB. Many think that at its current weight, it would simply be too fast.

How much of a difference would an extra 100 lbs make? To make things a little simpler, lets assume the weight will be put in the drivers side floor.

I'm just trying to get a better understanding of how much this would impact a car. What results has World Challenge seen when increments of weight has been added? At various tracks, what was the time difference?

Dave Gran
'87 Honda Prelude

07-20-2004, 08:35 PM
As always depends on track and car.

A really light ITC car with 90HP will see a much bigger difference than a 200HP/2800# ITS car.

If the track has a very narrow range of speeds it won't matter as much as a track with lots of really tight sections and long straights and/or hills.

The smaller the LB/HP ratio the less impact. The more the weight must be accelerated and decelerated the bigger the difference.

If you are looking for a time difference, way too many variables to put a concrete number on it. I'd venture anywhere from .2 second to 2 seconds a lap---that's a huge range, it is probably pretty safe guess and useless for real meaningful conversation.

07-20-2004, 11:40 PM

My car is already 100 lbs over. When I built my car I considered safety first and then performance second and hence the extra weight. I wish I could figure out a way to loose some of it.

Sure would be interesting to see what my car could do with a 120 lb driver.

Rick Thompson #99 IT7

07-21-2004, 07:26 AM
On a 2400lb car, I would say only fractions of a second on a momentum track. More along the lines of .1 or .2 seconds.

07-21-2004, 07:36 AM
my guess is jake is right for one lap, but due to the cumlative abuse on the tires i think it would be higher over the course of a 20 lap race.

07-21-2004, 07:37 AM
Good point. The larger effect would be the increase wear on the tires and chance of brake fade.

07-21-2004, 07:41 AM
On the bright side, being able to put ballast in the passenger side - could help out in all the right corners in a place like LRP. Also, putting back stuff in the truck (spare, jack, etc.) could help F/R balance on a Front heavy car. It may just work itself out.

When I used to autocross, I swear I ran better times with a passenger. My 200#'s on the left of a lightweight car made right corners nasty. A passenger, balanced it out nicely.

gran racing
07-21-2004, 08:37 AM
I realize there is no magic answer and depends on car to car.

At the same time, I really don't know how some of the PCAs and weight adjustments will impact the performance of a car (in a way that could be evaluated other then a guess).

Dave Gran
'87 Honda Prelude

07-21-2004, 02:41 PM
Golly, maybe we should use the same competition adjustments like the CRB uses for Production. http://Forum.ImprovedTouring.com/it/smile.gif http://Forum.ImprovedTouring.com/it/confused.gif http://Forum.ImprovedTouring.com/it/biggrin.gif http://Forum.ImprovedTouring.com/it/wink.gif

07-21-2004, 06:58 PM
Not relevant, but I remember a while back reading that a gallon of fuel cost an F1 car over a tenth of a second on a short course....

Which would explain why the F1 grids are so affected this year by fuel and pit stop strategy.

Jake Gulick
CarriageHouse Motorsports
ITA 57 RX-7
New England Region
[email protected]