Hatzenbach

Just out of curiosity, is there a rule of thumb how much your lap time improves by 100 lb saved, let's say on a 2 min track?

winders

There is no rule of thumb because there are too many variables.

zadar

What Winders said.
I can only tell my lap time is about 1sec slower when passenger is with me.

ace37

If you come up with one, it may break down if you significantly change weight, power to weight, tire compound, prep/equipment level, or aerodynamic setup. You might be able to do a lot of digging and use NASA results or something like that.

A lot of the street car rules of thumb for things like the quarter mile are based on a 3000-4000lb car with a 1:10 power to weight ratio, street tires, stock suspension, no aero, etc.

wanna911

This is about as close to a rule of thumb as you will get. An average size passenger (150-180 lbs) being worth about 1-1.5 seconseconds on an average 2.5 mile track.

winders

In what car? With what driver? On what track?

With some drivers, 180 lbs will make zero difference in their lap times.

There is no rule of thumb. The best you can say is that weight makes a difference. But you can't quantify the difference without considering all the variables. Even if you know all the variables, you still need to test to come up with a number.

Veloce Raptor

I agree that it varies. It is larger on tracks with more than minimal elevation change, and tracks with serious brake zones...

LexVan

Show me one Porsche driver that weighs 150 and I'll show you 20 that weigh +220.

Last year during the Mid-Ohio PCA event at Indy, I was taken out by an experienced CR in a Boxster Spyder, the driver said I cost him 1.5-2.0 seconds per lap. 215...6'3"....4.55.....run stopper.

wanna911

Had to account for the occasional girlfriend, wife, woman that rides too. Average range.

OlsenMotorsports

MAYBE a tenth of a second (driven back to back both at the ragged edge)

It's easy study professional motorsports and the BOP. Its common to see 50kg added and it really doesn't do anything to lap times. HP on the other hand is worth significantly more, (few tenths depending on what it is) and grip is worth seconds

Veloce Raptor

I think that pros are more able to extract 100% from the car regardless of a bit more weight. At the enthusiast level, IMO, the effects of weight in certain situations and on certain tracks will be more pronounced.

Again, purely based on my experience and observations.

linzman

I've heard the 10 lbs= 1 HP approximation, so you can guesstimate based on that, but like others have said, way too many other variables

hacker-pschorr

This is what happens when you forget about the extra ballast in the passenger seat.

Slakker

According to PCA and the SP996 rules, 20HP = 180lbs.

MarcD147

ballast can be added wherever is most beneficial which is typically very low in the car and in the spots that affects the balance least negatively or possibly even positively.

a passenger goes in the right seat and typically sits straight up which put its center of gravity 10+ inches above seat

additionally you can corner balance for ballast but few will corner balance for a passenger