Cal Club Autocross Forums

What's the average lap time improvement for every 100 lbs removed from an autoX car, assuming the typical 2,700 lbs - 3,500 lbs average street car weight.

Over a 60 secs course, removing 100 lbs reduces lap times by tenths, hundredths, thousands of a second?

My experience comparing autoX results reducing the weight on my car and a group of consistent drivers shows 0.3 secs per 60 secs of road course, using my 2,900 lbs GT3.

I wonder what you have found through years of driving in this Sport. More often than not, I have been in situation where I get a passenger (175 lbs average), and my times are slightly slower, I miss my braking marks and I feel the difference in power. At one time at Watkins Glen, dumping my instructor gave me another 3 mph on the speedometer (153mph vs 156mph) at the bus stop.

At the very least, you should look at it as a percentage. 100lbs. off a 2000lb. Civic (or sub-1000lb. A-Mod) will make a much bigger difference than off a 3500lb. Mustang.

Where it comes from matters to dynamics too - 100lb. off the nose of a F/R car will probably help more than 100lb. off the butt.

Then there's the whole "is it rotating or unsprung mass" thing too, and how fast it rotates, etc.

Hard to describe a situation where a passenger will speed a car up. Maybe a car with a really bad diff around a tight clockwise skidpad.

I find a dead wood passenger adds about .2sec. So that would equate to .1sec/100lbs for the 'normal' weight. But as Jason says above, where is very important. I felt my relocated 35lb battery (off the high nose to the low center) more than a passenger.

Jay W

My passengers consistently get me to slower times, when I'm driving well (extremely rare).

An interesting formula is power/weight ratio. In my GT3 every 100 lbs removed was the equivalent to another 13 Hp. For the 2006 SCCA Nationals, I got the car down from 2,900 lbs to 2,760 lbs, it was fast, very fast. The stock car was 3,130 lbs and ran the 1/4 mile at 12.2 @ 116mph. At 2,900 lbs the same car ran the 1/4 mile on the same track at 11.82 @ 120.6 mph. So the acceleration benefits are very easy to notice, and there are improvements in handling and braking, the interesting idea is to get the meaning of this saved weight on the timer, it seems to be in the tenths of a second per every 100 lbs, which I think it is a lot of time saved.

It would be interesting to rent a lot and run 20 laps with and with a passenger and look at the impact on lap times. Do this with a few cars, gets average, equalize the weight for all cars and determine a real difference at autoX.

Rad D__ wrote:My passengers consistently get me to slower times, when I'm driving well (extremely rare).

An interesting formula is power/weight ratio. In my GT3 every 100 lbs removed was the equivalent to another 13 Hp. For the 2006 SCCA Nationals, I got the car down from 2,900 lbs to 2,760 lbs, it was fast, very fast. The stock car was 3,130 lbs and ran the 1/4 mile at 12.2 @ 116mph. At 2,900 lbs the same car ran the 1/4 mile on the same track at 11.82 @ 120.6 mph. So the acceleration benefits are very easy to notice, and there are improvements in handling and braking, the interesting idea is to get the meaning of this saved weight on the timer, it seems to be in the tenths of a second per every 100 lbs, which I think it is a lot of time saved.

It would be interesting to rent a lot and run 20 laps with and with a passenger and look at the impact on lap times. Do this with a few cars, gets average, equalize the weight for all cars and determine a real difference at autoX.

Just leave your gold chains at home. :king:

Interestingly, my best lap a the the recent El Toro autox was WITH my mother riding (see avatar)...

I think there should be minimum weights in autox for car + driver (with enough room for a HEAVY driver)!
The same goes for K1 Speed... a scale at the entry to the track where they add weight to equalize the karts weights...

Been considering to get a Miata or a S2000, but had started to think about the weight disadvantage, so because of my size (6.3/230) I should probably stick with V8 grunt...

Jayson Woodruff wrote:I find a dead wood passenger adds about .2sec. So that would equate to .1sec/100lbs for the 'normal' weight. But as Jason says above, where is very important. I felt my relocated 35lb battery (off the high nose to the low center) more than a passenger.

Jay W

what's a non-dead wood passenger? Flinstone car style?

Jason Isley BS RX8 wrote:

Rad D__ wrote:My passengers consistently get me to slower times, when I'm driving well (extremely rare).

An interesting formula is power/weight ratio. In my GT3 every 100 lbs removed was the equivalent to another 13 Hp. For the 2006 SCCA Nationals, I got the car down from 2,900 lbs to 2,760 lbs, it was fast, very fast. The stock car was 3,130 lbs and ran the 1/4 mile at 12.2 @ 116mph. At 2,900 lbs the same car ran the 1/4 mile on the same track at 11.82 @ 120.6 mph. So the acceleration benefits are very easy to notice, and there are improvements in handling and braking, the interesting idea is to get the meaning of this saved weight on the timer, it seems to be in the tenths of a second per every 100 lbs, which I think it is a lot of time saved.

It would be interesting to rent a lot and run 20 laps with and with a passenger and look at the impact on lap times. Do this with a few cars, gets average, equalize the weight for all cars and determine a real difference at autoX.

Just leave your gold chains at home. :king:

Ouch... If it was a Lambo... that would be justified... hahahahahahaa ;)

One observation I would add. A few courses ago, I had a passenger(S2000 CR - AS) and was able to carry 3-5 more MPH on a longish left hand sweeper. Laid down a perfect slight 4 wheel drift.
Whereas the next lap, no passenger, I spun out trying the same speed with the slightest of lifts.
Having the extra weight on the outside of that turn was noticeable.

So, course layout and length of sweepers, to me, matters some too....

Pete Loney wrote:One observation I would add. A few courses ago, I had a passenger(S2000 CR - AS) and was able to carry 3-5 more MPH on a longish left hand sweeper. Laid down a perfect slight 4 wheel drift.
Whereas the next lap, no passenger, I spun out trying the same speed with the slightest of lifts.
Having the extra weight on the outside of that turn was noticeable.

So, course layout and length of sweepers, to me, matters some too....

You are in a stock car with no legal means of correcting corner weights.... Rad won't have that issue in ASP. But if you think heavy is faster make sure to run a full tank, a bigger muffler and some steel wheels.

Brett King wrote:
Ouch... If it was a Lambo... that would be justified... hahahahahahaa ;)

The guy has gold numbers on the car.... It is justified.

Jason Isley BS RX8 wrote:
The guy has gold numbers on the car.... It is justified.

guess what, those gold numbers were ordered to match the gold wheels. I just haven't found the time to get them powder coated gold, like the old Fiats from the 70s.

Jason Isley BS RX8 wrote:

Pete Loney wrote:One observation I would add. A few courses ago, I had a passenger(S2000 CR - AS) and was able to carry 3-5 more MPH on a longish left hand sweeper. Laid down a perfect slight 4 wheel drift.
Whereas the next lap, no passenger, I spun out trying the same speed with the slightest of lifts.
Having the extra weight on the outside of that turn was noticeable.

So, course layout and length of sweepers, to me, matters some too....

You are in a stock car with no legal means of correcting corner weights.... Rad won't have that issue in ASP. But if you think heavy is faster make sure to run a full tank, a bigger muffler and some steel wheels.

I know J , weight is the enemy with a low torque car, I was only suggesting one type of corner was better suited for a passenger aboard....