Scales: Discussion

[CMC17]

This post is get a feel for the scales and how accurate they are at the track. The reason I ask is I cannot believe I missed my weight/lap ratio by more than 40lbs. I've never been off more than a couple of pounds at most in my calculations.

Setup for R3:

47lbs ballast added (thx Glenn!)
Full tank gas

Car weight w/driver: 3233lbs. (weighed before race)
Race length: 24 laps (CMC)
Fuel ratio: .5 gal/lap (formula derived from previous race (4.5 gal. used in 9 laps)
Fuel used: ~12 gallons
Weight per gallon: 6lbs.
Total fuel weight lost: ~72lbs.

Car weight after race: 3198lbs.
Difference from total pre-race setup: 35lbs.

Something isn't right and I was wondering if anyone else thought something was off. Again, this is only for discussion and to see if there is an issue that needs to be addressed (constructively).

[mitchntx]

My car gained 35lbs, somehow ....

I had been coming off at 3312 or so in previous races and I was at 3347 post qual.

I filled the car to the brim (about 5 gallons) and ran 4 or 5 laps for Sunday's qual and came off at 3367

I should have weighed post race, but just never thought about it ...

The car didn't use as much fuel as I thought it would during the extended race.

[donovan]

Last year I was coming off the scales after a 20 min race, that I started with a full tank of fuel at 3150-3160 many times...

this past weekend, I dropped 24lbs off the car, started the 40 minute race with full tank of fuel and after the race weighed 3180... Huh?

donovan

[CMC17]

Thanks for the input guys.

I'm hoping others will chime in also with their weight reports. Something is definitely not quite right and with enough information we should be able to present this to those responsible for the scales and maybe get something done before the next event.

If I base my next setup on the weights used for this past event and then the scales somehow revert back to the "old" way, then I will be totally screwed and DQ'd. However, I'm going to keep my same weight log book and stay on course with it.

If the scales are off, we might as well not weigh the cars since it looks like no one would even be close to the minimum.

.02

Thx again!

/cheers

[Rob Liebbe]

I thought the scales were reading 40 - 50 lbs heavy as well.

Normally, I come off a 20 minute race at 1/2 tank and weigh 3170 lbs. This was consistent in the last couple of events.

R3 came off with under 1/2 tank indicated and weighed 3198. Seems wrong.

Remember, we had scale problems at Hallet last year as well. If I remember correctly, we had Johnny Phillips' Miata on and off the scale for back-to-back measurments and got varying results.

[AI#97]

Only input I can offer is that in Houston and Cresson last month, after filling the car to the brim and doing 20 minutes, I consistantly came off course at 3190 in Houston, and 3170 last month. I have since pulled 40 pounds off the car which would have put me at 3130 with the same fuel setup in a 20 minute race.

I was 2 gallons shy of a full load in R3...12 lbs, more than twice the minutes on track and came off at 3130... I usually use about 5.5-6 gallons in a 20 minute session so lets assume given my previous numbers and weight loss, I SHOULD have left the track at 3100 even....my minimum was 3069 so I was safe.

Before this weekend I was thinking of going after that other 10 hp and 10 tq I still left on the table but with the scales being off....I tend to want to play it safe.

[michaelmosty]

When I weighed after R2 I was exactly where I thought I would be, 3164. In Houston I weighed and came in @ 3175 but the race was about 3 min. shorter.
I didn't get to weigh after R3 last weekend. :cry:

[Todd Covini]

Check the specific gravity of super unleaded.
I've been using 7lbs/gal.

That'll account for some, but not all of your "missing weight".
Sounds weird...wish I was there.

-=- T

[oz98cobra]

Remember that for the scales to be accurate, they MUST be levelled - all at EXACTLY the same height. From what I have seen at NASA events, I don't think enough attention is paid to this, so some variation from event to event should be expected.

Interestingly, the CCRs only allow a 5 lb leeway on first weigh in and zero leeway on subsequent weight ins - 5lbs is only about 0.15% on a typical CMC car, and is not nearly enough to compensate for the innacuracies that could arise if the scales were not properly leveled and calibrated (and is probably not even enough to cover the tolerance of their scales!).

Good reason not to sail too close to the wind on weight.

[mitchntx]

Good reason not to sail too close to the wind on weight.

You suthunurs crack me up ...