Which scale is more accurate?

[LemonWedge]

A number of years ago I weighed my car at a local truck stop scale. At the time it weighed in at 3770 with me (175lbs) in the car. Since then, among other things I've swapped the orig. 383 for an aluminum headed 451; I've swapped out the stock leaf springs and slapper bars for Calvert split mono's & cal-trac bars; and I've traded the steel wheels for a set of lighter aluminum wheels. I figured I was in the 3700 lb range these days, maybe even dipping into the 3690 range. Well..... This past weekend I ran it across the scale at the track......... I couldn't believe it when I looked at the readout: 3820!!??

I suppose I'll hit another scale sometime soon to double check this, but it seems weird.

How accurate are race track scales (I would think REAL accurate)? How accurate are truck stop scales (I know they're regulated by the DOT)? which one would you trust?

 

[PurpleBeeper]

Well, a scale is only as accurate as it's last calibration (assuming the same type of scale). I'd have to be on the truck stop scale since it's used for commerce (e.g. gasoline tanker trucks charge their customer based on the before/after weight of their trucks). No telling if/when the track scale was calibrated.

On the other side of that same coin..... the scales "probably" are different types. Race cars weight A LOT less than fully loaded semi trucks, so their scales are made to handle much larger weights....but I'd still bet on the truck scale.

 

[bm02tj]

It cost to have the scales certified so I would go with the truck scale

 

[dvw]

66-67 B Body with light wheels, aluminum heads, and no cage will weigh less than 3750 unless the driver is really heavy.
Doug

 

[gkent]

Might be a hint to cut back on the Big Macs and fries !!!

 

[Budnicks]

I'd say the racetrack scales
IF It the track is a NHRA sanctioned track
the scales better be accurate,
they always weight the Pro's, T/A classes &
a few other Comp Elim. classes after they run
to see if they are in compliance with the rules, min. weights etc.
when ounces or a pound or 2 can make or break you,
being able to move on or the run thrown out & you lose etc.

 

[PurpleBeeper]

I'd say the racetrack scales
IF It the track is a NHRA sanctioned track
the scales better be accurate,
they always weight the Pro's, T/A classes &
a few other Comp Elim. classes after they run
to see if they are in compliance with the rules, min. weights etc.
when ounces or a pound or 2 can make or break you,
being able to move on or the run thrown out & you lose etc.

Ooooo.....Budnicks makes a good point. IF the track scales are calibrated, then they're designed for a weight range like a race car (say 2500-5000 lbs.) vs. a semi-truck (many tons). +/- 50 lbs. accuracy on a semi-truck would be less of an issue in the minds of a truck scale operator than a track operator IF they calibrate their scales.... like trying to use our bathroom scale to weigh a penny. So IF it's an NHRA track, then I have to change my vote to match Budnicks.

 

[LemonWedge]

The track is Pacific Raceways in Kent Wa. It's an NHRA sanctioned track that is basically the best / biggest facility in the Northwest. I was thinking the same thing, that the track scale would be the one to bet on, but 3820 just doesn't seem reasonable. I only weigh 175 dripping wet.

 

[HT413]

Go back to the same truck scale for a reweigh. Gotta eliminate some variables.

Edit: a local stone quarry sells stone via truck scale to homeowners and contractors alike. So I might be in my F150 in line behind a tandem dump. So my guess is that scale is precise for 3000 lbs to 80,000 lbs.

Also, keep in mind that a lot of truck scales are accurate to +/- 50 lbs... and that's it it's calibrated. I wonder if some calibration shops offer a lower cost calibration by eliminating the low end...

 

[Cranky]

Did you get on the scale by yourself? The NHRA track near me gave my accurate weight within a couple of pounds with just me on it. I also checked the weight of the car with me and without me. For what good that might mean.....

 

[66Satellite47]

Very interesting. I had a surprise when I ran my Satellite over the scales at Brainerd International Raceway, a NHRA national event track. This year it came in 100 lbs heavier than 2 years ago. Changes are a new 440 motor & new Cope 727 & 3300 Lb SS springs. The new motor could be a few pounds heavier since it's partially filled, trans should be close to the same, SS springs should be lighter than before. I'm the same weight. Apparently even the same scales can vary. The car even gained weight during the weekend and it wasn't me bulking up!!

 

[Cranky]

How often do tracks that have national events calibrate their scales? Just before each event or every several years?

 

[moparpoor]

Track scales have to be calibrated before every major event. They have a set process to do so. Nhra events they are checked before every car with premeasured ballast. Your Wednesday night test and tune or weekend bracket race probably hasn't been calibrated! Norwalk and Milan had two different readings so I did my homework. You have to ask to see it calibrated. They may piss and wine! That's part of what you pay an entry fee for

 

[Mike Gaines]

When 100 pounds (+ or -) equals 1/10 of a second (in our 3000 to 4000 lb category) the correct weight is pretty important

 

[LemonWedge]

They have not, to the best of my knowledge, had any sanctioned NHRA divisionals here thus far this year, so they could just have it on as a courtesy, but it may not have been actively maintained since last year??? I'll retry the truck stop scale; also I know the track manager a little, I'll ask him next time I'm there what their maintenance schedule with the scale is.

 

[Cranky]

Been years since I weighed a car but iirc, there was a tag showing the last calibration date on the window of the scale shack at the Houston track. It was taped to the inside of the glass so some moron couldn't peel it off I suppose...

 

[LemonWedge]

Well, I was at the track tonight helping a buddy with a new combo. I asked the track manager about the scale: he said they had just had it calibrated last week, just prior to when I used it on Sat. So apparently, I own the worlds porkiest 67 B-body. This thing doesn't even have a bar in it. Yikes!

 

[HT413]

Just took my car to the local stone quarry for a weigh. 3387 with me and a full tank of gas... so about 3100 empty.

Guess their scale needs a calibration too...

 

[Mike Gaines]

The track is Pacific Raceways in Kent Wa. It's an NHRA sanctioned track that is basically the best / biggest facility in the Northwest. I was thinking the same thing, that the track scale would be the one to bet on, but 3820 just doesn't seem reasonable. I only weigh 175 dripping wet.

I weighed my 66 Coronet at NHRA Scales at Famoso Auto Club Raceway. It weighed 3445lbs empty. With 5 gal of gas and me (215lb) it weighs 3695lbs. DANA 60, Cal track monoleafs, aluminum heads, no back seat, 1 battery, Heavy Fiberglass Hood with Aero scoop, 2 Recaro type upholstered seats, full dash board, fully carpeted, 6 point cage, fiberglass front fenders. Weld wheels, lite Moroso frt tires..take it from there....
.