Want to know how to weigh your car?

kc2005ptgt · Post by **kc2005ptgt** » Thu Feb 01, 2007 4:04 pm

Ok, here is something for you nerds out there... I learned this is Math class a long time ago, and I thought I would share the information for those of you who wanted to do this yourselves. Have fun, and good luck! Maybe post some results? I will, am going to actually go do this right now

Yeah, I am nerd, sorry.

To weigh a car, take two sheets of paper, a ruler, and a tire gauge to a smooth, hard-surface parking lot. Slide one sheet of paper under the front of a tire as far as it will go. Slide the other sheet under the back of that tire as far as it will go. Be sure the two sheets are straight. Then measure in inches this length of the tire’s footprint. Slide a sheet of paper under the outside of the tire as far as it will go. Slide the other sheet under the inside as far as it will go. Be sure the papers are parallel. Measure this width (distance between the sheets) of the tire’s “footprint” in inches.

Multiply these two measurements to find the area of that tire’s footprint in square inches. Then press a tire gauge on the valve stem to find the air pressure inside the tire in pounds per square inch.

When you know the air pressure inside one tire, and the area of its footprint, you should draw a rectangle and mark this area into square inches. On each square write the pressure inside that tire. When you add up those pressure-per-square-inches, that is how much that tire is holding up. Do this same thing for each of the other tires. When you add up all four tires’ hold-up force, that is the weight of the car!

Mr Josh Zombie · Post by **Mr Josh Zombie** » Thu Feb 01, 2007 4:06 pm

That's a bit to much math for me.

Post by **racer12306** » Thu Feb 01, 2007 4:09 pm

i might give this a shot tomorrow.

no such thing as too much math for me, im in calc 3

glasswars · Post by **glasswars** » Thu Feb 01, 2007 4:27 pm

That's so cool, definetly going to try it soon!

But what do you do add the tire pressure by the square inches, or multiply the tire pressure by the square inches??

kc2005ptgt · Post by **kc2005ptgt** » Thu Feb 01, 2007 4:30 pm

yeah, slide it so you can meassure the "footprint" of the car... it has something to do with air pressure in a tire vs how big the contact patch is. So, to weigh the contact patch, or footprint, you need a way to slip it in and get something close... hence, the papers slid in front and back, and side to side.

glasswars · Post by **glasswars** » Thu Feb 01, 2007 4:33 pm

kc2002acr wrote:yeah, slide it so you can meassure the "footprint" of the car... it has something to do with air pressure in a tire vs how big the contact patch is. So, to weigh the contact patch, or footprint, you need a way to slip it in and get something close... hence, the papers slid in front and back, and side to side.

I edited.

Diff question, hahaha.

kc2005ptgt · Post by **kc2005ptgt** » Thu Feb 01, 2007 4:37 pm

DOH! I think it is multiply....

SteelBlue · Post by **SteelBlue** » Thu Feb 01, 2007 4:41 pm

My brain hurts just reading that.

fixitmattman · Post by **fixitmattman** » Thu Feb 01, 2007 4:44 pm

F = P*A

If you know the contact pressure (in this case it's simplified to the tire pressure) and the area for each tire, you know the force also known as weight at that corner. Add all the corners together and you get the total weight.

It's good for a rough estimate, and everything has to be dry for obvious reasons. But I'd like to see someone slide a piece of paper under the tire. You'll have to jack up the tire and set it down on the paper, but when you do that the other tires may move and create a larger imprint on the paper throwing off your values.

I weighed my car in about 30 seconds by driving through a truck weigh station on a Saturday afternoon:

Scale empty ~590kg (the scale was snow covered)
With me sitting in Neon ~1875kg

Net ~ 1350kg or 2970 lbs

Curb weight is published as 1163kg or 2564lbs for 2000m/y

Have to do this again in the summer when the undercarriage (or the car itself!!!) isn't covered and packed full of ice and sand.

Had about 1/3 tank of fuel and I'm around 150lbs. So considering all the tools and crap I carry that isn't too too bad.

SlvrACR · Post by **SlvrACR** » Thu Feb 01, 2007 4:47 pm

LOL i did the same thing. Truck weight center lol

kc2005ptgt · Post by **kc2005ptgt** » Thu Feb 01, 2007 4:59 pm

yeah, contact patch is hard to get right/exact, but I just did it, and roughly, according to the meassurements I got, my car weighs 2640 lbs

SlvrACR · Post by **SlvrACR** » Thu Feb 01, 2007 5:00 pm

Gezz fatty. Time for the Subway diet.

kc2005ptgt · Post by **kc2005ptgt** » Thu Feb 01, 2007 5:02 pm

I wish it were lower... I wanna shed some lbs through the AC, rear seat, trunk stuff/spare... but you know, I gots kids, wife, stuff...

SlvrACR · Post by **SlvrACR** » Thu Feb 01, 2007 5:03 pm

I was wondering does the option ACR have the sound damping material in the trunk and under the carpet?

kc2005ptgt · Post by **kc2005ptgt** » Thu Feb 01, 2007 5:04 pm

no, it is just carpet

SlvrACR · Post by **SlvrACR** » Thu Feb 01, 2007 5:05 pm

So only a few things like AC, radio, antenna, power locks are added. Last time I was on the trunk stop scale I was around 2485 but who knows how good they are.

kc2005ptgt · Post by **kc2005ptgt** » Thu Feb 01, 2007 5:11 pm

I am gonan check out one just north of me some weekend. Just to see how good my meassurements were

SlvrACR · Post by **SlvrACR** » Thu Feb 01, 2007 5:26 pm

Im gonna have to check mine since i got alittle more removed and new wheels. I cant do math so this isnt for me.

yellowpatrol · Post by **yellowpatrol** » Thu Feb 01, 2007 6:18 pm

sounds cool, but too much paper

03sxt · Post by **03sxt** » Thu Feb 01, 2007 6:28 pm

SteelBluePearl wrote:My brain hurts just reading that.

I can get the two pieces of paper thing down.

Post by **Diablo0** » Thu Feb 01, 2007 8:11 pm

Thats actually a pretty clever idea...

I'd be very curious to know just how close it really is though.

kc2005ptgt · Post by **kc2005ptgt** » Sat Feb 03, 2007 2:24 am

^^ Yeah, you have to be realy close to exact, but it is a good way to do so if you have time, and whatnot to get it precise.

scneonchic · Post by **scneonchic** » Sat Feb 03, 2007 5:20 pm

SteelBluePearl wrote:My brain hurts just reading that.

My brain hurt reading the first paragraph of it.... Math > me

03blackrt · Post by **03blackrt** » Sun Feb 04, 2007 12:03 am

If you could take very good measurements this method would be very close. Basic mechanical statics. You would get a little error tho.... (because the sidewall takes some of the weight). Obviously if you have a run-flat tire this meathod is completly useless.