DIY weigh scales?

[Velix]

Hey everyone, I know at one point, after the suspension is done, I’m going to be needing a way to weigh all 4 corners. It seems people have been able to use a heavy duty bathroom scale and weigh the corners one at a time, but that doesn’t really interest me.

I was looking at this shipping scale unit that really cheap and with 440# max it should fit the bill.
Amazon

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I like the remote screen it has, as it would give the ability to build a box to house all 4 and charge them as well. If I was able to do programming I’d definitely look into a separate screen that shows all 4 and front/back splits on it.

If I can manage to find a 500# scale for similar price I’d definitely go for that

[davew]

I could not justify the cost of electronic scale(s) for a one time use. I was able to get two bath scales for less than $25. I fabricated a bridge that would span between bath scales and wide enough for the tire to set on the bridge. The bridge can be made from wood or steel, but the higher the bridge, the thicker the spacers will be required for the pads needed to level the set-up surface. Note You need to take care when locating and shimming your floor pads. You are going to end up with four different pads thicknesses to get a level surface in your typical garage floor. [Try to get all 4 pads within 1mm]
Note my garage floor sloped about a 1/4" in the length of the car's wheel base. That slope added about 7 or 8 lbs to each rear wheel, before installing leveling pads to the set-up. After the final spring adjustment, I went back and rechecked all four corners and verified the weights. This system was repeatable within 3 lbs using a bridge and bath scales for adjusting corner Wt.
Another option is flat flooring. This method is much easier and does not require scales but is not as accurate. Set the car on the leveling pads lay a straight edge across the leveling pads as a base line. I used an extruded aluminum bar but you could use fishing line. It just a simple matter of measuring from a common point, I used the front LCA bolt on both sides. Then adjust the springs perches to arrive at equal heights. I use this method first for setting up my car, and worst case, one wheel was 18lbs heavy Vs the corner wt method. To be honest you will probably not feel any road difference using the flat floor method when setting up your car, unless your middle name is Shumacher.
One disclaimer: I did use a transit to set the leveling pads in the garage floor. If you would like a photo of the scale/bridge, I could take a shot of it.
Davew

[Lonnie-S]

You might want to do a search here. Different ideas have come up over the years. One was a very simple use of levers (& springs? - Can't remember) doing one wheel at a time. It wouldn't be as accurate as 4 scales on a level floor, but if it was within 5-10 pounds, that would be good enough for my purposes.

Cheers,

[Velix]

Thanks guys. I know it might seem frivolous, but I’m pretty set on all 4 at the same time. And for $200 CAD it’s really not a huge expensive.

I plan on using them quite a bit during fabrication, right after my wheels are mounted so I can adjust battery, fuel tank, sump tank etc to maximize balance.

[Lonnie-S]

I've read about "levelling compound" to make your garage floor truly flat. It sounds like a liquid that you pour into a rectangular form and let dry to a hard surface (epoxy?). Has anyone tried doing that to get a truly level surface?

I sounds like a very good thing to do, if it's actually practical. I've got this nice British book on setting up Locost ride heights and alignments. The first thing they talk about is making the garage floor truly level.


Cheers,

[davew]

"The first thing they talk about is making the garage floor truly level."
Trying to level a garage floor the size, i.e. area, of an auto, would be very difficult. [I know and $$$]
Just mark 4 areas on the garage floor. Then make four shim packs, I used wood and sheet metal stock. Label each pack with the location, so it's easy to set-up, when you need to. Will take about a hour the first time, but can re-set in minutes.
Davew

[Lonnie-S]

"The first thing they talk about is making the garage floor truly level."
Trying to level a garage floor the size, i.e. area, of an auto, would be very difficult. [I know and $$$]
Just mark 4 areas on the garage floor. Then make four shim packs, I used wood and sheet metal stock. Label each pack with the location, so it's easy to set-up, when you need to. Will take about a hour the first time, but can re-set in minutes.
Davew

Do you have any photos, Dave?

Cheers,

[Warren Nethercote]

Not to mention that a truly level garage floor would be a PITA every time you drove into the garage on a wet or snowy day. For those of us who don't live in the dry south ....

[Johnsinski]

In RC car racing something as simple as a "seesaw" can be used to fix "tweak". You don't even really need a level floor, just close but flat. The 4 scale system for RC is about $100, so $200 for full size sounds like a steal! I would assume the 4 scale system still needs a flat plane of pads.

[KB58]

About the cheapest alternative is finding 4 Walmart scales which read high enough to handle the corner weights.

Years ago, my brother and I bit the bullet on real chassis scales. There was one solution which seemed promising at first, a lever type scale that lifts the tire just off the floor, and a pressure reading is taken. The problem is that tires (especially on light cars) run really low pressure, compressing maybe 1/4". With a wheel rate of maybe 300 lbs, 1/4" means an error of 300/4 = 75 pounds.

For a street car, a guess is probably fine, but if you ever change ride height or spring rates, they'll be needed again. "How much does it matter?" A fair question, which has the squishy answer of "it depends." If you just go to lunch in the car, it matters not. If you absolutely need that last 0.5 second of lap time, it matters a lot. Just keep in mind that it's possible to have the suspension screwed up enough that two opposite corners can end up supporting 85% of the car's weight yet appear perfectly normal. The only give away may be where the spring perches end up, or how compressed the tires are.

[rx7locost]

Here is an old discussion on DIY scales.

www.locostusa.com/forums/viewtopic.php? ... e&start=15


Don't forget to do the weighing with yourself in the driver's seat with all safety eqpt of you are going for the last few lbs of balance.

[Laminar]

The problem is that tires (especially on light cars) run really low pressure, compressing maybe 1/4". With a wheel rate of maybe 300 lbs, 1/4" means an error of 300/4 = 75 pounds.

That's only true if the body is fixed in space, which it's not. If you lift the lever higher, the body rises up. The extra spring compression is negligible until you start jacking it waaay up.

If the car is level (say with 1/4" spacers under the other three tires) and the tire you're measuring is just off the ground, that's true corner weight. If you lift it to where it's out of level, weight gets transferred to the measuring stick and the diagonally-opposite corner. The wheel rate doesn't factor into it.

You'll get way more error from trying to read a beam-type torque wrench while holding up the corner of a car. And the inaccuracy of your reading gets multiplied by the lever arm length for even more error.

[ntsqd]

Not set up correctly, the beam should be horizontal when the tire *just* lifts off the ground, the bolt in the support stand allows this adjustment:



The procedure requires a helper with a sheet of paper in his/her hands.
1. Lift tire off the ground, place paper under it.
2. Set tire down on paper.
3. Have helper gently pull on paper while lifting slowly.
4. When paper first moves take reading of "torque"
5. Multiply "torque" by beam ratio. In the picture it is 10:1 so 100 ft-lbs = 1000 lbs corner weight.

It is not as good as dedicated scales, but it will get you close enough to set a baseline.

The way that the team that I worked for leveled our scales was with a couple boxes of 12" X 12" linoleum floor tiles & an 8' level. Those resided in the race car trailer.

[TooBusy]

Not set up correctly, the beam should be horizontal when the tire *just* lifts off the ground, the bolt in the support stand allows this adjustment:



The procedure requires a helper with a sheet of paper in his/her hands.
1. Lift tire off the ground, place paper under it.
2. Set tire down on paper.
3. Have helper gently pull on paper while lifting slowly.
4. When paper first moves take reading of "torque"
5. Multiply "torque" by beam ratio. In the picture it is 10:1 so 100 ft-lbs = 1000 lbs corner weight.

It is not as good as dedicated scales, but it will get you close enough to set a baseline.

The way that the team that I worked for leveled our scales was with a couple boxes of 12" X 12" linoleum floor tiles & an 8' level. Those resided in the race car trailer.

I've seen a rig like this used before. It's remarkably repeatable. The guys I knew would take 5 or 10 fast readings and average them. They had a craftsman torque wrench with a Max torque tracer needle. Worked like a champ.

[TRX]

If you absolutely need that last 0.5 second of lap time, it matters a lot.

Laps imply a closed circuit, which will run either clockwise or counterclockwise. For something like the usual D-shaped dirt track, it's obvious that the optimum chassis setup isn't going to be anywhere near balanced. For a track like Barbour or VIR, the combination of fast and slow turns may be more important than the handedness of the track. A balanced chassis is a known starting point, but you are shooting for the lowest lap time, which will probably come with an asymmetric setup. Of course, once you find the optimum, the scales make it easy to return there after making a change.

Just keep in mind that it's possible to have the suspension screwed up enough that two opposite corners can end up supporting 85% of the car's weight yet appear perfectly normal. The only give away may be where the spring perches end up, or how compressed the tires are.

It'll show up primarily in braking, where the less-loaded front tire will lock up before the more-loaded one. If you have sufficient power, you'll either see wheelspin or the life of your limited slip differential will be noticeably shortened.