Measuring Springs

[speedy_w_beans 4272]

I've been building a small database of Tamiya springs for some time now, and maybe a few of you would be interested in seeing how I do it.  If anyone would like to contribute to the spring database using these measurement techniques, please PM me and I'll keep this image current.

First, here's the list as it stands today:

As far how I generated this information, all it takes is a hobby vise, calipers, and a small scale.

When it comes to counting the number of turns, I start right at the tip of one end and count straight down from there.  Here's a site with the technique:  http://springipedia.com/compression-counting-coils.asp

In the case of this TB03 silver kit spring, there are six turns.

Measuring the wire diameter is simple with calipers.  The combination wire thickness and number of turns dictates the spring constant (that feeling of stiffness as you squeeze the spring between fingers).  Thicker wire and/or fewer turns = stiffer springs.

For overall length I lightly squeeze the calipers on the spring and start loosening them until the spring is just about to fall out.  Here it's 26.6 mm.

Mass (or more accurately, mass as inferred from weight) is measured with the scale; in this case it's 3.4 grams.

I use the hobby vise to clamp one end of the caliper; the jaws are wide enough that the scale can sit on top without falling off.  I try to get the calipers as perpendicular to the active scale surface as possible and make sure there is contact between the scale and the bottom caliper jaw.

Once a spring is placed on the scale and the mass is measured again, I start lowering the other jaw of the caliper until it just starts to touch the spring.  The reading on the scale might be 0.1 gram to 0.2 grams higher.  Then the caliper is zeroed.

The caliper is pushed down a specific distance, like 3 mm or 5 mm and the scale is read again.  Here we have 3 mm of displacement and 683 grams (force).

Now there's enough information to do some math.  We have the initial reading under no compression (3.5 grams) and the reading with 3 mm of compression (683.2 grams).  These are forces as perceived by the scale, not masses technically.  So, the change in force divided by the change in distance gives us the spring constant:

(683.2 g-f - 3.5 g-f) / (3.01 mm - 0 mm) = 225.8 g-f/mm

That's pretty close to the blue spring in the 53440 hopup set.  Multiply 225.8 g-f/mm by 0.00980665 N/g-f, and that converts to 2.21 N/mm of displacement.

Ok, so why do this?

• When looking for softer or stiffer springs than what's in the kit, it's nice to know which springs are roughly the same length and have different spring constants.
• If you know other information, like weight distribution using some corner scales, along with suspension geometry, then it becomes interesting to select springs in proportion to the weight over each axle.  There are whole books written on the analytical aspects of car setup.

PetitRC has a number of spring and oil charts that are worth knowing about too:  http://site.petitrc.com/reglages/UniversalSpringChart.htm

Another resource that's interesting is this data from an RC shock dyno:  https://sites.google.com/site/rccarengineering/home

Enjoy!

 

[speedy_w_beans 4272]

Table updated with 58518 Super Clod Buster springs and multiple RM01 spring sets.  Also added a lb/in column.

[speedy_w_beans 4272]

Table updated with 53832 DT02 tuning springs and 54567 DT03 CVA kit.  Thanks @SlideWRX for these contributions!

[Vertigo35 81]

Hi, I am really happy to find this post. I made some measurements for 53333 mini springs, using a similar method (not sure it is quite the same, as images here have disappeared unfortunately). However the results do not fit the values found on most charts (petitRC etc.). I find 120/150/165 g/mm for red/yellow/blue, but most charts have higher rate values around 220/250/280 g/mm. 

Would you have any idea if there is something wrong with the method linked in my recent post : https://www.tamiyaclub.com/forum/index.php?/topic/103051-lost-in-tc-spring-rates/ ?

Thanks a lot for your help 

 

[SuperChamp82 743]

Legend - thank you sir @speedy_w_beans 👏

[Pylon80 2635]

Thank you @speedy_w_beans your table is particularly useful as you have been careful to include part numbers... I seem to recall that there has been similar attempts to measure and document springs on other forums but it would often just say "Tamiya silver" or "Tamiya Yellow" which could mean almost anything. I will definitely come back to your post for reference. Bravo!