One of the "methods" is to go from obviously over to obviously under. In other words if you can't feel a small adjustment throw a big one on. If that lights your bulb then you go on to narrow it down. So if you can't feel one hole in then go one hole up. :rolleyes: seriously

So has anybody here been able to prove mathematically that the oil in our shocks actually transitions from laminar to turbelent states at a higher piston speed? When I calculate it, it's always laminar. The force on the piston from the oil passing through the hole(s) is exponential with piston speed, which accounts for the much higher resistance in the shocks when landing jumps as opposed to low speed bumps, etc., and there is the hole entry and exit phenomena which also adds more resistance force per hole, but I'm just not seeing the "turbulent oil" part working out with the math.

;)

cool, can you post your calculations? just curious...

why are you summing the deltas ?

So they can merge with Southwest.

Ive done a fair bit of research into this and made spreadsheets to calculate shock force / velocity curves based on empirical measurements of 'real orifices' (rather than the more theoretical zero length orifice calcs which most textbooks show).

In all of the examples I have looked at, the oil flow has stayed laminar.

We are dealing with relatively heavy oils, and relatively low speeds, so the conditions don't really exist for turbulent flow.

The damper graph I have attached to this post:
http://www.rctech.net/forum/10587848-post4.html
was calculated using the formula I found in the reference shown on the graph.

Hope this helps.

Ray

Oil Units
 

Hi All,

This thread has really helped my understanding of the dynamics and set-up options for my buggy and so I'm hoping someone may be able to help on shock oil units of measurement.

I have created a spread sheet that helps give me a well balanced starting set-up for most areas of my buggy, leaving me to just tweek the handling using camber link positioning as per feel at the time. This has saved me huge amounts of time when racing away from my local track!

Currently I also have to adjust the shock oil manually too, but would love to be able to have the balance of oil calculable too, but I can't find out easily or definitively if the units of oil viscosity are linear or not :cry:

So could anyone here let me know please, is 200cst twice the viscosity of 100cst? Or is it just a dimensionless number for arbitrarily telling the difference between 2 liquids?

Thanks in advance :)

The problem with oil viscosity numbers is that since the viscosity changes with temperature, you never know exactly where it is at. A cSt rating is only valid at one reference temperature point and is different everywhere else. How linear that rate of change is with temperature will vary with the formulation of the oil. Unfortunately there isn't any real way to know how one weight or manufacturers oil compares with another in this regards. I used to have an excel calculator that had a few variable inputs. As long as I knew the viscosity at 0* C and 100*C, I could plot out a graph showing the viscosity change. It was pretty neat and was a tool that I used when I was making the mud pump oil specification recommendations for Weatherford when I worked there. Even if I could get a hole of that file again, I'd still have to find out what those numbers are for each oil. Unlike motor oils, they aren't published.

Thanks for the info, especially so quickly. I had a suspicion it wouldn't be such an easy situation when it was so hard to get an answer through detailed online searches! :eek:

As I said, the spreadsheet I've created gets me very close already so the oils will just have to be collated the old fashioned way with trial and error :D

For all you've helped confirm as correct in the rest of this thread a massive thanks FredSwain

From the calculations I've seen, for a given temperature (a big "if"), the viscosity ratings are linear. I've used the standard friction loss through the holes, plus entry and exit losses, piston thickness, blah blah blah, basically textbook stuff, but something doesn't quite work out comparing front to rear. Getting the ratio f/r balanced results in a car that is much lighter damped in the rear on the bench and on the track. The spreadsheet accounts for different shock mounting positions, sprung weight, etc., so I think my error is in the damping calculation. It very well could be, like Fred said, that the oil being used isn't truly what the bottle said. We are just messing with toy cars, after all. :weird:

I've seen your damper chart, Ray, and it doesn't agree with my data (which, admittedly, is a bit screwed up). With my data, the #3 smaller bore AE piston has the most "pack". By a long shot. Maybe I'll try working your data into my spreadsheet to see what happens.

Cody, I'd post the spreadsheet, but I don't think it's right, and there's enough inaccurate information out there to really screw a guy up as it is.

Just wanted to chime in and say this is a great thread. It provides a great step by step methodology to arriving at a well balanced vehicle. Thanks Fred! It also does a great job of separating the different components and what their respective role is. (even though it's one integrated system, each component has a main job). Keep it up!

Can you post a larger version of this? For some reason I can't blow it up and it's a little hard to read. THanks!

My instincts tell me you are correct. Although I wonder if the air in your shocks could allow it to happen. Especially as you get more air aka shock leakage. I don't see a reason to try and calculate it with that much air, but perhaps including some air in the calculations could allow for turbulent flow. I would expect viscosity to go down drastically with air. This is seems to be how it feels when you don't have enough oil….

Anyone have access to a shock Dyno? Also I wonder who has a spring testing machine or used a commercial one? It'd be nice to test older springs to see how they have worn versus new and also to do comparative testing between brands and such.