Hey Fred, I have a collection of losi pistons if you are interested I will PM you pictures. Some I have drilled to 5-5-6, 5-6-6 etc. I have a lot….:D

I might take them. My vintage cars all still run them and probably always will. I still drive them too.

Fred
I tried the "pack" on the slash, I went up to 32.5 from 30 in the rear and got 12" of pack.
I'll have my son try it there.
Thanks again!

Dave

well, i ended up with silver in the front and black in the rear. ran it tonight at our practice night with 25w oil all around. will go up to 27.5 then 30w in the front to slow it down a bit, and gain a lil bit more pack for the jumps. then, on to the next step. camber link tuning? am i correct? it handles really well now tho, not sure how much more i want to do to it. lol just need to become a smoother driver now! thanks for the insight into a whole new way of tuning.

As part of my attempt to re-tune my buggy, I did some experimenting with oils and pack. Previously, I ran smaller holes up front and a lighter oil up front. This worked pretty well, but I was never sure I had my pack equal front to rear. It certainly seemed close.

Anyway, I started off with my original setup. I had picked my oils previously based on how I test my springs - push down on the cg, release, and make sure each end rises as the same rate. Doing this, I assume my low speed dampening is equal on both ends.

The new step came in today. I dropped the car from varying heights in the air and watched what happened. With my setup, the rear end of the car would tend to chassis slap before the front. Hmm... I guess my pack wasn't equal.

I put a larger piston up front (but still smaller than the rear piston), and tried again. First step, push and release. My front end was now much quicker with the same oil I had used previously (as expected). At this point I should mention I had 20wt up front and 25wt in the rear. I didn't have any 25wt left, so I skipped up to 30wt in the front thinking it would be too slow. To my surprise, the front and rear end of the car rose at the same rate when I did the push/release test. Odd, but I decided to keep going. Doing the drop test showed the front and rear would chassis slap about the same time. Even more interesting.

In my basement where I do my work, there's a small 1/2" pvc pipe running from the water heater to the floor drain. I decided to do Fred's "hose test" while I was at it. Driving over the pipe at a constant speed (not accelerating) seemed to show both ends of the car bounced the same amount going over the pipe.

So now I'm left with a setup that seems to be empirically sound (it passes all tests), but doesn't seem to match the theory. I had always thought with a smaller piston hole up front, you would always end up with a lighter oil up front to be able to match the rear. I'm sort of confused on this, but I'll see how it works on the track. The track is closed for two weeks to put in a new layout for the summer, so I won't be able to test it for a while :(

Smaller piston up front larger in the rear you should be close to the same weight at both ends. Unless your holes are sized very differently.
My B44 has 2x 1.6 front and 1.7 rear. Stock setup is 35wt front & back. I run one step lower in rear spring and oil so 35/32.5.
When I was running a 4x 1.3 front & 1.4 rear on my Tekno I was also 2.5wt lower in the rear. Changed to 2 stage pistons since then but I'm thinking about opening up the holes in the rear pistons 0.1 to get back to a staggered piston setup.
Lots of variable in there, hole count, shock diameter & length but still should be close to the same weights.

+1 for Fq06!

@RC10Nick: I'm also experimenting with oil and pistons to achieve balanced pack on my 410 and currently it's very close with 30 wt oil all around and 4x1.3 hole pistons in front with 6x1.2 in the rear. I may end up going to even smaller pistons though and I would expect I will also need lighter oil in the front if I do go smaller so that I won't end up with slower static damping (which would change my spring rate a little bit).

As a general rule expect to have a lighter oil in front. Since the shocks are smaller (Less travel aka shorter means they require more pack to equal the rear and also must travel a little faster to keep the chassis level), Keep in mind you also have many other variables involved like weight distribution, arm length(leverage), shock position (leverage) etc. All that being said you often go with smaller pistons in front on a 2WD car (RM or MM?) and this means you would usually want lighter weight oil to try and stay close to the same static damping.

I will try to find some spring mass damper system diagrams that really help explain this concept…equations too.

Have been reading along and doing some experiments myself. I recently converted to the STRC LCG chassis, and also changed out stock shock mounts. The new ones are carbon fiber and although weigh same as the plastic, are much stiffer than even aluminum shock towers. The result, with essentially the same weight vehicle and the same shocks as my last pack test, I now have approximately 22" of pack or an increase of 10" over the stock chassis/shock tower set up. What the shock is mounted to will have a big effect on how well it performs!. That may be part of the source of of your discrepency if one of your towers is not as stiff as the other.

Dave

The one thing about the drop test for pack is that there are two goals. One is to equalize the pack front to rear. However you need to be sure that if you were to just hold the car down to the table that when you release, both ends rise at exactly the same time. It is possible to have equal pack but not have this happen. If that's the case, you need to go to smaller front piston hole sizes and lower front oil and try again.

Interesting that you mention that. My rear tower is CF, but my front is the stock plastic. That could account for what I'm seeing.

Either way, I'm not too worried about it. Both ends rise at the same rate when I do the push and release, and it drops level when I do the pack test. Like I said, I'll just have to wait two weeks when the track opens back up to see how it works.

If you really want to keep things equal, run the same number of holes in the pistons all around. Don't go 3 hole in one place and 4 or 6 in the other. You get the idea. Pack won't be as easy to balance out that way.

I have read through the thread and know the concept of balancing my springs, but my question is do I set the ride height before I do the drop test to test the rebound front and rear?

Generally, I'd say yes. Keep in mind after the oil is installed you'll readjust it again.

I've been getting all "Swain-y" on a new build in prep for summer outdoors. I'm finding myself a curious to know how temperature effects these RC shocks... I am building and balancing my buggy and setting Pack all in a comfortable 73 deg work room in my house how ever at the races in my area the mornings at the track can be quite crisp at under 55-60 deg for practice and qualifying however the mains can be 100+ deg in the afternoon. (yes desert in the Evergreen State) on the flip side later in summer we start racing at night to beat the heat so practice and quals are in the heat and mains are cool my question is it even worth paying attention to or should the shocks be pretty consistent through a temperature range? keeping in mind that different weights of oil are effected differently by temperature.

It's a valid concern but the difference in oil weight isn't going to be too far off. What works for you now may only need to be 5W higher in the summer. Most likely no more than 10.