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Old 09-14-2014, 09:22 AM   #1
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Default Shock tuning, springs, oil weight, etc

This thread is intended to give racers a place to list their shock tuning tips and tricks and to aid in resolving problems for newer racers (like myself).

Here's my issue:

After experimenting with the vented shock cap (drilling a small hole in the plastic cap on the TC6.2 shocks) I found the suspension to be very springy and bouncing through the turns. The results were a huge difference from the stock shock set-up.....and it was ugggllly. ....

I used the stock 40 weight oil Associated supplied with the kit for my test, and I installed the RSD 3 hole pistons with the 1.15mm holes....and I was not happy with the results. Should I have used a heavier oil to compensate for the vented cap and 3 hole pistons? After my test logic tells me that a heavier oil would be needed to reduce the bouncing, or are there other things I could do to correct the bouncing problem?....besides using a non-vented cap.

Spring selections made no noticeable difference in the bouncing so the only other variable would be the oil. So, if changing the oil is the remedy how much heavier weight oil would be needed to eliminate the bouncing?

Please feel free to give your advice on suspension and shock set-ups, I'm sure many others could learn from my mistakes....and yours.

So far my only advice to others is to NOT vent the caps on your shocks.
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Old 09-14-2014, 09:37 AM   #2
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Sorta depends on what you mean by a small hole
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Old 09-15-2014, 07:20 AM   #3
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Sorta depends on what you mean by a small hole
Care to clarify your comment, it's a bit light on details?


Since I'm just displacing air how much of a difference can the hole size make?

The hole is there to allow air to move freely into and out of the upper portion of the shock. Are you suggesting that a smaller hole is some kind of metering device? If you were moving a liquid then a small hole could be a metering hole, like in the shock pistons, but moving air I can't see how it would make any difference unless the hole was the size of the point of a pin. Even with that the amount of air being moved would still not be enough to create rebound air pressure in the shock, considering how little the shock moves while in use.



If someone here is running a car with vented shocks what weight oil and what springs are you using to eliminate the bouncing?
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Old 09-15-2014, 08:00 AM   #4
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Quote:
Originally Posted by OttoKrosse View Post
This thread is intended to give racers a place to list their shock tuning tips and tricks and to aid in resolving problems for newer racers (like myself).

Here's my issue:

After experimenting with the vented shock cap (drilling a small hole in the plastic cap on the TC6.2 shocks) I found the suspension to be very springy and bouncing through the turns. The results were a huge difference from the stock shock set-up.....and it was ugggllly. ....

I used the stock 40 weight oil Associated supplied with the kit for my test, and I installed the RSD 3 hole pistons with the 1.15mm holes....and I was not happy with the results. Should I have used a heavier oil to compensate for the vented cap and 3 hole pistons? After my test logic tells me that a heavier oil would be needed to reduce the bouncing, or are there other things I could do to correct the bouncing problem?....besides using a non-vented cap.

Spring selections made no noticeable difference in the bouncing so the only other variable would be the oil. So, if changing the oil is the remedy how much heavier weight oil would be needed to eliminate the bouncing?

Please feel free to give your advice on suspension and shock set-ups, I'm sure many others could learn from my mistakes....and yours.

So far my only advice to others is to NOT vent the caps on your shocks.
I find the opposite true. no holes in cap = very bouncy suspension on rebound(harder to compress and fast to rebound) as the bladder gets pressurized under shock compression.
What bladders are you using? A soft bladder will slow rebound.

Also how much rebound(how much extension after compression with no spring) did you have when you built the shocks?

FWIW, I run 1.1 or 1.2 3 hole pistons(depending on track), 14-16 lb springs and shock oil range 400-500cst ( 30-40 wt)
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Old 09-15-2014, 10:04 AM   #5
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I find the opposite true. no holes in cap = very bouncy suspension on rebound(harder to compress and fast to rebound) as the bladder gets pressurized under shock compression.
What bladders are you using? A soft bladder will slow rebound.

Also how much rebound(how much extension after compression with no spring) did you have when you built the shocks?

FWIW, I run 1.1 or 1.2 3 hole pistons(depending on track), 14-16 lb springs and shock oil range 400-500cst ( 30-40 wt)
Bladders are RSD soft, rebound after rebuilding the shock was zero. Front springs are the RSD gold 16 in lb, I ran the 14 in lb blue springs in the rear.

After some discussion in a few PMs with another RC tech-er I may have missed the step of pushing a small amount of oil out before capping the shock....I just don't understand how that is critical. (excuse my inexperience with these new-fangled RC cars. ...., I'm a throw-back from the 1980s 12th scale scene just getting back into RCs)
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Old 09-15-2014, 10:19 AM   #6
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Quote:
Originally Posted by OttoKrosse View Post
Bladders are RSD soft, rebound after rebuilding the shock was zero. Front springs are the RSD gold 16 in lb, I ran the 14 in lb blue springs in the rear.

After some discussion in a few PMs with another RC tech-er I may have missed the step of pushing a small amount of oil out before capping the shock....I just don't understand how that is critical. (excuse my inexperience with these new-fangled RC cars. ...., I'm a throw-back from the 1980s 12th scale scene just getting back into RCs)
if the bladder is pushed up from excess oil in the shock when installed, upon compression it will be pushed up further stretching it to the point where it will push back harder on rebound.
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Old 09-15-2014, 10:41 AM   #7
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Originally Posted by OttoKrosse View Post
Care to clarify your comment, it's a bit light on details?


Since I'm just displacing air how much of a difference can the hole size make?

The hole is there to allow air to move freely into and out of the upper portion of the shock. Are you suggesting that a smaller hole is some kind of metering device? If you were moving a liquid then a small hole could be a metering hole, like in the shock pistons, but moving air I can't see how it would make any difference unless the hole was the size of the point of a pin. Even with that the amount of air being moved would still not be enough to create rebound air pressure in the shock, considering how little the shock moves while in use.



If someone here is running a car with vented shocks what weight oil and what springs are you using to eliminate the bouncing?
Air flow is determined by the size of the hole. The larger the hole the faster the air flow. The difference between a liquid and a gas(air) in this situation is that with a gas, you can get some compression where in a liquid you cannot.

I was curious as to what size the hole was since that will affect the shock action.

Common sense should tell you that air will flow quicker thru a 1/4 inch tube than a 1/16 inch tube.
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Old 09-15-2014, 11:18 AM   #8
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Let me expand on my previous post. In a sealed shock(no hole) as the shock is compressed the air above the bladder becomes compressed as the shock shaft goes into the shock body, due to the displacement of the bladder. Thus as the shaft moves up it becomes meets more resistance. If you graph it the action is nonlinear. If you drill a hole in the cap, this allows some air to bleed out and the shock action becomes more linear. The larger the hole, the more linear the shock becomes because less compression of the air in the cap occurs.

Now whether this is significant or not is open for debate. For the most part, I feel this is a insignificant difference compared to the number holes and the size of holes in the piston. In your set up work, it seems to me that your time would be more constructively spent in those areas than this one.
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Old 09-15-2014, 11:22 AM   #9
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Originally Posted by Granpa View Post
I was curious as to what size the hole was since that will affect the shock action.

Common sense should tell you that air will flow quicker thru a 1/4 inch tube than a 1/16 inch tube.


Hole size is .067", or a #51 drill bit. It's the smallest bit my drill would hold. It's a hole that will allow air to move freely if you consider the amount of air your moving with each slight movement of the shock. FWIW: Rebound before putting the spring on is zero.

I'm no engineer but the concept of hole size and moving matter through a hole is not rocket science. I've spent 25+ years working on air compressors, fluid and air pumps, vacuum pumps, pneumatic tools...etc.

I was sent a detailed description of the assembly process for the shocks so I'll try doing it over to see if I missed something.
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Old 09-26-2014, 10:50 AM   #10
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Quote:
Originally Posted by OttoKrosse View Post
Hole size is .067", or a #51 drill bit. It's the smallest bit my drill would hold. It's a hole that will allow air to move freely if you consider the amount of air your moving with each slight movement of the shock. FWIW: Rebound before putting the spring on is zero.

I'm no engineer but the concept of hole size and moving matter through a hole is not rocket science. I've spent 25+ years working on air compressors, fluid and air pumps, vacuum pumps, pneumatic tools...etc.

I was sent a detailed description of the assembly process for the shocks so I'll try doing it over to see if I missed something.
UPDATE: Got to test the rebuilt shocks, as directed by another RCTecher, and they seemed to work well....although I haven't had much time with the new set up it's worth working on, .....now on to testing springs and sway bar combinations to dial it in.

Thanks to all that contributed.
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Old 10-24-2014, 07:26 AM   #11
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UPDATE: Got to test the rebuilt shocks, as directed by another RCTecher, and they seemed to work well....although I haven't had much time with the new set up it's worth working on, .....now on to testing springs and sway bar combinations to dial it in.

Thanks to all that contributed.
What did you change? I assume you rebuilt it with zero rebound aswell, but there was zero rebound before the rebuild aswell? I might be being thick but I dont know how this will affect handling?
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