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shock oil and piston choices

shock oil and piston choices

Old 07-09-2008, 12:29 PM
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Default shock oil and piston choices

I understand - or at least I think I do - that the viscosity of shock oil in conjunction with the piston define how fast - or at what speed the shock rod must be moving before a shock will "pack".

If given a particular piston will a higher viscosity oil pack faster than the lower viscosity? I'm thinking the lower viscosity will pack faster because its flow would be disrupted easier whereas the higher viscosity might resist turbulence more (the web link below appears to confirm). Please correct me if I am wrong.

Per http://users.pandora.be/elvo/
"Killer jumps or chassis-wrecking bumps require pistons with small holes to prevent the chassis from slapping the ground...if the track has lots of bumps or is very rutted, any packing up of the shocks would make the car bounce and thus very unstable. In that case you should try pistons with large holes."

This statement suggests that adjusting the piston only may be sufficient when tuning shocks. Why would somebody change both the piston and oil? I'm thinking one might choose an oil and simply adjust the piston or vise-versa. Is it a matter of finer tuning granularity? Does conventional wisdom suggest that some track types would use a certain viscosity and use piston changes to fine tune?

I never thought RC cars could be this complex when I started. Its been a fun learning experienc so far.
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Old 07-09-2008, 12:36 PM
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It just occured to me that one might change both piston and oil if the entire tuning range of a particular viscosity oil is outside the desired effect. In other words, if I'm still bottoming out after using the piston with the smallest holes possible I might increase the oil viscosity and start working with the pistons again. Does this sound about right?
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Old 07-10-2008, 05:25 AM
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Sounds like you're on the right path.

There's also the thing that pistons only come in a few sizes. Sure you could drill them out, but some seem to have bevel'd edges for different bound/rebound control.

The way I see it , it's the same as a spur/pinion combination. There's usually only a couple spur options, but a plethora of pinion's. You can mix them to get a very wide range, with very minor changes between them.

Swap to a bigger piston hole and thicker fluid , and you could end up with something JUST SLIGHTLY less/more resilient.

LOTS of combination to try out.

And personally, for shock tuning, if you've only got 1 set to work with, it's just easier to change the fluid only. That's really how I handle mine. I might adjust fluid, but I don't touch the piston much. I do some on-road touring car racing.
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Old 08-04-2008, 02:33 PM
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Don't forget that springs play a big role in your suspension as well as the mounting and angle of the shock itself.

Springs primarily are for the recoil but do factor into the dampening.

I am seeing a lot of folks at local tracks here running what used to be called a progressive setup.. a heavy spring with light oil in the shock. This works well on a rough rutted style of track.

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Old 08-04-2008, 08:24 PM
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Jerome - understood. I'm trying to break a car's components into is basic components in an attempt to simplify things and understand better.

Thanks.
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Old 08-15-2011, 11:10 PM
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Hi Folks i know this is an old thread. but i need some advice as i am into my first 4 weeks into driving my electric off road 1/10 truck.

I am having a few issues that i hope any of u can advice me.

Track layout.
1. bumpy track with big jumps.
a. Jumps starts with a big kicker double and in transition 3 smaller ones about 1/2 meter away from each other.

Shock setup.
Front weight 70
Rear weight 50

4 hole pistons in shocks. FnR

Springs
Front medium
rear light
both with sway bars

issues
1. when tuning and then on the bend there are a series of bumps, the car rear end kicks up a lot. making it hard to maintain a good line. understeering on bumps.
2. on jumps, the rear smacks into the ground.
3. on bumpy straights, on a few occasions, the car hits a small bump and went into cartwheels.

I bought 1 hole pistons and have the following oil weights on hand 40,50,55,70

while i think the front with the more damped, harder spring works well,

from what i read. I could use single hole piston with lighter oil. and the lighter springs.

But I am second guessing.
for the rear, should i use the single hole piston with a 40 wt or a lighter oil? if a lighter oil, should i be using 10-20wt or just stick to 40? and would it be advisable to change to heavier springs?

with the 40 wt and 4 hole piston, the car was drivable but bottoms on jumps too much as well. which was why i bought the single hole one.

or should i maintain 4 hole piston with a 70 wt oil instead and still run the lighter springs. I have gone heavier springs behind and the car was undrivable.

any advice on achieving balance?

thanks in advance guys
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Old 08-16-2011, 06:38 AM
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You forgot to tell us what type of vehicle you have
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Old 08-18-2011, 11:22 AM
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mucho apologies. i was out of town. didnt get any wifi there. sigh...

the car in question is a hobao hyper ST
i have a hyper 8.5 and a mini e-revo.


they all run on the same track so if i was hoping if i got the concept right, i would be able to apply it all around
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Old 08-18-2011, 08:25 PM
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You posted a pretty tough question cause all of these things are about driver feel. But to help you out I would break it down like this and try to eliminate one thing at a time

Start with the bottoming out.... don't worry about how the car handles or feels, just hit the big jump a couple times and check how it lands. Remember that you should be coming down the 'off' ramp and not over shooting it and landing on flat ground, and wen you do over shoot a little bottoming is okay (because you should be able to take the jump the right way 9 out of 10 times right...lol) just not a major thwack! Anyway find the oil and piston in the rear that you feel comfortable with that ends you bottoming issue....Then once you're good move on to the next and the next issue that you're having and eliminate them one at a time and then go back and recheck the bottoming and if it's still good then wallah!


I can tell you that the one thing you haven't said anything about is rebound and this drastically changes the way the shock performs and aids in bottoming out. If you don't know anything about setting rebound then youtube it. Just letting you know I run 1/8th buggy and can run 30wt all around with 100% rebound and the car will NOT bottom. However I can run 45 weight all the way around and run 25% rebound and it will bottom easily.

The only thing else I can say is 70f 50r seems really thick to me especially for the track you described. For a track like that in the buggy world I would be running maybe 40f 35-30r with 25% rebound front and anywhere from 50-75% rebound rear (whatever I don't bottom out with). Changing pistons actually has a more drastic effect on the handling of the car more then the bottoming out. Would it help yes, but it would change the way the car corners also, rebound is more of a bottoming out/overall traction thing. Lemme know whatcha think and good luck man
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Old 08-22-2011, 07:50 AM
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AH jabo5779! thanks.

sorry i forgot the link to reply here. finally found it!

driving style.. well cos its a 4wd, i like to power in on turns. go in to 90 bends and switchbacks without brakes but just releasing the trottle slowly. i run with 0 brake drag.

yes over the weekend, ran my truggy with new settings.

with all the readings and ur advice,
i ran 40wt oil in front with soft springs ( use to be 70wt front with medium front springs previously) and the stock 4 hole pistons without sways
rear i ran 25wt oil with single hole pistons and soft springs with sways.
somehow with the stock shocks i have the rebound rate was almost the same. but the dampening was different. i have more pack in the pack then the front. which was awesome across the bumpy straights.

The effects were great. awesome traction, awesome bump control. car kept straight on bumpy ground. overall lap time improved by heaps!

tuning the shocks did help a lot on the jumps. it stopped jumping with the nose down. even though i could control the throttle to keep the nose up...

removing the front sways sharpen steering a lot. i run 80, 100, 40 for the diffs.

thanks for the tips. i love my car more now.
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Old 08-24-2011, 11:40 PM
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Great man.... awesome that I could help you out and I have never driven or even seen anyone drive your car or your track .... For me I feel there is kind of a rule of thumb with off road. When you're lost just return to the basics.

For 1/10 scales
35-40front shock oil
25-30 rear
diffs 5000-7000-3000 or maybe heavier or lighter but keeping the ratio's about the same

For 1/8
same diffs but a little heavier all around for the shock oils 40-45F and 35-40R

I don't know the diff oils you're referring to but the ratios are close to what 5-7-3 so it should give you a basic feel.

Now that you've got a setup you can work with make sure you don't just throw in the towel in searching for better setup's. Remember where you started and tweak different things.... Do one thing at a time and write down or make a mental note of how it was better, worse, or unnoticeable. But I had to step in when I saw 70 in your front shocks lol... 50 max in off-road for me and that's pushing it and I wouldn't do it unless I had at least a medium traction track and not to many obstacles in my way. I think your setup before hand might have work good on astro-turf (something to keep in mind I guess)
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Old 08-24-2011, 11:50 PM
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o another thing was .... if the track turns against you and becomes tough for whatever reason (also applicable in cold weather) Use lighter oil by about 5-10 all the way around and for me I will increase rebound. Increasing the rebound and lightening the oil gives the car a nice planted feel to it.... It also gives you more of the 'pack' feeling that you were looking for without changes to your pistons. This makes the car easier to handle but actually slows your lap times down, thus making you more consistent.... this is for the situations where not many people are making clean laps or finishing mains and your willing to give up ur fast laps for a consistent time. You'll be surprised at how much you can slow your times down!
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Old 08-25-2011, 04:06 AM
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thanks Jabo, that is all good information! I started the initial tuning based before i got my car. lol. that is following some of the driver's recommendations. so which ended me buying the hard springs etc and changing the oil weights before i even drove it.

but i understand now. after a good ol' round of discussions. what i want to do is understand how making the car center diff more front bias or more rear bias would helps and then what no one uses heavy/thick oil in the rear diff.

i would think that once the diff oil changes, the planting of the car therefore the shock weights would have to be changed once more?
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Old 08-25-2011, 03:44 PM
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http://www.teamxray.com/teamxray/sho...p?file_id=4461
If that doesn't work google 'hudy setup guide manual'
Download the file and you'll have 40 pages of everything you could want to know.... This is not a bible however just a reference... Does every driver agree on what is said, no, but the changes stated in there give you something to look for once you make the change.

For center diff front or rear weight bias all that has to do with is giving the rear tires less or more traction.

For shocks vs diff oils, I treat them completely separate from one another. Yes the front diff oil will effect turn in, turn out, and on-of power steering. However the shocks need to be tuned to handle the track first and give you consistent lap times, then the diffs can be tuned to bring those consistent lap times down. Being a weekend warrior racer you really should focus on shocks, find the diffs that you're comfortable with and stick with them. When you start going crazy with racing then the diffs will be a tuning tool to run with the best. You can win the world championship running 5-7-3 for diff oil.... running bad shocks..... not so much.
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