Dino_D

Normally if I found a oil weight that I like, I prefer to use the same oil weight and adjust piston sizes. I only change oil wt due to temp.
Oil also controls weight transfer or how your car corners.
Given the same ratio, the low speed movements are the same (weight transfer) but the pack is different. Smaller holes give more pack on jumps, and larger holes are better on ruts.

I tend to prefer running slightly heavier and bigger holes as the tracks here are more rutted. Smoother tracks, you can use smaller hole sizes.

Now this changes if you increase the hole area or ratio by increasing the number of holes, I tend to use heavier oil. Going lighter oil will increase the speed of transfer with more holes, and pack even faster. You will need to experiment with heavier oil when the hole area or ratio increases.

Another thing is, lighter oil packs more easily as you stated, and faster with smaller holes. If you go very light and use many small holes 6x1.0mm, the piston can build enough pack and just stop halfway down the stroke and it will be abrupt upon compression.

WallyRC

Thanks Dino!!! I think I'm going to try some 3 hole Pistons in the 1.2 to 1.4 range.

fredswain

iTrader: (1)

The problem with using the same oil weight all around is that you have different pack in front vs the back. You want them the same. That means smaller holes and lighter oil up front and larger holes and heavier oil in the back. Which ones exactly can only be determined by testing but the front oil should always be lighter than the back and the total hole area in front should always be less than the rear. I know most people don't run this way but most people don't understand pack, including the pros. Their setups sheets are proof of this.

Mantis Toboggan

iTrader: (4)

You know Fred, you preach all this "the pros don't know how to tune cars correctly" but did you ever stop to think that you might not be fast enough to drive their setups? These guys and their team of engineers get paid to go as fast as possible. Do you think they have never tried thinner oil and smaller piston holes up front before? They get paid to do it, and you don't. You are not a racecar engineer, and you don't work for any of the manufactures. Vehicle dynamics is way different than designing oilfield equipment.

fredswain

iTrader: (1)

I never said I could drive. I'm definitely not talented there. I can tune though. I have a very thorough understanding of mechanical design. That's probably why I get paid to engineer things too. Here's something to think about. Does doing a job neccesarily make you an expert? Is a McDonald's employee a master chef? Is everyone good at their job? Is there anyone out there that is good at something that they don't do as a job? I've thought about how lots of things are done. I also wonder why the same bad information is constantly passed on and on. At what point has something been done wrong for so long that it becomes right in everyone's eyes? You can either believe me or not but you clearly haven't tried my method. If you aren't testing, you're guessing.

Mantis Toboggan

iTrader: (4)

No, a McDonald's employee is not a master chef, and attempting to draw that as a parallel is a bad example. There are world championship winning engineers that design these cars, and world class drivers that push the equipment to the limits. You are neither of these things so obviously you are missing something. Again, these guys get paid to do this, they have tried all sorts of stuff. Likely stuff you haven't even thought to try. If your way worked so much better, that's how they would be doing it. The clock doesn't lie, and their livelyhood depends on doing what works best.

Oh, your idea of equal length shocks was tried on the original HB D8. It didn't work and they went back to longer shocks in the rear. You may be a great mud pump engineer, but you are not a vehical dynamicist

Dave H

Does this lack of understanding by the pros only occur in RC? Or is there also a lack of understanding at the pro level in full scale off road, Nascar, SuperCross/MotoCross, Indy cars, F1, etc?

Dino_D

At the end of the day. No matter what combination you use with oil and piston, it needs to be closely balanced.

Ideally from a 8 inch drop test or you can even use 1ft. The suspension has to fully compress equally front and rear at the same time (both in distance compressed and time) and also rises about the same time.

If the rear sinks faster and raises faster than the front, then you need more pack. How this is achieved, via oil and piston combos is thru experimentation. Also the amount of compression has to be very close front and rear. You can't have the front compress 10mm, while the back does 20mm. This will result in front lifting off the ground over bumps, and the back of the car possibly slapping on jumps.

The end result that you want to achieve is equal compression and equal rise to static height and at equal speed. Once you achieve this, then your car will land more settled and go over jumps and bumps with minimal disturbance.

Keep in mind adding and removing weight will also affect these settings and may require additional tweaking. Sometimes you might find some setups that can achieve this, but many times it's not applicable to every car due to differences in the weight of the electronics used, or battery placement or lead or brass plates added regardless if it is the same model and brand. Also binding in the suspension and ball cups can also alter these settings.

In addition, sometimes people do make the front slightly stiffer mainly cause they are using heavy braking coming into a corner, and the front will swat too much under load and over steer, so they trade some bump handling for better corner entry as the front of the car doesn't compress as much. There is a trade off sometimes.

WallyRC

Fred, Dino was referring to using the same oil weight that I was previously using but changing Pistons to get the right amount of pack. I was asking in his or your experience that when you find dampening you like but not enough pack, do you usually end up with about the same oils weight as before or higher or lower once you change Pistons. I know you have to test it all again. Just wanted a good starting point if I kept hole area the same but tried to increase pack would oils change as well.
Thanks
I thought I also read where you were using like 50 wt in the front of your rc10 and something like 30 in the rear!?!?

30Tooth

iTrader: (1)

Well, I could take this to PM but this is a forum after all so let's share some wisdom.

I'm not Fred but I have enough knowledge about this subject. The original D8 had equal length shocks but the Motion Ratio was different front to rear AFAIK, that hurts more than the change in length could help. It was badly implemented. I'm not against unequal length shocks but would make it easier to "decode" our current shocks.

Yes only in RC. RC was modelled after the little understanding people had at the time about car dynamics. In the other classes they have teams dedicated solely to increase performance.

Bonus: What is so different fundamentally from the B5 and the RC10?

Dino_D

In my opinion, Oil controls the speed of weight transfer, and the pistons control pack. I dont' use oil to induce more pack, as sometimes you get the illusion of more pack with the oil as it takes longer and slower to compress just enough so that it won't bottom. but then it also will slow down the weight transfer front to rear and side to side. So I rather tune slightly more or less pack with piston changes. Its more subtle than changing the entire oil and piston combo.

I can understand the argument for the front oil being the same as the rear or lighter than the rear on a 2WD car as the front is much lighter. And you need the car to dive into the corners for steering. This is fine if you are using MM3 gear as the car drives flatter in corners and doesn't transfer weight around as much.

But as for MM4 gear, you have a lot more weight transfer happening. Having a very light front end will make the car dive more. How do you solve this? Either thicker oil or smaller holes (less hole area) Sure you can solve it with smaller holes and lighter oil, but you might be inadvertently cause the front to pack earlier in the stroke causing the front to hop around on a bumpy track. Alternatively you can have a larger hole area, maybe using 1.6 or 1.7s up front and thicker oil so you negate the affects of diving under deceleration yet have enough movement to absorb the bumps. But its all trial and error, and may ways to setup your shocks. There is no right or wrong. It all depends on the track, whether you are using MM3 or MM3, or rear motor, weight balance of the car, etc.

4WD... The front of the DEX410 is much heavier Also it's 4wd. You can't run light oil in front, or lighter than the rear for that matter. Its just gonna bottom the front end on heavy braking with light oil. I have even flipped the car upside down under braking testing lighter oils.

The hole area can be equal or less than the rear.
I find the stock spring to be good in most tracks.
Heck even jorn used the same springs front and rear for both indoor and outdoors.

As for springs - another option would be
AVID - Purple Front AVID - White or Yellow Rear. The Avid are less progressive than the Durango Springs so the feeling is a bit more direct, especially in the front. I don't get that push slightly on entry then massive steering. As the spring is not soft in the beginning and makes the car push then gets harder and the steering comes in hard.

In 4WD
I personally prefer 2x1.6 up front and Rear 2x1.7 or 3x1.4 or 4x1.2 depending on the surface and jumps. But I know some prefer a 4x1.2 combo up front.

Other combos I have seen are 2x1.7 or 3x1.4 or 4x1.2 front with 3x1.5 or 4x1.3 rears.

Oils range with temp and track surface (45/35 42/32, 40/30, 37/27)


In 2WD
I normally run 3x1.6 pistons both front and back. It's pretty good on bumps and ruts. but I used 35/30 for oils. I go up one wt or down one wt depending on temp. I have team mates who do the 3x1.4 front and 2x1.6 rears but they run lighter oils like 30/27. If you are using MM3, you will probably use similar oil wt front and rear. But like I said, it depends on your battery configuration and whether you are using 3 gear or 4 gear.

Dino_D

This chart is what I found online based on AE oils. You can see that 2x1.6 using 25wt has similar laminar flow (low speed flow) like a 2x1.7 with 30wt. But the high speed pack is totally different, 1.6 being much higher.

The AE 1 2 3 pistons are 2 hole
#1 Large (0.052)
#2 Medium (0.046)
#3 Small (0.043)

As you looking for a comparison between the different pistons and oils?
Does this help? Too bad I haven't found a graph showing the same oils, same hole area but different piston combinations. You will find the low speed to be equal but the high speed to be very different.

WallyRC

Thanks for finding that!!!
Another question, have you or anybody had issues with the aluminum chasis bending down where the rear droop screws hit?

Devin

My drivetrain got really loud over the past couple weeks. I am not sure what it is. I am pretty sure it is not the diff, and I recently did a full bearing change. Any ideas on what the noise might be?

Here is a short video I took of it:
https://www.youtube.com/watch?v=EvGZdV9cgRk

ekt

iTrader: (4)

Check that your motor plate screws aren't touching the slipper plate and that your spur/pinion aren't rubbing on the cover.