WallyRC

I totally agree Fred. Can't wait for you to "balance tune it." And see how she handles. Will be interested to see your setup balance compared to the "pros." And can't wait for your 3 gear laydown. 😜😁

micholix

+1 Same here!

PS.: i like that hint, Wally!

banx

i agree with the statements above as well..... but maybe the pro's are tuning for chassis flex as opposed to using the chassis itself to tune.... if that makes sense? maybe just a way of how they approach the problem. maybe the flex creates an increase in contact or increases the duration of contact with the ground through rough tracks?


I'd love to hear more of your guy's thoughts on this as I can only think of flex being good in the real world for off roading. in actual trucks and suv's with frames. racing rc's not to sure

fredswain

iTrader: (1)

I would say that IF chassis flex is a benefit, that it'll be on very rough surfaces which sadly offroad rc really isn't anymore. Even then the flex would need to be side to side rather than front to back. On rock crawlers flex is a great thing. I find it weird that tc racers use flex as a tuning aid. That's the last place that you'd ever want it. There's a fundamental lack of suspension tuning going on there.

Offroad rc cars have a few unique challenges and the approach between 2wd and 4wd tuning needs to be different. I am a big proponent of balance tuning but the front end kick on a 2wd really messes with that. There needs to be a different approach taken to shock pack and oils as a result than there would be on a 4wd or a car with less front rake.

The first thing I do is balance spring rates front to rear with no oil. I want the chassis to stay level in compression and rebound. Again, this is without oil. This is merely a baseline though. Once I find a combination that works, I then add oil. I'm trying to find a dampening characteristic that I like and a pack characteristic that I like. I'll empty and refill the shocks many times at this stage. I work out the proper piston and oil weights front and back to give me balance in compression and rebound that are equal, including pack. This gives me balance BUT only in heave.

Heave is the chassis going up and down only. Pitch and roll are also affected. Camber links and sway bars are used to tune roll. What tunes pitch? At the rear we use anti-squat to give a small change but we also use ride height to limit things. That front end kick really screws things up when it comes to pitch as pitch under braking is seen as front end dive and we've got lots of pro-dive geometrically built in. This is where it gets tricky as we are about to change half of what we've worked for up to this point.

Hopefully the spring rates are known. To control front end dive we need to make the front end suspension stiffer. But that upsets the balance! Yes, but you need to know how to compensate. Empty those front shocks again and use a spring that is about 20% stiffer. On a 4wd, it may only be a 5% stiffer spring. Maybe it's fine as it. Leave the rear end alone. Now refill with oil at varying thicknesses until you get one that results in the front and rear end rebounding at the same rate. The front end is noticeably stiffer at this point in compression so if you drop the car, the front end won't go down as far. This is a function of pack. You need to drastically reduce it to get that balance back. Once again you are emptying those shocks and are probably sick of the process by now. You need larger and larger holes but also thicker and thicker oil until you get that balance back. Once you finally get it, you once again have a balanced suspension but now you've controlled front end dive under braking. You can tweak it more by using stiffer and softer springs but you need to understand how oil weight and pack need to be adjusted as well. We balance heave this way, and have controlled pitch. What about roll? Now we've got more roll resistance at the front end than the rear. Use a rear sway bar to balance it out. A sway bar doesn't affect heave or pitch. Everything has a job and the key to proper tuning is to understand what those jobs are. Suddenly the camber links are fine tuning devices. Things get simple once the shocks are properly setup and adjustments are typically small and simple. If you were patient and did everything properly and carefully, any advice that says, "add weight" or "move your shock mounting points", or "change your oil" suddenly seem ridiculous because you now know that any advice that suggest that is based solely on a guess that has no foundation in suspension tuning knowledge. If you aren't testing, you're guessing.

Those guessers will tell you things like "we don't have the technology that full size suspensions do" but will then contradict it by saying things like "full size techniques don't scale". So which one matters? It's all ignorance. Physics is physics. They'll then justify their ignorance by saying "but the pros do it this way". And??? So what? Going back to the real world of racing, the best drivers don't work on their own cars either. They state what they feel the car is doing and their mechanic makes adjustments based on that feedback. Should these drivers be the ones asked for tuning or maintenance advice? They have a natural talent in area. That doesn't make them experts everywhere.

So lets hit that chassis flex thing again. Modern tracks are generally smooth but have jumps added. There isn't much suspension work other than landing jumps so it really comes down to keeping the car flat in corners. In the old days, with rough tracks, each side of the car was constantly responding to some bump that the other wheels didn't feel. Ultimate high grip cornering wasn't a priority as we aimed for the corner, slammed on the brakes, and slid the rear end around. The stiffer the suspension, the more critical a stiff chassis becomes. If the suspension is soft enough that it responds to bumps before the chassis does, the chassis is stiff enough. Today we may have lower spring rates but we severely over damp those springs. Best traction is with a dampening ratio between .5 and .7 but that's for another day. The problem with this dampening is that the suspension is primarily being used to prop up the car in corners whereas a sway bar and lighter dampening may be a better choice. The over damped, under sprung condition means that the suspension can't react fast enough when it encounters bumps and the wheels lose traction. Something has to give and it's not the suspension. People compensate with chassis flex. In essence the chassis works as another suspension spring in series with the shocks. Now the car twists a little and the wheels keep better contact with the ground, giving more traction. It's a band-aid to a problem of an improperly setup suspension. Then you get into the problem that you try to stiffen the suspension even more because of something that it is or isn't doing but going stiffer on a suspension that isn't moving enough anyways doesn't do any good. It's sending that force into the chassis. Now you are "tuning" your chassis flex for traction. What kind of archaic solution is that???? Stiffen that chassis and learn how to tune the car!

Sorry for the long rambling but this is why I don't like setup sheets, "expert advice", or copying others. When everyone is just as ignorant, the best setup is the one that is less bad than the others.

micholix

Hi Fred,

Great write down and description!

I realy would be interrested in a full sheet, or file of your suspension setting/tuning!
To my bad, i have to read it more often and have to translate some parts, cause of my lack of english knowledge...

fredswain

iTrader: (1)

One thing that blows me away is the concept of the "cheater" car, which led to the 210F, the Team C TM2, and the XRay XB4-2. On carpet and high grip tracks, people were using their 4wd cars without a front drivetrain. They converted them to 2wd. They were fast. Everyone assumed that it was because of the drivetrain and weight balance, and that was partially correct, but even a rear motor can be made fast in the corners if you know what you are doing. The real secret is the 4wd front end kick, or near lack of it. They are only raked back around 8 degrees or so. When you have a big front end rake, when you get on power, that kick shifts weight rearward, off of the front wheels. Those wheels are trying to steer! The problem is worst when you are on power in a corner. A lower front end kick will tend to keep those front wheels on the ground better in a corner, specifically the inside front wheel. Modern high grip car designs should really have a front end kick under 10°, not the 25° to 30° where they are now. Companies took those 4wd cars, converted them to 2wd, and then replaced the real secret that made them so nice on high grip to begin with, the front end. They put those 25° kicks back on them. Put an 8° nose on a 210 or 210F and see how much it transforms in corners on high grip. It'll be a different car.

WallyRC

Love it Fred!!!

WallyRC

Search "tuning with camber links". Fred goes over the whole process. Somebody has a link to a file somewhere in there that combines it all. Read it slow and take notes. About halfway through and you will be done. The later half is useless. SLO-MO video on our phones helps with tuning.

fredswain

iTrader: (1)

Since I never finished explaining things because I was being attacked by people that still have their parents tie their shoes, I never got into adjusting pitch through stiffer front springs and re-balancing oil and pack. I never explained 2wd vs 4wd tuning or why a 4wd almost always needs a sway bar at both ends but a 2wd only at the rear. I never explained tire loading and weight balance and the relationship. I only got through heave, which is half the story. There are probably lots of people out there running half assed setups based on that thread that still find it better than what they had and others that think it's crap because they don't realize it's not the whole story.

micholix

Thanks Wally, i did that already!

i did copy an past it by myselve out of this thread into a word file, to get the informations together, my file is already 3 pages long, but not 100% sure, i got it all together correctly, as the thread was getting so Long with the discusion and the notes from People that do not agree, i stoped reading that any longer, just to grab a fiew sentences out of one post and overfly 15 other unnaccesary posts...

...but as Fred sayed above, i always was missing somthing and when i did the spring/drop test on my schumacher k2, there were some strange things going on, i have a full set of front and rear Schumacher CORE springs and was not getting to get the correct spring, i ended at "so lala", with the hardes(black) rear spring and the softest(White) front spring and the front end is still swinging a bit to fast, compared to the rear!?

So a full sheet, or file, with just Freds explanation would be a tresure for me and i'm sure, for many other People too.


EDIT: And YES, it still does allready better, than before, when i was copying Setup Sheets...

So, enough off-Topic from my side!

fredswain

iTrader: (1)

I can tell you just by looking at those spring rates and knowing where the shocks basically mount on the arms and the general weight balance that the problem isn't the springs. You missed something. There's no way in hell that spring combo would balance without a serious redesign of the car.

One thing that I've found a few times, most recently on an original 5-link Losi JRX2 is that I could not achieve balance with the stock shock towers. I had to use a different shaped front tower from the JRX-Pro SE to achieve balance. The shocks didn't change and the arms and mounting points didn't change. Only the upper location did. It drove me crazy trying to figure this out. Unless you are missing something, you could be having the same issue.

fredswain

iTrader: (1)

I forgot to mention that I measured the width of the Exotek chassis. It it's widest point on the sidepods, it's 4-1/2". It tapers down a bit toward the rear to 4-1/4"

micholix

hi Fred,

I hope i did understand that right!?
Shocks are mounted at middle hole all arround, schumacher does have three holes at the a-arms and five holes on towers, but the fronts are leaning way mor to the inward at the top!

here is a foto, sorry for the crap picture, but i hope you can see it, what i mean?

micholix

I dont have scales to messure balance weight, but i run saddle packs at the rear and the max. weight is arround 1800 grams!

micholix

Oh, thanks for that!