Are people thinking about rc performance all wrong today?

[Jirka]

Someone mentioned using A&L style trailing arms in rear to save weight....

OK, on semi trailing arms You can not tune it as much as double wishbone systems could. Jrx2 5-link/multi-link system was more tunable, but it was a lot heavier like You said. But You can tune toe in and basic camber angles on trailing arms too.
Camber: Install shims between chassis and outer mounting attachment point.
Toe in: Move outer mounting attachment point more forward. I know that semi trailing arms makes bump steer too and that normally is disadvantage.
I just suggested this trailing arm idea because there just have to be something that could be made lighter and almost as good as than traditional cars have now. I know that this lightweight build will not be a great all around car, but if it will be good at even in some circumstances.

Comment about short shocks on an off road car...

I meant that if Optima or similar shocks are used, they are used because on smaller outer diameter and therefor lighter weight. This might be acceptable, since smaller diameter shocks could absorb lighter cars mass equally than thicker shocks on more heavily cars. Stroke is about same as on other shocks.

TTech / F1 style inboard suspension system

Isn't this a little too heavy for light weight build especially because there is more up and down and turning etc parts involved with them. TTech rear suspension might be different story.

Those are just things what came to my mind when fredswain's idea originally was with different words to ask "What are those unimportant parts that RC offroad cars carry with them that could be throw away without overall performance suffer?"

Reggie's last post was also very close what I felt too. See you guys in other topics.

Jirka

[fredswain]

I've only ever had one screen name here and have never been on as another so I'm not sure where that came from.

The concept of static vs effective (also known as dynamic) spring rates still doesn't seem to be registering or else the same person wouldn't be constantly asking me for an answer based off of incomplete information. Here it is in a nutshell so anyone can figure out what is going on. The static spring rate is what your spring is wound to. If you have a 4 lb spring, that's it's static spring rate. Simple. That doesn't change. Your effective spring rate is a combination of your static spring rate and it's leverage on the suspension system. If you have a spring that is mounted all the way out by the wheel, it has the most leverage and hence the highest effective spring rate. If you have the spring mounted halfway in on the arm, it has less leverage and hence a lower effective spring rate. If you have a spring that is vertical to the movement of the arm, it is going to be more effective than one that is laying over at 45 degrees. What is so hard to understand about this? It is your dynamic rates that you care about. They are the relevant numbers.

If you have a 4 lb spring and it is all the way out on the end of the arm, it has 100% leverage. Assuming there isn't something else going on the dynamic and static spring rates will match. The reality is that they will never match since the arms don't move in a pure vertical motion but rather in an arc. The shocks also lay over a bit which reduces their leverage. Their effective rate is highest when mounted farthest out and most vertically. Hopefully the concept is registering. What happens if you mount the spring further in where it has exactly half the leverage? It will have exactly half the effective spring rate. In order to get a spring mounted at this location that has the same overall effect on the suspension, you need to have a static rate that is twice as stiff. Yes it is in fact that easy.

Let's say we have a car that is perfectly symmetrical front to back. It has exactly 50/50 weight distribution, the center of gravity is in the exact center, and everything in the car is spaced perfectly so that no matter what happens, the weight is always balanced at the exact center. What would the perfect spring setup be? Not rates mind you but proportions front to rear? They'd be equal. In a perfect world the front shocks would be mounted at the same location on the front arms as the rear shocks would be on the rear arms. They'd have the exact same springs front to rear with the exact same preloads and would be set at the exact same angle. Everything would be perfectly balanced. Now what happens as you start to shift weight one way or the other? What happens to your spring rates? Do you leave them alone or do you change them to compensate? Let's say that we have 75% of our weight at the rear and only 25% at the front. Now what? Should you keep the same spring rates? Of course not. Remember it's not about static rates but rather effective (dynamic) rates that count. You want your effective spring rate at the back to be greater than the front. It should end up having 75% of the total rate at the rear and 25% at the front. It's balanced.

As we all know we don't run the shocks at the same location on the arms and we typically don't run the same shock lengths or springs front to rear. If you look at the advertised static rates of springs, you'll notice that the shorter front springs typically fall within a range that is higher than rear springs. The reason for this is obvious. The front shocks are mounted further inboard where they have less leverage which means they need to have a higher static rate. The front shocks are also shorter because their arc of travel is shorter mounted further inboard. This is why you don't need long shocks up front unless you mount them further out (and still have them standing mostly upright). Keep in mind that once you have balance, you shouldn't upset that balance. If you need stiffer springs for your track conditions, change all of them to stiffer springs but maintain that balance.

The nice thing about having a small model that we can hold is that we don't need fancy simulation to determine many things. We can very simply apply physics to the cars to get them setup in the ball park. You still need to drive them to get them fine tuned of course but by being smart about things and knowing what you are doing you can eliminate lots of the guesswork and interpretation that you'd have to if you tried to tune from scratch based only on how it drives. It's an in depth topic and this post only scratches the surface but it's logical, easy to understand, and methodical. Now you can try to discredit me all you want or you can actually think about this a little bit and realize that it's not so crazy after all. At the last place I worked at we had a saying. "Just because you've always done something the wrong way doesn't make it right today".

[AscotConversion]

it's called "wheel rate"....

[fredswain]

It's a term. The concept still applies.

[dspy8083]

Very interesting topic. I have recently been wracking my brain after my first night racing in about 22 years, last Friday. I felt so dumbfounded after that night to see that the fastest buggy on the track was a heavy TLR22. I could NOT believe that the chassis was as thick as my 1/8 scale gas car!

I could not understand this and I have been playing it over and over in my head as to why.

I also have real car racing experience and the adage, "light is might" and other pro 'lighten it up' for racing motos fly.

Lighter is always better it seemed. My graphite RC10 is surely the lightest car on the track and I did not win. I need more practice and I need to play around with balancing the car out. I am confident that once my suspension is tuned right and more practice I will get there.

I just ordered a 1S lipo because I need to know if my lighter car becoming lighter will cross some type of frontier against these new heavy weights. I will see and advise.....

[kaiser]

the tlr22 won because it was driven by the best driver.

just like the cactus classic, no losi's on the podium because the best drivers drove associated cars, same with the worlds.

[fredswain]

I think there is more to it than just weight. I think modern tire design has a lot to do with it too. Weight is used as a crutch too often today though. You see people ask how to make their car turn better and someone tells them to add weight up front rather than telling them how to tune it. There may be something valid about adding weight at times but I'm not convinced that more is always better.

[Coelacanth]

I think there is more to it than just weight. I think modern tire design has a lot to do with it too. Weight is used as a crutch too often today though. You see people ask how to make their car turn better and someone tells them to add weight up front rather than telling them how to tune it. There may be something valid about adding weight at times but I'm not convinced that more is always better.

More isn't always better, just as lighter also isn't always better. Try to envision weight, scaled down to the point where a car is ultra-light as if filled with helium so that it responds like a vehicle on the moon. Sure, the car weighs almost nothing, but is that the goal? Surely not, because that vehicle stops being a car and starts being something else entirely, subject to a whole different group of physics laws. I know this might come off as sounding ridiculous, but that's where we're going with this "lighter is ultimately better" argument, by extension. At some point, an earth-bound vehicle has to effectively trasmit it's power & forces to its environment, and if it's too light, it might not be able to.

[Mad Racer]

All the above points are true.

I have learn't that it is the "total package."

Car, Set up- ( Susspension, Roll centers, Springs & etc), Tires. Gearing, & most important Driver.

Corner speed is so important. Not straight line speed. As long as it's near on pace on the straights.

I was shocked to learn that at the 89 Worlds here in Australia that the times were still not being matched 20yrs on. ( Same track & layout ) Think about it Motors, 1200 or 1400 batteries, Tires & cars have moved on so much as well as electrics.

A lighter car is always better. More so in a controlled motor class. A lighter car will accellerate better. Reach top speed quicker. Have more grip with the same tire combo to a heavier car.

My new 22T will be my first new modern car build for over 5 yrs and can't wait to see how well it goes with todays electrics as it was designed too. All my older cars have had to lightend up in spring/dampning for the Lighter Li Po batteries.

[Coelacanth]

A lighter car is always better. More so in a controlled motor class. A lighter car will accellerate better. Reach top speed quicker. Have more grip with the same tire combo to a heavier car.

I agree with everything you said until the last sentence. "Grip" is a function of a lot of other variables than just weight. If this were true, how come a heavier 1:1 vehicle can get out of a snowdrift than a lighter one, which just spins its tires? How come Lamborghinis don't perform too good on a snow-packed highway? Obviously a Lambo has better weight distribution, aerodynamics & power than, say, a Chevy 3/4-ton with narrow, blocky-treaded tires and plow-blade mounted on the front.

Grip is influenced by aerodynamics, downforce, amount of power in addition to the common variables such as weight & tire type.

[fredswain]

Tires have become very different from what they were in the days of the lightweight cars. Then again tracks have gotten firmer and cars faster too. Today's tires are very very soft but use inserts. The older tires are made of a harder material but have no inserts. They behave very differently. The old softer loamy tracks needed a lighter car so it didn't sink in. Let the spikes on the tires take care of that. When you have little power, any added weight noticeably slows you down and we have a definite lack of power compared to today's cars, especially in stock class. Roll centers on the cars was typically higher than today's cars due to shorter arms and camber links which puts more down force on the outer wheel in corners. The loss is straight line stability didn't matter as much since the speeds were lower.

I still think bucking the adding weight trend today has merit. I still think a car at the minimum spec can be made to work well. The question is whether the tires we have today can work well on a lighter car? I think this is the number one problem. The older tires may be the better choice. In the scans section there is an article on building a lightweight RC10. One thing he mentions is that tire selection is very critical and I believe it. I think ROAR should really adopt a max weight into the rules now. They have a minimum. I think it's time to update things to give an acceptable weight range rather than specify only a minimum.

[Charlie don't surf]

Take a rectangle 9"x11" add suspension that is 1/3 the width, and 2/3 the length and use a control tire and a equal shock on all four corners. Make the car 3lb total but all the weight centered in a 4"x1"x1" space in the exact middle of the chassis.

Take the same platform and bias the weight equally on each of the four corners of the car.

What would be the difference in handling on an offroad track?

[fredswain]

Interesting that you mention that. Since I started playing with my mid motor car and it's sideways mounted battery, I've gone back to trying a sideways battery in rear motor just to see the difference. As with everything there are pros and cons but I've found that the sideways battery reacts very well to bumps and rougher surfaces. It does fly off of jumps and corner differently though and not necessarily in a better way. Weight may matter but I think where that weight is located matters just as much.

[foots]

After reading all this my head hurts...

[Coelacanth]

After reading all this my head hurts...

I guess it's better your head than your...foots.