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Old 01-27-2015, 11:07 PM   #1
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Default Chassis flex, huh, yeah. What is it good for? Uh-huh. Chassis flex, huh, yeah.

Really, what is chassis flex good for?

In motor sport, most, if not all race cars use ridged chassis platforms. Why isn't this transferring over to 1/10th scale race cars? Shouldn't the suspension be doing all the work? To me, the latest and greatest chassis flex design is just another gimmick to sell a kit. Also, I think adding chassis flex is counter intuitive to the suspensions main purpose. Is adding chassis flex a way to compensate for a poor setup?

Discuss!
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Old 01-28-2015, 12:12 AM   #2
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Chassis flex is just another way to generate extra traction through corners on a low traction track. Its not always a good thing. On high traction tracks it will slow down cornering speed and increase traction rolling. Modern TC cars are all about tuneability and therefore there are heaps of different things to adjust chassis flex.

So all in all, it depends (as always) on the situation
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Old 01-28-2015, 01:01 AM   #3
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You are right about full size cars. Chassis flex is bad there. If a more flexible chassis gives you better handling on a full size car, it means something is desperately wrong with the suspension.
Probably there's some aspect of toy car physics that is different enough from real car physics to make the flex thing work. I'm going to guess it's got to do with the drive belt forces bending the chassis and changing anti-dive/anti-squat when you are on or off the throttle.
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Old 01-28-2015, 02:40 AM   #4
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When I used to race Karts, the sidepods and bumpers etc were always mountied in a way that allowed them to be loosened off when running in damp conditions etc.
i.e. even karts used chassis flex.
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Old 01-28-2015, 03:07 AM   #5
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Hi All,
when racing cars, its all about having the least amount of wheel load alteration over a given time.
That is why a low Cg is better than a high... and so on (reason for this is the degressive character of rubber tyres ( decreases on higher vertical load)

Compared to real racing cars the "stiction" in the whole car and especially in the shocks is much higher in rc. "Stiction compared to whole stiffness of the suspension"

Now if we compare a stiff rccar with a soft (only the chassis stiffness is different, the springs, shocks and kinematics are the same) the stiffer car has a lot more wheel load change over time, because all the wheel travel caused by the uneven surface has to be compensated with the "high stiction and highly dampening" Shocks.
Lets say the soft car does not use its shocks at all and does all the needed wheel travel by chassis flex, there is very little dampening and stiction, but only the bare chassis torsional stiffness which determines the "spring rate" of the wheel.

Another reason: The typical rc shock increases its damping coefficient on higher shaft speeds, while a perfect damper should decrease. This characteristics result in a highly overdamped car especially on high frequency oscillations caused by the surface.
In real car dampers there are valves in the pistons which open at high speed to compensate for the rising damping coefficient.

Maybe my thinking is over the top, but as you really feel a difference on the track when changing chassis stiffness, that theory might apply.
In addition to that: When for example you decrease the chassis stiffness in a particular area, i.e. split blocks on the rear, you decrease the roll stiffness of the rear suspension(tendency to understeer) while keeping the same heave and pitch stiffness.

Last edited by Worst87; 01-28-2015 at 03:26 AM.
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Old 01-28-2015, 05:01 AM   #6
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Quote:
Originally Posted by EDWARD2003 View Post
Really, what is chassis flex good for?

In motor sport, most, if not all race cars use ridged chassis platforms. Why isn't this transferring over to 1/10th scale race cars? Shouldn't the suspension be doing all the work? To me, the latest and greatest chassis flex design is just another gimmick to sell a kit. Also, I think adding chassis flex is counter intuitive to the suspensions main purpose. Is adding chassis flex a way to compensate for a poor setup?

Discuss!
I agree. It's also a way to compensate for design problems in the suspension... which should be fixed at the source, not with flex.
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Old 01-28-2015, 05:16 AM   #7
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Everybody makes some valid points why/when/how chassis flex is used in certain applications. But I think the number one reason why you see r/c designers incorporate chassis flex into the car is because of the weight.

Any scale on or off road chassis may be the most "scaled down to the very last detail" in every way imaginable except for the weight. Could you imagine transporting a 250-300 lb 1/10 scale on-road car to the track every weekend?

The very notion that your comparing full scale cars' weight to r/c car's 1/100 scale weight should be the #1 argument for why chassis flex is used in r/c.
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Old 01-28-2015, 08:50 AM   #8
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Quote:
Originally Posted by Ropes View Post
Everybody makes some valid points why/when/how chassis flex is used in certain applications. But I think the number one reason why you see r/c designers incorporate chassis flex into the car is because of the weight.

Any scale on or off road chassis may be the most "scaled down to the very last detail" in every way imaginable except for the weight. Could you imagine transporting a 250-300 lb 1/10 scale on-road car to the track every weekend?

The very notion that your comparing full scale cars' weight to r/c car's 1/100 scale weight should be the #1 argument for why chassis flex is used in r/c.
Weight is related to volume and a 1/10 rc car should be 1/1000 the mass of a real car so 3 lb is about right.
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Old 01-28-2015, 08:57 AM   #9
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Even rigid race cars have a certain amount of chassis flex built into them. Every chassis flexes some whether it's an 8000 hp dragster or an 80 hp Honda civic.

Chassis flex just alters the tuning of the suspension. The more chassis flex the less you'll be able to tune but your overall setup will be more forgiving. The less chassis flex the easier it is to tune but your setup has to be spot on.

So if your having a rough time getting your setup spot on introducing some chassis flex can help even the curve.
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Old 01-28-2015, 09:09 AM   #10
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I was talking to a guy on the net about this a couple of years ago when I got back into RC racing. His take was, "We need chassis flex because of Brushless motors. Brushless motors have way more torque then the old brushless ones. Car lose traction when the contact patch of the tire are shocked and overloaded, with having some chassis flex some of the torque is absorbed into the chassis. Making your setup window larger." It sort of makes sense but I am sure there is much higher levels of phyics going on to.
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Old 01-28-2015, 09:53 AM   #11
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Maybe as the speed we race them works out about 5million MPH lol it needs to flex to get the grip,I'm sure if we raced them at scale speed we would have it as solid as possible lol
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Old 01-28-2015, 10:18 AM   #12
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I run an incredibly stiff touring car (the chassis is braced with a steel plate) and as long as I have the setup right you would never tell the difference driving around the track. I think the trend is reversing.
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Old 01-28-2015, 10:29 AM   #13
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One other thing: my personal experience is at odds with the whole "Setup Window" argument. Having run cars of all stiffness I have had situations where a flexible car was brutally sensitive to tuning changes and stiff car relatively numb where even reasonably large changes such as a drastic change in swaybars produced little change in the manners of the car. I would have to argue that the "Setup Window" is more a function of your tires and track surface, the higher the grip and more consistent your tires the larger your "Setup Window".
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Old 01-28-2015, 10:45 AM   #14
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http://www.thercracer.com/2015/01/st...ce-in-110.html
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Old 01-28-2015, 11:08 AM   #15
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After reading the above link, i interpret it like: if you have enough experience with the car and track, you should (especially at higher grip levels) run a more stiff chassis. But just look at the Worlds in Kissimee, most drivers were driving quite soft flex setup.

To come back to the theory of gaining maximum grip on an uneven surface: Carpet is very very soft compared to asphalt (literally :-D). And the bumpes are completely different (for example a kink in the carpet). The bumpes are maybe higher amplitude but at much lower frequency.
So the benefits of the soft chassis (lower wheel load alteration) doesn`t show up really, but the negative effect (less responsive to suspension setup changes) show up even more because of higher cornering g-forces.
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