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Old 03-26-2008, 08:07 AM   #1
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Default Chassis flex

Now reading up on some of the setup info given by company's lie x-ray and what not, they touch on a topic but never get in to the details of it. They say you can kinda use chassis flex as a tuning tool. Flex more, or stiffen it up more. What does playing with chassis flex do? I always thought that you want the least amount of chassis flex, but i guess it's an old train of thought.
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Old 03-26-2008, 09:12 AM   #2
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more flex = more roll = less traction roll = more grip = less understeer...
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Old 03-26-2008, 09:12 AM   #3
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Flex will give the chassis more grip which maybe you can not find in the normal setup.

I know someone who is head technician at a LeMans team and he told me you do not want to have flex because it is the part you have no control of, on the hole setup, shocks, anti rollbar etc. you have....
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Old 03-26-2008, 10:54 AM   #4
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Flex will give more grip but I don't know if this can be applied to gas cars since all the cars I've seen in the market have so many cross member that it won't be applied evenly......
It's a good set up tool in electric where they run rubber tires, softer suspension settings and carbon main chasis + the electric chasis is simetrical on most cars so it's pretty easy to apply chasis flex evenly from rear or front......
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Old 03-26-2008, 01:14 PM   #5
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It is something that you need to think about. The older Mugen sedans use to come with a 3mm chassis and the 4mm one was a up-grade. For most tracks the 3mm chassis would work out fine but when you had a track with high bite you would need the 4mm chassis so the car was less likely to traction role. Now they just sell the car with the 4mm chassis.
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Old 03-26-2008, 02:22 PM   #6
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well, i have a NTC3 with a lightened 3mm chassis, and a lightened 4mm chassis. Of course the 4mm is a little heavier but much stiffer (stock is 3mm not lightened), where the 3mm is a bit lighter, but has a lot of flex. I just didn't know if you could actually use the flex as a tuning tool along with your setup. Thanks for the wealth of info, and keep them coming if there's more to it. I'm a noob in training so, more info the better.
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Old 03-26-2008, 02:26 PM   #7
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Quote:
Originally Posted by Roelof View Post
Flex will give the chassis more grip which maybe you can not find in the normal setup.

I know someone who is head technician at a LeMans team and he told me you do not want to have flex because it is the part you have no control of, on the hole setup, shocks, anti rollbar etc. you have....

Roelof,

After spending most of my adult life working on full size race cars I totally agree with your friend.

In the big car world it is almost always better to use the suspension components (spring, shock, bars, etc) to adjust the set-up of a race car. However, in scale cars it seems that at times a more flexible chassis works better. Part of this could be because the stiff chassis sometimes makes the car very twitchy to drive, which in a full size car the driver can deal with but in R/C cars it is possible for a select few drivers but certainly not everyone.

I talked to a friend of mine last week that ran a very stiff chassis at Ft. Meyers and struggled all week, when he soften up the chassis he said it was like a new car and much easier to drive...therefore faster.

I can't explain why but I have seen many times that a more flexible chassis is faster versus a soft sprung car for instance. As I said, this is against good engineering rules but it does happen.
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Old 03-26-2008, 02:52 PM   #8
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Taking a look to the Formula-1 some drivers have the choice between their original chassis or the T-car and with the same setup most of them do choose the original (older) chassis, if that one is stiffer or has more flex I do not know....
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Old 03-26-2008, 03:36 PM   #9
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The main diffrence between RC and real cars. Is real race cars we have much more control over things like dampers etc. We have between 2-4 way adjustable dampers( you can adjust lowspeed bump, high speed bump, low speed rebound, and high speed rebound.. ) driver feedback is usually a lot better because they can feel what the car is doing.. Even if you belive your drivers smoking crack, you can conclude certain things from the data system and set the car up accordingly. Without the flexibility of multi adjustable dampers and the know how that goes with fine tuning a race car it would be easy to jump over the setup. A soft chassis in a real car forces you to run a softer setup(aero guys hate that) because if you make the chassis flex to much it makes the car inconsistent and hard to tune..

RC, especially in oval and rubber tire racing we tend to design cars that the chassis flexes more to make the tuning window larger so even the average guys don't jump from oversteer condition to understeer. Which makes the fast guys more consistent also.

One thing I would like to point out, its not an absolute, just because you soften a part of the chassis doesn't mean you always get more steering.. Great example is nitro touring cars with 3mm chassis on high bite tracks... the spring rates, traction and the load are such that stiffening the chassis at times can actually free up the car and make it more drivable at the same time..

and the idea of softening the chassis to make the Delta in grip front to rear isn't against the engineering concepts.. it just lessens the diffrence between the front and rear...
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Old 03-26-2008, 04:18 PM   #10
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Flex or not to flex, that is the question!
The 1/10 Xrays have a dial-a-flex approach that seems to work for them. In 1/18 it's another story. We have not been able to obtain competetive corner speeds with the flexible chassis. Maybe it's a size/weight thing. I make extremely stiff chassis for the M18 and for the 1/14 Recoil. They are WAY more competetive with the stiffer chassis.
The 1/10 Xrays seem to be at the top of the heap these days, with a fairly flexible approach.
In general, I go for the stiffer is better choice.
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Old 03-26-2008, 05:54 PM   #11
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Chassis flex is like adding a secondary soft progressive spring to the shocks, because the chassis tweists before the springs on the shocks react. (but it can make the car react lazy, on a big flowing track its not a big deal, on a tight technical one it is) A flexi chassis works better on a rough track I know that from Kart racing. But that said it depends on what frequency the chassis flexes at and the first order harmonics of the chassis. A stiff chassis is harder to tune but once its set it stays that way.

A flexi chassis will add steering, usually more than any gain in rear bite.
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Old 03-26-2008, 07:21 PM   #12
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has anyone really experimented with chassis flex on a 1/10th gas?
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Old 03-26-2008, 08:00 PM   #13
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Yup
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Old 03-26-2008, 09:09 PM   #14
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Quote:
Originally Posted by Baedarlboo View Post
has anyone really experimented with chassis flex on a 1/10th gas?
Although somewhat discretely. Darren (Muppet Racing) did alot of work on chassis flex with the G4. As Motorman also did I think.

One of the things Darren found was, given that the modular construction of the G4 made the chassis very stiff, he enlarged the holes in the rear of the top plate and did not tighten the screws down at that point! Sometimes omitting the screws altogether! This basically meant the rear and front of the car was only connected via the chassis plate. This gave the rear end alot of freedom to roll, flexing in relation to the front of the car/chassis. This fitted nicely with the high COG of gas cars at the rear compared to the much lower COG at the front.
Darren record with the car speaks for itself.

From a technical standpoint. It has already been noted that in full scale racing chassis flex is a no-no! Every opportunity is taken, even at the expence of weight gain (!!) to the car, is payed to rid the car of as much flex as possible. Unfortunately, the completely rigid chassis still eludes even top flight race engineers. It was this that had me struggling as to why R/C drivers, good ones too, still talk of having flex in the chassis.

I came to the conclusion, same as Ted Flack pointed out earlier, that a stiff, a very stiff chassis is still very hard to drive, harder then a more forgiving, softer chassis. AND in R/C, 80% is driver skill, with 20% car. Full scale is a different picture.

I think, as car components improve on R/C race cars, free-er but tighter suspention, better shocks/dampers etc. You will see stiffer and stiffer chassis enter the market and see success.

Good thread by the way. Good to see others sharing their views on this too.

Regards to all,
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Old 03-27-2008, 06:15 AM   #15
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all great info....thanks again to everyone!
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