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Old 02-23-2013, 09:49 PM   #1
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Default Chassis flex

Basically, i'm trying to find out why allowing one end or the whole car to flex more will achieve more grip. Running a thinner chassis or top deck , or running a front inner or rear inner split block vs a solid block allows the car to flex more, but how does this relate to more grip on the track? What does the increased flex allow the car to do differently that gives it more grip? Does it actually give it more grip ?
How would you know when you need to change a setting or part on the car that gives it the ability to flex more(or less)?

I've searched for the answer to some of these questions on this forum and google but cant seem to find an actual answer.
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Old 02-23-2013, 11:16 PM   #2
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If the traction is loose, loose/soft settings, they add flexibility/grip.
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Old 02-24-2013, 01:30 AM   #3
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Go from the softest setting to the hardest with a few test laps and observe how the car feels. Come up with a theory of how it works and see if you can predict how the car will handle with a setting somwhere in the middle.
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Old 02-24-2013, 04:38 AM   #4
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Think of your car as a mass at the centre of mass, suspended by four (mass-less) suspension arms that reach out to the tyres.

I'm sure you can imagine that if the chassis is softer, it is making that "virtual" suspension arm between the centre of mass and the tyre softer. A softer suspension arm acts like a softer spring/damper unit. Hence the feeling of more "grip" from a softer chassis.
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Old 02-24-2013, 05:52 AM   #5
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Softer means less weight transfer,thus more grip. Traction is normal force x coefficient of friction. Problem is tires are only linear within a certain range do normal forces. Beyond a certain point they make no more grip. So once you get to that point more weight transfer removes grip. A lot of people confuse roll with weight transfer. Then are not the same an are almost opposite.
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Old 02-27-2013, 07:22 AM   #6
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Quote:
Originally Posted by sosidge View Post
Think of your car as a mass at the centre of mass, suspended by four (mass-less) suspension arms that reach out to the tyres.

I'm sure you can imagine that if the chassis is softer, it is making that "virtual" suspension arm between the centre of mass and the tyre softer. A softer suspension arm acts like a softer spring/damper unit. Hence the feeling of more "grip" from a softer chassis.
I dont quite understand this concept or the use of 'softer'

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Originally Posted by slotracer577 View Post
Softer means less weight transfer,thus more grip. Traction is normal force x coefficient of friction. Problem is tires are only linear within a certain range do normal forces. Beyond a certain point they make no more grip. So once you get to that point more weight transfer removes grip. A lot of people confuse roll with weight transfer. Then are not the same an are almost opposite.
I dont understand the concept of 'softer'
What is 'softer'?, assuming the same thickness chassis, removing a brace from the chassis(solid to split block) doesn't make it any 'softer'.If you go to a split block in the front from a solid block it allows the front end to twist more under cornering forces in relation to the rear of the car, it doesn't make anything softer
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Old 02-27-2013, 09:33 AM   #7
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Quote:
Originally Posted by narcotiks View Post
I dont quite understand this concept or the use of 'softer'


I dont understand the concept of 'softer'
What is 'softer'?, assuming the same thickness chassis, removing a brace from the chassis(solid to split block) doesn't make it any 'softer'.If you go to a split block in the front from a solid block it allows the front end to twist more under cornering forces in relation to the rear of the car, it doesn't make anything softer
Surely something that "twists more when a force is applied" is softer??????
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Old 02-27-2013, 11:30 AM   #8
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Think of it as more or less rigid. As you remove top deck screws the chassis becomes less rigid, thus gaining flex and becoming "softer".
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Old 02-27-2013, 12:16 PM   #9
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Despit how rigid the chassis feels, it does flex when load is applied. Yes it is minute but its enough to change the way the car feels. A stiffer car responds faster to input but has less overall traction then a softer car. You need to find a balance between the two that yields the lowest lap time for your style of driving.

Sometimes you need to figure out how to drive the setup that's on the car before you start changing things.
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Old 02-27-2013, 01:04 PM   #10
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Quote:
Originally Posted by Brokenparts View Post
Despit how rigid the chassis feels, it does flex when load is applied. Yes it is minute but its enough to change the way the car feels.
On today's TC's, it doesn't seem minute at all. If you grab the car by the ends, and put your thumbs on the shock towers, you can feel them flex a lot. You can also see where the flex is happening with different top decks and different combinations of screws.

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Old 02-27-2013, 04:39 PM   #11
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I have a few different baseplates for my car, and found huge differences in feel from stiff to flexible. Strange thing is I honestly didn't think the flexible plate gave the car more traction. I know this is completely against what the experts say.

I did find the way they made their grip was very different. For example I found a soft plate gave a lot of initial response followed by midcorner push in fast sweepers, and on exit a lot of initial steering on first application of throttle followed by push a few feet out the corner. Also it seemed to stick more in slow turns.

A super stiff car seemed be quite unresponsive initally, often pushing all the way through sweepers. But very consistent if a little pushy on exit.

After some time experimenting I found a certain amount of flex was really good to help initiate the turn but was also stiff enough to preserve the midcorner steering in sweepers, and was sufficiently consistent on exit (and overall) so you could set your line and the car would stick to it onto the straight for example.

I ended up with a pretty stiff car. Much stiffer than the current crop of TC's.

Just to make things even more complicated I also found that if the car was set soft it worked a lot better with lower roll centres..(it never ends!)

Probably there will be someone who experienced the exact opposite of everything I did but if you can find a setup that works for you whatever the flex then that's got to be the best way to go regardless of the trend of the day.
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Old 02-27-2013, 05:22 PM   #12
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Imagine your RC car as just a chassis with wheels and an axle with no suspension at all. No grip right?

Actually the early RC cars were just that. At that time there weren't sophisticated materials or manufactering technologies to make the parts we have today. In fact in order to get more grip a chassis was created that flexes. These chassis were made out of Lexan; yes the very same material used for your RC body. The chassis flexed a lot which translated in the grip needed to work at that time.

Here's a post on RCTech about these cars: http://www.rctech.net/forum/9062849-post47.html
Here's a pic of one of those chassis:
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Old 02-27-2013, 06:34 PM   #13
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I’ve always thought of the whole flex thing is bit of a bodge to actually making the cars handle.

In just about every form of motor sport where there is chassis flex and deformed geometry it is a thought of as a really bad thing. One of the biggest reasons for this is because you can’t accurately control it. Remember chassis tweak? Flex is effectively doing this every corner.The only instance I know where chassis flex is desirable is in motorbikes and this is only because when they are leant over to extreme angles suspension can no longer cope with the load directions and flex becomes the suspension.

Flex basically works by distributing the forces and energy around the car. For example is you stuff a car hard into a corner the outside front would be taking all the force due to weight transfer. If this force exceeds the flexes rigidity the chassis would start to flex and this flex would absorb/store some of this energy and then distribute it to other areas of the chassis or even back to the same corner as soon as some of the input force is removed. It really just makes everything, in the way of setup, more forgiving and less likely to overwhelm things like damping, wishbone flex, wheel flex, chatter or bottoming out. Probably the reason why I’m finding myself making more adjustments like wheelbase, track widths, roll centres and diff resistance these days rather than shocks angles, springs and damping to get the car to react.

If you could totally eliminate flex and control things more accurately such as fast and slow speed damping, fast and slow rebound, progressive rates, wishbone flex, (awesomatix seem to be doing a good job of this!!!!) then you can control forces better and ultimately have a better performing car. Until someone comes up with micro Ohlins suspension then I guess we are stuck with floppy cars.

One thing that has been done with flex that really does seem to benefit is evening out flex throughout the chassis, it’s also been allowed along the centre of the chassis but not on a front to back axis. I think when the chassis were stiffer the flex was just so uneven that they had no progressive give in them and just kind of let go when forces got too much.

Last edited by YZFAndy; 02-28-2013 at 02:24 AM.
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Old 02-27-2013, 07:08 PM   #14
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I found this video to be very helpful. What I got from it is softer doesnt necessarily mean more traction. Its all about tire contact patch whether its flex tuning or springs etc. Its amazing how a square inch (total) of rubber controls our little cars at blinding speeds. I believe this video can be translated to our applications too.


Maximum Control -- The Chassis suspension

http://www.youtube.com/watch?v=DQ988oNdgqc
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Old 02-28-2013, 12:54 AM   #15
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Wow I remember (I think) Art Carbonell winning big with one of these Lexan Cars. Maybe 1980? 81? Happy days.

Quote:
Originally Posted by YR4Dude View Post
Imagine your RC car as just a chassis with wheels and an axle with no suspension at all. No grip right?

Actually the early RC cars were just that. At that time there weren't sophisticated materials or manufactering technologies to make the parts we have today. In fact in order to get more grip a chassis was created that flexes. These chassis were made out of Lexan; yes the very same material used for your RC body. The chassis flexed a lot which translated in the grip needed to work at that time.

Here's a post on RCTech about these cars: http://www.rctech.net/forum/9062849-post47.html
Here's a pic of one of those chassis:

Last edited by hana166; 02-28-2013 at 01:32 AM.
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