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Old 11-10-2011, 05:11 PM   #16
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Originally Posted by R3VoLuTiOn View Post
IThe softening of rubber tire is a chemical reaction to the compound, but flex is a physical change.
Even that is a physical change, think of it this way, water changing from ice to steam to liquid water again is still water, its chemical structure has not been altered, its still H2O, the same is of rubber, friction causes heat which changes the physical properties of the rubber, making it more elastic, but there is no chemical change in its chemical formula, it sill remains CH2=C(CH3)CH=CH2 polymerized.
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Old 11-10-2011, 08:28 PM   #17
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IMO its a bit of everything. The softening of rubber tire is a chemical reaction to the compound, but flex is a physical change.

Ff = µFn would be a better example then yours. µ changes as the tire gets softer, and the more the car flexes, the normal force increases on the outer tires.

How does this all work in terms of how much flex you want/need?

Don't ask me.
Incorrect about the normal force. The peak normal force applied to the tire is a function of weight transfer only and does not change with a more flexible chassis. Total weight transfer is only a result of the geometry of the car (WB, track, roll centers) and the location of the mass relative to this geometry. The rate of weight transfer is influenced by all sorts of things like roll stiffness, damping and chassis compliance (which feeds into roll stiffness). The reason that chassis flex makes the car easier on its tires is because you are changing the F/R roll stiffness distribution as you roll and reducing the rate at which weight is transferred.
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Old 11-11-2011, 12:04 AM   #18
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I'm intrigued.

So if I had a car turning right, you're saying a car with more flex wouldn't distribute more weight to the outer tires(FR RL RR)?
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Old 11-11-2011, 02:04 AM   #19
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I don't know if it works or not, but ive put conical washers under the top deck screws to increase surface area load to stiffen a chassis.

It is a very small thing to do though, maybe it would not be noticed on track.

But, because my top and bottom chassis is quite thin yet I race with foams, I thought I would try it and they have stayed on the car for 3 seasons now...
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Old 11-11-2011, 02:17 AM   #20
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Originally Posted by R3VoLuTiOn View Post
I'm intrigued.

So if I had a car turning right, you're saying a car with more flex wouldn't distribute more weight to the outer tires(FR RL RR)?
If you're turning right the outer tyres are LF and LR.

Chassis flex won't change the total weight transferred, it will just change how it is distributed between the front and rear tyres, and how fast it is transferred.
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Old 11-11-2011, 03:15 AM   #21
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If you're turning right the outer tyres are LF and LR.

Chassis flex won't change the total weight transferred, it will just change how it is distributed between the front and rear tyres, and how fast it is transferred.
+1 A more flexible chassis gives less abrupt transfers of weight, because the flex in the chassis acts against inertia. So i guess you could say it keeps the weight on the inside wheels longer. Much like what an anti roll bar does, as load is placed on the outside wheels, and upward force is applied to the anti roll bar, due to its shape and mounting position, the upward force is converted into torsional force which applies a downward force on the inside wheel. So as a chassis flexes it some of that force pushes the inside wheels back down. You cannot escape inertia, but if you understand how it works, you can use some of its properties to your advantage.
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Old 11-11-2011, 03:54 AM   #22
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Care to show that reaction in a balanced equation? The force of resistance between tire and road is called Friction, its a physical property not a chemical one. F = ma. 4 years of uni science degree at work here, my $40K was not wasted LMAO.

And friction can be changed by flex, in both positive and negative manner. Think of it this way, a steel ball and a rubber ball, one is going to have much more rolling resistance (friction) than the other because of material flex, the same goes with chassis, if a chassis flexes under certain conditions it can generate more friction in one part of the car and less in another.
perhaps I shouldn't make plain statements (of course friction) but in an interview with pirelli, they were explaining the "complex chemical reactions" that occur between the surface of the tyre and the tarmac. Also this article makes reference to it

(trackpedia.com/wiki/Advanced_grip)

and these are interesting readings

(insideracingtechnology.com/tirebkexerpt1.htm)

and

(brachengineering.com/publications/wheelslipmodel1.pdf)
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Old 11-11-2011, 04:12 AM   #23
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Originally Posted by daleburr View Post
If you're turning right the outer tyres are LF and LR.

Chassis flex won't change the total weight transferred, it will just change how it is distributed between the front and rear tyres, and how fast it is transferred.
+2 Some Kart racers undo the bolts on the chassis in damp and on long tracks to aid compliance. The only problem with our chassis flex is that at some point the chassis has to come back to equilibrium.
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Old 11-11-2011, 02:55 PM   #24
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Originally Posted by LitemodzUK View Post
(trackpedia.com/wiki/Advanced_grip)
This article is just plain wrong and kinetics explains why there is no reaction between the rubber and the bitumen pavement. To further illustrate this point, old tire rubber is used as a viscosity modifying agent in a number of bitumen related products like rubber bitumen binder.

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To produce rubber bitumen binder, the bitumen is heated to approximately 190°C to 210°C, at which the tire rubber is added via a hopper system into a pre-mix tank. This bitumen-rubber blend is then transferred into a curing (usually called reaction tank, but there is no real chemical reaction between the rubber and bitumen on the above mentioned process circumstances) vessel where it absorbs the lighter fractions of bitumen.
When you make an alloy of 2 metals you have a physical change in the crystalline arrangement of the atoms not a chemical one, bitumen and rubber interact the same way. Oh and with kinetics the ways to speed up a reaction are pressure and heat, so the chances of a reaction happening at the low temperatures and external pressures of our tires is almost non existent if there is no chemical reaction at 200 dec C.
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Old 11-12-2011, 05:24 AM   #25
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I want my car to be more stable under throttle.. more or less flex?
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Old 11-12-2011, 07:11 PM   #26
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Originally Posted by RogerDaShrubber View Post
Much like what an anti roll bar does, as load is placed on the outside wheels, and upward force is applied to the anti roll bar, due to its shape and mounting position, the upward force is converted into torsional force which applies a downward force on the inside wheel.


I think you've got that backwards there.

With an anti-roll bar, as the chassis rolls, an upwards force is put into the end of the swaybar on the outside of the car. The swaybar transmits that into an upward force on the arm, and eventually the wheel/tire, on the inside of the car.

-Mike
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Old 11-12-2011, 07:47 PM   #27
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Correct, an anti-roll bar actually 'lifts' the inside wheel of your car in a turn, which reduces the amount of roll your chassis experiences.

The reason more flex makes a car easier to drive is because the front and rear of your car do not have the exact same roll centre, or the same spring rates, or dampening rates, etc. The difference between the front and rear roll rates of the car at turn in, mid corner, and on exit is constantly changing; this difference in roll is equalized through chassis flex. The rate at which these two amounts of roll are averaged out is controlled by the chassis' flex.
As the grip level of a track increases the amount of force exerted on the chassis through a corner is increased. If the chassis allows for to much flex the front and rear roll rates will be able to fluctuate too much, so the chassis needs to be stiffened for more consistent control. The opposite is also true when the grip level is decreasing.


Please see: http://users.telenet.be/elvo/9/1.html
(main page: http://users.telenet.be/elvo/ (this is a good page, pretty nice semi technical explanations of the basics of chassis dynamics))
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Old 11-12-2011, 08:07 PM   #28
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IMHO, w/out getting too technical, the reason "flex" is engineered into rc touring cars is due to the crappy suspension. The things that pass as shocks do not react quick enough.
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Old 11-13-2011, 01:17 AM   #29
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I've played a lot with different chassis and top decks on a few different cars and in general I've found that chassis flex is a lot like shock oil, the more flex the more grip to a point but it also works the tyres harder.

That said, recently I've been running a kyoshos tf6 and it is stiff as all hell but still generates crazy grip. Go figure, I think it might be down to the velvet shocks
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Old 11-16-2014, 11:20 PM   #30
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Time to bring this thread back from the dead

Been about 3 years since the last post, but what's your consensus on chassis flex of TCs these days? Out of the box, is it designed more for mod than stock classes?
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