Sir 51D3WAYS

^Just guessing here, but it might be because the higher flex allows the tyre to lift and contact patch to reduce. The stiffer chassis forces the tyre down into ground and causes more grip. This might be peculiar to certain model of car though.

old_dude

iTrader: (1)

Here is a cool one. The new 3Racing Cero Ultra has two motor positions and two different top deck systems. This means a total of 4 motor positions and two layshaft positions. Only one of those 4 is mid motor with the layshaft behind it for a long front belt. The car rotates better (CRC black carpet) in the mid layshaft config and motor to the rear.

hanulec

iTrader: (28)

Rear motor cars to rotate better.... but MM cars are faster thru the corner.

glennhl

iTrader: (16)

I think the mid motor cars are faster, at least I picked up some time when I went from a rear motor to mid motor with my A800. However, I have a simple mind. I don't think it has anything to do with flex, I think it just comes down to weight distribution front to aft. And the end with more weight does not have more traction in a corner. That's only true for a straight line (drag racing). When you have to turn, inertia (more weight) is never your friend. Also mid motor cars have a lower polar moment of inertia (more weight near the center of the car) which allows the car to rotate better through a corner. That's why I like the new A800R, Oleg likes to use physics to make his cars faster. Physics like, an object with a lower cg transfers less weight to the outside in a corner resulting in the tire pairs gripping better. And physics like an object with a lower polar moment of inertia being able to rotate quicker.

Xrayray

RIght on. Pair of tires with near equal load will grip better than a pair of tires unequally loaded.
​​​​​​The inner tire will always lose more grip than the outer tire is gaining (by putting load on it)

rccartips

iTrader: (3)

For me flex tuning has a big effect. Whether xray, awesomatix, mugen. I am still not understanding the physics in effect when the rear is allowed to flex more there is more rotation rather than added traction and vice versa.

glennhl

iTrader: (16)

OK think about what XrayRay just said. The more you load the outside tire the less traction you have for that pair of tires for the exact reason he stated. So you can't do anything about weight transfer in a corner. It's a function of the speed around the corner causing centrifugal force. The force acts on the CG of the car and depending on the CG height and the width (track) of the tires the weight of the car is transferred onto the outside tires and unloads the inside tires.

So what can you do? Well, you can either stiffen or soften the front or the back. The stiffer end will share more of the overall weight transfer than the soft end. So the stiffer end will have less traction than the soft end. Mind you, you can't just soften both ends thinking you will get more traction on both ends, it doesn't work that way. All you can do is move the traction from one end to the other. So if your car is loose, you can stiffen the front or soften the rear (or a combination of both) to move some of the traction from the front pair of tires to the rear pair. Now, the normal way a full size car does this is to either stiffen or soften a pair of wheels by changing the spring rate of the main springs and/or the anti-roll bars. On the A800 with a typical setup, the anti-roll bars provide 1/3 of the total wheel rate. So the main springs are a larger factor and the anti-roll bars are used for finer adjustments. Now, as far as chassis stiffness, this is even a finer adjustment. However, I just don't like using chassis stiffness to tune my car because it's not as controllable. I like to tune my car by changing out the main springs and/or anti-roll bars.

There is one more way to stiffen or soften the front and rear of the car and that's by changing the roll center. A lower roll center will be softer than a higher roll center. Again if you want to move traction from the front to the rear, raise the front roll center (stiffen) and/or lower the rear roll center (softer).

Good luck.

rccartips

iTrader: (3)

Understood. But what I am observing is that more rear chassis flex gives more rotation. That can mean the rear is losing grip when the rear of the chasiis is flexing more. I don't understand the physics. Rear chassis flex is lifting the inner rear tire rather than keeping it planted?

trilerian

iTrader: (39)

At some point with enough chassis roll you will run out of suspension travel. This could be due to physical travel or due to something like your droop settings. Once you hit that point you no longer are working with an independent suspension, you are working with essentially a solid frame. When this happens any weight left to transfer instantly transfers to the other side of the car. Now what happens then is all predicated on how much weight is left to transfer. This could flip your car over if not enough weight transferred before this, or it could help unload the inside tire enough to get you through the corner faster. A stiffer suspension and chassis speeds up weight transfer and a softer suspension and chassis slow down weight transfer. You have to find the balance you want for the traction level you have.

rccartips

iTrader: (3)

Stiff Chassis
Make stiffer rear / higher rear roll center = less overall roll f/r = front more overall lateral grip (assuming front roll center is not increased). More rotation.

Increase Rear Chassis Flex
Rear roll stiffness is less effectively seen/transferred to the front, hence less increase in front grip. Less rotation.

But in my tests, making rear chassis flex more = more rotation. Still searching for the physics on this

h2e

I've seen a similar effect on my car when I lacked rear grip and tried to make springs softer. One expects rear grip to increase as per theory, but the opposite happened. It seems I was out of a good setup window such that weird wheel angles and droop limitations like mentioned above would happen.

My approach to chassis stiffness is more global: I either tune the chassis to be torsionally soft or stiff.
Soft chassis makes the reaction sluggish, but often more grippy overall. Just in shicanes it can unsettle the car.
A stiff car has sharper reaction but looses grip in a more snappy way, too.
As my own car design doesn't play with rear or front stiffness, i get little effect to the rear front balance (I have a vertical topdeck and motormount is not connected to it. Also no t bone stiffener behind motormount).

old_dude

iTrader: (1)

On the new carpet at NORCAR R/C Raceway (sorry Mike but I had to say that and thank you so much for your help) the rear motor was a handful on tight turns. The mid motor was much easier to drive and faster as you stated it would be.
I experience the same thing in a pan car with optional battery positions. Being able to move that mass forward and back is a huge tuning option.

Lonestar

iTrader: (14)

BUT BUT BUT everywhere on the interwebz people say that more weight transfer to the outside tire make more grip?!?!

Would everyone be wrong, then?!?!

rccartips

iTrader: (3)

More weight transfer to outside tires = more initial grip but less overall grip

gigaplex

iTrader: (2)

The cars are so light and nimble that they're going to get near 100% weight transfer to the outer tyres no matter what you do in some of the corners. So it's more about controlling how quickly that weight transfers.