EGGGGGGSACTLY!!!

for bumpy apshalt fibre glass car were the usally the the quickest tick around the track as they would twist and flex to generate grip and would be more forgiving over the bumps. A opposed to stiff graphite chassis. The supension design on these cars can only cope with conering loading as opposed to bumploading so to cope with the bumps it better to let the chassis deal with the bumps and the supension deal with the corners.

Unless you aren't relying on a hunk of fiberglass to control the side to side and fore and aft roll rates on your car. Maybe if you could vary the spring rate side to side as well as front to rear, the car could be tuned for differing levels of traction , as well as bumps. If only a car like that existed!!!

I think you would find the tyre would be doing the damping over the bump while the chassis flexes. the roll rate you are talking about would only occur when the car corner this where the there is tranfer of load in occuring within the chassis. The bumps are a vertical load not a side to side tranfer the the idea for the flex is to allow the wheel to roll over the bump rather than bounce up then crash over the bump and causing the chassis to bottom out. This causes the chassis to skid and slow down. Keeping the chassis the same height with repect to the road require the wheels to follow the contours of the bump the flex stop the car wheel lifting up of the ground when it intial hit the bump pushes the wheel back down as the chassis return to it normal position.

This is the simplest explaination unless you have driven car with European supension at Speed on english roads. Best one would be to compare the current model audi a4 vs the current model bmw 3 series over industrial used road at speed over 60+mph.

Or drive a Peugeot 205 206 306 at speed and compare it to a VW golf to get the picture.

What car is that? It comes with purple parts?

This is why a link car can run softer front to rear to absorb bumps, (as best a live axle car can), and still be sprung stiffly enough side to side to control roll rate while cornering. They're two completely different variables, both easily understood, but only two cars currently available offer the ability to tune separately for each.

TFR: That's a Rev. 2, I don't know if Bruce still carries the Purple goodies or not.

James35,

I just took a look at what you mentioned above and I don't think that your binding would have come from the upper eyelet, as it moves in conjunction with the upper arm and the wheel. The only point at which the king pin moves through the eyelet is the lower arm. If it did move through the upper one, the king pin would hit the inside of your wheel.

One thing I have noticed that can cause some issues is the hinge pins are not round on the end where the upper arm rotates on them. I put mine in a dremmel and polished the ends on a fine grit sharpening stone until they would spin freely by hand before assembly.

Greg

FYI. If you do find the Rocket City links, you will need to find some pivot balls to fit. The stock Associated ones do not work. I believe Du-Bro makes some Delrin ones that fit, but I'm not 100% sure about that...

Could this be why Speedmerchant Rev.4's went 1st and 2nd this year in Cleveland? Two fantastic drivers with two cars that soaked up every bump and still had the ability to scream through the corners. I wonder if anyone there was tempted to run a thinner chassis to help with the bumpier than normal track conditions?

Note I respect your knowledge and your probably faster driver than me.
But please look at what I am saying.

It is not a live axle car !!!! (live axle are a stupidly different ball game! and always considered to use eliptical springs,Panhard rods.)
When it uses links or de dion supension it is referred to as a trialing link supension or an de dion axle.Yes I study automotive engineering and have messed around with kit cars etc.
You also need to consider the tyre as the most effiecent point for the damping and springing to occur that why single seater race cars use tall tyres (inflated with nitrogen to ten to 15 psi) and very stiff supension so they can transfer the wings down force to the tyre contact patches. So you can do stupids thing such as pull 4g in braking, in a formula renault when braking from a 160 mph 30 mph in less tham 50meters. This is just data of a black box.
With heavier race cars such as rally cars and touring cars the rules are different and the reliance of Down force is much less so the tend to let the supension do the work rather than the tyres thus the use of low profile tyre the make the car more reponsive in terms of changing direction as they have a reduced slip angle.
It is very much akin to a go kart (t-bar) or a trailing link setup (link car). Any of these cars can be adjusted to cope with roll rate, i.e tweak springs on the carpet knife and the t-fource, changing the t-bar thickness will control roll rate. Chassis thickness won't it but may effect the effiency of the supension by absorbing the bumps of the car, that why you use an flexible chassis. this will not effect the roll rate.
Any way the roll rate is controled by the side damping of the plate or tubes no the fore aft damping of the center shock. That controls the fore and aft transfer of the cars mass around the point of inertia in the accelarating and braking.

I bought some of those links from BRP a while back, and he told me that RPM makes some delrin pivot balls that fit those cups. I believe they were from old losi truck ball ends, but I can't be sure.

-James

Quick question for the Speedmerchant drivers,

Does the Rev.3 come with the large D-ring axel (i.e. like the 12L4) or does it come with smothing else ???

Thanks,
Chris.... :nod:

Before I jump in and make myself look like an idiot I would like to say that I respect your obvious knowledge of automotive engineering. It takes a lot to grasp many of these concepts and you apprear to have your arms around them quite well.

My dad was an amazing engineer yet he couldn't understand why 12th scale cars looked the way they did. He like many others felt that full scale automobiles had the strongest design concepts and that 12th scale designers should pay more attention to them. The biggest thing my father and most engineers fail to understand is really the easiest of concepts. Call it what you will KISS or Ockam's Razor.

12th scale cars move at speeds of 30-45mph and weigh in around 1 3/4 pounds at maximum. Do the math, that's an F1 car per say that moves at 360-540mph yet only weighs 21 pounds. How on earth could you begin to compare the two?

Your example of tire density to create traction also seems a little skewed to me. What you are talking about is generating surface traction, full scale race cars using air pressure for tuning the same way we use foam density. They are not creating dampening at all, simply controlling the amount of physical traction to the surface.

The compression strength of our wheels seems to be quite high considering the load they endure and really should not be considered as part of the equation. The issue here is that if you take the load being applied to the tire and transfer that through your suspension system to the chassis flat materials will begin to flex. Think about how much force is being put on that chassis plate after the lever effect of the rear end. The only good way to overcome this flexing is to make the material thick enough or use material with higher torsional properties until this critical flex point has been overcome. If you allow this twisting you are just turning the whole car into a T-bar and allowing the chassis to provide spring effect totally unchecked and with no adjustability at all.

I have never liked the idea of a T-bar and have plenty of experience with them. You are relying on a hunk of fiberglass that flexes to remain consistent. Every time that fiberglass flexes it's properties will change and generate inconsistency. By using a T-bar you have created what I call a "minimum effect" to the car, no matter what you change there is no way to reduce the amount of tension side to side or front to back to a value less than what the T-bar is providing. The only real solution is to run an extremely soft T-bar and add springs to fine tune tension side to side along with the center shock. By moving to the link design you have no "minimum effect" in the car at all. The lack of a "minimum effect" allows you to maintain complete control over side to side and front to back tension with a much higher degree of consistency.

At any rate this is a great discussion with some interesting points being made.

hey guys,i finished the assembly on the display model of our new DB12.heres a few pics :)

Looks really good Jason. It's a t-bar car though, Nick-C will have your head! ;)

Just kidding Nick, have nothing but love for ya... :)