Interested to see what's next!
I have a feeling in the next 2-3 years an S550 car will be in my future.
Interested to see what's next!
I have a feeling in the next 2-3 years an S550 car will be in my future.
Event coverage of the Mustang 50th Birthday celebration. There are links in there to my Flickr page, where there are a ton of pics.
Mustang 50th Birthday Celebration, Charlotte Motor Speedway, NC
I ditched that tired, old stock clutch-type differential and replaced it with an Eaton TrueTrac:
http://www.motoiq.com/MagazineArticles/ID/3494/Project-Grey-Mustang-50-Part-5--Putting-the-Power-Down-with-Eaton.aspx
New exhaust, because I got sick of not being able to hear my fiance, or the radio.
http://www.motoiq.com/MagazineArticles/ID/3523/Project-Grey-Mustang-50-Part-6--Drone-Strike.aspx
Sky_Render wrote: I ditched that tired, old stock clutch-type differential and replaced it with an Eaton TrueTrac: http://www.motoiq.com/MagazineArticles/ID/3494/Project-Grey-Mustang-50-Part-5--Putting-the-Power-Down-with-Eaton.aspx
Tasty!
http://www.motoiq.com/MagazineArticles/ID/3538/Project-Grey-Mustang-50-Part-7-Testing-BMR-Suspensions-Rear-Control-Arms.aspx
So I replaced the panhard rod (and rear control arms) with BMR's combination arms that have a Polyurethane bushing on the chassis side and a spherical bearing on the axle side:
I noticed a substantial improvement in cornering, especially during fast transitions.
I would like to at this point have a discussion of panhard bars. The main disadvantage that I see attributed to panhard bars is the "unsettled" feeling of the rear end when going around corners, especially during fast transitions. After a steering input, it seems to take a finite (albeit brief) amount of time for the rear end to "settle" and correctly respond to the input.
Now, Newton's First Law states that an object in motion will stay in motion until acted upon by an outside force. Consider that you are driving your stick-axle car in a straight line. You then enter a sweeper and turn the steering wheel. The front of the car immediately follows the wheels, because they are turned. But how is the rear axle brought "in line" to follow the front wheels?
Mainly, it is through the panhard bar. That bar must either push or pull the axle to make it go around a corner. But before the force of the chassis can completely be transmitted through the panhard bar, it must compress the bushings at either end. And recall also that the rear axle is a heavy sonuvagun, weighing at least a couple hundred pounds. So that bushing deflection and compression is HUGE. Those bushings must compress before the axle "feels" the forces transmitted through the panhard bar.
My point to all this rambling is that the "unsettled" feeling of the rear axle during transitions has all but disappeared by replacing just one of those bushings with a spherical bearing. Thoughts?
You replaced it all at the same time, yes? That's a lot more than trading one bushing for a spherical. I would suggest that the whole package has an impact on the "unsettled" feeling- you replaced a large number of squishy joints with much less compliant ones, so a back to back test of JUST the panhard bar would be needed to actually verify that claim.
NONACK wrote: so a back to back test of JUST the panhard bar would be needed to actually verify that claim.
Hear hear!!
Also, the weight of the axle is inconsequential. It's the weight of the car pushing on those bushings.
In reply to tuna55:
Inconsequential provided the surface is smooth... any bumps and that unsprung weight+sloppy bushing combo makes it harder for the dampers to do their job, which could lead to an "unsettled" feeling.
NONACK wrote: In reply to tuna55: Inconsequential provided the surface is smooth... any bumps and that unsprung weight+sloppy bushing combo makes it harder for the dampers to do their job, which could lead to an "unsettled" feeling.
Sure, you're right. I just meant that the pure cornering force is due to the weight of the car, not the axle.
In reply to tuna55:
We are in agreement good sir.
tuna55 wrote:NONACK wrote: In reply to tuna55: Inconsequential provided the surface is smooth... any bumps and that unsprung weight+sloppy bushing combo makes it harder for the dampers to do their job, which could lead to an "unsettled" feeling.Sure, you're right. I just meant that the pure cornering force is due to the weight of the car, not the axle.
Certainly true, but I wouldn't discount having 200+ pounds at the end of a stick pushing it around.
I agree about the back-to-back test, as well. Simply wasn't possible in the timeframe I had to work with. I was more pointing this out for all the people who say you MUST have a Watts linkage in order to have a decent-handling car. That simply isn't true.
In reply to Sky_Render:
The car is pushing on the bar, and hence the axle. The axle is stuck to the ground with tires. The weight of said axle is not relevant to that particular analysis.
In a bump, that analysis is different.
F=ma; of course the weight of it matters, especially when you're considering bushing compression and deflection.
In reply to Sky_Render:
Are we talking about the intertia of the axle as part of the reaction? That's what I'm getting from this.
Sky_Render wrote: F=ma; of course the weight of it matters, especially when you're considering bushing compression and deflection.
The mass of the car.
Actually.
Nevermind. I can't teach physics on the internet.
tuna55 wrote:Sky_Render wrote: F=ma; of course the weight of it matters, especially when you're considering bushing compression and deflection.The mass of the car. Actually. Nevermind. I can't teach physics on the internet.
It complicates it a lot, but you can look at it as a mass/spring series.
Car(mass)-bushing(spring)-panhard(mass)-bushing(spring)-axle(mass)-tires(spring)-ground(fixed)
Just like analysis of every system, it depends what you consider negligible. FWIW, I agree with your analysis of axle mass being largely irrelevant to panhard bushing deflection.
They are right in that the effect of the axle weight is negligible on a smooth surface, especially if traction has not been broken (read drifting). In that case the axle is coupled to the ground through the contact patch of the tire and you are looking at the sprung weight interacting with the coupled ground AND unsprung weight.
Now, tire deflection is another consideration, but we are focusing on the effects of control arm bushing deflection. So, the case of the unsprung weight being coupled to the ground stands. It is a simplification, but a valid one for the sake of bushing analysis.
To really simplify, axle weight isnt really a concern in lowspeed movements, but moreso is higher speed movements where inertia is a larger factor. (bump control vs steady state turning) However, that is looking at it from a whole different angle.
Dont forget! All analyses take place in a frictionless vacuum!
Tuna, I'm not entirely sure why you even bother clicking on my threads, since all you ever seem to do is attempt to insult me.
I understand everyone's arguments. Let me try to explain why I think the axle's mass is not irrelevant.
If the axle is going straight and you turn the car, the axle must be made to go around that corner (deviate from the straight path it is on). The method by which the axle is turned/rotated is through the panhard rod and control arms. The "unsettled period" is the small amount of time needed for the axle to be pivoted or turned (even if it's still "coupled" to the ground, it is rotating), which consists of bushing deformation and the physical act of accelerating (angular mostly) the axle in another direction. Because the axle is so heavy, the bushings will deform a good amount in transmitting this force. That is why I'm saying the mass of the axle is relevant. You'll never completely remove the unsettled nature of a rear axle simply because it's a big heavy chunk of steel, but eliminating the bushings seems to cause a drastic improvement.
Its still lowspeed motion. Not saying that there is NO effect, but that it is not a very large effect compared to other things at play. As I said, more effects of the bushings in the highspeed motion where inertial effects (of the axle weight) are greater. That's where you will see the larger forces enacted.
Apexcarver wrote: Dont forget! All analyses take place in a frictionless vacuum!
Well in that case, the mass of the axle matters a whole lot! 
And we can consider shock loading from the tires stick-slip action, and the spring rate of the axle tubes themselves, and the buckling resistance of the panhard bar, and... maybe we should just all unwad our engineering panties and agree that it matters some amount.
Sky_Render wrote: Tuna, I'm not entirely sure why you even bother clicking on my threads, since all you ever seem to do is attempt to insult me.
Wow dude, I am pretty sure I have never leveled an insult at anyone on here ever. If you find somewhere were you think I insulted you, please PM me and we can look at it.
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