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Driven5
Driven5 SuperDork
1/10/18 12:44 a.m.
APEowner said:

For some reason Ford didn't do that with the Fairmont/Fox Body Mustangs and getting rid of the rubber bushings will cause them to bind.

Are you absolutely sure about this?  Have you ever experienced this first hand?

The only public comments I have found from people who have actually built mockups specifically to investigate the Mustang geometry with spherical joints at all 8 locations both (one actually being the Design Engineer at Maximum Motorsports) stated that it was completely free of bind.  Admittedly, they did also note that it experienced some less than desirable motions as it was articulated...But that is in no way, shape, or form the same thing as bind.

I'm not saying that improperly designed and/or implemented part combinations aren't causing binding and ripping up cars due to a lack of understanding of how the design works, nor that other options (Panhard, torque arm, etc) don't provide for better characteristics, but I am saying that all of the hearsay and speculation regarding how and why the Mustang suspension binds may not be entirely true.  I have yet to see any evidence (let alone proof) that this would occur with properly designed parts...In fact, quite the contrary when limited only to those with first hand experience working with the full spherical geometry on Mustangs. 

I hate to say it, but it seems that much of the Mustang community may have fallen victim to a lie told often enough becoming the truth.

Recon1342
Recon1342 Reader
1/10/18 1:49 a.m.
sleepyhead said:

  

re:wing vs. spoiler... sometimes it all comes down to terminology used by the sanctioning body / people... I don't think the wind cares that much wink... and I'm open to "creative interpretations" for what a spoiler is.

 

 

IIRC, Sleepyhead, there is indeed a distinct difference between a wing and a spoiler...

 

Wings, front and rear, are designed to do one thing- create downforce. Low pressure air on the underside of the wing + high pressure air on the upper side= air pressure forcing the car downward.

Spoilers, like those seen on every NASCAR vehicle in current use, do not create downforce. They are there to disturb, or “spoil” the turbulent pocket of air behind the car, which in turn lessens drag on the forward motion of the car. 

I love fluid dynamics... one of my favorite things to geek out about. 

This article has some really good science in it as to the differences, despite the author sounding like a douchebag...

https://oppositelock.kinja.com/wings-spoilers-youre-probably-doing-it-wrong-1665312667

sleepyhead
sleepyhead HalfDork
1/10/18 9:17 a.m.
Recon1342 said:
sleepyhead said:

  

re:wing vs. spoiler... sometimes it all comes down to terminology used by the sanctioning body / people... I don't think the wind cares that much wink... and I'm open to "creative interpretations" for what a spoiler is.

 

 

IIRC, Sleepyhead, there is indeed a distinct difference between a wing and a spoiler...

 

Wings, front and rear, are designed to do one thing- create downforce. Low pressure air on the underside of the wing + high pressure air on the upper side= air pressure forcing the car downward.

Spoilers, like those seen on every NASCAR vehicle in current use, do not create downforce. They are there to disturb, or “spoil” the turbulent pocket of air behind the car, which in turn lessens drag on the forward motion of the car. 

I love fluid dynamics... one of my favorite things to geek out about. 

This article has some really good science in it as to the differences, despite the author sounding like a douchebag...

https://oppositelock.kinja.com/wings-spoilers-youre-probably-doing-it-wrong-1665312667

so, the quick answer is: yes... I have read that... in reference to poking around looking for data on this subject.
and, yeah, aero/fluid-dynamics seems to engender a certain arrogance in people who've taken the time to learn it.

beyond that, I'm having trouble ordering my thoughts on this so that I don't come across as douche/pedantic.  Plus, I have a habit of falling back on allegory and metaphor... and I'm trying to get off that.

the best I can muster right now, is that "pressure" is really less about what's going on here... it's just easy to measure/predict... and it's really less about high and low pressure... since that's essentially relative.  Circulation... that is the key consideration.

I'll leave with the contention that the "elements hitherto called spoilers" on cars are really "flaps" (which Carlyle uses off-handedly):

and these are really spoilers:

loosecannon
loosecannon Dork
1/10/18 9:44 a.m.

The Mustang is so popular in many forms of motorsports, there must be lots of data/examples out there on how to make them handle better. I wouldn't try to re-invent the wheel, piggyback on somebody else's expense and time.

freetors
freetors New Reader
1/10/18 9:57 a.m.

I think where people get hung up on with triangulated four links is they see all these link going in different directions and think that the axle must twist or the chassis side mounts have to give for there to be any roll travel. Here's the thing though, the axle doesn't actually pivot around those two points of the diagonal links. Those links actually form a convergent point out in space called the instant center. This is where your axle is actually rotating about in roll. Imagine you remove those diagonals links now and replace them with a three link swingarm system. In the mustangs case imagine that the swingarm's axle connection is where the four link's IC could have been, roughly a foot or two behind the axle. Now this very obviously not going to bind in any direction because the axle only has three fixture points. Now imagine again you go back to the four link setup. You extend the those upper diagonals all the way back to their instant center. This would have some bad load paths but it would function identically to the swingarm system. This would also result in no roll binding, and the same goes for the conventional four link.

 

The beauty of the four link comes from being able to just choose where you want your IC, roll axis, etc. and then you throw the links in wherever they fall into place. The link lengths are important (longer is always better) but they can be shortened significantly and still accomplish their intentions without much compromise.

rslifkin
rslifkin SuperDork
1/10/18 10:05 a.m.

A 4 link (parallel or triangulated) also lets you play with things like passive rear steering via roll steer.  Depending on how the links are angled, you can get the rear axle to steer slightly outwards in a corner as the body rolls (which keeps slip angle down on the rear tires and can add some grip).  

GameboyRMH
GameboyRMH MegaDork
1/10/18 10:18 a.m.

I'll just say that as a rule, on a triangulated 4-link, if any joint resists rotation in any direction you will get some bind. Maybe a little, maybe a lot, it depends on the geometry of the suspension and how much the joint resists rotation and in what direction. If you want to eliminate bind, every joint should allow equal (and free) rotation on every axis. That means spherical bearings, or a Land Rover style hourglass-and-torus bushing arrangement (which while allowing equal rotation, is not as free as a spherical bearing). Spherical bearings at every joint is the setup you'll see whenever a triangulated 4-link is used on a serious purpose-built offroad rig, which is often.

Thinkkker
Thinkkker UltraDork
1/10/18 11:03 a.m.

The biggest issue you forget, not many racing classes allow full heim joints at all the pickups.  So, you are limited to some non-metallic setup there.  This precludes any type of heim or otherwise in there.

So, you may as well drop the 4th link and have a Poor man 3-link and get all the advantages.  Plus, this is actually a cheaper route than replacing all the links with heim joint so nothing binds.

Just my 2-cents there

Recon1342
Recon1342 Reader
1/10/18 3:19 p.m.

In reply to sleepyhead :

I like it! 

No need to worry about offending me. I enjoy learning new things, and I’m pretty thick skinned. 

I concur with your renaming. Now, we just need to make them moveable...

sleepyhead
sleepyhead HalfDork
1/12/18 8:55 a.m.

I'm not really worried about offending... it's more about being conscious of the long-tail of these posts.  It’s been 15-years since I studied this stuff, and I haven’t had the opportunity to keep it fresh at my fingers… and the way I learn things means that some of the more semantic aspects get lost more easily.  So, I try to shy away from “hey your wrong” internet fights, and the knee-jerk reaction to getting into them.  Hopefully, taking a more open approach will mean that if stafford1500, or someone else, drops in here with a knowledge bomb… I don’t feel like a complete fool.  Partial foolish, that I can deal with.  ;)

stafford1500
stafford1500 HalfDork
1/12/18 9:51 a.m.

In reply to sleepyhead :

Don't go dragging me into this...

I think the answer has already been given on the original question. Aero will only be worth fractions of a second for autocross with a 2500-3000 pound car. Also the limited power (200ish if I recall correctly) will not be a significant limitation for aero on an autocross car.

Basically, any aero added will increase corner/transition speed, with little to no impact on straight performance, except maybe increase braking slightly.

Throw the biggest spoiler you can at the car. At autocross speeds, drag is effectively a non-issue.

For the wing vs spoiler "discussion" there is no free lunch. If you are increasing the downforce or otherwise affecting teh air around the car, you are NOT reducing drag (at least locally, but may be in the overall view, but not likely). Moving the air in a direction it does not want to go costs energy. Spoilers can be considered to be split flaps on a car shaped wing device in very close ground effect, with really low aspect ratio (short stubby wing - width to length).

Smooth underbodies will help with downforce, but not until you get the car fairly low. More than about 4" of ground clearance and the flat floor is not doing anything significant.

The biggest challenge with aero is not assuming the air goes straight over the top, if rolls/twists around the car trying to take the easiest path to the back of the car. Aero does nothing but try to change that direction and make something useful out of the reaction.

STM317
STM317 Dork
1/12/18 10:19 a.m.

Newb question that I think I know the answer to, but would like more thorough understanding: If the tires are the biggest limit here, does increasing downforce still help? I mean, if the tires are struggling with the weight of the car as is, and downforce acts similarly to additional weight on an area of the car, does that mean the tires struggle even more?

stafford1500
stafford1500 HalfDork
1/12/18 10:28 a.m.

Downforce increases grip available , but does not have the downside of increased lateral inertial load like ballast would. Tire grip does increase with increased vertical load, but it also has a n upper limit which is different with tire compound, temperature, slip angle and a bunch of other stuff. It is very non-linear and can vary greatly from one brand/compound to another.

Long story short, more downforce will increase tire grip for most of the cars we typically mess with. Just keep in mind that you are looking at a small increase in vertical load (100lbs downforce in relation to a 2500lb car) and the lateral grip trade off includes another efficiency trade off (not one to one with vertical load).

If you get into really big downforce (or big banking loads) the increase in vertical load can push a tire past its peak grip to load point. YOu would have to start looking at tires in higher load range at that time.

KyAllroad (Jeremy)
KyAllroad (Jeremy) PowerDork
1/12/18 10:36 a.m.

In reply to STM317 :

Any added downforce will help with cornering speed.  The basic physics involved means that the car is the "object in motion tends to stay in motion unless acted upon by an outside force".  The grip generated by the tires is that outside force.  Their grip is a factor of the weight pressing down by the car and is attempting to change an equal amount of weights direction.  Adding downforce from aero generated more grip but without the added mass. 

In my experience the big rear spoiler (CSP Miata style) made the car much more stable under braking (especially trail braking where many cars get tail happy).  And for the whopping $30 I spent making it, cheapest speed I ever got autocrossing.

 

edit: looks like Stafford and I were typing the same thing at the same time.

sleepyhead
sleepyhead HalfDork
1/12/18 11:51 a.m.
stafford1500 said:

In reply to sleepyhead :

Don't go dragging me into this...

... ...

For the wing vs spoiler "discussion" there is no free lunch. If you are increasing the downforce or otherwise affecting teh air around the car, you are NOT reducing drag (at least locally, but may be in the overall view, but not likely). Moving the air in a direction it does not want to go costs energy. Spoilers can be considered to be split flaps on a car shaped wing device in very close ground effect, with really low aspect ratio (short stubby wing - width to length).

Smooth underbodies will help with downforce, but not until you get the car fairly low. More than about 4" of ground clearance and the flat floor is not doing anything significant.

The biggest challenge with aero is not assuming the air goes straight over the top, if rolls/twists around the car trying to take the easiest path to the back of the car. Aero does nothing but try to change that direction and make something useful out of the reaction.

sorry?  guess I should have written "if", instead of "when"?

even if there's no free lunch... I guess I owe a free beer sometime?

stafford1500
stafford1500 HalfDork
1/12/18 12:01 p.m.

In reply to sleepyhead :

No worries, I have been following but not posting until today...

Driven5
Driven5 SuperDork
1/12/18 12:42 p.m.
STM317 said:

Newb question that I think I know the answer to, but would like more thorough understanding: If the tires are the biggest limit here, does increasing downforce still help? I mean, if the tires are struggling with the weight of the car as is, and downforce acts similarly to additional weight on an area of the car, does that mean the tires struggle even more?

To put the explanations into an example: If your tire can support a lateral load equal to the vertical load (1.00 G)*,  then a tire loaded with 750l lb of car will be able to generate 750 lb of lateral load.  Now if you add 50 lb of downforce as well, the tire will now be loaded with 800 lb of vertical load and will subsequently support 800 lb of lateral load. However, since the car is still only throwing around 750 lbs for the tire in question, it can now corner at 1.07 G to reach the 800 lb of available lateral load.

 

* A gross oversimplification, but it works for the purposes of this example.

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