By Discosaurus on Monday, May 14, 2001 - 11:30 am: Edit

Here - let's move it.

keith
discosaurus

By pk on Monday, May 14, 2001 - 05:13 pm: Edit

I would be willing to bet $G has no real idea what stress the 3-link can or can't withstand.

They don't do it like that. They build it and hope for the best.

pk

By MA on Monday, May 14, 2001 - 05:29 pm: Edit

ok guys...the lower single link on the $G 3-link must endure 7 times the axial force of the stock one during both braking and accelerating. The 3 link is a idea headed in the right direction, but the hardware(the strength of the metal) Safari Gard uses is really poor.

By Wayne on Monday, May 14, 2001 - 06:36 pm: Edit

MA,
Are you suggesting the actual steel sections are too light or they should be looking towards a higher grade steel.

By MA on Monday, May 14, 2001 - 07:11 pm: Edit

higher grade steel, i am not exactly sure what grade of steel they use right now.

By MA on Monday, May 14, 2001 - 07:39 pm: Edit

Wayne, are you the one with 35" tires on your Disco? If so, what kind of gearing are you running? You should use 4.75 gearing(www.greatbasinrovers.com) at least for those tires. Anything less would wear down your engine. Also, if you looking for new heavy-duty driveshafts, go with Tom Woods driveshafts. He custom makes them to your specs for not that much $$$.

By Wayne on Monday, May 14, 2001 - 10:48 pm: Edit

MA,
Yes I have the 35's, with 4.1 diffs and a 4.6HSV engine. I didn't realise the 4.75 gearing was available to go into a Discovery diff. I thought that was on in a salisbury unit. I would be concerned about the strength of the 4.75 gearing in Disco diffs. Thanks for the tip on the drive shafts though.

By MA on Monday, May 14, 2001 - 11:14 pm: Edit

yeah no problem, for the diffs go here www.greatbasinrovers.com/catset.html and click on Drivetrain and then click on ring and pinion. They say that these are the strongest you could buy for your Disco. It would cost about $1000 for the new gearing(assuming that you do the installation yourself). You would also need a stronger flange adapter(which they sell for $150). You need to post some pics of that Disco!!! it seems like it is one great machine! Also, what kind of suspension do you have to accommodate those large tires?

By Mike Baumann on Tuesday, May 15, 2001 - 09:26 am: Edit

Good reference materials. (unsolicited plug)

Folks -
I suspect most Rover folks are like like Kyle (and me most times, and probably Greg too). They have a good mind for how mechanical things work, and can visualize them well, but don't usually work out just what is going on. Thus, the trial and error sizing of components.

Back in my SCCA days, I came accross some books that cover automotive engineering isses (and especially preperation_of modified vehicles) in a way that fabricators, drivers, mechanics and engineers can understand. Virtually every paragraph of these books contain some "bible truth" about good engineering, design and fabrication practice.
The books are by Carroll Smith, a long time pro racing crew chief. He explains proper shop practice, and justifies from theory (not too much) where these good ideas came from. The books are geared for users and builders of vehicles, not just designers. Although he is road racing centred, most items (except aerodynamic devices, and tuning fully independant suspensions) apply fairly directly to rovers too.The books are :

"Nuts Bolts and Fasteners..." the basics, the best book on how fasteners work, and how to use them that I have ever seen (a previous edition of this book was "Prepare to Win", almost as good, but it references older fastener types)

"Tune to Win" describes the kinematics of how a car works

"Engineer to Win" a lot of design and fabrication do's and dont's. Covers exotic materials, and aerodynamics also.

"Drive to Win" the least applicable to rovers, like the title says, covers race driving (mostly road racing.

These are my favorite auto engineering books, in fact they are so good, with down to earth explanations, that I use them when making cases for various air/space vehicle design schemes.

Just my opinion -
- Mike

Michael Baumann
97 Disco
Huntington Beach
KC6KBC

By Kyle Van Tassel (Kyle) on Tuesday, May 15, 2001 - 10:16 am: Edit

Mike , I am not just a "Rover guy". I didnt start out with rovers at all. I have built race cars on and off for about 13 years or so . Do this calculation for me. How much stress does the rear suspension components of a ladder bar car weighing 3500 pounds see during a 1.1 second 60 foot launch? The forces involved are very simmilar to a rover taking a 70 MPH nose dive on asphault.

Kyle

By Discosaurus on Tuesday, May 15, 2001 - 12:10 pm: Edit

Dammit...
take that 35" crap back to the other thread.
we started this one to get AWAY from it...

By Mike Baumann on Tuesday, May 15, 2001 - 04:26 pm: Edit

Kyle - Are you talking about a drag racing car?

Sorry, but I don't know for certain what a ladder bar car is, or what a 60 ft launch is.

If it is a drag car, and you are saying that the 60 ft. e/t is 1.1 sec, and the mass of the car is 3500 lbs then :
1) To get rear suspension forces, we would also need type diameter (at load, since these things squat for drag cars), wheelbase, and CG position.
or
2) we could simpliy by saying that all forces are exerted on rear axle (front barely in air), but not so much load transfer that the car is on the wheelie bars. We would then only need the tyre diameter.

Here is what we can figure out.
1) Force = mass x acceleration (F=ma)
2) mass = 3500 lb
3) since force (engine torque) is probably a constant, and mass is a constant, then acceleration will be constant over the 60 ft. (later on, when air resistance becomes a large force, this changes and acceleration dies off (ie: your 0-50 mph time is much less than your 50-100 mph time)
4) for constant acceleration, a=(v-vo)/t
average velocity = (distance/time = (v-vo)/2
5) average velocity is total distance/total time,
= 60/1.1 = 54.54 ft/sec
6) acceleration = 2*Vaverage / t = 2*54.54/1.1 = 99.17 ft/sec^2
7) Converting to g's, one gravity = 32.2ft/sec^2
thus g = 99.17/32.2 = 3.07 g forces.
8) Now back to force, which = m*a
Force vertically (due to mass of car = 3500 lbs)
Force horizontally = ma = 3500 x 3.07 = 10,800 lbs
Resultant force (rms) of 3500 and 10,800 = ((3500^2+(10800^2))^0.5 = 11,300 lbs force.
The force is at an angle of atan(3500/10800) = 17.9 degrees below horizontal.
9) for suspension, the torque seen at the axles is also important. That torque will be Lateral force x radius of loaded tyre.
For a 25 inch radius drag tyre, T = F*r = 10800 x 25 = 270,000 in lb or 22,500 ft lb
(Wow, Keith Black is God!)


What can a rover generate.
I went to Car and Driver's web site, and found a road test of a disco. They claim 199 ft for 70-0 ft stop. They test the cars light, so lets use the 4576 lb published weight for mass of their tests.
Vavg = v-vo/2 = 0-70/2 = 35 mph
35 mph = 51.13 ft/sec. (x ft/mile x hours/sec)
distance = 199 ft.
v=distance/time, time = distance/v = 199/51.13
time = 3.89 sec
A = v-vo/t = 102.26-0/3.89 = 26.27 ft/sec^2
g = a/32.2 ft/sec^2 = 0.82 g.
Force = mass x acceleration = 4576*.82 = 3752 lbs. for-aft per vehicle.

Sanity check for rover, the C&D skid pad test registered .73g. This makes sense, as lateral acceleration is never as good as for-aft acceleration in car design. (Due to dynamic oscillations in car/suspension/road interface)

So how do we answer questions about a particular rover. Well, unless we want to find m and cg of a vehicle (4 scales and a ramp will do) we can just make some conservative simplifying assumtions. In the old calc's I used 6000 lbs on one axle (not 4576 per vehicle) So we are now 52% higher than published loads (that's to account for the roof rack full of chain saws and bridging ladders, and the load transfer). The calc's then use 1g (instead of .81), thats another 23% of conservative margin.

When in doubt about design issues, always make a "worst case +" bounding assumption. When in doubt about that, just do what you think is right.
Although I have never seen an explosive graphite failure in 22 years (except flywheels), I still duck behind a blast shield every time we proof test a new piece. Heck, we don't even trust ourselves some times. A little fear is healthy.

Happy calc's
- Mike

Mike Baumann
97 Disco
Huntington Beach
KC6KBC

By Kyle Van Tassel (Kyle) on Tuesday, May 15, 2001 - 04:54 pm: Edit

Now that one I liked , LOL . Do you now agree that the force applied to the front end of the Disco is greater at greater speeds? Also that this is not a constant ? If you were to design the thing with all that in mind. let us know what you come up with. Then compare that to what you are getting from $G. I am honestly interested in what you end up with...

Kyle

By Kyle Van Tassel (Kyle) on Tuesday, May 15, 2001 - 04:56 pm: Edit

Oops , forgot to mention that it is quite common to get load spikes as the tires shake or break loose from time to time. When they hook again those numbers of yours get spiked.. And yes, 1/4 mile cars... Like being shot out of a gun....


Kyle

By Peter Matusov on Tuesday, May 15, 2001 - 05:31 pm: Edit

i like a lot all this stress analysis.
now imagine there ain't 1.1 second-panic
stop, but the link's got hit by a rock and
has a little ding in it... and not straight
anymore.

always enjoyed the sight of a drag link of
an FJ40 with 35" tires...

By Kyle Van Tassel (Kyle) on Tuesday, May 15, 2001 - 05:34 pm: Edit

I think thats part two Peter...

Kyle

By Peter Matusov on Tuesday, May 15, 2001 - 05:45 pm: Edit

what was part one?

naw, i didn't give it much thought until i saw
what may happen to the hinged rear radius arm.

a few hard miles from pavement.

nice to see rear axle held in place by a come-along! some ingenuity there.

and once the piece is bent, there's no use to it.

Peter

By Mike Baumann on Tuesday, May 15, 2001 - 08:31 pm: Edit

Peter and Kyle & MA- strength and acceleration

MA - The 3 link has more axial load than the stock setup because the three link is a truss, and trusses resolve loads into axial forces. Trusses are usually lighter, and stiffer, and they are for certain easier to design and analyze.

The stock setup reacts that torque by bending in the trailing arm. Look at the old analysis, the resultant stress for the sample case (P/A of 24000 lbs/.441 for 3 link, Mc/I of 51,000 inlb x 1.25 in / 1.27in^4 for stock) is close to the same (50,200 psi stock, vs 54,400 psi 3 link).

The stock part is probably a low (to me it's low, to the auto world it's high) carbon steel forging. Say 1018 forged. The SG stuff is advertised as Crome Moly for the trailing arms, so I suspect the centre link is also chrome moly. I suspect it is 4340. The 4340 should have more strength capability than the 1018 forging. (We would need to check Mil Handbook 5G for that, mine isn't handy now)

Many times a good engineering practice when you don't know the exact design conditions, is to just make the new part "as good as" the old part. Since the stock and SG setups both have similar stresses, I would say this was accomplished. The conclusion I draw is that the SG 3 link is not appreciably worse than the stock setup. Would I prefer even greater capabiltiy? hell yes, and here is where RTs beefo traling arms or someone else's custom unit may step in.

Kyle - Sorry, I still see the acceleration as constant, thus no increase with mph. But that's OK, being leery of high speed panic maneuvers is healthy.
Perhaps the difference in perception is due to what you see, vs what is driving it. At 10-0 mph the Rover doesn't dive very much, 70-0 it dives a lot. The force isn't greater, it's just that the springs have time to perform work at 70 that they don't at 10.
Example: You step off a 30 inch high loading dock. You feel a thump at your feet (impact), but that is it. You go to Cedar Point or Magic Mountain and ride the 400 ft freefall ride. You feel quesey and barf your happy meal up. Both cases have you accelerating at 1g (freefall), but in the second case, your guts have time to float free (performing work, like the spring), putting more pressure on your diaphram, and making you sick. The effect takes time to occur, but the cause is instantaneous.

Now, regarding shock loads. Hell yes they occur. How big are they, I don't know. That Kung Foo is too potent for the quick calculations we do here. However, I do know a little. The vehicle system, road, tyre, suspension, frame, mass work together as a system of springs. The shock load may impart more energy than you expect, or it may be damped out. The rubber tyre, with a soft spring constant damps out a hell of a lot of those road induced shock loads. That is a good thing. Otherwise,we would be driving M1 tanks, and wouldn't be able to keep fillings in our mouths. (OK the tank part is cool, but the dental part isn't.)
Because of shock loads you think you might put to the Rover, you may want to install a beefier than stock system.
Since there are so many Rovers, and Solihull probably has a MECHANICA software license, I am going to trust that the stock system is good enough to react reasonable shock loads (say, short of hitting the 15 inch ledge at 35mph).
For our Aussie friends with comp vehicles, I think I would want something stouter.

Peter, yes, bent links are bad. The skewed geometry now adds a moment to the axial load, and the stress is increased. If the part is generally lightly loaded (like a steering tie rod) and only gets a ding due to a non typical load (rock hitting it vs regular steering load) then it would probably be OK, but a 0 fault tolerant suspension member would be a great risk.

Now I scare myself with afternoon drive-
- Mike


Mike Baumann
97 Disco
Huntington Beach
KC6KBC

By Peter Matusov on Tuesday, May 15, 2001 - 09:18 pm: Edit

the idea here is that some - not all - vehicles come designed pretty good from the factory. if you trust the original design, you may improve somewhat upon that, but don't go overboard.

That's how it happens - you get pissed at the trailing arms' bushings, replace the arms with whatever that has a ball joint or heim joint. Top it off with a long-travel shocks, and on the next ride, your springs pop out, you cuss and swear, and come up with a patch to keep springs attached.
Now your springs are where they should be, but tires rub badly 'cause they have much more travel, your driveshafts bind, your steering geometry is screwed, etc. So you start fiddling with tires, offset rims, make slinkies out of your driveshafts, install dropped pitman arms and twice thicker but bent into an S-shape drag links, and so on.

you end up with an awesome looking rig that's barely driveable on the street - let alone emergency lane change on 405 (for that matter). It will be barely driveable on the trail, too.

that's all provided with flawless quality of the aftermarket parts you bolt on.

Before heading to Moab, I spent a couple of hours putting the $G sliders. Armed with an idea that my rover's now kick ass undestructible, I almost screwed the heck out of the body when I banged it hard on the slider.

I see a good way to improve upon that. But it's already a patch; if I didn't have sliders, I would have looked for a better approach line, that's all. But I wouldn't bet much on the $G quality, and design, either.

FWIW,

Peter

By Kyle Van Tassel (Kyle) on Tuesday, May 15, 2001 - 09:20 pm: Edit

Man , you still cant see that? Cmon , if you are doing ten MPH and you mash the brakes to the point that you are about to lock the wheels you have done it with "X" amount of weight being transfered. At ten MPH you wont transfer much so the ground pressure that the tires apply wont be that great either , therefore the traction they have can probably be measured with your calculation. At 70 MPH if you stab the pedal to the point just before lock up you will then transfer a fair amount of weight over on the front axle , therefore applying a greater amount of ground pressure and giving the front tires more traction , in turn you will be able to step harder on the pedal before the brakes lock , in turn you are loading that front link more.
If you dont think that is the casse then explain to me in your calculations what width tire it would take to propel that 3500 pound car to a 1.1 60 foot time? Tires are 32"tall. Cars dont ussually break when they spin , they break when they hook good. They hook good when they transfer well....

By Rob Davison (Pokerob) on Tuesday, May 15, 2001 - 11:44 pm: Edit

but kyle, you wont lock em if abs is working

rd

By Discosaurus on Wednesday, May 16, 2001 - 12:27 pm: Edit

Kyle, I'm curious...

If you had a known competent fabricator build a
copy of $G's 3-link with materials that are
known to be capable of the stress's that have
been heavily modeled, would you still be as
down on the design ?

I'm trying to figure out if it's the actual
DESIGN of the 3-link that gets your shorts in
a bunch or if it's a question of unknown quality
from the $G 'factory'...

thanks...

keith
discosaurus

By Kyle Van Tassel (Kyle) on Wednesday, May 16, 2001 - 12:37 pm: Edit

Keith , its the fact that the whole 3 link system is just a work around. Its working around the fact that it takes too much thought and cash for a company to develop a 4 link. The 4 link wont fit easily so what the hell , do a three and make some cash...In the whole suspension rainbow that we have now , the three link falls to the bottom in design. That center link is what "Gets my shorts in a bunch" Everything about its being is wrong.....

Kyle

By nadim on Wednesday, May 16, 2001 - 02:54 pm: Edit

what about having the same setup in the front as the original rear LR has...i mean with an A arm....except modified to clear the engine stuff?

By Ron on Wednesday, May 16, 2001 - 02:58 pm: Edit

Where does your lateral stability come from then?

Ron

By nadim on Wednesday, May 16, 2001 - 03:11 pm: Edit

well...

what if we keep the panhard rod, used the rear bolts of the radius arms only, and installed the A arm on the top part of the diff?

By Kyle Van Tassel (Kyle) on Wednesday, May 16, 2001 - 03:24 pm: Edit

There is a room issue. Keep in mind that the after market wants something pretty much anyone can bolt on. THey cant make any cash if its too complicated.

Kyle

By nadim on Wednesday, May 16, 2001 - 03:32 pm: Edit

OK?

first, i am arguing for the sake of benfiting from this thing, not for making a point (i don't have one for the 3-link)

BUT:

with the same ball joint as the rear, with similar links as the rear in the place of the radius arms, and with an A arm that will allow for the movement of the axle case without (1) affecting it "rolling on its own axis", (2)moving laterally (may be better to keep the panhard rod?)...and (3) have the same benefits as the rear?

well?...any one?...

By Ron on Wednesday, May 16, 2001 - 03:32 pm: Edit

exactly Kyle,

So along with those "sexy" bumpers a bolt on "sexy" four link made with C&Ced 4340 arms would be great.

Ron

By nadim on Wednesday, May 16, 2001 - 03:35 pm: Edit

sexy?
i'll buy!

By Kyle Van Tassel (Kyle) on Wednesday, May 16, 2001 - 03:37 pm: Edit

LOL....

Kyle

By Milan on Thursday, May 17, 2001 - 12:38 pm: Edit

I said this before. I think there's nothing wrong with a "3-link" system. That's what stock rovers have. The 2 radius arms and the track rod/bar or the trailing arms with the a-arm are both 3-link systems. Typically the track bar is used on the front because of lack of room for an a-arm under the engine and other related components. I think the a-arm would serve well in the front for lateral stability just like the one in the rear works. Only on the front all attachment points and all the links would have to be beefier than the rear because of more weight/load.

I always thought Kyle's issue was how the center link is mounted in relation to the lower mounts and how the whole thing is mounted in relation to the axle housing and the forces exerted on these mounting points. Right Kyle?

It's been quite a few years since I've done some math and I too fail to see how a 10mph stop results in the same force as a 70mph stop. I thought mass plus speed ment more force.

Sorry for being thick, Mike.

By Kyle Van Tassel (Kyle) on Thursday, May 17, 2001 - 01:09 pm: Edit

Mike is not accounting for weight transfer. And pre lock up force. He is talking about once the tire is locked and sliding along.. Atleast that what it sounds like.


Kyle

By Richard Hills on Thursday, May 17, 2001 - 08:24 pm: Edit

Hi guys,

I hope you don?t mind a d-90 owner posting on your list. As the engineer that set up the first twist-off and the poor fellow who documented it, I thought you may be interested in another opinion.

When Greg first built the 3-link for the twist-off, there was enough compliance in one of the set-ups that the bottom of the axle rotated under the vehicle, toggling the axle, taking out the drive shaft and the shocks. Greg did not seem to have this problem on his yellow d90 as he was using different radius arms. To fix the problem, Greg increased the vertical distance between the lower link and the top two links on the axle. As most of you have already observed, Greg?s second refinement was when he failed a cross member while jumping on the Hammer?s run. The cross member simply was not designed to take the larger forces exerted on it by the lower link.

I have not run out calculations to look at the vehicle dynamics of the 3-link, but reports by drivers indicate that it seems to do well. It does not have as much anti-dive while braking as the stock suspension. Those that install it notices the front diving more in braking and lifting more when on the gas. The same will happen when braking going off a rock ledge or climbing a steep water fall.

The major issue of a three link with the lower single link from a designer?s point of view is the amount of axial force on the lower link is somewhere around 6-7 times that on each of the upper links when braking. The lower link is in compression which means that it fails by buckling. This tends to be a catastrophic failure (i.e., a little buckling quickly leads to lots of buckling). Keeping the link straight is important in this case. Since the lower link is exposed to rocks, one should inspect it to make sure it is not bent.

If the link is designed with sufficient bending and axial strength to resist buckling, then there should be no problem with this design from a structural point of view.

One of the advantages of the stock front radius arms is that they are designed for heavy bending loads. As a result, they are not very susceptible to bending during rock-crawling. I did a finite element analysis (using Mechanica) on the stock front arms. If one assumes that all of the weight of a d-90 is on the front axle and one is doing a 1 g deceleration, then the safety factor (assuming mild steel) was a bit over 4.

However, I see no reason why a single link lower link design cannot be a good and safe design if designed and tested properly.

On another subject: If you vehicle is undergoing a 1 g deceleration, the weight transfer to the front tires and off the rear tires is the same whether you are going 70 mph, 10 mph, or minus 20 mph (i.e., accelerating backwards). There may be some differences in the effect of tire distortion on friction when the vehicle is going 70 vs. 10 mph during the transient from zero braking to 1 g braking, but I suspect these differences are subtle. Of course, at 1 g deceleration, it takes 7 times longer (in time, much longer in distance) to slow down from 70 than it does from 10 mph.

By the way, if any of you have some experience in strengthing the front axle/cv combination, I would appreciate hearing about it. Las Cruces is really hard on these. I recently went through a Maxi front axle (using the stock cv's with stronger cages) and twisted one of his rear axles on my d90.

Thanks,
Rich Hills

By Kyle Van Tassel (Kyle) on Thursday, May 17, 2001 - 08:59 pm: Edit

Hey Rich , dont mind the posting at all but I have to disagree about the speed and weight transfer thing. I also dont think that having a single bottom link can ever be an ok thing there is simply too much riding on that one little link there. If it was on top the loads would change and I might like it a little more.
ok , so lets get into the weight transfer thing here.
At 10 MPH you hit the brake , from that point to a complete stop the event will be very short. Not much transfer is going to take place.
If you are traveling 70 and hit the brake (Not try to lock but just hit the sweet spot)the transfer will start , once it starts the ground pressure starts to raise on the front tires. Once the ground pressure rises the traction of the front two tires rises , that in turn will allow you to press harder throwing more weight to the front and giving the front paws more and more traction. This cannot happen at 10 MPH. I suppose you could throw a small spike up there at 10MPH that somewhat resembles a 70 MPH stop but its a quick event and carries nowhere near the force.
I think you are a suspension guy right Rich? This is really no different then drag cars. The harder you hit the rear suspension the better the car will hook. This sets that transfer chain in motion that keeps it hooked up. If there was no decent transfer (I have seen this often) the car will break loose after the initial hit. Some may not see the relevance of my comparisons here but the two forces are exactly the same just at different ends.

Kyle

By Rich Hills on Friday, May 18, 2001 - 11:30 am: Edit

Kyle,

Once the vehicle reaches pitch equilibrium, then a 1 g deceleration will result in the same weight transfer to the front. But as you correctly point out, there is a transient that the vehicle has to go through to reach this point. Whether a softly sprung off-road vehicle can go through the transient to pitch equilibrium in the time it takes to go from 10 mph to 0 mph is not clear to me (hence, your argument has very good merit). I doubt whether it could from 3 mph. However, I do think that our vehicles can easily reach pitch equilibrium in hard braking from 30 mph. I believe the speed that we used during the twist-off was in slightly in excess of this. But I also know that the hard braking that Bill Burke put the vehicle under (i.e., the one that failed) was not near the traction limits of the tires, hence the link was not fully loaded.

As far as depending on a single lower link. Our vehicles have several failure points in the suspension that do not have redundency. For example, if a single panhard rod mount fails or a bolt falls out, the probability of rolling a d90 at speed is very high. So the design of such components should be very conservative (as are the stock d90 front radius arms).

I don't see anything wrong with the basic concept of a single lower link for the front suspension. However, since such a link is under compression during braking, the overall design should be very conservative.

Rich Hills

By Kyle Van Tassel (Kyle) on Friday, May 18, 2001 - 12:06 pm: Edit

Yes , you are correct about single points of failure. But these arent items that get the stress that thing will. Lets move on to the lower link front attaching point. It pretty much sucks. The housing should fall right in the center of all the attaching points on it (or very close to it). THe front one for that lower link is something like a foot behind the others. This is what I see as the majior downfall of the whole thing. Increasing the seperation helped some but its certainly not "fixed"

Kyle

By Rich Hills on Friday, May 18, 2001 - 02:48 pm: Edit

Kyle,

My comments are based on the suitability of a generic 3-link and are not directed toward the SG 3-link. I have not made a personal judgement on the strength of the SG 3-link as I have not run the numbers. To do so requires a lot of work since the lower link is more complicated (if I remember right) than a simple tube with rod ends at each end. My preference is for a front suspension with more antisquat than the 3-link has. Not so much for the vehicle dynamic effects while braking, but more for the antilift effect of antisquat when climbing the steep ledges we have here in Las Cruces. The antisquat designed into the stock suspension is more to my liking.

Rich Hills

By Kyle Van Tassel (Kyle) on Friday, May 18, 2001 - 04:47 pm: Edit

I hear you about the squating. But you cant come up with the numbers you have if you are just talking generic with no design idea in mind. The force applied to the center link is greater in the configuration $G uses because of the location of that forward mounting point. It being where it is right now compounds the force applied to it under braking. "Links" are always arranged to take the load straight on. With the $G link the force on that front attachment point is up more then back into the link. This deflection in turn compounds the force applied to it. That about correct in your book Rich?

Kyle

By Rich Hills on Saturday, May 19, 2001 - 11:54 am: Edit

Kyle,

Yes, because the front of the lower link is not attached just below the axle but a ways back of it, the axial forces (i.e., those forces along the link) on the link are greater for the reasons you describe. They are also greater on the brackets of the axle and frame. In addition, the forces on the upper links are also greater simply because of the lower link position. One has to consider these increased forces when designing all of the links and mounting points.

The most efficient (in the sense that the links take the least force) approach would be to have two parallel lower radius arms, a single upper link, and a panhard rod. This is what the industry calls a three link, even though there are actually 4 links. However, if the top link is not centered on the axle and in the frame, then one will get a roll effect when hard on the brakes.

Rich Hills

By KC on Saturday, May 19, 2001 - 12:55 pm: Edit

Does that mean that it's possibly unsafe for road use, but ok for an off-road trailer truck where I would be mostly slowly crawling?

By Rich Hills on Saturday, May 19, 2001 - 05:28 pm: Edit

If the suspension is correctly designed, it is safe for both on and off road.

Rich

By Kyle Van Tassel (Kyle) on Monday, May 21, 2001 - 09:20 pm: Edit

That about cover it for ya Keith?


Kyle