First serious outing - what bent, what broke and what almost.....

[Strange Rover]

Finaly took my rig out for a proper workout at a competition.

The day before I went I took it for a drive up a moderate hill near home for a bit of a testdrive (as I hadne driven it anywhere with the big tyres on except my back yard) before I loaded the thing on a trailer and went to the comp.

The hill is fairly easy and with the 42s I could idle up the track in first with open diffs (needed the rear locker on to drive up this slowly before with the 36s) so I was really happy with that. One thing I did notice was that when I got a bit of wheel spin (still ideling in first low) the back end would start to hop but cause the hill was so easy it would just do about 3 or 4 small hops and then continue. I figured that bit of hopping was caused by the extra lift I was running with the 42s (about 1.5in more) giving me more anti squat (links angled more upwards).

Previously with the rangie-trayback body and the 36s the rear would never hop. It would hook up in the rear really well. If the rear started to spin I could just plant the throttle and smoke up the rear and the tyres would spin and work back and forth (left and right) and either progress forward (in this case I would give it even more) or it would just sit there spinning(and in this case I would also give it even more throttle ) but it never got that hopping motion (you know the chirp, chirp, chirp).

So right the thing now hops. Major PITA. Cause when you hop you break stuff and go nowhere. Its good to be able to drive up stuff, get into a bit of trouble and be able to plant the throttle. But now it wants to hop. So I figger too much rear anti squat so the night before the comp I remount the stock rear lower arms from below the axle tube to on top of the axle tube figgering that this will solve the hopping problem. Essencially I lifted the rear lower arms up 3 inches taking the vertical distance from the upper centre balljoint to the lower links from 2inches bigger that stock to 1 inch less than stock (about 7.5 inches). I was a bit worried about the strength with the arms so close to each other but I thought WTF it will have to do for now cause its getting late and I still got to pack.

So I load it on the trailer and off to the competition (about 2hours drive away). The competitions that are starting to run here are no where near as extreme as the stuff that I see pics of on POR. We are only just starting to get this type of driving competitions (where the challange is to drive the stuff without hitting bunting, loosing momentum, reversing etc) where previously everything was just on speed and lots of winching (which doesent appeal much to me). The courses in the competition were a lot easier than the stuff I drive around home but of course the challenge is to drive it in one go and not muck around.

The first track was just driving up a rocky gully. With the 42s it was really easy, didnt get hung up on anything, didnt get caught behind any rocks nothing. Drove with open diffs really easy. These tyres are good.

Second track drove easily except on a few of the down hill sections the rear was wanting to slide sidways when driving across the slope down hill. At one section it was a steep down hill and just before the bottom on the right side there was about a near 3 foot vertical drop that the right (drivers side) wheels had to go through. I thought "shit thats a bit steep" and drove down as slowely as I could under brakes. Almost at the bottom the rear started to lift and I got off the brakes. Then the right front tyre got caught behind a 6inch round log at the bottom of the drop and the steering wheel flung out of my hands (something to do with 42in tyres, about 1in backspancing and stock steering) and the front wheels went to full right lock and the rear went to near vertical. At that point I stood on the gas and just managed to drive out. The spectators reckon it went to about 80 degrees and was going over for sure. Good job I have got the first iteratrion on my roll cage installed I think that if I didnt have it I would of needed it for sure. At this point Im thinking that the rig needs a bit more work in terms of weight destribution and balance. Drove the rest easy, it was another horizontal gully with big rocks in it(not really boulders).

The next sourse was a reletivaly steep up hill gully with lots af loose rocks and a some big boulders thrown in to make it interesting. It was here that the troubles began and the rear started hopping. Driving up the first part of the hill over a couple of boulders with heaps of traction everything was going fine. Could of done with a bit lower gearing but I just kept the revs up in first (I would guess about 1500rpm) to keep traveling. Closer to the top where the rocks are looser is where I could feel the rear wanting to hop as I fought for traction and the torque came in and out of the rear diff. Picked a wrong line near the top and got hung up on the rear suspension ear (I honstly thought that with 42in tyres I couln not get hung up on anything). Kept the tyres spinning and tried to work it a little bit to the left to move around the big rock. Got the ear off the rock and the thing is still hoping. Im thinking bloody POS landrover with 42in tyres carnt drive this hill and everyone is watching. So not wanting to reverse I plant the thottle. And what happens bloody big hopping, where talking boing, boing, boing (as opposed to chirp chirp chirp) and going nowhere. So I back up, move my line over a bit and give it plenty and drive out.

The last track was a man made gouge run with logs, boulders, and couple of rock climes (say 1.5 car lengths long). The sort ov stuff you can idle over (with the big tyres) or get a run up at (the rock climes) so again my rig went well and did it easily.

So at the end of the day Im really happy with my hybed went and it just shows the problems that can happen with such a large revamp of my rig (much lighter body, totally different weight distribution, bigger tyres, more suspension lift (+1.5 in) and greater chassis height (+4in).

So what broke - nothing (I think)

What bent - my rear axle housing where the hoop over the pumpkin attaches to the axle tubes. This is caused mainly because there is not enough reinforcement where the hoop is welded to the tubes and also because of the reduced distance between the upper and lower links increasing the loads on the links and of course the amount of throttle I gave it when it was hopping.

And what almost - did a front ways endo cause I now really dont have enough weight on the rear end on my rig. So I gotta start to move some things back and build some more weight into the rear. First thing that Im going to do is to get it weighed so that I can see where its at.

What I really need to do is to stop the rear from hopping because in its previous configuration (rangie tray back) it never hopped. I been giving it a lot of thought and I think I understand the problem.

So my question is how many of you guys have had trouble with the rear end hopping when you are spinning wheels in the rocks and what have you done to fix it or do you just live with it??

Oh yea, sorry this ended up so long, it sort of got away from me. Must be the

Cheers
Sam

[evilfij]

"build some more weight into the rear. "

How about a spare 42

Ron

[Strange Rover]

Originally posted by evilfij
"build some more weight into the rear. "

How about a spare 42

Ron

HA!! True - that would probably do the job. Although Im thinking winch, battery, fuel tank, tyre carrier (an empty one) and some water.

Sam

[rhills]

Sam,

As you noted, you now have more anti-squat, which leads to wheel hop. This problem is not only caused by the suspension lift, but also by the larger diameter tires. The critical quantity to look at is the angle with the horizon of a line that goes from the tire contact patch through the effective pivot point of your rear suspension. The smaller this angle, the less wheel hop you will have.

The pivot point of the suspension that I am referring to is at the intersection of a line running along your lower trailing a-arm forward, and a line running along your arm forward, when looking at your vehicle from the side. You now place a line from the contact patch of the rear tire through the intersection of the trailing arm and a-arm lines and look at the angle of this third line with horizontal. Too big an angle, and you will get wheel hop problems.

Even if you didn't lift the rear suspension but put on larger tires, in which case the pivot point would be unchanged relative to the frame, the third line would have a steeper angle since the vertical height from the contact patch to the pivot would be more. The fact that you raised the rear, also raised this pivot point, is making things worse. The extra traction of the rear tires also allows the suspension to anti-squat more, leading to more motion when the tire lets loose.

Wheel hop problems become even worse when climbing 30 degree rock hills. This is because the more of the weight of the vehicle is supported by the rear trailing arms, less by the springs, and the rear can actually sit higher. This is counter intuitive since one expects the rear to sag because of the weight transfer toward the back. But the trailing arms are actually supporting a greater percentage of this increased weight. Look at pictures of vehicles with short rear trailing arms about to go over backwards and you will note that they are not squatted down on their rear springs. This raises the pivot higher, leading to wheel hop. I occasionally get this on my d90 with 35s on 30-35 degree climbs, even with the hard top. TJ's on 35s are much-much-much worse than a d90 as far as wheel hop because of the pivot point location. I find I can crawl up things that TJ's require momentum and a lot of wheel hop to climb.

To fix this, you must redesign the suspension so that the pivot point is either lower, or more forward, or ideally both. This usually requires longer arms. I would suggest that you look at you previous and present configuration to get a feel for what you will need to do to get that anti-squat in control.

[Strange Rover]

rhills,

Excellent post!!! Where were you when we were having the barnie on over in general on anti-squat. You would have been a great help.

Yes pretty well what I was thinking except I tend to think of the problem in terms of a pushing force and an axle torque acting at the axle centre as opposed to a force only at the tyre contact point (of course this is the same thing) and in my thinking the increased tyre diameter has increased the torque loads on the housing for a given amount of needed push and in your case the bigger tyres moves the point of application further away.

What I think that the biggest problem causing my rear suspension hop on moderate climbs is mainly to do with the bigger tyres (increase torque loads on rear axle housing for given amount of push or in your thinking line of action of force further away from instantainous (sp?) centre of suspension links) and also to do with the greatly reduced vehicle weight on the rear springs and also reduced rear spring rate that I am now running (I was running 170lb/in and now have 130lb/in). The combination of these three things has turned my rig from a hill climbing weapon (with the 36s and the rangie-trayback body) into and absolute POS on the climbs.

The beauty of this whole anti squat thing (this is my own opinion)is that anti squat is a very useful thing when the whole system remains stable (and doesent hop). When it is stable means that the amount of lift on the rear generated by the links is less than the extra weight on the rear caused by the acceleration effect of the cog placing extras weight on the rear tyres (ie the body trying to squat). On a flat surface a vehicle with lots of anti squat will hook up better and accelerate faster than a rig with little anti squat. Driving up moderate hills a vehicle with more anti squat (while still remaining stable) will get more traction out of the rear and in most cases will drive up the hill easier than one with no anti squat. What happens though (as you state) is that as the hills get steeper more weight is on the links, less weight is on the springs and the rig ends up with more lift in the rear which causes a greated anti squat effect.

The killer is that when the angle of the climb is increased the rig that climed well on the moderate climbs with the assistance of the anti squat will suddenly become unstable and start to hop. While the rig with minimal anti squat will remain stable (not hop) and continue to drive well.

With my lower links on top of the axle tubes my rear geometry is better now than it has ever been but now with my reduced rear weight the amount of anti squat I get (of course with the increased axle torque needed from the bigger tyres) is able to throw the lighter rear of my rig around much more easily.

Also with my greatly reduced rear spring rate when I drive up rock climbs the rear will of course unload a greater distance (because of the lower spring rate) for a given amount of load taken off the springs and placed on the links. This places the rear suspension at a much greater amount of lift giving me lots more anti squat and makes the problem much worse.

So my steps to solve the problem will be to first get some extra weight onto the rear springs (this will also help my endo forward problem on steep down hill sections). Im thinking about an extra 200 - 300lb should be a starting point. With the extra weight I may be able to run stiffer springs which will help also. Finally the next step will be to lengthen my rear trailing arms which I will do eventually.

AH - You gota love this theory, it took me ages for me to get my head around this stuff (and also took me a bit of time sitting at the top of the hill trying to work out why my rig drives up hills so badly compared to how it went before)

Sam

[rhills]

Sam,

As you noted, anti-squat is a real mixed bag. If you are trying to build a machine that climbs things with sudden bursts of throttle, then anti-squat will help you hook up during the transient, giving you more momentum. The down side is you are now putting a lot more torque on your rear axle components, requiring stronger components. I really think competition rock crawling is going to come to this, as there is often no substitute for momentum. However, as you point out, there cannot be so much anti squat that wheel hop initiates.

Anti-squat can also help clear those ears (or trailing arms) when crawling over steep ledges. Unfortunately, if one is just about to clear a ledge and the rear tires loose traction, then the rear unloads, setting down firmly on the ears or trailing arms, with not enough weight remaining on the rear tires to re anti-squat. Forward progress comes to a grinding halt and one has to back up and try again.

The other disadvantage of lots of anti-squat on really steep rock climbs is it raises you cg, transferring more weight backward, unloading the front. You also loose the ability to articulate the rear since the links are supporting more of the vehicle weight. The result is a front tire can end up clawing the sky, which raises the cg even more.

As you point out, the easiest way to control this is to go stiffer on the rear or put more weight on the back. However, both of these approaches create other problems. The ideal approach for Las Cruces (in my opinion) is to put the instant center of the rear suspension way forward. I have watched Walker Evan's rig on our steepest climbs. He is extremely light in the rear, but generates no visible anti-squat when climbing things that most others can't climb. His rear suspension design is basic off-road desert racing. Very long trailing arms and upper links attached to the frame just behind the cab. As a result, his instant center is very far forward. In watching rock crawling contest, one can almost predict how well one will climb based on where the instant center is for the vehicle. For example, the Scorpions have instant centers very close to the rear axle. They have a hard time climbing in Las Cruces (even the long wheelbase version).

If the type of 4x4ing one does is in mud or other loose surfaces, I think one would want more anti-squat to hook up. What do I think is the ideal anti-squat for my application and driving style? I really don't know and won't until I can do some experimenting. I think we are all watching your experiments with 42" tires with great interest. Your progress will help us all formulate our opinions on what will work best for our rigs.

Rich Hills

[Strange Rover]

Originally posted by rhills


The other disadvantage of lots of anti-squat on really steep rock climbs is it raises you cg, transferring more weight backward, unloading the front. You also loose the ability to articulate the rear since the links are supporting more of the vehicle weight. The result is a front tire can end up clawing the sky, which raises the cg even more.

I only realised this point since I have been wheeling my hybred which also now does this really bad even on moderate obstacals when previously (again with the rangie-trayback) it would climb staying crossed up and keep both front wheels on the ground. I previously thought that this problem was mostly to do with weight distribution and the matching of roll stiffnesses of the front and rear suspension. Before it was really well behaved but now, even though I have a much greater percentage of weight on the front and I still have equal roll stiffness front and rear (same spring rate all round and a hinged arm up front), it wants to lift the front wheel and square up on the rear suspension (and then it wants to fall over ). As you say this is also now due to the exact same anti squat problem that gives me the wheel hop.

Damn my rig needs some work but I think that a couple of sand bags thrown in the rear will do the job in the short term.

Originally posted by rhills


If the type of 4x4ing one does is in mud or other loose surfaces, I think one would want more anti-squat to hook up. What do I think is the ideal anti-squat for my application and driving style? I really don't know and won't until I can do some experimenting. I think we are all watching your experiments with 42" tires with great interest. Your progress will help us all formulate our opinions on what will work best for our rigs.

Rich Hills

mmmm, I think that if you want your rig to really perform on the really steep stuff then you got to minimise the rear anti squat. The only problem with this that I have found is that when you go wheeling with your mates who have a bit of anti squat they will do the moderate climbs so much more easily and trying to explain to them why your full custom rear link set up works worse than there stock lifted rear is both very time consuming and not easy

I think that the best thing to do is to realise that the angles and lengths of the rear links have a major bearing on how the rig will perform when driven off road up hill. And if you do something major in terms of tyre size or weight distribution or suspension links then you have got to expect some problems. If you can design into your first build up some flexibility in terms of link lengths and angles then this would be the best setup. And Rich, by the sounds of it this is what you are planning.

Doug Marbourg I hope your are listening cause you are gonna have some fun.

And of course plenty of beef and lots of loud pedal can make up for a lot of suspension design flaws but for those of us that are running too big a tyre on not enough axle do have to be carefull.

Sam

[Strange Rover]

Just went and had a look under the rear of my rig and it is interesting how the links are at the moment. Heres the picture from the side and it can be seen that the lower outer link is fairly well horizontal (this is a stock link mounted in the stock frame position to on top of the axle tube)

Sam

[Strange Rover]

Here is the view from the back. The camera height is in the same horizontal plane as the rear ball joint (well it seemed like that anyway) and again it looks as if the top link is again horizontal. The little green dots are where I have marked the ends of the links.

[Strange Rover]

From the angle of the links I would have thought that there would be hardly any anti squat. Both links are fairly horizontal and parallel. But here is my thinking:

The rear springs I am running are early Range Rover front springs and I believe them to be 130lb/in (so the total rear spring rate is 260lb/in). Which is very light. I can easily grab hold of the rear bumper and lift the rear up an inch (lifting up I guess with 260lb). This means that any lift by the links (via anti squat) will easily lift the rear a long way. So driving up hill any anti squat effect will translate into a lot of additional rear lift and because the rear stock arms are so short this then creates a lot more anti squat very quickly the the process gets out of hand very easily. Meaning it starts to hop.

Also the free length of the rear springs is 395mm, when sitting in the rear they are compressed by 40mm to 355mm. So the 40mm is about 1.6in multiply by the spring rate (130lb/in times 2 springs) gives a total rear weight sitting on the springs of only 416lb. Which is stuff all. Not wonder the rear gets thrown around by the anti squat so easily.

So basically with the big tyres (42s), light rear sprung weight (416lb) ,low rear spring rate (130lb/in) and short stock links that are essencially parallel and horizontal, the rear anti squat can very easily get out of control.

I really need to lengthen my lower rear links.

I think that keeping the short upper A link will also help reduce the anti squat effect with the suspension at greater lifts because as the suspension lifts the tension in the upper short link will tend to pull the rear down.

AH, at least now I have a plan.

Sam

[rhills]

Sam,

Sounds like a plan. Keeping the top a-arm short will move the instant center behind the axle and closer to the ground when the rear lifts.
As you note, this will help pull the rear down when the rear wants to lift due to climbing. It will also tend to lift the rear when going down over those nose dive ledges. You may want to put in several mounting points so that you can try mounting the forward part of the a-arm a bit higher. The higher location should help even more with anti squat. It sure would be nice to see a side view picture of your rig on a steep climb as presently configured to check if our theories are right. A front picture would be nice to see what drive shaft torque is doing to you. If you take these pictures, use your hand brake rather than the foot brakes to simulate the drive shaft torque effect (assuming the hand brake can resist the torque of those 42" tires).

I'm also thinking of this same approach (longer lower arms with stock length upper arms repositioned to give more anti-squat).

Rich

[rhills]

Sam,

Another thing that may work is to mount another spring where the air-bag is when a self leveler is used (i.e. to the top of the a-arm). This would control vertical motion while allowing for articulation.

Rich

[RockRover]

Originally posted by Strange Rover


Doug Marbourg I hope your are listening cause you are gonna have some fun.

Sam

WHOA! I take a couple of days' off for Easter, and you guy's are running a "muck"...

How about a limiting strap in a V from the top of the ball-joint on the a-arm to each side of the frame rails? Do that front and rear.

Also I would put a "boner" bar (endo' bar) on the front bumper if your going to do a bunch of down stuff. I'm thinking of one on the rear of the rig too...Watching the antic's of Bill R. on Dump Bump has tweaked my brain.

My rear trailing arm connection points (via my old SG HD trailing arms) are now right at the center of T-case break drum (near CL of the frame rails when looking at it from the side). That's about as good as you can do and still have a reasonable length arm...Heck with the rear axle position I'm playing with, I measured 54" for the trailing arms! That is if I decide to go with the 110" wb. I kinda' like the idea of having a 110 90. I forget what the font's measured out at, but I think they were about 38" using the stock radius arm mounting points. That's about 7" forward from stock.

I think all the problems we are seeing is the result of trying to fit a square peg in a round hole...That is using all the stock mounting locations for the control arms, and trying to make it work. Personally, I'm trying not to make it all that complicated (KISS). All I'm doing is simply increasing the lengths of all the components proportionately to the increase in ride height and tire diameter. That is, make um' longer. I was always satisfied with the 3-link and the longer rear trailing arms, so I'm just gonna' do the same, with heavier and longer components (read same mounting locations for axles that are spread 18" farther than stock.

Like Rich said, just watch a lifted TJ with big tires and short control arms and you'll see a show.

--D

[RockRover]

O'yea Sam...One more thing...That's ONE NASTY TRAILER YOU GOT THERE!!!

[Strange Rover]

Originally posted by RockRover
O'yea Sam...One more thing...That's ONE NASTY TRAILER YOU GOT THERE!!!

Yup its nasty and its old. And it looks the same now as when we bought it. Need a complete rebuild now cause my rig wont fit on it with the 42s on cause its too wide (that is why its sitting there with the 31s on.)

But hey at least it still goes

Sam

[Strange Rover]

Originally posted by RockRover


WHOA! I take a couple of days' off for Easter, and you guy's are running a "muck"...

How about a limiting strap in a V from the top of the ball-joint on the a-arm to each side of the frame rails? Do that front and rear.

Also I would put a "boner" bar (endo' bar) on the front bumper if your going to do a bunch of down stuff. I'm thinking of one on the rear of the rig too...Watching the antic's of Bill R. on Dump Bump has tweaked my brain.

My rear trailing arm connection points (via my old SG HD trailing arms) are now right at the center of T-case break drum (near CL of the frame rails when looking at it from the side). That's about as good as you can do and still have a reasonable length arm...Heck with the rear axle position I'm playing with, I measured 54" for the trailing arms! That is if I decide to go with the 110" wb. I kinda' like the idea of having a 110 90. I forget what the font's measured out at, but I think they were about 38" using the stock radius arm mounting points. That's about 7" forward from stock.

I think all the problems we are seeing is the result of trying to fit a square peg in a round hole...That is using all the stock mounting locations for the control arms, and trying to make it work. Personally, I'm trying not to make it all that complicated (KISS). All I'm doing is simply increasing the lengths of all the components proportionately to the increase in ride height and tire diameter. That is, make um' longer. I was always satisfied with the 3-link and the longer rear trailing arms, so I'm just gonna' do the same, with heavier and longer components (read same mounting locations for axles that are spread 18" farther than stock.

Like Rich said, just watch a lifted TJ with big tires and short control arms and you'll see a show.

--D

Doug your absolutely right. The long arms are the go.

What just amaizes me is how well it behaved before (with the rangie-trayback body which was 36in tyres, 170lb/in springs and a lot more rear weight im guessing an extra 400-500lb at least). And this was with absolutely stock rear links.

Now with about 1.5in more lift, much better angle on the lower arms (by placing them on top of the axle) and bigger tyres and lower weight the rear just performs so badly.

But it is all good fun.

Sam

[Strange Rover]

Originally posted by rhills
Sam,

Another thing that may work is to mount another spring where the air-bag is when a self leveler is used (i.e. to the top of the a-arm). This would control vertical motion while allowing for articulation.

Rich

Yes this would produce similar results to Doug's V strap idea (I guess by running the strap in a V would give a much lower stiffness than straight up)

The spring in the centre would essencially give me the greater vertical spring rate that I need.

Still think the longer links are the go.

I should do the photos and I know a place close by that would do the job.

Sam