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Discussion Starter #1
My rig with the d44s and the 42in tyres has been together for about a year now and so far I have broken:

5 rear axles
2 front inner axles at the inner splines
4 297 x steering u joints
4 front free wheeling hubs
1 front knuckle where the steering link attaches to it (basically broke the end off)
1 sector shaft in the steering box sheared off (steering was stock rangie)
1 front crown and pinion

But all in all ive really had an absolute blast and driven some wicked shiat but Im sick of the breakage so now its time for the MOGS.

On the weekend I broke a rear axle and also a front u joint which stuffed the front inner axle as well so thats it, my rig is comming off the road and is going to come out bigger and better than ever. It needs to be going again by the 22nd March for a competition and Ive got heaps to do so I will see how I go.

Sam

I have seemed to have lost my star so if anyone wants to see some wheeling pics check out:

http://www.outerlimits4x4.com/PHP_Modules/phpBB2/viewtopic.php?t=1823

http://www.outerlimits4x4.com/PHP_Modules/phpBB2/viewtopic.php?t=1845
 

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Discussion Starter #4
Actually, just thinking about it, Ive only had the 42s for about 8 months and everything was broken since then except of one rear axle which I broke with the 36s.

33s would prpbably cure my problem but I wouldnt know for sure :flipoff2: so I should try the mogs. Maybe the mogs and 33s would be a safe bet??

For coils Im still going to run rangie coil springs, for the rear links almost going to use the stock rangie 3 link setup with extended upper and lower links which is what is on the rig currently and works well. The centre ball does limit things but I think its good enough. Im starting to get away from the mega travel thing. For the front maybe a three link and panhard like Doug M's or a four link and panhard - not quite sure.

Sam
 

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Sam,

Now that you have been down the big tire large travel route, what are your thoughts about the performace gains of this route (assuming things were strong enough)?

Rich
 

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Discussion Starter #6
rhills said:
Sam,

Now that you have been down the big tire large travel route, what are your thoughts about the performace gains of this route (assuming things were strong enough)?

Rich
Having the 42s really has been a huge learning curve. If you want to know whats deficient about your suspension setup, throw on a big set of tyres and let your rig behave really badly.

The gains from using big tyres really can be huge although its much harder to get everything to work with them. When I first put them on I really struggled with getting my rig to behave. On a lot of my old track which were easily driven on 36s, Id have trouble on the 42s which was a real eye opener. I could still drive them and crawl slowely but if i got any wheelspin or a bit offcamber or a bit vertical things would fall apart. The big tyres did allow me to drive much harder stuff but the easy stuff was harder and the impossible stuff was more possible. At that point having the 42s gave me much better clearance, approach and departure angles and the ability to make small rocks and ledges insignificant. This allowed me to try and drive a lot more harder stuff. At this point a was really carefull with the throttle and not driving aggressively bacause if I did things would get out of control and start to bounce and hop. Couldnt drive anything too vertical cause it would fall over backwards (which I thought was just a too much lift with too much tyre on too short a wheelbase but this was proved wrong)

In my rigs current form it really does work well. Its got the bwt18 gearbox which gives a crawl of 85:1 which is really good, stock radius arms in the front with drilled bushes (instead of a hinged arm) which I think works really well and longer upper and lower arms in the back that are parallel so gives really low anti squat (dont know the percentage but i should work it out)

Now that everything is sorted (and it is sorted better now than it ever has been with any tyre size) the big tyres really do work amazingly well. The stuff I was driving before with the 36s is now just nothing but a road and not even worth thinking about. Some of the old hard obstacles that I used to play on and test things on (with the 36s and initially the 42s) I now just come up to them and drive them without any thinking. I would use more throttle now and hit things faster than I ever did before and is probably the reason why im breaking so much more. I can really use a lot more throttle because it doesent bounce or lift front wheels (obviously there are limits). Im a lot more confident on the verticle stuff (short climbs that are longer than my wheelbase) which again means I use more throttle (I also got a racing seat and a 4 point harness which helps as well).

But what I am thinking is that as you get into bigger and bigger obstacles then tyre size doesent really matter as much. If the abstacles are in the 0 to 3 foot range a 42 is going to do much better than a 35 or 37. But as the rocks become boulders and the steps become ledges then the size of the tyres isnt as important IMO as long as you still have the approach and departure angles and clearance. For example if the abstacle is composed of rock that is in the 5 to 10 foot slab range tyre size isnt as important as long as you have enough clearance.

I think same thing goes for wheel travel. Once you start playing in big obstacles 5 to 10 foot and bigger range the whole rig tends to be on the obstacle at once so that wheel travel isnt as important and stability (not falling over sideways and not falling over backwards) becomes more so. Which in my mind means that stiffer captured springs, less travel and low C or G would be really advantageous in a lot of situations. I think you still need adequate wheel travel for the type of stuff that you drive but IMO you really should aim for the least amount of wheel travel that you can get away with as opposed to the most amount wheel travel that you can create.

So given this, on my new rig I really want to try some 37 MTRs on the mog axles, run about a 220lb/in springs all round and the killer mod is that I want to put a vertical air ram on the centre of each axle so that I can control the ride height of the rig and also the vertical spring of the centre of the axle as well (can do this by running pressure on both sides of the piston - havent worked out the numbers but, for example, if there was 100psi on both sides of the air ram it will have a much heigher spring rate then say 10psi). Given that my front axle centre line will be totally in front of the motor this will be easy to do. And given the extra lift needed to run the mogs being able to set the rig up with only 1 or 2 inches of up travel will be necessary in some situations(to give you some idea with only 2in up travel I will be at the same ride height as I am now (and ATM i have about 5in up travel))

Sam
 

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Sam,

Thanks for the very complete response. Your and my thoughts on mega travel and large tires on big ledges are the same. That is one reason why I am staying with 37" tires and focusing on keep my cg low (light top and tub, gas tank between the frame rails), my moment of inertia small, and suspension controlled. I plan to keep my semi-hinged link in the front (I really like the simplicity of your drilled bushings) as they are already built and work well. I will also go with constant, retained rate springs in front, at 220 lbs, but have not decided about coil-overs vs LR springs in back. I was also thinking about centered springs (I like your air ram idea better) to keep the cg low whenever possible but will not includes these for now.

I ordered a set of 303 axles several months ago, but don't know if I will put them on this vehicle at a later date (several years down the road - for now I will go with the 9" in the rear) or whether I will put them on a lightweight tube buggy after I finished the mods to the d90.

Still shooting for next years CC for my d90. Things are starting to go faster with the fiberglass now that I am getting the hang of working with it and have completed the mold for the most complex part. Hopefully, by next year, most of the bugs will be worked out so that we can see how well it does compared to Doug's mega rig.

Rich
 

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So to paraphrase:

"42's kick fawking ass when you have a rig set up to handel them"

:flipoff2:

Good work Sam....Look for a similar write-up soon.

--D
 

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How about keeping the D44s, getting some warn shafts all around, 760 or CTM ujs, and slapping the 37s on? I bet you could even run 37" boggers.
 

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Discussion Starter #11
Busto said:
Sam,

That is an eye opening (and well thought out) response. Have you done any mud with your setup? Thoughts?
I dont really go looking for mud but I think that anything with 42in tyres would go OK but given that with mud you get a lot less traction I think that I would want a lot more antisquat in the rear to make use of any traction that could be found. That and a lot more horsepower.

Sam
 

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Discussion Starter #12
RockRover said:
So to paraphrase:

"42's kick fawking ass when you have a rig set up to handel them"

:flipoff2:

Good work Sam....Look for a similar write-up soon.

--D
This is absolutely true. I drove around for a long time with a setup that worked well with 36in tyres and struggled with the 42s. Its only been since I swaped in the BW t18 and redone the rear upper suspension links (three months ago) that has got everything really working well. For a long time I thought that the 42s were an awesome tyre but created a lot of trade offs in a lot of areas. But in reality they really do work well everywhere as long as you got the rig to hang onto them (both suspensin setup and strength).

Sam
 

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Discussion Starter #13
4x4Guy said:
How about keeping the D44s, getting some warn shafts all around, 760 or CTM ujs, and slapping the 37s on? I bet you could even run 37" boggers.
This is what I would have done if I hadnt gotten hold of my Mog axles.

Sam
 

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Strange Rover said:


Having the 42s really has been a huge learning curve. If you want to know whats deficient about your suspension setup, throw on a big set of tyres and let your rig behave really badly.
i agree with it all, but this part would most describe my current setup :eek:
 

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Discussion Starter #15
rhills said:
Sam,

Thanks for the very complete response. Your and my thoughts on mega travel and large tires on big ledges are the same. That is one reason why I am staying with 37" tires and focusing on keep my cg low (light top and tub, gas tank between the frame rails), my moment of inertia small, and suspension controlled. I plan to keep my semi-hinged link in the front (I really like the simplicity of your drilled bushings) as they are already built and work well. I will also go with constant, retained rate springs in front, at 220 lbs, but have not decided about coil-overs vs LR springs in back. I was also thinking about centered springs (I like your air ram idea better) to keep the cg low whenever possible but will not includes these for now.

I ordered a set of 303 axles several months ago, but don't know if I will put them on this vehicle at a later date (several years down the road - for now I will go with the 9" in the rear) or whether I will put them on a lightweight tube buggy after I finished the mods to the d90.

Still shooting for next years CC for my d90. Things are starting to go faster with the fiberglass now that I am getting the hang of working with it and have completed the mold for the most complex part. Hopefully, by next year, most of the bugs will be worked out so that we can see how well it does compared to Doug's mega rig.

Rich
I think its easy to understand that bigger tyres arnt always better in a lot of situations. I think that a 37 is much better than a 28 but something like a 54in tyre or something stupid like a 76in tyre wouldnt be any good at a lot of things (even if the side wall and compound were OK)

IMO as you go from a 37 to a 44 you are in that magic tyre size range where a lot of things happen. Issues with COG, axle size (weight and clearance) and tyre structure (especially tread type and compound) over this tyre range means that there are many ways to build a rig.

Sam
 

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Sam, I agree. Around here, it seems like 35" tires work well with a 93" wheelbase. Going up in size while maintaining the same wheelbase does not clearly provide a significant advantage. However, most of the hard core guys around here are now at 100" wheelbases with 60-66% of the weight on the front wheels. They do benefit from larger tires (37-38" tires), assuming they have also modified their rear suspensions to overcome the increased tendency to wheel hop. I suspect that as long as one scales up everything (wheelbase, track width, axle strength, suspension geometry, engine torque) “appropriately” with tire size, the resulting overall performance will also scale up (assuming one does not have to fit between trees.). How to scale up is not clear and I doubt if it is a linear relationship (i.e., increase tire diameter by 10% does not imply that wheelbase should be increased by 10%).

As the sport progresses from rock-crawling to rock-racing (if you call this progress), I suspect this will change the equation somewhat. Dynamic wheel control becomes more important and one cannot control 300 lbs of tire with a light buggy. One does not see 44” tires dominating desert racing. Acceleration is another issue. A racers rule of thumb (a gross simplification) is 1 lb in rotating weight is equivalent to 3 lbs in non-rotating weight. Any good dirt bike rider knows that momentum is the key to climbing steep hills and being able to build momentum in short distances at the bottom of the hill is a real advantage. Likewise, being able to put the front tires of your 4x4 over the top of a ledge and blipping the throttle to get those rear tires to bang into the ledge hard enough to increase traction (momentarily) is also an advantage.

Finally, as tires become larger relative to the rim size, wheel hop can be more likely due to the increased distortion of the tire between slips and catches. This increased distortion also makes it harder to keep the vehicle on line as the vehicle becomes less responsive to steering.

I don't have a feel for what wheel base and track width work best for our conditions on 42" tires. That is why I am happy to see people, such as you and Doug, experiment with this.
 

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Man...This is the best thread I've read here in a while...

I'm VERY curious to see how my rig reacts in Cruses, Moab and Farmington....If she does all right then I'm heading to the Hammers for the final verdict.

I have a feeling she's gonna' hook-up well. My track is about 14" wider than stock, but my lift (not CG) is about 8" higher than stock....My tire diameter is huge, but my wheel-base is at 110.

Now the issue I've already experienced is turning radius. I can see 4 wheel steer in my future (maybe). At a minimum I can see ditching the detroit up front in favor of an Electrac...Maybe... I hear the whole key to turning with a front detroit is driver technique....A little on-off blip of the throttle (I hear) is the key to unlocking the front and allowing it to swing around...Dunno' yet, but everyone I've talked to says the same thing.

So far, in the little driving I've done, she feels very stable. I plan on adding a rear sway-bar and a center limiting strap in the rear. I'll use the winch cable in the front for vertical ledges....I simply can't wait to really romp on the skinny and see if she bounces....The good news there is that my upper and lower links are close to parallel (but not perfect; read some anti-squat).

Will the 1.5" diameter axles hold up? I dunno'....I honestly can't see breaking too much shiat with the stock 3.9, but stranger things have happened. If I start breaking rear axles I might consider putting Dana 80 side gears on my rear 70 detroit and running 38 spline Dana 80 axles...But I think that's gonna' be on the lunatic fringe of overkill.

Stay tuned....The rest of my break parts should be here Friday :bounce:

-D
 
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