De Ranged

It also brings up an interesting issue..... if I am right and it does pivot on the axle panhard mount then that brings up the issue you've mentioned that instead of tipping evenly from the center it tips with a pivot off to one side... this means that tipping to one side will have more resistance than the other Yrs ago in the trials scene here there was a move to short panhards mounted to the center of the diff (still alot of trucks running this) I have play'd on trucks with this setup and from an anecdotal point of view I felt they flexed free'er and since the panhard was mounted in the middle of the diff at low to med speed there was minimal bump steer, alot less than I expected, unfortunately I wasn't able to push them on sidelings to see handling changes... but it makes sense it should be more predictable and even side to side .... now I'm not even remotely suggesting this for a road going truck, it would take very carefull consideration if you were to do this! Oh and 3 link is still panhard based, the ones I was thinking about is triangulated 4 link or "A" frame styles

I'm not saying it doesn't.... just that instead of the RC height being half way between chassis and axle mounts on the panhard as is in all the automotive books I think due to our slow speed I see the body pivoting on the axle mount of the panhard which makes this lower This is why I was hopeing to find some people who have gone from say radius arm front to a triangulated link setup to see what they noticed... or if I'm being daft, challenge my logic

Something I've had in the back of my mind for a bit now, I've brought it up now as it may have implications to do with Bills thread on retained coils... I'm curious to see if I'm right lol Now please bear in mind I'm looking at this from a low to med speed point of view (typical 4wd'n speeds) How a Panhard suspension systems rollcenter height performs compared to a triangulated system with no panhard I know this may sound daft but.... I have come to the conclusion at low speed the panhard systems is not as is commonly thought "Half way between a virtual line between the two mounting points of the panhard bar, so effectively half way between axle mount and chassis mount..." Here's my thoughts on it I'll start first with a comment that I think is why most miss what I'm getting at "speed"... most of the calculations for forces in automotive handling are worked out for vehicles with motion and inertial mass.... now we are trying to apply these to our sport but where we are going alot slower, alot of the time we will have minimal inertia so a minor change of direction wont have the same resistance or possibly no resistance at all (Sorry to all those who know science speak, I know I'm not describing this right lol please bear with me ) Right let me describe something so this makes sense, I'll start with the triangulated system, lets say the rear "A" frame setup of a coil sprung landy .... the rollcenter is the ball at the end of the "A" arm, now forcing the body to pivot on this is the "A" frame so this locks the body into this relationship... this can't change due to speed, orientation to a side slope (yes I know it changes in relation to the body CoG due to extension and compression of the suspension but both front and rear do this so I'm ignoring it) Now on a panhard system what is to resist and force the relationship so that rollcenter height stays there Most books and people I've talked too say... that it is the sideways motion of the body as the panhard bar swings under compression or extension, as the bar swings in an arc that creates a sideways motion between the chassis and the axle In my opinion this amounts to little to no resistance at our speeds, also the amount of sideways movement is not that great compared to the weight that is in the body and supposedly pivoting on it Even if it did have some resistance lets look at what is resisting it... imagine the truck with the front panhard bar under compression, this wants to force the front of the truck to one side so what resists this, remember there is little force from inertial change so the only real resistance is the wheels in contact with the ground at the back of the truck and a long lever (length of the truck) working against these... remember its only a few mm or sideways movement The way I see it... it is the axle pivot for the panhard is the real rollcenter height, I can't see any resistance to the body's movement coming from the chassis pivot at low speed I haven't put this to any of the trials guys over here yet..... but curious to see if anybody out there that has gone from a panhard to triangulated suspension and noted an improvement in roll resistance, but with similar RC heights? Comments ?

Nice, this was pretty much what I wanted to start with for my next project lol instead... well thats a story for another thread The free wheeling hubs are aftermarket, but here in New Zealand you could get them fitted off the show room floor...a good addition especially if your doing lots of road K's as they will improve your fuel economy So what are your plans?

I would do the same apart from the fact I'm fitting an auto lol Just a wee note on this project, things have started to appear lol not that I wanted any of this till the Toy was finished but I have a wrecked SII 5 door, that will provide me the back passenger door, rear deck, floor, and passenger side Also got paid for a rust repair job.... a running 202 powered SII 109 ute with a good body So the only things I need landy wise are A 109" 2 door station wagon right hand side SIII front guard faces the bits that have the headlights and a SIII grill and a rear station wagon door guess I might have to start lol

Here ya go Lol your comparing apples and oranges, your running a stiff short coil and if you were to tie them in you are right it would hold up the down hill wheel and due to front weight bias pull/tip the truck Also you have your system setup for more down travel than up the stiff dislocating spring allows this, a retained spring system will be linear in its rate (unless you can bind up coils under compression) this means that its ride height must be in the middle of its travel that means to set it up for less up travel you need to add a jounce or bump to increase the rate on up travel (hyd bumps do this very well) What I'm getting at is to do either properly you need to design a system around this.... if you adapt from one to the other you will compromise it in both Just on a side note.... does wildfing balance on the front or rear axle, it is very hard to get suspension truely balanced, normally one is stiffer and more dominant, normally the front due to the stiffer springs required because of the greater weight, but given the level of your mods lol and the narrow front spring mounts..... you wouldn't have any video of it walking over articulating terrain

My PC crashed on me yesterday lol after I had typed up a huge post Right condensed down (and hopefully posted this time, really should buy a new pc lol) My last post described a dislocated case, the retained spring is a bit different in that its weight is transfer from one wheel to the other is linear.... using the example i did above as the axle articulates for every cm one compresses the other expands 12.5kg of weight is transfered to the compressed side.... this weight transfer is linear right up untill full articulation and the weight is only on one wheel how this effects your grip, the more weight you have on a wheel the better the grip, so at full flex the dislocated axle due to its pivot effect putting more weight on the dropped wheel will have better grip and driver further but an ARB will counter this to a point, consider at an extreme if the grip conditions are loose or muddy and you need that weight to get grip the retained ARB setup won't be as good as a dislocated ARB setup Now lets lets consider control and feel, this is a tricky one due to how Rollcenter Height to Center of Gravity can effect body roll and since most people struggle with CoG calculation I'll gloss over it and just play with some of the mechanics Now I don't know about the rest of the world but here in NZ the rule of thumb is if your rolling into something extreme (sidling or climb) you do it with the front locker out, the main reason for this is control.... as you push hard the uphill wheel will brake traction and the front axle loses drive (hopefully stopping you going to far lol) Now this works simply for a retained spring..... the steeper the slope the more weight that is transfered to the downhill wheel as this is linear the driver feels this happening in the form of grip as they get closer the wheel slips more and more till its spinning and the front axle no longer drives Lets consider this with dislocation as I showed in the above post untill the shock or limit strap lifts the wheel there is a constant weight forcing that wheel to grip if this is enough to not break grip then you drive till you tip, on a positive you will go further lol Now from my experience driving logging skidders with pivot axles, you want that axle that is staying on the ground to be as heavy as possible, we used to full the tyres on the pivot axles with water so they would hold the body when you tipped Now for the catch lol the body is a big leaver working on the suspension, most people look at a truck and the wheel track and and feel confident that a wide axle makes it stable.... this is part of the story lol remember the bulk of the weight is resting on the suspension... the springs are the width for this weight Body roll is what tips most trucks, imagine a triangle.... the top point of it is the CoG for the body (no wheels axles and only half the suspesion weight) so this is alot higher than you'd think or want lol now the bottom of this triangle is the springs As you drive along a sidling getting steeper you will reach a point where the CoG tips on the lower spring mount.... now this will happen sooner than you think because remember these lower points are springs so the lower is compressing and the upper is extending so the base of the triangle is tipped more than the terrain Now if your springs are retained you feel this as the top side getting very bouncy as the weight on the springs gets lighter, this transition is linear as the situation goes from weighting the top wheel to the tipping point where the spring is pulling on the axle At this point the uphill side is being levered up by the body and in most trucks standard axles don't weight that much so over you go.... it gets better if you've engineered for this say american buggy's with HD braces axles and minimal bodys, why I tend not to be too concerned about adding weight on axles Now if your springs are dislocated your only interested in the lower spring mount, if the CoG tips past it your away, there is no warning of the topside getting bouncy you continue to drive till you tip.... at this point it depends how much free movement you have, if its alot lol well, body moves further out gaining more leverage and lifts the axles easier Now there is a catch to all those that will say dislocated springs don't work, right up untill the body tips the dislocated suspension has more weight on the uphill wheels so has the potential to out drive the captive sprung truck before it ends up on its side lol And from experience you do develope a feel for where that tipping point is lol I've typed all this to point out there is alot more going on than springs dislocating or not as to stability (and I haven't gotten to the Rollcenter height, or RC/CoG relationship lol) In articulation that bottom wheel is seeing more than its normal axle weight because you are tipping the axle on an angle, and this will be opposite if its on a sidling As for how much weight from the body this will work the same as your shared platform your going to use on the bathroom scales.... the spring is the weight the axle is the platform so if your in the middle half the weight to each side of the platform, if your 3/4's along (or 25% from the end) your weight on the light side is 1/4 of that applied

Yrs ago when I lived with mum n dad, we had a couple of landy's one was pretty much ignored delt with the mud from the farm and never had a problem... I'm certain dad did the brakes but I can't remembering him touching the brakes other than replacing shoes The other landy I can remember him swearing and cursing come warrant time and that was the road truck so didn't see any of the carp going on the farm.... go figure Disks are a set and forget system and with the size caliper and good dia vented disk I am confident this will out brake drums, ( the double diaphragm booster will help a lot too lol) the other bonus is heat dissipation, if I head inland from home I'm looking at twisty roads with lots of hills, big hills and mine is going to be a tow wagon so disks are definitely worth the trouble Love the pic... that is impressive, especially on the big wheels! As for price had a look on our version of ebay and $300 for a set of calipers, $100 for a booster and master, around $150 for a pair of new disks and from a guess the mounts for the disk and the caliper about $500 for the materials and machine time, so for those that don't know NZ$ about 400-500 pound, I don't think I will have done too bad.... now this isn't something I'm planning on building and marketing lol so if anyone is keen I'll post up so you can copy

Been thinking about your suspension Bill (been labouring today so the mind wonders while I shovel lol) Bill this is something to do with what you posted the other day... forced articulation, You mentioned the bumps don't touch that the uphill spring becomes the pivot and you gain forced articulation.... I have been thinking about this and I think you maybe wrong, here is my thinking.... once you reach this state your spring is only acting as a pivot so this makes it only slightly different from a tractor front axle and the difference is that the pivot isn't centred..... I do see an advantage in this in that you will get a set amount of force (weight) on that lower wheel eg front weight on the front suspension is 500kg, if like a tractor you centred the pivot then its 250kg per wheel, if your spring was off to the side say 25% along the length of the axle the down hill side would still see 125kg of weight from the body (axle becomes a lever) this extra weight on the downhill wheel would add traction As for my idea of forced articulation by putting the bump stop outside the spring..... its a catch 22 lol here is some simple math to show what I mean lets setup the above with the bump just to the outside of the spring so 20% along the axle and I'll use a spring from my post above 12.5kg/cm So since the pivot has now moved to 1/5th the weight oon the lower wheel is only 100kg due to it being so far from the pivot (bumpstop) compaired to the uphill wheel, but we have a spring pushing down and it is below the bumpstop so it should force the lower wheel down catch is it is acting on a lever the wrong way lol Right if the difference was 5% (spring is at 25 and bump at 20% of axle length) that means once it hits the bump in articulation we loose 20% of axle length (the bit uphill of the pivot bumpstop) that now makes the difference between the spring and the bump now becomes 6.25% so this is the % of the springs force that will be applied to the weight on the downhill side.... so that works out at 500kg x 0.0625 or 31kgs of force from the spring so a total of 131kg on the bottom wheel a gain that could be worth it Till I realised the bumpstop is sharing the weight with the spring and the 6kg of difference in weight on that lower wheel is gone lol..... so there is no gain for the forced articulation hope your able to follow this lol clear as mud as they say All this got me thinking about Wildfings setup.... bill ages ago I remember you mentioning the suspension has the spring mounts narrowed (moved to the center of the axle) all this math got me thinking about the difference between the leverage on the springs between a square hit compression and an articulated compression hit on the springs..... when you take a square hit your spring rate will be the actual spring rate of the springs, but when you take a articulated hit (just one side) the spring rate will be a % of the actual rate based on the leverage ratio of where the springs mount on the axle This would mean Wildfing has a lot softer springs on corners than in a straight line Sorry guys I've just spent almost 45min's getting that typed and sorted and I'm past my bedtime... will post up the rest of my train of thought tomorrow lol

Mate please get on topic What have rock crawlers got to do with what bill was talking about, they mainly use air-shocks or coil overs.... and what does budget, to do with things lol you think that lack of understanding and a big wallet garrentees you the perfect setup lol So why do the top teams use compression shims in there shocks, if your using a linear rate spring with equal up travel and down what this would cause a race truck in short woops / hard corrugations to compress and not come back before the next hit so progressivly you would loose suspension up travel, On a single hit with no compression valving you'd hit the bumps alot harsher.... this isn't a good thing! Come on Rock crawlers run limited up travel why would they run linear lets talk some specifics say there truck weight is 1000kg and even per wheel so thats 250kg per wheel, spring rate is 12.5kg per cm of travel... so that means he has 20cm of travel to hold the weight of the truck and at full articulation you will have another 20cm of travel up (all the end weight applied to one axle is now on just one spring).... hang on that means he has to sit in the middle of his travel or he will bash bumpstops all the time....... this is why they use air shocks, or coil overs and progressive rate springs so they can have less up travel and a lower CoG None of the others will say this so I will, mate your posts have little to do with the subject, if you have some thing about this topic "Coil spring dislocation or captivation and its effects" all good but if your just going to dribble..... please don't To the mods yes I have edited this... to try and nicely point out some examples and hopefully get this back on topic... nicely lol

Part of our road worthy-ness test (cert) is a road brake test where the truck has to stop hard 3 times in quick sucesesion from 100km+ with no brake fad and conditions, this test is very hard to pass with bigger (35") wheels on heavy trucks Now I'm not planing on 35"s but I am going to 33"s and adding alot of camping mods and my motor/box is at least twice the weight lol so I want vented disks and 4 pot front calipers I'm not certian what they are out of but there is a military disk salsbery here that is available if you search catch is they are dear to get your hands on lol Don't know much otherwise, if it helps its a chunky cast housing with a square profile and the calipers looked like a double system like the Rangie and I think they were a solid disk.... and it has been a few yrs since I last seen one, was 10yrs ago when I had my RRC and was playing with rover stuff lol

Never thought of that and its a good point and would apply in an articulation event.... on a sidling this wouldn't apply and would make the truck more stable Just thinking about it.... it maynot apply when I'm driving I control the point where I tip by progressing into the tipping point now if the spring is in negative load the spring will pull the axle up and I tip as I drive where as if the spring dislocates there is nothing tieing the weight of the wheel to the body other than the shock and it has extra movement so the body will tip out of control once you get over the tipping point lol clear as mud I have driven trucks with dislocation on the rear springs, and they were "floppy" to the point of making me cautious lol particularly on sidlings, but as I wasn't able to progress the trucks through there mods I can't say if that was due more to the dislocation than anything else

We are aloud spacers 5mm bolt through so long as the wheel nut has 6+ full turns other wise we may have bolt on spacers up to 27mm, but in both cases you require certification to prove safe, but due to the other mods planed we are both up for cert anyway so not a biggie to add to the list In my case I will put spacers on as I don't mind a bit of guard cutting and the extra wheel track will improve handling but the other truck I'm doing for my mate he wants the original look Argh just a note on the swop to 60 series axle, if your diff is early 40 series, some had course splined side gears and inner axles that means the diff head may not swop into the finner splined 60 series axles, the coarse splines were common on our 45 (flat deck ute ) model for some reason but I have heard of them on the 40

Lol I love your threads I think your looking at this from just one angle, articulation and you are right the dislocation allows a forced articulation but with one catch your bump stop must be outside (compression side of the spring) as your spring isn't your pivot point the bump stop is The dislocation creates a catch 22 lol, it will allow you to drive a cross axle alot deeper without flopping (if your suspension is balanced) but when you do reach the depth where your going to lift a wheel there is free movement in the suspension allowing the body to flop more violently creating a potential to tip you on your side, you could run to a heavier shock valving to limit this but this has adverse effects at speed I prefer the augment for retained springs, when you are on a sidling you don't have the shock of the dislocation "flop" of the body The up hill wheel is tied to the body via the spring so it is very predictable as the body rolls providing the driver with alot more confidence when it gets extreme, with lockers you will still have drive, even if it is only 3 wheels in contact I would throw a few more things into the mix like roll center height and CoG height, if you could get the roll center up and CoG down, the closer these are the more you could mitigate the "flop" from the free movement

Right first off, I may have an answer to my original idea so disk brake improvement maybe happening on the original axles, will post up in the original thread And Bill a little tip for you to "restore" the balls on your cruiser axle POR15 strip down your housing prep the balls, paint a couple of layers with the brush, your filling the holes so thick is good let it cure a few days then sand it smooth, you'll need to get serious, I use flap disks smooth up your ball and then prep and paint a couple of smooth layers on and you have better than new Next trick is one I use on the hilux felt seals, put them in a cake tin lid with a handfull of grease and heat it gently till the grease melts into the seal this helps water proof the seal edit looks like I didn't have a thread up here about disk conversion, well that was the whole goal of the axle swop but a mate has just put me onto the Mazda RX7 calipers a 4 piston caliper that from my CAD will fit under a 15" rim with near on 300mm dia 22 wide vented disk and the only funky bit it will need is the caliper backing plate That plus the hilux double diaphram booster and master and I think i'm going to meet the brake upgrade lol

Hmmm might have to look at this.... don't know about coiler axles fitting, I measured up a RRC axle and the tie rod conflicts with the leaf springs catch is the moment I start modifing the steering the dramas involved skyrocket lol I don't mind doing this sort of thing for my own toys the challange of getting it pass'd is part of the fun.... but when its a mates toy there has to be limits

Gidday Got a SII 88" that I'm doing up for a mate, part of his wish list is disk brake front axle After talking to the certifier (dude, who does the legal stuff to allow mods for road running) he has shot down all my cheap options which leaves me with Axle swop options One option is a Coil sprung salsbry disk brake front axle, catch is it has been yrs since I've seen one and I can't remember if the tie rod will work with leaf springs Any guru's who can shed some light, bear in mind ackerman must stay original, so no swopping swivel housings Is this axle an option? Cheers Reece

I didn't think it would be diff lock anyway for the amount of twisting motion the tyre sidewall flex would have countered it, but it could have been part of the resistance.... as I've said I think its the rear roll center height that is creating the resistance here, I'm just not convinced I have the forces correctly worked out as to "how" I would suggest raising the panhard, and I'd be game enough to put a box on it that it won't change this effect lol On a practical note even if I'm wrong, packaging concerns are going to limit the lift you can get and thus the change in effect If I am right this brings up the issue of where the compromise is between good handling characteristics (oversteer/understeer) and improving this ability to climb obstacles But I'll wait till after you've proven me right or wrong lol

Right I'm back on a pc (joys of working away) This may get a bit messy there is a few things to reply to in the above posts and my head is in cotton wool lol got the flu Bill you made a mistake in your drawing.... I am guessing you pivoted the axle at the rollcenter height in the center of the axle this will bias the result, remember the front axle is pivoted on a panhard with pivots at the axle and the chassis, now if your front suspension was an A frame top link your drawing would be right.... the length of the panhard is the important dimension for this as it is the arc the axle swings in Toy your comment about vehicle front and rear rollcenters and wanting the rear to be higher is due to understeer/oversteer characteristics by having the front lower the front axle suspension will move and track better than the rear (similar to front and rear swaybars) having the front track and the back lift will mean the rear will break traction and drift meaning the driver will be oversteering, this will make the vehicle feel "forgiving" And your comment about CoG to Rollcenter is spot on, keeping or getting the CoG makes more difference than lifting the RC as the RC is basicly body roll.... in most trucks this is what tips them, they get to a point the body moves and this tips the high mass outside the triangle from CoG to tyre contact patch.... If they could get the CoG lower then the triangle is flatter and takes more to tip it and when the body flops there is less high mass to act like a lever Now back to what I was hinting at and what I think the real reason for your observations Bill Dan Now when you get to the rut the front wheel pushes up, as it cycles up there is some sideways motion from the high rollcenter lets look at this a little bit closer how is this being resisted by the body.... we arn't hurtling along at speed so there is no inertia, so this only leaves the rear axle and suspension to resist it on a 2.2m long lever Lets simplify things first lets remove all slop from suspension tyre sidewalls etc yes I know this is totally unrealistic but it will show something now if we were to turn the truck on the rear axle like a wheel barrow (thanks jamie a bloody good way to look at it lol) it will rotate on the center of the diff due to the rear diff.... Does Wildfing have a welded rear diff? Now add in all the other movements suspension slop, tyre sidewall flex, chassis flex Now if we consider rear RC as the front suspension tries to articulate and twist the body it is forcing against the rear rollcenter the higher the rear RC the longer the lever it has to resist the body roll from the front suspension, so this should push down harder on the wheel that is trying to rise out of the rut ? I was struggling to sort it in my head last week and I'm not much better now but it fits with what Dans found and your mate with the Zuk..... I just feel like I'm missing something lol it hasn't quite clicked.... even tho I don't quite have it right I'd suggest looking at making the rear RC height adjustable

It was a rough estimate lol based on a couple of liberties... the same length panhard (1m), in both cases panhard at rest was level and the axle length was the same (1600 to outside of wheels) I did this so that it just focused on the changes from the higher rollcenter the extra height from the portals and the tyres was there There are a few things that will make the lateral movement greater, shorter panhard length and mounting angle and wider length for the axle Going to be a bit busy with work, a new contract so might not be able put much input into this But I'll leave you with this.... sort of explain my thinking about the rear suspension being involved as you walk the front wheel up, I don't have it clear in my head and don't have time to play it out but Right up front you have resistance from your lateral movement not that much when you consider mounting flex slop and tyre sidewall distortion but its part of it.... the wheel goes up this pushes up on the spring which tips the body this is resisted by the rollcenter of the rear suspension lol sorry getting the hard word I have to go

LOL thats what prompted the idea but it doesn't change the fact I have too many compromises to to run the leaf springs and a full chassis Was only ever going to be a short term thing to race... as I want to build a class 10 offroader, hyabussa powered mini offroader lol Got some time on the toy today..... got the parts LT95 so pulled that and started rebuilding the toy's transfer case looks like the gamble is going to pay off, rough measurements show the diff can swop, but the low gear on the diff has different mountings so I'm in the process of swopping all the gears from the parts one.... I know its only going to do low k's but it feels wrong to mix gears lol

I didn't plot the instant center I did a front elevation of an axle with tyres (think it was 1600 wide to the outside of the tyres) I then swung this on a panhard bar of 1m length mounted evenly over the centerline, imitating articulation on the left hand side up (100mm at the axle end of the panhard bar) and measured the lateral difference between the outside of the lifted wheel and the original contact patch.... so the amount the axle and panhard would have to push the body sideways as it articulates That was the base line for the RRC 21mm I then lifted the pan hard mounts by 200mm (120 for the portals and 75 for the tyre dia) and rotated the axle again and got 34mm of lateral movement So this gives a difference of 13mm between the two trucks LOL just noticed your original post you said the panhard was another 80mm above the housing..... applying rough math if 200mm of panhard lift gives 13mm of difference, 80 goes 2.5 times into 200 so 13 divided by 2.5 = 5 so I'd expect with the extra 80mm of height to be around 19mm total difference between the two trucks So 19mm more sideways motion due to the change in arc from the higher rollcenter Well the ball joints shoot my theory of slop in the links creating a twisting motion on the axle I still think the rollcenter difference and that difference of sideways movement is not enough.... I suppose it is almost double the RRC lol you've now got me thinking about adding adjustable panhard mounts to the toy hmmm just had a thought that looking at just from one axle point of view was my mistake..... if the suspension is balanced as you articulate a wheel out of the rut this will roll the body getting resistance from the other suspension as well

4 wheeler motorbikes use this, they run more tyre pressure in the front tyres to increase the dia so the front slightly pulls the rear, supposed to make a big difference in handling.... and climbing But I don't think its what Bill has noticed I think Sorren could be onto something, but I don't think its the angle of the lower links from memory Wildfing doesn't have links hanging down and if both vehicles have flat links there is no change in the forward movement.... but the extra leverage from higher mountings and bushing flex you could get that effect..... Bill is wildfings suspension on bushing or rod ends

I find it hard to believe 13mm of sideways motion is that significant, that was at the outside lower edge of the wheel the point of greatest distance too..... I can get that amount of movement just pushing on the axle, let alone side wall flex.... so how could this restrict things that noticeably hmmm I know its fishing but how about tyre pressure and contact patch, would the RRC be running more pressure? that aside the smaller tyre will have a lower contact patch and less sidewall so it holds its shape better and more able to climb up out of the "rut" If your talking at crawl speed I don't think the weight would be much of a consideration As for your mates zuk... raising the rear A frame ball joint at the axle will also have increased the AS on the rear axle so this could be what he is feeling (again fishing lol)

Well after all this time on CAD I am admitting defeat... I was getting too many compromises in an attempt to fit the chassis rails within spec's for offroad racing and given the few times I want to have a play.... back to the original plan lol