Axle Strength

[sheeppimp]

I've been thinking about this for a while as part of my vapour build plan, I'm toying with a lightweight build which will obviously involve compromises of weight/strength.

I know that some parts are stronger than others, i.e toy axles stronger than LR axles.

The question is how much of this strength is related to the overall weight of the finished vehicle. A heavier vehicle will need more power/torque which then leads to more strain on the rest of the drivetrain so in theory a lighter build needs less power for the same performance, hence less strain so conceivably what in most cases would be weak could actually be strong. For arguments sake if you reduce the weight by 25% do you also reduce the strain by a similar amount?

At the same time there are also forces acting on the other side of an axle from the unsprung weight of wheels and short of fitting smaller/lighter wheel/tyre combos I can't see how to reduce this

Is this right or am I missing something fundamental?

[muddy]

I have always thought a reasonably hi unsprung weight is bennificial due to the increased stability so maybe you could fit toyo axles to have a very strong and stable set up? or how about upside down portals a so the weight of the car is below the centre of the wheel-2cvs are like this and i remember watching someone trying to tip one over and failing miserably much to our dissaprovel

as for lightweight is that using 5mm plate instead of 6mm on my furry dice mount?

[Hybrid_From_Hell]

Axles breaking are a combo of things

Quality of parts - not all parts are as good a qulaity as maybe you'd wish

Build quality of the axle - ie new bits vs 150,000 miles hangers

Rotating Mass - ie the bigger and heavier the tyres etc

Too Much grip - ie types of tyre

Weight of the truck itself

BHP or maybe more the Torque the engine gives out

Oh.........And lastly driving stylee

ALL of the above have a bearing IMHO and should be considered where poss

Nige

[Astro_Al]

Did someone mention vapour?

What you say is true - build in more beef and you need more beef to carry the extra weight. As well as: build in more beef and you need more power and torque to match the performance. Its all circular.

But then it all depends what you mean by performance. Some people would claim that a Unimog (for example) performs well offroad. But it has little power and a lot of weight. So you need to define what you are after better.

Is it achieving the job in the smallest possible time? Carrying a load while doing it? Etc etc.

Anyway, a dash of common sense suggests we are talking about a one seater(?) tube buggy type device. Why not look to gearing to help you out and allow you to save weight? How about a motorbike engine with loads of gearing? You've got the revs going in the front end and give something sensible in terms of wheel rotation rates even with silly low gears. Just an idea. I bet you could make that light. Output from the bike final drive straight into a mega low transfer box? You've got your gearbox in there too (6 gears?! useful), and its a nice small package which would save you structural weight (as well as being light). Cage, winch and 44s on a hayabusa?

Of course you must remember that using more gearing and a lower input torque does not save you from having to deal with large final output torques - it just changes where it comes from!

Er... sorry imagination running off again - what was the Q?

We're gonna get down to money again here. For mega light you need to think more about materials to make it mass efficient - no chocolate shafts, gun drilling, thinwall tube where possible (so you actually have to think about load paths and the structure etc...). Of course cage tubing needs to resist impacts too, so you can only save weight by using thin wall on certain members. Large diameter tube is more efficient per unit mass, but worse at withstanding impacts for the same final mass.

For a really intelligent design (this is gonna get flamed, but its true - just not on a Land Rover forum) you need to integrate all your requirements into a single system level design where you can specify the requirements and produce an optimal solution. Ok enough balls on that.

Regarding axles - you've got shafts and casings (for solid axle) and you need to separate the jobs for each. Do you even need axle casings...? Unspung mass will never be great with reasonable size tyres, unless you go pizza-cutter thin on spoke wheels. There are some nice thin agricultural tyres out there...

Remember too that the force of the sprung mass acts through the suspension mass on the axle, so you don't necessarily need a beefy axle everywhere, just in the right places. How does the weight / inertia get from the chassis suspension mount to the ground?

There are lots of suspension systems out there. Think about other possibilties than solid axle.

There's some things which might give you brain fodder on unsprung mass. B)

For arguments sake if you reduce the weight by 25% do you also reduce the strain by a similar amount?

I know what you're driving at, and to a certain extent, yes. But its not gonna be as simple as that. In some aspects you won't save much weight at all, in others you will. The relationship isn't linear. (The word strain is meaningless here - unless you mean my pendantry is a strain... ).

I like bouncing ideas around - its all I can do from my armchair 300 miles from my vapour-filled garage! Bring it on!

Cheers, Al.

[sheeppimp]

I have always thought a reasonably hi unsprung weight is bennificial due to the increased stability so maybe you could fit toyo axles to have a very strong and stable set up? or how about upside down portals a so the weight of the car is below the centre of the wheel-2cvs are like this and i remember watching someone trying to tip one over and failing miserably much to our dissaprovel

as for lightweight is that using 5mm plate instead of 6mm on my furry dice mount?

someone else suggested reverse portals (you know who you are no names but they might have a fairly bright hybrid) my issue with that would be the loss of ground clearance beneath the diff compared to a standard beam- one of the main benefits of 'normal' portals.

As far as stability goes I thik it's more about a low centre of gravity rather than a lot of weight, again a deisgn issue.

However a heavy wheel/tyre combo spinning and then gaining traction will transmit a large shock load through the axle - as I understand a major part of breaking things. What I want to know is if by making the sprung weight less and so the power required to move and thus transmitted to the wheels less it will make a standard LR axle effectively stronger?

The light question - looking for sub 1000kg in combat trim

[Astro_Al]

Sorry for the ramble... Too much moldy cheese.

What I want to know is if by making the sprung weight less and so the power required to move and thus transmitted to the wheels less it will make a standard LR axle effectively stronger?

Yes, provided you put less into it.

Al.

Short n sweet.

[sheeppimp]

Flippin heck while I answered another couple of points came up. Cheers Nige you made my point far more clearly than I managed.

Al you been reading my mind??

Anyway, a dash of common sense suggests we are talking about a one seater(?) tube buggy type device. Why not look to gearing to help you out and allow you to save weight? How about a motorbike engine with loads of gearing? You've got the revs going in the front end and give something sensible in terms of wheel rotation rates even with silly low gears. Just an idea. I bet you could make that light. Output from the bike final drive straight into a mega low transfer box? You've got your gearbox in there too (6 gears?! useful), and its a nice small package which would save you structural weight (as well as being light). Cage, winch and 44s on a hayabusa?

very close, the bike engine has been percolating for a while tho not jap race rep (peak torque and HP at v high revs) more italian and shaft drive...

For a really intelligent design (this is gonna get flamed, but its true - just not on a Land Rover forum) you need to integrate all your requirements into a single system level design where you can specify the requirements and produce an optimal solution. Ok enough balls on that.

- do you mind this is like being at work I do know where you're coming from.

to be honest this idea will not be LR based - the only way I can see to produce this is to fix the final end in mind and select the components to acheive it and not start with a vehicle (with all the compromises the entails) and change it. This is why it's still in vapour form - I don't really want to do this twice if i can avoid it

[muddy]

someone else suggested reverse portals (you know who you are no names but they might have a fairly bright hybrid) my issue with that would be the loss of ground clearance beneath the diff compared to a standard beam- one of the main benefits of 'normal' portals.

Sorry fingers didnt type what was spinning round in my head- indi setup to maintain centre ground clearence.

I can see what your saying about the COG vs unsprung weight so how about using large tyres that are of course proportionaly heavier, there fore if you are in a cross axle situation where the care is maybe going to diaganoly roll over one front corner(dropping off a F steep hill at an angle type thing) then you have a large mass dangleing the furthest away from the roll centre* thus exerting the most leverage to try and keep the thing upright?

*: this possibly isnt the best terminolgy but is all my brain can conjure

[Corrode Finger]

someone else suggested reverse portals (you know who you are no names but they might have a fairly bright hybrid)

The light question - looking for sub 1000kg in combat trim

Hey, i am pleased to see that other people think like me!!

Equally, i also saw the flaw in the suggestion when you hit the floor laughing!!

I will not bring that up again!!

Having had a discussion with sheeppimp on this before, and not wanting to hijack his thread, (ok peeps?) the idea revolves around the principle that a 90 with LR axles in full trim causes them to be chocolate, but for arguments sake, if the same LR axles were put under a SJ, jimny type for example, then would they be stronger, cos the sj is half the weight, and the LR axles are 'ok' in a normal 90, so by default they are 'stronger'?

[Astro_Al]

Muddy - you mean pivot point - roll centre has other meanings when discussing suspension etc (God I'm being pedantic today... sorry...)

Good point though. I can't believe people are discussing inverted portals on an off-road forum - any idea what the diff clearance would be? Would you even get over a speed bump? I'm also defo NOT a fan of bulking things up low down to pull the CoG south. Think a bit smarter than that. What's the point in pushing every aspect for low weight only to add it again later on? Waste of money and effort IMHO. Better to use some kind of dymanism in your suspension setup. Dynamic coilover mounts / Air suspension - bags or rams / forced articulation etc etc. Sure they add a little bit of weight, but it gives you a lot more control too (and, I reckon for less mass).

Al you been reading my mind??

Just workin' my mojo, man B)

Shaft drive makes life that little bit easier I guess - unless you can just mate a shaft to the engine output shaft directly - depends on geometry. Actually, you could probably run the chain to a sprocket on the transfer box input shaft and mount the engine and t.box laterally as a pair across the vehicle - might help keep it small / short if you need to (you do for lightness)? I'm liking the wide torque band. Or you could just use a jap engine stuck at 12k and some kind of torque converter arrangement to engage as much drive as you want...? B) I'd love to see it idling through Sainsburys car park at wide-open throttle.

Agreed starting with a landy is suicide for this build. Custom everything. By the way, if you go motorbike engine, use the handlebars too - I just like the idea. I've only seen it on one build and its cool. B)

You could probably do this quite cheaply too...

Damn - I might throw it on the vapour list.

Al

[biasbilt]

Having read what others have to say and given it a bit of thought in the past, it fairly obvious in my opinion. Forget thinking about axles and wheels/tyres for a moment - work with me here, you'll se where this going soon, and consider the half shaft to be a transmitter of torque and the wheel/tyre combo to be a lever. Obviously, a bigger diameter equates to a bigger lever. The amount of resitance that lever is able to exert is a result of the friction between the tyre and the ground. Finally, your engine, gearbox, transferbox, diff combo will supply a orque o the driveshaft.

Asuming that there is enough friction, when torque is applied to the halfshaft, it is transmitted to the lever, which drives the vehicle forward. If the rolling diameter is small, the lever is unable to place a huge torque on the axle (equal and opposite reaction and all that good stuff), so it doesn't break, which is why comp safari cars (which generally run 205R16s as a fairly standard size, can put big power on to the ground and not break bits all the time.

As the rolling diameter gets bigger, the lever gets bigger and can exert a greater amount of torque on the halfshaft. Equally, as the tyre gets bigger, it weighs more and has a bigger contact patch which gives greater amount of friction, and these two allow the amount of torque holding the end of the halfshaft still to be that much greater. If the torque applied by the transmission and that applied by the wheel in the opposite direction are greater than the capacity of the halfshaft to transmit torque then it will snap.

If the vehicle is on flat hard ground with a low rolling resistance, there will not be enough force applied to the wheel end of the halfshaft, so ther are unlikely to be breakages, which is why poser trucks survive wit big whels and tyres and standard halfshafts. Conversely, offroad, up hill, axle deep in the mud equates to a huge rolling resistance so the torque the wheekl is able to resist with is huge, which equals carnage!

To conclude, bigger equals heavier, so more likely to break. Go light, and you can get away with smaller everything, but you have to compromise between tiny wheels and tyres with no grip that won't exert any force on your halfshafts, cos they're always spinning or off the ground due to your negligible round clearance, versus lot of grip, ground clearance and strength which means upgrades. From this, perhaps the way forward is fairly small, but wide flotation tyres, to reduce the length of the lever, but still give grip and reduce ground pressure. Independant suspension to give good ground clearance under the diffs, or perhaps a curved beam axle running an independant diff with halfshafts driven by UJs/CVs at both ends (could be a lattice type structure to be lighter than a traditional enclosed beam axle), and a very light drive train (transverse engine with auto box driving straight into the diffs - nice low ratio and very simple) and spaceframe chassis, to continue the light weight theme.

Hope it all makes sense, it's late and I can't be bothered to reread it.

[FridgeFreezer]

Small, light, strong drivetrain - why not just buy an SJ for £100 and stick NOS on it? Job done - they weigh half a packet of crisps and the halfshafts are bigger than LR ones.

[Lewis]

Fridge forgot to mention being stuck with 31 x 10.50 as the maxium tyre size