Thread: portal axles

Originally Posted by wagoo

I think the D0T 50mm 1imit re1ates t0 the stress p1aced 0n the ax1e h0using due t0 the extra 1everage fr0m the p0rta1 gear cases height and width;
The extra king pin be10w beefs up the swiveI h0usings but n0t the ax1e h0usings, which w0u1d require reinf0rcing t0 c0pe with a bigger track increase;If I were an engineer that had t0 sign 0ff 0n a p0rta1 c0nversi0n I w0u1dn't permit a bigger track increase either, un1ess it was d0ne 0n the ax1e h0using bef0re the swive1 ba11s and appr0priat1ey reinf0rced
S0rry,a few keys 0n my keyb0ard have g0ne 0n strike again;
Wag00;

what about reinforcing the stock housing and using the likes of MD portals and a stock LR rim???

dont worry Bill, after all, all this computer stuff is just 0's and 1's

Originally Posted by uninformed

what about reinforcing the stock housing and using the likes of MD portals and a stock LR rim???

I'm certainly no mechanical engineer Serg, but if that was my profession I would be a real barsteward to get approval from and say that your proposal is not acceptable due to scrub radius concerns. See my edited post below. I fixed my keypad with a hammer
Wagoo.

Originally Posted by uninformed

which would be a problem for LR axles using MD??? I do wonder if they have the acception if laminating/strengthening the axle case???

IIRC as I read it ( a while ago), if you narrow or extend the axle width then the track alters for the axle by the amount of the extension or shortening. MD will fall under this. I would assume that the spirit of the guideline relates to maintaining geometry and bearing loadings.

Also, if you narrow then you cant lift.

Originally Posted by wagoo

Do you still have the Volvos John? The 50mm track increase allowance which is the same that Vic Roads allow on normal beam axles anyway would make a landRover track width the same as a Volvo at 60.5''. With Volvo axles you would be allowed to go to 62.5'', in which case you might just be able to squeeze in a disc brake conversion and remain within the regs.

Although I agree with the track increase restriction from a structural engineering perspective,it does present an issue of stability for anyone adding Maxidrive or Tibus portals onto their vehicles.Perhaps you could apply your engineering skills to clearing up any misconceptions to the following?
I had originally thought that if you raised a vehicle 1'' and widened the track by 1'' then original centre of gravity would be maintained.This works wth a cube of constant density material,Eg a cube will overbalance once the gradient exceeds 45 degrees. But, and I'm not sure how it was calculated, and can't recall where I read it (probably Pirate),and I think it would have to vary between different vehicles, but the commonly believed equation seems to be, if you raise a vehicle 1'', then the track width should be increased by 2'' in order to maintain the centre of gravity at original levels.If that is true then if Maxidrive/Tibus portals raise the vehicle roughly 5'',and 35''dia tyres an additional 1.5'', then a Defender for example would need to have its axle housings widened out by 13'' to give a track width of 71.5'' to restore the centre of gravity to original specs.
Wagoo.

If you raise a vehicle the width of track does not impact the CoG as such unless you add weight down low as a result of the wider track. The raising of CoG and increase in track may keep a triangle of CoG to trackwidth constant which is a stability measure.

Originally Posted by slug_burner

If you raise a vehicle the width of track does not impact the CoG as such unless you add weight down low as a result of the wider track. The raising of CoG and increase in track may keep a triangle of CoG to trackwidth constant which is a stability measure.

As I get a bit older I get a bit thicker. I read this last night when sleepy and could not understand it. I had another go this morning, Ditto!
Anyway, I did a simple drawing of an exact 50mmx50mm square mounted on a 45degree side slope,and placed the COG at the centre of the square.(centre of balance).
I then moved the COG higher up by 5mm and discovered that I had to widen the base by 10mm to restore the centre of balance.
Thing is, if I place the COG 10mm below the centre of the square and find the angle at which point of balance is reached, and then move the COG back up 10mm I find that I must widen the base by 14mm to restore stability on that angle. Now I'm really confused
Wagoo.

Originally Posted by wagoo

Do you still have the Volvos John? The 50mm track increase allowance which is the same that Vic Roads allow on normal beam axles anyway would make a landRover track width the same as a Volvo at 60.5''. With Volvo axles you would be allowed to go to 62.5'', in which case you might just be able to squeeze in a disc brake conversion and remain within the regs.

Although I agree with the track increase restriction from a structural engineering perspective,it does present an issue of stability for anyone adding Maxidrive or Tibus portals onto their vehicles.Perhaps you could apply your engineering skills to clearing up any misconceptions to the following?
I had originally thought that if you raised a vehicle 1'' and widened the track by 1'' then original centre of gravity would be maintained.This works wth a cube of constant density material,Eg a cube will overbalance once the gradient exceeds 45 degrees. But, and I'm not sure how it was calculated, and can't recall where I read it (probably Pirate),and I think it would have to vary between different vehicles, but the commonly believed equation seems to be, if you raise a vehicle 1'', then the track width should be increased by 2'' in order to maintain the centre of gravity at original levels.If that is true then if Maxidrive/Tibus portals raise the vehicle roughly 5'',and 35''dia tyres an additional 1.5'', then a Defender for example would need to have its axle housings widened out by 13'' to give a track width of 71.5'' to restore the centre of gravity to original specs.
Wagoo.

Volvos sold to another member here. I was concerned with gearing (with low revving diesel) and disc brake conversion, while being registrable (wheels and tyres). Replaced by Marks GU Nissan portals.

AFAIK Marks had their portals engineered for 35" tyres and wheels with 50mm offset (inward) to achieve acceptable scrub radius. Off hand I can't remember what track increase this gives, so will have to check.

As slug_burner stated, COG height will increase with lift, but is not changed by track change. What does change with track is the allowable side slope for stability - increasing height of COG reduces the allowable side slope, which can be increased by increasing the track. As side slope increases the COG is moved toward the down hill side - as the COG approaches a position vertically above the down hill tyre contact the risk of overturning increases (remember some margin for dynamic upward loading is required).

Marks strengthen the axle tubes, provide a third (lower) "king pin" / swivel pin bearing, and strengthen (using webs) the neck of the swivel balls to compensate for the larger track change and hub offset. The final stub shaft and spindle diameters are also increased.

This is some information I recieved from Marks 4wd a while ago, seems that it is easier to make the Toyota portals compliant in QLD compared to the Nissan that need custom offset rims.

"We have been granted provisional approval on the portal axles, we have to make some changes to comply in QLD.
The biggest change is the track width cannot increase by more than 50mm over standard. The Land Cruiser portals have been changed to comply with this and we can run off the shelf rims from the 100 series IFS vehicles.
After the Land Cruisers are finished the Nissan's will be redesigned to comply. With the redesign there will be added benefits of upgrades, GVM upgrade, air operated hubs from inside the cabin and brake upgrades.

For QLD transport the portals will only be approved running 33 inch tyres as they will not approve 35 inch tyres under any circumstances. Running the 33 has many advantages over the 35 including weight, scrub radius closer to standard, cost, availability, brakes don't need to be ungraded, etc. You only loose 1 inch of diff clearance, the clearance is the same as running 41inch tyres."

Originally Posted by Bush65

As slug_burner stated, COG height will increase with lift, but is not changed by track change.

Thanks John, but this is where my understanding runs off the rails a bit.
Surely COG must be lowered by an increase in track width?
Disregarding lift for now, A standard Defender has a track width of 58.5''.If I were to widen the axles out so that the track width now measures 70'' then surely the vehicles COG is lowered? Maybe lower COG is not the correct term and I shoulld just say the wider track just increases stability. But in the context of this discussion this is just semantics and distracts from the supposition that fitting portals will result in a less stable truck, unless quite drastic measures are taken to compensate for the height increase by an appropriate increase in track width.
Wagoo.