Axle Configurations

[agent006]

Passing the time on a trip to London today, and being a huge truck nerd, I was pondering the various axles of the trucks we passed.

I know the various layouts. Single rear axle, twin with both mid lift and rear (tag?) lift. I'm not sure on the benefits of each.

I've seen mention of needing twin axles to be able to take the full weight limit; but then you see things like new FH 750s with single axles. Surely they would be able to take max weight or it defeats the point of the power?

I assume there are various differences in handling/manoeuvrability between mid and rear lift, is this the case?

Is the lifting axle likely to be driven on a standard unit or is this likely to be only for more specialist things? Or if driven does it not lift?

[ZR1cliff]

The renault unit I drive has a tag axle forward of the rear drive axle and is meant give you an extra 4 tons in carrying weight. It can also be locked into the drive axle for extra traction. It can be lifted or lowered manually.

The benefit of having a tag axle to the rear of the rear drive axle, is when it is lifted it gives the unit a smaller wheel base and a tighter turning circle.

Edited by ZR1cliff on Saturday 29th December 23:24

[chilistrucker]

agent006 said:

Passing the time on a trip to London today, and being a huge truck nerd, I was pondering the various axles of the trucks we passed.

I know the various layouts. Single rear axle, twin with both mid lift and rear (tag?) lift. I'm not sure on the benefits of each.

I've seen mention of needing twin axles to be able to take the full weight limit; but then you see things like new FH 750s with single axles. Surely they would be able to take max weight or it defeats the point of the power?

I assume there are various differences in handling/manoeuvrability between mid and rear lift, is this the case?

Is the lifting axle likely to be driven on a standard unit or is this likely to be only for more specialist things? Or if driven does it not lift?

it really is horses for courses mate.
there are so many variable, i could, but won't bore you with. its mainly job specific. and region.
uk, if you have the right setup, 3+3 on air, you can if correctly taxed and plated, run 44 tonnes.
in europe, if i'm still up to date, (maybe not) i believe its still 40/41 tonne, hence the reason most euro outfits run a 2 axle tractor unit with a 3 axle trailer.

i just read that back, and have realised i'm a boring tt

[4key]

I feel like I could bore a trainspotter sometimes.

Regarding big power units on 4 wheelers, it really does depend more on where you are working more than what your gross weight is. If all you are doing is cruising motorways in the netherlands you wouldnt need any substantial power regardless of how much you weighed, If you was spending a lot of your time going up and down mountains you want the biggest engine you can get.

Axle configurations are widely varied, you can get almost anything you can think of but the main thing that most go for is the ability to carry weight.

Most lift axles do not drive but people who regularly want more traction do spec them that way, you can also get traction buy raising the lift axle and therefore putting more weight on the drive axle. Most vehicles also have an electronically operated diff lock.

Something else that people do is to slide the 5th wheel about, my one gives me a few feet to play with so I can distribute the weight further forward on the unit and stop it skipping about everywhere.

Having the lift axle behind the drive axle gives the tractor unit a tighter turning circle, a lot of lift axles also steer following the front wheels, some mechanically and some by hydraulics. Almost all 6 wheel units will have a lift axle, its only really bulk tippers who spend a lot of time off road who have them all fixed.

[chilistrucker]

agree with the bhp thing.
although with some hauliers, there may be abit of willy waving involved, by having the latest volvo/scania running at the 700-750 bhp mark
the firm i do the tours for have all dafs, and most of their new ones are 410s, which tbh i think is underated. most of the loads on a tour are light, to middle weight, but if you get rigging or another heavy load you could be 35-40 tonnes.
imho, on the roads of europe this isn't enough. we go anywhere, holland 1 night, austria, spain etc the next, and there are some big hills out there

[ZR1cliff]

Bit of a struggle with 410s, isn't it Neil. We run mainly 460's and getting up Reigate hill on the M25, fully loaded, has us down in the 30 something mph zone.

[chilistrucker]

yeah its a pain when on the hilly stuff mate.
there are a fair few long uphill drags in europe
plus, all the trucks are manuals, so plenty of gear changes.
mind you i much prefer the manuals when coming down something like the somo sierra in spain, or mont blanc in france, nice to have abit of manual control, i prefer it for keeping the gears low and the revs high

[Chipchap]

The UK has a different Gross Train Weight or Gross Combination Mass at 44t on 6 axles compared to other EU nations such as Germany. Taking Germany as an example, they have a GCM of 40t on 5 axles, however the drive axle is rated at 11500kg there, whereas in UK it is 10500kg. Steer and mid lift axles with single 295/80R22.5 tyres are rated at 7500kg. 315 tyres are sometimes used but capacity does not increase unless the actual axle beam etc has a greater design capacity.

So a 4x2 tractor coupled to a triaxle trailer in Germany can carry 40000kg [40t] Gross. So in reality you need 400 BHP [10 BHP/Tonne] Wheras in UK we run at 44000kg on 6 axles and need 440 BHP as a minimum.

The 10 BHP/Tonne thing is not law, just a standard that I apply when specifying trucks.

For example A 6x2 tractor if it were a rigid would be rated as 25500kg = 10.5t + 7.5t + 7.5t, add to this 3 x 9000kg per axle on the trailer and you have a possible capacity of 52,500kg !! However we have a thing called "Bridge loading" which limits us to an overall of 44,000kg Train weight but to avoid individual axle overloads we use the individual axle ratings.

Bored yet ???

So anything over 10 BHP/Tonne is wasted on Uk motorways with an average of 6% gradients.

The bigger horsepowers are aimed at the 60t stuff from Scandinavia or really mountainous terrains.

Allan

[bigfatnick]

Chipchap said:

So anything over 10 BHP/Tonne is wasted on Uk motorways with an average of 6% gradients.

The bigger horsepowers are aimed at the 60t stuff from Scandinavia or really mountainous terrains.

Interestingly, here in australia you dont see lifting axles, with i recon 99% of articulated trucks running 6x4 and very occasionally 4x2. Different laws i guess.

Having worked on a lot of farms in my time here ive chatted with a lot of truck drivers (almost always driving american stuff in the outback.) And it seems the 10bhp/ton rule isnt quite as simple here. Firstly, when you can run up to 130ton the power just isnt avaliable, but also, that euro trucks are snubbed, most of the drivers ive spoken to reckon that an american engine rated at 600bhp would offer similar performance to the new 680 to 720bhp euro trucks. I dont really know why. They also mostly seem to run eaton crash gearboxes. In my head a euro truck with a modern auto gearbox, especially the twin clutch stuff would downchange quicker mid hill, losing less momemtum, that said, i have only ever driven yank trucks, not european.

[s p a c e m a n]

iirc American BHP is less then ours, they measure it from the flywheel on an engine dyno and we measure it at the wheels so we get transmission loss on our figures, other than that torque is the key really not BHP. I've never driven yank stuff so can't comment, but they may be better in that respect.

[powerstroke]

s p a c e m a n said:

iirc American BHP is less then ours, they measure it from the flywheel on an engine dyno and we measure it at the wheels so we get transmission loss on our figures, other than that torque is the key really not BHP. I've never driven yank stuff so can't comment, but they may be better in that respect.

I think you are getting a bit mixed up!! the major truck manufactuers quote flywheel hp mind its torque that gets the job done Yes yank is best!! have a mate who runs a foden with a C12 caterpillar 450hp and it is so torquey it just romps up hills but he is looking for a C15 acert (twin turbo)650 hp,I cant wait to have a shot in it He also runs a ERF re engined with a 14 liter cummins that has been messed with and as its pre limiter it upsets the scania and volvo boys when the old shagger with lowloader blows past them uphill, it will do about 70mph with ease!!!!

Edited by powerstroke on Thursday 3rd January 20:02

[agent006]

Thanks for all that. Another passenger seat journey last week brought it back to mind with one last question.

if a rear lift is better for manoeuvring, why do you see so many mid lifts? Seems that all fleet stuff is mid and the only rear lifts I see around are smaller companies and owner/drivers.

[ZR1cliff]

Scanias do rear lifts aswell as the other sort. Good question though!

[chilistrucker]

agent006 said:

Thanks for all that. Another passenger seat journey last week brought it back to mind with one last question.

if a rear lift is better for manoeuvring, why do you see so many mid lifts? Seems that all fleet stuff is mid and the only rear lifts I see around are smaller companies and owner/drivers.

i'd never thought about it till you asked.
i'm not sure either?
i'd take a stab in the dark at cost, seems to drive most of this industry.

[martin mrt]

Cost is the main factor, a tag (rear)lift is usually more expensive than the now industry standard mid lift

This is not the only reason, a tag lift also takes a greater level of skill to drive, the shorter wheel base makes the unit rather snappy and skittish if the axle is lifted when empty which could easily lead to a jackknife in the wrong hands. Low speed manoeuvres round tight junctions in slippery conditions often sees them pushing straight on with the axle down and loaded

I would not, as an operator put any inexperienced driver on a tag lift truck, a mid lift I wouldn't have an issue with.

I've driven tag lift Scanias for the past 5 years, and quite simply I can't see past a tag lift now, far better traction and manoeuvrability than a midlift, when I go used to go onto a midlift unit occasionally, my reversing was like I had just passed my test, as they are slow slow to come round.

The offset is comfort, a tag isn't as comfortable as a midlift in my experience on the Scanias, however I got used to the ride relatively quickly, not as comfy as an XF DAF I had before it, but the Scania was 10 times the lorry besides that

Edited by martin mrt on Monday 28th January 19:09

[GC8]

martin mrt said:

Cost is the main factor, a tag (rear)lift is usually more expensive than the now industry standard mid lift

Even though the mid lift axle would be a steer? That has surprised me.

[martin mrt]

GC8 said:

martin mrt said:

Cost is the main factor, a tag (rear)lift is usually more expensive than the now industry standard mid lift

Even though the mid lift axle would be a steer? That has surprised me.

Only manufacturers to offer a steer midlift as standard are DAF and Scania, I think Scania are now offering a lower cost pusher axle now too.
Iveco may also do a steer axle but I'm not sure
Man, Mercedes, Volvo, Renault, all do pushers as standard

The increased cost comes from the low volume produced, 50 midlifts to 1 tag on average in the uk