Scammell Rammel

[oman5]

and I'll raise you one of these..

 

middle east spec Leyland marathon with hoofing great AEC engine. fitted with sink and cooker as standard- and this was late '70s. pre-limiter so they were good for 80 mph.

 

I also drove a Bedford TM with an 8v71 detroit once upon a time- a lovely truck so long as you weren't paying for the diesel

[CIH]

quick question fo the truckers; what's the purpose of lift axles, like this ie; where the middle "axle" wheels are lifted and carried ?

 

I always like a good Cargo;

 

The local highbrow AstonMartin dealership has a battered old Cargo recovery truck.

[Guest Leonard Hatred]

Are the axles dropped when laden?

[dollywobbler]

Lift axles reduce tyre scrub. Imagine the battle going on between the four close-together tyres each side of a truck when it's doing a tight turn. You can hear it sometimes.

 

What I don't get is why some trucks don't lift them high enough. Followed a truck for a good hour after collecting the Saab and even when we were about a mile behind it, I could tell we were catching it by the pungent smell everytime he'd braked. The lifted tyres were pouring with smoke when I finally caught it up near a roundabout, every time the driver hit the brakes.

[CreepingJesus]

Note also the first trailer axle's lifted. In this case, the two lifted axles put more weight on the four which are on the deck. So on one hand, it makes a tall curtainsider (notorious for falling over in crosswinds when unladen) a bit more stable; but on the other, it reduces rolling resistance a little, thus saving on fuel. It's a bit of a compromise between driveability and economy.

Plus, it'll put a bit more weight on the unit's drive axle, thus reducing wheelspin in low gears - even that tiddler Daf's relatively modest 2000lb/ft or so, will smoke 'em if you aren't careful.

 

What I don't get is why some trucks don't lift them high enough. Followed a truck for a good hour after collecting the Saab and even when we were about a mile behind it, I could tell we were catching it by the pungent smell everytime he'd braked. The lifted tyres were pouring with smoke when I finally caught it up near a roundabout, every time the driver hit the brakes.

Someone has maintenance issues, it really shouldn't be doing that. Lucky for them that they didn't get a pull, some stern questions and a defect notice would've followed.

[CIH]

I had always assumed any tyre scrub saved would be negated by carrying the weight of the wheel, tyre axle etc.

[CreepingJesus]

I had always assumed any tyre scrub saved would be negated by carrying the weight of the wheel, tyre axle etc.

 

TBH, I actually rehashed my post a few times last night, until I gave up, and posted the simple answer. Therein lies the truth; in all honesty, it's a percentage game played by fleet engineers, and is pretty complicated. They stand or fall by making a couple of percent saving here and there; for us drivers it's all part of the tool for the job. If it gets the job done, and gets us home/to the pub/to the bacon rolls before time runs out, then that's fine and dandy.

The tyres fitted to lift axles (at least on units anyway) are mostly the same ones fitted to steering axles. They're designed to take big lateral loadings, so don't really suffer too much. On trailers, lifting an axle really does have tyre life benefits. If there isn't 3 axles 'winding up', there's less tendency for one tyre to start skipping about, and getting damaged. At roughly £300 a tyre, you can see the point! Plus, inevitably, some smartarse driver will point to the chunked tyre, and refuse to take it out, until it's fixed . They don't like that very much...

Like I say - it's a case of someone number crunching, and coming out with a 3% gain one way vs a 2% loss the other, and deciding the 1%'s worth the extra whatever, over the life of the vehicle.For example; I was driving a triaxle trailer yesterday, with a positively steered rear axle: it achieves better turning, and tyre life, at the expense of build cost, weight and increased maintenance. It's all a balancing act!