damoq:
When you turn corners, the trailer tyres should be turning at different speeds but can’t as they are linked.
Is incorrect. Each side has its own separate hub with a stub axle on. They rotate independently.
The reason tractor units have diffs on is to allow power to be applied to each driven wheel differently otherwise the tractor unit would always want to try and go in a straight line when cornering.
Moose:
I wish I was as mechanically minded as you!
Really you don’t.
When Halfords first got them, they had a series of failures caused by drivers screwing them round at shops with tight yards. Many of these drivers were used to short trailers with twin axles and thought that turning a fully loaded tri-axle, with diddy wheels, and the tractor at 90 degrees to the trailer was OK.
Santa:
When Halfords first got them, they had a series of failures caused by drivers screwing them round at shops with tight yards. Many of these drivers were used to short trailers with twin axles and thought that turning a fully loaded tri-axle, with diddy wheels, and the tractor at 90 degrees to the trailer was OK.
You’ve obviously never seen a Tesco double decker store delivery then… 95% require them to be screwed around in the (tight) yard.
Conor:
damoq:
When you turn corners, the trailer tyres should be turning at different speeds but can’t as they are linked.Is incorrect. Each side has its own separate hub with a stub axle on. They rotate independently.
The reason tractor units have diffs on is to allow power to be applied to each driven wheel differently otherwise the tractor unit would always want to try and go in a straight line when cornering.
Moose:
I wish I was as mechanically minded as you!Really you don’t.
So explain how a diff works
I know but I would be buggerd if I had to tell somebody else.
Its a superb ,elegant piece of engineering that is a mystery to everybody tlll you strip one.
But the man who first thought of and solved the problem of how you use torque to drive 2 wheels on the same axle at different speeds was a true genius.
lankyphil:
Santa:
When Halfords first got them, they had a series of failures caused by drivers screwing them round at shops with tight yards. Many of these drivers were used to short trailers with twin axles and thought that turning a fully loaded tri-axle, with diddy wheels, and the tractor at 90 degrees to the trailer was OK.You’ve obviously never seen a Tesco double decker store delivery then… 95% require them to be screwed around in the (tight) yard.
Then you hear a ‘pop!’ as a tyre catches a divot in the concrete. I always grimace when spinning them round fully loaded.
Bking:
So explain how a diff works
I know but I would be buggerd if I had to tell somebody else.
Its a superb ,elegant piece of engineering that is a mystery to everybody tlll you strip one.
But the man who first thought of and solved the problem of how you use torque to drive 2 wheels on the same axle at different speeds was a true genius.
You have a big gear which is driven from the gearbox called a ring gear and attached to this big gear is a cage containing two gears called pinion gears. The whole cage rotates with this big driven gear as you drive down the road. On the end of each drive shaft is a small gear that mates with these pinion gears.
When you’re driving in a straight line with both wheels going the same speed the pinion gears don’t rotate but stay fixed, effectively locking the whole thing together and because the whole cage is turning this turns the drive shafts which in turn turns the wheels.
When you’re going round a corner so both wheels need to turn at different speeds, the pinion gears start to rotate which therefore allow the driveshaft gears to rotate at different speeds. The inside wheel spins slower than the cage, the outside wheel faster.
When you engage diff lock, it engages pins in the pinion gear shafts to prevent them rotating thus ensuring at all times that both wheels rotate at the same speed.
Conor:
Bking:
So explain how a diff works
I know but I would be buggerd if I had to tell somebody else.
Its a superb ,elegant piece of engineering that is a mystery to everybody tlll you strip one.
But the man who first thought of and solved the problem of how you use torque to drive 2 wheels on the same axle at different speeds was a true genius.
You have a big gear which is driven from the gearbox called a ring gear and attached to this big gear is a cage containing two gears called pinion gears. The whole cage rotates with this big driven gear as you drive down the road. On the end of each drive shaft is a small gear that mates with these pinion gears.
When you’re driving in a straight line with both wheels going the same speed the pinion gears don’t rotate but stay fixed, effectively locking the whole thing together and because the whole cage is turning this turns the drive shafts which in turn turns the wheels.
When you’re going round a corner so both wheels need to turn at different speeds, the pinion gears start to rotate which therefore allow the driveshaft gears to rotate at different speeds. The inside wheel spins slower than the cage, the outside wheel faster.
When you engage diff lock, it engages pins in the pinion gear shafts to prevent them rotating thus ensuring at all times that both wheels rotate at the same speed.
And theres me thinking it was called a crown wheel.And I always thought the lock ring engaged into the diff carrier face but WTF do I know.
Bking:
And theres me thinking it was called a crown wheel.And I always thought the lock ring engaged into the diff carrier face but WTF do I know.
Apparently not a great deal, as you constantly seek to prove.
thing is that’s a pic/ diagram for a drive axle … most DD are independent with no axles I thought , the whole point is no axle so the load bed is lower to the floor giving max height 
but hell what do I know I only pull em 
Inside wheel has less distance to travel when turning corners so will rotate at a slower speed, any ex military men will be able to compare to left and right wheel when inside man almost marks time and outside man almost has to run.
Christ but this thread is worrying, does any bugger look underneath their vehicle any more.
Juddian:
Christ but this thread is worrying, does any bugger look underneath their vehicle any more.
only if I aint gotta get on all 4’s
Underneath? That’s what a mirrors for innit?
the maoster:
Bking:
And theres me thinking it was called a crown wheel.And I always thought the lock ring engaged into the diff carrier face but WTF do I know.Apparently not a great deal, as you constantly seek to prove.
In the land of the blind the one eyed man is king!!!
nick2008:
thing is that’s a pic/ diagram for a drive axle … most DD are independent with no axles I thought , the whole point is no axle so the load bed is lower to the floor giving max height
Your thinking of radius arm trailers eg Glass carriers with no floor.Most DDs are just standard beam axles but with poxy little drums and wheels
Bking:
[quote=“nick2008”
''Your thinking of radius arm trailers eg Glass carriers with no floor.Most DDs are just standard beam axles but with poxy little drums and wheels
[/quote]
‘’
end quote
Those really low riding deckers that Tesco/Budgens used had the radius arm short indy stub axle suspension, bloody good too when set up right and rode and pulled really well, but a bit on the complicated side for setting ride heights etc for a general fleet, big advantage as you allude to being proper full size brakes.
Don’t remind me about those small drummed set ups, old style lorry and drag car transporters had them with tandem axle drags, the brakes wore so quickly that i used to carry a 9/16 spanner and adjust them up weekly, luckily unless the deck centre was covered (as new stuff is) access was easy peasy from above, some of them were 3 deck drags carrying 6 large cars (used on Jags a lot so 6 bloody S types on two 17" wheeled axles ) you could nearly watch those silly little linings wear down.
damoq:
the maoster:
damoq:
I thought my theory was right cos whenever I am reversing into a tight gate or whatever, the o/s/f tyre seems to turn at a different speed in relation to the others. I thought this was because the n/s of the trailer takes a wider line when turning like this causing the o/s to scrub. Maybe I should have studied harder during physics lessons at school.:lol::lol:
I think what you’re seeing is the tyre being pushed sideways so its rotational speed is reduced by the sideways forces. There, Mr Wright would be proud of me.
Thanks maoster. Probably explains what I see. Good job I’m not a mechanic. Heavens only knows what Moose would think of me.
Remember that the pendulous bosom never quite reaches as high on their subsequent upswings. Neither does your pendulum as you get older.
the maoster:
damoq:
When you turn corners, the trailer tyres should be turning at different speeds but can’t as they are linked. One side will be scrubbing as you turn hence why they wear out quicker.Not so Damoq, trailer wheels (well, standard trailer wheels that is) are independent otherwise you’d be measuring tyre life in days rather than months. Next time you see a trailer with a wheel jacked up try spinning that wheel, as long as the brakes aren’t on it should quite happily turn even with it’s opposite number firmly on the ground.
Thats why rear steer trailers either use a full turntable system or the Akermann track rod where the inside wheel turns to a deeper angle than the outer wheel.By using king pin inclination and castor angle the wheels can turn at different angles even though they are connected by a rigid bar.