Different sized wheels on different axles

[alangla]

I spend a lot of time tramping up & down the M80 just now. As a result I pass a lot of HGV traffic, including the tankers from Grangemouth going to the Glasgow/Lanarkshire/Dumfries area. Something I've noticed is that on the tankers, but not on any other HGVs is that the mid axle seems to be a lot smaller than the others on the unit. How come? Every other 3-axle unit seems to have 3 rows of equal diameter wheels, but not the tankers. It's not just one manufacturer either - last night I spotted Scanias and MANs with similar configuration.

Any idea why?

PS - I've noticed the odd car transporter with uneven sized wheels but they're usually weird shapes/sizes anyway - the tankers just look like normal units with day cabs, pretty much the same as any supermarket short-haul machine.

[scanner102]

They are a type of lightweight axle that some people have retrofitted to vehicles so that they can go up to 44t but minimising the extra weight of the tractor unit. Typically found on tippers and tankers.

Edit: I don't think they are factory options, they are an after market thing but I cannot think of the name of the company who does them.

Edited by scanner102 on Wednesday 3rd September 11:34

[alangla]

Cheers - never occurred to me that they might be aftermarkets. I suppose the reduced fuel capacity isn't really an issue on something that just shuttles from Grangemouth to a few petrol stations & back.

[scanner102]

Exactly, it doesn't make much difference for units running back to the yard each night as the tanks are plenty big enough (most of the time )

[pja]

They are mainly factory fitted, its very difficult & expensive to get type approval for aftermarket axles these days,

they are being used more and more on modern tractor units & i think they will catch on for rigid's soon

the advantages are mainly weight (they are lighter so the weight imposed on the 5th wheel can be greater) this is very useful when running tankers or bulk tippers but not such an issue with a curtain-side or box

[Nickyboy]

These i'm assuming you mean?

[alangla]

Pretty much, though usually a lot less blingy. On a lot of them the wheel arches seem to be unpainted chequer plate.

[StuntmanMike]

I think that's a requirement on fuel tankers, it's to contain tyre debris, the little wheels look gay.

[scanner102]

pja said:

They are mainly factory fitted, its very difficult & expensive to get type approval for aftermarket axles these days,

Ah thanks for the info, I did not know this. Every day is a school day! Cheers.