Current Double-Decker design

[Trapper John]

It is blindingly obvious that the chassis of double-deckers has markedly changed in the last 15 years or so. I'm guessing (so correct me if I'm wrong) that the EEC have dictated that the lower deck of ANY bus shall be flat, in order that they can take wheel-chairs (though it's mostly prams that fill the designated place). As a result, the front wheel arches now take up more room internally, comparatively speaking. 15 years ago, you could stick 3 or 4 seats on them. Nowadays, it's luggage space, or somewhere to stash copies of "The Metro".
Is it possible to have 4 SMALLER wheels at the front on a Double Decker (Bedford VAL style)? I'm not a Mechanical Engineer, so I can't comment. The only disadvantage that I can see is that if dual doors are fitted, the scope of location of the centre doors are marginally reduced, as is the location of the stairs.

John the Trapper

[billyboy]

I think that today it would be a case of "Extra axle= extra tyres. Extra maintainence =higher costs.
Agree with you that it could be done though and quite effectivly too!

[billyboy]

I think that today it would be a case of "Extra axle= extra tyres. Extra maintainence =higher costs.
Agree with you that it could be done though and quite effectivly too!

[G-CPTN]

You forget, maybe, that smaller wheels mean smaller brakes (a major weakness of the Bedford VAL - at least for coach use).
Then there is 'balancing' the load - the VAL had a big rear overhang (although rear-engine would compensate for this).

[Trapper John]

Another possible drawback comes to mind, due entirely to the wheels being smaller.
With smaller wheels, the rotational velocity will be greater. Therefore the wear on the axle components may be greater. Also with an increased speed, the wear on the brakes could be greater. Would the fact that the axle weight has now decreased have any effect on wear? I'm only half-guessing, as mechanics is not my forte - I'm an Electronic Engineer.

John

[G-CPTN]

Smaller wheels means lower unsprung weight and inertia (per axle) and (with lower axle loads) gives better ride quality. As you suggest (and I hinted at) the wear on the brakes (and tyres) is greater, though being smaller they are cheaper (apart from labour). Wear of the rotating parts shouldn't be a problem (I'm pondering about drive-axle ratios . . . ).
The brakes on the VAL suffered from fade, especially when used for Continental Coaches operating in mountainous regions. Use for service buses (except, perhaps in Sheffield) shouldn't cause problems - though some may have better-informed information than mine.
Perhaps some operators running small-wheeled trailers have some useful input?
The VAL used conventional semi-elliptical metal leaf springs, whereas modern designs would undoubtedly use air suspension (this is almost universal for kneeling buses). Again, air suspension gives improved ride quality, so the benefits would be compounded (and further reduce mechanical wear - assuming sensible sizing of components).

[billyboy]

I saw an arrangement on a southdown Harrington once that would be rather good on a six legger decker. It was fitted with a Thelma electric retarder. This was controle by the footbrake pedal. As you went to apply the brakes the four notches of the thelma came in before the brakes even started to be applied. Cold brake drums ready for when needed. if four notches were applied as in an emergency situation you could fetch the passengers out of the seats. On service work i think an arrangement like this would be a Godsend. Think how many miles without a brake reline or adjust!

[G-CPTN]

Yes, I've driven Telma retarders, and they were effective though heavy and expensive (I believe). Also the bearings were susceptible to wear. It would be interesting to receive comment from those who ran them on large fleets for their 'cost of ownership' figures.
Nowadays there are hydraulic retarders (for manual as well as automatic transmissions) that are probably more effective, saving brake wear, though there is a capital cost penalty of course.