Cycling UK Forum

Any body out there happen to know the original specification for an Orbit Mercury ladies tourer, just in the process of converting it from a butterfly bar to drops with bar end shifters for SWMBO. At present there is an 8 speed cassette fitted but chain alignment seems to be a tadge suspect. Any help would be greatly appreciated.

It's not one of those with an offset rear end is it? Orbit built a few models like that - avoids the need to dish the rear wheel. Orbit cycles are still on the go or at least they still have a website up http://www.orbit-cycles.co.uk/about-us/ . Maybe they can help with spec details.

Thanks pete75 but I have tried Orbit as it stands at the moment but they have been through so many reincarnations over the years although personable they were unable to help. I think that the wheels are possibly original (but soon to be replaced) and don't appear to have any eccentric dishing but with the 8 speed cassette the alignment is a bit "squiffy", although worked fine with the rapid fire setup as fitted. I have done a few calcs and even if I reduce the outboard distance by reducing the BB width I still would not get centre sprocket centre chainwheel alignment. I was wondering if the thing was originaly fitted with a 7 speed cassette, at the mo it has a 12-34 rear on an 8 (as previously mentioned) and a 42-34-22 triple.; so obviously set up for serious heavy touring.

Any how thanks again

KTHS

First question before I can offer any spec - what is the frame? Earliest models used a lugged 531 frame with either 24 or 26 inch wheels. (hese were usually supplied in cream although some had custom colours from new. Late models used a tig welded tange frame with 26 inch wheels.

As spec varied a lot between them I can't tell you more without identifying what you have.

(Orbit sales manager 1998 - 2004)

Orbits with an offset back end had (both) rear dropouts offset 4mm to the right.....this is quite difficult to see, and the difference between a standard wheel and a wheel for these offset dropouts is also difficult to see.
Further to that, I have seen more than one Qrbit with offset back end which has been erroneously fitted with a standard back wheel, and although it doesn't fit right between the stays and back brake, the bike rides well enough. To ride no hands its only necessary to ride with the saddle under one cheek, and that's not uncommon with bikes fitted with the "right" wheels.
So, to check whether the existing wheel is offset or not, take the wheel out and reverse it in the dropouts. A symmetrical wheel will end up in the same place regardless of which way you put the wheel in the frame, an offset wheel will be out by 8mm if you reverse it.
To find out if the existing wheel is the right wheel for the frame, just follow this thread....https://forum.cyclinguk.org/viewtopic.php?f=1&t=59332&hilit=string
You can also check your frame for straightness using string, and check your wheel using a dishing gauge.....this will show 8mm discrepancy between the 2 "sides" of the wheel.
Chainline will depend on many things......
MTB triples have a different chainline to touring (road) triples, measured from the centre of the seat tube....I can't remember the numbers, somebody will know....google, or Sheldon Brown.
Rear hub width and number of sprockets both have an effect.
From memory (its cold and raining, I'm not emptying the garage to check just now)
.......with a 4mm offset back end, road chainline, 135mm rear hub, the middle ring lines up pretty much with the middle of a 7 or 8 speed cassette.
..... most triples are actually worse than this

531colin wrote:Orbits with an offset back end had (both) rear dropouts offset 4mm to the right.....this is quite difficult to see, and the difference between a standard wheel and a wheel for these offset dropouts is also difficult to see.
Further to that, I have seen more than one Qrbit with offset back end which has been erroneously fitted with a standard back wheel, and although it doesn't fit right between the stays and back brake, the bike rides well enough. To ride no hands its only necessary to ride with the saddle under one cheek, and that's not uncommon with bikes fitted with the "right" wheels.
So, to check whether the existing wheel is offset or not, take the wheel out and reverse it in the dropouts. A symmetrical wheel will end up in the same place regardless of which way you put the wheel in the frame, an offset wheel will be out by 8mm if you reverse it.
To find out if the existing wheel is the right wheel for the frame, just follow this thread....https://forum.cyclinguk.org/viewtopic.php?f=1&t=59332&hilit=string
You can also check your frame for straightness using string, and check your wheel using a dishing gauge.....this will show 8mm discrepancy between the 2 "sides" of the wheel.
Chainline will depend on many things......
MTB triples have a different chainline to touring (road) triples, measured from the centre of the seat tube....I can't remember the numbers, somebody will know....google, or Sheldon Brown.
Rear hub width and number of sprockets both have an effect.
From memory (its cold and raining, I'm not emptying the garage to check just now)
.......with a 4mm offset back end, road chainline, 135mm rear hub, the middle ring lines up pretty much with the middle of a 7 or 8 speed cassette.
..... most triples are actually worse than this

The Mercury was never made with the offset rear triangle.
The only models built this way we're Columbus tubed Gold Medals and Romany's, the rest of the range all used 'normal' rear triangles.

And not all Romany's have the offset rear end I have 2 without normal symetrical rear triangles.

Should read "with" normal rear triangles.
Was it only the Columbus tubed frames that used the offset triangles?

I bought from Simon at Orbit a Romany which had been out to a magazine or two for testing....it was a bit cheaper as it had been ridden a bit.
The original paint is long gone, and my memory is rapidly following.....however, I'm certain it was 853, and built by a UK framebuilder, although I forget who. It certainly has offset back end. (I also have a Gold medal in Columbus tubing, also with offset back end.)
OP is worried about the chainline on his bike, its a few minutes work with a bit of string to see if the frame is deliberately offset, or perhaps even bent in an accident.
Its possible that every Mercury ever built was made to the exact same spec., but I would rather trust my own observations.

PhilD28 wrote:Should read "with" normal rear triangles.
Was it only the Columbus tubed frames that used the offset triangles?

The Romany was built originally with a standard rear triangle and yes, in 853. Some later Reynolds frames were built assymetric before we changed to Columbus tubing at which point the GM started to get the offset too. (all the blue and silver frames). The only Columbus frames built with 'normal' rear ends were the very rare Photons, the red race bikes and like mine, black audax frames.

All the Columbus and 853 frames were UK built and finished by a very good builder in the Midlands. The Tange frames were designed in Sheffield but made in Taiwan although painted in the UK as some had bits and pieces added before the paint was applied.

No harm in checking the OP's frame for straightness but if it's a Mercury there won't be the built in offset.