6703 chainrings on 7803 chainset?

[Cugel]

Both the summer bike and the winter bike have triple chainsets of the Shimano 30/39/52 variety - a Dura Ace 7803 on the summer bike and an Ultegra 6703 on the winter bike. Although I'm generally good at preserving chainrings and cassettes for many years (careful chain cleaning and replacement) I do like to have spare rings just in case. This doubly (or is it triply) so with the Shimano 6703 and 7803 chainsets as they seem to have somewhat proprietary aspects that makes finding new ones other than Shimano difficult or impossible. And both chainsets are now old-hat, so Shimano spares will soon disappear.

I already have spare 6703 inner (30T) and middle (39T) rings. My question is:

Will 6703 chainrings fit a 7803 chainset and vice versa?

They have the same bcd but I read here and there that the machining of the interfaces between rings and chainset arms may be a bit "special" with the Dura Ace 7803.....?

Although I need to find a spare big ring (I'd really like a 50T rather than a 52T) I intend to have just one spare set of rings for both chainsets if possible. Or I might have two spares for the middles as they get used the most.

Any advice and/or experience with these rings and chainsets will be gratefully received.

Cugel

[iandriver]

Can't speak for Dura Ace, never been near one. I have the last model Ultegra tripple (can't remember the FC number off hand).

I have a 105 FC-5703 50t in the outer position, the std 39t in the middle and a 26T Spa on the inner. All works fine. So a not too expensive solution to one chainset hopefully.

[Brucey]

you could try it out with the bits you have at present, before you invest in more?

cheers

[Cugel]

Can't speak for Dura Ace, never been near one. I have the last model Ultegra tripple (can't remember the FC number off hand).

I have a 105 FC-5703 50t in the outer position, the std 39t in the middle and a 26T Spa on the inner. All works fine. So a not too expensive solution to one chainset hopefully.

Interesting that you could get a 26T inner ring on. Is the 105 triple not like the Ultegra & Dura Ace with their queer 92mm bcd for the inner rings? Or do Spa sell a non-Shimano 92bcd ring?

Cugel

[Cugel]

you could try it out with the bits you have at present, before you invest in more?

cheers

I suppose this is the most certain method albeit requiring the extraction-replacement & disassembly-assembly-disassembly-assembly of a chainset. Still, they do go in and out easily these days.

Would I also need to test it in anger, I wonder? The rings may go on but will they be sitting aright or displaced slightly and affecting the front changes? Also, I have no spare 6703 big ring to try on the Dura Ace yet, although they look very similar to the 7803 big rings in web pics.

The Shimano technical stuff seems to imply that 6703 and 7803 rings are interchangeable but doesn't say so unambiguously. The rascals like one to buy within-groupset, (or so it often seems). Many of us have successfully mixed and matched different groupset parts, though, as you will know better than anyone probably.

Cugel

[iandriver]

Can't speak for Dura Ace, never been near one. I have the last model Ultegra tripple (can't remember the FC number off hand).

I have a 105 FC-5703 50t in the outer position, the std 39t in the middle and a 26T Spa on the inner. All works fine. So a not too expensive solution to one chainset hopefully.

Interesting that you could get a 26T inner ring on. Is the 105 triple not like the Ultegra & Dura Ace with their queer 92mm bcd for the inner rings? Or do Spa sell a non-Shimano 92bcd ring?

Cugel

It's definitely a 74mm bcd. Just taken a pic, which is probably more useful. I believe it to be the last model Ultegra triple produced.

[Cugel]

Can't speak for Dura Ace, never been near one. I have the last model Ultegra tripple (can't remember the FC number off hand).

I have a 105 FC-5703 50t in the outer position, the std 39t in the middle and a 26T Spa on the inner. All works fine. So a not too expensive solution to one chainset hopefully.

Interesting that you could get a 26T inner ring on. Is the 105 triple not like the Ultegra & Dura Ace with their queer 92mm bcd for the inner rings? Or do Spa sell a non-Shimano 92bcd ring?

Cugel

It's definitely a 74mm bcd. Just taken a pic, which is probably more useful. I believe it to be the last model Ultegra triple produced.

That's a 6603 and it does have a 74mm bcd for the inner ring. The last Ultegra triple was the 6703. the one I have, which (along with the Dura Ace 7803) has that strange 92mm bcd for the inner ring. It will make spare-hunting difficult before long.

Cugel

[peetee]

I have a 7800 triple crankset and bought an Ultegra 6703 39t middle ring as a replacement. The chainring bolt circle diameters are the same but the middle ring design is different. The Dura ace is much thicker and uses narrower spacers for the little ring. I substituted a set of spacers from a load of wheel axle spares and it works just fine. They are 2mm deeper than the Dura ace spacers but larger inside than normal triple crankset spacers which is why I had to use axle parts.
I have also substituted the ridiculously large outer ring for a 50t Stronglight item. The front mech however is not at the ideal height for this as the inner cage plate of the front mech fouls the middle ring. Shame really as I actually wanted to fit a 48t

[Cugel]

I have a 7800 triple crankset and bought an Ultegra 6703 39t middle ring as a replacement. The chainring bolt circle diameters are the same but the middle ring design is different. The Dura ace is much thicker and uses narrower spacers for the little ring. I substituted a set of spacers from a load of wheel axle spares and it works just fine. They are 2mm deeper than the Dura ace spacers but larger inside than normal triple crankset spacers which is why I had to use axle parts.
I have also substituted the ridiculously large outer ring for a 50t Stronglight item. The front mech however is not at the ideal height for this as the inner cage plate of the front mech fouls the middle ring. Shame really as I actually wanted to fit a 48t

Ah ha! Perhaps the offhand comment I read somewhere that 7803 rings have "different machining" from the 6703 rings is here somewhat illuminated. It seems I must either find 7803 spare rings or find (as you did) a means to adapt the 6703 rings so they configure as would the 7803 rings.

Even now, 7803 rings other than the 30T inner seem hard to find....

On the other hand, I last wore out a chainring about 20 years ago, on a Shimano bio-pace chainset of (I think) the Sante series that seemed made of cheese anyway. Modern Shimano chainrings do seem to wear much better than they used to.

Cugel

[peetee]

I will see if I can find a set of suitable spacers for you. Then you would just have to get hold of a Ultegra middle ring. I got mine for about £15, IIRC, six months ago.

[Cugel]

I will see if I can find a set of suitable spacers for you. Then you would just have to get hold of a Ultegra middle ring. I got mine for about £15, IIRC, six months ago.

That would be very kind & helpful, deserving of reciprocation. Perhaps we could do a swapsie? I have various redundant bike parts, including two stems, a wheel or two, chainsets and rings of the 110 bcd ilk and who knows what other odds & sods lurking in the bit box that I may never need. Do you have a need of anything just now or is your bike bit box even fuller than mine?

Cugel

[peetee]

That would be very kind & helpful, deserving of reciprocation. Perhaps we could do a swapsie? I have various redundant bike parts, including two stems, a wheel or two, chainsets and rings of the 110 bcd ilk and who knows what other odds & sods lurking in the bit box that I may never need. Do you have a need of anything just now or is your bike bit box even fuller than mine?

Cugel

You have a private message sir

[The utility cyclist]

Can't speak for Dura Ace, never been near one. I have the last model Ultegra tripple (can't remember the FC number off hand).

I have a 105 FC-5703 50t in the outer position, the std 39t in the middle and a 26T Spa on the inner. All works fine. So a not too expensive solution to one chainset hopefully.

Interesting that you could get a 26T inner ring on. Is the 105 triple not like the Ultegra & Dura Ace with their queer 92mm bcd for the inner rings? Or do Spa sell a non-Shimano 92bcd ring?

Cugel

The weird 92mm BCD inner originally started on the 7703, the first 10 speed Ultegra 6603 has a 74mm BCD (as did the 5603) unlike your 7803, the later 10 speed Ultegra 6703 repeats the 92mm for some strange reason yet the 5703 still keeps the 74mm BCD. Obviously Shimano did not produce a triple at DA level for that second gen 10 speed and it's clear where their direction is having pretty much ditched the road triple.

You're left with the garbage 10 speed Tiagra 4703 which is a 4 Bolt 74mm BCD so can only take a 30T min again The Sora 3000 series triple is the highest spec road triple that can be retro-fitted with a ring smaller than 30T, Shimano are absolute cretins and clearly aren't interested in the majority of bicycle users but just pump out rubbish 'solutions' like a 50T cassette sprocket. More money, more weight, massive jumps in the ratios. grrrrr.

Not being able to fit a smaller c/ring on the Ultegra 6703 was the primary reason why I bought a Miche Evo Max triple instead, less costly anyway and far prettier IMHO.
Considering they have Di2 it's baffling that they only produce one triple front derailleur (XTR) and that is supposedly limited to 42T max (apparently it'll do 48t)

[Cugel]

Can't speak for Dura Ace, never been near one. I have the last model Ultegra tripple (can't remember the FC number off hand).

I have a 105 FC-5703 50t in the outer position, the std 39t in the middle and a 26T Spa on the inner. All works fine. So a not too expensive solution to one chainset hopefully.

Interesting that you could get a 26T inner ring on. Is the 105 triple not like the Ultegra & Dura Ace with their queer 92mm bcd for the inner rings? Or do Spa sell a non-Shimano 92bcd ring?

Cugel

The weird 92mm BCD inner originally started on the 7703, the first 10 speed Ultegra 6603 has a 74mm BCD (as did the 5603) unlike your 7803, the later 10 speed Ultegra 6703 repeats the 92mm for some strange reason yet the 5703 still keeps the 74mm BCD. Obviously Shimano did not produce a triple at DA level for that second gen 10 speed and it's clear where their direction is having pretty much ditched the road triple.

You're left with the garbage 10 speed Tiagra 4703 which is a 4 Bolt 74mm BCD so can only take a 30T min again The Sora 3000 series triple is the highest spec road triple that can be retro-fitted with a ring smaller than 30T, Shimano are absolute cretins and clearly aren't interested in the majority of bicycle users but just pump out rubbish 'solutions' like a 50T cassette sprocket. More money, more weight, massive jumps in the ratios. grrrrr.

Not being able to fit a smaller c/ring on the Ultegra 6703 was the primary reason why I bought a Miche Evo Max triple instead, less costly anyway and far prettier IMHO.
Considering they have Di2 it's baffling that they only produce one triple front derailleur (XTR) and that is supposedly limited to 42T max (apparently it'll do 48t)

Although I wouldn't describe Shimano as "garbage" - not even their puzzling design decisions concerning gear ratios - like you I'm frustrated by Shimano's seeming blindness to the needs of cyclists who aren't some kind of racing fellow. My biggest moan is their apparent inability to understand that a cassette of 14-36 would be far more useful to most road bikes living in hilly places than is 11-28.

The increasing lack of triple chainsets and their limit to a 30T small ring is also puzzling. Why throw out the tried and tested design solutions of yesteryear? It's not as though all cyclists have suddenly become Cav or Wiggo-like albeit many seem to pretend that they have.

Is it just marketing and fashion-cycles serving the need for constant "growth" of their bottom line? Probably.

Happily I found Ultegra 6703 components at prices a fraction of what they were, presumably because they are now unfashionable. The 7803 Dura Ace chainset was an unused gift from a lad who acquired it for complex reasons, never used it and took agin' the notion of triples altogether. He is also leery of eBay so I benefitted from his gift (reciprocated with a large flow of books I'd finished with in the other direction).

Cugel

[satanas]

IMHO, the "strange reason" Shimano chose not to use a 74mm bcd on 7703, 7803, etc is a bit complicated, but boils down to economics.

1. Racing cyclists generally hate, loathe and detest triples, so weren't going to buy any; the potential market was MAMILs
2. All the cranks using the adapter-style middle rings and 92 bcd inners have hollow arms. A different forging would be required if a 74mm bcd was to be incorporated, and this would be expensive, and difficult to justify given limited sales
3. Instead, the inner flange (below/inside the inner ring) was machined off the existing forging. This enables the new middle ring to extend past the spider and incorporate mounting points for the inner. The BB spindle is longer but that's easy to change
4. Racers and wannabes don't need/use/want very small rings, so extending the middle ring further in would just add weight, plus 92 bcd locks customers in for spares

Another option would be to use a TA or Stronglight triple adapter middle chainring. This would look a bit less elegant and the pins and ramps might not line up as well but they have a 74mm inner bcd, allowing inner rings down to 24T.

The problem of the outer sitting too high can be reduced or eliminated by using a 5703 (105) FD; these are intended for 50x39x30, so are expecting 11T between the two outer rings, not 13T as with 7803 and 6703; the FD can sit ~4mm lower before the inner cage plate will hit the middle ring.

See, it's all simple really.

Later,
Stephen