Skewer

One of my old bikes has a triple DA 7703 crankset on it. When I took the crankset and rings off to thoroughly clean the crankset, I noticed that, unlike a triple Ultegra 6503 crankset, the spider has no place to attach the small 30T chainring. Instead, the small 30T chainring just screws directly in to holes on a special, middle 39T 130 BCD chainring as pictured below. For fun I put the crankset back together just using the middle and outer ring, and the crankset then looks just like a normal double 7700 crankset, except I don't have a normal 7700 crankset onhand to compare it to. But this makes me wonder if indeed the 7703 triple crankset is really just a standard, double 7700 crankset with a special middle 39T ring and triple BB.

If so, I would like to use this DA crankset as a normal double crankset with a normal 130 BCD DA 7700 or 6500 39T chainring and 7700 or 6500 double BB on one of my other bikes. Does anyone see any problem with this? Is a 7703 crankset really just a standard, double 7700 crankset with a modified 39T chainring and triple BB? It looks that way to me.

Jeff Wills

No.
Yes.

IMO, Shimano went a little nutty with the Dura-Ace 7703 triple. They may have been trying to reduce the number of forgings they needed for the product line since the triple right arm is just a double arm with the inner chainring lips removed. Then they create a whole new pair of chainrings with a unique bolt circle! Why they didn't make the inner ring with a 74mm bolt circle (like the TA adapters) I'll never know.

Al1943

Sure, you can use it as a double just fine, but I don't think it's not the same crankset as a double. The chainline and Q factor will be different but OK. The shifters are not the same as D-A double shifters that don't have the extra click-stops.

Al

Skewer

Thanks! It looks like I have two different answers from two different posters. Your answer sounds most likely to me. Shimano probably didn't do a different forging for the triple DA 7703 crankarms versus double DA 7700 crankarms! I suspect they didn't make the BCD for the inner ring 74 BCD because Shimano wanted to force folks to buy both the expensive middle and inner DA chainrings if someone wanted to try to convert other 130 BCD double cranksets in to triple cranksets using Shimano rings. However, for going the other way, converting triple to a double, I suspect that I can use any 130 BCD 39T chainrings for my new double inner chainring. I will probably use a 6500 39T. Of course I could just leave the funny looking chainring on with the extra holes, but that chainring has a lot of miles on it and is probably due for replacement anyway.

Do you see any issues with chainline if I connect the converted double to a regular double 6500 BB? Seems like the chainline would be exactly the same as any regular 7700 double crankset using a 109.5 Octalink BB.

As for shifters, the other bike already has a left double shifter on it, so no worry there.

Thanks for the Peter White link!

Jeff Wills

Nope, I wouldn't anticipate any issues with chainline since you're using a double BB. Put it together, tune it up, and go ride.