trprud

I have a, I think, 1988 Miyata Seven Twelve. It has a biopace FC-1050 crank. I was wanting to go a little smaller on the chain rings. I can get Deore XT-FC-M730 rings that are 46/38/28. I wanted to take the two larger rings and put them on the old crank. I don't have the rings yet so I can't check to see if they fit. Does anyone happen to know if these are interchangeable?

PS54811 56

Colnago Mixte

The ring diameter will likely be different (130 bcd on the road crankset, and 110 on the Deore) you may need to move the whole crankset over. I use MTB cranks on several road bikes. I take the inner ring off, and that will generally give enough clearance.



vs.

bluehills3149

I just put a mtb crank on my road bike and just kept the outer 42-32 chainrings and chopped off the 22 granny gear. But the cranks are much wider than the original road cranks so the chainrings sit very far from the frame and the chain alignment was terrible. I swapped in a very narrow bottom bracket (107mm I think) that brought the cranks back closer to the fame so the cranks almost touch the bottom bracket and now the alignment is OK. So bottom line is that MTB cranks may result in alignment issues if you don't replace the bottom bracket spindle length. And yes, the BCD of the mtb cranks (Suntour) was 110 so chainrings were compatible with road cranks.
However, the shifting with the original road derailleur is fine and the gearing ratios are great.

ThermionicScott 

As @Colnago Mixte posted, the Deore rings are almost certainly the wrong BCD. But you can use pretty much any 130 BCD rings on your FC-1050 crank to lower the gearing. I used the same crank on my rando bike for a while and used one of these Sugino 38T rings on the inner position: https://www.amazon.com/Sugino-38t-13.../dp/B001GSQITW