Bicycle Mechanics - converting from stem shifters to downtube shifters - question

I just got an '85 Nishiki Riviera and I'm replacing a few components, learning about things as I go. I want to get rid of the stem-mounted friction shifters. Using clamp-on downtube friction shifters (also 6-speed) seems like the easiest option because it won't introduce any compatibility issues with the existing derailers and freewheel. Is that correct?

Also, I'm wondering about the diameter of the downtube. Is the diameter standardized, or does it vary among different tubing manufacturers (the Nishiki has Tange 900)? In other words, do I need to worry about getting a shifter mount with the same diameter as my downtube, or are they all the same?


Thanks,
William

Downtubes were almost universally 'same sized' in that era.
Clamp on should be fine. Main problem might be lack of a
brazed on 'stop' to prevent the shifter from sliding down the
tube under shifting torque and scratching the paint. If there
is no 'bump' on the bottom side of the downtube where the
shifter would mount, drill a small hole ( 3/32" is about right)
and screw in a #4 or #6 self tapping screw to serve as a
stop. Shifter would clamp on just above the stop.

If your stem shifters are indexed, you might have a problem finding clamp-on downtube shifters that are also indexed. If you are willing to have friction shifting, finding suitable clamp-ons should be no problem.

If your stem shifters are indexed, you might have a problem finding clamp-on downtube shifters that are also indexed. If you are willing to have friction shifting, finding suitable clamp-ons should be no problem.

Not likely that an '85 bike had indexing stem shifters, as SIS was introduced in '84('85?), aimed at racers and higher level systems initially.

I doubt if there were any indexed stem shifters in '85. I recall SIS coming out in '86(?) from the top of the line down.
Right :o Dura Ace was Shimano's first indexed group and hit the consumer marker for the '86 model year. It certainly didn't offer stem shifters!

It is possible the OP's bike was upgraded after it was built and there were indexed stem shifters sold on some bikes later on. If it still has the OEM shifters, they are certainly not indexed.

The stem shifters are friction, and I'm going to stick with friction for the downtube shifters, so there's no problem there.

I just checked my downtube and there's a nice little heart-shaped braze-on on the underside, holding the shifter cable guide mount in place, so it looks like I'm good to go. Thanks for all the info!

I just checked my downtube and there's a nice little heart-shaped braze-on on the underside, holding the shifter cable guide mount in place,

Bingo! We have a winner!