So I have had this quad chainring adapter for a very long time; I vaguely recall seeing advertisements in mountain bike action magazine in the late 80’s for the “Mountain Tamer Quad” but I’m not sure that’s what this is:
18/24/34/46
It uses a thread on cog from a SunTour freewheel; this particular one is 18 tooth for a super low gear.
There were some other versions; one of them was the Avid MicroDapter which wasn’t a quad but rather an adapter that allowed you to use a freewheel cog as a smaller granny ring. I have one of those as well that I may use in place of this quad adapter; that one is 20 tooth. Another was the White Industries Limbo Spider, another adapter to allow a freewheel cog to be mounted as the third, small chainring.
These were all made obsolete once SunTour released their Micro Drive (1991?) and then Shimano released their version a year later. Up until this point, the smallest ring you could fit on a 74mm BCD was 24 teeth; the Micro Drive allowed a 20 tooth with a 56mm BCD while Shimano employed a 58mm BCD and 22 tooth small ring.
The bike came with a low profile compact (58/96 mm BCD) crank and 22/32/42 tooth rings but I find the older style with the various adapters to be more interesting.
The quad will require a friction front shifter and a longer BB; fortunately I have both in my parts stash. Unfortunately; I don’t have a matching indexed 8 speed shifter for the rear. What I have is an XT M735 front thumbshifter and a SunTour XC Pro 7 speed rear thumbshifter. These are the best candidates to drive this transmission but the mismatch drives me nuts. Plus the SunTour shifter won’t work with an 8 speed cassette. If anyone has an old 7 speed XT thumbshifter they don’t have a match for I could give it a good home😁
Then I could drive that 8 speed rear end using the famous ghost click those old thumbies are known for.
It can be frustrating but I rather enjoy working out the details and finding a solution that is both possible and affordable.
I’ll have to do some pondering, testing, and scrounging around the collective to see what solution I can come up with. It may make sense to just run the Avid MicroDapter and not the quad as that will allow me to use the SunTour Ergotec shifters, which are an interesting bit of kit as well.
Thanks for watching!
Edit to add: The Avid MicroDapter was intended to allow you to use not a freewheel cog but a 20t chainring that were becoming available with the advent of compact cranksets. It was marginally cheaper to get the adapter and a chainring than it would have been to replace the entire crankset.... The one I have and will post pics of later is the White Industries Limbo Spider.