Accushift 6s is the same spacing as Shimano SIS.

Accu-7 is different than SIS-7, with just the largest cogs spaced closer together on the Accu-7 freewheels and cassettes.

Suntour Accushift and normal 6-speed freewheels are both 5.5mm spacing, which is the same as normal 5-speed freewheel spacing (which shouldn't matter to anyone since that's usually friction anyway).

I only make the 5-speed point in case someone needs a bargain freewheel for use with a Suntour Accushift setup. You can use a 5-speed freewheel and lose a cog, but has the same spacing as 6. Maybe somebody finds a swap bargain on a 5 sp freewheel that is so cheap they'll forgo a cog.

Sheldon Brown's Bicycle Frame and Cassette Spacing Crib Sheet

Not quite true, technically. SIS merely just stands for Shimano Index System. So on its face your statement that Accushift is the same spacing as SIS isn't accurate, since each speed in the Shimano indexing world has its own cog spacing standard. Sure Shimano had SIS on 6sp Dura-Ace but that kit is almost a unicorn. To the point that Sheldon Brown doesn't even reference Shimano SIS 6-speed spacing on his freewheel/cassette crib sheet. Shimano 7sp SIS spacing and every Shimano spacing standard from 8-11 are not compatible with Accushift or "normal" 6sp.

Be careful using the term Accu-7. Sheldon Brown refers to the two Suntour 7-sp standards as Ultra-7 (freewheel) and Microdrive-7 (cassette). They are different. Ultra-7 is the SAME as Shimano HG, IG, Sachs, SRAM, etc. at 5.0mm. Using the term Accu-7 just invites trouble because it isn't clear if you're talking about Ultra or Microdrive 7. However, if one were using a Centeron or floating upper pulley on their derailleur, I'd be shocked if the narrower cog spacing on Microdrive-7 even mattered. The pulley should correct the variance, I would think.

Nothing says you can't buy a couple of different ones, then mix and match the cogs. Not the most cost efficient method, but it would provide results.

Aaron

Something I've wondered: Why in the world make the spacing different between different cogs? Is it just vendor lock-in? You've got a derailleur which I believe moves in a linear fashion, and a shifter with a circular groove for the cable to ride in. Given a certain angular movement of the shift lever, you should see the same linear movement of the derailleur pulley cage, right? If I'm screwed up in my thinking about one or the other, wouldn't a Shimano, SunTour, Campy, or other derailleur move in almost exactly the same fashion?

Please clue me in.

I have used IRD freewheels and think they are great. If you want to re-configure freewheels, make custom freewheels, search for vintage freewheels on line have at it. If you want to ride you bike and do what most people do which is forget about the t freewheel, than IRD is great option.

In addition I have found that the cheap freewheels have a wider body or more spacers or whatever. They sometimes have trouble fitting into vintage road frames. The IRD freewheels I have used, have never had this problem. Also some of the cheapies make indexing difficult because of what I am guessing are loose quality control tolerances and the spacing between the cogs is off a little bit. Not an issue with IRD.

If you like to tinker, freewheels will give you plenty to tinker with. I am not interested in saving $25 and relying on the cheapest possible option, 40 miles from my house.

Thanks for all the offers and the advice. I have been away from this thread for a day or two. I've been doing some shopping and gear ration calculations, etc.

One frustration - none of the web sites list freewheel threading, not even IRD. I need to match an existing hub.

The IRD (and other) photos all look like cassettes, not freewheels. Thoughts?

Yep, that's the only way I can think to, as well. And then you're left with an extra FW body (or two, depending on what you wanted to build) and most of the same cogs.

These ones are freewheels, guaranteed: Classica Freewheels 5/6/7-Speed ? Interloc Racing Design / IRD

They'd be BSC threaded. Something like French or Italian threading would be a niche within a niche.

All the new freewheels are threaded ISO or not Italian or French. What type of hub do have? Chances are if you were running a Suntour then you need ISO threading so any of these will be good to go.

I am pretty sure that the wider spacing between the smaller cogs was to improve shifting.

Even with a slant-parallelogram rear derailer, with most sizes of freewheels there will be an increase in chain gap as the chain is shifted to smaller cogs. I've looked at this very closely using Suntour derailers.

So Suntour figured out that they could use slightly narrower cog spacing between the largest cogs and still get reliable, precise shifting performance, which allowed them to use the wider cog spacing where it was needed (between the smaller cogs) for good shifting, while keeping the overall freewheel width narrow.

As far as implementing this, they had to create an indexed shifter with uneven detent spacing, a freewheel with cog spacing to match, and find or make a narrow-enough chain.

They pushed the limits with chain width, cog spacing and the shifter's overshift freeplay however, which all conspired to make shifting to the larger cogs rather touchy as the chain often contacted (or shifted momentarily to) the next-larger cog than the one the rider was trying to shift to, and the adjustment range tolerance was positively miniscule by today's standards, even with fresh cabling.
This is why Suntour Accu-7 freewheels enjoy so much better shifting with narrower (outside width) 9s chain.

By comparison, the original Accushift (which was standard 5s/6s spaced) gave much more robust shifting action than the subsequent Accu-7, if a decent chain was used. The problem back then was that only Shimano made a decent-shifting chain, and really only after their UG-Narrow chain was introduced for use with 5, 6 and their (Shimano's) new SIS-7 cogsets. And yet the Shimano UG Narrow chain was still on the wide side for use on Suntour's Accu-7 freewheels (which had both thick teeth and asymmetric cog spacing).

A stock Accu-7 drivetrain, with only the addition of a modern 9s chain, shifts much better and stays within a decent adjustment range far, far longer than it ever did back in the day, so much so that I think that a better chain alone might likely have saved the company.

unless specified, new freewheels are iso (standard/english).

it's been my experience that iso freewheels thread perfectly with italian threaded hubs.