canklecat

Has anyone measured the original chain length/link number on an Ironman with 52/42 chain ring and 13-24 freewheel? Have you found a longer than usual chain length to work better?

I just realized this week I may have cut my new KMC Z72 chains incorrectly. I used the Suntour chain that came with the bike as a guide, assuming it was the original and therefore the correct length. But this week I noticed what felt like unusual resistance, almost like binding, with the new chain in the 42T chain ring and 24 freewheel cog.

Over the summer it seemed like I was struggling more on hills, despite being faster overall. It was unusually hard to climb with the Ironman in the 42 chain ring and 21 or 24 tooth freewheel cogs. It was less strain climbing with the heavier Univega hybrid in the same gear ratio.

The crank spins freely. Ditto the hubs and freewheel. No brake rubbing, etc. But when I spun the crank backward I could feel unusual resistance in the 42/24 combo.

One thing I'd changed which affected chain tension was moving the rear wheel as far back as it would go in the adjustable dropouts. But that amounted to only 1/4" from the original setting.

I disassembled and cleaned the jockey wheels again (I did this back in July). They were already a bit sluggish, so the Park CL-1 lube wasn't a good choice. For now I'm leaving them dry until I decide on a more suitable lube. But even with the dry, free-spinning jockey wheels there was still unusual resistance in the 42/24 gear combo.

The rear derailer cage seemed to be at an unusual angle, and since I was swapping to a 13-25 SunRace freewheel I didn't want to risk damage. Especially since I might go to a 13-28 freewheel later, depending on how it goes with the 39T chain ring next week.

I added two links to the KMC Z72 chain. Now there's much less resistance when spinning the crank backward in the 42/24 combo with the original Suntour freewheel, and 42/25 combo in the new SunRace freewheel. Apparently the chain tension was much too tight. It still doesn't spin as freely as it should, or as freely as my other two bikes.

Subjectively, the bike felt a bit quicker on Saturday's ride, but that didn't include any serious hills where I'd normally need the 42/24 combo. I'll tackle that Sunday or Monday on some pesky climbs that have defied any improvement in speed.

So I'm guessing the Suntour chain that came with the bike was way off and I should have measured from scratch via the usual methods.

Anyway, just curious whether anyone else has measured their chains or has specs on the original chain length.

(Additional note: I measured the new KMC Z72 chains at 53", which should be appropriate according to various chain length calculators, accounting for the largest chain ring and freewheel cog, chain stay length, etc. But adding an inch seemed to result in less binding.)