blueskytheory

hello,

I have a late 80s Centurion Ironman Expert, the pink/yellow color scheme. I love the bike, rides beautifully, and has generational significance since it was my Dad's when he used to ride around the Tracy/Livermore hills. Right now it has the full Shimano 105 component group, downtube indexed shifters, with a 13/24 freewheel and 42/52 biopace chainrings (all standard stuff, nothing ever upgraded on the bike.)

I would like to change the gearing to be a little easier on hills; I can (just barely) climb steep grades in 42/24 but it wreaks havoc on my knees. I'd also like for my aging Dad to ride the bike more often, but he can't with the current gearing. So, before I buy the parts, I have a few questions about this upgrade:

1.) I want to put on a Shimano 6-speed Megarange freewheel, with a 13-34 range. ( https://harriscyclery.net/itemdetails...9&catalogId=39 ). The site says it will work with indexed shifting; does anyone have any experience with this? I'll be picking up the wide-range "Shimano MegaRange C201 rear derailleur." Essentially I guess I'm just wondering how clean the shifting is with a 10t jump from 24 to 34 in the rear; seems like it would have problems??

2.) The harris cyclery page recommends the SRAM PC-58 chain. When I initially went to a LBS to talk about upgrading, they expressed some skepticism because, apparently, modern chainrings are designed to work with modern chains, and modern chains are more narrow to accommodate 8-9-10 speed spacings. Was the LBS misinformed, or?

3.) Finally, because I can't go below a 42 on the biopace 130mm chainrings, I was considering changing to round rings (i ride round on my other bike.) I've never quite understood if the crankarms are part of the biopace setup; can I just change both chainrings to round (a 38 and 50 probably), and leave the same crankarms? or are the crankarms "biopace" too? I don't see why the crankarms would matter since its the elliptical shape of the ring which makes biopace unique, but I'm not sure.

If anyone has experience with upgrading an old Ironman in this way, please let me know if you did something similar. Thanks!

Halthane

1. Might need a new rear derailer... though I'm not certain I know the harris and/or sheldon's website should have the answer.

2. Chain width has more to do with fitting between the cogs on the rear, not the chainrings in the front, so there shouldn't be a problem.

3. The crankarms you have will work just fine with other rings as long as the biopace rings you have are bolted on to the cranks and not swedged, I don't think the 105 would be.

Paul

top506

I have the same bike in pieces in the shop as I overhaul it; same color and everything!

1) Is it 6 0r 7 speed? Mine is 7, and I used a 13-30 frewheel. This will work with the short cage 105 RD no problem, as I have the same set-up on another bike. I think I'd try a freewheel with a 28 or 30 tooth low gear before I swapped out the RD.

2)PC-58 will work fine. Running them on two 7-speed bikes at the moment.

3)The 105 crankset on your bike will take any 130 BCD rings, but you might want to give the Biopace rings a try. Opinion varies widely (and with some heat as well!), but my beat-up old knees find them a bit better over the long haul, especially on hills.

You might want to cross-post on the Classic and Vintage forum, as lots of folk over there own and ride Centurion Ironman bikes and love to talk about them.
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blueskytheory

Thanks for the replies.

It is a 6 speed (i've heard upgrading to a 7speed freewheel isn't that difficult, but i like indexed shifting when im lazy or listening to music when riding). A 13-30 sounds good too, but the closest I can find for 6-speed is a 14-28 (at harris cyclery). There is also a 13-32 by IRD, but I think anything above a 28 would require a new wide-range rear derallieur? Maybe a good option would be a 14-28 and a 38 middle chainring, hmmm.

yeah, the chainrings are bolted on. I've heard wildly different things about biopace--that it is GOOD for knees...that it RUINS knees...that riding one bike round and another biopace is a sure way to hurt yourself, etc. etc. I've rode this bike a bit and didnt feel anything bad, and my dad said he liked that it didn't hurt his knees. In fact, the LBS told me that biopace basically went away because it didn't give any real performance increase in the pedal stroke for racers. I guess there is no substitute for personal experience My main concern was rather with getting a slightly easier gearing. I don't race, and 42/52 is a little too aggressive for my tastes. Especially since this is a double and I love to climb, I think 38/48 might be better--all I'd really lose is extra speed on long descents, I think.

top506

Index 6 to index 7 can be as simple as swapping freewheels and shifters (it was on my Miyata 512). That bike also has 53/40 Biopace chainrings, but the 40 is really hard to find.
One of my other bikes has 50/38/28, and I seldom use the granny ring. Works well on hills with the 13-30 rear.
The Centruion build will have 52/42 and 12-28. Another advantage to converting to 7 speed is the greater range of freewheels. Shimano, IRC, and SunRace all sell 'em new, and Sachs, Sun Tour, Regina, and many others can be found on the used market.
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Sheldon Brown

Those were great bikes, comparable frames cost over a thousand bucks these days. Not everybody is down with the "Miami Vice" color scheme though...

Should work just fine, I've got the same jump on the 11-34 7-speed freewheel on my Rambouillet, and it works like a charm.
The PC-58 isn't all that narrow, won't work with 9- or 10-speed setups, but it is my primary choice for 8-speeds or fewer.
There is nothing "Biopace" about the arms, any 130 BCD chainrings will work with these, but I would leave the rings alone. Biopace is gentler on the knees, and it's a lot of expense to just lower the gearing by 10%

Sheldon " https://sheldonbrown.com/biopace " Brown