Hi everybody. I have a mid 1980's Centurion Ironman with stock gearing that is too tall for the North East area I live in. The bike has Shimano 600 cranks with 52-42 Biopace rings and Shimano 600 MF-6208, 6 speed freewheel with 13-24 cogs. Shimano is selling some low grade 14-28 freewheels that I would rather not use. Any advice on other component options would be appreciated .

The way I see it you have two options: triple crank, or a new wheel with a Freehub and cassette. Do you have friction or indexed shifters? If they're friction I'd just get a new wheel with the cassette of my choice. Heck, get a 10 speed. That way you won't lose your Biopace.

You do not say what the Bolt Center Diameter of your crank is, but if it is the 'standard' 130mm, you can go as low as 38t on your small ring. This will give you quite a bit lower gears than the 42 you have now.

Yes,I have indexed shifters and the Bolt Center Diameter is 130mm,but I'd like to keep the bike as original as possible. I've just located a new old stock Shimano 600 freewheel on Ebay for $54.95 . The cogs' sizes are 14-16-19-23-28-34. I'm thinking that I could replace the 34 with maybe a 25 or 26 and still retain the stock chainrings and derailleur. Any thoughts?

If you want to keep the bike original, don't change anything. As soon as you change one item, it's no longer original.

If you're going to change it, then might as well do it for the functionality you need. So you'd change the ebay freewheel from 14-16-19-23-28-34 to a 14-16-19-23-28-25 or 14-16-19-23-28-26? Doesn't make sense.

I would do this:

1. get 38t inner chainring

2. get 14-28t Shimano freewheel. Don't know what you mean by "low grade" but the Hyperglide freewheels outperforms the 600EX Uniglide freewheel by a tonne!

Agreed. I use that same FW on a lot of bikes and with the 53/39 (an EZ swap for that 42) I can climb any hill around here.

And we have some bigguns.

You may also want to check what the largest cog your rear derailleur can handle is.

Get a MEGARANGE 6 speed freewheel with a 34 teeth granny. Don't buy that overpriced $50 shimano 600 one. Megarange freewheels can be had for so much cheaper. They shift better too since they have ramps built into them. Newer technology.

IRD brand, currently makes Freeweels in 5, 6 and 7 speed, a 24,28, 34t shifts better in most situations,
than mega range, which jumps directly from a 24t to a 34..

they , new, are $40 [I think]

or you can buy them new in a 13-28 cog size, to stick in the range of your stock
RD.

Yeah, I doubt if the 600EX RD will handle 34t. About 28t is max.

If your intent is for steep climbs, why would you get rid of that 34T other than the fact that your RD can't handle it? The 39 chain ring up front already suggested is good advice, as is the non-600 freewheel. My contribution to your thread is to use a reasonably priced long cage 8 or 9 speed mtb rear derailleur (Deore). That way you can have the 39 up front and a 34 in the back by just changing 3 things (front chainring, cassette and RD).

With a mtb long cage RD, if you find that 39 front / 34 rear is still too tall for you (gearing-wise), you can still get a Triple-izer that will allow you to add that 3rd ring (28T). Or you can get a triple crankset. With a triple, you'll probably need a new bottom bracket with 5mm or more spindle length.

Good luck.

tk

Sorry for the confusion. What I meant to say is that I could modify the freewheel I found on Ebay (14-16-19-23-28-34) and leave everything else intact. If I get rid of the 34 and instead use a 26 between 23 and 28 that should give me a low enough gear ratio (1.5 / 1) while not having to modify anything else.Maybe just a longer chain.

Thanks for all the inputs.

You can buy a Shimano 6 speed freewheel for $20.00 new. The 600 deraileur will shift a 28 and the 39 tooth ring will make your bike a lot more usable. Also these shifters a cheap enough to switch to 7 speed and the freewheels are the same price as 6 speed.

That's an odd progression of gears and doesn't give you even steps between them:
Better gearing for that range would be this:
This combined with a 38t small-chainring would give you two lower gears than you have now. And you won't even have to get a longer chain.