Bicycle Mechanics - Biopace Advice

I have a centurion ironman. I don't know what year it is. I have owned it for a month.

I did a century last week. During the ride, a friend gave me some upgrade advice that I want to look into this winter. He suggested going to a 52-39 or 37 front chain ring. Currently, I have a 52-42. I would like just one more gear up hills, and I think going to a smaller chainring would make a bigger difference than changing to a different cassette.

Here is the problem. This is a late 80's 6 speed rear cassette with biopace chainrings. I will have to do some searching for the biopace that fits.

Sheldon Brown suggests that a round/Biopace combo doesn't work very well.

Here are the questions:
1. Is it worth replacing with Biopace?
2. Should I just go to a round 52-39?
3. Will I have to adjust the FD or chain length?

If you really have a cassett rather than a freewheel,cuz 6 speed cassettes are history, you cannot do a lot of gear changing there easily. The smallest front you can use with your 130BCD is a 38.A round and a biopaace will work mehanically but your legs may not like the effect.Nothing wrong with a 39 biopace if you can find one.Lots of people just don't like biopace. Nashbar has inexpensive 130BCD rings.Witha samller ring the chain will be ok and the derailer might be too.Friction front derailer adjust is easy anyway.

Cassette... Freewheel... sorry, I am a novice speaking here.

As for the Bolt Circle Diameter, what is the best measurement suggestion. Center of a bolt to the center of the next bolt is 8 cm, which converts on a chart to 110 mm BCD. Also, the Biopace chainrings that are available at the Harris web site and on Loose Screws (http://www.thethirdhand.com) web site only show up for 110 mm BCD.

It is a 5 bolt crank BTW.

BCD,on 5 arm cranks,c of bolt, to c of bolt:64.7mm=110BCD, and 76.4mm=130bcd. Another way on 5 arm cranks is to measure C-C of 2 non adjacent bolts and divide by.951. you said cassette,so I assumed. 6 speed cassette and freewheels look virtually the same.If it's a Shimano freewheel,remove wheel from bike,remove quick release from hub.On the side of the hub where the gears are,and the axel end sticks out,there is a hole around the axel which will have 12 hard to see notches or grooves that a splined removaltool fits into. a 6 speed cassett setup looks virtually identical,but does not have the grooves for a removal tool,because it removes differently.If its a suntour freewheel,there will be 2 or less commonly 4 large notches on the right end of the cogs that a removal tool fits into.

How large is your low gear cog? When I needed an emergency grannie gear on my Bianchi, I kept the 42T inside chainring (my 144mm BCD supports a minimum of 41T) and replaced the 6-speed 13-15-17-19-21-23 freewheel with an equal-width 7-speed, which duplicated the 6 previous gears and added a 26T bailout gear. I very rarely use the 26, but it is reassuring to know it is there, should I either bonk or face a very steep hill.

If you like the Biopace (I don't), just keep them. With a 110mm BCD, you can drop to about a 34T or a 38T ovoid.

On the small end is an 11, I don't know what the large end of the rear is.

I am doing some more looking, and I am not finding a 130 mm 39T chainring. So, it looks like the logical thing to do is to convert to round. So much for retro!

Has anybody converted one of these?

If you are into non-round chainrings, you should check out
http://www.argonet.co.uk/highpath/cycle.htm

Changing out the biopaces is no big deal.Unbolt them and bolt on the new ones.The front derailer will probably need to be repositioned a bit lower.

Hi Iowa,

I just wanted to point out that changing the rear freewheel instead of the chainrings would be...

a. More effective: a change of, say, 3 or 4 teeth in the rear sprocket will have a greater efect on gear ratio than the same change in a chainring -> the minimum size chainring you can fit, as pokey points out, is only 4 teeth smaller than what you are currently running. It would only take a 3 tooth increase in the largest rear sprocket to achieve a similar reduction in gear ratio.

b. Way cheaper: New freewheel ~$30 @ nashbar. I think a 7spd would work fine, too. New round chainrings ~$30 each give or take $10.

c. Retro Orthodox: If that matters to you. Personally, I dig Biopace on the larger chainrings over long distances.

my 2 cents
BK

I have had this problem with 2 6-speed road bikes.
And too, I have had biospace. Re: a posting, above, yes,
the man at that engineering works - argonet.... - tells me
biopace sucks ie. stinks. His oval chainrings are for the
elite! Ie. expensive and not really necessary.
Solutions: For one of my bikes I got Shimano old stock triple,
30.42.52. This was from sjscycles.com here in England and i paid the paltry sum of dollar equiv. c. 18 dollars.

The second bike I am going to stick at deore xt mega derailleur on it, with a large sprocket cassette.
Ps. there is no prob. putting a circular ring ie. non oval ring
on the biopace - you can go down to 39 teeth - available everwhere.
tim parker

i had the same prob. also bio pace , i changed the free wheel cluster, original was 13--21 . replacement 14--28 world of differance !!! no probs with gear changes , in fact better as the new cluster has all the sis ramps & cut outs. i allso have ex-age group set (not the most popular i know, but i have no trouble with that either, the front changer needs to be finely adjusted every now & again if you want to rely on the indexing, due to the changing circ.)im not fussed either way about bio-pace, my cruising cadence is around 100 rpm @ 30kph, i find bio- pace most benificial when pushing a headwind for lengthy periods. im not sure but i think a 42 is the smallest biopace c/ring you can get for a 110 spider but i dont think there made any more, there must be heaps gathering dust in garages .
if you change the rear cluster it would pay to fit a new chain too. be carfull with the length.:thumbup:

[i] im not sure but i think a 42 is the smallest biopace c/ring you can get for a 110 spider .... [/B] What??? try a 38 and possibly smaller.Biopace was also made for the old 110/74 MTB cranksets.

Am I the only one with a 6 speed cassette and nonbiopace? :)

Originally posted by WorldIRC
Am I the only one with a 6 speed cassette and nonbiopace? :) No,but do you have downtube friction shifters with it?:D

Unless you are just dead set on sticking with BioPace, just get a round 38T chainring. Personally I can't stand Bio Pace. I am trying to develop a nice round pedal stroke, and I don't think BP lend themselves to that. At least they don't for me. I have stripped them off the cranks that had them and gone with round.

Harris Cyclery has Rocket Rings with 38T for $17.95 or your LBS can get you an Engagement Ring (a QBP brand) for a little more. Rocket rings are kind of neat because they come with bolt holes for 130 or 110 bolt circle diameter (BCD) spiders.
Just my $.02,
Raymond

Originally posted by pokey
What??? try a 38 and possibly smaller.Biopace was also made for the old 110/74 MTB cranksets.
i bow to your superior knowledge but i did say i wasnt sure :rolleyes: i think the bloke in the lbs just told me that to get me of his case :p