Biopace

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Holdsworth

Holdsworth

Guru
Location
Crewe, Cheshire
My roadie formerly had a double Shimano Exage Biopace chainset until some numpty at the LBS stripped the thread on one of the crank arms earlier in the year. That made me purchase a new Sunrace chainset which is all the another LBS sold. I believe that my new chainset has a smaller big ring (50T) than my Biopace which I think came in 52/42 size but I am not sure about that. I preferred the range given by the BP setup, the top speed was higher although I never did any big climbs with the small ring.

Another reason that I'd be looking at going back to BP is that there don't seem to be many chainset for a reasonable price with a larger big ring and that fit a square-taper BB.

There are a few on eBay that I wish to purchase but I want to know that I would be getting the right one. Did Shimano every make more than one size of Biopace chainrings? There are some triples about and a few from the Ultegra range which may or may not differ from my 90s model.
Unfortunately I no longer have my chainset to hand to get precise details as the LBS took it off me for scrap back in March/April.
 
Alembicbassman

Alembicbassman

Confused.com
Biopace was a non-round chainset designed to give a more even power transfer when pedalling (good in theory, but for most riders it didn't make any difference). They made both MTB and road bike versions, they are not available as a compact 30/50 etc.. I had a 39/52 Exage 300 on a 90s road bike, the bolt circle diameter is 138 I think so the theoretical smallest is a 38t unless you fit an MTB triple. but you may need to swap out the bottom bracket and which means more searching for the correct size.

This is a square taper 39/52 set http://www.rosebikes.co.uk/article/shimano-crankset-fc-2300/aid:417040

1506750_1.jpg
 
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Holdsworth

Holdsworth

Guru
Location
Crewe, Cheshire
I first had no clue what Biopace meant until months after I bought the bike. The thing that clocked it for me was the weird feeling of going uphill in the smaller ring and seeing an oval shape instead of round when I inspected that area. Whether or not it had any effect on my performance I'll probably never know but it certainly didn't hold me back.

I however now more confused than ever about the best gearing for my bike after playing around with Sheldon's gear calculator page. First thing to note is that with my current setup I have a really low top gear of 93.9 gear inches (kinda knew this already), low compared to what he says is normal for a road bike (110 or so). This may be both in part to the smaller large chainwheel and also the comparatively large high gear on my bike (14t), unfortunately I can only get a smaller cog by replacing my wheel or hub with a cassette rather than a freewheel.
Second thing is that there a massive gap between my two most used ratios (34/20 and 50/22) of 15 gear inches. The former is my slow speed a pootling gear but I am often found comfortably spinning in the top range and on the verge of changing up on the rear. But since the 20t cog is 4th I do not want to go into a smaller gear without going into the big ring as the chain will rub on the front dérailleur. I could adjust the FD so tat it doesn't rub but I have no idea if the line of the chain will be acceptable. Furthermore I need to double shift to maintain a comfortable cadence which is still tricky as even with a double shift I still feel a lot of strain when down-shifting. This could be more comfortable if I went into 34/18 (5th) and then from there to 50/22 but again the chain line issue and having to shift up 2 cogs at the back at once whilst going up at the front.

The difference in ratios is lessened with the 52/39 chainset you linked to with a comparatively small 10.9 gear inch gap. Still with the larger small ring I have the issue of gearing up all of my low ratios which may have an impact on hill climbing. There is little chance of an upgrade to the rear freewheel for reasons explained above. Also I do not think my RD will accept a larger cog, 28t seems its limit.

Gah!!! So confusing :wacko:
 
Alembicbassman

Alembicbassman

Confused.com
I ran a 38/52 on my old steel bike with a 13-26 8 speed cassette, found it fine for anything but the steepest hills.

My Raleigh has a 34/50 with 12-25 10 speed, but I find I'm swapping between chainrings too often

You may be able to swap your small ring for a 36 or 38 ring without changing the whole crankset. Spa Cycles sells a range of separate rings for £10 upwards
 
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Holdsworth

Holdsworth

Guru
Location
Crewe, Cheshire
I don't think i was fobbed off as such, rather just supplied with what they had in.

AlemBB, would any of the small rings that Spa Cycles sell be compatible with my chainset or do I need to go a Sunrace-branded one to match?

Then again I could get an entirely new chainset, either the Sunrace one or the Shimano double linked to earlier. The addition of a 39 ring would probably mean less down-shifting and less of a gap between rations when doing a double shift.
 
youngoldbloke

youngoldbloke

The older I get, the faster I used to be ...
When buying new chainrings it is important to know the BCD# of your chainset - if it is a compact I would think it is 110mm - and then order 110mm rings as required. (I have a Biopace chainset on my winter bike and have replaced the 'oval' Shimano rings with 'normal' ones from Spa Cycles).
# 'Bolt Circle Diameter'
 
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