On 2017-06-15 15:42, James wrote:
On 15/06/17 23:28, Joerg wrote:
On 2017-06-14 19:08, James wrote:
On 15/06/17 08:33, Joerg wrote:
On 2017-06-14 15:28, James wrote:
On 15/06/17 06:31, Joerg wrote:
On 2017-06-13 19:09, John B. wrote:
In a recent discussion I suggested changing from the old square
tapered BB to a modern Shimano outboard bearing bracket. The
argument
was that this would destroy the perfect chain line of the original
three piece BB.
Now, I have changed back and forth between the original square
tapered
axle to the outboard bearing BB and to my recollection the chain
line
didn't seem to change noticeably.
Over the weekend we took a trip "up country" to visit some of my
wife's relatives and as we used my wife's car she drove. It is about
250 Km, one way, so I had a lot of time to think abut things and one
of the things I thought about was how could I change bottom brackets
with no appreciable difference in chain line.
This morning I turned one of my bikes bottom up and did some
measuring
and it turns out that with the old fashioned three piece BB there is
slightly over 10mm clearance between the inner edge of the crank arm
and the outer edge of the BB. The outboard bearing "flanges"
measured
12mm in thickness and the old sty;e BB flange is `1mm..
Thus the changing from the old style to the more modern BB
results in
very little, if any, difference in chain line. Certainly less then
the
difference between two cogs on the cassette.
Granted that bicycles are all different but the above does explain
why
I, after switching from one type to the other, and back again, have
seen no noticeable difference in chain line.
The discussion you were referring to was about Shimano 600 gear
which is
what I have on my road bike. The clearance from the inner edge of the
drive side crank to the outer surface of the BB is 3mm. Now assume
your
12mm measurement minus the 1mm that the regular cartridge BB has.
That's
already 11mm of chain line offset. A lot. You could reduce the
clearance
to 2mm but that much wiggle room you really need for square taper and
that would still leave you with a chain line 10mm off from where it
was.
On my previous frame, I migrated from Campagnolo square tapered BB &
cranks to Campagnolo outboard bearing BB assy, and the chain line
didn't
shift 10mm.
Did you buy new cranks? If not, was there sufficient clearance to make
up for the added millimeter of the outboard bearing? On my bike there
isn't.
Is there an outboard BB bearing assembly that uses a square tapered
axle?
I don't know. I bought a Campag Ultra Torque crank & BB assy back in
2007-8. I've replaced the bearings once, about 5 years ago. No bearing
slop noticeable yet.
Sure, if you buy matching cranks it's all fine. However, in the
referenced thread it was not the objective to throw away a perfectly
good set of cranks just because of a new BB.
Five years is good but that depends on how many miles you put on, the
amount of uphill sections and whether you usually spin or mash.
In recent years I raced A grade veterans (over 35) and generally ride
over 10,000km per year. I often head for the hills. I use 175mm cranks
and my cadence is usually around 90 on the flat and less while climbing.
Where I live now, a gentle hill is 5%, and most are up around 10%.
My cadence is lower but yes, that is certainly hard use.
I don't think you could claim I give the BB an easy time. I used to
kill square taper cartridge BBs within a season - Shimano and Campagnolo.
Same here, one year used to be it for BBs. This one I rode longer but I
pushed it well past the point where others would call it shot. Where you
had to trim the front derailer when shifting more than one cog in back
because of the chain ring sway. Without friction shifters I couldn't
have kept using it.
Why do you think you are special?
See above. There simply is no room for another 11mm without the crank
moving at least 10mm outward. Naturally, the goal was to keep the
Shimano 600 cranks. Installing a UN55 internal cartridge bearing
allowed
me to do that and so that is what I did.
So you think you're special because you want to keep cranks that aren't
compatible.
I am not special but among the people who wish not to belong to a
throw-away society.
Good luck.
Not needed. I received the new BB a while ago, installed it and all is
well. Cost me all of $20.
As I said, good luck. It will last a long time if you don't use it.
You think the UN55 BBs aren't up to snuff? From what I read it should
hold up quite well. It is heavy which is one reason why some pros
frowned a bit but weight is of no concern to me.
--
Regards, Joerg
http://www.analogconsultants.com/