bottom bracket sway on indoor trainer
hoffman
response so I'll just repeat it because this problem
is driving me nuts.
I started using an indoor bike trainer (not the "rollers" type)
which I picked out of my neighbors garbage (how nice of him
to throw out a perfectly good $150 Performance brand trainer).
Anyway, when I ride this thing it gets me nervous because
I see my bottom bracket sway quite alot. I also have to leave
the bike in a rather low gear; if I try to switch to a high gear
52 x 11-16 the extra force required to pedal just makes
the BB sway very badly.... If I had a metal bike, especially
steel (which is a very ductile & fatigue resistant metal) I could
care less about the BB sway... but since I have a rather
old carbon fiber bike (old carbon fiber bikes are notoriously
over-flexible) I'm afraid I might snap the frame..
Is it normal to observe a little sway in the BB?
Another question... Since I did not have the directions to
this unit, I am not even sure I have my biked properly
hooked-up to the trainer. The trainer has 2 clamps
which are supposed to attach to the back wheel..
I assume (?) that you were just supposed squeeze this
clamp very very tightly against each side of your quick release
skewer... Is that correct? I have the feeling that your not
supposed to attach these clamps to your own QR skewers,
but rather maybe the trainer comes with some kind of
special skewer which you are supposed to replace into your
rear hub that fits more snugly into the trainers back wheel
clamps.. If you can help me out it would be appreciated.
Cameron Vaughan
My bottom bracket sways a good bit when I am pushing big gears or standing.
It used to worry me quite a bit, but after three years I have learned to
ignore it. My steel bike does not appear to be suffering from the sway. I
don't know what to tell you about carbon fiber frames.
The directions say to tighten the rear end two complete turns after making
contact with the quick release nut. Two turns does not seem tight enough to
me, I usually give mine three complete turns. If you really crank down on
it you can see the rear triangle squeeze. You just want it tight enough
that if you lean on the bike (while reaching for the remote) it won't come
loose.
Mine didn't come with a special nut or axle. However, the cheesy plastic
nut on my Shimano QR was getting pretty scraped up from the trainer. I
picked up a really beefy looking nut from the LBS and use that instead. In
the winter time I just leave it on the bike and put the light weight one
back on in the spring.
hoffman wrote in message
<01be1879$95ff5280$f5ab...@northeast.northeast.net>...
M. Marletta
Most people I know get a cheap and nasty quick
release skewer for trainer use, to save their
good skewers from being chewed up.
I use an old Reynolds 531 bike in my trainer
and it flexes a lot at the bottom bracket.
This is not what one needs to worry about, since
there is that much flex at the bottom bracket
in regular use. What you have to worry about is
possible additional stress on the rear triangle,
which is not normally fixed in a clamp while
riding. Of course the fact that you have a back
wheel installed and tightened securely means that
the whole back end of the bike forms a very strong
structure, just by virtue of its geometry - that,
after all, is why the rear triangle can be made of
small diameter tubes, while the main triangle uses
much bigger tubes.
My guess, therefore, is that your bike is safe.
However you may want to have another look in your
neighbour's trash to see if he has an old steel
frame in there....weight is hardly an issue on
the trainer!
Marco
.
Anna Delfin
hoffman skrev:
....
> Anyway, when I ride this thing it gets me nervous because
> I see my bottom bracket sway quite alot. ....
> Is it normal to observe a little sway in the BB?
> ....
> I have the feeling that your not
> supposed to attach these clamps to your own QR skewers,
> but rather maybe the trainer comes with some kind of
> special skewer which you are supposed to replace into your
> rear hub that fits more snugly into the trainers back wheel
> clamps.. If you can help me out it would be appreciated.
I ride a trainer from Tacx with my steel bike. I have noticed that the
bottom bracket sway a lot as well. At least I think 1 cm is a lot for a
steelframe. I have also heard that steel frames can get cracks from this
type of use.
My trainer came with a special QR skewer, that fitted in the clamps on
the trainer. But I also use some of my other skewers. Just as long as I
get a god fit in the clamps I have not had any problems with it. My old
trainer, bought 8 years ago did have the same clamping system but didn't
come with a special skewer. So I guess it isn't a big deal.
I hope this helps.
/ Anna
Johan Bornman
Anna, the BB sways just as much when you're pedalling on the road. The
difference is that on the road your bike sways and your line of sight on the BB
is constantly altering, giving you the illusion that the BB is static in
relation to the frame's central line. Compounding that illusion, is the fact
that you can't really stare at your BB for long times at end without crashing
and on the trainer, you have a permanent frame of reference.
1CM flex isn't much for a steel frame but what really matters is whether the
chain rubs on the front deraileur during flex.
BTW, you can compare on-trainer flex with road flex by looking at the front
deraileur, if it doesn't rub on the trainer, the flex is similar in both
instances.
Johan Bornman