Bicycle Mechanics - Strength vs. Frames

I've noticed while putting miles on my trainer while sitting on my road bike that I can flex the frame quite a bit by simply pedaling. Being new to the whole road bike thing, is this normal or something that should concern me?

Most bikes will have some flex in them. Some more then others. I have never used a trainer so i do not know how much a bike will flex on one but I do know that all the road bikes I have ever owned always flexed when pedaling. I would assume that it would flex more since the rear wheel is locked in place where as on the road it may move from side to side.
I do not think you need to worry.

Slainte:beer:

Originally posted by dirtbikedude
[B....... but I do know that all the road bikes I have ever owned always flexed when pedaling.

Slainte:beer: [/B]You must be a gorilla or never rode a Cannondale or a Klein aluminum framed bike.That's the short list.

This is an aluminum frame and that is what bothers me outside of my being a gorilla.

I've been riding Cannondale MBs for thirteen years and I've never seen anything flex like this. I just worry that I'll pull it apart whilst riding.

Being 6'2" and 275lbs I tend to flex frames realy easy. Especialy when climbing.
I would not worry about the frame braking on you while riding. I have had my alloy frames flex so that the large chain ring hits the chain stays and the frames have yet to brake.
If it does concern you alot then i would just say make sure to always spin the pedals smoothly.

I would not worry.

Slainte:beer:

Merci!

I recently read an article, forgive me, but I cannot remember where, written by bike shop owner who also was a Custom titanium frame-builder. He received a lot of complaints regarding the amount of flex in the frames he made.
So he went about doing tests, to determine where the frames could be stiffened to produce a better ride.
He claimed that after doing many tests, and also checking Steel and AL frame-sets, that his frames were actually stiffer than steel frames from a few years back, but the "flex" was actually attributed to all the lightweight components on the bicycle, mostly the wheels handle bars and stem.
But, seeing that on a trainer, the wheel is held at the axle, which isolates the rear wheel from the equation…
The flex must be coming from the stem, handlebars or front wheel / fork, if his theroy about the frames is correct in your case too.
But hey, this is good in a way, you can work on keeping your upper body quiet. And ride like Lance, Knees down… till you need the power!

Some frames are more noodly than others. I have a Cannondale touring bike, with big, massive stays and tubes-this bike hardly flexes at all. OTOH, I have a 25-year old Trek steel frame (Reynolds 531, silver brazed), and it's really flexy. Both frames are about 62cm in size. The Trek frame is about as light a steel frame as you can get in that size, too.

Bike frames flex alot more on trainers, thats my experience. Don't know if its a problem or not, it certainly made me think a few times though. If it bothers you buy a beater to use in the trainer.

DonTx - you have the right idea - get a beater bike.
Actually, trainers are very hard on the bike in 2 areas;
(a) Sweat + Steel = Rust
(b) Headset - since the front end of the bike does not move much(assuming not rollers), the headset remains fairly static and I have heard of the bearings seating themselves into the headset, whereby after a winter in the garage, the headset needs to be replaced before getting back onto the open road. This is an especially difficult situation with the new integrated headsets.

Anyway, back to the topic...the frames flex mainly in the bottom bracket area. In the olden days (mid 1980's) frame builders used to braze in an extra supporting piece right behind the bottom bracket - this really helped stiffen the frames. As lightness became the craze, they eventually stopped including these reinforcers, therefore, modern frames do flex more. Get an old beater bike to use - the heavier the better.

I have as well recently aquired a trainer. I noticed the oodles of flex at the BB and downtube on my Specialized Allez even during smooth in the saddle sprints. Nearly half an inch. I went and talked to my boss at the bike shop I work at and though he said that yes, the trainers do put more stress on the bike than regular riding, the stress is neglidable. The flex that you see on a trainer is happening to a lesser extent while you are riding but you can't see it because you are moving. About the headset though, that does make sense, but the "seating" can probably be avoided just by turning your wheel back and forth every couple of minutes while you are on the trainer. Besides you always see the pros warming up on trainers before a race. The frames may not be held as dear to them as our bikes are to us, but still, I highly doubt their coaches would have them warm up on the bike they will race with on a trainer if it had the possibility of causing much more dammage than regular riding.