Frame Flex - Durability?
Discussion
This morning I was reading the 2012 Pinarello Brochure, and was intrigued by the suggestions in it. Apparently a top end sprint cyclist can put out up to 1500w of energy when out of the saddle, and can cause the frame to flex up to 5mm in one direction and 2mm in the other (apparently unbalanced due to the chain being on one side).
This set me thinking. Ultimately the flex can be over a range of 7mm.
How does this affect durability of the frame? Over time would you end up with stress fractures or weak points in the frame (especially in metal frames where you could get metal fatigue). Or would it take so long to become seen as to be irrelevant for the normal cyclist?
This set me thinking. Ultimately the flex can be over a range of 7mm.
How does this affect durability of the frame? Over time would you end up with stress fractures or weak points in the frame (especially in metal frames where you could get metal fatigue). Or would it take so long to become seen as to be irrelevant for the normal cyclist?
Track sprint frames are significantly different to road sprint frames, but generally speaking professional riders will be given 3 or 4 bikes for a seasons racing and then give them back at the end so long term durability is not really an issue.
Mere mortals won't get anywhere near that sort of power output
Mere mortals won't get anywhere near that sort of power output
I don't agree with that, itsnotarace.
Loads of club riders can get out 1500w, and they keep their bikes for years, so obviously it doesn't cause an immediate issue. The flex is more noticeable in the wheels than the frame though, and if they flex into the brake blocks then they slow you down too!
Loads of club riders can get out 1500w, and they keep their bikes for years, so obviously it doesn't cause an immediate issue. The flex is more noticeable in the wheels than the frame though, and if they flex into the brake blocks then they slow you down too!
Nothing to do with the fact they want to sell you one of their frames which miraculously don't flex to the same degree no doubt?
All a load of marketing chat. I have put 1500w through my Cervelo on many occasions and not had anything noticeable from anything other than the bars and the wheels. (I'm just a club rider, many people can put out that wattage)
All a load of marketing chat. I have put 1500w through my Cervelo on many occasions and not had anything noticeable from anything other than the bars and the wheels. (I'm just a club rider, many people can put out that wattage)
okgo said:
Nothing to do with the fact they want to sell you one of their frames which miraculously don't flex to the same degree no doubt?
All a load of marketing chat. I have put 1500w through my Cervelo on many occasions and not had anything noticeable from anything other than the bars and the wheels. (I'm just a club rider, many people can put out that wattage)
Well it does detail quite deeply how the shape of the frame is altered asymmetrically to take account of the flex and dial it out.All a load of marketing chat. I have put 1500w through my Cervelo on many occasions and not had anything noticeable from anything other than the bars and the wheels. (I'm just a club rider, many people can put out that wattage)
I guess also that by eliminating flex it means more power goes to the road rather than into the flex, thus giving fractionally better performance.
daz3210 said:
Well it does detail quite deeply how the shape of the frame is altered asymmetrically to take account of the flex and dial it out.
I guess also that by eliminating flex it means more power goes to the road rather than into the flex, thus giving fractionally better performance.
Yes, no doubt trying to justify those stupid bends they put in their frames. (in my opinion of course).I guess also that by eliminating flex it means more power goes to the road rather than into the flex, thus giving fractionally better performance.
You won't eliminate that flex, and as I said, even if you did, the other stuff you attach to the frame will flex anyway.
When microseconds count, maybe its worth deciding your bike purchase on the mm of flex, but for mere mortals (even ones who can put out mentioned power) it's just marketing spiel.
The way it reads it does eliminate flex.
As an example the chain-stays taper, but the left side tapers in the opposite direction to the right. It also mentions that it is easier to stop the flex in carbon frames - probably another marketing attempt to make people buy more expensive carbon frames I guess.
As an example the chain-stays taper, but the left side tapers in the opposite direction to the right. It also mentions that it is easier to stop the flex in carbon frames - probably another marketing attempt to make people buy more expensive carbon frames I guess.
Pina make some great framesets but are full of PR crap: they claim the Dogma models weighs X grams, a fantastically low weight, but what they don't mention is that doesn't include BB shell, headset races, bottle boss inserts, paint, dropouts... Also the forks are very heavy.
The weight of a frame isn't a massive deal in the grand scheme of things but the stuff they come out with makes them look a bit silly IMO. Take everything their blurb tells you with a pinch of salt.
The weight of a frame isn't a massive deal in the grand scheme of things but the stuff they come out with makes them look a bit silly IMO. Take everything their blurb tells you with a pinch of salt.
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