chain rub while sprinting, Ti frame

[Claus Assmann]

According to my searches of the archives of this newsgroup, it means
that a frame is not very stiff if the chain rubs against the front
derailleur when you get out of the saddle and accelerate hard. So
far I thought this would happen only with cheap frames or very
strong/heavy riders, but it happened to me while test riding a
Serotta Concours CS. I weigh only 60kg (175cm) and I am certainly
not a good sprinter. This (demo) bike is equipped with a Chorus
triple, which, according to the bicycle dealer, would contribute
to that chain rub. Someone else told me that a Ti frame would simply
not be very stiff. Would this apply to the Concours CS? I have a
Serotta Atlanta (steel frame) and can't get the chain to rub against
the derailleur by sprinting when using this bike.

 

[Robert]

Claus Assmann wrote:
> According to my searches of the archives of this newsgroup, it means
> that a frame is not very stiff if the chain rubs against the front
> derailleur when you get out of the saddle and accelerate hard. So
> far I thought this would happen only with cheap frames or very
> strong/heavy riders, but it happened to me while test riding a
> Serotta Concours CS. I weigh only 60kg (175cm) and I am certainly
> not a good sprinter. This (demo) bike is equipped with a Chorus
> triple, which, according to the bicycle dealer, would contribute
> to that chain rub. Someone else told me that a Ti frame would simply
> not be very stiff. Would this apply to the Concours CS? I have a
> Serotta Atlanta (steel frame) and can't get the chain to rub against
> the derailleur by sprinting when using this bike.
>

This could be caused by so many things, the most basic being the
distance between the derailleur fork and the chain. If the distance is
already minimal prior to loading, then just about any
frameset/crankset/BB combination will cause some rub.

I think the most extreme example of frame flex I experienced was with my
Alan frame from about 1981, whose delivery, apart from a very pretty red
frame and fork, included a phenomonon known as "phantom shifting" if
you kicked hard enough.

Those days of frame flex seem to be over now . . .

/Robert

 

[jim beam]

Claus Assmann wrote:
> According to my searches of the archives of this newsgroup, it means
> that a frame is not very stiff if the chain rubs against the front
> derailleur when you get out of the saddle and accelerate hard. So
> far I thought this would happen only with cheap frames or very
> strong/heavy riders, but it happened to me while test riding a
> Serotta Concours CS. I weigh only 60kg (175cm) and I am certainly
> not a good sprinter. This (demo) bike is equipped with a Chorus
> triple, which, according to the bicycle dealer, would contribute
> to that chain rub. Someone else told me that a Ti frame would simply
> not be very stiff. Would this apply to the Concours CS? I have a
> Serotta Atlanta (steel frame) and can't get the chain to rub against
> the derailleur by sprinting when using this bike.
>
first, check for derailleur adjustment, but bottom line, yes, this frame
could be flexing. quickly looking online, the concours doesn't appear
to have oversize tube, something i consider essential to lower modulus
materials like ti & aluminum.

 

[Mark Hickey]

Claus Assmann
<ca+sendmail(no-copies-please)@mine.informatik.uni-kiel.de> wrote:

>According to my searches of the archives of this newsgroup, it means
>that a frame is not very stiff if the chain rubs against the front
>derailleur when you get out of the saddle and accelerate hard. So
>far I thought this would happen only with cheap frames or very
>strong/heavy riders, but it happened to me while test riding a
>Serotta Concours CS. I weigh only 60kg (175cm) and I am certainly
>not a good sprinter. This (demo) bike is equipped with a Chorus
>triple, which, according to the bicycle dealer, would contribute
>to that chain rub. Someone else told me that a Ti frame would simply
>not be very stiff. Would this apply to the Concours CS? I have a
>Serotta Atlanta (steel frame) and can't get the chain to rub against
>the derailleur by sprinting when using this bike.

In general, titanium bikes that "look like steel bikes" will tend to
have a lot more flex than a typical steel bike. I can say with great
certainty that it's quite possible to build a titanium frame that
flexes less than most frames (and that can handle riders MUCH larger
than you without chain rub). They just don't look like steel bikes.

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $795 ti frame

 

[[email protected]]

Claus Assmann (no-copies-please) wrote:
> According to my searches of the archives of this newsgroup, it means
> that a frame is not very stiff if the chain rubs against the front..<snip>

Other replys aside I've seen the same thing caused by stupid light
aftermarket cranks and Bottom Brackets ..

 

[Qui si parla Campagnolo]

Claus Assmann (no-copies-please) wrote:
> According to my searches of the archives of this newsgroup, it means
> that a frame is not very stiff if the chain rubs against the front
> derailleur when you get out of the saddle and accelerate hard. So
> far I thought this would happen only with cheap frames or very
> strong/heavy riders, but it happened to me while test riding a
> Serotta Concours CS. I weigh only 60kg (175cm) and I am certainly
> not a good sprinter. This (demo) bike is equipped with a Chorus
> triple, which, according to the bicycle dealer, would contribute
> to that chain rub. Someone else told me that a Ti frame would simply
> not be very stiff. Would this apply to the Concours CS? I have a
> Serotta Atlanta (steel frame) and can't get the chain to rub against
> the derailleur by sprinting when using this bike.

A friend of mine got rid of his Serotta Legend for this reason. Serotta
'can' make the frame with bigger diameter tubes, to make it
stiffer...the groupset has NOTHING to do with this issue...bike shop
dealer just wants to sell ya something...Look at Moots, Seven...way
before Serotta..IMO-

 

[Phil Lee, Squid]

Mark Hickey wrote:
> Claus Assmann
> <ca+sendmail(no-copies-please)@mine.informatik.uni-kiel.de> wrote:
>
>> According to my searches of the archives of this newsgroup, it means
>> that a frame is not very stiff if the chain rubs against the front
>> derailleur when you get out of the saddle and accelerate hard. So
>> far I thought this would happen only with cheap frames or very
>> strong/heavy riders, but it happened to me while test riding a
>> Serotta Concours CS. I weigh only 60kg (175cm) and I am certainly
>> not a good sprinter. This (demo) bike is equipped with a Chorus
>> triple, which, according to the bicycle dealer, would contribute
>> to that chain rub. Someone else told me that a Ti frame would simply
>> not be very stiff. Would this apply to the Concours CS? I have a
>> Serotta Atlanta (steel frame) and can't get the chain to rub against
>> the derailleur by sprinting when using this bike.
>
> In general, titanium bikes that "look like steel bikes" will tend to
> have a lot more flex than a typical steel bike. I can say with great
> certainty that it's quite possible to build a titanium frame that
> flexes less than most frames (and that can handle riders MUCH larger
> than you without chain rub). They just don't look like steel bikes.

I should get a picture of a 6'7" 230-lb rider in my college town. He
specified 2" top and down tube diameters on his XACD custom 62-64 cm Ti
frame. Gigantic. Light. Definitely doesn't look like steel.

--
Phil Lee, Squid