Technical query, RSX/Sora rear mech



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Martinm

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My old RSX rear mech has finally given up the ghost. I have ordered a short reach Sora as a
replacement but it says in the blurb, max chainring 27T. Is this due to clearance or just an
arbitrary figure to do with chain length? My current set up with the RSX is 47/39 on the front and
13-28 on the back. The 28 was a cop out to avoid the hassle of going to a triple.
 
"MartinM" <[email protected]> wrote in message
news:[email protected]...
> My old RSX rear mech has finally given up the ghost. I have ordered a short reach Sora as a
> replacement but it says in the blurb, max chainring 27T. Is this due to clearance or just an
> arbitrary figure to do with chain length? My current set up with the RSX is 47/39 on the front and
> 13-28 on the back. The 28 was a cop out to avoid the hassle of going to a triple.

As I remember it Sora has a slightly bigger diameter jockey wheel than RSX.

So I tink you be stuffed, it certainly buggered my 28. Don't forget chain length isn't really
relevant because you will be on the small front chain wheel.

Although you can take the jockey off the RSX and put it on the sora.

Mind you I did have long reach rear mechs.
 
MartinM wrote:
> My old RSX rear mech has finally given up the ghost. I have ordered a short reach Sora as a
> replacement but it says in the blurb, max chainring 27T. Is this due to clearance or just an
> arbitrary figure to do with chain length? My current set up with the RSX is 47/39 on the front and
> 13-28 on the back. The 28 was a cop out to avoid the hassle of going to a triple.

It's to do with clearance to the sprocket but chain length does affect this as it can pull mech away
from the sprocket. Shimano's (and Campag's) figures are conservative - you can often push them a
bit. It helps to keep chain as short as possible for the big-big (47x28) and screw in the b-tension
screw. The screw can even be replaced for a longer one as a last-resort bodge.

Dozens/hundred's of users on rec.bicycles.tech say they've used their "27T" mechs with larger
sprockets with no problems. (I've personally exceeded the specs with Campag mechs but not
Shimano's).

~PB
 
MartinM wrote:
> My old RSX rear mech has finally given up the ghost. I have ordered a short reach Sora as a
> replacement but it says in the blurb, max chainring 27T. Is this due to clearance or just an
> arbitrary figure to do with chain length? My current set up with the RSX is 47/39 on the front and
> 13-28 on the back. The 28 was a cop out to avoid the hassle of going to a triple.

I have not exceeded the range on rear mechs, I have on front with no problems, by 1 tooth is worth a
try but I wouldn't try to shift to a 30 or
32.

You could always fit a mountain bike rear mech that will shift to 32 and 34 toothed sprockets.

--
The Reply & From email addresses are checked rarely. http://www.mseries.freeserve.co.uk
 
I wrote:

> Dozens/hundred's

That's one for Lynne Truss.

~PB
 
"MSeries" <[email protected]> wrote in message news:<[email protected]>...
> MartinM wrote:
> > My old RSX rear mech has finally given up the ghost. I have ordered a short reach Sora as a
> > replacement but it says in the blurb, max chainring 27T. Is this due to clearance or just an
> > arbitrary figure to do with chain length? My current set up with the RSX is 47/39 on the front
> > and 13-28 on the back. The 28 was a cop out to avoid the hassle of going to a triple.
>
> I have not exceeded the range on rear mechs, I have on front with no problems, by 1 tooth is worth
> a try but I wouldn't try to shift to a 30 or
> 32.
>
> You could always fit a mountain bike rear mech that will shift to 32 and 34 toothed sprockets.

Thanks for all the advice. Yes the big jockey wheel was what got me thinking. The jockey wheels are
completely shagged on my RSX, one reason I'm replacing it.Actually my set up is not quite a 13-28, I
was given a 28 rear cog and took apart my 13-23 HG50 cassette to give me an granny gear for those
big hills (works fine on the way down but changing from 28 to 21 is quite a shock). This is the
problem when they have stopped making 7 speed cassettes, relying on old stock. A _real_ MTB rear
cassette is hopeless, far too big difference between gears for road use. Perhaps I should just put
the 23 back and stop being such a wimp ;-)
 
"MartinM" <[email protected]> wrote in message
news:[email protected]...
> "MSeries" <[email protected]> wrote in message
news:<[email protected]>...
> Thanks for all the advice. Yes the big jockey wheel was what got me thinking. The jockey wheels
> are completely shagged on my RSX, one reason I'm replacing it.Actually my set up is not quite a
> 13-28, I was given a 28 rear cog and took apart my 13-23 HG50 cassette to give me an granny gear
> for those big hills (works fine on the way down but changing from 28 to 21 is quite a shock). This
> is the problem when they have stopped making 7 speed cassettes, relying on old stock. A _real_ MTB
> rear cassette is hopeless, far too big difference between gears for road use. Perhaps I should
> just put the 23 back and stop being such a wimp ;-)

You could buy a repalcement small diameter jockey wheel for the RSX or Sora. Or you could buy an mtb
mech. There will be no need to use an mtb cassette simply because you've got an mtb mech. The
difference with an mtb mech is not only the longer cage which takes up slack chain, of which there
is more with wider range gears, but also the body is longer to keep the top jockey from clouting the
bigger sprockets.
--
Pete http://uk.geocities.com/[email protected]/Playtime.html
 
"Peter B" <[email protected]> wrote in message news:<[email protected]>...
> "MartinM" <[email protected]> wrote in message
> news:[email protected]...
> > "MSeries" <[email protected]> wrote in message
> news:<[email protected]>...
> > Thanks for all the advice. Yes the big jockey wheel was what got me thinking. The jockey wheels
> > are completely shagged on my RSX, one reason I'm replacing it.Actually my set up is not quite a
> > 13-28, I was given a 28 rear cog and took apart my 13-23 HG50 cassette to give me an granny gear
> > for those big hills (works fine on the way down but changing from 28 to 21 is quite a shock).
> > This is the problem when they have stopped making 7 speed cassettes, relying on old stock. A
> > _real_ MTB rear cassette is hopeless, far too big difference between gears for road use. Perhaps
> > I should just put the 23 back and stop being such a wimp ;-)
>
> You could buy a repalcement small diameter jockey wheel for the RSX or Sora. Or you could buy an
> mtb mech. There will be no need to use an mtb cassette simply because you've got an mtb mech. The
> difference with an mtb mech is not only the longer cage which takes up slack chain, of which there
> is more with wider range gears, but also the body is longer to keep the top jockey from clouting
> the bigger sprockets.

Thanks, but I'm a bit wary about changing the set up too much. A triple is probably the way to go. I
could get a 26 to replace the 23.
 
"MartinM" <[email protected]> wrote in message
news:[email protected]...

>
> Thanks, but I'm a bit wary about changing the set up too much. A triple is probably the way to go.
> I could get a 26 to replace the 23.

A 26 Should be Ok. There are only a few hills that really require more.

Mind you I will definitely get a triple on my next road bike.
 
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