What rear derailleur will fit?

[Alex Graham]

Hi everyone

I have a fairly cheap racer with a 7 speed freewheel and a shimano acera rear mech with sora double
shifters. its a 52/39 chainwheel I seem to remember.

The shifting to anything except the smallest 3 or so rear sprockets isnt fantastic - I have to puch
the lever a bit further to make it change up to a bigger sprocket. Is this the cheapo mech or the
gear shifters at fault? If I buy a 105 or Tiagra rear mech (which are fairly cheap) will it improve
my shifting at all or do the sora levers limit it?

Also if I buy an 8 speed 105 or tiagra rear mech will it still work on my 7 speed freewheel? I will
upgrade to a cassette later... Would even a 9 speed work (that would allow for some upgrades)?

cheers,

--

-Alex

----------------------------------
[email protected]

http://alexpg.ath.cx:3353/cycling/ http://www.westerleycycling.org.uk
----------------------------------

 

[George F. Johns]

I've replaced the rear derailleur on older bikes with newer 105 or LX der's and was amazed by the
improvement even when retaining the old shifters and freewheels. They virtually eliminate the need
to overshift. Any newer der (with proper chain wrap-up) will work. Can't really comment on the Sora
shifters since I've never used them but I suspect the problem is entirely with the derailleur.

George F. Johnson

 

[Sheldon Brown]

Alex Graham wrote:
> Hi everyone
>
> I have a fairly cheap racer with a 7 speed freewheel and a shimano acera rear mech with sora
> double shifters. its a 52/39 chainwheel I seem to remember.
>
> The shifting to anything except the smallest 3 or so rear sprockets isnt fantastic - I have to
> puch the lever a bit further to make it change up to a bigger sprocket. Is this the cheapo mech or
> the gear shifters at fault?

Most likely not. The symptoms you describe are most commonly the result of friction in the cable
system, or poor adjustment of the rear derailer (especially the "B-tension" screw.

See: http://sheldonbrown.com/derailer-adjustment.htm

and: http://sheldonbrown.com/cables.htm

> If I buy a 105 or Tiagra rear mech (which are fairly cheap) will it improve my shifting at all or
> do the sora levers limit it?

Probably not. All Shimano rear derailers use basically the same geometry, and shift about
equally well.

> Also if I buy an 8 speed 105 or tiagra rear mech will it still work on my 7 speed freewheel? I
> will upgrade to a cassette later... Would even a 9 speed work (that would allow for some
> upgrades)?

Yes. The derailers don't care how many speeds, that's only an issue for the rear shifter and
cassette. (Also the chain, in the case of 9-speed systems.)

Sheldon "Adjust, Don't Replace" Brown +----------------------------------------+
| When I am grown to man's estate | I shall be very proud and great, | And tell the other girls
| and boys | Not to meddle with my toys. | -R. L. Stevenson |
+----------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone
617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

 

[Alex Graham]

Thanks for the info.

So would a 9 speed 105 rear mech work with my normal chain and 7 spd freewheel and sora shifters?
It seems to me that would be a sensible futureproof upgrade. Also when it says 29T capacity or
whatever the short arm 105 is, does that mean the biggest sprocket the mech will reach is a 29T?
Presuming my freewheel comes within the capacity of the 105 short arm is that the one I should go
for over the long arm?

Cheers,

-Alex

On Sun, 9 Feb 2003, Sheldon Brown wrote:

> Alex Graham wrote:
> > Hi everyone
> >
> > I have a fairly cheap racer with a 7 speed freewheel and a shimano acera rear mech with sora
> > double shifters. its a 52/39 chainwheel I seem to remember.
> >
> > The shifting to anything except the smallest 3 or so rear sprockets isnt fantastic - I have to
> > puch the lever a bit further to make it change up to a bigger sprocket. Is this the cheapo mech
> > or the gear shifters at fault?
>
> Most likely not. The symptoms you describe are most commonly the result of friction in the cable
> system, or poor adjustment of the rear derailer (especially the "B-tension" screw.
>
> See: http://sheldonbrown.com/derailer-adjustment.htm
>
> and: http://sheldonbrown.com/cables.htm
>
> > If I buy a 105 or Tiagra rear mech (which are fairly cheap) will it improve my shifting at all
> > or do the sora levers limit it?
>
> Probably not. All Shimano rear derailers use basically the same geometry, and shift about
> equally well.
>
> > Also if I buy an 8 speed 105 or tiagra rear mech will it still work on my 7 speed freewheel? I
> > will upgrade to a cassette later... Would even a 9 speed work (that would allow for some
> > upgrades)?
>
> Yes. The derailers don't care how many speeds, that's only an issue for the rear shifter and
> cassette. (Also the chain, in the case of 9-speed systems.)
>
> Sheldon "Adjust, Don't Replace" Brown +----------------------------------------+
> | When I am grown to man's estate | I shall be very proud and great, | And tell the other girls
> | and boys | Not to meddle with my toys. | -R. L. Stevenson |
> +----------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone
> 617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide
> http://captainbike.com http://sheldonbrown.com
>
>

--
----------------------+ Alex Graham | [email protected] | ----------------------+

 

[Gregr]

The shimano road and MTB rear derailleurs for 7-8 and 9 speed are interchangeable (except pre 97
DuraAce). The cable pull ratio to the paralellogram is the same.

The 29T capacity means it can take up to a 29T difference between the (large chainwheel+large cog)
minus (small chainwheel+small cog) and still maintain tension on the chain. You can exceed this, but
your chain will slack in the small chainring/small cog combination.

The largest rear cog a derailleur will take is detemined by the paralellogram of the RD, and I think
the typical road RDs are rated for 27-28T. I f you really want a 32t cog, you best go with a MTB RD.

G

On Sun, 9 Feb 2003 12:02:03 +0000 (UTC), Alex Graham <[email protected]> wrote:

>Thanks for the info.
>
>So would a 9 speed 105 rear mech work with my normal chain and 7 spd freewheel and sora shifters?
>It seems to me that would be a sensible futureproof upgrade. Also when it says 29T capacity or
>whatever the short arm 105 is, does that mean the biggest sprocket the mech will reach is a 29T?
>Presuming my freewheel comes within the capacity of the 105 short arm is that the one I should go
>for over the long arm?
>
>
>Cheers,
>
>-Alex
>
>
>On Sun, 9 Feb 2003, Sheldon Brown wrote:
>
>> Alex Graham wrote:
>> > Hi everyone
>> >
>> > I have a fairly cheap racer with a 7 speed freewheel and a shimano acera rear mech with sora
>> > double shifters. its a 52/39 chainwheel I seem to remember.
>> >
>> > The shifting to anything except the smallest 3 or so rear sprockets isnt fantastic - I have to
>> > puch the lever a bit further to make it change up to a bigger sprocket. Is this the cheapo mech
>> > or the gear shifters at fault?
>>
>> Most likely not. The symptoms you describe are most commonly the result of friction in the cable
>> system, or poor adjustment of the rear derailer (especially the "B-tension" screw.
>>
>> See: http://sheldonbrown.com/derailer-adjustment.htm
>>
>> and: http://sheldonbrown.com/cables.htm
>>
>> > If I buy a 105 or Tiagra rear mech (which are fairly cheap) will it improve my shifting at all
>> > or do the sora levers limit it?
>>
>> Probably not. All Shimano rear derailers use basically the same geometry, and shift about
>> equally well.
>>
>> > Also if I buy an 8 speed 105 or tiagra rear mech will it still work on my 7 speed freewheel? I
>> > will upgrade to a cassette later... Would even a 9 speed work (that would allow for some
>> > upgrades)?
>>
>> Yes. The derailers don't care how many speeds, that's only an issue for the rear shifter and
>> cassette. (Also the chain, in the case of 9-speed systems.)
>>
>> Sheldon "Adjust, Don't Replace" Brown +----------------------------------------+
>> | When I am grown to man's estate | I shall be very proud and great, | And tell the other
>> | girls and boys | Not to meddle with my toys. | -R. L. Stevenson |
>> +----------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone
>> 617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide
>> http://captainbike.com http://sheldonbrown.com
>

 

[Alex Graham]

Right - its beginning to become clearer now

So as Ive currently got a 14-28 freewheel the short arm version of the 105 is the one I want?

thanks,

-Alex

--
----------------------+ Alex Graham | [email protected] | ----------------------+

 

[Sheldon Brown]

Alex Graham top posted:

> Thanks for the info.
>
> So would a 9 speed 105 rear mech work with my normal chain and 7 spd freewheel and sora shifters?

Sure.

> It seems to me that would be a sensible futureproof upgrade.

That's true _if_ there's something wrong with your Acera unit. If the Acera isn't damaged or worn,
replacing it with a 105 will just save a bit of weight.

> Also when it says 29T capacity or whatever the short arm 105 is, does that mean the biggest
> sprocket the mech will reach is a 29T?

No. See: http://sheldonbrown.com/gloss_ca-m.html#capacity

> Presuming my freewheel comes within the capacity of the 105 short arm is that the one I should go
> for over the long arm?

I don't generally recommend the short cage units unless you live in the flatlands; the long cage
versions cost the same and are more versatile.

Sheldon "If You Do Live In The Flatlands, Ditch The Derailers And Go Fixed!" Brown
+---------------------------------------------------------+
| "Contrariwise," continued Tweedledee, "if it was so, | it might be, and if it were so, it would
| be; | but as it isn't, it ain't. That's logic!" | --Lewis Carroll, "Through the Looking Glass" |
+---------------------------------------------------------+ Harris Cyclery, West Newton,
Massachusetts Phone 617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts
shipped Worldwide http://captainbike.com http://sheldonbrown.com

 

[Alex Graham]

Sorry abt top posting btw

the thing that still confuses me is if 8 and 9 spd mechs work with 7 speed, why have different
models for 7,8,9 spd?

and what actually is the advantage of a long cage?

thanks,

-Alex

--
----------------------+ Alex Graham | [email protected] | ----------------------+