Campag Mirage Rear Mech Question

[NeilM]

I'm sure this information is readily available on line... if you know where to look, but can anyone please tell me the maximum cassette cog size for a short cage 8 speed Campag Mirage rear mech.

Crankset is 52/38 if I remember correctly.

Thankee.

 

[foz]

theoretically probably about 26t, but if it's the same dimensions as other campag short cage mechs then you can probably use it with a 29 no trouble at all (I have 10 speed chorus short cage, works fine with 53/39 and a 13-29 cassette)

 

[NeilM]

Re:

Thanks Foz, that's what I have been reading elsewhere on the net, but I wanted to check.

It is for the Little Lloyd I posted pictures of in the bikes section, at present it has something like a 14-23, and still little Donna is managing 12% plus climbs.

 

[foz]

nice little bike that one it has an 8 speed mech, you're probably ok but I can only confirm with the 10 speed models...

 

[NeilM]

Re:

I think we'd be pretty safe with a 26, if that would make enough difference to be worthwhile.

Donna is such a tough little rider I think it might just be enough, especially as the bike is on 650C wheels.

 

[gfk_velo]

theoretically probably about 26t, but if it's the same dimensions as other campag short cage mechs then you can probably use it with a 29 no trouble at all (I have 10 speed chorus short cage, works fine with 53/39 and a 13-29 cassette)

Cage length is "a factor" but not "the factor" in gear capacity and tooth capacity - esp in retro situations where the gear hanger / dropout configuration is potentially a lot more complicated.

Cage length has some influence over how much chain can be wrapped but again it's not the only factor - and chain wrap itself is not the only deciding factor on tooth capacity.

Upper body design is important as this decides the angle at which the body tracks across the sprockets and therefore the distance at either end of the cassette that the top jockey is from the sprockets - than in itself affects shifting performance, especially as things wear out.

Hanger length and position relative to the axle of the rear wheel is important as it decides how far "below" the cassette the RD hangs - we have seen instances of users trying to use 11s Campag witha 29T bottom gear on classic frames with short road dropouts who can't because the RD doesn't hang far enough away from the casette.

Different generations of different makers all have different travels for B screw / H screw so how the relative tensions on upper and lower pivot springs can or can't be set - this again affects the max size of the biggest sprocket.

Where on the dropout the "hook" that the B-screw or the rotation stop of the RD sits against affects max sprocket size.

Max effective chain wrap is also affected by hanger length, BB drop and chainstay length - in some cases it makes one full link of difference - which can be the difference between big to big being useable along with small-to-small, or not ...

So even where cage lengths and jockey wheel sizes are the same, I'd be cautious about just saying "yep, it'll work".

Best to borrow a cassette / block or two and physically try it in your circumstances, on your bike. The max figures quoted by manufacturers usually come with some caveats around ranges of frame geometry and design of hanger / dropout.

Remember that whatever system you are running, when it is operating at it's max, it's likely not to be as accurate and to be more prone to faster wear and tear. Important in older gear systems because with RDs for instance, when fully extended "forwards", there is a lot of leverage on the top pivot bolt - it can cause failure in the housing, especially as materials age. Seen that plenty of times on Shimano and on Campag.