9 speed chain on 7 speed gears?

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This has probably been done before but you guys might also have some additional answers. I have an old Trek 750 I want to keep alive. I need a front derailleur and I tried a Tiagra 9 speed which needs too much trimming due to a narrow cage. It looks like it is going to be hard to find a model that will work with a wide chain and will handle my 48 chainring. Two people have told me a 9 speed chain will work
and the local bike shop says it won't work with the 7 speed freewheel ( I got a deal on some Shimano Mega-range freewheels but I never use the 34t ring). I can live with the trimming but if there is a better solution I would welcome it.

Thanks

This has probably been done before but you guys might also have some additional answers. I have an old Trek 750 I want to keep alive. I need a front derailleur and I tried a Tiagra 9 speed which needs too much trimming due to a narrow cage. It looks like it is going to be hard to find a model that will work with a wide chain and will handle my 48 chainring. Two people have told me a 9 speed chain will work
and the local bike shop says it won't work with the 7 speed freewheel ( I got a deal on some Shimano Mega-range freewheels but I never use the 34t ring). I can live with the trimming but if there is a better solution I would welcome it.

Thanks

If you have index/click shifting a 9s chain will probably be too narrow. A chain needs to be of a sufficient w
idth to be 'grabbed' by the next cog when shifted, particularly shimano, which doesn't overshift, like indexed Campagnolo.

If you are friction, it doesn't matter.

A couple of options are;

1. go to a bicycle recyling place and pick up an old 7 speed FD

2. If its a 7 speed shimano spline on the rear and you have friction shifters, buy a 9 speed cluster and use one less sprocket to get 8 speed, using a 9 speed chain.

3. Convert it to a fixie, those old bike are just great for making fixies out of.

Personally I'd just go for picking up an old 7 speed FD

So it looks like the 9 speed chain won't work (makes sense) and I have to either deal with trimming or find something somewhere, new or used, that was made for older chains. I already have a supply of 7 speed freewheels and I do want to keep my index working.

Does anyone know what current SRAM or Shimano FDs might work? My front chainring is 48T so I have stumped the local shop. At least for a worst case scenario I could get a 46T ring and go with an Alevio but the ring costs more than the FD and I really don't want to give up steel for aluminum.

So it looks like the 9 speed chain won't work (makes sense) and I have to either deal with trimming or find something somewhere, new or used, that was made for older chains. I already have a supply of 7 speed freewheels and I do want to keep my index working.

Does anyone know what current SRAM or Shimano FDs might work? My front chainring is 48T so I have stumped the local shop. At least for a worst case scenario I could get a 46T ring and go with an Alevio but the ring costs more than the FD and I really don't want to give up steel for aluminum. Do 2 teeth really make such a difference that you cannot use an Alevio with your 48T ring? It does not seem that the extra two teeth would increase the diameter of the chainring that much so that the Alevio would not work.

Do 2 teeth really make such a difference that you cannot use an Alevio with your 48T ring? It does not seem that the extra two teeth would increase the diameter of the chainring that much so that the Alevio would not work.I cannot be sure other than the Shimano specs say 46T.