Tourney Gear Swap Question
 

My bike has an A050 front derailleur and an A070 rear derailleur. Current setup is 42/52 in the front and 12-28 7-speed in the back. Is it possible to swap the front out with a 34/50 crank and the rear with a 14-34 without changing anything else? Thanks!

Probably not. You'll likely need a longer chain and possibly a longer cage rear derailleur.

Rear specs and capacity
​​​​​​https://bike.shimano.com/en-EU/produ...0/RD-A070.html

Nothing available on specs for front. try it and see.

Thank you both!

That puts the capacity at 37T with a 28T max rear sprocket size.

OP wants 34T. That may be pushing it a bit for a 34T rear sprocket, although there may be options to increase the hanger length.

(34-14) + (50-34) = 20+16 = 36, so the derailleur capacity should be OK.

Front derailleurs are often pretty forgiving of changing chainring sizes. Capacity is a bit of a difference and will depend on the seat tube angle.

By changing from 11T or 12T to a 14T in the rear, you may be saying that you don't need the highest gears.
And changing from 28T to 34T on the rear means you want lower gears.

You can achieve some of the same by going with even a smaller crankset. 48T/30T? Smaller?

Ultimately you could probably keep the current 12/28 cassette, or even go to 11/28.

A side note: 12-28 is a cassette, but can you get a 14-34 7 speed cassette now? AFAIK, Shimano no longer makes them. 14-34 freewheels - yes, but not the cassettes. Of course you can get a Sunrace 11-34 cassette or build a custom one.

Thanks, Clifford. Do you know of any good links where I can learn about "capacity" and what it means?

Correct - I didn't place much emphasis on the highest gear on the cassette (or freewheel, in this case) since I don't spend much time in that neighborhood. The quest for a change in gear sets is due to a couple of good sized hills I've encountered on a new route. If a freewheel happens to have fewer teeth than 14 in the highest gear, that is not of much concern to me unless it would have an impact on whether or not this swap would be possible.

That was my mistake as I did not clarify - yes, this is a freewheel. Thank you for catching that.

I found some specs for the A050 under the Technical Documents section of the Shimano website [the A050 is discontinued]. Looks like everything I found for the A050 lists the smallest gear size as 39.


So I may just replace the FD-A050 with an FD-A070. The chainstay angles and chainlines are the same values for both units. The band clamp diameters appear to be different. Based on the info below from Shimano, is it safe to presume an A070 can be retrofitted to a frame currently using an A050 provided the A070 uses an adapter? Is there anything else I need to take into consideration when doing a swap like this? Thank you.

A070
Mount Clamp Band: 28.6mm [w/ S size adapter]
Mount Clamp Band: 31.8mm [w/ M size adapter]
Mount Clamp Band: 34.9mm

A050
Mount Clamp Band: S(28.6mm)
Mount Clamp Band: M(31.8mm)

https://sheldonbrown.com/gloss_ca-g.html#capacity

Are you sure you need to change the FD? Do you think that with the new crankset the difference between the large and the small chainring will be so high that the chain will drag on the FD cage when it is on the small chainring in the front? I would first try it and see.

Thank you for the link, Csport. We'll give it a try first :)