Derailleur Compatability

[stixmaster1]

Hi Folks,
Bit confused here about what derailleur to buy. I've just fitting a shimano MageRange Freewheel to my bike. Tooth Ratio 14-34. link here

http://www.sjscycles.co.uk/product-Shimano-Shimano-MF-TZ31-7-Speed-Mega-Range-Screw-On-Freewheel-14-34-1240.htm

and now I need a derailleur to go with it. I don't really want to spend more than £20. £30 at a push. so I've been looking for various derailleurs.
The closest I've found is this.

http://www.chainreactioncycles.com/Models.aspx?ModelID=38673

which states "For use with 28 to 34 tooth low rear sprockets, total capacity 43 teeth"

I don't really understand what this means. (A freewheel with 28-34 tooth sprockets would be slow right??) but will it be compatible with my freewheel?

alternatively, can anyone recommend a reasonably cheap derailleur or tell me how to decide whether a derailleur will be compatible with my gears. I keep hoping to see one saying "suitable for 14-34 tooth rear sprockets" but no such luck.
TIA
Dave

[cyclerUK]

The Acera derailleur will be fine.
The 28 to 34T is the size of large sprocket that it's designed for.
So, for instance, 14/28 to 14/34 would be O.K.

If you wanted to run a large sprocket under 28T then you would be better of with one of the road derailleurs.

Have a look at Sheldon Browns explanation of "derailleur capacity".

http://www.sheldonbrown.com/derailleur.html