non-fixie
Senior Retro Guru
Thank you for the picture of your bike. Great "garage" door portrait!
That looks like a very useful starting point. You've already got a long cage Shimano rear derailleur, which will handle the considerable chainwrap needed for a broad gear range.
Your current lowest gear progression is about 40" (distance traveled per full pedal stroke). With just the replacement of the inner chainring with a 34T, this will be lowered to 32". That is a very noticeable improvement, and already lower than my bike I pictured above.
I can't tell the exact derailleur model from your pictures, but chances are it can handle a bigger cog than your current 28T. Exchanging that for say a 30T, will get your lowest gear below 30". Any lower than that and walking will probably be faster.
If you want to play with the options and numbers, have go at Sheldon Brown's gear calculator.
110 BCD 34T chainrings can be had for 10-20 pounds plus shipping, even in black. A 7-speed cassette with a larger cog might take a while to find, due to current low stock levels, but shouldn't need to be more than about 25 pounds.
In case you want to upgrade the cassette, make sure to check out the specs of your derailleur, and be aware that Shimano's official specs tend to be rather cautious, so check the various bicycle forums as well. If you move the wheel back a bit in the dropouts, you can often get away with a couple of teeth more.
Good luck!
