Mike,
Nice work. I always appreciate seeing varied line weight.
There is one thing that caught my eye though: why, on the back tire, did you not continue the thick outline all around (between the gear and chain looks odd to me not having the same lineweight consistency as the rest of the tire)? I sort of felt the same about the inner frame of the seat or the rear framework. It might just be me, but that's what I might fix. Otherwise, great work.
Thanks for posting! I'd love to post up what I've been working on, but due to the nature of most of my illustrations there is little likely-hood that I'll ever be able to share. My plan is to share the work I have been doing on the War of the Worlds project when I get to start back up on it late this summer.