Pretty flat. Only the bridges and a few highway ramps are steep climbs. The pace in the front part, where I normally find myself, is pretty fast, around 17-18. That means the assist is almost useless. But I was with a sick friend for the first 27 miles and we were going pretty slowly so I didn't use the assist at all. The extra weight is no real problem on the flats, in fact it sort of helps keep up momentum. But I sure wouldn't want to be going up hills without the assist. Maybe you can borrow an extra battery from someone...