Oltrarno side is your safest bet for actual running without vespa roulette. Start ponte vecchio head west along arno south bank proper riverside path minimal scooter traffic can run all the way to parco delle cascine florences biggest park dirt trails car-free about 6km total loop

For elevation san miniato climb is brutal but rewarding 2km steep ascent incredible views early morning before 7am ideal to avoid crowds and heat. Avoid historic center cobblestones will destroy your knees plus too many oblivious tourists learned this painful lesson day one

Routes range 3-8km depending how far along river you go elevation varies wildly cascine park is flat san miniato climb about 100m vertical gain