I ride 35 series on 20" the rides ok but watch the pot holes ive seen the side wall blow out
I rode 35 series with my 20's on the daily in Michigan back and fourth from one city to another everday for work with no problems..just dont let the air pressure get low.
You will be fine with a 35 series.
thanks but noone has commented on a 30 series tire.....a 225 30 20....the smallest f'n 20" tire they make I believe...how do those suckas ride?