In the early days of Klunker/Mountain biking I used a Schwinn Varsity Klunker with 26" x 1.75" tires to race with in Northern California. I equipped my bike with a Favorit rear coaster brake and a Mafac tandem cantilever front brake. Had a builder braze the cantilever studs to the indestructible Schwinn forged fork. On long steep downhills I used the coaster brake to slide the rear wheel for speed control. You can not use a coaster brake for any length of time as a modulated drag brake. They will get hot enough to cook on and quit working as a brake. Not good. However if you lock the rear wheel up there is no real heat buildup and you just slowly sacrificed the tire instead of losing your brake to heat. Keep in mind that you don't lock up forever. One has to let the rear tire rotate every once in a while to maintain balance and direction control. When more deceleration was needed I'd add the front brake. Vintage Schwinn is absolutely right about having an independent front brake that can stop you when coaster brake equipped. That said one speed non suspension bikes really don't have chain breakage or falling off the sprockets issues. One speed chain is heavier duty and very durable. Riding off road in real bumpy racing conditions I never lost a one speed chain in a race or any other time due to chain failure or coming off the sprockets. I geared my race bike on the slower end of the system in order to ride up moderate grades. I used to tell people a coaster brake one speed is actually a three speed off road bike. 1. Pedaling the bike. 2. Running while pushing the bike uphill. 3. Walking the bike uphill by pushing or carrying. Also you are never in the wrong gear to tackle the trail. It is always full out all the time. I never felt at a disadvantage using a coaster brake bike in off road racing and did well in all the races I tackled. Today I would use a full suspension bike with disc brakes and modern derailleur system. We got beat to death by those non suspended race bikes of yore