freewheel stress and possible difficult removal with super underdrive gear?

Question

I tried to research this online but didn't see any examples of this exact concern, which is if I gear down a very cheap mountain bike that has a 7 speed freewheel, do I run the risk of creating so much torque magnification that something bad could happen? Is it possible that something could break from the high torque? What about if and when I need to remove the freewheel? Might it be stuck from the high torque pedaling in the lowest gear?

Stock lowest gear is 24/28 and I will attempt either 20/28, 24/34, or 20/34 which is about 15.3 gear inches. I ride mostly on the street at a slow pace (about 10 MPH average) but I also like to ride thru grass slowly and even in grass uphills so I put a good deal of force on the pedals in that situation.

Answer 1

Yes - chains can be broken and will also wear quicker when under stress from low gearing.

I have snapped a almost new KMC chain while on a 15% climb. I would have been in 26/42 on a 26" MTB. Fortunately I was going very slow. The pedals spun, so I clamped on brakes while unclipping. The slope meant I couldn't reach the ground straight below the seat, and so the whole bike and I fell over to the left (our footpath side) and tried to slide away down the hill. Was quite embarrassing, but fortunately not painful or damaging. One of the chain's side plates had come off the pin, so it was only a matter of time before it wrenched the other side out completely. Never buying another KMC chain!

Removing the freewheel can be hard, so remember to apply copperslip or anti-seize or even plain old marine grade grease to the threads before assembly. The leverage of the rim means you can exert a lot of force when undoing the freewheel, provided the nut is held firmly in a bench vise (and said bench vise is fastened to a bench!)

Freewheels tend to seize their threads, but sufficient power can undo them. Cassettes can "erode" their way onto a freehub body, and be unrecoverable completely.

Finally never underestimate the torque advantage of a handy piece of pipe.

Answer 2

The problem I've had in the past with cheap freewheels is that even with standard gearing I could bend the gear teeth. Even inexpensive cassette types don't have this issue. This happened so frequently, I carried a freewheel removal tool with me and when I spotted a DSB in the trash I'd stop and pull the freewheel. It kept me in freewheels for a couple of years until I upgraded.

In short, do the swap if you want to. You should not have any extra problems due to this configuration change... although, you may have issues with shifting and RD capacity (but removal of the FD and shortening the chain will address that for $0)

Do not worry about freewheel removal nor the chain. Those will be fine. The hubs generally have plenty of material around the threads and those would fail long before the chain broke... unless the chain was defective/damage or worn-out.

15 gear inches is not that terribly low... My tandem has a 20 chainring and a 28 cog... and 700c wheels with 25mm tires... about 18.8 Gear Inches... and we hammer it up hills with 2 people plus a corider (with child--about 50lbs extra for that)... and a 30lb trailer with 50lbs of gear in it.....

I would guess this is way more stress than you will generate on your single. Now, the tandem does have a nice freewheel from the early 90's... but you get the idea. (the chain is nothing special either.)