Ev0lutionz

Riding a Brompton as my daily commuter, realised I'm already at 0.5 wear close to the 1000km mark, on my bigger bike I can get more mileage out of a single chain and cassette.

sweeks

I speculate (ie, without actual evidence) that chains on derailleur-based drivetrains on small-wheeled bikes may be subject to faster wear because of their closer proximity to the road surface and any debris that may be kicked up by the front wheel. All my bikes with 20" wheels (folders) have internally-geared rear hubs, and the chains are not so close to the road. I typically get about 3,000 miles before the chain hits the 1.0% wear mark. When it reaches 0.75% I order a new chain so I'm ready to replace. "0.5" sounds like you have a lot of wear left in that chain if we're talking in the same units.

Bill Kapaun

Have you checked the accuracy of your chain checker? Mine shows .5% on a chain that's only .25% worn when measured with a measuring tape.

Andrew R Stewart 

Agree with the above. I'll add that without more info I can't say much more but conditions and cog counts come into play too. If those are the same...but we don't know about that. Andy

Johnathonbenfie

It has so little influence that one can say no.

70sSanO

The other part of this is could be excessive cog/cassette wear impacting the life of the chain.

John

dsbrantjr

It seems to me that just the fact that smaller wheels have to make more turns to cover the same ground they would wear chains, etc. faster.
Also, throw away your chain checker and measure your chain with a good steel rule, if you want to know what is really going on.

FBinNY 

Yes, using smaller sprockets shortens chain life.

2 reasons for this.

1- driving torque, both input and output, is the product of sprocket radius and chain tension. So any system using small sprockets to achieve a given gear ratio wii have the chain running at higher load.

2- smaller sprockets cause the links to bend more as they wind onto and off the sprockets. More flex = greater wear.

This is why it is SOP in industrial applications to use the largest sprockets practical to the situation.

Hondo6

^^^This.

Per the late Sheldon Brown's online gear calculator, a bike with a 50T front sprocket, an 11T rear sprocket, and 700c x 25 tires rolls approximately 9.6 meters for each turn of the crank. A bike with 20x1.75 BMX wheels/tires and the same front/rear gears rolls only 6.8 meters for each turn of the crank - or approximately 70.83% as far. The crank (and chain and sprockets) on the bike with smaller wheels thus must turn more times in order to cover the same distance - in this case, around 41.2% more. They can therefore be expected to wear out after covering less distance.

2_i 

Are you swapping sprockets when you change the chain? Simultaneous change is a standard for Brompton, but some people miss it and change the sprockets only every few time they swap the chain. I did not notice a difference in the pace of wear for Brompton vs a full size bike, but I did not study it carefully either.

KerryIrons

Yup. And the post that says "small wheels have to make more revolutions" is completely irrelevant. It's how many "engagements" of the chain and cogs / chain rings not how many wheel revolutions. To get the needed gear ratios with small wheels, they use small cogs on the cassette and that means faster wear. Whether this is the source of the OP's issue is not clear because if the gears are worn that would have a bigger effect.

Hondo6

Since with the same gearing bigger wheels move a bike more each rotation, the chains and sprockets on the bike with smaller wheels have to make more turns to cover the same distance. Since (like tires) chains and sprockets are mechanical devices, more turns = more wear.

Hondo6

When using the same sprockets, a bike with smaller wheels travels less per crank rotation than one with larger wheels. That means to cover the same distance using the same gearing (e.g., 50 front, 13 rear) you'll rotate the crank more times - and will thus engage the teeth on both chainwheel and rear sprocket more often on the bike with smaller wheels to cover that same distance.

You can compensate to a point by using larger front chainwheels on the bike with smaller wheels. But there's a practical limit there due to less ground clearance on smaller-wheeled bikes (I've read that up to a 60T front chainwheel can be used with a Brompton). And even then, 60/50 = 1.2 - and the wheel size difference gives the smaller bike a disadvantage of over 40% in terms of ground covered per wheel rotation.

And as you noted, using smaller rear sprockets to compensate more simply wears them out faster. 60/11 with 20" wheels has roughly the same development as 50/13 with 700c x 25 (8.1m per crank rotation) - but the 11T rear cog is going to be toast far sooner.