700 Chainring adjustment

My bottom bracket was getting pretty rough recently. I took it out (easy job) and re-lubed it even though it is supposed to be a sealed bearing on each side. It was somewhat better, but I went to FleaBay and bought another bottom bracket. They seemed to run $20-25.

When I got the new one, I downsized it from 137 mm width to 127 mm wide. It fits noticeable better than the original bottom bracket. Some folks had commented that the chain would drop off the chainring too easily; this modification helps. It moves the chain inwards about the width of one sprocket in the back. Mine never fell off on me while riding, but would fall off the chainring or the cassette easily if I was in gears 1,2 or 3 on the cassette and backpedaled. Now I can backpedal in 2 without it falling off.

I would not suggest going any narrower than 127 mm on the bottom bracket. There is a little clearance between the chainring and the chainstay, but not much. The first thing that would get chewed up by the chainring will be the derailleur cable housing.

My guess is that a 127 mm bottom bracket was spec'ced by R1U, but the chinese factory did not have them in stock, so they just put whatever they had laying around in there. Part of what we deal with by getting a relative bargain price compared to Specialized/Trek/etc.
 

haneyrm

New Member
Region
USA
City
Boca Grande, FL
Hi. Great info. I want to do the same on mine. Do you happen to know what the spacing is on the stock chainring? 104, 110, 130, etc.?
 

GenXrider

Well-Known Member
I haven't had this issue on my 700. I'm almost always riding in the top few gears.

Someone was just reporting in the FB group about an issue with the chain coming off when pedaling backwards, and it was due to his chain.