phelps

Was on the phone the other day with Terracycle ordering underseat carriers and thought I might as well get one of their fancy idlers for my Rocket. I'd heard such great things about them, so why not? I haven't had any complaints about the stock one, but if I can improve efficiency with no cost other than monetary.....Haven't mounted it yet, wait 'til spring, when the roads are cleaner, but I'm trying to understand how using a sprocket rather than a roller makes any diff if it's only guiding a chain. I imagine there've been tests though.
The other thing that's somewhat related, most derailleur pulleys have 11 teeth. Some of the cheapest and the most expensive have 12 or 13. Wouldn't you think that the larger ones would give a smoother redirection of the chain regardless of whether the wheel has a bushing or a bearing in the center? Couldn't we all reduce drag and vibration just a bit by putting the largest pulleys on that we can get?

BlazingPedals

I've wondered if removing the power side idler completely from my V-Rex would increase efficiency. If it needs anything, just stick a short piece of chain tube there to prevent chain flop? Anyway, I've never noticed enough drag or noise to make me want to actually perform the experiment. Same with derailleur pulleys. It would seem the bigger pulleys would be better, but considering there's not much tension on them, the difference is probably minimal.

Shaman

Phelps; I've done a lot of work on idlers in this case, for a recumbent trike. The problem with non-cog'd idlers is that you are putting pressure on the sideplates of the chain. This wears out the idler... eventually. By putting a cog so the chain rides on the chain's rollers as it is suppose to, the idler is made more efficient, and will let the idler last longer.

Indeed, if chain deflection is small, there is actually very little pressure on the idler. In the case of trikes, the deflection is nearly 30 degrees and the tension on the chain is great. In your case, the idler is probably more for chain management than actual deflection. That Terracycle idler will be a good upgrade if not for efficiency, then reliability. The idler will be more efficient than chain tubes. regarless, chain tubes should alsways be Teflon if you do use them (very efficient chain guards).

BlazingPedals

Just for reference, I rode my V-Rex for 5 years at about 3500 miles/year, before the bearings on the idlers gave out. At that point I went to the local sports store and bought a pack of bearings for roller blade wheels and replaced all 4 bearings. Since getting my lowracer, the V-Rex is seeing less ride time, so the bearings have been fine for the last 6 years. Other than being slightly yellowed with age (not a bad thing since my V-Rex is yellow,) the idlers themselves are almost like new. About the only reason I can see for replacing them would be if you want to make it a little bit quieter when you're really humping - 300W or greater; at that point the stock power idler makes a slight amount of buzz. Or if you think the replacements would look cooler, of course!

Goatbiker

I'm with you on this. I think the idea of having simple, unsealed bushings on such fast turning wheels is a horrible idea. They have got to be creating a lot more drag than they should. They get dirty easily, and they are a pain to dissemble and re-lube. I would love to find that someone makes a (low friction) sealed bearing for the SRAM jockey and idler wheels.

Tom