estasnyc

What is considered an acceptable clearance between the rear derailleur and the spokes of the rear wheel?

I've just built up a commuter frankenbike having a rear wheel with a Shimano 7-speed freehub and 130mm O.L.D. and an old Campagnolo friction-shifting rear derailleur that's mounted to the frame through a claw-hanger adaptor.

What I now find is that the rear derailleur clears the rear spokes by 2.1mm which I measured with a feeler gauge at the apparent closest approach between the RD's jockey pulley and the spokes while engaging the inner-most cog of the cassette. The same kind of measurement on another bike having both a Shimano hub and a Shimano RD shows 5.0mm.

While riding this bike for the first time, I started worrying about all of this when I started to hear a periodic clicking sound while climbing a hill. I now believe that this sound was the result of the RD cable contacting the spokes because I haven't gotten around to trimming off the cable's excess length yet.

How much should I worry about this? I don't see anything bad happening with normal use. I can't remember the last time that anything struck the rear dearilleur of any bike that I was riding.

I see that there's another thread currently in this forum about a bent derailleur hanger. Perhaps I should check to see if the claw adaptor is bent or even deliberately bending it outward slightly?

Bill Kapaun

What happens if you hit a big pot hole with the rear wheel and flex it over a bit?

FBinNY 

There's no magic number, but if your hanger is straight, and the freewheel/cassette is typical distance from the spoke line, there's no reason the RD would be any closer than 2-3mm or so.

Of course you have to shift to low, then it becomes a question of what you're comfortable with. If you keep the RD well adjusted and don't do anything like drop the bike on the right side, you can probably work down to the last millimeter, but you have to be very attentive to any changes.

zukahn1

On a tight and right proper bike you often see 2mm for a frankenbike your good with 3mm everyhting solid but 4+ would be better and more realisrtic.

Andrew R Stewart 

Just monitor the cage/spoke clearance periodicly. Any pro wrench would eyeball the der and whether it hangs down square to the cogs. If not then correct it. Again, with so small a gap between the cage and spokes you need to keep on top of it. As the wheel gets miles on it the spoke tension settles in and minor wobbles develope. Also the low gear limit screw might need attention as it beds into it's stop. Setting inward travel is not a one time thing. Andy.

Looigi

It depends on the hub (dish etc.) as much as anything. On a couple of 10sp rear wheels here, the gap between the inside of the RD cage and nearest portion of the spoke (at the crossing) is ~3.5 mm on one and less than 2mm on the other.

onespeedbiker

The fact that the extra rear derailleur cable maybe bouncing off the rear wheel spokes in the low gear is really a none issue. What is an issue is how close the derailleur cage is to the spokes. If the cage never gets any closer than than 2-3mm, than all you need to do is cut the extra cable or just bend it away from the spokes.. If the cage gets closer than that then you may need to look at the derailleur hanger or if it is hitting just one or two spokes, maybe the wheel has a loose spoke or two.

estasnyc

Thanks to all for responding.

The bouncing of the extra rear derailleur cable on the rear wheel was simply something that called my attention to the possibility that the derailleur could strike the rear wheel spokes.

I've screwed around with frankenbikes, having components I've accumulated and used outside of manufacturers' design specifications, enough to understand that there's always an overlooked small detail that can screw you up. It goes with the territory. A case in point is a current thread here about Shimano UN-55 bottom brackets and the problem someone ran into after mounting one with a bottom bracket spacer.

The smart move now would be to replace the campy RD with a Shimano road RD. I do have a Deore RD but I think that it would give the same clearance: It was designed for rear wheels having 135mm O.L.D.

I doubt that I'll need to do this at just this moment but I'll be keeping an eye on Craig's List for something that becomes available.

I did give some thought to doubling-down on this parts-mixing: There is enough clearance between the cassette and the drive-side dropout that I could theoretically put in a 1.0mm cassette spacer to shift the cassette out by that amount (Shimano does sell such a thing intended for their 10-speed cassettes) but I can already anticipate the next problem that this may create: How well might the outermost cog sit on the freehub?

onespeedbiker

Why not give us a photo to work with? The issue may be obvious if we can actually see it.

Kotts

Personally, I'd throw a "dork disk" on there and call it good. After all, they were invented to prevent the very thing you're worried about. This is a commuter frankenbike, so why not?

estasnyc

Here's a photo of the bike with the Campy rear derailleur along with that of another bike with a Shimano 105 RD-5700 rear derailleur for a visual comparison:



Notice how the derailleur cage is about a spoke's-width away from the spokes.

I don't know which model the Campy RD may be. Only that it's from the early-1980's era. I believe that it's only possible claim to fame may be that it was the last friction-shifting RD Campagnolo manufactured before they followed Shimano over to index-shifting. The Shimano 105 RD-5700 is much more recent.

I'm thinking about getting the Shimano Sora RD-3500 -SS1 RD because I don't want to spend more for a higher-end brand-new component. I don't know if the RD-3500's cage will be more like that of the RD-5700 or that of the old Campy RD. It PROBABLY is but I'm not certain.

I did find a local Craig's List seller offering a Shimano 105 RD but the person is not responding to my e-mails. Time to go with Plan B. I was planning to rant a little but I've dwelled on this subject long enough.

FastJake

I think you're fine. I think I've had non-franken setups where the cage was closer to the spokes.

+1 Get the low limit screw set really well.

+1 Throw on a dork disc and don't worry about. Do those two things and I bet you'll never have even another hint of a problem.

FBinNY 

Spoke protectors (dork discs) can be a Catch-22 in many low clearance situations. Most are effectively about 2mm thick, (old fashioned rimless steel ones are the thinnest). So the disc ends up rubbing on the cage, giving you a choice between the protection a disc affords, but with the noise of rubbing, or go without and be able to work close, but the need to be very aware of any hint that the hanger got bent in.

LesterOfPuppets

I often put spacers behind 7-speed cassettes.

Dfrost 

There's plenty of room between your smallest cog and the inner face of the dropout, indicating that you could add the suggested spacer (they are available as thin as 1mm, and are also used to adjust the chain line on sealed bottom brackets) behind the cassette, and not have any clearance problem at the other end of the range.