rseeker

What would you consider a minimum safe distance between the jockey wheel arm and the spokes?

I assume that with a correctly shaped frame and hanger and a correctly adjusted RD designed to go with it, everything should just work, but as a check step - how close is too close?

FBinNY 

As close as 2mm in low is fairly typical and fine. On some bikes it's more like 1mm.

Keep in mind that you have no say in this. It's determined by the distance between the innermost sprocket and the spokes. If you feel the clearance seems too close, check that the hanger isn't bent, and the RD cage is straight.

rseeker

Wow, not much tolerance. My appreciation for successful mechanics only grows.

Retro Grouch 

This^^^

Shift your bike into a gear combination that makes the derailleur arm point straight downward. Prop your bike against something so that it's standing up vertically. Now walk around and look at your derailleur from the back of the bike. If it looks like it's pointing toward the rear tire - that's it.

Cheap bike, you can probably bend it back with your hands. Quality bike you'll probably be better served by having a shop align it with a gauge. That's about a $15.00 service.

Andrew R Stewart 

Too close is when the der catches on the spokes during riding. Enough clearance is when it doesn't. There's no spec that's commonly quoted to my knowledge. Having said that a lot of people will say it should be this or that amount.


Also don't confuse what's happening on a stand with actual riding. The added forces acting of the chain, der and spokes will change the static clearance. Andy

TimothyH

The derailleur should be set up in relation to the largest sprocket on the cassette, not the spokes.

The derailleur will not be near enough to the spokes to cause a problem if this is done properly and everything else is in working order.




-Tim-

Kontact 

That isn't true. On many hubs there is room to put a spacer between the cassette and freehub to move the low sprocket away from the spokes. I've done that with two 8 speed wheels I'm using with Mavic derailleurs that have rather thick inner pulley cage plates. 1mm spacers solved the problem with no other issues.


But a derailleur that is "too close" will pluck the spokes when climbing out of the saddle, announcing that it is "too close" without doing any damage. This is just one of those things where even the tiniest clearance is enough if there is no real way for the derailleur to actually hook a spoke - which requires considerable overlap. If the derailleur and spoke don't appear to touch in the stand and you can't get them to touch while climbing forcefully, there really isn't a way that they can interfere with each other.

fietsbob

Your 'dork disc' is a safety devise.. when the clearance is tight..

Kontact 

If the clearance is already tight, how are you going to get a disc in there?

79pmooney

I haven't done any surveys but I have observed different maker's derailleurs differ in how likely they are to be grabbed by a passing spoke. The older SunTours were quite tolerant of real contact. My triples using a wide range in front, a GT derailleur and a racing FW regularly rubbed in low gear, esp on the granny in front. Never an issue. I've had other derailleurs where minor contact was bad. I've even taken to grinding the bolt head on offending derailleurs to a shape the spoke couldn't grab.

An option you can play with to minimize spoke contact, esp when you are 'honking" is to lace the rear wheel with the
pulling" spokes laced from the outside to the inside, ie so the heads face out and have the spoke crossing outside the last static spoke on the outside as would be done normally. (Pulling spokes - those that come off the top of the hub flange and point back.) Laced this way, the inside spokes will do their best to straighten as you pedal hard, pulling the outboard spokes in and improving clearance with your derailleur. Lacing in the opposite direction will have the opposite effect, making contact more likely.

Ben

79pmooney

The disk will act as a spacer, moving the FW outboard and increasing the distance between the spokes and the required derailleur inboard setting.

Ben

fietsbob

I did not measure my stuff for your convenience., sorry

Kontact 

Depends on the disc. The oldest ones had a sheet metal part that went under the freewheel. But most of them for the last 30 years just attach to the spokes.

79pmooney

It's been 40 years since I pulled a new bike out of a box. Never bought one with a disc. (Last bike I purchased of that price range was before they existed.) Now that you have reminded me, I do recall seeing the clip-on ones at the non-profit shop I've volunteered at.

Ben

fietsbob

I have some made years ago by Huret, for freewheels , center is aluminum the , disc-ring around it molded plastic .
lays close, touching the drive side spokes ..

My Long distance solo touring bike , veteran of several multi month EU tours..

SJX426 

Or the hub flange
[IMG]P1030871, on Flickr[/IMG]

Kontact 

And uses up several millimeters of extra clearance on top of the spokes, even after accounting for the thin metal center.

Adding more stuff between the spokes and derailleur isn't going to solve a clearance problem.

fietsbob

Oh you have them too?

Slightspeed

I had a spoke ticking the RD on my Super Course with a Suntour GT Luxe and 6 speed freewheel. I used a modern 1.37" id cassette spacer on the inside of the Shimano Megarange freewheel. It moved the whole chain and rd cage out just enough to clear the spokes. I also used the same size spacer under the fixed bearing cup to move the crank out and away from the frame so the inner chain ring bolts clear the frame. These spacers are very useful little devices, and look a lot cleaner than a dork ... sorry, ... spoke protector.

Kontact 

What thickness spacer did you use? I had luck with 1mm spacers - the spacers can be used on freehubs, BB cups and freewheel hubs.

Slightspeed

Pretty sure they were 1mm. I used two on the bottom bracket, but one probably would have worked. Didnt want to do it twice.

Kimmo

Except that a dork disk isn't going to grab the RD and rip it around over the cogs.

TimothyH

No, but the dork disk presents other, very real dangers. -Tim-

Kimmo

Indeed. Far be it from me to advocate actually employing one; I'd do everything possible to ensure one of these damn fuglifiers was redundant, myself.

I have a 10s billet cassette that I had a mate machine a few mm off the back of. It sits on a 7s cassette body I mounted on my RS-81 wheel, with the axle at 132mm. Non-drive spokes tightened a turn and a half or something like that. The Red RD clears the spokes by 3-4mm, even with the cassette overhanging the hub flange, partially due to the greater angle on the drive-side spokes.

Kontact 

Neither will having the derailleur Low stop set correctly.