Advice needed setting up derailleur with horizontal dropouts
 

It didn't occur to me until now that I have only ever set up shifty bikes with vertical dropouts or thru-axle, and I have only ever set up horizontal dropout frames as single speeds. This seems to add a new dimension to consider (or not?)

Looking at my current build (Centurion Lemans) last night, it looks like the fore/aft position of the axle in the dropouts could affect the shifting, kind of like the B tension adjustment screw? FWIW it came with some nifty little spacers to avoid going to the extreme end of the dropouts. They're out of the frame now but I can add them back.

Ideally, I want the tire as far back as possible to increase clearances and, secondarily, to make my effective chainstay length a little longer, but I will also be running as wide range cassette as possible for my derailleur and I am wondering if the relative axle position in the dropout will affect the ability to shift to the largest cog... what's the "IDEAL" position?


I can take some pics if you guys want

I've only used the space to attempt to adjust for better shifting and pulley wheel clearance. Not sure I got anything better in my case.

Clearance to seat tube on a tire might bite you if you get too big a tire and can't get the wheel on or off the drop out while tire inflated.

Horizontal dropouts are not truly horizontal, so this helps you a little bit.

Since you plan to run a "wide range" cassette any distance you can (effectively "lengthening" the derailleur cage) impart will help to some degree.

It will also give a you little more wiggle room for the B adjustment aspect. This will typically get more chain wrap on the smallest cog, as this is desirable. I have found that by going almost all the way back on the dropouts gets me up to an additional tooth of engagement. That is actually a big deal on these old drivetrains.

You should utilize the limit screws (within the dropout) unless you can get perfect wheel alignment/centering with the axle bottomed out. Not likely, even on the best of vintage frames. When the frame maker knew that there was adjust-ability designed in, sweating perfect bottomed out alignment wasn't the top priority.

Anyway, long story short, with what you are trying to achieve, the farther "back" you go the better. You are getting a longer cage for free, albeit a small difference, it does help.

Side story- When I was a kid, we ran our axles as far forward as we could. Everybody knows that stiffer is better, and a short wheelbase was the ticket. But then again, we had straight blocks and 16 year old legs! :lol:

That's awesome, your side story that is! I was thinking going farther back would hurt me, I'll bottom out the axles, center the wheel (I am good at that from my track-frame experience)

Quick follow up question, as I have set up more single speeds than I have shifty bikes - on the B adjustment screw - where would you START with that? screwed all the way in? All the way out? I am actually very comfortable setting up limit screws and cable tension (this build my be friction shifting so the latter may not matter too much) but the B screw is a mystery to me.

FWIW I plan on running an Ultegra long-cage (touring version I think) RD6600 with a Deore 11-36 BK Cassette. If that doesn't work I have an Ultegra 12-27t cassette lying around OR I can pick up any number of 11-32, 11-34 10speed cassettes these days for next to nothing.

I believe pushing the wheel all the way back was one of the "tricks" to running a 29 tooth FW with a Campy NR rear derailleur. I never ran Campy derailleurs so this is from vague memories. Might be interesting to see if wheel location can be seen on Mt. Washington bikes pre 1977 when most would have had horizontal dropouts and all the strong road racers running 28 tooth FWs,

Concerning the RD being forward of the FW, in the early days of derailleurs, there were bikes with the derailleurs mounted on the chainstay, far forward! Didn't work as well, but it does suggest up to an inch shouldn't be a big deal.

Ben

Makes sense. Also, don't forget that a shorter wheelbase should give more nimble handling.

Start with it all the way in (the screw out), so that the RD can swing the farthest "up" if you will. Go to the smallest cog and see that the top pulley is as far forward as possible and still runs smoothly. You need to maximize how many teeth on the smallest cog are in play. If you go too far back, you can get the chain to skip under power.

You will probably have to rotate the B screw so that the RD comes "back" a little, but err on the side of getting more teeth into play on the smallest cog. That being said, sometimes you have to crank the B screw out more just to get some additional tension in the system. It's a little bit of a balancing act, but no big deal either way.

So considering all this, is indexed shifting going to be a problem since it's possible the wheel won't be "perfectly" aligned in the dropouts, as is the case with vertical dropouts?

I didn't consider this before. I do have an old wheel I can screw in to the DR hanger to check alignment I guess on the final buildout, similar to how one would correct a bent hanger....I am sorry guys and thank you. I wasn't around during the golden age of horizontal dropouts!

You will be fine if nothing is bent etc. There is a margin of error built into the system to include some pully float (left/right).

True, vertical dropouts were at least partly invented to help with index shifting, but the reality is horizontal dropouts usually work just fine.
Set the doodads for the middle and if you can't get perfect shifting then try moving it in or out some.

https://cimg8.ibsrv.net/gimg/bikefor...1703fa15d.jpeg

Why wouldn't it be aligned as "perfectly" as it needs to be?

Are these without the little adjustment screws that stop the axle at the position you want it at when removing and replacing wheel? If you don't have the adjusters, then I'd tend to just go all the way back in the drops with the wheel and then align wheel for side to side with brakes and stays every time.

Yeah, no stop screws. I am pretty good at eyeballing from my days of riding a track bike. I guess it's no big deal once you get it right because I don't remove my rear wheel very often at all.

My other bike is thru axle so NO chance of it being off, makes running disc brakes a breeze

I used horizontal dropouts with 8 sp indexed shifting - doesn't make a difference. If your wheel is aligned correctly - either by eye or by using the dropout screws - it doesn't matter to the RD whether it a little forward or back - as long as it's straight.

Yeah it's having the one side more fwd relative to the other I was worried about but as long as it works if it's visually aligned, then I am happy

No problems with indexed shifting (using 105 5800 11 speed 50/36 and 11/32 on two different frames (de rosa and 85 team miyata)

I set the wheel toward the back but no all the way and use the adjuster screws to get good alingment and then don't fiddle

this has worked so well that I recently go a new wheel set (same hub 6800 and cassette) and swapped them in I did not have to adjust the rear derailler at all (probably just lucky)

Your history is a little off. Vertical drops (on high end racing frames) were not rare in 1977. The high end Fuji had them. 1978 I had to request horizontal dropouts as change when I ordered my Mooney. I'm sure the SunTour/Shimano engineers were working on indexing then but it was still behind solidly closed doors and not driving the frame making industry.

Since the wheel slot isn't parallel to the ground, going further back can get you clearance for a larger cog on a road derailleur.

This Suntour Superbe RD has a book max 23t cog. With the wheel all the way back, a 26 fits with room to spare. Pretty sure a 28 would work, though I haven't tried it yet.


https://cimg9.ibsrv.net/gimg/bikefor...086ed71a52.jpg
Freewheel

--Shannon