I know this has been covered before but what the heck.

If your bikes have dropout adjustment screws, how do you set them? And why?

I've heard about wanting to get the guide pulley position right w.r.t. the FW. I did that subtle tweaking on one bike though the real reason was to tweak the effective chain length. Otherwise I generally set the screws in moving the axle forward. Since the bikes feel different and have different geometries I'm not sure there is much correlation between them all.

So what do all you world-class experts do? Edjukate me on your motivashinul reasons.

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...if the dropouts are really long, I use the screws to either set the wheelbase longer or shorter, or sometimes to allow for a fatter tyre if moving the wheel way back will help with fender and stay clearances.

Otherwise, I just mostly use them for fine tuning a centered position for the wheel alignment. And I'm not sure I ever change it much once I have a particular bike set up. I'm working on one of those Gios Compact frames now, with adjustable dropouts. The rationale for those was you could adjust the wheelbase and thus your handling for a particular style of racing. (you probably already know this)

I believe you when you say you set the wheelbase longer or shorter, but do you set the wheelbase longer or shorter?

I do know about changing the handling, or at least supposedly doing so. My question is really about what people actually do here. I have never actually experimented with it. Don't know how much I could learn doing it.

With modern stuff I get the wheel straight and move on. With vintage gear the position of the guide pulley can make a big difference in the ease of shifting and lack of ghost shifting IMO.

I always figured if the wheel was far back in the drop out that the screws stuck far out. In my experience, far-out screws got bent.

My two bikes that have them are second hand Craigslist buys. I believe both are pair are set approx. half way. Assumed it was for micro centering the wheel left/right, and having approx half way gave plenty of adjust either way while still having plenty of drop out for the skewer to bite. I actually have no idea though. Never noticed any problems, so have never touched them.

I have always run them full in to keep the wheelbase tight and they get bent if left hanging out. I tweak them a little to center the wheel in the stays. That because bicycles used to be hand made or at least touched by human hands and as such were never absolutely perfect like computer robot machine stamped out in the box factories modern bicycles.

A while ago I set them back as far as they would go to help maximize chain wrapping around the freewheel, and hoping to prevent skipping... but I don't think it was that effective.

However, recently I was reading that it can be used to set the jockey wheels closer to the freewheel, hopefully improving shifting performance.

adjusting further back can help allow for larger rear cog as the wheel slides back and up, away from the derailleur.

Maximum short wheelbase for maximum street cred.

...some of the older rear drops are pretty long (at least the ones I have. You can get about an inch of wheelbase either way, and I can feel that if I'm paying attention to stuff like how it climbs out of the saddle.

But it's not a real big deal with me now. I'm olde enough and slow enough (and I have enough different bicycles) that if I want something with quicker/slower handling, I just ride a different bike.

I don't set the adjustment screw the same for all bikes. It's dictated by a lot of factors such as max cog, chain gap, tire clearance, etc. Rather than restate what T-Mar already wrote with great clarity, I'll simply quote him here:

Re too-long adjustment screws, if you settle on a particular setting for a given bike, you can loosen the end cap, cut to size, chase threads by backing out into the dropout, reposition screw, screw on end cap again for a flush fit.

That's a major reason for me. Shifting characteristics can be altered with wheel position in the dropouts. If your RD doesnt have a "B" screw, this is all you have for that purpose.

+1, only reason I have for setting the adjusters in a particular position. I set the wheel first, then I set the adjusters to the axle. Once they are set, as long as the cogs stay the same I leave them alone. Past that, I am not sensitive enough to the slight change to the geometry that altering the wheelbase would bring. No bike with those really long dropouts here, and I ain't that good, by any means or measure.

Bill

@gaucho777, thanks for the T-mar quote.

Some of those points make sense but may not be so significant.

I have only one bike for which the handling is, ah, quick enough that I'd care to lengthen the rear. (And my ego won't let me anyway.) After a weekend on the tandem every solo bike I own feels like a twitchy sonova' for the first mile. After a few days commuting on the Grandis even its handling begins to feel normal.

For chain alignment, I don't see that it matters. A 1cm change in the screw position will give you a variation in the effective distance from the top of the selected ring to the top of the selected sprocket between, say, 46 to 47cm, or a bit under 2.2%. If the FD moves, say, 6mm (the nominal sprocket separation applied to the rings), that 2.2% is equivalent to re-aligning your BB by only 0.13mm, essentially insignificant. Even if I'm off by a cumulative factor of 3 this is still less than 1mm re-alignment of the BB.

I'd argue that any generalities about the guide pulley/FW position apply only to specific cases, if you take my meaning. On different RD's the guide pulley moves differently as chain take-up happens. On some the pulley moves fore and aft, on others it moves in a tight circle, on others it is mostly vertically.

With a Rally/GS style cage, the movement is almost entirely vertical by design, giving a similar effect as a slant parallelogram. But unlike a true slant-p design, the vertical position of the guide pulley changes with a front shift as well as with a rear shift. To put it another way, a pulley to sprocket distance optimized for one ring will not be ideal for the other. Since it must accommodate the higher position when on the small ring, the big ring will always have a greater distance than optimal. The bigger the front shift the worse this problem will be.

Which brings me back to the subject of this thread. When I first set up the Masi (Henry III long cage on a NR body) it didn't shift well. I concluded that the pulley-sprocket distance was too great. A larger guide pulley helped some but of course it occupied slightly more chain, moving the pulley down and negating some of the gain. Adding or subtracting chain links meant changing the length by an integer number of inches, not what you'd call subtle.

By far the most significant effect on the drive train from dropout screw position is effective chain length. Move the screws, say 1cm, and you change the effective chain length by 2cm. That's 0.78". With a Rally-type cage that has an arm ratio of about 3:1 that raises or lowers the pulley by a bit more than a quarter of an inch. That let me fine-tune the vertical position of the guide pulley to a good working distance for the big ring while still not too close for the small ring. The fact that the rings are 47-42 helped, of course. That the ultimate axle position came out to be forward anyway was an added benefit to my ego and street cred.

The Grandis has a similar setup (Soma long cage on a NR body) but I'm not sure about the cage's arm ratio. Its gearing is different and maybe I lucked out find in a good screw position, but it shifts just fine.

Anyway, for this type of RD cage the vertical position of the guide pulley is the real test, and the only reason I've found for tweaking the screws one way or another.

On the bike I built in 1975 they would no longer turn, so I broke them off.



For Most people .. so wheel goes back in the same place to Index shift like it did before ..
brake pads still contact the rim the same ..

Thats why Vertical dropouts are paired with indexed shifting.

./.

My experience is that modern, machine built frames are no better aligned than old-school frames with horizontal dropouts. One of the advantages of the vertical dropout is consistent placement of the derailleur pulley with respect to the cogs; this became particularly important with indexed shifting, and I suspect this is the primary reason vertical dropouts have come to dominate on modern frames.

Most any framebuilder can nail the center of the rear wheel with vertical dropouts, which is what most bikes are built with now. I think older frames used Campy 1010's because "that's what all the racers used", not because the were incompetent.

5 out of 7 of the people in my UBI framebuilding course used vertical dropouts, the other two were building fixies and used one form or another of adjustables to take up chain slack as they wore out.

Each and every one of us had a rear wheel that was dead on centered. It was the first frame build for all of us. A good frame jig makes it relatively easy.

Are you asking if we have an innie or an outie?

Wow...didn't know this detail. I never reall thought about it much. I just use them to center wheels in frame with the the chain length used, approx in middle of drop out.

just makes putting the wheel back on an centered a lot faster.

I use them to align my wheel but I confess I don't really know much about what they might otherwise accomplish.

To me it seems the key feature I'd like to use them for would be to possibly extend my rd capacity a few cogs via adjusting the effective chain length. AFAIK this is done by moving the axle back as far as possible to increase chain tension. This increased tension pulls the rd forward a bit, moving the upper pulley away from the nearest cog. Do I have this correct? Any potential gotchas when doing this adjustment?

PS: I recently had occasion to buy some d.o. screws and the were plain old 3mm -- no need to buy special screws. I think around 30mm length would be about optimal. Note that ends are more difficult to come by and your d.o. threading may vary.

Yes, that's an old-school trick to get your Nuovo Record derailleur to work with a 30T cog instead of the maximum rated 28T cog Campy specs. But as you suspect, it does come with a cost. The pulley is further from the cogs, allowing a larger cog to be used, but shifting performance can suffer as a result. This is more of an issue with indexed shifting, which is more sensitive to pulley position than friction shifting where you can overshift briefly to compensate for this.

Like gaucho777, I use them differently depending oh the bike. Derailleur function, wheeelbase and fender clearances are factor in. So does having excess screw exposed. Now, on my commuter fix gear, I set it to accurately set the chain tension and make for quick wheel installs in the dark, cold or wet.

(My good fix gear was built to accommodate the screws but I found that the technique of pulling the wheel back with my left hand on the left chainstay and pulling the tire over to hit it, then tightening the right axle nut worked so well to get the chain tension right that I scrapped the screws. This requires an accurate and round crankset and rings. Thank you, Sugino 75, for making my life easier.)

Ben

For some reason, it used to be very popular for racers to ride fixed gear in the off and early season. The long campy dropouts made it pretty easy to throw a fixed cog on there and get your chain tension right.

Surely someone else remembers this... Not sure if it's still done. I'd imagine long base miles are probably more effective in the early season.

One has to remember that it was a different world 40 years ago. Many of the European frame builders did not use jigs because that was the way they had been taught. Many held to the belief that restricting a frame in a jig during the brazing process created undue stress in the frame. Many frame builders were still just tacking or pinning a frame together prior to brazing, so the dimensional accuracy and precision that we have to-day was not present.
Even so highly respected a figure as Tullio Campagnolo touted the virtues of variable wheelbase.