Bicycle Mechanics - Adjusting adjustable dropouts

My roadbike has adjustable stops in the rear dropouts that will allow me to position the wheel closer to the seat-tube. It's fairly close right now but I was wondering if I could gain a bit of extra climbing effeciency by scooting it forwards a little more. Should I bother playing with this? I figure if I do change this, then I'd most certainly have to readjust my brake pads. Is there anything else I should worry about adjusting such as on rear derailleur? Would I need to shorten my chain? Would the resulting larger angles of the chain at the extreme gear combos require me to adjust the limits on my front derailleur? Should I just take my bike to the shop and have them do this?

Upon further analysis I think my questions are moot since I'm only changing the wheel position and not that of the whole drivetrain.

Why on earth do you think placing the rear wheel further forward will help your climbing efficiency? It will certainly place more weight on the rear wheel, but i can't see why you think that's a good thing.

As far as re-adjusting your rear brake....no, it's not necessary and the same brake pad position should hold regardless of where your wheel is. That's because your rear dropouts are mostly likely positioned perpendicular in line with the rear brake.

George

Why on earth do you think placing the rear wheel further forward will help your climbing efficiency? It will certainly place more weight on the rear wheel, but i can't see why you think that's a good thing.

Moving the wheel closer effectively shortens my chainstay which should increase traction on the rear wheel as it is brought more underneath the rider. It should also increase acceleration.

Moving the wheel closer effectively shortens my chainstay which should increase traction on the rear wheel as it is brought more underneath the rider. It should also increase acceleration.
You know, that's one of those things people say a lot, but I can't see how it could be true.

Increase traction? On a road bike? It's not like you're slipping any now and what difference would a few cm of chainstay make?

Increase acceleration? Why? Physics applies to bicycles too.

(Or maybe I just bit a hook.)

I was always told that those adjustment screws in the back were for frame alignment. When a frame is welded the tubing moves slightly and those screws in the back allow for the rear wheel to be adjusted in alignment with the frame.

So if you move those screws you may mess with your alignment.

So if you move those screws you may mess with your alignment.Well, I don't see it as 'messing up your alignment' .....the rear wheel can easily be aligned & centered in a matter of seconds using these screws.... Besides, when frames were sold with these dropout adjusting screws, they were never 'set' at any particular position.... they were simply screwed all the way in.

George

I have 2 bikes with Horizontal dropouts, one with screws and one without.
I have played with different positions on the "without" bike, and do notice a more lively feel. I can decrease the wheelbase by about 2cm, and increase the stiffness of the rear triangle by a noticeable amount. The dropout is the bendiest part of the chainstay, so the less dropout inside the wheelbase, the better. Bits of dropout placed behind the rear axle are not part of the rear traingle structure.
With extreme movements, you may need to adjust the small set screw on the derailleur mounting, but I havent so far.
Go ahead and play, you wont be doing any harm.

Well, I don't see it as 'messing up your alignment' .....the rear wheel can easily be aligned & centered in a matter of seconds using these screws.... Besides, when frames were sold with these dropout adjusting screws, they were never 'set' at any particular position.... they were simply screwed all the way in.

So what is the function of adjustable drop outs? Why did the industry go to fixed ones?

So what is the function of adjustable drop outs? Why did the industry go to fixed ones?Well, besides being able to fine tune your wheelbase distance, it allows you to exactly center your rear wheel to maybe compensate for minor rear triangle misalignment. (???) Maybe the dropouts are fixed today due to better (???) materials, welding, etc.... which produces frames which don't need much tweeking once they come off of the jigs. (???) That's just my guess....

George

I'm sure there'll be adjustments needed, but nothing you can't probably handle. Here's what comes to mind:

* The cogs will be closer to the chainrings by the cosine (correct?) of the angle between the dropout slot and the chainline. With a close-to-horizontal dropout, that will be a shade less than 1.0. The difference in the effective chain travel will be twice that, since the chain goes "out and back". So if you move the wheel, say, 0.6 inch, and the cosine of that angle makes that about 1/2 inch, the chain should actually be a full inch shorter. That's one link.

* Taking out that link of chain will probably make up for any change in the "wrap" of the chain around the cogs. If you don't take out that link, you may have to adjust the angle stop of the rear derailleur to adjust the wrap.

* The relationship between the rim and the brake pads will change slightly. Possibly enough that the pad may touch the tire with the wheel in its new position. That would be a Bad Thing. I'm sure there's enough in the slotted ears of the caliper or cantilever to allow you to move the pad to more squarely contact the rim.

* Your extreme chain angles will increase slightly, but unless you've got the min and max on the front der. set with extremely little clearance, you should be fine.

And yes, I would bet you will get better performance from a shorter wheelbase and (esp. with removing a link) shorter driveline. That, after all, is one of the advantages of racing bikes with very tight rear triangles.

nobody mentioned this, adjusting the position of the rear wheel will also affect the handling of the bike. a shorter wheelbase will make the bike handle sharper. thats what i always thought the purpose of horiz-drops were for, but i guess there lots of reasons.

Those adjusting screws are there for adjusting to different tire sizes. The small difference in wheel base won't really be felt.

Okay, so I played with the adjusting screws without messing with any other adjustments and managed to tuck the wheel in a little closer but the effects were not noticable. I have returned it to its original position since it was so close that I was worried that any small rocks that might get stuck to the wheel when I ride in the wet may end up wedging itself against the tyre and the frame and wind up scoring the chainstay near the BB. This would be especially troublesome given that the frame is CF.