BykOfALesserGod

Aside from easier SS or fixie conversion?

My new bike has horizontal d/o and set screws to keep the rear wheel from moving in the dropout while under load.

RollCNY

IMO
1) Easier to center wheel between chainstays if frame isn't fabricated perfectly.

2) Slightly easier to remove rear wheel and clear RD pivot. On vertical dropouts, some QR's are a PITA to clear.

rpenmanparker 

Horizontal dropouts were normal until about 25 years ago or so when vertical dropouts began to take over. They facilitated fine tuning the centering of the rear wheel between the stays using the adjustment screws. Where they fell down was in allowing the rear wheel to be pulled off line by the force of hard pedaling. As lighter, less secure quick release skewers have become more popular, it has become more difficult to keep the rear wheel straight under hard pedaling with horizontal dropouts. Also horizontal dropouts are difficult to use on a compact geometry bike. As bike manufacturers became more convinced that frames could be built and maintained "straight", the need for horizontal dropouts greatly diminished. And nowadays there is not enough room behind the seat tube for the wheel to be removed and replaced with horizontal dropouts. While they are perfectly useful on the older frames they have been installed on in the past (grandfathered as it were), they are not suitable for modern frame designs.

I don't know what you mean regarding your screws being for the purpose of keeping the rear wheel from moving. There are contraptions like this, but most of the screws one sees are for adjusting the initial line of the wheels. They don't help keep the wheel from being pulled out of line.

Bottom line is horizontal dropouts were right for their time and any frames built back then, but not for frames built now unless they are throwbacks to an earlier design aesthetic.

eja_ bottecchia

I seem to recall seeing, in one of my rides, a Quintana Roo that had horizontal dropouts. The dropouts, however, were facing backwards.

David Broon 

You see that a lot on TT/tri bikes, it allows the rider to get the wheel closer to the seat tube, thus making it more aero.

eja_ bottecchia

thanks for the explanation...that makes sense.

merlinextraligh

Which direction do your drop outs face?

I think what you're describing is rearword facing horizontal drop outs.

The purpose of those is to fine tune the space between the rear wheel and the seat tube for aerodynamic purposes.

My Cervelo P2 is built like that.

It's different than traditional horizontal drop outs that open forward.

Edit: beat to the punch above.

datlas 

Back in the day, people would often adjust the screws so the rear wheel was as far forward as possible, to create a shorter wheelbase and thus supposedly improve handling. At least that's how I remember it.

I think they are a major hassle with getting the rear wheel centered and far prefer the vertical dropouts that are pretty much standard now.

Rearward facing ones are for fixed gear/track bikes so you can adjust the chain slack for different cogs.

BykOfALesserGod

Ok, the tri/TT bike explanation seems to cover it. Yeah my new bike is a Roo Kilo. I feel smarter now!

merlinextraligh

here's a pic of my P2, as you can see the distance to the curved seat tube is governed by the position in the drop outs.

bikemig 

I pretty much agree with this with a few caveats.

I have a compact bike (or semi-sloping if you prefer) with horizontal dropout and it's no problem removing the rear wheel but then the bike has slightly longer chainstays than a racing bike (it's a salsa casseroll). So the problem with there not being enough room behind the chain stay for wheels to be removed with horizontal dropouts applies primarily to short chain stay bikes but it is not an issue with a slightly longer chain stay. Yes you do need to use a stronger quick release with horizontal drop outs than has become the norm but to me that's a plus not a negative. This is one place where I want my gear to be overbuilt.

I don't agree that horizontal dropouts have no place in "modern" bikes and/or are a "throwback." Horizontal dropouts make it easier to run the bike as geared or a single speed which some end users may like. Some users may prefer a more versatile frame. As with most design decisions, there are trade-offs.

BykOfALesserGod

Yep, my d/outs look like that but there little screws that come in from the front

merlinextraligh

There on a P2 as well. regulates distance to the seat tube. Just can't see them in that pic.

99Klein 

The only thing I really dislike about the Klein's and the only advantage I can really see is that no matter how many watts you can dial up, your rear wheel is NOT going to slip forward. Makes changing a tire/wheel a PITA.