I've got a late 80s specialized hardrock and I am curious about these rear dropouts. What is the purpose of the hole in addition to the regular slot dropout? Can I mount the wheel through here? I am curious because it could provide more clearance for some cushier tires.

I am also curious about the rear hub. It has a nut on each side that locks the wheel into the dropouts instead of a quick release. At first I thought I could just remove these nuts and the axle and replace it with a quick release. But the axle seems to be part of the hub. Is it possible to put a quick release on this hub?

Thanks all

The purpose of the built up area it properly position the FW over the derailleur so the index shifts to its best potential.

While the hole may be big enough for the axle to slip through you likely couldn't spread the frame enough to get the wheel in without damage.

A quick release would require a hollow and much shorter axle.

Googling around the dropout is normal for that bike - didn't really find an answer other than just because.
You can replace the axle with a hollow quick release axle if you can find cones that match - they have to be replaced at the same time. I've done it on generic replacement wheels before.

I never understood those dropouts. You find them on a few other frames out of Japan. It gives you the look of a horizontal dropout without the functionality. Shoulda just gone with vertical dropouts, IMO. I took a grinder and a file to one of my daughter's bikes, which was an old Hardrock as well, since I was converting it to an 8 speed Nexus IGH, and needed the ability to adjust chain tension.

Read post 2.

Understood, but why did they make it look like a horizontal dropout? A vertical dropout would achieve the same purpose, and make it easier to remove and replace the rear wheel. One of the advantages of a horizontal dropout is that they're much more tolerant of misalignment during brazing/welding. This dropout has neither advantage. Additionally, why is this derailleur so dependent on wheel placement when many bikes from that era had horizontals and didn't have this issue.

There's really no adjustability in this dropout. When I sold Hardrocks in the 80's and this dropout came out, we all scratched our heads. You just put the wheel in and slammed it all the way back, and they were all centered to our eyeballs.

I really think this was done because people's eyes were used to seeing horizontals, so they made them look like that. The fact that I could grind and file it down to look exactly like a regular horizontal dropout leads me to believe that this was the intention:

I agree it may have just be a looks thing. Perhaps large amounts of horizontal dropouts were modified like this to use up stock. Perhaps vertical drops were still trickling down from on high. Also fitting the vertical drops is likely a more precise operation so maybe there was s learning curve too

I'm guessing this was a stop-gap measure until the new forging dies for vertical drop-outs were ready and the assembly process was ready to use the new parts.
I agree it's not a great solution and if it were my bike, I'd probably file the dropouts also.

+1 on the all the advice about replacing the axle. It should come out one side or the other and if one bearing surface is part of the axle you will need new cones. If the axle is just an axle, you should be able to re-use the existing cones. Be sure to check the threading and diameter of the axle, they are not all the same. You might also want to get some new lock nuts made for quick-release axles since they will have ridges on the face and have rounded edges to help the wheel stay in place and to make it easier to insert.

I think certain things just set me off because of memories of a past life as a bike shop employee.

When these dropouts came out on Hardrocks, everyone in the shop gagged when we saw them. WTF?

Black anodization is another thing that bothers me. When you scratch black ano, there's silver underneath. Whenyou scratch silver, more silver. Building up a bike one had to be very careful not to scratch the merchandise. I couldn't count the number of times a customer would see a very small scratch on a black anodized part and want a discount. Every LBS employee that ever turned a wrench knows what a black anodizing tool is - Sharpie!

Alright, alright, I'll go get my adult beverage and calm down now...

It does give you an option to cut and file if you need that extra room.

I have seen these before what I believe was done is they took a horizontal dropout and added a bridge in the middle to make a fixed position dropout, normally a 1/4 inch or so plate block is used for this .These have left many a mechanic a bit confused when looking at these it took me a good five minutes the first time saw one to figure it out. As said you can't really use the hole for anything but yes you can grind the bridge out and use these like a horizontal dropout.

I doubt it. Vertical dropouts have been available for many years before the OP's bike was spec'ed. Here's some SunTour examples from the late 70s:



I suspect it was a marketing decision to go with the then-fashionable horizontal dropout look.

Yep, I was just thinking about those late 70's Centurion Pro Tours with vertical drops, since I have one hanging in my garage...

The first bike I ever saw with vertical dropouts was a Panasonic built 1977 Schwinn Volare: E-Bay Photo - 1977 Schwinn Volare Photo by EmailNBheleu | Photobucket



Was there anything earlier?

SunTour and Shimano both released their vertical dropouts in 1975 and they immediately were spec'd on several top line Japanese racing bicycles including the 1975 Kabuki Diamond Road, 1975 Miyata MX-P and 1975 Panansonic Pro. The USA marketing brands quickly followed suit with examples such as the 1976 Nishiki ONP. Proprietary vertical dropouts were also the choice of many of the state-of-the-art, alternate material, frames of the mid-1970s, such as the Teledyne Titans and Kleins.

However, Shimano and Suntour were not first with vertical dropouts. Simplex released their version in 1974 and Campagnolo offered vertical dropouts as facr back as catalogue #15 (1967).

Some manufacturers of the era were building bicycles with radically short chainstays, to the point where the tyre had to be deflated to insert the wheel into the dropout. Vertical dropouts permitted shortening of wheelbases with out this impracticality.

Very interesting, thanks for all the details!

Just a reminder that the french constructeurs did a lot of things we think of nowadays as very modern. Here's a Rene Herse with vertical dropouts, vitage unknown, but pre-dates the 70's SunTour verticals by at least a couple of decades: