loky1179

I picked up a '95 aluminum A1 comp Rockhopper last fall. Thought I'd use it as a winter bike and not have to worry as much about corrosion in the MN winters. I'd been scanning craigslist obsessively, checking bikepedia, etc, etc, so when I saw this for $100, it seemed like a no brainer. Rigid fork, ready to ride, in really good shape.

It wasn't until I got it home that I noticed the rear dropouts did not have eyelet/holes for a rear rack. I was surprised; all the steel Rockhoppers of that vintage had rack eyelets. Anyway, it wasn't a deal killer, I put on some stainless P-clamps to mount my fenders and have been riding it all winter.

Just last week I see a '98 aluminum Rockhopper frame on Craigslist - appears to have almost identical rear dropouts, but these are drilled to accept a rack. Before I saw this, I wasn't going to mess with it - wasn't quite sure if I'd be compromising the strength. But now it looks like it would be easy to do, especially using this photo as a guide. Not to mention I have a couple extra rear racks in the parts bin.

Anyone drilled rack holes on rear dropouts before? Any non obvious pitfalls I should be worried about?

CustomSteel

Measure twice, drill once. Cliche I know, but sound advice. Aluminum is softer and easier to cut through, so you want to set everything up right and drill carefully. Once you have measured and marked where you are going to drill your hole, use an awl or other pointed metal object to tap a dent into the center of the spot where you are going to drill through. It will guide your drill bit and help prevent it from "walking" and causing damage to the dropout. The threads will be easy to cut, just keep your tap well oiled and again start off right by taking your time and going slow. You should have professional results when you are done.

Also FYI, since you are going to be using this in the winter weather, when steel comes into contact with aluminum a unique form of corrosion know as galling is formed when exposed to moisture. Use some antiseize or other anti-corrosive sealant on the threads to prevent this from happening. You can use aluminum bolts instead of steel if you wish, but aluminum does corrode as well, so anti-corrosives are a good thing to use. Stainless fasteners will not be an issue, and are best for your situation.

fietsbob

Racks can be installed using the QR skewer without punching Holes.

CustomSteel

I think that is a great option if he has access them fietsbob.

dsbrantjr

Electrolytic corrosion rather than galling is the concern with dissimilar metals in contact. I recommend Tef-Gel as an anti-seize agent. It was specifically designed to keep salt brine from corroding metal fasteners. I would not recommend aluminum bolts as they lack strength and are easily sheared

Also not the position of the welds attaching the dropouts to the frame tubes. You will either need to position your new holes so that the rack will clear them, which might put you into a rather narrow area of the dropouts, or put washers between the rack and the dropouts as spacers. You could also just reef down on the bolts abd let the rack ears bend over the welds but that would not be my preference.

BTW, what is the problem with the p-clamps, which appear to have given satisfactory service? I tend to just leave things which are working alone.

Retro Grouch 

If it was my bike I'd do it. It's a '95 Rockhopper. What do you have to lose?

rydabent

There is no reason at all that I can see that you couldnt drill and tap the drop out. Just pick an area away from the edge.

HillRider

Given that Specialized thought it was safe in a later model of the same bike I expect you will be too. As mentioned, use a sharp drill bit, deburr the hole edges and use a clean well lubricated tap (M5x.8). Anti-seize on the bolt threads is a good idea but don't use aluminum bolts. They aren't strong enough to be reliable supporting the weight of the rack and it's load over rough roads.

If you want to remount the fender struts to double up on the new rack mounting holes, be sure to locate the rack struts on the inboard side nearest the dropout.

Amesja

Drill baby drill.

I'd go for it too. You don't have much to lose. If you had access to a drill press that would be great. Otherwise drill carefully and use a lot of lube. I like RapidTap as it is good stuff.

Keep an eye on that hole and the area around it on the DO for a while to make sure it isn't causing the DO to fail. It'd suck to lose the rear end in traffic. I'd also be sure to put a short bolt back into it if I ever took the rack off. It'd be stronger with a bolt filling up the hole than just empty. I daresay that the DO would be as strong with a bolt tightly threaded into it than it was before it was drilled and tapped -just heavier for the addition of the bolt. But an open hole would be slightly weaker. The rounder the hole, the stronger the part with the hole in it.

On a similar note, I have drilled/tapped DO's to accept modified claw-type derailleur hangers on a droupout that didn't have an integrated derailleur hanger. I ground off that little tab at the back of the slot so that the claw hanger slot sat flush with the slot of the DO and the axle could come fully back to the rear of both dropouts. That's the issue with the claw-type derailleur hanger, you lose that rear 3/8" of the dropout. After grinding off that tab I then clamp the claw tightly against the DO with a vise-grips and use a couple of bolts to keep it aligned perfectly to the DO. Drill and tap the dropout for the bolt at the rear of the claw and Viola! A replaceable integrated derailleur hanger for a dropout that didn't have one before. I wouldn't do this on an aluminum frame but on a steel bike with stamped dropouts (where you usually find the lack of a derailleur hanger) this works just fine.

loky1179

The p clamps work fine for fenders; I don't think they're strong enough for a rack, and they are positioned too far forward anyway.

I was concerned about where exactly to place the holes. Like you say, the welds could get in the way if they were in the wrong place. Using the craigslist photo as a guide gives me a better starting point.

loky1179

Now you're just making too much sense. I think I'll wait for the weather warm up just a bit before I try this. Like maybe 100F - supposed to be -22F tomorrow morning.

Thanks everybody for all the tips.

Darth Lefty 

Just for reference... My 02 Hardrock has holes in essentially the same place as the above photo, in front of and above the skewer. The rack interfered with the seat stay. I had to stretch out the rack to big enough, then use some longer bolts and add some washers under it to make it work. I'll post some photos later when my phone is charged...

JohnDThompson 

Or using P-clamps on the seat stays.

But if the OP does insist on drilling the dropouts, make sure that the rack will actually fit where you intend to drill the holes, without interference from the hub axle or stays. And make sure you leave enough metal between the hole and the edge of the dropout to prevent failure. With aluminum, I'd go for locating the hole at least as far from the edge of the dropout as the diameter of the hole itself; that is, for a 5mm hole, the edge of the hole should be 5mm from the edge of the dropout, the center of the hole therefore 7.5mm from the edge.

loky1179

Good reminder. I'll shoot for 8mm on center.

loky1179

I may try to make a hardwood drilling jig. If I do it right, it should fit either side. Clamping it onto the dropout takes a lot of the "skill" out of the equation, and that is always a good thing.

bobotech

I usually use a drill bit a size or two smaller than the given drill size for a particular tap when drilling alloy metals for tapping especially if I'm not using a drill press with a solid vise to hold the material in place because bit will wobble a tiny bit and make the hole a little larger.

When tapping a steel hole, you want the proper sized hole but when tapping an aluminum hole, the hole can be smaller than the hole for steel and provided you use cutting fluid, the tap will still run through the smaller hole like butter. And it will leave a bit more material behind so the screws/bolts will lock in place better.

HillRider

I assume you are referring to "number" drill bits where adjacent diameters are very close together, not fractional size where the differences are 1/64". For an M5x.8 thread the tap drill is a #19 which is 0.1660". The next size smaller is #20 which is 0.1610". There are no fractional drill bits close enough as 10/64 (5/32") = 0.1563 and 11/64"= 0.1719"

Darth Lefty 

As promised. Hole in the same place and washers to space it out from the seat stay.

howeeee

there are racks that mount on the seat post and have no truss rods,,this is a much better option.

dedhed

I did this on a Trek tag along so we could mount a rack. Not a big deal.

loky1179

That was another reason why I hesitated initially - seemed like the weld would interfere with the rack struts. I guess if Specialized isn't worried about, I shouldn't either.

loky1179

I suppose for light loads . . . But I don't know if I'd want to throw panniers with 40 lbs of stuff on a seatpost mounted rack. And I don't currently have one of those in my parts bin.

bobotech

Yes! I should have explained that, I meant the next size smaller in number drill bit sizes. Just a bit smaller, not a whole 1/64ths smaller.

scooternut

Considering this myself. I think someone at Specialized is just playing games with us and sending out random bikes with no DO eyelets. I have four specialized bikes, older hard rock, newer hard rock 29er, an allez triple sport, and a tricross triple. Now they all have eyelets everywhere except the tricross lacks the DO eyelets, but has them on the seat stay and forks. WTH, isnt this supposed to be the do all bike??? AT least its the one I really want to mount a rack to for commuting. Really wanting to do the mod as I have all the tools and have cut many threads, but its just a scary place to play with tools like that

fietsbob

Anyhow drill should be no larger than the minimum width of the valley bottoms of the screw..
then you buy a 5 x .8 tpMM tap to cut the threads and a tin of oil to put on the tap so the cut goes cleanly.

the machine shop trade has a Cutting Oil , but you may not use up a dropper vial in your lifetime ..

1/2 turns cutting, 3/4turns backing out, and then repeat, continue the cut, clear chips of metal, removed , cut

process slowly, so the thread cut is clean.


NB Specialized does not make their bikes , they contract that out..
they design and market them.
distribution warehouse and warrantee services .