nishiki12

So i have a nishiki anasazi hybrid aluminum framed bike, and i wanted to attach a bike rack onto it. the rack holes were blocked by the rear disc brake, so instead i drilled 2 holes all the way through the seat stays, near the base close to the derauiler and brakes. I added 2 panniers, and the whole setup weighs close to 10 pounds in the bike. Ive had them for about a month now and its been fine, but i want to know if there could be any long term effects.

rhenning

The frame will eventually break without some kind of reinforcment around the holes. You basically have destroyed that frame at this point. Roger

AnkleWork

Yes, there could be so keep a close watch on the area around the holes.

Kontact 

Bad news on a disc brake bike, because the discs put even more strain on the bottom of the stays.

There are devices made to let you mount racks without drilling holes in thin frame tubing.

Iride01 

Clamps that wrap around the tubes probably will have been a better idea, but it's a heavy bike so maybe the tubes will handle it. It's also likely a low strength allow which is why the bike is heavy. The tubes are thicker to give it the strength it needs. And that is a plus actually. A quick catastrophic failure is less likely because the aluminum is softer.

But who knows for certain. Just watch it and at the fist signs of cracking or deformation, decide if it's worth fixing or getting another.

nishiki12

what should i do to prevent any damage
ive been hit by a car on this bike 1 time, so i thought it was fine

AnkleWork

1. Don't drill the holes.
2. Damage will come from fatigue and that from use, so don't ride it.

Marcus_Ti

Bingo. Frame compromised.

There's a right way to do racks on a bike... And then there's this.

nishiki12

I don't know much about biking, but my seat stays were too large for the p brackets included with the rack. I just assumed that my bike had larger than average seat stays, so i figured it wouldn't be too bad to drill holes into them. The holes drilled were small, just big enough for the drum lugs I used for bolts to go in. I just looked, and there seem to be no cracks in the paint or the frame, even though I've had the holes there for a good four months, and one of those i had the 10 pound panniers on. I don't do any trick riding, just commuting daily, and occasionally light cross country riding. Are yall sure that the frame is completely trashed, or is there some hope it will be fine with the rack. also, if i weld the parts together, will that solve the issue?

nishiki12

also why would they have 2 predrilled holes in the tops of the seat stays if holes in the frame is frowned upon

Kapusta

Problem is not just the rack, it is the holes in the frame.

The fact is that the frame is now weakened, but by how much is impossible to quantify. It may be fine indefinitely, or it may eventually crack.

It is aluminum, so at least it won’t rust.

Whether this is something I would personally continue to ride I can’t tell without seeing a picture.

Kontact 

Your homemade holes are frowned upon, not the ones designers planned for.

Racks are never mounted to holes in tubing. Some tubing is reinforced with a welded threaded eyelet for mounting racks, but you will never see a simple hole in frame tube that is supposed to bear a load.

The clamps included with the rack are for common steel tubing diameters. Your aluminum tubes are unlikely to be oversized for aluminum.


Your bike may not crack from what you've done to it so far, but since you say you really don't know much about bicycles, how about quitting while you're behind and not ruining the heat treatment on the tubing with a welder?

79pmooney

Look at those top pre-drilled holes. Are they just holes drilled in the aluminum tube or is there a sleeve welded into a larger hole? Way to see is to look into the holes. Is there threading all the way through or is there a couple of mm's of tube wall, nothing, then the opposite wall. In other words, if you dropped a small ball bearing into the hole, would it fall into the seatstay or roll out the other side of the hole? If it falls in, the manufacturer believes that maybe what you did will be ok. If it rolled through and falls out the other side, the manufacturer believed what you did was not OK.

Ben

davidad

It's aluminum, therefore it will crack at some point weather you have drilled it or not. I am afraid that you have hastened it's demise. Ride it until it dies and get a steel bike for toting loads.

WizardOfBoz

Nishiki, there are three ways to think about metal failing.
1) Yield. That is, bending. Depending upon the type of metal and the heat treat of your bike, your seat stay could bend if the stress (force per area) gets high enough. So if your heat-treated frame happens to be tough, it will bend with high force.
2) If the heat treated alloy is brittle, it will just break with sufficient stress. Or, even if your frame alloy is tough, if the stress exceeds a certain level, it will break. Again, stress is force per unit area (e.g. pounds per square inch in our little backwoods country) and when you drilled the holes you reduced the area of metal that the seat stays use to handle the force. So your frame is now weaker. Will it bend or break outright in normal use? Maybe. It would take some engineering analysis, knowing your weight, your riding habits, and the streets you ride on to say for sure. But these type of failures would be from, say, hitting a bit pothole with a full bike rack.

There is another type of failure, called fatigue failure. Turns out, there are stress levels where the stress is not high enough to bend or break your bike outright, but that will cause failure if the stress is applied and removed many times. The drilling you did is a double whammy for this type of failure. By drilling, you reduced the area of metal in the frame. Any force (e.g. from hitting the pothole), is spread out over less area. So the stress (force per area) is higher and more likely to be over the fatigue limit. Second, when you drill there are sharp edges and corners that act a "stress concentrators". These increase the local stress, and hasten fatigue failure. As a last issue, if the metal heated up significantly, that may affect the aluminum's strength.

The holes that were pre-drilled in the frame were probably chamfered or at least de-burred (to reduce the stress concentration) and were likely drilled pre-heat-treatment.

You could ride this until it fails, taking a chance that it won't fail at a bad (dangerous) point. You could buy a replacement frame or a new bike. Or you could try to jury-rig a strengthening collar of some sort.

One thing you absolutely should not do on an aluminum frame is fix it by welding. Don't get me wrong: you could weld it. But this leaves a "Heat Affected Zone" in the metal which almost certainly would fail quickly. But aluminum frames are welded! you say? Yes, that's true. But they're heat treated afterwards to get rid of weak and brittle areas. You could do this, too, if you had a huge heat treatment oven and were willing to repaint the frame. So, welding's not usually practial for al repairs.

Wish I had better news. Hope the explanation helped at least.

3alarmer 

...why did you decide to ask a month after drilling the holes instead of before ? It seems counter-intuitive.

wrk101

You ruined the frame. Find a replacement. The good news is used hybrids are typically cheap.

SkyDog75

??!!

Because those factory holes are most likely reinforced by a threaded insert. Even if they aren't, the frame's designers would've been able to make accommodations for any increased stresses caused by the factory holes, but they didn't account for the ones you added. Also, the holes you added will be under more stress since they'll be bearing the weight of the rider and the rack load. The top hole(s) don't bear the weight of the rack; for the most part, they just stabilize it against fore/aft forces such as from acceleration and deceleration.

That could possibly make the problem even worse. Aluminum frames are heat-treated after welding. If you weld a part of the frame, it'll weaken the aluminum in the area around the weld -- by 30-40% according to this thread on the American Welding Society's forums. You'd have to heat-treat the entire frame again after welding.

In a nutshell... The frame's significantly compromised and would probably cost less to replace than repair. I wouldn't ride a bike with extra holes drilled in the stays -- especially ones big enough to take a bolt big enough to bear the weight of a loaded rack.

Kontact 

This isn't true.

fietsbob

+1) start looking for another bike.

maybe if there were rivnuts expanded in those holes it would have been better..







...

Kontact 

What sort of brazing compound do you prefer for aluminum?

fietsbob

you missed the revised edit.. trying hard to play gotcha.


JB Weld is Epoxy with an aluminum powder filler, in the resin.. maybe that will help.

travbikeman

Just curious but if the OP had tapped the holes that were put into the frame and inputted a screw, wouldn't that provide support?

Marcus_Ti

There's no material to tap into. The pipe is too thin for threads.

fietsbob

Too late now, should have bought a QR Skewer mounted rack, and not bodged up the frame..