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I have an aluminium frame, and would like to add another bottle cage. But there are no mounts below the downtube. I've installed rivnuts into a steel frame before, which worked well.

Can I install rivnuts into an aluminium frame? If the thickness governs yes-or-no, then how would you measure the thickness before drilling?


Searches turn up conflicting information, ranging from "OMG no!" through to statements like:

Some have expressed fear of weakening the frame by drilling holes in it. If done properly with the right kind of rivnut, the rivnut adds strength back to the frame around the hole. If you use steel rivnuts on an aluminium frame it is actually stronger than the metal it replaces.
from https://www.electrifybike.com/technical/installing-rivnuts-in-bicycle-frames#/

So, should one install rivnuts onto a frame made from Aluminium?

Inspired by What are velcro alternatives for frame mounted bag?

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    I'd bet some money that on a light aluminum frame, like the aluminum road racing bikes in the 2000s, the answer is no, because those tubes are really very thin - and anyway, would you really need to add extra bottle bosses to a racing frame? I am guessing that you are dealing with an aluminum frame with thicker tubes than that, however.
    – Weiwen Ng
    Sep 5 '20 at 13:59
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    You can (non-destructively(!)) gauge the thickness with the technique of ultrasonic thickness measurement. Sep 5 '20 at 14:31
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    I would not recommend this on an aluminum frame. Sep 5 '20 at 17:18
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    Steel rivnuts in an aluminum frame sounds like a great way to get corrosion.
    – MaplePanda
    Sep 5 '20 at 19:04
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    Regarding corrosion: Are the stock rivnuts in an aluminium frame not steel? Is it even possible to make them out of aluminium? What about the steel screws used everywhere?
    – Michael
    Oct 11 '20 at 8:16
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I would recommend you not do this. I have first hand experience with drilling holes in frames, albeit only one hole. Although it was a success, the situation was different.

The short version...on two separate bikes, I drilled into the seat tube to allow for a dropper post routing. I have had no trouble.

I did my homework, considered pros and cons, and most importantly considered the cost of ruining the bike. After drilling, I would ride it and then inspect it, gradually increasing the amount of rigor of the test, to the point that I was going over jumps and landing flat.

Other posts suggested that there could be cracks that I don't see. It is possible, yes, but based on the amount of abuse this bike has gone through, I feel like if it were going to fail, it would have failed by now.

Your situation is different, you would need two holes, and they are proposed on the downtube, where there is more stress. If you have a butted frame, the material is thinner in the middle, right where you would want the holes to be.

I do not think the rivnuts will add strength to any holes you drill. This might be the case if it were a perfect fit, and welded in with no voids. But that is not the case. They are not designed to add strength to anything, just to add threads to something that is already plenty strong.

You will not be able to figure out how think the material is without drilling into it, at least not that a layperson can do. I expect someone scientist with the right xray or ultrasound could do it, but practically speaking, your guess is the best you can do.

I would suggest a similar approach to what another user mentioned. But here is how I would do it. Cut a strip of old inner tub, about 2 cm wide. Wrap it around your frame once or twice where you would have wanted to drill the holes. If you want to glue it on there, you can, but you don't need to. I'd suggest Barge Cement, just do it outdoors, that stuff has some pretty serious fumes. Now just zip-tie the water cage on there, nice and tight. If the zip tie slips of the spot on the water cage where the bolt would go, just bend a little lip into it.

Lastly, I get the hunch you are the kind of guy that likes to tinker with stuff. Me too. In this case, I would suggest your tinkering skills with drill bits would be best applied somewhere else.

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    zip-tie the water cage on there Hose clamps are probably better. Oct 23 '20 at 21:22
  • Sure...I agree that a hose clamp is also a good choice. For me, I like the zip ties because I have about 50K of them already.
    – Ben Stokes
    Oct 23 '20 at 22:24
  • I have successfully added a water bottle cage under the downtube by using two 5mm wide zip ties per side (two around the top eyelet, two around the bottom one). I used inner tube strips, held in place with electrical tape (just for installation, afer tightening the ties, the tape does nothing. The installation went zero problems for four 500+ km rides on asphalt (both smooth and rippled/cracked surfaces) carrying a 750 ml bottle.
    – Jahaziel
    Nov 16 '20 at 22:58
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Best solution is to find some velcro strapped cage mount. Dissimilar metals touching each other can cause ionic corrosion due to electrolysis, especially in humid weather, rain, salty conditions.

I live in San Diego, USA, 1/4 mile (400m) from a bay and 4 miles (6.5km) from ocean spray and my aluminum window frames have 1/2 inch (12.7mm) holes in those facing the ocean, no damage at all in windows facing east.

Average humidity is 60-80 percent every night, and 30-60 percent during the day. These frames are easily the thickness of a bike frame and anodized but 25 years old. You may be OK but the metal will be bare inside that will speed up the process. Why risk it?

Derek, Ex Aerospace engineer.

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    Hi and welcome to the site! The corrosion is only one aspect of having holes in the frame. Compared to window frames, bicycle frames experience dynamic mechanical loads, and weakening the frame via drilling is arguably a more serious problem than additional holes (a bike frame already has many holes). Oct 11 '20 at 14:45
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    Aluminum rivnuts in aluminum frame would not cause this issue.
    – Mołot
    Oct 11 '20 at 20:24
  • @Mołot But drilling hole(s) exposes bare metal and is quite likely to add stress risers - both will make the frame much more susceptible to corrosion. Oct 23 '20 at 21:26

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