Ask a Mechanic | Loose Water Bottle Bosses & Curing Brake Squeal on a Mavic Exalith Rims

Welcome to our Ask a Mechanic column where our expert mechanic Daniel Slusser answers your bike maintenance questions. If you have a question for Daniel, please post it on our Facebook Wall or e-mail Daniel directly at Today’s column will review how to repair a loose water bottle boss and how to dial in brakes used in conjunction with Mavic Exalith Rims.


I have a Cervelo R3 with a lose bottle cage boss. It is the lower bolt on the downtube. Is there a way I can get this repaired without sending it back to Cervelo? From: Steven

The nut is too big to be threaded onto the bolt. It is just there to keep the rivnut from spinning as you compress it.

Ever since aluminum became a common frame material loose bottle cage bosses have become a common problem, as they are not brazed into the frame tubing like those found on steel frames. Carbon bikes often suffer the same problem and your Cervelo is no exception. Fortunately, the fix is quick and easy. The bottle boss insert is aluminum and is essentially what is known as a rivnut (combination rivet and nut).

To tighten down a bottle boss rivnut you should first find a long steel M5 bolt that will engage with all of the rivnut threads and still leave 10mm of thread exposed between the top of the rivnut and the bottom of the bolt head. In this gap you need to place a nut for an M6 bolt. Slide the oversized nut over the bolt and then thread the bolt into the frame. When it is hand tight, place a 10mm wrench on the M6 nut to hold it steady while you torque down the M5 bolt. This will keep the boss from spinning as the rivnut is compressed against the carbon and tightened down. Use about 6-8mn of torque on the bolt and you should be good to go.

Short, rounded button head bolts will protect your frame from water bottle bosses.

Keep in mind that the problem you are experiencing is likely preventable. I tend to see these types of issues when riders choose larger socket head water bottle bolts that protrude above the bottle cage to the point that they are impacted every time a bottle is inserted into the cage. This repetitive impact loosens the rivnut until it eventually rattles loose. So, find a low profile M5 button head bolt to use instead so that the bottle can more easily deflect off of it in case any bottle-on-bolt contact occurs.


My Mavic Ksyrium SLR Exalith rims really squeal and vibrate when I use the brakes at high speed. The high pitched whine that Exaliths are known for that I get at lower speeds is fine. My problem is only at high speed. I am using the pads that came with the wheels and set them up the same as I have always done with standard alloy rims. Any ideas on how to fix it? From: Dale


The Exalith rims are really cool with their wet weather braking performance, stealthly grey sidewalls, and the fancy whine that you get when you are on the brakes; but they do have a tendency to vibrate if the brakes aren’t adjusted correctly. It is just a matter of getting your pads toed in as I described in an earlier post. However, you will likely need to do an extreme toe with a 2-3mm gap between the trailing edge of the pad and the rim.

Daniel Slusser is a professional bicycle mechanic with over ten years of experience. He holds a bachelor’s degree in business administration from HSU and a master’s degree in history from Cal Poly University. When he is not riding, wrenching, or writing he enjoys spending time with his wife and two children.