The other day a customer came into the shop saying his front brake kept rubbing on his front rim and he couldn't figure out why. Upon examination, we saw his rim was dangerously worn, worn to the point the rim had deformed. What had been a straight, vertical braking surface was now bent and bowed out. Since this fellow needed to get back on the road quickly, we outfitted him with a replacement wheel rather than rebuild his wheel with a new rim. This guy was lucky, thin rims can blow out while riding, and that can be more exciting than most folks prefer.
Cyclists in drier climates, or those who only ride on dry days may never wear through a rim, but here in the Seattle area where intrepid commuters, randonneurs and other high mileage folks ride through the wet and the crud, bicyclists can and do wear through rims.
The prudent thing to do is pay attention. A handy dental caliper like the one pictured below will tell you if your rim is dangerously thin (less than 1 mm) but most folks don't have one of these in their tool kit.
Visual examination of the outside of the rim can give you some indications of rim-thinning. Some rims have wear indicators but even if your rims lack this feature, you can look for signs of deep wear on the braking surface. A thin rim also often deforms a bit and you'll feel this as a rider via a pulsing when you apply the brakes.
Britain's CTC has published some letters discussing thin rims and other wheel issues here:
http://www.ctc.org.uk/DesktopDefault.aspx?TabID=3827
and one method they recommend is over-inflating your tires (or tyres as they say over there) for test purposes. If your rim doesn't blow out with the over-pressure tyre, you're OK. If it does, I guess the theory is that it's better to find that out in the shop instead of on the road.
You wouldn't think that soft rubber brake pads could wear through metal rims, but the real culprit isn't rubber, it's road grit. Some commuters and cyclo-crosser riders use wheels with disk brakes to avoid this problem altogether but there are a few things you can do to preserve the life of your rims.
First off, try to keep your bike clean. Don't let the grit build up on your brake pads and rims.
Second, some brake pads do a better job in wet conditions. Sheldon Brown and lots of other smart riders have found Kool-Stop salmon pads pick up less grit and stop better in the wet than anything else on the market. We carry a wide range of Kool-Stop salmon pads at Bike Works.
Finally, be aware of your rims and your brake pads. Don't let worn rims catch you by surprise.
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14 comments:
thin rims can blow out while riding, and that can be more exciting than most folks prefer.
Wee bit of an understatement, don't you think?
I would be interested in acquiring one of the "handy dental calipers" - do you have a source?
thanks,
Jack
My pal Tony owns a dental lab and he hooked me up. I'd check with your local dentist or dental lab.
This was pretty common back when mountain bikes used rim brakes. The schrapnel can be horrifying.
http://www.ybmdental.com/products/dental-calipers.html
$18.50
Kent...great article. I'm one of those people who use disc brakes on my commuter bike. Totally worth it...I figure it saves me money for each time I don't have to get wheels rebuilt. Just replace the rotors and/or pads, which can be done in a matter of minutes.
The braking performance of the road-compatible mechanical models made by Avid and Shimano aren't that much more powerful than dual-pivot calipers, but they're much more reliable in wet conditions. Also...they modulate gradually and have an "anti-lock" brake effect because they don't seize up the wheel right away. With rim brakes, a big percentage of braking force gets applied as soon as the pads hit the rim, especially with those soft compound (grabbier) salmon pads.
I've noticed the salmon colored pads don't trap bits of metal discarded off the rim like the black pads do. My first set of commuting wheels got chewed up pretty quickly. Was really easy to see where the metal was gouging the rims during braking.
Happy trails...hope to bump into you soon Kent.
Tai
This happened to me recently!
I've been commuting year-round in Seattle for the past two years on the original wheels of my 15-year old Canondale touring bike. A few weeks ago, after a particularly thorough cleaning and lube session one Sunday afternoon, I pumped up the rear tire, capped it, set it down, and 10 seconds later -- BOOM!
Some photos here: http://picasaweb.google.com/bikeman7/RimShot?feat=directlink
I had never seen this before and was just glad it happened at home, not while flying down the hill in the Arboretum on my regular commute.
My mechanic said it typically happens on rear wheels because they bear the brunt of the braking.
.andy
Andy, the rear rim blowing out first b/c of bearing the brunt of braking forces doesn't make much sense: the front wheel typically does 70% of the braking (assuming you're using it properly). Ergo, the front rim should wear out first. I can't quite figure out why the mechanic would tell you that... maybe it was a test to see if you were paying attention or testing your knowledge?
About which rim wears out first, it comes down to braking styles. Although the front brake is the most effective and experienced cyclists use it far more than the rear, many riders have a fear of going over the bars and mistakenly overly rely on their rear brake. Since the rear brake is less effective, they wind up using the rear brake a lot. At the shop, I see lots of interesting wear patterns on brakes and gears.
So, why is it that the front is the more effective braking wheel?
Care to give any pointers on braking techniques? (I imagine this has been written about lots already...)
.andy
As is almost always the case, Sheldon has the answer. See:
http://www.sheldonbrown.com/brakturn.html
Also the latest issue of Jan Heine's excellent magazine Bicycle Quarterly has a great history of brakes and a wonderful discussion of braking technique.
Well, thanks for the pointer to Sheldon's article, Kent. (and happy birthday and welcome to the sixth decade ;-)
Basically it seems that I've had the wrong idea in my head about braking for quite some time and I've changed my riding habits accordingly.
I was very intrigued by Sheldon's suggestion about switching the brake controls so that right control operates the front brake.
This makes sense to me since one is often signaling a turn with the left arm up in the air when braking for the turn.
But I wonder if anyone has any experience or thoughts about that practice?
Thanks,
.andy
Andy.
I've been running my fixed/singlespeed bike with a right-front brake and find it works very well. When I'm in fixed gear mode I generally slow and stop with my legs (though without skidding since brake pads are cheaper than tires), but in freewheeling mode I like the right-front brake a lot. Signaling is an issue, as is hand dominance. I don't have a big strength difference, but there is a dexterity component when modulating braking power, and that comes a bit easier with the right hand (if you're a lefty you can switch it). Rear braking, being less powerful doesn't need as much control. You can, more or less, slam on the brake and slow on down.
As Sheldon mentions, you just have to remember what sort of set up you're riding with if you ride multiple bikes, or borrow someone else's. And you should warn folks borrowing yours. Slamming on the front brake by mistake, thinking it's the rear, could lead to some... inconvenience.
For those who've been seduced by the Dark Side, there's also the issue that motorcycles have the front brake on the right hand. A friend of mine had his Fat Chance set up "backwards" since he also rode a Honda Hurricane.
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