Measuring rim sidewall thickness

If you're using rim brakes, it's a certain fact of life that at some point you'll have deal with rim wear. Braking gradually grinds down the sidewalls of a rim, and at some point they become so thin that they will break. If you're lucky, this will happen at home while you're pumping up your tires. If you're less lucky, it'll happen somewhere in the middle of nowhere, leaving you stranded. And if you're even less lucky, the exploding rim will cause you to crash. How long a rim will last is very hard to predict, as it very much depends on riding style, brake type, and environmental conditions. I have so far only had one rim failure (I was medium lucky: no crash, but I had to walk home three kilometers through freezing rain), and that happened on my everyday bike after less than 10 000 km. Rims can last much, much longer, or they can fail even earlier.

Sidewall failure

Most modern rims will have indicators for telling you when the sidewalls are getting to thin. There are basically two types: Either it is a thin groove machined into the sidewall, visible from the beginning. With that type it's time to change your rim when the groove is no longer visible. The second type is a little hole not visible on a new rim, and only once enough material has been taken off the rim it will appear. Since the first type can cause some problems with brake pad wear, the second type is more common. The issue with that type, however, is that you basically have no way of telling how close you are to the point of having to change the rim. Additionally, sidewalls often wear unevenly, caused for example by slightly untrue wheels. That means that even if the indicator hasn't appeared yet it's possible that some parts of the sidewall are already dangerously thin.

My somewhat sad attempt of a DIY measuring tool

Consequently, it would useful to have a different way of measuring the thickness of your sidewalls. Unfortunately, you can't just use your calipers because of the lip that holds in place clincher-type tires. Some people use calipers on the outside of the rims, taking one measurement with a deflated tire and then one with a fully inflated or overinflated tire. As a general indicator this is certainly useful, but not very precise. A more precise measurement can be had by using a nifty DIY tool made from an old spoke that will allow you to measure the wear of your rim using calipers. You can find extensive instructions here, but the basic idea is that you have two pieces of a known diameter -- a regular straight gauge spoke measuring 2.0mm --, put them on the rim, measure with the calipers and the subtract the diameter of the spokes times two. I have tried building that tool according to the instructions but even my second attempt doesn't look nearly as nice as the one shown in the article, and that made the measurements tricky and not very precise.

Iwanson gauge on a rim with about 1.25mm sidewall left

If you're similarly mechanically challenged there is hope, though. Fortunately, dentists have similar measurement needs, and they have come up with a dedicated instrument, the Iwanson gauge or Iwanson calipers. Cheap ones can be had for less than 20 dollars shipped on Amazon or on Ebay. With the Iwanson gauge you can measure quickly and directly. Jobst Brandt thinks that 0.5mm is the absolute minimum, and other sources suggest that anything under 1mm is problematic. This, of course, refers to the thinnest spot on the rim. So make sure to take several measurements all around the rim, no matter which measuring method you use. In addition, it might be a good idea to measure your sidewalls when they're still new, in order to have a point of comparison for later measurements.

Winter's toll. And a winter bike?

Winter is far from over here in Montreal. But because of a snapped gear cable I decided to do a spring tune-up on Wolfgang, my all-purpose, all-year bike. A lot of people have "winter beaters," but to me that never made too much sense: I really like my bike and don't see the point of riding an inferior quality bike at a time that places the highest demands on bike and rider. Especially, I wouldn't want to give up on my hub generator and LED lighting at the darkest time of the year. So far, this has worked well for me and the wear and tear of components didn't seem to be particularly bad. But somehow this winter seems to have been worse than previous, if not in weather but in damage to parts. My rear rim was destroyed a couple of weeks ago, after less than 10 000 km.

Busted rim

And during my tune-up today I discovered a whole bunch of other issues:

• my bottom bracket feels noticeably grindy
• the front brakes, Avid Single Digit 7, didn't turn that well around the brake bosses
• the Tiagra front derailleur is sticky and doesn't want to go to the smallest chainring any more
• all the cables and housing are in miserable condition and have to be replaced
• a lot of the bolts, despite being made of stainless steel, show a lot of surface corrosion
• one of the Shimano M424 pedals feels crunchy in the bearings

I'm not quite sure why this winter has been worse than others. I might have ridden more (last year I didn't ride between mid-January and the end of March because of a broken wrist), Montreal winters might be somewhat harder than those in Ithaca, and in some cases it is probably just accumulative damage.

This can't be good for your bike, can it?

It seems tempting to add a dedicated winter bike to the stable, and if I had the resources (and permission from the accomplice) I would probably get a bike with the following features:

• dynohub and lower quality LED lighting (e.g. the B&M Lyt): As stated above, I wouldn't want to give up on my dynohub-powered lighting system. However, for riding in the city I don't need a B&M Cyo or Philips SafeRide light. It's more about being seen than about seeing.
• frame with upright position: A frame that allows me to ride in a more upright position would help in snowy and icy conditions.
• SPD-compatible pedals: I also wouldn't want to give up on SPD pedals and I'm happy with my Lake winter cycling boots.
• plastic saddle: Whereas for long rides a leather saddle is an absolute requirement, for commuting a plastic saddle will do and also take care of the issue of having to cover your saddle---this season I managed to lose 3(!) saddle covers.
• drop bars: A lot of people prefer straight, Albatross, or North road bars for a winter bike; this makes sense from a balance and control perspective; however, my wrists are not built for any kind of non-drop bar, even on reasonably short rides.
• good and wide studded tires: Wheel size is not particularly important for me but good studded tires are a must. And some wideness helps with floating over snow.
• disc brakes (at least in the front): Rim brakes with drop bar levers can be pretty problematic in wet conditions, and most of the time winter means wet roads. Therefore I want disc brakes, probably mechanical ones like the Avid BB7 because of the drop bars. In addition, rim wear is not an issue with disc brakes.



Not a good studded tire

• 2-speed Sturmey Archer Duomatic kickback hub with low gearing: I'm not a single-speed or fixed gear person because my knees don't like me mashing up hills (and hills I like!); at the same time, derailleur systems don't particularly like road salt and constant wetness. A 2-speed Sturmey Archer kickback hub thus would be perfect: no cables, allows to use a 1/8" chain, and has more than one gear. I've never ridden a Duomatic hub so maybe it's not as good as I think.

I don't really see me building up this bike any time soon. But one may dream while wainting for spring...

New Front Wheel for Gunnar

I don't really have a good excuse for doing this, but I've built a new front wheel for Gunnar. As you might remember, currently he's running Wolfgang's old Alex-DA16-on-Deore 36 spoke wheel. While this works just fine, the internal rim width of the DA16 is 16.3 mm (at least according to their website) and thus technically a teeny tiny bit to small for my 700x23 tires. But I admit: this is a lame excuse for my urge to build a new wheel. An additional boost to this urge actually came from a gift from my friend Löby, who gave me an old but functional dial indicator. The idea is to mount it to my truing stand, theoretically allowing me to true wheels down to 0.01mm. Well, I'm still working on the attachment to the stand which turns out to be a bit tricky.

But I've built up the wheel anyway. It's a 32 spoke Mavic Open Pro with DT Swiss Comp 2.0/1.8 spokes on an Shimano Ultegra HB-6600 front hub. After lacing the wheel the wrong way twice, three times was the charm and now it's all trued and tensioned. Figuring out the correct spoke tension was a little tricky because my Wheelsmith tensiometer's calibration table only gives values for their own double-butted spokes which are 2.0/1.7 and not 2.0/1.8. But since the absolute value for spoke tension is not that crucial anyway (Mavic recommends 1050-1100 N) it shouldn't matter too much.

One final note about the wheel: the Open Pros don't come with a wear indicator. Therefore I've measured the thickness of the rim's sidewall. A trick to do this: attach a little magnetic ball to your caliper in order to get around the flange of the rim. My measurements came to almost exactly 1.5mm. This should give me a good point of reference for judging rim wear.