Wet Season Training: An Option to Side-Pull Caliper Front Brakes

18 02 2013

I have to remark, after converting the front end of my road bike to a disc brake, the difference is quite noticeable. One of our team’s training courses called “three-hills.” While aptly named, the respective slopes or distances upgrade are nothing to get wrapped around the axle about. This route is decent training route. What goes up, must come down, and so slowing for the merging lane halfway down or the stop sign at the bottom gets interesting when the road is wet and/or when it is raining. That is to say that most of our off-season rides are in the wet.

What I needed was to find a 1-1/8″ straight steerer-tube carbon road fork with the ISO mounts for a disc brake. Here are three:

picture of Whisky no.7 cross fork

Whisky No.7 Cross Fork ~$410

picture of Bike Island CX Fork

Bike Island CX Fork ~$145

picture of Tange Prestige CX Carbon Disc Fork

Tange Prestige CX Carbon Disc Fork ~$249

I ordered the fork from Bike Island. All I needed it to do was to allow adequate braking during the off-season’s accumulation of base miles. No eye-popping sprints, no destruction of wheel rims, just hours of steady riding in the cold wet that is Seattle. A nice-to-have was the fender stay mounts at mid-fork. (Fenders during the off-season are mandatory for our team’s “rain bikes.”) The one installation difficulty was the lack of a thru-hole for the fender mount. Note in the picture below where the bolt nut would usually be located. I had to use a nylon lock nut inside the steerer tube with a shorter fender bracket bolt through the existing front hole.

Picture of mounted fender

Mounted fender, front of fork crown

Picture of the rear of the fork crown

Rear fork crown

The next item was the caliper and rotor itself. I could choose between the apparently higher-end Shimano disc road brake, the Hayes CX-5, or the model from SRAM, the BB7:

avid_AVB71665

SRAM BB7 Road

I bought the BB7 and the corresponding rotor. It’s been around for a while. Lot’s of people have used them, and parts are available just about anywhere you go. I reminded myself that this gear was going to be used in otherwise crap riding conditions. It didn’t need to be top-shelf bling, just simple and reliable.

Installation was fairly straight-forward. After mounting the crown race I measured and cut the steerer tube. Cabling and other assembly proceeded as usual—no issues. Centering the calipers on the rotor took a bit of time, but following the instructions provided by SRAM made it easy. An important note is to follow the bed-in procedure. This will help make sure that your disc system provides the braking you want.

I’ve ridden this conversion for about a month now. I’m satisfied to report that since prematurely wearing my conventionally braked wheelset, I have enjoyed fade-free braking without worry. IIRC, the total cost to convert was about $283, much less than having to buy another middle-grade wheelset.

Thanks for reading.

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Rim Wear – How to Trash Your Nice Alloy Wheelset

8 02 2013

Like I spoke of in an earlier post, the Seattle winter weather mixed with the down-hill portions of my team’s training routes was making short work of my HED Belgium C2s. When we moved here in July the braking surfaces were flat and smooth. Our mileage really stepped-up in October and the weather, of course, wasn’t to be outdone. If I recollect correctly there have only been three instances where I’ve returned home somewhat dry. Nonetheless, the quantity of water, road grime and other debris created the perfect abrasive for taking-down alloy rim braking surfaces. I was wearing-out Ultegra brake pads at a rate of one set every two weekends. (That’s something over 100 miles every weekend.) I had tried SwissStop GHP2 pads and found that they lasted a little longer and allowed a more tactile modulation for braking in the wet, but the end effect was the same. Eventually, I tried some Kool-Stop Salmon pads, but was fairly into the disc brake upgrade at the time—I didn’t test the pads under the same conditions as the Ultegra and Swisstops. I was fairly disgruntled.  OK… I admit it, I was pissed. I had put much care and effort into the two quality builds. In retrospect, the wheelset had performed as I had intended them to, that is to say, for the time the wheels were in service, I never had to re-true them. Nor did they yield when I  inattentively bashed them into some road-born hazard like a pothole or concrete slab edge misaligned with its neighbor. To date I have not found rim or hub cracking or other signs of fatigue. Have I mentioned the road surface conditions here in the Greater Seattle Area?

I built the rear wheel in September of ’10 and the front wheel in December of ’11. According to my PowerTap database, the rear wheel has 8532 miles of use, and the front has 4334 miles. I had intended this wheelset to last many more miles. However, considering the amount of metal that has worn away, I’m in doubt about the rim’s longevity. In order to find  what usable life remained in the rims I needed to know a couple of things: how much metal in the rim hook wall remained, and the minimum (safe) thickness of that wall. To measure the thickness of the rim hook wall with some degree of accuracy, I needed something like the caliper pictured below. Fortunately I found one online for about $18 excluding shipping costs.

Picture of Outside Caliper Tool

Precision Outside Caliper

I learned this idea from a blog article that I found while searching for information on rim wear and allowable limits. The small offset jaws of this instrument allow for measuring inside the tiny space between the rim hook and the rim bed. This would give me some quantification as to the severity of wear. However, there are two problems that I can expect right-off-the-bat: the first is that measuring at the indicated points in the picture, Fig. 1, will likely give the depth of wear at a point offset from the maximum depth of wear because of the concave wear pattern. This is indicated by the longer blue line in Fig. 2. Granted that I may be splitting-hairs, but I think the measurement should be at the shorter yellow line in Fig. 2. A better method could be to use the depth blade of a typical dial or digital caliper (“3” in Fig. 3) and take measurements at the yellow line in Fig. 2.

The second problem is that I needed a minimum wall thickness designation. Alternatively, I could use a figure for maximum wear before becoming unsafe. Either way, this whole effort will be for naught without a minimum value. I contacted HED Cycling Products in Minnesota by phone and email around January 15th and followed-up with same, but haven’t been able to receive a usable figure since then. I also asked if a wear indicator (pin-punch) was present, because I couldn’t remember seeing one (I think the answer was “no.”) Other sources on the web have been more forthright with a wall thickness value. A discussion on the Weight Weenies forum suggests 1 mm, and E. C. Zimmermann suggests a minimum of 1 mm or more. I’ve read Jobst Brandt’s posts to find suitable references, but haven’t found a figure as of this writing. (I know I read of one in one of his posts, but haven’t found it yet.)

(Edit 2/13/2013) There are three types of wear indicators that I know about: brake-surface pin punch, brake-surface groove, and an “interior” indicator. The two former indicators allow you to monitor the surface as it wears down. The interior indicators only “appear” after you have worn down to the minimum limit.

Picture of HED Belgium C2 rim

Fig. 1 Cross-section of rim

So what is known? Well, 20 sample depth measurements were taken for each side of the front wheel. Why 20? A sample size of 20 will cover about 78% of the population at a confidence level of 95%. I’m certain that the sample mean represents the true measure of depth around the rim. The mean thickness for the drive side was .5 mm, the non-drive side thickness was .34 mm. I found the difference between sides interesting. Apparently there is  something different going on between the left and right side pads, and rim wear is not symmetrical. I can’t measure the rear wheel because the PowerTap hub is being repaired. I’m going to bet that its wear rate is about the same.

Graphic of rim measurement points

Fig. 2 Measurement points

Graphic of a digital or dial caliper blade probe

Fig. 3 Blade probe for a typical caliper

So there it is. I think I can conclude that the rims are done and it’s time to replace them. The question is, should I use the same C2 rims from HED or search for a suitable replacement? If I use the same rim, there will be no wear indicator, and I’ll have to be especially watchful. If I buy another brand, I could opt for a rim with a pin-punch or groove as an indicator. I really like the ride quality of the wider C2 rims and I’ve grown accustomed to their appearance. I’d prefer to stay with the same hub and spoke so that somewhat limits the ERD of a 700c candidate rim to 592 or thereabouts. What other rims might I choose for the rebuild? Note: the prices are as seen online, without shipping/handling added, weights are approximate.

Brand Joint Wear Indicator Braking Surface Wt (g) Width (mm) Depth (mm) Drilling / ERD/Notes Cost ($) Picture
Pacenti SL23 weld & sleeve Yes CNC 450 24 26 20, 24, 28 / 588 / slightly angled 98 Picture of Pacenti Aero Tubeless
HED Belgium C2 weld none CNC 475 23 24 18, 24, 28, 32 / 592 / angled 119 Picture of HED Belgium C2
A23 sleeve none CNC 426 23 19.5 20, 24, 28, 32, 36 / 601 / angled 82.50 Graphic of Velocity A23
H plus Son Archetype weld none CNC 470 23 25 20, 24, 28, 32 / 594 / slightly angled 69.95 Graphic of H Plus Son Archetype rim
BHS C472w pinned none CNC ~477 23 28 20, 24, 28, 32, 36 / 584 / center drilled 57.95 Grahic of BHS C472w rim

What rim characteristics are important in the final selection? First and foremost is drilling pattern. I’m going to keep my current hubs and spokes so the availability of a 20h and 24h is a must. I understand that the HED Belgium C2 is no longer offered in a 20h. I’m not going to switch from a perfectly usable 20h Chris King R45 front hub. Regrettable for certain. I really liked the C2 rim’s appearance, ride feel, material quality, and durability.

Without belaboring why I’m not going to choose all the other rims. I just discuss why I choose the Pacenti SL23 as the replacement rim. The second factor was rim width. The SL23 has the wide rim, which I’ve grown fond of riding. Since moving to Seattle late in July, I’ve not pinch flatted at all in seven months. (Comparatively, this area has the worst riding surfaces I’ve ridden over.)  I’m not saying that the wide rim has been the direct cause for no pinch-flats, but I’d like to think it was a contributing characteristic.

The tertiary factor was the rim wear indicator. The question for this whole exercise was to decide if the C2s were safe to ride or not. If the Belgiums would have been produced with a wear indicator, this effort would have been far less of an event. (That however, is a moot point as a 20h is apparently not available.)

As far as lessor factors, this rim has a sleeve and weld joint. Although the joint does not necessarily need to be welded, I like the appearance of a smooth, uninterrupted brake surface. The CNC machine work just adds to this effect. The rim’s weight is ball-park with all the others, that being fairly light. This is a training or everyday wheelset. I’ll save the gram-chasing for when I build a set of racing hoops. The fact that the new rim has an ERD of 588 is of some concern. The C2 ERD is 592. Without my spare spoke and Polyax nipple from the original build in front of me I am unable to discern how much take-up is available. I’d like to re-use my CX-Ray spokes if not limited by the ERD. Inspection of the front wheel spoke nipples shows that the tip of the spokes are even with the bottom of the nipple drive slots. How many turns-of-thread that remain is unknown. Plan “B” is to use HM nipple washers to create “artificial” ERD, somewhat like thickening the rim after the fact. The reference suggests adding 1.5 mm to the spoke length calculation so I should be OK here. The addition of 10 grams or so to the wheel build will be insignificant. If that doesn’t work plan “C” is to buy a shorter set of spokes for ~$80. Last, but not least is a (very) subtle aero benefit. I’d like to think that the longer, hub-side of the rim will keep more boundary layer flow than the Belgium, but hey, this is a training wheelset.

So there you have it. The Pacenti SL23 is my replacement choice. Once I get my PowerTap returned from the factory I’ll have to start planning my wheelset rebuild. On that note, many thanks to Brandon from The BikeHubStore for his valuable advice and for discussion on the SL218 rear hub (16:8 drilling). You should check his site out, better yet give him a call. Also, thanks to Andy at the The Bike Repair Shop for his hands-on discussion of rim wear and consequential effects.

Hope your race season starts well!








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