sourdoughT

I'm a commuter that puts on over 5,000 miles a year on my Motobecane Fantom CX between work, church, and training for long rides.

In the last two years I've gone thru two rear rims. First one (original) because of the weight carried in the rear panniers and me - vertical stress fracture at one of the spoke openings. So I had a Velocity rim built last year and in the course of one year I made the rim sidewalls go concave and on the left side seam of the rim develop a crack about an inch long horizontally on either side of the seam. The rim was still true, I'm religious on cleaning the pads and rims every week. That was $200 for that rim.

I just replaced the rim with a second Velocity rim. Now I know Velocity rims are great rims, I just put it thru a lot of use. I've been using both brakes equally but dollars and cents wise got me to thinking of not only using the front brake more often but in 2011 switch the front fork and go to mechanical disc brakes for the front for greater braking power, save some $$$, and keep the rear brakes the same.

Any thoughts of my game plan?

Dan Burkhart 

Since changing to a disc brake on the front means changing the hub as well, you might consider going to a drum brake hub instead. That way, you can keep your present fork. You just need to work out a way to secure the reaction arm, but a hose clamp will work if you're not too concious of style.
Sturmey Archer makes band clamps with a slip in pocket in various diameters as well.

sourdoughT

Forgot to mention there would be a new front rim and most likely with a dynamo hub generator.

Dan Burkhart 

Well, even better. A Sturmey Archer XL-FDD has a dynamo and a 90mm drum brake. Lotsa woah power.
https://www.sturmey-archer.com/products/hubs/cid/2/id/48

LarDasse74

I think it is a good plan. I primarily use my front brake and my rear rim still wears out faster and I could never figure out why. Maybe because the rear brake is so much less effective you actually have to use it more? Maye rear brake pads get filled with grit faster?

Luckily (or unluckily) for me, most of my rims die from 'misadventure' before they ever get their sidewalls worn down. Although I had better start riding more carelessly as I noticed this past weekend on my hybrid that they are starting to get concave.

Anyhoo, any type of hub brake will eliminate rim wear, obviously. And in my opinion, the only time you need to use the rear brake is in very low traction situations when crashing is likely due to the front tire skidding, or braking while going around a corner. So you can save your rear brake for when you need it.

Also, if you paid $200 for just a rim and spokes to be built onto your old hub then you paid too much. Subsequent replacements should be done on the same hub and should cost you just a little over $100, IMHO.

dabac

On good road conditions the front brake should be the one seeing more use, so maybe there's room for some technique improvement.

If you are going for a new front wheel there's an excellent chance to switch brake solution as well. S-A has a drum brake/dynohub combo. Shimano has a roller brake/dynohub combo. I'm not currently aware of any disc brake/dynohub combo, but I can't say that I've looked for one.
IMO there's a small advantage to drums when compared to discs for a commuter. Although discs these days don't require a lot of care, drums are an even more fit & forget type of thing.

cyccommute 

First, the rim fracture around a spoke hole isn't because of the load you are putting on the bike. It's most likely due to a poorly tensioned spoke that was allow to move within the rim. The constant flexing of the rim around the spoke cracks the aluminum and leads to failure. I'll bet you didn't check the spoke tension when the bike was new.

Secondly, $200 for a rim! They saw you comin', boy! $200 for a hand built wheel with a new hub and spokes would be steep! I'll agree that the wheel should have failed in a year but then we don't know all the details of your usage. Do you ride with wide tires on narrow rims? Drop off curbs? Just happened to pick up a bit of rock in the pads and have it score the rim? Hit potholes while sitting in the saddle?

I don't think that this is about how you use your brakes or which one you use. I think it has more to do with how you use your bike. I've ridden mostly mountain bikes with rim brakes and I haven't had all that many rim failures. I have had rim failures due to loose spokes and I have had a couple of rims wear out. Rim failures due to loose spokes are more random events than rims wearing out...and more common. To wear out rims takes more than the amount of riding you are putting your bike through. I'm not religious about cleaning pads and rims and I've only worn out a couple of rims.

There's nothing wrong with going for a disc if you want it but you are going to be looking at a lot of expense to do it. You'll need a new hub, spokes and wheel as well as the caliper and fork. If you go to the guy that sold you the $200 rim, you're going to be looking at $$$$$$$$$ for the conversion Find another shop.

But do look at the way that you ride. Try to ride the bike lighter which means using your body to absorb the impacts instead of making the bike do it.

FBinNY 

I'm not sure that I accept that wearing a road/commuter through because of braking as quickly as you did is either normal or acceptable. I'm curious did your rim show cracks after wearing down to the wear indicator (if it had one) or before.

Two things I've seen cause premature rim flange failure is over-inflation of larger section tires, and brake shoes bearing too high on the rim.

Many commuters, including myself use large section tires to make us more carefree about the condition of our local streets. That's fine, but you need to keep in mind that the pressure stress on the rim is proportional to both the tire pressure and the tire section. The same pressure in a tire twice as wide causes double the stress on the rim flange. Larger tires don't usually need to be inflated to their max rated pressure to obtain best performance, and riding on somewhat lower pressure will improve rim life, traction, and make for a better ride.

Brake shoe position is also important. When the shoes are high on the flange of the rim, brake shoe pressure flexes the flanges, and over time can cause metal fatigue and stress cracking. Mounting the shoes so they strike at the box section if possible reduces the flex and related fatigue.

You might also consider your choice of brake shoe compound, and how you use the brake. Long braking cycles as on descents heats the metal and increases wear, you're generally better off using wind drag to advantage for speed control, combined with pulsed braking which gives the rims a chance to cool.

AEO

pay no more than $90 for a velocity rim. Even then, it should be more like $60.

at $200, you're better off with a DT swiss, Mavic or Ambrosio rim.
And even those rims are $100 tops. Spokes should be no more than $1 each for the cheaper straight gauge and $1.50 for the better double butted kind.
OF course, I am talking in USD prices.

FBinNY 

I assumed (maybe wrongfully) that the OP was including rim, spokes and labor for a rebuild with the Velocity rim, not $200 for the rim itself. At that it's isn't low, but not as far out of line.

Side note about rebuilding and this forum. I'm a big believer on rebuilding on existing hubs as the best value for wheels, of course depending on the quality, and condition of the hub. But I find that whenever people ask about rebuild vs. factory wheel they're told that factory wheels a re a better value and a high price is quoted for rebuilding as the basis of comparison. Now when someone has rebuilt, he's told he paid too much and it should have been less. No comment except that I find the floating economics interesting.

HillRider

I also use my front brake as the primary one and my rear rims (and brake pads) still wear out much faster. I'm fairly sure it's because the rear wheel lives in much dirtier conditions particularly if you ride in the rain or other bad weather. The rear gets all the spray and grit thrown up by the front wheel so it lives is an abrasive bath and wears accordingly. Fenders help but don't completely even out the wear. If you want to reduce wear on the rear rim a REAR disc brake would be the way to go.

Agree. I recently had a rear wheel rebuilt with a Velocity Aerohead rim and DT straight 14 ga spokes using an old but excellent Dura Ace 7700-series hub that was too good to discard. The cost of parts and labor from my LBS was $115 including sales tax.

I also recently purchased a complete "Dimension" rear wheel from Jenson USA with a Tiagra hub, an Alex R390 rim and 32 DT spokes for less than $100 complete. It came properly tensioned and true and only needed a small amount of dish adjustment to make it nearly perfect. So far it's worked extemely well.

fietsbob

It's the friction of brake shoe on rim that stops you, of course,
clean rims, and brake pads free of embedded grit
make your rims last longer,
.. wash your bike, at least that part.


I have 20 trouble free years of use on my Sturmey Archer Elite UK made hubs.

Now the Sun Race owned expansion of the S-A product lines
includes a S type Cassette Rear Drum/freehub..

AEO

sturmey archer steel hub shells and flanges are heavy, but almost infinitly reusable, since they don't get notches like aluminum flanges.

fietsbob

But the bend in spokes is assuming thicker alloy flanges, so build needs washers on the hook
if you use thinner steel flange hubs.

... Or seek out Galvanized spokes from that older era.

AEO

spoke washers are cheap and easily had.
you can also go for cutting down a 2.3-2.0mm single butted spoke.

JohnDThompson 

I just use a vinyl-coated P-clamp:

prathmann

I use the front brake primarily and have only had rim wear issues on the front. Fortunately our area is pretty dry and we only get rain during the winter and early spring so that reduces the number of rides where grit is thrown onto the rims. My front rims last about 60 kmiles before the brake surface becomes too thin and I've never worn out a rear rim. So for me rim brakes are acceptable - especially since I get replacement Sun rims for about $20, reuse the old hub and spokes, and spend about an hour switching out the rim.

But the OP is seeing much more wear - which might well be due to different riding conditions. Commuting on rainy days on streets with lots of surface grit can wear the rim down quickly. So I'd agree with his plan to switch to a hub brake (either drum or disk) on the front and to use the rear brake only when really necessary (i.e. emergency stops and sometimes on slippery surfaces).

HillRider

Am I missing something? The OP is wearing out REAR rims yet most posters are discussing improving his FRONT brakes. As I mentioned, if he wants to protect his rear rim, substitute a drum or disc brake in the rear.

BCRider

I'm guessing that sourdough lives in a region where there's a good amount of rain. During my own rainy weather commuting I found that the rear wheel got far, far, far dirtier than the front. I'm guessing it was because the front stirred up all the gunk and grit which got sprayed onto or picked up by the rear wheel. In any event my own rear rims wore out at least twice as fast as the front rims. I wore out two sets of rims in about 4 or 5 years. It would have been more frequent but I was sharing ride time between 4 bikes. This wearing away at the rims is why I finally went with disc brakes on two of my trail and commute bikes.

And yes, the rear does wear out far more quickly because of all the sprayed up or disturbed grit and grunge that the rear sees compared to the front which runs through "clean" water for the most part. Even if you use the rear much less than the front it will still wear just as fast or faster than the front.

waldowales

FNinNY said: "That's fine, but you need to keep in mind that the pressure stress on the rim is proportional to both the tire pressure and the tire section. The same pressure in a tire twice as wide causes double the stress on the rim flange."
Would you mind explaining how you reached this conclusion?

Dan Burkhart 

Surface area. Do the math.

Shimagnolo

+1
I learned the hard way that just because a 1.9" tire is rated for 75psi, doesn't mean the rim can handle it.
The first rim (Mavic) lasted a year before the sidewall cracked.
The second (identical) rim lasted a month before the sidewall cracked.

AEO

well, take a look at a cross section of a tire. It's basically a tube with a slit down one side.
When you inflate the tire, it wants to expand in all directions, but the rim and casing keep it from doing that. The tire casing, in it's natural state is sort of a"U" shape instead of being a tube or completely flat. Of course, if the tire is allowed to expand freely, the tube will burst. Now a narrower tire on a rim can only expand so far until it gets into a "U" shape, at which point it's maxed out. On a wider tire with the same rim, the tire won't max out to it's "U" shape, and put extra pressure on the rim, trying to split it down the center.

FBinNY 

You know this already, you just don't know that you know it.

It's a concept that anyone who sails is familiar with. As the wind picks up you reef the sail to reduce it's area so it or the rigging isn't blown apart. It's also something you probably learned as a child when you noticed that balloons get easier to blow into as they get larger. You can also demonstrate it with bubble gum.

Here's how it translates to tires.

Keep in mind that pressure is force per unit area. Since the circumference of the tire is constant (roughly) the area is proportional to the cross section of the tire. Doubling the area, doubles the total force acting on the tire, which is in tension and, constrained by the rim flange, pulls it outward.

It's pretty hard to blow a rim apart with an 18mm tire, but easy with a 2.125"

sourdoughT

I appreciate the information. I don't bunny hop, jump curbs, etc. I avoid potholes wherever possible. The tires I ride with are Schwalbe Marathon Plus 700 x 28's at 85 psi for most of the year and Schwalbe Marathon Winter 700 x 35's at 75 psi for winter. Yea it rains here in the Puget Sound area just a wee bit