CYCLING PERFORMANCE TIPS
After you have been riding in the rain or suboptimal road conditions, you may notice a sound of metal on metal when you brake. Generally this is from grit picked up by the pads. Over time, this additional abrasion can accelerate wearing down of the rim metal itself.
This is an extreme example from a cycling blog. Their assumption was that it was road debris that somehow adhered to the pad (or rim) and was embedded during regular braking.
To clean pads, first pick out the larger pieces of foreign material with an awl, penknife or the tip of a small screwdriver. Then using a fine grained sandpaper, lightly sand the rubber surface. And while you are at it, check the grooves on the pad. If it has been a few years, you might consider replacing pads as they can hardened with age.
A smooth rim will also improve braking performance. But you don't want to go overboard and remove the metal itself. A Scotch-Brite pad works well for this purpose. It's a gentle abrasive that won't remove material from the rim but will take off rubber deposits to ensure optimum braking.
Disc brakes have been a defacto standard for mountain bikes for years. They are now here for road bikes as well. If you buy a new bike, odds are it will come with disc brakes standard or as an option.
This is a nice summary of the pros/cons as well as the state of the art of discs.
An added benefit may be to save a few dollars on rim replacement. I clearly remember the time someone pointed out the "dishing" on my aluminum Ksyrium rims from brake pad wear. And suggested I replace them before I developed a strategic failure on a long ride. Spent a few $$ that might have been saved if I was using discs.
To check for maintenance status remove the wheels from the bike. Turn the axles slowly with your fingers - you will feel a slight but smooth hydraulic resistance. If an axle either turns roughly or spins freely with no resistance, you need to do some maintenance. Roughness can indicate damaged bearings, too little resistance means the lubrication is gone, usually because it's been washed out by lots of rainy rides or improper bike-cleaning techniques (using high-pressure sprayers or getting solvent into the bearings).
Rear hubs are a bit more complicated to handle, front hubs are more user friendly. It does help to have the right tools. To regrease a hub, pull off the dust caps or pry them out by carefully wedging an X-Acto blade between each cap and hub. You'll see the plastic seals covering the bearings. Lift these by slipping the blade beneath, being very careful not to bend the seals.
Once you see the bearings, you can add grease if they're just dry, or take the extra step of cleaning them with solvent, drying them, and repacking them if they're gritty. The seals will pop back into place with gentle hand pressure.
This link is one of the best reviews I have seen. It provides the math and then puts things into real life perspective with examples. (Want more detail? Take a look at my favorite site.) Here are some numbers he calculated for a training ride - a 6.5 hour solo ride, 1200m/3940ft of climbing, and an average speed 31 kph/19 mph.
I decided to see if I could use online information to pull together a few online links for my friend. The goal - to find a solid $500 - $750 wheel set for his training bike upgrade. Here is what I found this AM (1/27/2016).
Spokes - it is true that the more weight further from the hub, the harder it is to accelerate a wheel. Total wheel weight is related to the number (and weight) of the spokes as well as the rim itself. So if you have fewer spokes, but need a stronger (read heavier) rim, the over all performance improvement from less weight, but the weight further from the hub, is a negative. Think about it, if you are considering low-spoke-count wheels to maximize performance, they almost never list the weight of the rim versus spokes . Instead, you're told the overall wheel weight. So if you are looking at two sets of high end wheels, of equal weight, find out the rim weight and go for the lighter rim.