Answers Back To Basics
The Semiannual Correction Factor Question
So, what's the deal with that "corrected quarter-mile" thing in Motorcyclist's performance specs? Why is it always a little quicker than the uncorrected numbers I see floating around?
Hacienda Heights, CA
Because, Dave, beautiful Los Angeles County Raceway-where Kent Kunitsugu and Andrew Trevitt from Sport Rider magazine help us do our drag-strip testing-is located in beautiful Palmdale, California, elevation approximately 2700 feet. Oxygen, you'll recall, is less plentiful the higher you go. Therefore, engines make less horsepower at altitude-hence, the correction factor. The actual quarter-mile time clocked gets multiplied by 0.9761, and measured terminal speed is multiplied by 1.022 as per National Hot Rod Association (NHRA) edict. This type of thing makes it possible for drag racers in Denver, Colorado (some 5000 feet above sea level), to swap credible disinformation with their sea-level brethren.
Cut Me Some Slack
I put 800-1000 miles per month on my Suzuki Katana 600. I can take the slack out of my drive chain on Sunday, and by Thursday it will have three times the recommended amount of slack (per the owner's manual). I started having this problem when the bike had about 10,000 miles on the odometer. I installed a heavy-duty O-ring chain, but the problem persists.
Obviously, Marcus, you're being punished by The Man Upstairs for laboring on the Sabbath. Seriously, though, did you replace your bike's sprockets when you replaced the drive chain? If not, that's almost certainly your problem. Worn sprockets can reduce a brand-new chain to has-been status quicker than just about anything else.
More Trail, Less Flail
You guys are always yakking about rake and trail and offset ... yadda, yadda, yadda. You've written in the past that my first-generation Honda CBR900RR will corner with more stability (and steer more slowly and with more effort) with a few millimeters more trail. Don't you need more rake to have more trail?
Visualize an imaginary line drawn through the center of your bike's steering stem down to the ground. The distance between that point on the ground and your front tire's contact patch is called trail. The more trail you have, the greater your bike's tendency toward self-centering its front wheel, thus the heavier its steering.
Offset is the distance the fork tubes are carried in the triple clamps relative, fore and aft, to the steering stem.
Rake is simply the angle at which your bike's fork tubes are set relative to vertical. (Some motorcycle manufacturers such as BMW-and all bicycle manufacturers, incidentally-measure this relative to horizontal and call it caster.)
Rake and offset are used to achieve a given trail measurement, but trail is the thing that defines a bike's steering characteristics. It's entirely possible to alter trail without changing rake at all. A slight adjustment in offset is the simpler modification. On your CBR, for instance, aftermarket triple clamps that move the fork tubes a few millimeters rearward will move the front tire's contact patch a like amount, thus increasing its distance from that imaginary line descending through the steering stem. More trail, therefore, equals less flail. And vice versa.