Originally Posted by jonsam
I'm pretty sure that the arcsin will give you the angle between the horizontal and the bike. Arccosine on the other hand gives the angle between the vertical and the bike. Also subracting the answer the calculator gives you from 90 will do the same thing. For example, I get an answer of 62 degrees which I know isn't right bc my bike pedal strikes like a mother. 28 degrees puts me in the training wheels catagory. Sweet.
Also for those of you in the 60 degree lean range some quick calculations show that your top tube would have to be about 16 inches from the pavement for a bike with 32.5 inches of standover. YIKES!
uh, but my math
does use asin. Remember that my formula calls for the horizontal measurement along the ground from the centerline of the tire contact points to the point directly beneath the top tube. I guess you could measure the height leaned and not leaned too and work it with acos, but I picked the other way for some reason when I came up with this last night. I maintain that my calculator works correctly. Enter a 32" standover and a 1" lean and you'll get almost 0 degrees. Enter a 32" standover and a 30" lean and you'll get almost 90 degrees. Most angles start with 0 degrees at horizontal, but we're using 0 degrees as vertical here to make the numbers mean more. A bigger angle means you can lean further before the pedal hits the ground.
To the guy who asked why not to just use a protractor, you're more than welcome to do that if you have a protractor and some halfway accurate way of measuring the centerline of the bike. This question was originally raised in the commuting forum and someone suggested that measuring would be easier than finding and using a protractor for most people, thus the choice.
Originally Posted by ink1373
this is a silly poll. pedal strike is a silly thing to fear. unless you're doing something completely wrong, it won't happen often, if at all.
get narrow pedals.
get short cranks.
don't use a touring frame.
i remember being very concerned about BB height and pedal strike when i started out, but it's really not worth the worry.
Well, I don't "fear" pedal strike; this is more of a scientific endeavor. Your default response is precisely the reason I decided to undertake this experiment and beg you all to take weird measurements of your bike(s). Whenever pedal strike is brought up, the standard response is something along the lines of your advice. I was curious and decided to take this on from a slightly more technical angle to get some hard numbers with which to compare things to in the future.
Originally Posted by mattface
I sucked at high school algebra, but I'm thinking we need more than high school level algebra to measure the lean angle where pedal strike occurs on a bike with a rider.
Without your weight on the bike this measurement is meaningless. If we accept the fact that 2.5mm makes a noticeable difference in pedal strike, then the tire compression from a 150 pound rider is going to change both effective top tube height, and the angle at which pedal strike occurs. Then we need to recognize that centrifugal force add additional pressure further compressing the tires while turning. Is the additional compression significant? I don't know, but to measure the additional force applied we need to know what speed the rider will be traveling at the point where pedal strike occurs so that we (and by we I mean someone who can do math not me) can calculate the quantity of any additional compression in the tires. I also wonder wether side-wall deformation of the tire while leaned might make a difference.
Basically what I'm trying to say is that although I don't know a lot of math I understand the variables involved in calculating this, and I think you are leaving out a lot of important ones. WIth your method we learn the lean angle of a static riderless bike, but what we really want to know is how far we can lean over while riding.
Besides if that's all you want to know why not just get someone to hold the bike with the tires up against the wall, and put a protractor up against the center line of the back tire?
Your observations are correct. With a rider squeezing the tires a mm or three, you will indeed have a reduced pedal strike angle than when measured weightless. I thought about a few of the things you present, but I also realized that pavement is rarely perfectly level and smooth, so that throws things off by a few mm either way on the average corner. I decided to go with the simplest method just for the sake of having a standard, but you are correct that there are variables I am ignoring. Rather than a 100% accurate measurement of the angle of doom, look at this more as a benchmark for different bikes for comparison purposes.