Pedal strike is talked about quite a bit when people are putting together a new bike or upgrading parts, but there are so many variables involved that short cranks or a high BB doesn't mean that much alone.

Since the angle of lean is what ultimately causes a pedal strike, how about doing a bit of a survey to see what angles are common. This isn't a hard measurement to make, but it's a bit more involved than just measuring a seatpost or something. Bear with me; here's how to do it:

You'll need a tape measure, a plumbbob, and a level floor/pavement with a seam or line running along it. A piece of string with a washer tied to the end makes a plumbbob accurate enough for what we're doing here.

Find a sidewalk seam or a line on your linolium floor or something to make measuring easier. Set your cranks so that the crank on your side of the bike is pointing straight down and stand the bike with both wheels centered on the line/seam. Extend the tape measure a few feet and put the zero mark on the line somewhere beneath the top tube and extending perpendicular to the seam/line.

Now tip the bike sideways until the pedal just touches the ground. Rotate the pedal so your clips/straps are up or the pedal is in whatever orientation it usually is when you are riding. Hold the bike in this position and run the plumbob over the top tube. Get the measurement of where the plumbbob touches the measuring tape, which tells you how far your top tube is sideways from the point where the tires touch the ground. You will need to add or remove about a half inch to compensate for the plumbob string hanging over the side of the top tube instead of directly from the center of the tube (which is impossible). Make this correction to the measurement.

Now stand the bike back up straight and measure the height of the middle of the top tube from the floor. If you have a sloping top tube, be sure to measure to the same point where the plumbbob was hung.

Now you get to do some high school level algebra and geometry. Remember the quadradic formula? The law of sines? All that fun triangle ****? Here's the real life application. Trust me; your old geometry teacher would be proud. Or something.

Anyways, here's the formula:

a = distance from ground/floor to center of top tube with bike stood up straight
b = distance horizontally from center of top tube to tire contact line at point of pedal strike
C = angle of lean (straight up = 0 degrees, fallen over on your side = 90 degrees. pedal strike angle is somewhere in between)

C = asin(b/a)

Since I think nobody wants to do trig and geometry without getting paid or being carroted by a GPA, I made a little web calculator to do this. Just punch in your two measurements and it spits out the angle.

http://www.basementfreaks.com/member.../pedal_strike/

Reply with your angle and any pertinent info you can muster, such as crank length, frame type (track, road, cyclocross, etc.) and pedal type.

I'm running 165 cranks on a Raleigh Grand Prix road frame conversion with Nashbar double-sided SPD clipless pedals and it strikes at 35 degrees from vertical. The pedals give me a good bit more angle than I would get with flat pedals since they don't stick out nearly as far.

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!

i drift my bike through the turns.

The pedal ground / strike sux but the pedal in the front wheel on a
wet turn sux even suxier

You should hit up the Touge and show Keiichi Tsuchiya what's up.

my hair is much more fast and danger than his.

Well then damn. You made the man cry!

Win.

i skid through all my corners.

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?

on which bike?

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.

I don't think this poll is silly at all.

I'm actually quite curious as to whether my new (to me) Bianchi, with 700x28s, spds and 172.5 cranks will lean farther than my Apollo with 27x1.25s, clips/straps and 170 cranks.

Of course, I can't measure until I get a bottom bracket =[

I just thought of a way to adjust for rider weight. Have someone measure the top tube height while you're on the bike with normal tire pressure. then measure it unweighted. If the difference is significant, let some air out of the tires until the top tube is at the same height unweighted as it was weighted. Now the tires should be compressed about the same amount as if you were on the bike, and your measurements should be closer to actual riding conditions.

I was told there would be no math on this test.

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.

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.

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.

Quite right, I didn't read that well enough.

i suck at math. so my answer is based on the fact that the one time i did have trouble with pedal strike, i was about to lose traction, but didn't, because my pedal hit the ground first.

ooooooooh asin.
i was reading that as a*sin(b/a) and I was wondering what kind of shiat you were smoking.

Nice intentions from the OP.

re: concerns about rider weight and tire compression,
yes, factors to consider, per case,
but if we all use the same baseline (static, no rider, close to 100psi) in measuring
the results will give a reasonable comparison between combinations of frame and running gear.


An engineer uses judgement and available data to make decisions
A scientist will look for the absolute accurate answer and make no useful contribution

nerds :p

I see quite a few votes on the poll, but can anyone report back with their results and also tell a little about the bike? The poll results don't mean much unless we know what kind of bike and parts are involved. A track frame with 160mm cranks and eggbeaters is going to get a much higher angle than a road conversion with 175mm cranks and BMX pedals, etc.

As I posted originally, I measured 35 degrees with my Raleigh road frame conversion. 700x23 tires, 165mm cranks, and fairly narrow SPD-type pedals.

Tag; you're it.

There's a big problem with the method described by OP:

Changing the angle of your fork/front wheel will change the position of the contact patch when the bike is leaned. The contact patch will move forward as the bike is leaned down. What makes this even more complicated is that leaning and turning the wheel are not directly mappable, but are generally related to speed (again, no strict association).

Really any question of "What pedal strike angle?" should be "What pedal strike angle, angle?". Pedal clearance is a function of both lean and wheel angle. At a 90deg wheel angle, I know that no lean angle will cause a pedal strike (of course I'm not going far with a 90deg wheel angle either). At 0 degree lean angle, I know that no wheel angle will cause a pedal strike (but i can't be going very fast at all or turning would require leaning). In between, there's a lot of figuring to do.

Another good point. Once again, remember that this angle measurement will not have a ton of usefulness on it's own in the real world and does not need to. The measurement has been simplified to an easily reproducable standard in order to allow easier comparison between the values, which is the primary goal.

Saddle height, stand-over height, and wheelbase all fluctuate widely when a bike is leaned and turned, but people still measure them with the bike fully upright and bars straight because they are a laboratory-esque standard measurement, not an indication of a real-time condition. I'm trying to treat this angle measurement in a similar manner.

On a related note, I doubt that you're going to have the fork turned far enough to measurably raise the BB if you're cornering hard enough to be approaching pedal strike and are moving with any good speed at all.

Nashbar road/touring frame. Originally it had 27 inch wheels but I converted to 700c. 28mm tires and 170mm cranks. Pedals are fairly wide, steel platforms with toe clips. The worst of all worlds for pedal strike. I've struck my right side pedal three times but luckly I've never gone down.

Personally, you got me thinking about solving the real problem:
F(x,y) = ?
x = lean angle
y = wheel angle
Given: BB height, crank length, pedal height, q-factor, wheelbase, wheel size

I think it would make a pretty picture.