Tapebubba’s Grip King pedal mod

My RBW list (and etsy) friend TapeBubba modified his Rivendell/MKS Grip King pedals to have more lateral support. Watch the video and see how he does it.

I think it’s a great hack. I’ve had that ‘roll off the side of the pedal’ feeling myself, and my feet are fairly narrow.

He removes the cage pieces from the pedal, makes a U out of aluminum strap to go around the body of the pedal. The bottom of the U makes an outside edge for the pedal, and the cage pieces are screwed back on, sandwiching the strap in place.

Optimal Tire Pressure for bicycles

Here’s a short overview of tire pressure on the Problem Solver’s blog. It’s a little more concise than this page, and has more pictures.

The Calculator

The pressure calculator was created by Dave Adams, who sent it to me because of a tire pressure post I’d put up with an extended chart. You can open the spreadsheet in Open Office, Excel, or Google Docs and use it for free. Just remember “Dave Adams” when you use it.

How to Use It

Fill in the yellow fields in the spreadsheet (tire width; bike and rider weight; percent of weight on each tire). Go pump your tires. You can make (copy) a tab for each of your bikes, and make the tires and rider fatter or thinner over time (or adjust for touring loads).

The Science

According to Frank Berto and Jan Heine (of Bicycle Quarterly magazine), two top bicycle science guys, the most efficient bicycle tire pressure is one that gives you a 15% drop in tire height when you get on the bike. “This tire has too little air!” It’s squishy and hard to turn. “This tire has too MUCH air!” It loses energy bouncing off small surface irregularities. “This tire is JUST RIGHT!” Fifteen percent is the Mama Bear of tire drop.

Given that you want each tire to ‘drop’ 15%, and bikes don’t weight the front as much as the rear, you don’ t want the same amount of air in each tire. It seems obvious when you think about it, but it was  revelation to me.

Most bikes put 60% of the weight on the rear, for a 40-60 fore-aft weight distribution. The “Quickbeam” tab in the spreadsheet is set up this way, and I actually weighed the bike with me on it to get the split. I could have saved some work and trusted to Bicycle Quarterly, but I like to check things for myself.

Low-trail French Randonneuring bikes are different, with only 55% on the rear. The “Ross” tab in the spreadsheet is for my low-trail Ross Super Grand Tour fixed gear tourer. Also weighed out accurately to confirm the BQ numbers.

Dave says his equation looks like this:
PSI = 153.6 * Weight / (TireSize^1.5785) – 7.1685

History

A few years ago, in the Spring of 2007, Bicycle Quarterly had a “Tire Drop” article based on Frank Berto’s research about proper inflation for best efficiency, in which they published a very useful graph, and instructions on how to set up your tires.

It didn’t have a line for 35mm tires, which I used at the time, so I added another line, and extended it to allow for heavy loads. Jan Heine gave me permission to republish the Bicycle Quarterly graph with my additions, and it turned out to be pretty useful for some people. I actually had an internet friend send it to me, not knowing I’d posted it in the first place.

graph showing optimal inflation for bike tiresDave Adams saw the post in his research on the same subject, and sent me a copy of his spreadsheet, which I’ve been using ever since. With his permission, I posted it to the  RBW (Rivendell Bicycle Works) Google Group, where it’s also archived.

Grant Petersen shows how to draw a bicycle frame.

This is pretty cool. In the “Peeking through the Knothole” section of Rivendell Bicycle’s site, Grant is going to walk people… the world, I guess, through how to draw a bicycle frame, one baby step at a time.Grant Petersen's favorite eraser

Step 1. Get the drawing tools. 11×17 graph paper, 360° protractor, metric ruler, metric triangle, pencil… and an eraser.

I think in an old Reader, he did a similar thing, where he showed you how to make a full-size production drawing of a bike frame. Maybe it was the Bridgestone Catalog.