If we were talking simple mathematics the answer to that would be simple enough. The fraction and the decimal are always the same. But in the world of bicycle tires it is an altogether different ballgame. The answer is no, it is not the same. I know … it sounds crazy and as far as I am concerned it is crazy. It is one very confusing messed up system which has been developed. When I was a kid it wasn’t this way. It was all pretty much straight forward and simple … easy to understand. I have written about this subject before. Click HERE to read about it.

Just take a look at this chart below and you can readily see what I am talking about. It almost gives me a headache.


Schwalbe has information on tire sizes HERE.  I like their chart as it seems easier to read than some others I have seen.  HERE is an article by the late Sheldon Brown about tire sizes. He has a section a short ways down the page he has called “Does Point Seven Five Equal Three Quarters?”.  HERE is another article on tire sizes.

Be certain what size wheels you have on your trike before buying new tires or inner tubes. Most tadpole trikes with 20 inch wheels have 406 rims, but a few may have 451 rims. The tires and inner tubes for these two sizes are not interchangeable. This is what happens when you try to install a 451 inner tube in a 406 tire:


As you can see the 451 inner tube is much larger in diameter than the 406 tire. Some of the sales people in bike stores don’t know this and will hand you a 451 inner tube even if you specify you need a 406 inner tube. It has happened to me. I got clear back home before discovering the sales person selected the wrong tube. I had to return to the store to get the right one. Now I look before buying it since I learned you can’t entrust the matter to the store.

For most of us we don’t have to concern ourselves very much about all of this. It is when you go trying to make major changes in wheels and tires that you encounter the complexity and need to “get it right”. If we simply stick with buying pretty much the same tires by the size shown mounted on our rims we should be safe enough. Just remember about the 406 vs 451 matter. Try to avoid getting a headache and simply …


FREE GIFT awaits you!

Author: Steve Newbauer

I have a few current blogs (tadpolerider1, navysight, truthtoponder and stevesmixedbag) so I am keeping busy. I hope you the reader will find these blogs interesting and enjoy your time here. Feel free to email me at tadpolerider2 at gmail dot com (@gmail.com)

2 thoughts on “WHEN IS .75 NOT THE SAME AS 3/4?”

  1. Hi Steve, I have just installed an Efneo Internal Crankset & here is my review if you wish to use it be my guest. (Published on Facebook in Trike Groups.)

    For those that have been waiting for the past couple of years for this Internal Crank Set to come to market I can finally say, mine is installed. If you are not familiar with this crankset it is similar to a Schlumpf or Patterson Drive with one big exception. It gives the equivalent of a 18 -40-50 tooth crankset while the other 2 give you a 28-45 only. The unit quality seems on par with the Patterson & from only seeing a Schlumpf drive (I have never owned one) Installation is very straight forward as long as you have the right bicycle tools & you don’t need any special facing of your housing to make everything fit. Shifting comes with your choice of a Paddle Shifter or a Twist Grip Shifter. Included in the price & attached, ready for installation. This is a nice touch & makes installation very easy. I think most trike owners would prefer the twist grip shifter as the paddle shifter will require installing upside down for the correct orientation of your left thumb. As I am already using Paddle shifters with my Alfine 11 the upside orientation doesn’t bother me. Shifts are crisp & instanaeous up or down the range. Very nice clean look and a decent gear spread. all in all a worthwhile purchase. http://efneo.com/gearbox/

  2. Unfortunately Steve the tire mess is more than just the 406 or 451 mismatches. Even if you get the correct size tire from one company, Kenda for example & buy a Schwalbe tire with the same markings you may still run into a fitting problem. The problem evolves around the BSD or Bead Seat Diameter which is the measurement where your tire bead & your rim flange meet together. Since there have been various industry & country standards the ETRO system is a way of standardizing the tolerances & measurements and It is getting better but Chinese inches vs German inches can still give you headaches.

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