Axle to crown length 650B

[Ted Wojcik]

I'm going to help someone draw a 650B frame design. Would someone help with an axle to crown dimension for a 650B X 38 tire and with fender clearance. I know it depends on the fork crown used, but maybe you can give us some idea of what you used. We don't have a mounted wheel to use to check ourselves.

Ted Wojcik

[Brian Chapman]

Hey Ted,

I'm building one right now at 365mm with a Mutsugi crown which I think is 18mm.

Good luck,
Brian
--
Chapman Cycles
Providence, RI
http://www.chapmancycles.com/

On Jun 27, 2012, at 8:05 AM, Ted Wojcik wrote:

> I'm going to help someone draw a 650B frame design. Would someone help with an axle to crown dimension for a 650B X 38 tire and with fender clearance. I know it depends on the fork crown used, but maybe you can give us some idea of what you used. We don't have a mounted wheel to use to check ourselves.
>
> Ted Wojcik

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[Doug Fattic]

Thanks Ted for providing a teaching opportunity moment to those at the beginning of their learning curve.

One way to find tire radiuses for design drawings - when they aren't in hand to measure directly - is to use the tire size chart on a Cateye (or any company's) computer's instruction sheet (that is used to set speed and distance traveled).  For example in my Cateye tire size chart, the tire circumference for a 650 X 38B tire is listed as 2105mm.  We want to convert that circumference to radius but first we need to find the diameter by dividing it by pi (π = 3.1416).  We divide that result in half to get the radius (the distance from the center of the front hub to the edge of the tire).  So lets do the math.  2105 ÷ 3.1416 = 670 (rounding to a whole number).  That is the diameter of the whole wheel from tire edge to tire edge.  Now we divide the diameter in half to get the radius.  670 ÷ 2 = 335mm.  Again, that is the distance from the center of the wheel to the top of the tire.  It would be possible, of course, to use a one step instead of two step formula but doing it that way doesn't always make it as clear for some to see the whole picture.  

If we use Brian Chapman's 365mm axle to crown number, we can deduct he is figuring on using 12mm as his clearance between the top of the tire and the bottom of his 18mm crown.  365 – 18 = 347 – 335 = 12.  Sometimes if one is going to use a bicycle in northern climes - which may include mud and snow besides just rain water - that 12mm clearance (not counting fender or boss thickness) may want to be increased so that crud doesn't get stuck up in there.  Of course the greater the clearance the more likely water will get around to the outside.    

The tire radius can be used in several frame building formulas including how much fork blade to cut off after raking and brazing in the dropouts or where to put the bottom of the head tube on the design drawing.  In that last formula you would also have to add the headset lower stack height.  The default measurement is 13mm like a King headset but it can range from 11 to 15mm.

Doug Fattic

Niles, Michigan   

[M-gineering]

On 27-6-2012 21:11, Doug Fattic wrote:
> Thanks Ted for providing a teaching opportunity moment to those at the
> beginning of their learning curve.
>
> One way to find tire radiuses for design drawings - when they aren't in
> hand to measure directly - is to use the tire size chart on a Cateye (or
> any company's) computer's instruction sheet (that is used to set speed
> and distance traveled). For example in my Cateye tire size chart, the
> tire circumference for a 650 X 38B tire is listed as 2105mm. We want to
> convert that circumference to radius but first we need to find the
> diameter by dividing it by pi (π = 3.1416). We divide that result in
> half to get the radius (the distance from the center of the front hub to
> the edge of the tire). So lets do the math. 2105 ÷ 3.1416 = 670
> (rounding to a whole number). That is the diameter of the whole wheel
> from tire edge to tire edge. Now we divide the diameter in half to get
> the radius. 670 ÷ 2 = 335mm. Again, that is the distance from the
> center of the wheel to the top of the tire.

Another fast approximation is to use the ERTRO sizing, thus a 650x 38B
which is marked 584-38 would have min. radius of (bead diameter/2) +
tyre height ie 584/2 + 38=330mm. (tyre width equals tyre height) With a
65mm deep brake the crownhole distance to dropout could be somewhere
near 65 + 584/2= 357mm. But always check with the actual parts in hand,
you might have to correct for forkrake etc

--
mvg

Marten Gerritsen

Gerritsen & Meijers, Ingenieurs
Framebuilding & Imports

Dorpsstraat 132
9605 PD Kiel Windeweer
Netherlands

Tel: +31 598 491865
www.m-gineering.nl


leveringsvoorwaarden: www.m-gineering.nl/leveringsvw.pdf

[Ted Wojcik]

I'd like to thank all who took the time to lend a hand here. The real value is the person I'm helping hopefully will learn there are amny tools available to find the information they are seeking. It appears to me that the framebuilders group is the most valuable.

Ted

---

From: "M-gineering" <in...@m-gineering.nl>
To: frameb...@googlegroups.com
Sent: Wednesday, June 27, 2012 3:44:17 PM
Subject: Re: [Frame] Axle to crown length 650B