Math Problem?

[Bill G]

Am I getting full range on my Enviolo 380?

My Enviolo hub was making a noise. My LBS got rid of the noise, but I’m not sure I’m getting the full range on the hub. My highest (hardest) gear might be a little low. Does it make sense that given that I have 27.5 inch tires, a hub with a 0.5-1.9 ratio range, I should be able to put my bike into the highest and lowest gears, pedal at a fixed rpm (say 75), and by the speed achieved, know that I am getting the full range on my hub?

Do any of you know how to calculate what speed I should achieve at 75 rpm at the 0.5 and 1.9 ratio given a 27.5 wheel diameter? Thanks.

 

[Roamers]

There are many gear/speed calculators online. Not endorsing this one as accurate, but an example. Keep in mind these will be "close" because your tire circumference varies based on tire pressure.

Ritzelrechner - Graphical Gear Calculator for Bicycles

The bicycle gear calculator displays graphically the gearing of derailleur gears and gear hubs. It can be used to compare different setups to find the optimal gearing for all kinds of bicycles.

www.gear-calculator.com

 

[Bill G]

Many thanks. They even listed the Enviolo Trecking hub. Now I'll have to road test it.

 

[JohnDavis]

There are many gear/speed calculators online. Not endorsing this one as accurate, but an example. Keep in mind these will be "close" because your tire circumference varies based on tire pressure.

Ritzelrechner - Graphical Gear Calculator for Bicycles

The bicycle gear calculator displays graphically the gearing of derailleur gears and gear hubs. It can be used to compare different setups to find the optimal gearing for all kinds of bicycles.

www.gear-calculator.com

Thanks, that helps! I often have problems with projecting. I also often use this service https://plainmath.net/secondary/calculus-and-analysis/calculus-2 to calculate and answer other math questions. It helps to save a lot of time and explains many math terms in simple terms.

 

[Ed B]

Another potentially useful site would be https://www.bikecalc.com/speed_at_cadence

 

[Roamers]

How many decimal place accuracy are you looking for!

Your biggest inaccuracy contributor is going to be true tire circumference while riding. It changes based on total weight on the wheel and tire pressure

 

[dodgeman]

Let’s see, 27.5 squared times the square root of pi times the integral of e under the curve x and y…….equals 5. The answer is 5.

 

[Stefan Mikes]

27.5

It is not 27.5". 27.5" is the nominal wheel size. The 27.5" wheel has the rim diameter of 584 mm. Add to it the twice of the tyre width/height and you will get the approximate wheel diameter. If you want to calculate the wheel circumference, it will be 2 * Pi * Wheel Diameter. And it will be inaccurate still because of different outer tyre diameter with different inflation pressure and rider's bike weight.

 

[tomjasz]

There are some excellent charts that will satisfy most.

Tire Size Charts - BikeTiresDirect 117

A useful chart for determining the tire size you need for your bicycle.

www.biketiresdirect.com

Common Bike Tire Sizes​

Tire Size	Use/ Discipline	ISO Designation
700c x 23mm – 32mm	Road/Track	622
700c x 35mm – 50mm	Gravel and Mixed surface	622
650b x 23mm – 25mm	Small road bikes	584
650b x 45mm – 50mm	Gravel and Bikepacking	584
26” x 2.1” – 2.3”	Cross Country MTB	559
26” x 2.3” – 2.5”	Trail	559
26” x 2.4” – 2.6”	Enduro/ Downhill	559
27.5” x 2.1” – 2.3”	Cross Country MTB/ Gravel	584
27.5” x 2.3” – 2.5”	Trail	584
27.5” x 2.4” – 2.6”	Enduro and Downhill	584
29” x 2.1” – 2.3”	Cross Country MTB	622
29” x 2.3” – 2.5”	Trail	622
29” x 2.4” – 2.6”	Enduro and Downhill	622

 

[dodgeman]

Stefan, you do realize I just put a bunch of random math phrases together when I posted that.

 

[Stefan Mikes]

Stefan, you do realize I just put a bunch of random math phrases together when I posted that.

Why would you do that?

 

[dodgeman]

A weak attempt at humor. I guess nobody got it but me?

 

[AHicks]

A weak attempt at humor. I guess nobody got it but me?

5 what? Kidding, I got your point without a problem - in a manner of speaking.....

 

[J.R.]

This thread, and the comedy, took me back to the 70's...

 

[Nvreloader]

This site will give just about any combo of tires/rims, along with lots of other information: https://www.bikecalc.com/wheel_size_math
HTH's,
Don

 

[Kayakguy]

5 what? Kidding, I got your point without a problem - in a manner of speaking.....

Yeah, I got it too. My favorite math peeve is when "estimates" consist of very precise numbers. Doesn't estimate mean an approximation--i.e. round numbers? So you see stuff like "An estimated 2,349,807 people will suffer a fatal big toe aneurism in October this year."

(Just kidding, this is not a real statistic. Please don't quote it in a letter to the editor)