More fun with gear/crank/rpm MATH

[Hell and High Water]

I have 39/53 in front

7-speed freewheel in back (14-16-18-20-22-24-28)



I want to keep my RPM above 100, but don't have a cadence meter.


My basic math tells me that with these numbers, as long as I'm going at
least 11 MPH, my cadence is at least 100.


How's my math?


-Bob

 

[Clive George]

"Hell and High Water" <[email protected]> wrote in message
news:[email protected]...
>I have 39/53 in front
>
> 7-speed freewheel in back (14-16-18-20-22-24-28)
>
> I want to keep my RPM above 100, but don't have a cadence meter.
>
> My basic math tells me that with these numbers, as long as I'm going at
> least 11 MPH, my cadence is at least 100.
>
> How's my math?

I think your arithmetic is fine, but your phrasing of your question doesn't
fit.

If you're going 11 mph, your cadence could be anything from 0
(freewheeling), through 37rpm in top gear, to 100rpm in bottom gear.

Ie if you're going 11mph, your cadence is no more than 100.

cheers,
clive

 

[Kerry Montgomery]

"Hell and High Water" <[email protected]> wrote in message
news:[email protected]...
>I have 39/53 in front
>
> 7-speed freewheel in back (14-16-18-20-22-24-28)
>
>
>
> I want to keep my RPM above 100, but don't have a cadence meter.
>
>
> My basic math tells me that with these numbers, as long as I'm going at
> least 11 MPH, my cadence is at least 100.
>
>
> How's my math?
>
>
> -Bob
>
>
>
>

Bob,
If you ride 27" or 700c, or something similar; your math's good. If you ride
a 20"; maybe not so much.
Kerry

 

[Ben C]

On 2007-10-16, Hell and High Water <[email protected]> wrote:
> I have 39/53 in front
>
> 7-speed freewheel in back (14-16-18-20-22-24-28)
>
>
>
> I want to keep my RPM above 100, but don't have a cadence meter.
>
>
> My basic math tells me that with these numbers, as long as I'm going at
> least 11 MPH, my cadence is at least 100.
>
>
> How's my math?

About right.

Speeds (mph) in gears for cadence 100 (inches)

39 14 22.03 (74.04)
39 16 19.28 (64.79)
39 18 17.14 (57.59)
39 20 15.42 (51.83)
39 22 14.02 (47.12)
39 24 12.85 (43.19)
39 28 11.02 (37.02)
53 14 29.94 (100.62)
53 16 26.20 (88.05)
53 18 23.29 (78.26)
53 20 20.96 (70.44)
53 22 19.05 (64.03)
53 24 17.47 (58.70)
53 28 14.97 (50.31)

 

[Zog The Undeniable]

Hell and High Water wrote:
> I have 39/53 in front
>
> 7-speed freewheel in back (14-16-18-20-22-24-28)
>
>
>
> I want to keep my RPM above 100, but don't have a cadence meter.
>
>
> My basic math tells me that with these numbers, as long as I'm going at
> least 11 MPH, my cadence is at least 100.
>
>
> How's my math?
>
>
> -Bob
>
>
>
>
This only really works for a fixed-gear or singlespeed bike, when road
speed is unavoidably linked to pedal speed. I don't even have a
computer on my fixies, as I concentrate more on cadence (and it's too
scary when 35mph flashes up on a computer and you realise that means
175rpm).

 

[Leo Lichtman]

"Hell and High Water" wrote: (clip)How's my math?
^^^^^^^^^^^^^^^^
It's okay if you stay in your lowest gear. If you shift up it will drop
below 100, falling to about 36 in your tallest gear.

 

[Hell and High Water]

In article <[email protected]>,
[email protected] says...
>
> "Hell and High Water" wrote: (clip)How's my math?
> ^^^^^^^^^^^^^^^^
> It's okay if you stay in your lowest gear. If you shift up it will drop
> below 100, falling to about 36 in your tallest gear.

I've got these numbers:



39 52
28 10.9 14.5
24 12.7 17.0
22 13.9 18.5
20 15.3 20.4
18 17.0 22.6
16 19.1 25.4
14 21.8 29.1



I'm not sure how you got 36.


At 36 RPM, I've got these numbers


39 52
28 3.9 5.2
24 4.6 6.1
22 5.0 6.7
20 5.5 7.3
18 6.1 8.1
16 6.9 9.2
14 7.8 10.5

 

[Hell and High Water]

In article <[email protected]>, clive@xxxx-
x.fsnet.co.uk says...
> "Hell and High Water" <[email protected]> wrote in message
> news:[email protected]...
> >I have 39/53 in front
> >
> > 7-speed freewheel in back (14-16-18-20-22-24-28)
> >
> > I want to keep my RPM above 100, but don't have a cadence meter.
> >
> > My basic math tells me that with these numbers, as long as I'm going at
> > least 11 MPH, my cadence is at least 100.
> >
> > How's my math?
>
> I think your arithmetic is fine, but your phrasing of your question doesn't
> fit.
>
> If you're going 11 mph, your cadence could be anything from 0
> (freewheeling), through 37rpm in top gear, to 100rpm in bottom gear.


I've got these numbers for 100 RPM:



39 52
28 10.9 14.5
24 12.7 17.0
22 13.9 18.5
20 15.3 20.4
18 17.0 22.6
16 19.1 25.4
14 21.8 29.1


-Bob

 

[Hell and High Water]

In article <[email protected]>,
[email protected] says...
> I have 39/53 in front

That was a typo.

I have a 39/52 in front.

Here are the numbers (MPH) I have for 100 RPM:


39 52
28 10.9 14.5
24 12.7 17.0
22 13.9 18.5
20 15.3 20.4
18 17.0 22.6
16 19.1 25.4
14 21.8 29.1




So...with those numbers, if I'm going 11 MPH, I know that my RPM is at
least 100.


And, 700-23 tires.


Thanks,


-Bob

 

[[email protected]]

On Oct 16, 8:02 pm, Hell and High Water <[email protected]>
wrote:
> I have 39/53 in front
>
> 7-speed freewheel in back (14-16-18-20-22-24-28)
>
> I want to keep my RPM above 100, but don't have a cadence meter.
>
> My basic math tells me that with these numbers, as long as I'm going at
> least 11 MPH, my cadence is at least 100.
>
> How's my math?
>
> -Bob

http://software.bareknucklebrigade.com/rabbit.applet.html

Joseph

 

[Clive George]

"Hell and High Water" <[email protected]> wrote in message
news:[email protected]...
> In article <[email protected]>,
> [email protected] says...
>> I have 39/53 in front
>
> That was a typo.
>
> I have a 39/52 in front.
>
> Here are the numbers (MPH) I have for 100 RPM:
>
>
> 39 52
> 28 10.9 14.5
> 24 12.7 17.0
> 22 13.9 18.5
> 20 15.3 20.4
> 18 17.0 22.6
> 16 19.1 25.4
> 14 21.8 29.1
>
> So...with those numbers, if I'm going 11 MPH, I know that my RPM is at
> least 100.

No, with those numbers if you're going 11 mph, you know your RPM is no more
than 100.

cheers,
clive

 

[Leo Lichtman]

"Hell and High Water" wrote: I'm not sure how you got 36.
^^^^^^^^^^^^^^^^^
At 11 MPH his wheel is turning 137 RPM. In his tallest gear, the pedals are
going 14/53x137=36 RPM.
(I assumed a 27" wheel, which is about 7 ft in circumference. 11 MPH =
about 960 feet/minute, which, divided by 7 = 137 RPM.)

These numbers look right to me. Did I slip up?

 

[Lou Holtman]

Hell and High Water wrote:
> In article <[email protected]>,
> [email protected] says...
>> I have 39/53 in front
>
> That was a typo.
>
> I have a 39/52 in front.
>
> Here are the numbers (MPH) I have for 100 RPM:
>
>
> 39 52
> 28 10.9 14.5
> 24 12.7 17.0
> 22 13.9 18.5
> 20 15.3 20.4
> 18 17.0 22.6
> 16 19.1 25.4
> 14 21.8 29.1
>
>
>
>
> So...with those numbers, if I'm going 11 MPH, I know that my RPM is at
> least 100.
>
>
> And, 700-23 tires.
>
>
> Thanks,
>
>
> -Bob
>


No of coarse not. The answer is in front of you. Not at least... but max.


Lou
--
Posted by news://news.nb.nu (http://www.nb.nu)

 

[Hell and High Water]

In article <[email protected]>,
[email protected] says...
>
> "Hell and High Water" wrote: I'm not sure how you got 36.
> ^^^^^^^^^^^^^^^^^
> At 11 MPH his wheel is turning 137 RPM. In his tallest gear, the pedals are
> going 14/53x137=36 RPM.
> (I assumed a 27" wheel, which is about 7 ft in circumference. 11 MPH =
> about 960 feet/minute, which, divided by 7 = 137 RPM.)
>
> These numbers look right to me. Did I slip up?



If I'm in my big chainring (52) and my smallest rear cog (14), and I'm
spinning at 36 RPM, I'm going to be going about 10.5 MPH:

However, If I'm in my small front ring (39) and my biggest rear cog (28)
and I'm spinning at 36 RPM, I show that I would be going 3.9 MPH.


At 36 RPM, I've got these numbers


39 52
28 3.9 5.2
24 4.6 6.1
22 5.0 6.7
20 5.5 7.3
18 6.1 8.1
16 6.9 9.2
14 7.8 10.5

>
>
>