Does any decent wired bike computer with average cadence exist?

For discussions about bikes and equipment.
User avatar
Syd
Posts: 1227
Joined: 23 Sep 2018, 2:27pm
Location: Lothian

Re: Does any decent wired bike computer with average cadence exist?

Post by Syd »

Manc33 wrote:
I thought about maybe strapping a Go-Pro to the chainstay and filming the cassette while riding, that would be cheaper than Di2 :lol:
That would be interesting to see. Image
User avatar
Tigerbiten
Posts: 2268
Joined: 29 Jun 2009, 6:49am

Re: Does any decent wired bike computer with average cadence exist?

Post by Tigerbiten »

Jamesh wrote: 20 Sep 2021, 8:28am In Yorkshire I'm too busy worrying about the next hill to work out cadence!

Cheers James
Knowing your optimal cadence may let you tweak the gears to make hill climbing easier.
You hit a second aero wall at around 30 mph where it more efficient to tuck and freewheel down hill rather than keep pedalling.
The first is around 15 mph where the aero resistance starts to ramp up badly.
So if you have a naturally slow cadence (60-70 rpm) then a top of 50/11x27 or 122.7" is a useful top gear as you'll hit around 30 mph just as you start to spin out.
But if you have a naturally high cadence (90-100 rpm) then a 44/11x27 or 108" may be a more useful top gear.
You'll again spinout around 30 mph but a 44t big chainring may also give you a couple of lower gears to make hill climbing easier.
I see no point in being able to pedal downhill at ~35 mph if you cannot climb the same hill easily ..... :lol:

YMMV ....... :D
fastpedaller
Posts: 3006
Joined: 10 Jul 2014, 1:12pm
Location: Norfolk

Re: Does any decent wired bike computer with average cadence exist?

Post by fastpedaller »

Wouldn't it be possible to set up a 'regular' computer to give average cadence? If the sensor is on the crank rather than on the wheel, every turn of the crank will be 'monitored' and can be expressed as a maximum or an average speed. All it will then take is working out how to interpret the reading. I guess the way to start is to pick a number, say, 100 rpm. Calculate what rolling diameter will give a reading of 25mph for 100 revs of a wheel (in this case it will be a crank of course). Input the rolling diameter into the computer, and whatever reading comes up as the average - just multiply by 4 and you have the cadence. I think I've got that correct, and I hope it makes sense (It does to me :lol: )
Jamesh
Posts: 2320
Joined: 2 Jan 2017, 5:56pm

Re: Does any decent wired bike computer with average cadence exist?

Post by Jamesh »

Tigerbiten wrote: 20 Sep 2021, 7:28pm
Jamesh wrote: 20 Sep 2021, 8:28am In Yorkshire I'm too busy worrying about the next hill to work out cadence!

Cheers James
Knowing your optimal cadence may let you tweak the gears to make hill climbing easier.
You hit a second aero wall at around 30 mph where it more efficient to tuck and freewheel down hill rather than keep pedalling.
The first is around 15 mph where the aero resistance starts to ramp up badly.
So if you have a naturally slow cadence (60-70 rpm) then a top of 50/11x27 or 122.7" is a useful top gear as you'll hit around 30 mph just as you start to spin out.
But if you have a naturally high cadence (90-100 rpm) then a 44/11x27 or 108" may be a more useful top gear.
You'll again spinout around 30 mph but a 44t big chainring may also give you a couple of lower gears to make hill climbing easier.
I see no point in being able to pedal downhill at ~35 mph if you cannot climb the same hill easily ..... :lol:

YMMV ....... :D
Sounds about right. But on longer rides above 20mph down hill I tend to rest the legs and bum!

Uphill I tend to drop to the inner / middle chain ring before it start to ramp up and use the gears progressively. Any Ramps are often best attacked out of the saddle to maintain the same gear in the flatter sections.

Cheers James
Manc33
Posts: 1833
Joined: 25 Apr 2015, 9:37pm

Re: Does any decent wired bike computer with average cadence exist?

Post by Manc33 »

fastpedaller wrote: 22 Sep 2021, 8:34pm Wouldn't it be possible to set up a 'regular' computer to give average cadence? If the sensor is on the crank rather than on the wheel, every turn of the crank will be 'monitored' and can be expressed as a maximum or an average speed. All it will then take is working out how to interpret the reading. I guess the way to start is to pick a number, say, 100 rpm. Calculate what rolling diameter will give a reading of 25mph for 100 revs of a wheel (in this case it will be a crank of course). Input the rolling diameter into the computer, and whatever reading comes up as the average - just multiply by 4 and you have the cadence. I think I've got that correct, and I hope it makes sense (It does to me :lol: )
Bike computers won't let you put the circumference of something the size of a dinner plate, otherwise it would work.

It would be the radius from the center of the BB to the center of the magnet on the crank x 6.2832 to get the rolling circumference. Maybe if 2x that diameter was entered, then part of the final calculation would be to divide the "distance" by 2, maybe?! It's complicated lol, at least for me anyway. :oops: If it's set at 2x the circumference it really is then it's registering 2x the distance so yeah I guess it's that /2.

Then it would be a case of looking at the time taken along with half the distance. It's all possible but it's faffing, then again I like faffing. :)

I still can't grasp how crank revolutions would be worked out from knowing the distance and time. The rolling distance has to also come into it. If I ever worked it out I'd make a calc for it :mrgreen: where you enter three things: Crank radius, time taken and distance. It would have to stipulate that you must set the circumference x2 in the bike computer.

EDIT: Changed x3 to x2 since a 175mm crank x2 (diameter) x2 = 700mm, roughly the size of a wheel.
Last edited by Manc33 on 23 Sep 2021, 5:41pm, edited 1 time in total.
When two cyclists get married, they should throw anodized cable crimps instead of confetti.
Jdsk
Posts: 11162
Joined: 5 Mar 2019, 5:42pm

Re: Does any decent wired bike computer with average cadence exist?

Post by Jdsk »

Manc33 wrote: 23 Sep 2021, 5:32pm
fastpedaller wrote: 22 Sep 2021, 8:34pm Wouldn't it be possible to set up a 'regular' computer to give average cadence? If the sensor is on the crank rather than on the wheel, every turn of the crank will be 'monitored' and can be expressed as a maximum or an average speed. All it will then take is working out how to interpret the reading. I guess the way to start is to pick a number, say, 100 rpm. Calculate what rolling diameter will give a reading of 25mph for 100 revs of a wheel (in this case it will be a crank of course). Input the rolling diameter into the computer, and whatever reading comes up as the average - just multiply by 4 and you have the cadence.
Bike computers won't let you put the circumference of something the size of a dinner plate, otherwise it would work.
But, as suggested, you could set it so that there's an easy conversion from the displayed value into the desired unit of measure.

Jonathan
Manc33
Posts: 1833
Joined: 25 Apr 2015, 9:37pm

Re: Does any decent wired bike computer with average cadence exist?

Post by Manc33 »

Jdsk wrote: 23 Sep 2021, 5:41pm
Manc33 wrote: 23 Sep 2021, 5:32pm
fastpedaller wrote: 22 Sep 2021, 8:34pm Wouldn't it be possible to set up a 'regular' computer to give average cadence? If the sensor is on the crank rather than on the wheel, every turn of the crank will be 'monitored' and can be expressed as a maximum or an average speed. All it will then take is working out how to interpret the reading. I guess the way to start is to pick a number, say, 100 rpm. Calculate what rolling diameter will give a reading of 25mph for 100 revs of a wheel (in this case it will be a crank of course). Input the rolling diameter into the computer, and whatever reading comes up as the average - just multiply by 4 and you have the cadence.
Bike computers won't let you put the circumference of something the size of a dinner plate, otherwise it would work.
But, as suggested, you could set it so that there's an easy conversion from the displayed value into the desired unit of measure.

Jonathan
Don't tell me it will work because I'll have to do it :lol:
Last edited by Manc33 on 23 Sep 2021, 5:45pm, edited 2 times in total.
When two cyclists get married, they should throw anodized cable crimps instead of confetti.
Jdsk
Posts: 11162
Joined: 5 Mar 2019, 5:42pm

Re: Does any decent wired bike computer with average cadence exist?

Post by Jdsk »

Manc33 wrote: 23 Sep 2021, 5:42pm
Jdsk wrote: 23 Sep 2021, 5:41pm
Manc33 wrote: 23 Sep 2021, 5:32pm Bike computers won't let you put the circumference of something the size of a dinner plate, otherwise it would work.
But, as suggested, you could set it so that there's an easy conversion from the displayed value into the desired unit of measure.
Don't tell me it will work because I'll have to do it
: - )

It will work as long as the pulse rate (or whatever) from the sender is in the acceptable range. Neither the sender nor the computer know where it's actually been placed, nor your cunning plan!

Jonathan
Manc33
Posts: 1833
Joined: 25 Apr 2015, 9:37pm

Re: Does any decent wired bike computer with average cadence exist?

Post by Manc33 »

I've been working it out on my current calc - I know the gear I'm usually in on the flat and on my calc, if you juggle the cadence figure around until you get the speed for that gear (at the entered cadence) you have the cadence. This is how I worked out my average cadence is about 56. I'm trying to get that increased but I hate pedalling fast.
When two cyclists get married, they should throw anodized cable crimps instead of confetti.
User avatar
Tigerbiten
Posts: 2268
Joined: 29 Jun 2009, 6:49am

Re: Does any decent wired bike computer with average cadence exist?

Post by Tigerbiten »

Manc33 wrote: 23 Sep 2021, 5:45pm This is how I worked out my average cadence is about 56. I'm trying to get that increased but I hate pedalling fast.
I upped my cadence not by pedalling fast but by pedalling light.
If you pedal very slowly then you need a lot of pressure on the pedals, cycling like this relies totally on leg strength and is horribly inefficient.
As your cadence increases then the pressure on the pedals decreases and you get more efficient.
This increase in efficiency levels out as you enter your optimal cadence zone.
At a guess you're a lower edge of yours.
But once you exit the zone on the high side, your efficiency tanks.
It takes energy to spin your legs and like wind resistance it goes up at the square of the speed.
So once out of your cadence zone, a small increase of cadence takes a lot of energy so less is left to power the bike forward, hence the drop in efficiency.
So next time you go out, try and ride at a comfortable cadence and a light pressure on the pedals.
Now try and keep this light pressure no matter what.
As the only way to keep this light pressure is to up your cadence slightly, over time it will be normal to ride with a higher cadence.
I used this "pedal light" trick to naturally up my average cadence from around 60 rpm to close to 80 rpm.
If I'm very fit then I can pedal at 85 rpm, but once I'm over 90 I'm out of my zone and my heart/breathing rate increases with no gain in speed because my efficiency drops.

YMMV ........ :D
fastpedaller
Posts: 3006
Joined: 10 Jul 2014, 1:12pm
Location: Norfolk

Re: Does any decent wired bike computer with average cadence exist?

Post by fastpedaller »

Manc33 wrote: 23 Sep 2021, 5:32pm
fastpedaller wrote: 22 Sep 2021, 8:34pm Wouldn't it be possible to set up a 'regular' computer to give average cadence? If the sensor is on the crank rather than on the wheel, every turn of the crank will be 'monitored' and can be expressed as a maximum or an average speed. All it will then take is working out how to interpret the reading. I guess the way to start is to pick a number, say, 100 rpm. Calculate what rolling diameter will give a reading of 25mph for 100 revs of a wheel (in this case it will be a crank of course). Input the rolling diameter into the computer, and whatever reading comes up as the average - just multiply by 4 and you have the cadence. I think I've got that correct, and I hope it makes sense (It does to me :lol: )
Bike computers won't let you put the circumference of something the size of a dinner plate, otherwise it would work.

It would be the radius from the center of the BB to the center of the magnet on the crank x 6.2832 to get the rolling circumference. Maybe if 2x that diameter was entered, then part of the final calculation would be to divide the "distance" by 2, maybe?! It's complicated lol, at least for me anyway. :oops: If it's set at 2x the circumference it really is then it's registering 2x the distance so yeah I guess it's that /2.

Then it would be a case of looking at the time taken along with half the distance. It's all possible but it's faffing, then again I like faffing. :)

I still can't grasp how crank revolutions would be worked out from knowing the distance and time. The rolling distance has to also come into it. If I ever worked it out I'd make a calc for it :mrgreen: where you enter three things: Crank radius, time taken and distance. It would have to stipulate that you must set the circumference x2 in the bike computer.

EDIT: Changed x3 to x2 since a 175mm crank x2 (diameter) x2 = 700mm, roughly the size of a wheel.
The chainring (or indeed) cranks size doesn't matter. Think of it as the wheel! All you need is to be able to get a readout of an imaginary wheel.
3333 as an input circumference......... 3333 x 100rpmx60 minutes gives a reading of 20kph. so multiply readout by 5 to get our RPM of the crank. Can a computer be set to 3333mm circumference? it's 1060mm diameter (a very small 'ordinary' front wheel.)
User avatar
Tigerbiten
Posts: 2268
Joined: 29 Jun 2009, 6:49am

Re: Does any decent wired bike computer with average cadence exist?

Post by Tigerbiten »

You still need to input your gear size somewhere in equation even if its only chainring/sprocket.
I spinout at just over 90 rpm.
In my 9.4" first gear I'll be doing around 2.6 mph when I spin out.
But in my 179" top gear at the same cadence I'll be doing very close to 50 mph.
You must take the speed variable from the gears into account unless you're riding a fixie.

Luck ........... :D
Manc33
Posts: 1833
Joined: 25 Apr 2015, 9:37pm

Re: Does any decent wired bike computer with average cadence exist?

Post by Manc33 »

Have you got 5 chainrings? :P

I did have 22x40 on my bike a while back and that seemed to be my limit for low gearing, it was about 14" gear inches on my bike. I'm scared of bending spokes in gears like this.
When two cyclists get married, they should throw anodized cable crimps instead of confetti.
fastpedaller
Posts: 3006
Joined: 10 Jul 2014, 1:12pm
Location: Norfolk

Re: Does any decent wired bike computer with average cadence exist?

Post by fastpedaller »

Tigerbiten wrote: 24 Sep 2021, 12:29am You still need to input your gear size somewhere in equation even if its only chainring/sprocket.
I spinout at just over 90 rpm.
In my 9.4" first gear I'll be doing around 2.6 mph when I spin out.
But in my 179" top gear at the same cadence I'll be doing very close to 50 mph.
You must take the speed variable from the gears into account unless you're riding a fixie.

Luck ........... :D
Gearing isn't involved. the sensor is on (ideally) the seatube, and the magnet is on the left crank. You aren't measuring road speed, but you are measuring pulses of an 'imaginary wheel ' . each pulses (revs of the crank) of an imaginary wheel set on the computer as 3333 gives a readout of 20. Multiply by 5 and you have your crank rpm, which for most computers can be displayed as an average. It will even take account of those freewheeling moments, more or less, as most computers have auto turn-off and restart after a few seconds.
fastpedaller
Posts: 3006
Joined: 10 Jul 2014, 1:12pm
Location: Norfolk

Re: Does any decent wired bike computer with average cadence exist?

Post by fastpedaller »

No response from the OP....... I know I may not have explained it well, but it makes sense to me :wink: . If you have any questions I'm happy to add more.
Post Reply