Go Back  Bike Forums > Bike Forums > Road Cycling
Reload this Page >

Computer sensor placement....

Notices
Road Cycling “It is by riding a bicycle that you learn the contours of a country best, since you have to sweat up the hills and coast down them. Thus you remember them as they actually are, while in a motor car only a high hill impresses you, and you have no such accurate remembrance of country you have driven through as you gain by riding a bicycle.” -- Ernest Hemingway

Computer sensor placement....

Old 01-27-07, 08:35 PM
  #1  
not revenge...punishment
Thread Starter
 
interceptor's Avatar
 
Join Date: May 2005
Posts: 611
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 40 Post(s)
Liked 21 Times in 12 Posts
Computer sensor placement....

My sensor for the computer is about two thirds down the fork (most look like the are about in the middle).
Does it matter? I was going to hold on to someones car to test for accuracy. Do I need to?
interceptor is offline  
Old 01-27-07, 08:42 PM
  #2  
Senior Member
 
Join Date: Nov 2006
Location: Charlotte, North Carolina, USA
Posts: 1,643

Bikes: '71 Raleigh Sports, '84 Schwinn LeTour on the trainer (and available for hill repeats), '06 Scott CR1 SL (Ksyrium SL), and a yet-to-be-determined TT bike.

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 2 Times in 2 Posts
Um. What computer, specifically? Holding on to a car?
VegaVixen is offline  
Old 01-27-07, 08:47 PM
  #3  
not revenge...punishment
Thread Starter
 
interceptor's Avatar
 
Join Date: May 2005
Posts: 611
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 40 Post(s)
Liked 21 Times in 12 Posts
Just a basic cateye computer. Don't know if the accuracy is dependent on the placement on the fork.
interceptor is offline  
Old 01-27-07, 08:52 PM
  #4  
Defenestrator
 
Join Date: Jul 2005
Location: MD
Posts: 200
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
nope, as long as the correct tire size is entered in the computer, it doesn't matter...
frischtr is offline  
Old 01-27-07, 08:52 PM
  #5  
Dirt-riding heretic
 
DrPete's Avatar
 
Join Date: Aug 2005
Location: Gig Harbor, WA
Posts: 17,413

Bikes: Lynskey R230/Red, Blue Triad SL/Red, Cannondale Scalpel 3/X9

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 5 Post(s)
Likes: 0
Liked 8 Times in 7 Posts
As long as the computer is picking up the signal from the sensor you're fine. The sensor just ticks off every time the magnet goes by, then multiplies by the circumference of the wheel to calculate speed/distance. 100 rpm at the hub is the same as 100rpm at the rim.
__________________
"Unless he was racing there was no way he could match my speed."
DrPete is offline  
Old 01-27-07, 08:55 PM
  #6  
Well, duh, Mr Obvious.
 
dekalbSTEEL's Avatar
 
Join Date: Jul 2005
Location: NIU town
Posts: 2,271

Bikes: see sig, and others

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
If you do that holding on to a car thing, could you video tape that for us?
dekalbSTEEL is offline  
Old 01-27-07, 08:58 PM
  #7  
Double Secret Probation
 
R900's Avatar
 
Join Date: Aug 2005
Location: Eastern Indiana
Posts: 2,578

Bikes: Madone 6 series SSL, Cannondale CX9, Trek TTX, Trek 970, Trek T2000

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 4 Times in 4 Posts
I like mine high on the fork, putting the magnet as far from the hub as possible. But I guess the rotational weight guys would say put it as close to hub as possible. I don't think it really matter. No testing required, just measure your wheel/tire combination.
__________________
Time to Ride...
R900 is offline  
Old 01-27-07, 08:59 PM
  #8  
not revenge...punishment
Thread Starter
 
interceptor's Avatar
 
Join Date: May 2005
Posts: 611
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 40 Post(s)
Liked 21 Times in 12 Posts
thanks..........ok.
interceptor is offline  
Old 01-27-07, 09:10 PM
  #9  
Dirt-riding heretic
 
DrPete's Avatar
 
Join Date: Aug 2005
Location: Gig Harbor, WA
Posts: 17,413

Bikes: Lynskey R230/Red, Blue Triad SL/Red, Cannondale Scalpel 3/X9

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 5 Post(s)
Likes: 0
Liked 8 Times in 7 Posts
Originally Posted by interceptor
I was going to hold on to someones car to test for accuracy. Do I need to?
I don't know. Ask this guy:
__________________
"Unless he was racing there was no way he could match my speed."
DrPete is offline  
Old 01-27-07, 09:17 PM
  #10  
Senior Member
 
Join Date: Nov 2006
Location: Charlotte, North Carolina, USA
Posts: 1,643

Bikes: '71 Raleigh Sports, '84 Schwinn LeTour on the trainer (and available for hill repeats), '06 Scott CR1 SL (Ksyrium SL), and a yet-to-be-determined TT bike.

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 2 Times in 2 Posts
Originally Posted by DrPete
I don't know. Ask this guy:
Ouch! Got a feeling that if he was a lefty before, he's a righty now. <hurts Vega to look>
VegaVixen is offline  
Old 01-27-07, 09:24 PM
  #11  
Senior Member
 
garysol1's Avatar
 
Join Date: Apr 2005
Location: Traverse City Michigan
Posts: 10,244
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 78 Post(s)
Liked 17 Times in 11 Posts
I like my sensor high on the fork if it is wireless so the transmitter and the reciever are as close as possible.
__________________
BMC Roadmachine
Kona Jake the Snake
garysol1 is offline  
Old 01-27-07, 09:47 PM
  #12  
I eat carbide.
 
Psimet2001's Avatar
 
Join Date: Jan 2006
Location: Elgin, IL
Posts: 21,627

Bikes: Lots. Van Dessel and Squid Dealer

Mentioned: 25 Post(s)
Tagged: 0 Thread(s)
Quoted: 1325 Post(s)
Liked 1,306 Times in 560 Posts
I like to place mine as close to the hub as possible. It reduces the imbalance effect that the magnet has on the rotating wheel, and (more importantly) allows me to get the sensor-magnet gap close without having to push the sensor into the area between the fork and the wheel.

BTW-mount the sensor in such a way that if it gets pushed into the wheels by accident the next spoke to hit it would push it back out of the way again.
__________________
PSIMET Wheels, PSIMET Racing, PSIMET Neutral Race Support, and 11 Jackson Coffee
Podcast - YouTube Channel
Video about PSIMET Wheels

Psimet2001 is offline  
Old 01-27-07, 09:55 PM
  #13  
pan y agua
 
merlinextraligh's Avatar
 
Join Date: Aug 2005
Location: Jacksonville
Posts: 31,273

Bikes: Willier Zero 7; Merlin Extralight; Calfee Dragonfly tandem, Calfee Adventure tandem; Cervelo P2; Motebecane Ti Fly 29er; Motebecanne Phantom Cross; Schwinn Paramount Track bike

Mentioned: 17 Post(s)
Tagged: 0 Thread(s)
Quoted: 1428 Post(s)
Liked 697 Times in 353 Posts
If you feel compelled to test clibration against a car, have the carmeasure exactly a mile, and then see ifthe bike computeris highor low: don't try to match speed by holding on or otherwise.

But realize car speedometer calibrationis not that accurate. One, tire size (which might notbe OEM, or may be an OEM option not calibrated for) affects it, and Two, manufacturers often purposely make speedomters read a tad high.
merlinextraligh is offline  
Old 01-27-07, 09:59 PM
  #14  
not revenge...punishment
Thread Starter
 
interceptor's Avatar
 
Join Date: May 2005
Posts: 611
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 40 Post(s)
Liked 21 Times in 12 Posts
Originally Posted by DrPete
I don't know. Ask this guy:
ok, I guess I don't have to know EXACTLY how fast I'm going.................ouch!
interceptor is offline  
Old 01-27-07, 10:25 PM
  #15  
The cake is a lie!
 
Alasdair's Avatar
 
Join Date: Feb 2006
Location: Upstate South Carolina
Posts: 550

Bikes: 2006 Fuji Team Pro

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Originally Posted by interceptor
I was going to hold on to someones car to test for accuracy. Do I need to?
Why not just ride pace with a group and all compare moment in time speeds and then see if your mileage is close to theirs at ride's end. Works for me if I have doubts.
Alasdair is offline  
Old 01-27-07, 11:35 PM
  #16  
Senior Member
 
Join Date: Nov 2006
Location: Charlotte, North Carolina, USA
Posts: 1,643

Bikes: '71 Raleigh Sports, '84 Schwinn LeTour on the trainer (and available for hill repeats), '06 Scott CR1 SL (Ksyrium SL), and a yet-to-be-determined TT bike.

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 2 Times in 2 Posts
Originally Posted by interceptor
ok, I guess I don't have to know EXACTLY how fast I'm going.................ouch!
mmkay. We've now established that you're a very smart roadie.
VegaVixen is offline  
Old 01-28-07, 12:13 AM
  #17  
Senior Member
 
Join Date: Jul 2006
Location: SoCal
Posts: 756

Bikes: custom built roadie

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Originally Posted by Psimet2001
I like to place mine as close to the hub as possible. It reduces the imbalance effect that the magnet has on the rotating wheel
LOL. wow this made my day.
stea1thviper is offline  
Old 01-28-07, 12:24 AM
  #18  
Now 100% Mullet Free!
 
Ironic Mullet's Avatar
 
Join Date: May 2006
Location: The 512
Posts: 451

Bikes: 2019 Alchemy Eros, 2003 Litespeed Tuscany

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
100 rpm at the hub is the same as 100rpm at the rim.
True, but the magnet is moving faster relative to the sensor at the rim than the hub. I try to get as close to the hub as possible.
Ironic Mullet is offline  
Old 01-28-07, 12:24 AM
  #19  
.
 
blickblocks's Avatar
 
Join Date: Sep 2006
Posts: 3,860
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Originally Posted by DrPete
I don't know. Ask this guy:
Oh my god, did he make it out alright? It looks like the rear tire is about to run over his shoulder or possibly his head...
__________________
https://blicksbags.com/
blickblocks is offline  
Old 01-28-07, 02:27 AM
  #20  
Senior Member
 
Shortrider06's Avatar
 
Join Date: Oct 2006
Location: Chula Vista, San Diego
Posts: 219
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
^+1 would like to hear more on the matter?
Shortrider06 is offline  
Old 01-28-07, 05:35 AM
  #21  
Senior Member
 
Retro Grouch's Avatar
 
Join Date: Feb 2004
Location: St Peters, Missouri
Posts: 30,225

Bikes: Catrike 559 I own some others but they don't get ridden very much.

Mentioned: 16 Post(s)
Tagged: 0 Thread(s)
Quoted: 1572 Post(s)
Liked 642 Times in 363 Posts
All that the computer sensor does is to count the revolutions that the wheel makes. The hub makes exactly the same number of revolutions as the rim so it doesn't matter how high on the fork you mount it.

What does matter is how close the sensor is to the wheel magnet. Mount the sensor wherever it's necessary to get it to within a couple of millimeters of the wheel magnet.

One other thing. Mount your sensor on the front of the fork. That way if it ever gets bumped into the magnet the rotation of the wheel will push it out of the way rather than into the spokes.
Retro Grouch is offline  
Old 01-28-07, 05:36 AM
  #22  
Sua Ku
 
rollin's Avatar
 
Join Date: Aug 2006
Location: Hot as hell, Singapore
Posts: 5,705

Bikes: Trek 5200, BMC SLC01, BMC SSX, Specialized FSR, Holdsworth Criterium

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 1 Time in 1 Post
Originally Posted by Ironic Mullet
True, but the magnet is moving faster relative to the sensor at the rim than the hub. I try to get as close to the hub as possible.
The sensor doesn't "care" how fast the magnet is going - just if it's going past.... I guess it could mis-read if it was faster....

I set it out quite far near the rim - as close to opposite to where the valve stem is to balance the wheel is it only cyclists that worry about the most pointless details??
rollin is offline  
Old 01-28-07, 05:41 AM
  #23  
Senior Member
 
Retro Grouch's Avatar
 
Join Date: Feb 2004
Location: St Peters, Missouri
Posts: 30,225

Bikes: Catrike 559 I own some others but they don't get ridden very much.

Mentioned: 16 Post(s)
Tagged: 0 Thread(s)
Quoted: 1572 Post(s)
Liked 642 Times in 363 Posts
Originally Posted by rollin
I set it out quite far near the rim - as close to opposite to where the valve stem is to balance the wheel is it only cyclists that worry about the most pointless details??
Interesting. I've found that most of the time the valve stem is the lightest part of the wheel. I assume that's mostly due to the steel pins that are used to pin the rim joint together opposite the valve stem. When I put a bike with a nicely adjusted hub on the workstand, the front wheel usually rotates until the valve stem is near the top.
Retro Grouch is offline  
Old 01-28-07, 06:31 AM
  #24  
Dirt-riding heretic
 
DrPete's Avatar
 
Join Date: Aug 2005
Location: Gig Harbor, WA
Posts: 17,413

Bikes: Lynskey R230/Red, Blue Triad SL/Red, Cannondale Scalpel 3/X9

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 5 Post(s)
Likes: 0
Liked 8 Times in 7 Posts
Originally Posted by Shortrider06
^+1 would like to hear more on the matter?
Apparently the guy DID end up (relatively) OK. Here's the link to the whole series of photos...
https://www.cyclingnews.com/photos/20.../qinghai066/14
__________________
"Unless he was racing there was no way he could match my speed."
DrPete is offline  
Old 01-28-07, 07:08 AM
  #25  
A Little Bent
 
Hammertoe's Avatar
 
Join Date: Mar 2006
Location: Struggling up a hillside in Vermont, USA... ..........................................
Posts: 2,858
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Originally Posted by interceptor
My sensor for the computer is about two thirds down the fork (most look like the are about in the middle).
Does it matter? I was going to hold on to someones car to test for accuracy. Do I need to?
Does it not matter where you put the sensor when calculating the speed and total distance???

By setting the radius of the wheel, you know the circumference of the wheel. The magnet/sensor combination works by counting the number of revolutions that the wheel makes. From this it computes a rotational velocity with the help of a clock (i.e. revolutions per second). Using the radius of the wheel it can find the tangential velocity...

For the distance it just counts the number of revolutions. Each revolution means that the bike had gone a distance because that is how far any point on the wheel has moved in a circle, and since the wheels don't slip, the bike has moved that far...

In both cases, the positioning of the magnet/sensor was not needed, as the total number and frequency of the revolutions are all that is needed given the radius of the wheel...

I put my wheel magnet at the location needed for the sensor to sit on the chain stay where it can pick up my cadence magnet on the pedal axle....
__________________

Last edited by Hammertoe; 01-28-07 at 07:16 AM.
Hammertoe is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.