Cycle computer on 29" wheels?

Simonb256 · May 2007

If I'm running 29inch wheels and get a normal off the shelf cycle computer, would that in turn mean that all distance and speed measurements would be more inaccurate?

I assume this as a 29inch has a larger circumference than a 26, so one revolution would be a greater distance than a 26, hence your would be traveling faster at say 90rpm with a 29inch wheel than a 26inch.

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lobes · May 2007

No, because the speed is read by how fast the Gadget on the spoke passes the gadget attatched to the fork.

If you were doing 10mph on a BMX or 10mph on a 29er, the two peices are still crossing at the same speed.

As for distance measurements im not sure, but i wouldnt have thought so because there is no specific part of the spoke or fork where the little "Things" have to be attatched.

If that makes sense?

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ride_whenever · May 2007

Most cycle computers allow you to set what type of wheel you have, usually it is either radius or circumference.

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coldomc05 · May 2007

Most cycle computers require some form of user input in order to work correctly. Usually when you turn on your cycle computer you have to set a few parameters first. On mine I had to state the following time/date, weight, age, wheelsize, MPH or KMH, Km or M, degrees C or F, and finally how many miles you do before a service is due. Once setup though they are usually pretty accurate.

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Mike Skinner · May 2007

As above, all cycle computers I've used have asked for the wheel circumferance.

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Simonb256 · May 2007

Ahh thanks for that guys.
I thought they did, but best to check I guess.

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Big Red S · May 2007

They always ask for a tyre circumference. Otherwise they'd only work on one particular tyre.

And, besides, they all do MtB and road.

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Crazy Dave C · May 2007

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by lobes

No, because the speed is read by how fast the Gadget on the spoke passes the gadget attatched to the fork.

If you were doing 10mph on a BMX or 10mph on a 29er, the two peices are still crossing at the same speed.

As for distance measurements im not sure, but i wouldnt have thought so because there is no specific part of the spoke or fork where the little "Things" have to be attatched.

If that makes sense?
<hr height="1" noshade id="quote"></blockquote id="quote">

You really have no idea do you? They don't measure the speed that the magnet passes the sensor, but the amount of times it passes the sensor in a time period. You need to set it up so it calculates the speed by knowing the circumference of the wheel and calculate your speed from the amount of times the wheel turns every second (or whatever the time period is).

If a BMX and a 29" wheeld bike were travelling at the same speed the BMX wheel would be spinning faster than the 29" wheel due to the smaller circumference.

LostAndConfused · May 2007

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by lobes

No, because the speed is read by how fast the Gadget on the spoke passes the gadget attatched to the fork.

If you were doing 10mph on a BMX or 10mph on a 29er, the two peices are still crossing at the same speed.

As for distance measurements im not sure, but i wouldnt have thought so because there is no specific part of the spoke or fork where the little "Things" have to be attatched.

If that makes sense?
<hr height="1" noshade id="quote"></blockquote id="quote">

Not at all... [;)]

mbukfan · June 2007

<blockquote id="quote">quote:<hr height="1" noshade id="quote">
Not at all... [;)]
<hr height="1" noshade id="quote"></blockquote id="quote">
the cycle computer uses a priximity switch to count the number of RPM (revolutions per minute) of the wheel. If a wheel is moving at 120rmp then the magnet passses the sensor 120times
The sensor then works out how far you have gone in a minute by multiplying the circumfrence of the wheel by the number of passes the magnet has made. On my bike this is just over 2meters X 120

on a 700c road wheel it might my 2.25meters times 120. The magnet is tavelling at a speed which can be calculated by the rpm X the distance of the magnet to the axel X 3.142 (roughly as this is pi to 3dp) Since the distance from the axel is about the same the magnet is travelling at the same relitive speed to the sensor regardless of the overall wheel size. You will get a slightly better reading if the magnet is travelling at a faster relive speed which is why you are recomended to put the magnet as close to the rim while still getting a good reading.

If the wheel size isn't in the scope of the sensor oyu can do some maths and get a speed by using the computer in Kmh but giving the correct speed in mph or vise versa (my brothers got one attached to a mini moto) if your wheel is too big divide by 8 and then times by 5 and run the computer in miles but your true speed is in Kmph and if your wheel is too small times by 8 and divide by 5 and set your speedo to Kmph but your true speed is mph

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jAckAsS o__0 · June 2007

Surley you should get one that is specificly for 29"ers??

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Tartanyak · June 2007

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by jAckAsS o__0

Surley you should get one that is specificly for 29"ers??

<hr height="1" noshade id="quote"></blockquote id="quote">

Why?

When you set the things up, they ask you for the circumference of the wheel...

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downhill · June 2007

Fairplay some people chat bollox, it's quite funny. all computers ask you for the circumference of your wheel i aint to sure if you can use 29er's because there normally only compatable with common wheel sizes eg. 26, 24, 20, 16, 14, 12 and 700

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mbukfan · June 2007

some ask you to enter the circumference of the wheel in mm so can workwith more sizes, these are also more accuarte as not all tyres for 26inch wheel will give a 26inch wheel, the wheel diameter will change slightly depending on how wide the rim is as it changes the profile to an extent

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Cycle computer on 29" wheels?

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