Sigma sport cycle computer - what tyre size

[PaulaT]

Yep as suspected,the OP needs to measure the circumferance of the tyre to get an accurate reading.

I've read that even that wont give totally calibration because of how the tyre deforms when you're sitting on the bike. I think it makes the effective circumference smaller that you'd get by measuring around the wheel. I bet it's also dependent on tyre pressure too as the lower the pressure the more tyre deformation you'll get.

[tatanab]

Manual --- https://www.sigmasport.com/en/images/pd ... en_SP3.pdf taken from https://www.sigmasport.com/en/produkte/ ... nu=manuals
Item 12 at the bottom shows you how to measure the wheel diameter. Item 7 towards the top shows you how to enter this value into your computer. Or, you could use the generis value for 700 C (shown in 12) but that will give errors since the tyre could be anything from 23 upwards.

Like many of us, the answer is --- read the manual.

[Mike_GMT80]

Done...measured the circumference and input into the computer. Will see if this improves accuracy.

Thanks
Mike


I'm a trendy consumer. Just look at my wobbly bog brush using hovercraft full of eels

[reohn2]

Yep as suspected,the OP needs to measure the circumferance of the tyre to get an accurate reading.

I've read that even that wont give totally calibration because of how the tyre deforms when you're sitting on the bike. I think it makes the effective circumference smaller that you'd get by measuring around the wheel. I bet it's also dependent on tyre pressure too as the lower the pressure the more tyre deformation you'll get.

You could sit on the bike whilst carrying out the measurement.
Though as you so rightly say tyre pressure can make a difference,as can riding up hill when less weight is on the front wheel*,or even riding down hill when more weight is on the front wheel.That said if you chose each ride with with equal ups and downs it could even out any discrepancies.

*unless you climb out of the saddle which puts more weight on the front wheel

Ho hum life's problems

[sjs]

I've always just started with a random or default setting for tyre size, ridden a known distance, then applied a correction factor to the original size setting.
ie
correct size = random size X (known distance)/(incorrectly measured distance)

[Jdsk]

That's an excellent approach because it removes a whole pile of possible errors.

(And the way I recommend for car speedometers, using GPS speed as the reference standard.)

Jonathan

[igauk]

Or you could just look it up on one of the many charts that provide this info?

https://www.cyclinguk.org/cyclists-library/components/wheels-tyres/tyre-sizes

https://www.cateye.com/data/resources/Tire_size_chart_ENG_151106.pdf

[thirdcrank]

Unless something is obviously way out, I'd say it's not worth bothering about, on the world-wide scale.

I must have posted before that I bought a Cateye (Mity 2?) and decided to check it on a measured mile. To give a bit of local detail, I chose the one in Baildon, just along the road from where Ellis Briggs shop used to be. I manually set it to what it said in the manual for my wheel size, then road backwards and forwards (always going forwards of course) along the measured mile, fine tuning the computer at the end of each mile ridden. After doing that for some time, I checked the setting and I was back to the setting recommended in the handbook. I suspect one of the things that this shows is that the slight deviations from a straight line when riding, especially in busy traffic, have more effect than a minute difference in wheel circumference.

There are better ways of getting the miles in.

[Pebble]

Unless something is obviously way out, I'd say it's not worth bothering about, on the world-wide scale.

I must have posted before that I bought a Cateye (Mity 2?) and decided to check it on a measured mile. To give a bit of local detail, I chose the one in Baildon, just along the road from where Ellis Briggs shop used to be. I manually set it to what it said in the manual for my wheel size, then road backwards and forwards (always going forwards of course) along the measured mile, fine tuning the computer at the end of each mile ridden. After doing that for some time, I checked the setting and I was back to the setting recommended in the handbook. I suspect one of the things that this shows is that the slight deviations from a straight line when riding, especially in busy traffic, have more effect than a minute difference in wheel circumference.

There are better ways of getting the miles in.

A MITY 2 I'm on the Mity3, its well battered and glued and soldered in place but still working.

Annoyingly the setting of the wheel size on the mity3 leads to inaccuracy, calibration is to whole centimetres and wheel circumference is 2136 mm - that could knock my yearly total out by 15 mile (and 15 mile is 15 mile especially into the wind)

I do calibrate all mileometers with bike-hike http://www.bikehike.co.uk/mapview.php, very important to do so with vehicles if you are interested in true mpg figures. cars and vans are notorious in over-reading distance, (my van is 4.5% out and the car 1.3% out). In comparison my bike is pretty near spot on 99.7% accurate.

However when it comes to my weekly average of 150 mile, this is done purely through bike-hike and no ride can be less than 10 mile. So little rides to the shops don't count take the SUV instead.