Sigma sport cycle computer - what tyre size

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Mike_GMT80
Posts: 30
Joined: 23 Jul 2020, 8:37am

Sigma sport cycle computer - what tyre size

Postby Mike_GMT80 » 1 Aug 2020, 4:58am

Hi, with my cycle to work voucher picked this cycle computer up. First use comparing speed, distance, etc to Strava seems not aligned. The spec for my Triban RC500 bike details wheels as 622 x 17c and also 28inch front and rear. I understand that 622 = 700c, and this is what I have entered as the size into the computer. Would it be more accurate if I entered as 28inch?

I now see the reviews for this computer aren’t great, with limited stock in the store I didn’t have much choice so will see how I get on.

Thanks
Mike

Mike_GMT80
Posts: 30
Joined: 23 Jul 2020, 8:37am

Re: Sigma sport cycle computer - what tyre size

Postby Mike_GMT80 » 1 Aug 2020, 6:54am

Quick 5 mile ride this morning with the wheel size set to 28inch showed a c3% variance to Strava for top speed and distance. Is that difference to be expected on a lower end cycle computer?

Cheers
Mike


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PaulaT
Posts: 159
Joined: 20 Dec 2018, 6:41pm
Location: Staffordshire

Re: Sigma sport cycle computer - what tyre size

Postby PaulaT » 1 Aug 2020, 7:33am

My cycle computer has the ability to enter the actual wheel diameter (including the tyre). I don't bother using it and it doesn't worry me in the slightest that speed and distance might be a few percent out. A nice day out on the bike isn't going to be any better or worse because your computer reads a few percent different to the distance you actually cycled.

DaveReading
Posts: 182
Joined: 24 Feb 2019, 5:37pm

Re: Sigma sport cycle computer - what tyre size

Postby DaveReading » 1 Aug 2020, 8:05am

Mike_GMT80 wrote:Quick 5 mile ride this morning with the wheel size set to 28inch showed a c3% variance to Strava for top speed and distance. Is that difference to be expected on a lower end cycle computer?

Plot your ride on, for example, cycle.travel and see what that says.

Mike_GMT80
Posts: 30
Joined: 23 Jul 2020, 8:37am

Re: Sigma sport cycle computer - what tyre size

Postby Mike_GMT80 » 1 Aug 2020, 8:14am

DaveReading wrote:
Mike_GMT80 wrote:Quick 5 mile ride this morning with the wheel size set to 28inch showed a c3% variance to Strava for top speed and distance. Is that difference to be expected on a lower end cycle computer?

Plot your ride on, for example, cycle.travel and see what that says.

I’m using Strava, so assume that should be accurate. The 3% divergence is between cycle computer and strava. It’s not going to impact my enjoyment of riding, just wondering if 3% is what to expect and if 28inch is the correct wheel setting for my 622-17c wheels.


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Jdsk
Posts: 2865
Joined: 5 Mar 2019, 5:42pm

Re: Sigma sport cycle computer - what tyre size

Postby Jdsk » 1 Aug 2020, 8:18am

Mike_GMT80 wrote:Hi, with my cycle to work voucher picked this cycle computer up. First use comparing speed, distance, etc to Strava seems not aligned. The spec for my Triban RC500 bike details wheels as 622 x 17c and also 28inch front and rear. I understand that 622 = 700c, and this is what I have entered as the size into the computer. Would it be more accurate if I entered as 28inch?

If you want the highest accuracy possible without going to extraordinary lengths (!) I recommend finding a convenient place, marking the wheel and measuring the distance that corresponds to a known number of rotations.
https://www.sheldonbrown.com/cyclecomputer-calibration.html
...

Can't comment on using a Strava distance without knowing its provenance.

...

Sheldon Brown article
https://www.sheldonbrown.com/cyclecomputer-accuracy.html
It's not great on the metrology but it does list the errors of cycle computers.

Jonathan

reohn2
Posts: 39934
Joined: 26 Jun 2009, 8:21pm

Re: Sigma sport cycle computer - what tyre size

Postby reohn2 » 1 Aug 2020, 8:34am

Make a mark on the wheel circumferance or use the valve as a reference,mark it on the floor,wheel the bike one revolution of the mark.measure the distance in mm.Enter that into the computer for wheel size.
Job done.

I've been using Sigma computers for years,they're the most reliable ones I come across.

PS,are you sure your tyre is 700 x 17c?
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Mike_GMT80
Posts: 30
Joined: 23 Jul 2020, 8:37am

Re: Sigma sport cycle computer - what tyre size

Postby Mike_GMT80 » 1 Aug 2020, 8:50am

reohn2 wrote:Make a mark on the wheel circumferance or use the valve as a reference,mark it on the floor,wheel the bike one revolution of the mark.measure the distance in mm.Enter that into the computer for wheel size.
Job done.

I've been using Sigma computers for years,they're the most reliable ones I come across.

PS,are you sure your tyre is 700 x 17c?

Good idea, will give that a try, thanks.

My tyres are 622 x 17c. I understand that to be the same as 700c. Is this correct?


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Jdsk
Posts: 2865
Joined: 5 Mar 2019, 5:42pm

Re: Sigma sport cycle computer - what tyre size

Postby Jdsk » 1 Aug 2020, 8:58am

Mike_GMT80 wrote:
reohn2 wrote:Make a mark on the wheel circumferance or use the valve as a reference,mark it on the floor,wheel the bike one revolution of the mark.measure the distance in mm.Enter that into the computer for wheel size.
Job done.

Good idea, will give that a try, thanks.

It's more accurate with more turns, as above.

Mike_GMT80 wrote:My tyres are 622 x 17c. I understand that to be the same as 700c. Is this correct?

"Tire Sizing Systems"
https://www.sheldonbrown.com/tire-sizing.html

Jonathan

tatanab
Posts: 4227
Joined: 8 Feb 2007, 12:37pm

Re: Sigma sport cycle computer - what tyre size

Postby tatanab » 1 Aug 2020, 9:03am

Mike_GMT80 wrote:
reohn2 wrote:My tyres are 622 x 17c. I understand that to be the same as 700c. Is this correct?
the 17 is the internal width of the rim, nothing to do with the tyre which will be 23/25/28/32 etc. Ten years ago 18mm tyres were available but I've not seen them in some time, and certainly not 17. On your computer set up there are usually one of two ways of entering wheel size. I think all of my Sigma computers (I have at least 4) allow precise wheel measurements as others have said above. The other way some manufacturers use is you select the wheel size from a menu, in your case 700C by whatever the tyre size is (23/25/28 etc NOT17). You've not told us which model of computer you have so we cannot look up the manual online to tell you what method it uses.

reohn2
Posts: 39934
Joined: 26 Jun 2009, 8:21pm

Re: Sigma sport cycle computer - what tyre size

Postby reohn2 » 1 Aug 2020, 9:10am

As per tatanab,I think you have the tyre size wrong,the 17 part not the 700,which will alter wheel size and give a false reading.
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Mike_GMT80
Posts: 30
Joined: 23 Jul 2020, 8:37am

Re: Sigma sport cycle computer - what tyre size

Postby Mike_GMT80 » 1 Aug 2020, 10:09am

reohn2 wrote:As per tatanab,I think you have the tyre size wrong,the 17 part not the 700,which will alter wheel size and give a false reading.


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Mike_GMT80
Posts: 30
Joined: 23 Jul 2020, 8:37am

Re: Sigma sport cycle computer - what tyre size

Postby Mike_GMT80 » 1 Aug 2020, 10:11am

tatanab wrote:
Mike_GMT80 wrote:
reohn2 wrote:My tyres are 622 x 17c. I understand that to be the same as 700c. Is this correct?
the 17 is the internal width of the rim, nothing to do with the tyre which will be 23/25/28/32 etc. Ten years ago 18mm tyres were available but I've not seen them in some time, and certainly not 17. On your computer set up there are usually one of two ways of entering wheel size. I think all of my Sigma computers (I have at least 4) allow precise wheel measurements as others have said above. The other way some manufacturers use is you select the wheel size from a menu, in your case 700C by whatever the tyre size is (23/25/28 etc NOT17). You've not told us which model of computer you have so we cannot look up the manual online to tell you what method it uses.

Hi, model is SIGMA SPORT BC 9.16 ATS WIRELESS BIKE COMPUTER.

Bike size taken from website:

Image


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Jdsk
Posts: 2865
Joined: 5 Mar 2019, 5:42pm

Re: Sigma sport cycle computer - what tyre size

Postby Jdsk » 1 Aug 2020, 10:15am

tatanab wrote:You've not told us which model of computer you have so we cannot look up the manual online to tell you what method it uses.

Mike_GMT80 wrote:Hi, model is SIGMA SPORT BC 9.16 ATS WIRELESS BIKE COMPUTER.

Screenshot 2020-08-01 at 10.14.33.png

Jonathan

reohn2
Posts: 39934
Joined: 26 Jun 2009, 8:21pm

Re: Sigma sport cycle computer - what tyre size

Postby reohn2 » 1 Aug 2020, 10:22am

Mike_GMT80 wrote:
reohn2 wrote:As per tatanab,I think you have the tyre size wrong,the 17 part not the 700,which will alter wheel size and give a false reading.


Image


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