Wheel size for Sigma Sport?

My front wheel is a 37 x 406 and I can find no wheel that size in the Sigma Sport BC 600 chart or in
the Cateye Astrale 8 chart. It seems to run long by about 1/10th mile on speedometer when checked
with GPS or the mile markers on the trail.Right now it's at ws 990. I have tried several setting and
can't seem to get it right. A lot of you have that size tire and some may use the Sigma computer as
well. What WS setting do you use? By the end of the year if I get to ride as much as I hope to, it
could be off by 500 miles. Thats like a trip from Prescott to Bakersfield and not acceptable.

Jerry

Do the roll out test. Mark the tire, go in a straight line for a complete
mark to mark tire revolution, multiply by 25.4, and enter it as the constant
into the computer. That does it for most.
"gcdoss" <gcdoss@cableone.net> wrote in message
news:1025k2dhrvdimf6@corp.supernews.com...
> My front wheel is a 37 x 406 and I can find no wheel that size in the Sigma Sport BC 600 chart or
> in the Cateye Astrale 8 chart. It seems to run long by about 1/10th mile on speedometer when
> checked with GPS or the mile markers on the trail.Right now it's at ws 990. I have tried several
> setting and can't seem to get it right. A lot of you have that size tire and some may use the
> Sigma computer as well. What WS setting do you use? By the end of the year if I get to ride as
> much as I hope to, it could be off by 500 miles. Thats like a trip from Prescott to Bakersfield
> and not acceptable.
>
> Jerry

"gcdoss" <gcdoss@cableone.net> wrote
> [cyclometer] run[s] long by about 1/10th mile on speedometer when checked with GPS or the mile
> markers on the trail.Right now it's at ws 990.

If the didstance cross checks are accurate, simple calulation will give the accurate setting:

990 / 1.1 = 900

Only slightly more advanced is proof that for a trip with half uphill and half downhill, the overall
average speed can be no more than twice the average speed on uphill sections... %^)

Jon Meinecke

In article <d5BUb.11726$jH6.10872@newsread1.news.atl.earthlink.net>,
williams722@earthlink.net says...
> Do the roll out test. Mark the tire, go in a straight line for a complete mark to mark tire
> revolution, multiply by 25.4, and enter it as the constant into the computer. That does it
> for most.

Or you could just measure in Millimeters and skip the math.

> "gcdoss" <gcdoss@cableone.net> wrote in message news:1025k2dhrvdimf6@corp.supernews.com...
> > My front wheel is a 37 x 406 and I can find no wheel that size in the Sigma Sport BC 600 chart
> > or in the Cateye Astrale 8 chart. It seems to run long by about 1/10th mile on speedometer when
> > checked with GPS or the mile markers on the trail.Right now it's at ws 990. I have tried several
> > setting and can't seem to get it right. A lot of you have that size tire and some may use the
> > Sigma computer as well. What WS setting do you use? By the end of the year if I get to ride as
> > much as I hope to, it could be off by 500 miles. Thats like a trip from Prescott to Bakersfield
> > and not acceptable.

I am a little confused about the wheel size input for a Sigma Sport. The nominal wheel circumference
for a 37-406 would be ~1507mm. Most bike computers calibrate to a wheel circumference in
millimeters. If this is true with the Sigma Sport, you should be using a number closer to 1507mm

As suggested, the roll-out measurement is more accurate than any chart in an instruction booklet. I
would suggest several revolutions and take an average for a better approximation of wheel
circumference.

FWIW, Most GPS I have found to be off(short) by 1%-2% in any non linear route..

I have records on several 406 tires. Perhaps if you let us know the tire make and model, someone on
the list can provide the wheel circumference that they use for your tire. Who knows, you might even
get a consensus.

--

Cletus D. Lee Bacchetta Giro Lightning Voyager http://www.clee.org
- Bellaire, TX USA -

Cletus Lee wrote:
> In article <d5BUb.11726$jH6.10872@newsread1.news.atl.earthlink.net>,
> williams722@earthlink.net says...
>
>> Do the roll out test. Mark the tire, go in a straight line for a complete mark to mark tire
>> revolution, multiply by 25.4, and enter it as the constant into the computer. That does it
>> for most.
>
>
> Or you could just measure in Millimeters and skip the math.
>
>
>> "gcdoss" <gcdoss@cableone.net> wrote in message news:1025k2dhrvdimf6@corp.supernews.com...
>>
>>> My front wheel is a 37 x 406 and I can find no wheel that size in the Sigma Sport BC 600 chart
>>> or in the Cateye Astrale 8 chart. It seems to run long by about 1/10th mile on speedometer when
>>> checked with GPS or the mile markers on the trail.Right now it's at ws 990. I have tried several
>>> setting and can't seem to get it right. A lot of you have that size tire and some may use the
>>> Sigma computer as well. What WS setting do you use? By the end of the year if I get to ride as
>>> much as I hope to, it could be off by 500 miles. Thats like a trip from Prescott to Bakersfield
>>> and not acceptable.
>
>
> I am a little confused about the wheel size input for a Sigma Sport. The nominal wheel
> circumference for a 37-406 would be ~1507mm. Most bike computers calibrate to a wheel
> circumference in millimeters. If this is true with the Sigma Sport, you should be using a number
> closer to 1507mm
>
This series of Sigma computer is unusual in that if you select miles rather than kilometers for
distance, the wheel circumference must be adjusted by the miles/kilometer ratio, or about .62137.
Most brands do the conversion math and you still enter the circumference in mm or cm, but not Sigma.
If the 1507 number is good, 936 would be the right number for a Sigma, at least for the BC600 (not
sure about the newer models).

> As suggested, the roll-out measurement is more accurate than any chart in an instruction booklet.
> I would suggest several revolutions and take an average for a better approximation of wheel
> circumference.
>
> FWIW, Most GPS I have found to be off(short) by 1%-2% in any non linear route..
>
> I have records on several 406 tires. Perhaps if you let us know the tire make and model, someone
> on the list can provide the wheel circumference that they use for your tire. Who knows, you might
> even get a consensus.
>
Roll-out is better than someone else's number. Your tires should be at you usual pressure, you
should have your full weight on the bike, and measure for more than one revolution for best
accuracy. While a GPS might give slight corner-cutting error on very twisty routes, they should be
very accurate on fairly straight routes. Most charts I've seen with cyclometers list too-high
circumferences, making distance and speed read too high.

Dave Lehnen

Get an accurate tape that measures mm. Sit on your bike bracing against a wall or other object with
the tires inflated to what you normally inflate them to. Have an assistant measure the front wheel
from the center of the QR to the floor in mm double it, multiply it by 3.14 then divide it by 1.61.
Use this as the cal number. This is the Sigma method as spelled out in the instructions except for
the measuring method. Mine is more accurate. Jude

"Dave Lehnen" <dclehnen@worldnet.att.net> wrote in message news:mNOUb.61921$6O4.1838451@bgtnsc04-
news.ops.worldnet.att.net...
> Cletus Lee wrote:
> > In article <d5BUb.11726$jH6.10872@newsread1.news.atl.earthlink.net>, williams722@earthlink.net
> > says...
> >
> >> Do the roll out test. Mark the tire, go in a straight line for a complete mark to mark tire
> >> revolution, multiply by 25.4, and enter it as the constant into the computer. That does it for
> >> most.
> >
> >
> > Or you could just measure in Millimeters and skip the math.
> >
> >
> >> "gcdoss" <gcdoss@cableone.net> wrote in message news:1025k2dhrvdimf6@corp.supernews.com...
> >>
> >>> My front wheel is a 37 x 406 and I can find no wheel that size in the Sigma Sport BC 600 chart
> >>> or in the Cateye Astrale 8 chart. It seems to run long by about 1/10th mile on speedometer
> >>> when checked with GPS or the mile markers on the trail.Right now it's at ws 990. I have tried
> >>> several setting and can't seem to get it right. A lot of you have that size tire and some may
> >>> use the Sigma computer as well. What WS setting do you use? By the end of the year if I get to
> >>> ride as much as I hope to, it could be off by 500 miles. Thats like a trip from Prescott to
> >>> Bakersfield and not acceptable.
> >
> >
> > I am a little confused about the wheel size input for a Sigma Sport. The nominal wheel
> > circumference for a 37-406 would be ~1507mm. Most bike computers calibrate to a wheel
> > circumference in millimeters. If this is true with the Sigma Sport, you should be using a number
> > closer to 1507mm
> >
> This series of Sigma computer is unusual in that if you select miles rather than kilometers for
> distance, the wheel circumference must be adjusted by the miles/kilometer ratio, or about .62137.
> Most brands do the conversion math and you still enter the circumference in mm or cm, but not
> Sigma. If the 1507 number is good, 936 would be the right number for a Sigma, at least for the
> BC600 (not sure about the newer models).
>
> > As suggested, the roll-out measurement is more accurate than any chart in an instruction
> > booklet. I would suggest several revolutions and take an average for a better approximation of
> > wheel circumference.
> >
> > FWIW, Most GPS I have found to be off(short) by 1%-2% in any non linear route..
> >
> > I have records on several 406 tires. Perhaps if you let us know the tire make and model, someone
> > on the list can provide the wheel circumference that they use for your tire. Who knows, you
> > might even get a consensus.
> >
> Roll-out is better than someone else's number. Your tires should be at you usual pressure, you
> should have your full weight on the bike, and measure for more than one revolution for best
> accuracy. While a GPS might give slight corner-cutting error on very twisty routes, they should be
> very accurate on fairly straight routes. Most charts I've seen with cyclometers list too-high
> circumferences, making distance and speed read too high.
>
> Dave Lehnen

I did the roll out and came up several times with 58 3/4" and using the
25.4 multiplier came up with 1492.25 kmh. Don't know how the guy I bought Tour Easy from came up
with the 990 kmh size. Little wonder it was off so much. Will admit that instruction sheet is
confusing as it trys to convert to mph. example : 20 x 1.75 =1590kmh or 988 in mph column. I'm
hoping that by putting the size in mm and then switching the cyclocomputer to mph it will
convert automatically. Thanks to all that gave such good advice. The tires are standard
equipment Comets for the Tour Easy. Would find model # but barn has no lights and it's cold out
there tonight. Jerry

> I am a little confused about the wheel size input for a Sigma Sport. The nominal wheel
> circumference for a 37-406 would be ~1507mm. Most bike computers calibrate to a wheel
> circumference in millimeters. If this is true with the Sigma Sport, you should be using a number
> closer to 1507mm
>
> As suggested, the roll-out measurement is more accurate than any chart in an instruction booklet.
> I would suggest several revolutions and take an average for a better approximation of wheel
> circumference.
>
> FWIW, Most GPS I have found to be off(short) by 1%-2% in any non linear route..
>
> I have records on several 406 tires. Perhaps if you let us know the tire make and model, someone
> on the list can provide the wheel circumference that they use for your tire. Who knows, you might
> even get a consensus.

Dave Lehnen <dclehnen@worldnet.att.net> wrote in message news:<mNOUb.61921$6O4.1838451@bgtnsc04-news.ops.worldnet.att.net>...
> Cletus Lee wrote:
> > In article <d5BUb.11726$jH6.10872@newsread1.news.atl.earthlink.net>, williams722@earthlink.net
> > says...
> >
> >> Do the roll out test. Mark the tire, go in a straight line for a complete mark to mark tire
> >> revolution, multiply by 25.4, and enter it as the constant into the computer. That does it for
> >> most.
> >
> >
> > Or you could just measure in Millimeters and skip the math.
> >
> >
> >> "gcdoss" <gcdoss@cableone.net> wrote in message news:1025k2dhrvdimf6@corp.supernews.com...
> >>
> >>> My front wheel is a 37 x 406 and I can find no wheel that size in the Sigma Sport BC 600 chart
> >>> or in the Cateye Astrale 8 chart. It seems to run long by about 1/10th mile on speedometer
> >>> when checked with GPS or the mile markers on the trail.Right now it's at ws 990. I have tried
> >>> several setting and can't seem to get it right. A lot of you have that size tire and some may
> >>> use the Sigma computer as well. What WS setting do you use? By the end of the year if I get to
> >>> ride as much as I hope to, it could be off by 500 miles. Thats like a trip from Prescott to
> >>> Bakersfield and not acceptable.
> >
> >
> > I am a little confused about the wheel size input for a Sigma Sport. The nominal wheel
> > circumference for a 37-406 would be ~1507mm. Most bike computers calibrate to a wheel
> > circumference in millimeters. If this is true with the Sigma Sport, you should be using a number
> > closer to 1507mm
> >
> This series of Sigma computer is unusual in that if you select miles rather than kilometers for
> distance, the wheel circumference must be adjusted by the miles/kilometer ratio, or about .62137.
> Most brands do the conversion math and you still enter the circumference in mm or cm, but not
> Sigma. If the 1507 number is good, 936 would be the right number for a Sigma, at least for the
> BC600 (not sure about the newer models).
>
> > As suggested, the roll-out measurement is more accurate than any chart in an instruction
> > booklet. I would suggest several revolutions and take an average for a better approximation of
> > wheel circumference.
> >
> > FWIW, Most GPS I have found to be off(short) by 1%-2% in any non linear route..
> >
> > I have records on several 406 tires. Perhaps if you let us know the tire make and model, someone
> > on the list can provide the wheel circumference that they use for your tire. Who knows, you
> > might even get a consensus.
> >
> Roll-out is better than someone else's number. Your tires should be at you usual pressure, you
> should have your full weight on the bike, and measure for more than one revolution for best
> accuracy. While a GPS might give slight corner-cutting error on very twisty routes, they should be
> very accurate on fairly straight routes. Most charts I've seen with cyclometers list too-high
> circumferences, making distance and speed read too high.
>
> Dave Lehnen

Thanks, Having the help of 2 friends , we did the roll out thing again and came up with same number,
1492.25 mm. Using Dave Lehnen's formula I end up with 927.24 mph. This sure sounds good and I will
test it out on my next ride. We have a measured straight stretch that's 2 miles long so it should be
a good test. I'm glad someone knew the Sigma Sport didn't do the conversion internaly as I thought I
had it set.

Jerry

I mark start and end of ten (10) revolutions of rollout and measure in cm for entry in mm - simple, easy, and no calculations needed

mike