Cycling UK Forum

HELP!
I have a Brompton which has 16" (349) wheel size. I also have a new Sigma Computer which is fitted and is working very well.
However it has not been correctly set up for the Brompton wheel size!.
Please can someone tell me the correct input figure for this size wheel for the SIGMA computer?
I may be slightly mathematically challenged here as I can setup computers for bigger wheel bikes OK. Its just this size. By the way it is a FOUR figure number required.
John.
www.pbase.com/john28july

depends upon what size tyres you have on it, what air pressure yo have in them and how much weight it carries as you ride.

Best way to do it is just to measure it in mm. Get valvue to bottom of the wheel, precisely mark on the floor where it is, ride forward (in straight line) until the valve is at the bottom again, mark it and meaurse between the two marks.

The problem with smaller wheels is that a) some computers won't allow you to go down that far and b) any error in the circumference reading is somewhat more critical than on a larger wheel because the same amount of mm out will be a higher proportion of the total on a smaller wheel!

Thanks for the fast response.
Not very helpful! Sorry.
I know how to do all that you mentioned.
However the circumferece is 133 cm which when multiplied by the computer setting notes comes out at 82!
I am not mathematicaly inclinded. My 16 year old daughter is. She cannot make head nor tail of it either.
The Sigma allows for small wheels but on its chart supplied it only shows 16 x 1,75 which I have input as its fairly close. I have used a computer previously on small wheelers but am at a loss with this Sigma!
John.

The sigma that I have takes two readings. Either the circumference of your tyre in mm (which would be 1330 for you) if you have the readout set to km, or the circumference of the tyre in mm divided by 1.6 (1330/1.6 = 0831 for you) if you have the readout set to miles.

So, if the little "M" is visible on your computer then use 0820*, else if the "KM" is visible use 1330.

*As 1.6km doesn't actually equal 1mile, but is only an approaximation, I'd suspect that having it set to KM is the most precise way to use the computer, thus the varience in figures of 0831 and 0820.


This, of course, all assumes that your computer works the same as mine

Hello,
This looks good as I just set the computer to.........0820!!
Thanks for the help.
John.