tyre

4F

Active member of Helmets Are Sh*t Lobby
Location
Suffolk.
Iainj837 said:
I am swapping my front tyre size 700 x 38c to 700 x 28 would I need to change the setting on the computer
yes
 

TheDoctor

Europe Endless
Moderator
Location
Stevenage
Your speed and distance readings will be 2.9% low if you leave the settings as they are.
This wouldn't bother me that much, but may bother you.
 

gavintc

Guru
Location
Southsea
Iainj837 said:
I can't find the instructions for my computer, so I don't know what to set the computer to can any onehelp the size i am putting onis 700X28c
Google is amazing tool. Look for your computer instructions and you may well find a pdf file that will show the details. It certainly worked for me when I had the same problem.
 

4F

Active member of Helmets Are Sh*t Lobby
Location
Suffolk.
gavintc said:
Google is amazing tool. Look for your computer instructions and you may well find a pdf file that will show the details. It certainly worked for me when I had the same problem.
Agreed, that worked for me on an obscure brand computer which came on a bike I purchased second hand
 
HLaB said:
Its probably the same. Can you recall the dimension for 700x38C wheels, if its is 2180mm; they are the same.
Or as others have suggested google the strada :sad:
Yes I have check the dimensions and indeed the setting is 2180mm.
Thank you allforthe replies
 

battered

Guru
If you ever can't get the figures then you can do it yourself, but you need 2 special tools in the form of a tape measure and a piece of chalk. Put your bike on the road, mark the road and the tyre. Roll the bike forward by one turn. Mark the road again. Measure the distance between the 2 marks with your specialist NPL calibrated tape measure, available in Wilko for 99p, or Poundland if you want a flash one.
 

andrew_s

Guru
Location
Gloucester
for 700x38 it would be pi x (622 + 38 + 38) = 2193mm
for 700x28 it would be pi x (622 + 28 + 28) = 2130mm

That assumes that your tyres are the size they purport to be, and that they are pumped up hard enough not to squash when you are riding the bike.

They would squash a bit, so those figures are upper limits.
Some computers calibrate in centimetres (eg Cateye Mity)

If you don't change anything, a reading of 20mph will actually be 19.4mph
 
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