From the PowerTap manual= 2152mm. Would be better to measure it with a roll out. - TFH2oknine said:Found a Raleigh 555SL at a garage sale purchased for $20. The tire size is 27X1 1/4. trying to set up bike computer to match the tire size but doesn't have the tire size in its memory. What size is comparable to match the 27X1 1/4 size I have.