Glue Posted March 14, 2006 Share Posted March 14, 2006 Afternoon all, Could some body please help a newbie to the forum. I drive an 1992 ex MOD 110 FFR on 7.50x16 tyres. The speedo has never been particually accurate, but following the replacement of the gear box it now reads about 110% of actual speed. ie if I'm doing 60, (from my GPS) then the speedo shows about 66 or 67 mph. Can anyone suggest a solution or is it time to have the speedo recalibrated. Thanks in advance Glue Quote Link to comment Share on other sites More sharing options...
John_T Posted March 14, 2006 Share Posted March 14, 2006 Hello and welcome. Are you sure the transfer box was not changed? Changing the gearbox will not alter anything as the speedo drive is in the transfer box. You do not need to re-calibrate the speedo, just get the right drive gear in the transfer box (much simpler). Having said all this the speedo my TD5 90 on 265/75 tyres still over reads compared to the GPS. Quote Link to comment Share on other sites More sharing options...
mmgemini Posted March 14, 2006 Share Posted March 14, 2006 Afternoon all,Could some body please help a newbie to the forum. I drive an 1992 ex MOD 110 FFR on 7.50x16 tyres. The speedo has never been particually accurate, but following the replacement of the gear box it now reads about 110% of actual speed. ie if I'm doing 60, (from my GPS) then the speedo shows about 66 or 67 mph. Can anyone suggest a solution or is it time to have the speedo recalibrated. Thanks in advance Glue That's about right. Mine reads exactly the same against the GPS. I eat rat poison mike I can cause trouble in an empty house !! Quote Link to comment Share on other sites More sharing options...
headhunter Posted March 14, 2006 Share Posted March 14, 2006 My 110 with 265/75-16 tyres (which are the same circumfrence as standard ) reads 5mph more than true GPS speed, across the speed band, certainly between 30 and 90 mph. At least I am aware of it and will just live with it unless there is a simple solution such as changing the speedo drive gear. I have a merc with electronic speedo etc., that reads 3mph above true at 70-80 but 2mph at 30. I suspect most speedos are inaccurate to some degree John Quote Link to comment Share on other sites More sharing options...
simonb Posted March 14, 2006 Share Posted March 14, 2006 The Law allows them to read faster than u are going (by up2 10%?), but they are not allowed to read slower than u are going. Interestingly when i checked my series 3 against the GPS, it was spot on at 60mph.. Hence the 10%+2mph for speed cameras to take into account inaccurcies, if your caught exceeding a 30 limit you must have been doing more than 35mph, and your speedo if reading fast, maybe showing closer to 40mph...... if you do an indicated 30, chances are u may only doing about 25-27mph.. Quote Link to comment Share on other sites More sharing options...
Ex Member Posted March 14, 2006 Share Posted March 14, 2006 Every one I have seen reads 10% high on 32" tyres. Quote Link to comment Share on other sites More sharing options...
western Posted March 14, 2006 Share Posted March 14, 2006 (edited) 'Speedo Drive Gears' Edited March 14, 2006 by western Quote Link to comment Share on other sites More sharing options...
JST Posted March 15, 2006 Share Posted March 15, 2006 i fitted the 7.50R16 speedo pinion (old std is 205 pinion) GPS gives about +10% on speed with 235/85s (same dia as 7.50s). with 255/85s speedo is bang on. so if your +10% with 7.50 fit the 205 pinion (different no of teeth) and it will be bang on. Dont most cars read high anyway? Quote Link to comment Share on other sites More sharing options...
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