DW Posted December 31, 2003 Share Posted December 31, 2003 When I took the car to a rolling road in the summer, they told me the speedo was out - when I'm doing 60 the speedo says 71 - it's about 20% out across the range. Presume that I have the wrong something - what's the best procedure for working out what I've got, and then what I should have? Also, just posted some pictures etc at http://groups.msn.com/WilkesCaterhamPages 😬 David 1700XF - Life is Loud Link to comment Share on other sites More sharing options...
Myles Posted December 31, 2003 Share Posted December 31, 2003 Is is electronic or mechanical - guess the latter if it's an XF. If it's the former, there are usually some dip-switches on the back you can play with - there are only a limited number of options, and the best I could get with my 13" CR500s was from +10% to +5-6%. If it's mechanical, ISTR there is a firm who can recalibrate them - do a quick search for 'calibrate' and 'speedo' in techtalk, and you should come up with the name (it's been mentioned quite often). Alternatively, fit a bike speedo and forget about the standard one... Keep BC free and open for ALL. Membership No. 43xx Alcester Racing 7's Equipe - 🙆🏻™ Link to comment Share on other sites More sharing options...
Normans_Ghost Posted December 31, 2003 Share Posted December 31, 2003 David, Funny you mention this. I've just fitted a SPA speedo. The 2" x 1" thingy. Calibrate by measuring the tyre circumferance of the wheel with the mag sensor fitted. When the SPA reads 70 the mechinical speedo reads about 62. Havent had time to check fully yet but one of them is way out. norman verona 1989 BDR Link to comment Share on other sites More sharing options...
ChrisC Posted December 31, 2003 Share Posted December 31, 2003 try here and get your speedo calibrated. They did a mini speedo for me a few years back, and it only cost £25 , don't know what it would cost today. Chris.... H15 SVN Get it ! Link to comment Share on other sites More sharing options...
jerrypike Posted December 31, 2003 Share Posted December 31, 2003 where abouts in the arc is it misreading? 😬 i thought they all did that jerry Link to comment Share on other sites More sharing options...
Myles Posted December 31, 2003 Share Posted December 31, 2003 Calibrate by measuring the tyre circumferance of the wheel with the mag sensor fitted. If the speedo is overreading, that suggests your measured circumference was smaller than in real life... The standard (and completely reliable) calibration method for bike computers (which also need the circumference measured) is to get a tape measure, chalk (optional), a helper (optional) and a short, flat bit of road. Roll the car forward until the valve of the measured tire is at the 6 o'clock position, mark this with the chalk (or carefully lay the tape down starting at that point). Now push the car forwards until the valve is back in the 6 o'clock position and chalk/read off the distance. This will give you an accurate rolling (rather than static) circumference - and even allowing for variables such as the driver weight and centrifugal expansion at speed, the bike-speedo seems to tie in very closely with GPS, so should work equally well for the SPA. I did try multiple revolutions to increase the measured accuracy - but found that it gave the same result (to the nearst mm or so) and have used a single revolution ever since. FYI, on my 1.6k 500kg Academy roadsport, I get a rolling circumference of 1665 mm with half-worn 13" Bridgestone RE720s and 1615mm with 13"CR500s. YMMV... Regds, Myles Keep BC free and open for ALL. Membership No. 43xx Alcester Racing 7's Equipe - 🙆🏻™ Link to comment Share on other sites More sharing options...
DW Posted December 31, 2003 Author Share Posted December 31, 2003 Thanks guys. Myles, I'll try and make more noise when going through Alcester. Clearly the false speedo meant I was driving too slowly - wondered why the flash bulbs never pop on the Studley road. Given it's an XFlow you're right to assume it's mechanical (the oil pressure guage is deficient too). Thanks for the link Chris. Link to comment Share on other sites More sharing options...
budgie Posted December 31, 2003 Share Posted December 31, 2003 Nverona -get your tyre circumference and diff ratio and set it up as per the manual (the SPA one).Spot on to 1/10th mph. Can always check it against rev counter as well. Link to comment Share on other sites More sharing options...
CHRIS CLARK Posted January 1, 2004 Share Posted January 1, 2004 I bought a cheap GPS to check this out under 'proper' conditions ie. on the real road. I had changed from 15" wheels to 13"'s, five speed g/box to a six, diff from a 3.92 to a 3.62 etc etc. It was .8 mph out at 70 indicated (actual was 69.2) & it was .6 mile out at 100 mph indicated (actual 99.4). This last figure was done on a private test facility obviously . Much better/more accurate figures than when the car was supplied with the other bits from new. Borrow a GPS and give it a go! Link to comment Share on other sites More sharing options...
Normans_Ghost Posted January 2, 2004 Share Posted January 2, 2004 When it stops raining/snowing I'm putting sons Road Angel in and see which is out. If SPA unit I'll recalibrate. norman verona 1989 BDR Link to comment Share on other sites More sharing options...
J A T Richardson Posted January 2, 2004 Share Posted January 2, 2004 Ummm, there are 2 schools of thought here: 1) "They all do that, sir" Mine certainly does, and I now rely on a bike computer (BTW: has anyone found a good way of illuminating it at night?) 2) Depending on the final drive you have, you can get speedo drive gears with 20, 21 or 22 teeth. This won't fix a 20% problem ,but could reduce it to say 10%. Mine is the longest fdrive (3.65:1 approx.) and I use the 22 tooth one. Changing it is a doddle, just whip the engine and box out, rebuild both, change all the oilseals in a vain attempt tp make the thing oil-tite, then lever the speedo drive cover plate off the gbox and stick in a new one. Then put it all together again. A bike speedo is easier... If you want to know what ratio diff you have, jack one wheel up and count wheel and propshaft revs and divide the resulting ratio by 2 Link to comment Share on other sites More sharing options...
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