Phil Irwin Posted February 9, 2002 Share Posted February 9, 2002 Do I understand that speed sensors near the wheels drive the speedo? If so, front or back? My car will have to go through an SVA and accuracy of the speedo is one of the tests. This is not the accuracy of the unit itself, but whether it shows a true speed. This can obviously be effected by the wheel/tyre size. At the moment the car has the standard 16" wheels which I want to change to 17s. Whatever, for the SVA it will need "E" marked tyres. So I am considering buying a couple of 16" cheap-as-chips tyres to put either front or back to make sure the speedo is accurate. Alloys. Does anyone know of suppliers who give a good discount? Link to comment Share on other sites More sharing options...
Phil Wall Posted February 9, 2002 Share Posted February 9, 2002 Where are you in UK, I have a spare set of 16's with 5mm rubber all round you could put on for SVA. If I remember correctly speedo signal is picked up off the gearbox. Sensors on the wheels are just for ABS and Traction. Link to comment Share on other sites More sharing options...
Matt Harwood Posted February 9, 2002 Share Posted February 9, 2002 Don't take this for granted but my car was recently SVA'd with 18's on it. With input from others on here, I have realised that my speedo is fairly inacurate, (about 6 mph over at 90 mph, actual speed 84) but passed the SVA test with no problems. Perhaps my inspector was having a lazy day Link to comment Share on other sites More sharing options...
mark brown Posted February 9, 2002 Share Posted February 9, 2002 Speedo signal is definitely driven from the gearbox. Mark Brown Link to comment Share on other sites More sharing options...
THOR Racing Posted February 12, 2002 Share Posted February 12, 2002 For your information again. The TRL DSC (Digital Speed Converter) has +/-10% calibration in 1.25% steps (16steps in total) on the main outputs. The unit has 1:1, 5:8 and an SLD output and all are affected by the calibration adjustment. This is to calibrate speed after fitting different rolling radius wheel/tyre package or changing the ratio of your rear diff etc. I've done this for a couple of guys in NZ with exchanged diffs, they had -15% and -8% respectively so even specials are possible. http://www.trlperformance.com/dsc.html Regards Pete Link to comment Share on other sites More sharing options...
Simon Posted February 12, 2002 Share Posted February 12, 2002 Quote: from Phil Irwin on 8:32 am on Feb. 9, 2002[br]Do I understand that speed sensors near the wheels drive the speedo? If so, front or back? My car will have to go through an SVA and accuracy of the speedo is one of the tests. This is not the accuracy of the unit itself, but whether it shows a true speed. This can obviously be effected by the wheel/tyre size. At the moment the car has the standard 16" wheels which I want to change to 17s. Whatever, for the SVA it will need "E" marked tyres. So I am considering buying a couple of 16" cheap-as-chips tyres to put either front or back to make sure the speedo is accurate. Alloys. Does anyone know of suppliers who give a good discount? Speedo is driven from gearbox. Speedo is allowed a 10% tolerance factor. For example, with 18" 265/35 on rear, my speedo is +5% (could explain why I didn't get pulled over the other day when I was doing an indicated 100 - 110.) Link to comment Share on other sites More sharing options...
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