EcoModder Forum Compensating for New tyres? Calculating the % out my milometer will be..

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 01-18-2012, 07:31 AM #1 (permalink) Master EcoModder   Join Date: Jun 2010 Location: scotland Posts: 1,423 The Mistress - '88 Bmw 320i Touring SE Team m8 Last 3: 27.17 mpg (US) Germany Beadle - '91 Mercedes 300td (estate, N/A) 90 day: 24.63 mpg (US) The Bloodylingo - '05 Citroen Berlingo Multispace Desire 90 day: 39.77 mpg (US) Shanner Scaab - '03 Saab 9-5 estate Vector 90 day: 26.19 mpg (US) Thanks: 88 Thanked 86 Times in 72 Posts Compensating for New tyres? Calculating the % out my milometer will be.. Hi, I've just replaced 2x 205/60/15's with 1.6mm of tread for 2 new tyres of the same size with appox 9mm of tread. My BMW takes its milometer feed from the diff, so the increased circumference of the new tyres will change that.. whats the best way to factor in the % difference, or does anyone know a way to calibrate an electronic speedo/milometer? thanks __________________ My Blog on cars- Fu'Gutty Cars http://fuguttycars.wordpress.com/ US MPG for my Saab 9-5 2.0t Estate ---------------------------------------------------
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 01-18-2012, 02:00 PM #2 (permalink) ...beats walking...   Join Date: Jul 2009 Location: . Posts: 6,190 Thanks: 179 Thanked 1,525 Times in 1,126 Posts ...does Scotland have "mile-post" markers? If so, simply drive at steady 60 mph (using cruise-control helps) and measure the time (stop watch) between 1 and 2 mile posts. MPH(x) = 3600 / sec for "1-mile" marker MPH(X) = 7200 / SEC for "2-mile" marker ...the "correction" factor (%) will be: % = MPH(x) / 60 mph or % = MPH(X) / 60 mph Last edited by gone-ot; 01-18-2012 at 06:19 PM..
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Quote:
 Originally Posted by 320touring I've just replaced 2x 205/60/15's with 1.6mm of tread for 2 new tyres of the same size with appox 9mm of tread. My BMW takes its milometer feed from the diff, so the increased circumference of the new tyres will change that..
You could use a GPS to calibrate the meter.

BMW likely calibrated it with fresh tyres though.
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Join Date: Jun 2010
Location: scotland
Posts: 1,423

The Mistress - '88 Bmw 320i Touring SE
Team m8
Last 3: 27.17 mpg (US)

Germany Beadle - '91 Mercedes 300td (estate, N/A)
90 day: 24.63 mpg (US)

The Bloodylingo - '05 Citroen Berlingo Multispace Desire
90 day: 39.77 mpg (US)

Shanner Scaab - '03 Saab 9-5 estate Vector
90 day: 26.19 mpg (US)
Thanks: 88
Thanked 86 Times in 72 Posts
Quote:
 Originally Posted by Old Tele man ...does Scotland have "mile-post" markers? If so, simply drive at steady 60 mph (using cruise-control helps) and measure the time (stop watch) between 1 and 2 mile posts. MPH(x) = 3600 / sec for "1-mile" marker MPH(X) = 7200 / SEC for "2-mile" marker ...the "correction" factor (%) will be: % = MPH(x) / 60 mph or % = MPH(X) / 60 mph
cruise control?unfortunately not...

cheers for the formula though

Quote:
 Originally Posted by euromodder You could use a GPS to calibrate the meter. BMW likely calibrated it with fresh tyres though.
Fair shout- I may try to get my dad's one..
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 01-21-2012, 03:28 AM #5 (permalink) Wanting more for less     Join Date: Jan 2011 Location: New South Wales, Australia Posts: 312 Metric - '94 Honda Magna 250 Motorcycle 90 day: 69.83 mpg (US) RedCelica - '94 Toyota Celica ZR 90 day: 35.97 mpg (US) i30 - '12 Hyundai i30 Elite 90 day: 39.84 mpg (US) i30-22 - '12 Hyundai i30 Elite 90 day: 38.91 mpg (US) Thanks: 23 Thanked 73 Times in 45 Posts The previous owner of my Mazda Astina (323F in Britain) fitted smaller profile tyres (195/50 15 verses 195/55 15). I checked the speedo against my GPS on the motorway and it reads about 4.5% fast, as expected. I checked the odometer against a measured 5 kilometer "speedometer test" sign posted on the motorway and found it to be accurate.....Huh? I checked the odometer against the GPS driving to work. The GPS said my commute is 51.9km, my odometer said 52.0km, close enough to perfect. Again I say.......Huh? My point is, don't assume the speedo accuracy reflects the odometer accuracy, as I always did in the past. If you really have to adjust your speedo, this might help. Speedo Corrector MkII Kit "Kit Back Catalogue" - Jaycar Electronics I haven't tried this kit myself, but it sounds OK.