Buy all your VW California Accessories at the Club Shop Visit Shop

Speedometer calibration for larger tires

  • Thread starter chris ratay traveler
  • Start date
chris ratay traveler

chris ratay traveler

Overlanding South America w T6.1 Ocean 204, 4M+
VIP Member
Messages
161
Location
Budapest
Vehicle
T6.1 Ocean 204 4 motion
Looking to convert my 18" alloys, 255/45r18 (27x10) to 17"Steel, All Terrain 225/65r17 (28.5x8.9).

I'm wondering if the speedo will be more accurate, or will I need to adjust the speedo. What are people using for speedo adjustment?

I found this one from GTV-Vans: https://www.gtv-van.com/en/speedometer-calibration-kit.html?id=251321552&quantity=1

View attachment 102777

View attachment 102779
I would personally just measure the speed diff using a GPS speedo on the phone and keep the difference in mind when driving. Currently with 235/55/17 - I know that the van speedo reads ~3mph less than the GPS speed ... and there is an ~10% error margin in the speed cameras here in the UK.

The speedo will never be accurate as the wear on the tyre will also cause to give a different value.

Unless the change is massive, I would not bother with the device.

Measure the difference between reported and true speed with a GPS app on the phone and then decide if it is worth 545 Euros.
 
I would personally just measure the speed diff using a GPS speedo on the phone and keep the difference in mind when driving. Currently with 235/55/17 - I know that the van speedo reads ~3mph less than the GPS speed ... and there is an ~10% error margin in the speed cameras here in the UK.
I'd probably do the same... however I see OP is planning to fit a wheel/tyre combo that will cause speedo to under-read by nearly 6% (versus the original calib).

The UK norm for speed prosecutions is speed limit + 10% + 2 mph (ie 68mph in a 60 limit) so a substantially under-reading speedo is not ideal unless you keep it constantly in mind. Or as you say, at least check calib with new tyres against a GPS app so you know exactly how you're rolling.
 
I see VW dealers now offer 275/35/20 as an altenative fitment on Transporters and they claim no speedo adjustment is necesary. Current our van is fitted with 275/40/20, I chose 40 profile for a tad more comfort.
After testing on a level dual carriage way against GPS on Google maps, I figure the speedo reads about 8% (err on side of caution when compared to the standard 16" wheels) under.

To stay legal, I figure a speedo reading of 27, 37, 47, 56, 65 approximates to 30, 40, 50, 60, 70 mph respectively, bit less at the lower end, bit more at the higher end.
 
Back
Top