Speedo vs. GPS speed

invalid@example.com (Z3 in Melbourne), Z3 in Melbourne
Fri, 27 Feb 2026 17:59:05 +0000

Hi everyone,
New to this forum. I’ve measured speed by GPS and it seems to be about 5% slower than what the speed reads. I have a 98 2.8 with 3.15 rear diff with 235/45-17 tires. Any idea why I have such a big difference from actual speed?

Thanks!