Speedometer question

[mrmike]

    I bought a '23 People S 150i ABS this year. I've got it all modified and accessorized the way I want it and am very happy with it. The speedometer is consistently 2 mph faster than actual GPS speed. Over the winter I'm going to get new City Grip 2 tires for it. The question is: If I upgrade the front tire from a 100/80-16 to a 120/80-16, how will this affect my speedometer?

[Iahawk]

The sidewall will be 96mm high vs 80mm on old tire..x2, tire should be 32mm taller x 16” diameter….x 3.14 squared…= I have no idea! …but it will read slightly lower..your speedo might be dead on…or not..only GPS will know

[rjs987]

Just a note: MOST vehicle speedometers are offset from actual. It's a percentage so how many mph it is off by should vary by how fast you are actually going. Less if the actual mph is slower and more if the actual mph is faster.
Cars are usually, on average, 3-6% offset from actual and motorcycles/scooters are, on average, up to 10-11% offset from actual. But always faster than actual. Manufacturers would be in serious legal trouble if any speedo showed slower than actual speed. My Subaru Legacy is spot on with a GPS and my Rav4 as well as my AK 550 are both 5.5% offset. My Burgman 650 was 10% or 11% offset depending on the tires. My CTX1300 was spot on with my GPS device. GPS devices are typically 0.3% offset from actual... so essentially accurate with an insignificant deviation.

[Stig / Major Tom]

www.tiresize.com

Stig

[mrmike]

Just a note: MOST vehicle speedometers are offset from actual. It's a percentage so how many mph it is off by should vary by how fast you are actually going. Less if the actual mph is slower and more if the actual mph is faster.
Cars are usually, on average, 3-6% offset from actual and motorcycles/scooters are, on average, up to 10-11% offset from actual. But always faster than actual. Manufacturers would be in serious legal trouble if any speedo showed slower than actual speed. My Subaru Legacy is spot on with a GPS and my Rav4 as well as my AK 550 are both 5.5% offset. My Burgman 650 was 10% or 11% offset depending on the tires. My CTX1300 was spot on with my GPS device. GPS devices are typically 0.3% offset from actual... so essentially accurate with an insignificant deviation.

   This is my 4th Kymco scooter. All 4 have their speedos read about 2 mph too fast. Why doesn't Kymco just adress thw issue and correct it?

[Stig / Major Tom]

   This is my 4th Kymco scooter. All 4 have their speedos read about 2 mph too fast. Why doesn't Kymco just adress thw issue and correct it?

I've had 5 Hondas, a Suzuki, a Kymco and a Piaggio.
They've all read a little optimistic.
Never saw it as a problem.
Stig

[CROSSBOLT]

I undoubtedly have an obsession with accuracy but have been spoiled by aviation, navigation (deep water, celestial) and radiation (amateur radio) with their modern instruments that are almost exactly right on. Even the speedos in the KIA and Subaru motor cars (maybe others) are exactly in tune with GPS.

It CAN be done but what the cost? Would it not be great if we could adjust to compensate for different tire sizes? With the fixation of law enforcement/courts with speed fines accurate indicators are mandatory!