GT w/17 Wheels Speedometer is Slow?

[m4VibeGT]

I got my Vibe GT this past Monday. Yesterday, I drove it with a Garmin GPS and noticed that the speedometer was showing a lower speed than my GPS. When the car's speedo hits 65 mph, the GPS shows a speed of about 67.6 mph. At 75 mph, the GPS shows a speed of almost 78 mph.Anybody else notice this?

[DVDvibe]

I have the base vibe with the 16" wheels and my gps reports the same speed as the speedometer. They may not have adjusted it for the GT with the 17" wheels. Would like to know if anyone else with the 17" wheels is having this problem though.

[NovaResource]

The tires for the 17" wheels are slightly larger.16" wheels = 205/55-16 = 24.9" diameter = 78.2" circumference = 811.0 revolutions/mile17" wheels = 215/50-17 = 25.5" diameter = 80.0" circumference = 792.0 revolutions/mileThat is a 2.4% difference so if the speedo indicates 60 mph you are actually traveling 61.4 mph.

[d_m_kolb]

This link should help you alot a lot.http://forums.genvibe.com/zerothread?id=171

[wrench79]

The speedo is faster than actual speed. I got a speeding ticket on my way home from work today. I was in 55mph zone and had my cruise control set to 70mph and got a ticket for 68 in a 55. The speeding ticket wasn't accurate to a tenth of a mph, but still that's about 2mph. From what i've read on other cars i think that most speedo's are a little bit faster than you're actual speed.

[m4VibeGT]

You can't really use a speeding ticket to establish your actual speed. Usually, the cop will understate your speed if you are already way above the speed limit to give you a break on the effect on your driving points and hence your insurance rates (unless you really pissed off the cop). That is if you are going over 10 mph over the speed limit, they will give you a ticket going about 8 mph over the speed limit. I believe speeding points are based on 5 mph increments. Based on my experience, I never got a speeding ticket going 9 mph over the speed limit. Just my 2 cents.

[hesredbird]

I have 16" wheels on a base. It "feels" like I am going slower than the speedometer reads. It may just be me.

[mu_ohio]

The nice thing about the slightly larger rims is that you will get more miles out of your lease if you go that route. The bad thing is a slight increase in the gearing which hinders acceleration, though the tires do have better grip.