Hey guys. I got new tires a few weeks ago (same stock size as previous tires -- 245/40/18) and I'm convinced my speedometer is now off. I travel the same highway every day to and from work (and have for the past 10 years), and for the past few weeks, the speedometer says I'm going 80, but it feels more like 70 (and cars are passing me).

Here's one other piece of information. I checked the mile marker signs against my odometer and they're spot on. In other words, a physical mile on the road according to the mile marker signs matches up exactly with my odometer.

Are the speedometer and odometer connected? In other words, if the odometer is accurate, does that necessarily mean that the speedometer is accurate as well? Thanks for any help.

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Not all car vehicle odometers are accurate, there is usually - or + 5%

If you want to best test how accurate your is, use a gps device that measures speed. As GPS is pretty accurate.

 

Thanks. But if the odometer and speedometer were accurate (or even slightly inaccurate) before I got new tires, I wouldnt expect any change now.

I guess what I'm asking is whether the odometer and speedomter on a 3GS are connected. My odometer sees to be accurate, but my speedometer seems to be off.

Good suggestion on the GPS. I have a Garmin that I could throw in the car this weekend to check the speedomter.

3,000th post!!!!

 

Most likely the speedometer is connected to the odometer

 

Great app to use is Ulysse Speedometer... that'll check your actual speed to compare to your speedometer

https://play.google.com/store/apps/d...edometer&hl=en

Not sure on your original question though..

 

The odometer is spot on, UNLESS you have aftermarket rims and screwed up the rolling diameter. The speedometer is always off (you're actually driving slower than actual speed at all times) this is so people hit 70 in a 65 and still stay within the limit range so they don't get pulled over. Manufacturers do this for a reason.

 

Garmin GPS will do the job.
Went through many street speed radars, I noticed my GS350 speedometer is about 2 mph less.

 

GPS is accurate? LOL So many times standing still and I see my GPS reads 1 or 2mph. Our civilian GPS is not accurate.

The only accurate one is the cop laser gun and by law they need to check it accuracy periodically.

 

Yup, otherwise it's debatable in court and charges can potentially be dropped.....

I think the speed signs are accurate too! (the ones that scan you and tell you how many mph you're running).