My speedometer did not agree with GPS
 

I know all the idiosyncrasies in my 2017 Fit LX pretty well at 95K miles, but recently, I noticed a new finding. I spent the night at a rest area along US10 from LA to Houston. The next morning, my iphone default weather app indicated the temperature was 34 deg F. After warming up the engine,and defrosting the windows from all the condensed moisture, feeling good, I took off.

Immediately, I noticed that the speedometer reading was low, 61 mph, compared to what my Garmin Nuvi 50LM GPS indicated 63 mph. My intution suggested that the speedometer reading is wrong since the GPS had tracked the highway speed indicators (at work areas) accurately in the past. My conclusion is that the tires were slightly deflated due to the cold temperature. And, when they warmed up, the speedometer reading accurately compared to the GPS’s

Anyone suggests a different conclusion? BTW, I love the Honda Fit, and it's too bad that Honda wants you to replace it with the HR-V, which is more money.

3mph is only a few needle widths. Sound like you are honed in on your FIT;)
Using nitrogen instead of air will negate the pressure fluctuations. 34f sounds balmy to me though. Thats a warm morning even in May and June. We can have frost any day of the year.

Air is already mostly nitrogen.

As tires wear down they would spin faster and therefore indicate a higher speed. Are they new tires? Car manufacturers have to decide what tire circumference to use when setting the speedometer.

I did say that ......And, when they warmed up, the speedometer reading accurately compared to the GPS’s
The Fit is 100% stock.

Yes it is. But without the oxygen it’s less affected by temperature changes.
I can be at -40 inland and above freezing at the ocean within 3 hours of driving here. Have you ever had Fred Flintstone type tires in the morning? Pure purged nitrogen filled tires gets rid of that!
With low tire pressure warning systems this also helps remove the idiot lights from the dash. Especially with the heavy and light tire load settings on my truck. So I don’t know why you threw that comment in there? It makes enough difference as the original poster of this thread was concerned about 2-3mph, I think nitrogen only loses about 2% psi for every 10°. My suggestion was valid. It was my 1st post on here. Probably should be my last if this what goes on. If it makes that much of a difference with my 6.7 L it’s actually quite beneficial to these little 1.5 L engines when everyone’s trying to hyper mile with them.

That's not what I've read:
https://www.tirerack.com/tires/tiret...jsp?techid=191
https://www.aaa.com/autorepair/artic...late-car-tires
Essentially the difference is negligible for auto tires in normal conditions.