If you stick with the recommended tires, the outer diameter of the tire is essentially the same as the 15", so there would be no difference.

It's folks who have off-size tires that need to worry about that.

JonasM

 

I went on the interstate recently and through several construction zones where they had your speed posted on a big light board letting you know to slow down. The speed that came up for me was right on.
The best way to find out go through Mississippi or Alabama on I-10 around 85 or 90 a State trooper will tell you how fast you're going.
By the way the guy in the red convertible Corvette was upset that my Fit was keeping up with him.
He could have stomped on it I know and left me in the dust but he was already running 85 to 90.
I don't reccomend anyone try this themselves unless you can foot a $300 ticket and get points on your insurance.

 

Speedo (etc.) accuracy:

About 30 years ago I started running road rallies. Most of these are of the TSD variety (time-speed-distance.) In a TSD rally, you go a certain speed for a certain distance, and it will take a certain amount of time.

For example, at 60 mph, you cover 1 mile in 60 seconds. At 80 mph, you cover a mile in 45 seconds. At 30 mph, you cover a mile in 120 seconds, etc.

When you run these rallies, there are checkpoints, where they check to see how accurate you are. You get penalty points for being either early or late - so you need to be VERY accurate.

With this accuracy in mind, one of the first things done with any rally is what is called an odometer check so that you can calibrate yours to what the rally master set it up from.

When I ran one, back in June, in my Fit, I noticed quite a bit of odometer error. Which I have later confirmed with the ScanGaugeII unit that I got a week ago. (More on this in a minute.)

Anyway - from all my years of doing this, here is what I have learned:
- all cars have some speedometer/odometer error, including police vehicles which have "certified" speedometers.
- tire pressure makes a difference
- tire size makes a difference
- road surface makes a difference
- temperature and weather make a difference (basic physics affecting the pressure inside the tire)

Our Fits, like most modern cars have an electronic link from the transmission to the instrument cluster in the form of a Vehicle Speed Sensor (VSS.) The VSS takes the electronic pulses that come to it and indicate what the speed that you are traveling.

I have found that my speedometer is quite accurate (at 7,000 miles on the stock tires) while the odometer is reading fast by about 1.5%, which I find very odd and will continue to monitor and argue with my local Honda dealer about...

Remember basic physics from high school? Let's look at something here:
- On the Fit Sport, the tire is 195/55-15. (Side bar: 195 is the tire width in millimeters, 55 is the aspect ratio of how tall the tire is in comparison to the width, and 15 is the size wheel that it fits on.)
- To find out what the diameter of the tire is (also different manufacturers have different "standards" to how exact a tire width/height actually is - just to mess with things some more!!!) - we need to calculate this out. 55% of 195 is 107.25 mm of sidewall height, which is 4.22 inches (25.4 mm/inch.) Since, when you look at the tire from the side, you see, going from top to bottom, tire, wheel, tire - you have to add the same way. 4.22+15+4.22=23.44" wheel/tire diameter.
- Now, let's introduce some variables into the mix!!

All tires have tread. The tread wears. As it wears the diameter of the tire becomes smaller. As the tire becomes smaller, it has to rotate more times to cover the same distance. This translates to the transmission sending back more pulses to the VSS which shows a faster speed than you are physically travelling.

We run on radial tires, which have some sidewall deflection built into them. How much deflection depends on the manufacturer, the tire temperature, air pressure, etc. All this affects how much the sidewall deflects, which affects how much of an effect there is on the real-world rolling diameter of the tire/wheel combination.

OK - that's enough for early morning!! Suffice it to say that all vehicles are going to have some error. If it doesn't, just wait:
- the tires to wear
- the tires to be replaced
- the weather to change
- etc.

 

fast odo = less warranty time...

 

the
The odometer problem is Acknowledged in another thread:
Some Fit Odometers may overstate mileage
the article mentioned in the thread indicates that Honda will extend warranty on affected cars by 5% (more than the identified error)

Oh, and lawyers get some $$- which is fine with me

 

I'd followed my gf with her honda civic si. We zeroed the odometer and she got 25.9km and I've got 26.3km. My Garmin GPS 60CS displays everytime less than my Fit does. How can we correct the situation ?

 

it would be better to ask an automotive engineer or a physicist to answer your question,i dont think im intelligent enough nor fit freak owners are intelligent enough to answer your question.i guess your in the wrong website to ask this question.

 

I'm sure you remember correctly, but the Fit speedometer doesn't work that way. The dash gauge is driven from the ECU, which knows from digital sensors exactly how fast the wheels are turning. (What it doesn't know, unfortunately, is how big the wheels are, and therefore exactly how to translate wheel speed in to ground speed.) There's a self-test you can start by key fiddling that sweeps the gauge needle from end to end.

 

I'll speak to this.

On my CRX, is has a mechanical connection between the transmission and the gauge cluster.

On the Fit, it is purely an electrical connection.

It makes no difference.

Both of these drive a Vehicle Speed Sensor. The VSS gets "pulses" from the drivetrain telling it that the vehicle is moving, and what the rate is. The faster the pulses, the faster the rate of travel. The VSS passes the information along to the electronic speedometer gauge which indicates how fast the car is moving.

It is kind of freaky, but there are test that can be done (if you have the Helm manualy) where the speedometer with sweep across the scale.

It is simply a gauge which reports information that it is getting from the gauge cluster via the VSS.

 

To start the gauge test, for those who want to try it:
1. Press and hold the trip reset button until step 5.
2. Turn the lights on.
3. Turn the key to position II.
4. Turn the lights off, on, and off. Take between 2 and 5 seconds.
5. Release the trip reset button, then press it 3 times within 5 seconds.

 

Again I followed my gf with her Honda Civic SI on a 25.9 km trip. This time my Garmin GPS was on. Results: her speedo indicates 25.9km, my GPS 25.9km and my Fit 26.3km. If you could do the same exercise, please tell me your results. Thanks!

 

For whatever it's worth, in the UK there is a legal requirement that speedometers be manufactured and maintained to -0->+10%. IOW they aren't allowed to under read but they can overread by up to 10%. I would have thought most countries had similar regulations.

 

I stick with the recommended tires and I've 2% difference!

 

Interested in the vehicle speed sensor (VSS) - what happens if you unplug it?

 

During a from a 1900 mile trip (concluded 12/14/07), I passed a speedometer (and odometer) test. I set the cruise control at 60 MPH but did not reset either of the trip odometers, because they were each being used to calculate individual fill-up mileage and total trip distance. Here are the results:

1. The speedometer was less than one second off during the 3 mile test.

2. The odometer was approximately 1/10th off a mile fast during the 3 mile test.

3. I was pleased and surprised.

 

Wow this thread is old!!

Generally GPS is accurate within about 3 feet depending on the model, for our construction sites we use a system that is accurate to about 12" to locate things.

That being said if the Fit uses the same speedo in each of it's models then there will be discrepancies as the stock, sport and sport option tires are all different sizes in diameter. I doubt they do a calibration on each one, just something in the middle so they can keep costs down.