Saw the dealer today about my speedometer error

The same tire size is actually a larger tire on a 17 inch rim- by about an inch.

Tire size like 285/70R16 vs 285/70R17 but have the same width (285) and the same sidewall ratio (70% of 285) but the rims are an inch different. So "same size" is kind of a misnomer.


And thru testing- We (Chris4x4) are pretty sure the Odo is right and the speedo gauge is the only part that is showing the incorrect reading.

 

What was your original tire size?

TIA

 

I have this problem as well. What tire size would get the odometer right on?

 

Calculate how far it is off as a percentage and then play with the TW Tire Calculator under the Mods & Tutorial button to see what will correct it by the percentage it is off.

 

Looks like about 8% off so I am getting a 32.6" tire to correct it. Maybe I should just go with 33's?

 

bottom line to the start of the thread is, if you already know its 5mph off, just keep living. thats what i do in my reg cab. these are all quirks with every car ever made, never owned a car/ vehicle that was perfect, dont expect it to be when they build thousands upon thousands of them. i pay for the durability and resale value, and overall fun factor of my truck. if i knew the speedo was 20mph off, i would deal with it because its no longer a secret. my 2 cents.............

 

Is the odometer running up faster too? I can deal with the speed thing but miles? thats resale $$ !

 

Thanks

 

my truck's is off too. I've used 2x GPS's to calculate it. Almost 5mph off at hwy speeds!!! that's BS!! My F250 was only off by 1-2 mph. How can they say 5mph over what I'm doing is "OK"??? STFU toyota and fix it.

 

Another option for correcting the speedo error is to open up the gauge cluster and tweak the needle one way or the other...if it really bothers you all that much.

 

You have to careful pulling needles off of electronically driven speedo's and reinstalling them. You can easily break a speedo.

 

i always thought they did it on purpose so people think there going 5 over but there really going the speedlimit

 

Since its not an exact science, due to variances in operating conditions they usually read a little high but I think +-4MPH is normal. Cops usually give you 10MPH due to inaccuracies of their radar/laser and your speed-o being a little off.

 

I'm a math teacher and I have to say, reading this thread is very agonizing!!! If I may, I'd like to clear up a few misconceptions.

#1: If your speedometer is giving a reading that is too LOW, then getting bigger tires will only make the problem WORSE. Speedometer readings are based on counting the number of revolutions. A tire diameter is programmed so that the computer (or mechanical device) can compute a vehicle's distance traveled based on one revolution and compare that to the time traveled. If you get larger tires (and the computer doesn't know it) you are traveling even further per revolution (larger circumference = longer distance per revolution), which means you are actually going even faster than your speedometer will display. Bottom line, if your speedometer reading is too LOW, then the solution is to get smaller tires, not larger tires.

Example: Anyone who has gotten a lift and installed bigger tires (33's, 35's etc) knows that their speedometer is now too low and that they are actually going faster than what their speedometer says. To correct this issue, they would replace their bigger tires with their SMALLER stock tires, not put on even bigger ones!

#2: Your speedometer is not off by a constant amount! The faster you are going, the more your speedometer will be off. There is no simple rule where someone's speedo is "always off by 5 mph". If that's true, then there is a completely different issue than tire diameter size. To find out how far your speedometer is off, simply divide your actual tire diameter by the diameter the computer "thinks" you have. Then multiply this ratio by the indicated speed on your speedometer.

For example: Suppose you have 30" stock tires (and this is what your computer thinks is true) and you "supersized" to 33" tires. Just take (33/30) = 1.1. Then multiply 1.1 by your speedometer reading. So when your speedo says 30 mph, you are actually going 30 x 1.1 = 33 mph. When your speedo says 60 mph, you are actually going 60 x 1.1 = 66 mph. (This actually is a linear relationship for the person who said it wasn't. The constant ratio (or slope) is the actual tire size/supposed tire size).

#3: Your speedo reading is not affected by rim size. I saw some posts asking about how much a 17" tire will affect the speedo reading. The 17" refers to the rim size, not the tire diameter. Technically, you can increase rim size without increasing tire diameter and not affect your speedo at all.

For example, a 265/70/R16 tire measures about 30.6" in diameter. A 265/65/R17 tire also measures about 30.6" in diameter. If a person were to go from the former tire size to the latter, they would experience a negligible error in their speedometer reading.

I think that's it for now.

 

Mine's off too... I just use the speed on the scan gage

 

It's not that hard, and they're not as fragile as you think. I've pulled mine apart three times so far. And if can be broken, I'm the one to break it.

Also, my post was mostly sarcasm. This speedo error is kind of a minor problem to have, and should be overlooked.

 

Even in BMW World 5-6 mph fast or slow is considered acceptable....and there are so many variables at play in so many of the cars now...including but not limited to tire size, tire wear, gearing and so forth...soo there is a margin of error that is acceptable to pretty much all manufactures

 

This thread wore me out Now I don't even know how fast the wheels in my head are turning. FTW! I want exact 100% speedo. readings! Is it true that a scanguage can be more accurate if it's getting the same data that the normal guage is receiving Sounds like a pretty blatant contradiction to me.

 

You won't get a 100% exact speedo with an analog gauge- There will always be some error. I'll bet none of the vehicles you'e ever driven were 100%. Like TRDKen said- Too many variables to make them perfect. You can try to minimize it, but the more effort they put into a "perfect" speedo...The more you are going to pay for it.

If the scangauge is more accurate (and IDK if it is) it makes perfect sense- The scangauge is not using the same Digital to Analog conversion...so it can show more exact information.