Wrong Tire Size - What Does it Mean? - Automotive Education

In our video about tire sizes, we mentioned that the vehicle had the wrong tire size on it. We did not talk about what that will cause and what it can mean for you as a driver. In this video, we dive into the math behind how incorrect tire sizes cause your speedometer to read incorrectly

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[VanSant]

The more important point is that the wrong size of tire can show that your car has more miles on it than it actually has. A smaller tire over 6 years can really mess with the odometer. Not to mention this throws of your service schedule. Oil changes etc. I guess you could put larger tires, notate the difference so you don't speed and keep your cars mileage low. lol. Thanks for the video.

[halhansen]

+1” tire height (roughly) = 2 mph actual speed over the gauge. Great geek work, thank you!!!

[timwynn]

Tire lesson and math in one video, brilliant !

[therevolutionoflove]

I've totally learned something new. Thank YOU!!!

[anthonyariola]

I know for a fact that he didn’t mention was that by going 1 in more higher makes the ride more comfortable because there’s more rubber to absorb the road p.s.I went from 235 60 18 to 235 65 18, much better ride

[cypresspeter]

I think the more concerning issue is how the tire size affects the longevity and performance of the car, in my opinion.
Also, I heard most cars of today have their speed set lower than what their speedometers display. Using my car app such as Waze, I can notice my speed in some cars to be 2 to 3 miles lower than what is displayed in the dash.
So, in this case, should I still get a tire that is bigger than what is specified for my car?

[Mac]

Why is everyone blowing off about the speedometer readings!? There should be actual talk on upsizing on the same rim with handling issues and clearance etc.,

[Idksomething]

Got a BMW 335i. Went through 17 tires in a 3 year period. Therefore, I had zero confidence in the reliability of the vehicle. Well, ironically enough, I garaged the thing for 2 years bc I was sick of driving somewhere, blowing out a tire and then waiting for AAA to come give me a tow bc the vehicle has no spare. Well, after taking it out of the garage recently, I realized that the back tires (which calls for a larger width) was the same as the front. So these dipsticks at NTB we’re sticking on the wrong size for 3 years. No idea how I never caught that. So, shame on me for trusting someone else that should know their job.

[rishiromer]

Dose it effect milage ? Fuel economy ?

[alexanderspear]

Does taller sidewall provide more cushion for suspension components?

[tifino]

Nice to see your method of displaying the calculations.
I myself have simply ignored my car's dinosaur terrestrial speedo'... for over 15 years, in favour of GPS!

Reason: my '91 seven seater FrontWheelDrive (FWD) mazda's speedo has an inbuilt inaccuracy far beyond what I personally deem practical;
for example at Speedo 100kmh, I am doing GPS 92kmh.
At Speedo 80, I am doing GPS 73kmh etc etc.

The vehicle has only one size on it's manufactures' chart - being 185/70-14.
I'd like to go for 185/75-14 instead. ( I don't want to go 195/65-14 etc etc)

I want to achieve a longer rolling distance; smoother ride

From the above figures:
PROs: I will have no need to worry the Speedo will ever under-read, compared to the GPS' as according to calcs' I would expect to see a 3% increase in Rolling Distance with the 75% tyres on.
I can see I would achieve a softer ride;
lower RPMs for any given GPS speed;
I don't need to worry about larger wheel rim width changes;
I would achieve a higher area of footprint for better hold, for, when applying power I therefore expect to never again have to suffer the tyre skid when accelerating from standstill.
This being due to the extra rubber on the road, from the larger Diameter.

CONs: There might be some small compromise to tyre wall deformation upon hard cornering?
An Insurer might refuse to pay out, if the tyre is not exactly as stipulated on the Plate?
My Mazda seven seater is FWD, and is well known for the tyre skid upon acceleration from standstill. Most of it due to being FWD, but I also have long blamed the original diameter of a 185/70-14 contributes to it.
A more modern vehicle's ECU would report to the owner that it's next due Servicing Schedule would for example come due at 97000km instead of

[AstroVanTribe]

This is good stuff, BUT just the tip of the iceberg as many here are here because we go with larger tires because we're modifying our vehicles to perform better off road and we're curious how to manage the differences with MPH, fuel economy and For instance, I have an '04 AWD Astro van I converted to 4x4 with an s10 transfer case and I have a decent lift on it. My tires are now about 2" taller than stock and my speedometer is off 4mph... There are charts out there that point out the relation to tire size, gearing and rpms - There are "sweet spots" to aim towards, for instance, according to what I've seen you can get better gas mileage but have a loss of power at the same time.

This video is great for what it is but most people who go with larger tires already/quickly learn/understand the speedometer is off without needing to understand the math involved (I enjoyed this explanation, anyhow) - What they really want to know is how to reprogram the computer to work with the new tire size so the speedometer in in sinc as well as to get the mpg readings to be accurate - I'll be looking to see if you've done anything on that as I believe you'd probably be the perfect guy to explain all that

[ronch]

Great info. Just a question though. What if you're switching from highway tires to those all-terrain or rugged-terrain tires with all those biting edges? Not sure if the tire makers all factor those in.

[halalan]

Excellent video, is there any effect on actual MPG, for gas only vehicles. Thanks!!!

[cleytonvieira]

Thanks for sharing with us about I just bought the wrong size tire ...and I will get a close look about the speed

[lakeforkwiring]

Your very smart Sir ... nice math ...I always wandered how that worked.

[adrienbastarache]

Thanks for showing me that, i leaned you are good, subcribed and liked.

[marshalkrieg]

I had to put slightly smaller tires on my truck. I just drive it around town, in light traffic, doing errands, so I think everything's ok.

[jimlyexclamador]

How about the tire size I'm using at the back 215x60 R17 and in the front 225x60 R17, Is there any effect on the performance of the engine car? Please give me advice. Thank you!

[phuctaochi]

Thank you so much for this information.