Speedometer is way off

[HarvLC]

Regardless of tire math, I think it’s unlikely that Toyota purposely calibrated the speedometer to align with some assumed size larger than the OEM spec.

 

[surf fishing offroader]

I think you think you are schooling us here but 285 is a width measurement only.

...he is schooling yall.

It just takes a simple google search to confirm. Yes, aspect ratio is a percentage, but some don't know where to apply that ratio percentage toward.

There isn't a random floating constant that you apply the ratio toward and you magically get 33.7"

 

[No15]

...he is schooling yall.

It just takes a simple google search to confirm. Yes, aspect ratio is a percentage, but some don't know where to apply that ratio percentage toward.

There isn't a random floating constant that you apply the ratio toward and you magically get 33.7"

View attachment 19971

You obviously have not read the whole thread.

Read all the posts and you will see the issue. 285 is a tire width, not a tire size.

 

[surf fishing offroader]

You obviously have not read the whole thread.

Read all the posts and you will see the issue. 285 is a tire width, not a tire size.

You're missing the point entirely. Yes, I get it, different diameters will change the speedo.

But, the width has an impact on the diameter. It's in the freaking calculations lol

But your probably like my friend and went either the medical or law route, because math doesn't seem to jive with you

 

[No15]

Is a 265/70R18 the same height as a 285/70R18? No. The width has a direct relationship to the height. Therefore, changing the width does change the speedo.

So what if I use a 285/65r18 ? How much is the width changing the speedo in this scenario?

 

[No15]

You're missing the point entirely. Yes, I get it, different diameters will change the speedo.

But, the width has an impact on the diameter. It's in the freaking calculations lol

But your probably like my friend and went either the medical or law route, because math doesn't seem to jive with you

In the original post he said he was upgrading to 285. That's it. So perhaps your school taught you to come to conclusions with 33% of the facts, mine taught me to gather all the info before making decisions.

 

[surf fishing offroader]

In the original post he said he was upgrading to 285. That's it. So perhaps your school taught you to come to conclusions with 33% of the facts, mine taught me to gather all the info before making decisions.

You're just on another level buddy

This one's all for you, you did great

 

[izzysanchez]

Okay, lets do the math. Lets assume a 70 aspect ratio is a constant.

A 265/70R18 is 32.6 inches tall.
A 285/70R18 is 33.7 inches tall.
They both have a 70% aspect ratio.
The only number to change is the width.
The 285 is 3.38% taller than a 265.

Now back to original purpose of this thread.

If the speedo reads 70mph on 265s and the GPS says your speed is 67.5mph, that is a 3.70% error. Now switch to 285s and the speedo reads 70 mph, the vehicle is 69.8 mph.

You can go to tiresize.com and check my math. It is pretty close I am sure.

I reject your math and replace it with my own new math which works with my reality.