Calculator: How Tire Size Affects Speedometer Accuracy

[syndicate1]

People are always asking how tire sizes affect speedometer accuracy. I came across this link today and thought I would pass it along.....

Tire Size Calculator - Compare Tire Sizes

 

[bimrunner]

Seems off to me in the rpm department. Even with 4.56 gears I'm only around 2000 rpm at 65 on the speedometer which I know I'm going a little faster.

 

[mdogg]

Seems off to me in the rpm department. Even with 4.56 gears I'm only around 2000 rpm at 65 on the speedometer which I know I'm going a little faster.

revolutions per MILE is for the tire - completely separate from the engine speed (revolutions per minute)

 

[Ol'Baditude]

revolutions per MILE is for the tire - completely separate from the engine speed (revolutions per minute)

At the bottom(where it says gear ratios / RPM @ 65mph), those are engine RPM values and they seem 500-600RPM too high to me, at least with my stock gearing and 285's at 65mph.

 

[Intruder]

I like this site a lot better since you can also calculate based on different wheel widths and offsets Custom rims, wheel tire packages for your ride - RIMSnTIRES.com

The RPMs on the TW calculator are probably based on the stock Tacoma engine (different than ours) and gearing.

 

[4RBob]

did you factor in overdrive transmission ratio?

I always liked the calculators on the following site (calculator links are at top of left nav bar).

4LO.COM :: On-Line Gear/Tire Size Calculators

 

[03_4x4Runner]

Just use a gps to get the accurate speed and compare that to your speedometer.

 

[1engineer]

http://www.toyota-4runner.org/5th-gen-t4rs/156378-5th-gen-tire-fitment-guide.html#post1550444

This is in the Sticky FAQ's now.

 

[syndicate1]

http://www.toyota-4runner.org/5th-gen-t4rs/156378-5th-gen-tire-fitment-guide.html#post1550444

This is in the Sticky FAQ's now.

Just use a gps to get the accurate speed and compare that to your speedometer.

did you factor in overdrive transmission ratio?

I always liked the calculators on the following site (calculator links are at top of left nav bar).

4LO.COM :: On-Line Gear/Tire Size Calculators

How did this thread go from Speedometer reading accuracy to Tire Fitment? Nice Hijack... HAHA!

 

[1engineer]

How did this thread go from Speedometer reading accuracy to Tire Fitment? Nice Hijack... HAHA!

Because the link you posted and are discussing is in my post and the speedo differences are too. Reading comprehension is not one of your strong suits I see.

 

[eddiebx]

Because the link you posted and are discussing is in my post and the speedo differences are too. Reading comprehension is not one of your strong suits I see.

What he meant is, make your spreadsheet more interactive so we can just plug in the numbers and it will spit out the actual speed difference automatically.

What do you expect us to do with the % differences you listed in your spreadsheet for every conceivable tire size specific to our 4runner? calculate by hand?!?! :crazy:

 

[4RBob]

How did this thread go from Speedometer reading accuracy to Tire Fitment? Nice Hijack... HAHA!

actually, my post had nothing to do with tire fitment and was in response to questions (in this thread) around engine RPM's due to tire size change. calculators in my link are also for gear changes, speedo, etc.

 

[1engineer]

What he meant is, make your spreadsheet more interactive so we can just plug in the numbers and it will spit out the actual speed difference automatically.

What do you expect us to do with the % differences you listed in your spreadsheet for every conceivable tire size specific to our 4runner? calculate by hand?!?! :crazy:

My bad. I should have known how hard it is to multiply a number by one point sumthin'.