Tire height for speedo correction

[Drewhenry]

I just had the Toyo OC Mt installed on my truck. 35x12. 50R17E The Toyo website shows 34. 8" nominal Diameter. For those of you that have used this tire and have found the correct diameter to input to your Speedometer, what size do you use? I will be using Smarty to change my speedo.



Andy

 

[p-Bar]

I just used a GPS and got mine dialed in perfectly. The tire size was close but not perfect

 

[Regcabguy]

A GPS is the way to go. My 285-75-17 Toyo AT's w/a height of 33. 8"(according to Toyo) dialed in@33. 3" with my Smarty and GPS.

 

[AWise]

Same here. I think I set my MTs at 34" (with a SmartyJr) and then clocked with my GPS and it was on the nose. It has since gone to 1mph over what my GPS says, but I think that is just due to tire wear and because I lowered my pressures a bit.

 

[Big_Horn]

From what I read, you need the total revolutions per mile. Your tires are 596 revs per mile. you can see the entire chart here:



OPEN COUNTRY M/T | Toyo Tires



then select "see Complete Sizes and Specifications" for all your tire info.

 

[Drewhenry]

At 596 revs per mile wouldn't that come out to 33. 8 actual tire diameter? I seem to have been duped. I was under the impression that the tires I am running are 34. 8 loaded height. Also, where does it say the revs per mile? I didn't see that info anywhere on the Toyo site. ?????



Andy

 

[Motorhead]

I would set them at the Toyo measurement then check with a GPS or I use the speed limit signs that have a "Your speed" readout.

 

[Big_Horn]

I'm not too sure how to comment to your reply. I went to the toyo site and that's the measurements I found for your specific tire size. There may be an oversite on my behalf but that's the info I had found. Sorry I couldn't help any further.

 

[brods]

At 596 revs per mile wouldn't that come out to 33. 8 actual tire diameter? I seem to have been duped. I was under the impression that the tires I am running are 34. 8 loaded height. Also, where does it say the revs per mile? I didn't see that info anywhere on the Toyo site. ?????

Andy

34. 8 is the unloaded diameter. When you put weight on the tire the bottom flattens out. This is the loaded radius, which according to the Toyo chart is 16. 2" for that tire. This is what matters when adjusting the speedo. Now it gets more complicated since when the tire is rolling the loaded radius changes (think of a dragster back tire that grows taller going down the track). That is why you must use the manufacturer's rev per mile data.

Click on the SIZES & SPECIFICATIONS tab under the tire on the Toyo page and then click on SEE COMPLETE SIZES AND SPECIFICATIONS for a pop up window that gives all the specs for your tire.

On edit: Your 33. 84 number is the correct number to put in the smarty. Adjust as needed from there.
Here is a link to one of the many threads on this subject: https://www.turbodieselregister.com.../204254-tire-size-adjustment-295-toyo-mt.html

 

[Drewhenry]

Thanks for helping clear that up for me.



Andy