I just purchased 4 Hankook ATM 285/70 R17 tires to replace the stock michelin ltx a/s tires 265/70 R17. I will be using the Smarty to adjust the tire size. Anyone know what value I should enter to correct the speedo??

I tired to read the specs on the Hankook tires but the spec sheet is just too blurred to read.

thanks for your help
Lane

 

Well I am trying to download the Hankook spec sheet now. Gernerally 285/70R/17s are listed around 32.7" diameter. But when the pdf finishes downloading I will see what Hankook says.

My experience is the the manufacturer specs for tire size diameter are new, mounted on rim and aired fully. When actually put on the vehicle the rolling diameter will be less, depending on weight and air pressure.

The best way to get as close as possible is the set at manufacturer diameter spec and then use a good GPS to verify actual.

My BFG 285/70R/17 A/Ts are listed at 32.7" diameter. But at 50% tread and on the truck with 60psi air I set my Smarty diameter to 32.1 and that puts me very close to actual using GPS and point to point mileage.

 

Most 285/70 R17s, including the ATMs are listed a diameter of 32.8".

I've been using 32.4" on the Smarty to get very close to dead on with my speedometer.

 

does it really throw it off that much?

 

Ok finally finished the Hankook spect sheet. There website is SLOW. I assume this tire:

Dynapro ATm_RF10 LT-Metric

S-Code 2001405
Size LT285/70R17
Ply 10
LI & SS 126/123S
Measure Rim 7.5 - 9.0
Rim Width Range 7.5 - 9.0
Maximum Air Load S 80 3,750
Maximum Air Load D 80 3,415
Overall Diameter 32.8
Section Width 11.6
Tread Width 8.7
Tread Depth 16.5
Revs Per Mile 634

Set Smarty to 32.8" to go by the manufacturer spec.

 

Well if your **** like me about some things yes. I generally see that with manufacturer specs your Speedometer and OD will be 1-1.5% off on the high side.

Probably not enough to worry about, but I like to know as close as possible what my speed and mileage are.

 

WOW, I have those same tires and to get my speedometer correct I am at 31.8 in the smarty. I have checked this with 2 GPS's and it is darn near right on. When my smarty is set on stock it sets the tire at 30.65 for the stock 265's. I tried the 32.8 and mine was way off. Maybe the diff is the 4.10's??

 

I had a similar situation when I added an aftermarket magnetic pickup speedometer to my motorcycle. I filled the tire to proper pressure. With the bike I also have to put on all my typical riding gear. I Then took a white grease pencil and a 90 degree builders square and had my wife mark a vertical line on the tire and a mark on the ground at the point of the mark on the tire with the assistance of the square. Then I carefully rolled forward until the line on the tire was vertical again checked against the square. Then measured the distance between the two marks on the ground. This will give THE ACTUAL rolling distance of the tire. Next I divide by PI (3.1415... I used ten decimal places) to arrive at the effective rolling diameter IE: 103 3/64 inches roll-out would be 103.046875/3.1415926586 = 32.80083... inches in diameter. If you need the result in metric multiply the result by 25.4 and you will have the measurement in millimeters. IE: 32.80083 * 25.4 = 833.141082mm or .833141082meters

This is a little cumbersome, but is extremely accurate at measuring the effective rolling diameter of a tire on anything. I also use this method for my bicycles. Everything measured against GPS is spot on.

 

I didn't have to make any adjustments with the tire size change. My speedometer was indicated faster than actual anyway with the stock tires. Now it's right on the money with the 285/70's. Verified with two different GPS's.

MikeyB

 

Went up to 285/70/17's and according to my gps, when the speedo reads 62, I'm doing 60.

 

I set the tires at 32.5. I check it following my son-in-law at 45mph and it was right on.

 

I am looking at this same tire- how do like them so far?

Can you post some pics? trying to decide between these and Nitto terra grapplers.

 

I like them but I only have about 30 miles on the tires. They are stiffer than stock. Time will tell and I will post a follow up..

Here is a link to some pictures but I do not have any pictures.
https://www.dieseltruckresource.com/...hlight=hankook

 

One tire was bad causing a virbation however discountire took care of me by replacing the tire.Now I have a very nice ride. I have reduced rear tire pressure to 55PSI. I found a radar sign and finished dialing in the speedo to 32.00 with the Smarty.

Happy Camper..

 

Why not just get a tape measure and measure the od ? set a level on top of the tire, measure that to the ground. every time i've used the formula the result is not true. for 285 70 17........ 285 X .70 X 2 / 25.4 + 17 = 32.71 the tire actually measured less.