2nd Gen Non-Engine/Transmission Smarty ABS tire height

[dflesher65]

I got my new Smarty but can't figure out the ABS height for a 305-70-16. The parameters are from 25 to 45. I looked it up in BFG website and I found tire diameter is 33. Is this the number I'm looking for? :--)



Thanks,

Dwight

 

[BILLVO]

you got it down now. From what I have read you may need to play with it to get speedo right. It isn't real accurate.

 

[Rhinohd]

check out this site. . It may help you...



http://www.4lo.com/calc/gearmetric.htm

 

[dflesher65]

That's about what BFG had it at, 33. the link from Rhinohd was 32. 8. I'll give that shot.

Thanks guys.



Dwight

 

[fest3er]

Your best best is to drive 100 miles on the highway, noting the mile markers at the start and end, and your odometer at the start and end (including tenths). The resulting ratio will let you compute the exact tire size to program. The reason for using 100 miles is that individual mile markers are not always very accurate, but over 100 miles, they're pretty close; also *some* of the math is a little easier.



For instance, suppose you have programmed in 33" tires. Drive 100 miles on the highway, as measured by the mile markers.



If your odometer shows you've travelled 105. 8 miles, the ratio is 105. 8/100, or 1. 058. The corrected tire diameter to program in is then 33/1. 058, or 31. 2". Program this in, then drive back, measuring again. Your odometer should be almost dead-nuts on.



If your odometer shows you've travelled 96. 3 miles, the ratio is 96. 3/100, or 0. 963. The corrected tire diameter to program in is then 33/0. 963, or 34. 3". Program this in, then drive back, measuring again. Your odometer should be almost dead-nuts on.



I did this with my TruSpeed; my odometer has never been off by more than 1-2% since. I occasionally adjust it to account for the loss of tread as the tires wear. Yes, I can be anal about things once in a while, and it helps to keep the math fresh.



Once you have your odometer recording correctly, your fuel economy calculations will more closely reflect reality.

 

[Beast2B]

or get ahold of a GPS and compare miles driven or speed. i run 1/4" under mfg size listing to get pretty close. the other problem is that the factory speedo is not accurate through the full spectrum. if i'm right on at 30mph, it's off at 70mph (or vice versa). i get mine close for highway use and call it good...

 

[DiTrani]

I measured from the center of the rear axle to the ground and multiplied that by 2. Theoretically that's exactly correct, takes into account tire wear and inflation, and I'm dead on with my GPS this way.

 

[WestTN]

And the reason DiTrani's method is more accurate is that it accounts for the load on the tire. I found out a long time ago the loaded radius of a properly inflated tire is about 0. 4" shorter than the unloaded radius. I found this using tire size table data from Goodyear in an Excel spreadsheet and working with 'goal seeking'. At least I think that is what it was called. That 0. 4" applies across a broad range of sizes.

 

[Beast2B]

doesn't account for pressure changes at different temps, or the total lack of accuracy in the gauges!

if you like the measuring device methods, try marking a spot on the tire at dead center bottom (truck should be stopped). roll the truck a complete revolution and divide the distance (measured as accurate as possible) by Pi (3. 1416) to get a semi-precise diameter.