Odometer difference with tire size?

[osmith]

I bought my '96 used and it already had 305/70 tires on it with 355's. What I'm wondering is how much of a difference will this make with my odometer reading which hasn't been calibrated from the factory setting. I'm not sure what tires came on this truck from factory either.



Can I use a percentage to calculate the actual distance mileage? With a multiplier or percent I could more accurately figure out my fuel consumption



Oh btw, when your all calculating your mileage are you using imperial or us gallons? as I've got to convert from metric.



Thanks for the help...

 

[BCFAST]

This should help you out on your speed/miles. Try http://pw1.netcom.com/~sgalaba/tiresize.htm#ustires

 

[jrobinson1]

US gallons according to the stamp on the containers. Not quite sure what an Imperial Gallon is. (Ingnorant Americans) But I have heard of one. Chemistry class I think.



james

 

[osmith]

BCfast thanks for the link, great java calculator. It looks as though I'll be able to get a % difference which is what I needed for finding actual distance.



jrobinson1

the imperial gallon is larger than the us gallon. 1 imperial (british) gallon is 1. 20095 us gallons.



Now I just have to find out the factory tire size for my truck and the transmission ratio.



Thanks to all for the replies.

 

[JHansen]

I believe factory tire size was 245-75R16-and I can't remember whether you have an auto or a stick (sorry man!)-NV4500 is 0. 75 to 1 in OD and the autos are 0. 69 to 1-info from my FSM.



HTH

Jason

 

[Ted Constantine]

osmith chec out 4lo.com. They have calculators for all sorts of gearing and speedo changes.



I am off by about 6% with 295s from my stock 265s. You do need to know what your stock tire size was.

All the info of stock ratios can be found at dodgeram.com

Ted

 

[osmith]

man... what did I do before I joined this site :--)





I used 245/75 as a basis and 0. 69 for transmission ratio as mentioned by JHansen. For the tires I cam up with 7. 69% as a difference. My calculated mileage was 19. 9 mpg unloaded 70mph average. I'm pretty happy with that.



thanks again for the links and info

 

[jrobinson1]

Mee to... . the brain power on this site I love it.



If you got a question the answer is in here.



Sounds about right. I have been correcting but 7. 75% for running 285/75 vs 245/75. I guess 305/70 and 285/75 are close



Mileage too ... 19 till I put in US gear OD keep RPMs down and easily can get 20mpg doing between 75 - 80 mph. Before I had to drive too slow





James