Now that I have both 14 and 15 inch wheel combos available to me, which ones give the lower engine RPM at cruising speed? Does tire height affect that rpm more than wheel size? Im wanting to lower the highway rpm if I can and increase mileage for some trips this summer. Can someone that understands this tire size ratio thing, explain it to me in laymans terms? This is all greek to me at this point.
Thanks in advance for some ideas. graemlins/beers.gif
graemlins/thumbsup.gif

Hi, click. Think of it this way... If you put a roller skate wheel on the rear the engine would have to spin like crazy to get any speed. The taller the tire the lower the rpm. The size of the rim does not matter.

overall height determines your, rpms @ speed , 1" might give you 300rpm or so less/more<up or down in size>

jim, overall tire diameter is what its all about. the smaller rim would just give you more sidewall area given the same tire overall diameter. try this formula to compare what you can expect from the overall height change, tire to tire; RPM= (MPH x gear ratio x 336) / tire diameter (diameter is your 25 or 26) if you thinking of a pair of "long trip" tires, i'd consider looking for a 27 or 28" tire, you'll be amazed at the reduction of cruising rpms. check it out! hope that helps graemlins/beers.gif

thanks guys, after posting that I left town for 3 days, now back to the postings to catch up.
Now its time to negotiate with the local tire store on some trades. :D