From owner-xj-digest-at-digest.net Fri Oct 28 16:08:00 2011 From: xj-digest To: xj-digest-at-digest.net Date: Fri, 28 Oct 2011 23:08:11 +0000 Subject: xj-digest V1 #3336 xj-digest Friday, October 28 2011 Volume 01 : Number 3336 Forum for Discussion of XJ cherokees and wagoneers Brian Colucci Digest Coordinator Contents: xj: tire math xj: RE: tire math XJ Digest Home Page: http://www.digest.net/jeep/xj/ Send submissions to xj-digest-at-digest.net Send administrative requests to xj-digest-request-at-digest.net To unsubscribe, include the word unsubscribe by itself in the body of the message, unless you are sending the request from a different address than the one that appears on the list. Include the word help in a message to xj-digest-request to get a list of other majordomo commands. ---------------------------------------------------------------------- Date: Thu, 27 Oct 2011 01:05:31 -0700 (PDT) From: john Subject: xj: tire math looking for some winter tires for my J10... it currently has some 265/75/16's on it... should have 235/75/15's... it's about 10% off right now... meaning when I'm doing 40 on the go meter it's really around 45 mph... wouldn't be all that bad if I had lower gears... but I've got the looney 2.72's... so... to get some more oomph off the line thinking I could drop tire size a bit... found some 215/70/15s... that's going to be about 6% less than stock, assuming 235's were stock and not 225's.... any one know what a long bed 83 J10 with a 360 and 2.72s should have for tires? so if I'm 10% over now, and go with 6% less than stock, that means I'll be going slower than indicated... and should reduce overall gearing 16%? what's that in ring and pinion numbers? (I've got the forumlas somewhere, will look if I don't hear from anyone..) john ----- - ------------------------------------------------------------------------ -o|||||o- fahrvergnugen y'all Snohomish, Washington - where Jeeps and VWs don't rust, they mold http://AMSOIL.com/redirect.cgi?zo=283461 TRSTGZS http://JohnMeister.com HTTP://WAGONEERS.COM http://fotomeister.us - ------------------------------------------------------------------------ ------------------------------ Date: Fri, 28 Oct 2011 16:07:44 -0700 (PDT) From: john Subject: xj: RE: tire math thanx, just remembered this page as well: http://www.miata.net/garage/tirecalc.html of course they don't do 30/31, etc... and you can't cut and paste the results. ;) john ----- - ------------------------------------------------------------------------ -o|||||o- fahrvergnugen y'all Snohomish, Washington - where Jeeps and VWs don't rust, they mold http://AMSOIL.com/redirect.cgi?zo=283461 TRSTGZS http://JohnMeister.com HTTP://WAGONEERS.COM http://fotomeister.us - ------------------------------------------------------------------------ On Thu, 27 Oct 2011, Tesar Landon-R16884 wrote: # # Speed/hr = rpm * (60 min/hr)* tire circumference/(final drive ratio * trans gear ratio) # Circumference = diameter * pi = tire width * profile * 2pi) # All other things the same, what is the effective final drive ratio? # # The ratio of circumferences is the ratio of radii, converting wheel radius to mm, # ((7.5*25.4) + (215 * .70)) / ((7.5*25.4) + (235 * .75)) = 93% # # The final drive ratio is inverse to the circumference: # Eff final drive ratio = stock drive ratio / circumference ratio # # Eff final drive ratio = 2.72 / .93 = 2.924. # # - Landon # -----Original Message----- # From: owner-fsj-at-digest.net [mailto:owner-fsj-at-digest.net] On Behalf Of john # Sent: Thursday, October 27, 2011 3:06 AM # Subject: fsj: tire math ------------------------------ End of xj-digest V1 #3336 *************************