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Re: ACCURATE SPEEDOMETER?
Tracie wrote:
> On Sep 17, 11:17 am, Mike Romain <roma...@sympatico.ca> wrote: >> Tracie wrote: >>> Hello all. I have a 2006 Wrangler X with 6 speed manual tranny, 3.07 >>> gearing, and D30 front/35 rear. I recently upgraded my tires from the >>> stock 215/75/15 to 31/10.5/15 BFG All Terrain T/A KO. I am looking >>> for a reliable way to tell if my speedometer is off at all with the >>> tire upgrade. I do not have access to a GPS system. What I HAVE done >>> is to use the tripometer (with tenths), and hold steady at 60 mph (my >>> speedometer said 60) for one mile while watching my clock. I am >>> EXTREMELY close to going 1 mile in 1 minute by using this method. Is >>> this reliable to tell whether or not my speedometer is dead on? I >>> have NOT changed the speedometer gear yet, or had the computer changed >>> to reflect the larger sized tires. Also, I am not using my OD (6th) >>> much on the highway, but when I get up to 65 (the speedometer says >>> 65), I am running at about 2500 rpms in 5th. Is this bad, or should I >>> be shifting into the OD (6th)? I do fine with 1st through 5th. Just >>> not sure what speed or what rpms I should be using 6th. Any help is >>> really appreciated. >> The (ones that have posed here) older TJ speedometers became correct >> when 31" tire were put on. >> >> Your mile per minute is a good base to tell it is close. >> >> The only other way is to find a measured mile or a friend with a GPS or >> even ask a cop to pace you because 'you just got new tires and don't >> want to break the law'. Only a cop's speedometer would be reliable for >> this, cars can be off too according to tire size. >> >> I find 'my' engine 'much' prefers to be running at 2300-2500 rpm on the >> highway which I get with my 4th gear. (have 33's and 3.31 gears) That >> rpm gives me good throttle control and prevents engine lugging. I also >> get a pretty stable 11L/100km or 23 mpg running there. >> >> If I go to overdrive or 5th gear, the rpm drops to 1750 or so at 65 mph >> which makes for the need of the full gas pedal travel to adjust speed or >> hold a hill or wind vs a twitch of the pedal in 4th. This low rpm drops >> my gas mileage by at least 5-8 mpg. >> >> You can find out easy. Just compare gas mileages when using only 5th on >> the highway and when using 6th mostly. I have one trip I do lots to get >> bush camping which is 201 km from gas station to gas station so I have >> an easy check point. >> >> Mike >> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 >> 88 Cherokee 235 BFG AT's - Gone to the rust pile... >> Canadian Off Road Trips Photos: Non members can still view! >> Jan/06http://www.imagestation.com/album/pictures.html?id=2115147590 >> (More Off Road album links at bottom of the view page)- Hide quoted text - >> >> - Show quoted text - > > So, assuming that my speedometer is correct, running approximately > 2500 rpms in 5th gear at 65 mph will NOT hurt my engine or cause > increased engine wear? If I were to shift into OD (6th), what is the > approximate rpms that I should be running so as to not cause lugging > or increased engine wear? > > THANKS > Running in the higher gear is the bad thing, not running in the lower. Lugging is bad. 'You' engine has it's own 'sweet spot' of the rpm where it seems to run the best with the best response and best mileage. That is usually where it likes to sneak to when you are not paying attention. In 'my' engine's case this is 2300 rpm. Anything below 2000 on the highway starts the 'lugging' process and causes engine 'ping' or a rattling noise under load. 1750 or my OD (5th) at highway speeds is way too low for my setup. Mike |
Re: Re: ACCURATE SPEEDOMETER?
On Mon, 17 Sep 2007 08:36:28 -0700, Tracie <brainart@upstate.edu>
wrote: >Which would probably be somewhere in the neighborhood of 70-75 mph in >6th at approximately 2500 rpms. Your speedo is way off.(big tires will do this) In 5th with current tires, 2500RPM would yeild about 74 MPH and 6th (.82 OD) 2500 would yeild about 91 MPH based on quoted tires sizes and axle ratios. Again you can do the math yourself http://www.snoman.com/HTML/axlecalc_5a.html ----------------- TheSnoMan.com |
Re: Re: ACCURATE SPEEDOMETER?
On Mon, 17 Sep 2007 08:36:28 -0700, Tracie <brainart@upstate.edu>
wrote: >Which would probably be somewhere in the neighborhood of 70-75 mph in >6th at approximately 2500 rpms. Your speedo is way off.(big tires will do this) In 5th with current tires, 2500RPM would yeild about 74 MPH and 6th (.82 OD) 2500 would yeild about 91 MPH based on quoted tires sizes and axle ratios. Again you can do the math yourself http://www.snoman.com/HTML/axlecalc_5a.html ----------------- TheSnoMan.com |
Re: Re: ACCURATE SPEEDOMETER?
On Mon, 17 Sep 2007 08:36:28 -0700, Tracie <brainart@upstate.edu>
wrote: >Which would probably be somewhere in the neighborhood of 70-75 mph in >6th at approximately 2500 rpms. Your speedo is way off.(big tires will do this) In 5th with current tires, 2500RPM would yeild about 74 MPH and 6th (.82 OD) 2500 would yeild about 91 MPH based on quoted tires sizes and axle ratios. Again you can do the math yourself http://www.snoman.com/HTML/axlecalc_5a.html ----------------- TheSnoMan.com |
Re: Re: ACCURATE SPEEDOMETER?
On Mon, 17 Sep 2007 08:36:28 -0700, Tracie <brainart@upstate.edu>
wrote: >Which would probably be somewhere in the neighborhood of 70-75 mph in >6th at approximately 2500 rpms. Your speedo is way off.(big tires will do this) In 5th with current tires, 2500RPM would yeild about 74 MPH and 6th (.82 OD) 2500 would yeild about 91 MPH based on quoted tires sizes and axle ratios. Again you can do the math yourself http://www.snoman.com/HTML/axlecalc_5a.html ----------------- TheSnoMan.com |
Re: ACCURATE SPEEDOMETER?
Tracie wrote:
>>> - Show quoted text - >> Oh, nevermind. I think I just answered my own question. : D >> >> I am assuming that the approximate 2500 rpms would apply to the OD >> (6th) gear as well to prevent increased engine wear and lugging?- Hide quoted text - >> >> - Show quoted text - > > Which would probably be somewhere in the neighborhood of 70-75 mph in > 6th at approximately 2500 rpms. > Yup, that is where my OD starts to have good power, over 75 mph. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's - Gone to the rust pile... Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pi...?id=2115147590 (More Off Road album links at bottom of the view page) |
Re: ACCURATE SPEEDOMETER?
Tracie wrote:
>>> - Show quoted text - >> Oh, nevermind. I think I just answered my own question. : D >> >> I am assuming that the approximate 2500 rpms would apply to the OD >> (6th) gear as well to prevent increased engine wear and lugging?- Hide quoted text - >> >> - Show quoted text - > > Which would probably be somewhere in the neighborhood of 70-75 mph in > 6th at approximately 2500 rpms. > Yup, that is where my OD starts to have good power, over 75 mph. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's - Gone to the rust pile... Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pi...?id=2115147590 (More Off Road album links at bottom of the view page) |
Re: ACCURATE SPEEDOMETER?
Tracie wrote:
>>> - Show quoted text - >> Oh, nevermind. I think I just answered my own question. : D >> >> I am assuming that the approximate 2500 rpms would apply to the OD >> (6th) gear as well to prevent increased engine wear and lugging?- Hide quoted text - >> >> - Show quoted text - > > Which would probably be somewhere in the neighborhood of 70-75 mph in > 6th at approximately 2500 rpms. > Yup, that is where my OD starts to have good power, over 75 mph. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's - Gone to the rust pile... Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pi...?id=2115147590 (More Off Road album links at bottom of the view page) |
Re: ACCURATE SPEEDOMETER?
Tracie wrote:
>>> - Show quoted text - >> Oh, nevermind. I think I just answered my own question. : D >> >> I am assuming that the approximate 2500 rpms would apply to the OD >> (6th) gear as well to prevent increased engine wear and lugging?- Hide quoted text - >> >> - Show quoted text - > > Which would probably be somewhere in the neighborhood of 70-75 mph in > 6th at approximately 2500 rpms. > Yup, that is where my OD starts to have good power, over 75 mph. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's - Gone to the rust pile... Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pi...?id=2115147590 (More Off Road album links at bottom of the view page) |
Re: ACCURATE SPEEDOMETER?
SnoMan wrote:
> On Mon, 17 Sep 2007 08:36:28 -0700, Tracie <brainart@upstate.edu> > wrote: > >> Which would probably be somewhere in the neighborhood of 70-75 mph in >> 6th at approximately 2500 rpms. > > > Your speedo is way off.(big tires will do this) In 5th with current > tires, 2500RPM would yeild about 74 MPH and 6th (.82 OD) 2500 would > yeild about 91 MPH based on quoted tires sizes and axle ratios. > > Again you can do the math yourself > > http://www.snoman.com/HTML/axlecalc_5a.html > ----------------- > TheSnoMan.com Your site appears to be totally useless garbage. No one 'knows' their freaking tranny ratio or their t-case ratio, most do good to have their tire size and gear ratio. 'Comparing' tire sizes of old vs new to get a new speedometer reading is garbage. The old tires were 'not' certified to have the correct speed vs the gauge speed, so that is a GIGO situation. Garbage In Garbage Out. If I punch in my numbers for how fast I should be going at 2300 rpm and say my T-5 tranny in 4th is 1:1 and my Dana 300 t-case in high is 1:1 and my gears are 3.31 and my tires are 33", the 'calculator' gives me a NaN If I put in my tire size and gear ratio I get infinity for a 'new' gear ratio. Gee I thought gear ratios were set by the 'physical' gears, not by some mythical number. Care to explain? Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's - Gone to the rust pile... Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pi...?id=2115147590 (More Off Road album links at bottom of the view page) |
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