4bangerjp.com
General Forums => The Mess Hall => Topic started by: lumpylowell on November 08, 2014, 07:20:36 AM
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I just put 245/75-16" Goodyear MT/R's on my 95 YJ and i'm wondering if i need to change my speedo gear? Q-tec sells them but i need to know how many tooth gear i need. I think that my new tire size in inches is 30X9.65-16 according to http://www.crawlpedia.com/tire_size_converter.htm
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http://4bangerjp.com/forums/index.php/topic,731.0.html
I've bought mine from the Dealer for around $12 but they don't carry many of them anymore. I had to spend a lot more to buy my past one from AA. http://www.advanceadapters.com/search_all.php?keywords=speedometer+gear&search=Go
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Last time I had a Q-tech catalog in front of me, there was a little graph that showed if you have 'this' gear ratio and 'this' size tire then you need 'that' speedo gear. I think they are worth the time and trouble. It keeps all the computers from 'lieing' to each other.
'98 TJ, 2.5L, auto, 3.73 gears, 31/10.50 T/As mileage was 12.1 mpg. Speedo gear and TB spacer and the mileage is 17.9 mpg. Call me a liar for the fractions, but that is a 50% increase in mpg.
Hunter
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Last time I had a Q-tech catalog in front of me, there was a little graph that showed if you have 'this' gear ratio and 'this' size tire then you need 'that' speedo gear. I think they are worth the time and trouble. It keeps all the computers from 'lieing' to each other.
'98 TJ, 2.5L, auto, 3.73 gears, 31/10.50 T/As mileage was 12.1 mpg. Speedo gear and TB spacer and the mileage is 17.9 mpg. Call me a liar for the fractions, but that is a 50% increase in mpg.
Hunter
where you using the shown mileage on your odo to calculate the mpg? or were you adjusting for the error (say you travelled 200miles based on odometer but actual was 240 by calculating for the error). if the former then the comparison is not relevant as it was not real mileage but shown mileage with the inherent error in it, if the latter I doubt 50% is an actual increase / real world scenario, it could show more miles than you are travelling and going to the other end of the spectrum, that result and increase in efficiency would yield a bsfc better than the most efficient diesel engine :)
Maybe a combination of both (got better due to the correct impulse per mile and you weren't adjusting for the actual miles travelled)
Dakota digital has a box you can install and adjust the freq of the impulses to provide compensation for tires/gears/etc, makes it easier as if you change your tires or gears again you only have to re-calibrate the box and not look for another speedo gear (which in most cases is not dead nuts accurate anyway).
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The chats may no be 100% accurate depending on your setup. In my YJ the transfer case has the "wrong" gear but the speedometer is right on compared to a GPS.
So you may require some trial and error.
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The chats may no be 100% accurate depending on your setup. In my YJ the transfer case has the "wrong" gear but the speedometer is right on compared to a GPS.
So you may require some trial and error.
my odo was fine with 4.88 and 33s, now with 35s my speedo is accurate and odo shows less than distance travelled, though what the speedo shows is irrelevant for the PCM which goes by impulses/mile so replacing the gear is a good thing.