Most people would say 27 because 31" tires on the chart are normally close to that. I'd personally never change a gear without pulling what I have and counting the teeth, measuring how far off the speedometer is now with GPS and then doing the math.
I know its wrong based on my mileage and speedometer vs speed on navigation apps. It used to be off by around 10% and then I got these tires and its more like 5%. I just figured I might as well do it since I'm going to change the fluid in the case soon.Most people would say 27 because 31" tires on the chart are normally close to that. I'd personally never change a gear without pulling what I have and counting the teeth, measuring how far off the speedometer is now with GPS and then doing the math.
Keep in mind that the difference between 27 and 28 is about 3.5% so you're not going to get it exact. I think the fluid level is below the gear sitting level so it's not going to spill out or anything. If you're within a five percent already you really should find out what you have, those gears aren't cheap. It's probably stock but that's allot of work only to overshoot the wrong direction 5%.I know its wrong based on my mileage and speedometer vs speed on navigation apps. It used to be off by around 10% and then I got these tires and its more like 5%. I just figured I might as well do it since I'm going to change the fluid in the case soon.
Haven’t you just answered your own question?What’s the consensus on rounding up or down? I went from stock 3.73 on 215/75/15 to KO2s on 285/70/17 and can’t figure out if I need a 31 or 32. I’d rather be doing 60 and have it display 65 than other way around.
If I'm thinking about this the correct way, wouldn't that then mean your odometer would be going higher faster?? In a 2-hour trip, you'd then have 10 extra miles on the odometer that you never really drove. Then your TJ looks older than it really is ;-)What’s the consensus on rounding up or down? I went from stock 3.73 on 215/75/15 to KO2s on 285/70/17 and can’t figure out if I need a 31 or 32. I’d rather be doing 60 and have it display 65 than other way around.
More speedo gear teeth will slow the reading on the gauge down. So you would probably want to err on the 32 tooth side of things. Plus as the tires wear down your speedo will become more accurate.What’s the consensus on rounding up or down? I went from stock 3.73 on 215/75/15 to KO2s on 285/70/17 and can’t figure out if I need a 31 or 32. I’d rather be doing 60 and have it display 65 than other way around.
1 tooth is roughly 2-3 mph at highway speed so it would be close either way. Maybe more accurate on 32 over time but no big deal. Talking minimal difference long term.I went with a 31 and based on gps it’s pretty accurate.
Agreed, 285/70/17 calculates out at 32.7 I think I was good either way and close enough based on tire wear and general margin of error.1 tooth is roughly 2-3 mph at highway speed so it would be close either way. Maybe more accurate on 32 over time but no big deal. Talking minimal difference long term.
You are correct, but the other way has potential for speeding tickets. From the factory most vehicles are calibrated to read about 2mph higher than actual on the highway. So technically most all vehicles have more miles on the clock than they actually drove.If I'm thinking about this the correct way, wouldn't that then mean your odometer would be going higher faster?? In a 2-hour trip, you'd then have 10 extra miles on the odometer that you never really drove. Then your TJ looks older than it really is ;-)
Excellent info but I must be missing something or just not smart enough to catch on. Bought an ‘02 TJ that has 33’s on it. Build ratio and the tag both say 3.07 however that’s just a dash on your chart. What am I missing?
Excellent info but I must be missing something or just not smart enough to catch on. Bought an ‘02 TJ that has 33’s on it. Build ratio and the tag both say 3.07 however that’s just a dash on your chart. What am I missing?
Admittedly I have not checked speed with GPS but I’m fairly certain it’s not correct at highway speeds.