If it works for your needs, there's no reason to regear it. I know people that run 33s and 3.07 gears and don't mind it. I had them and swapped in some 4 cylinder Jeep axles with 4.10 gears. Total cost was $300 for both axles.
What RPM should my 4.0 be running at?
- Thread starter Eddie Greenlee
- Start date
Mudflat
TJ Enthusiast
I'm thinking you don't know how gears work, at all. There is no slippage or clutch between the side gear in the differential and the wheel lug studs that the tire mounts to. If the gear ratio is 1-1 or 100-1, that is exactly what it means, the driveshaft turns the pinion 1 time or 100 times to turn the ring gear one full revolution. If the ring gear turns one full revolution, that means the tire is also turning 1 full revolution regardless of its size.Maybe to you? my 3.07,s with my 6 speed I Change at the revs that sound right and that's just over 2000 RPM, If I gun it I change at 2500RPM no higher because no higher is needed.
Miss matched wheel and tire size to gear ratio is the problem not gears installed at factory!
The lack of 3.07 power on bigger tires is because 3.07 revolutions of a drive shaft doesn't turn an oversized tire one full revolution like it does a recommended max tire size, its that simple.
Flame away lol
Regearing will reduce the load on the engine and will also reduce the shift RPM on your transmission. With automatics lower load means lower shift point. If you are asking about getting the RPM higher a re-gear isn't going to do it as far as day to day shift points. All it's going to do is increase the RPM on the freeway. Get the tires first and see how you like it, it's not going to damage your engine in any way. After you drive it for a bit consider gears if you want more power.
Last night I did another search for used 31" tires and found an okay set of four for $275. Mounted them this morning and just got back from a test drive. I couldn't detect any difference related to gearing. I will run these for a while before I start into the gearing change discussion again.
Not 100% sure about this.
Tire size and gearing are factors to consider.... meaning it "isn't one size fits all."
A local example.... 215 north... i run at 70mph in 5th and/or 6th gear... engine purrs at 2200ish.
Torque is readily available.. no lag.
It would be a hard sell to convice me I am lugging my engine.
I said I like MY TJ to have those rpms due to my particular tire, transmission, and engine size combination. I wouldn't need those rpms with 30" tires or a 7L V8 engine.
3,07 diff gears turn a 28 or stock tire one revolution to 3.07 turns of the drive shaft!
I mentioned nothing about slippage? 3,73 gears takes 3.73 rotations of a drive shaft to turn a stock wheel one revolution and so on! put 33,s on a 3.07 gearing and it doesn't turn the full rotation causing it to be sluggish.
Again, you don't know how gears work. 33's on 3.07 gearing still turn exactly 1 full revolution for every 3.07 turns of the driveshaft, as do 35's, 28's, or any other size you can bolt up and any size you can't. You could hack the sides of the tub off, build and adapter and bolt up a 60" tall tractor tire and it would still turn exactly 1 full revolution for every 3.07 turns of the driveshaft. The only way it could not do that is if there were some magical mechanical connection between the differential and the tire and there isn't. There is nothing about a larger tire that will let it turn less or more than the gear ratio dictates.
The reason it is sluggish is the larger tire is effectively a longer lever which creates a mechanical advantage against the gears, not in favor.
You do however get points for the most creative confusion about how things work that I've encountered in a very long time.
Jeep released the TJ Rubicon with 31" tires and 4.11 gears as "stock". I'd guess their engineers probably did a fair amount of testing and research to land on that ratio. If you are planning to stay at 31", 4.11 is probably your best bet. If you think you'll get the itch to increase to a larger tire size later, you might be better off waiting to re-gear until you decide on what size that is.
Pauliewiseguy
New Member
Pauliewiseguy
New Member
My guess would be because we have NA engines that use atmosphere pressure to get their air and at higher elevations the air is thinner meaning the O2 sensor is going to sense less air being pulled in therefore the ECU is going to give less fuel to keep the air fuel ratio correct. This also means we have less power at higher elevations.
Less air, less power. Also I think there's something to the slope... You use almost no fuel on those long descents which more than makes up for the extra you use going up. My LJs best tank ever was one where the second fill up was 5,000 ft lower than the first.
I think it doesn't have to just depend on the O2 sensor though. I think the older systems use a reading from the MAP sensor when you turn on the key before starting the engine and log it as the barometric pressure for that drive. Then if you start the engine and gain or lose thousands of feet, that's when your O2 sensors will have to adjust for it.
Re visited! If I change gears at 3000 RPM or above I am going over the speed limit before 4th around town.
admittedly our speed limit is low 60KPH 50KPH in built up areas and 40KPH school zones.
recently got another $100 fine for 4KPH over 60. Lucky you guys haven't got all the speed cameras we have.
admittedly our speed limit is low 60KPH 50KPH in built up areas and 40KPH school zones.
recently got another $100 fine for 4KPH over 60. Lucky you guys haven't got all the speed cameras we have.
Although I agree with you I think you are missing the point of his misunderstanding......what he fails to realize is that while the 3.07 does turn any size tire one revolution for 3.07 turns of the drive shaft, the effect work (in this case the distance traveled) increases with tire size. In other words, a 30" diameter tire travels 94.2" while a 35" tire would travel 109.9" for one revolution........
Defending idiots is not a good look on you. Read what he stated again, there is nothing to do with distance travelled.
LOL, I, Sir, am certainly NOT defending him, merely trying to give a possible perspective of his completely bass akward thinking. I agree, distance traveled was never mentioned in his post, hence his ignorance to how the gearing actually works.
Oh, and thank you for the compliment, I think..... LOL