Gear Ratio & Tire Size Chart
08-21-2009, 07:13 PM
#1
JK Super Freak
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Gear Ratio & Tire Size Chart
I just figured I'd post this because I don't believe we have something like this on the forum -- if we do, whoops! I missed it. Anyway, I hope this helps everyone decide on gears a bit easier. Maybe WOL or one of the Admins will put this in the FAQ...
http://www.4lo.com/calc/geartable.htm
http://www.4lo.com/calc/geartable.htm
08-21-2009, 08:11 PM
#2
JK Super Freak
I just figured I'd post this because I don't believe we have something like this on the forum -- if we do, whoops! I missed it. Anyway, I hope this helps everyone decide on gears a bit easier. Maybe WOL or one of the Admins will put this in the FAQ...
http://www.4lo.com/calc/geartable.htm
http://www.4lo.com/calc/geartable.htm
08-21-2009, 09:10 PM
#3
JK Super Freak
Automatic Transmission
Gear Ratios 1st 2.84
Gear Ratios 2nd 1.57
Gear Ratios 3rd 1.0
Gear Ratios 4th 0.69
Manual Transmission
Gear Ratios 1st 4.46
Gear Ratios 2nd 2.61
Gear Ratios 3rd 1.72
Gear Ratios 4th 1.25
Gear Ratios 5th 1.00
Gear Ratios 6th 0.84
So, for a good idea how one tire/gear option stacks up against another, the chart gives a pretty good indication. It doesn't attempt to give an optimal solution for every case, nor would I expect it to.
Really? I guess you haven't been reading some of the sponsoring manufactures recommendations on this forum. Unless, of course, you don't consider them experienced. Personally, I think your statement comes off as being a bit arrogant. You posted some great advice. Too bad the rest of the post comes off as "Jane, you ignorant slut".
08-21-2009, 09:35 PM
#4
JK Enthusiast
What about running 33's with the 4dr 6 speed? I'm considering finding someone who has 3.73 gears they've taken out and trying to get them used on the cheap. Right now I've got 3.21 gears and starting off in first it seems really really weak and 6th gear on the highway is all but useless because of lack of power. Would the 3.73's be worth messing with putting in? Would I notice much difference? I don't have money to buy new gears, carriers, lockers, etc right now just wanting an improvement.
Last edited by Rtwill78; 08-21-2009 at 09:42 PM. Reason: Left out the question.
08-21-2009, 09:36 PM
#5
JK Enthusiast
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I am not getting into who is right or wrong here, but it is misleading. if you look at the chart it says that 4.11 and 31's are ideal. well the TJ's (2.5 liter) came with FACTORY 4.11 and 29's....Rubicon 4.11 and 31's VERY BIG DIFFERANCE. and the JK is the same. My 07 Unlimited X came with 4.11 and 29's and now I am running 4.11 and 35's. That is a huge difference and I think the 6 speed and 4.11 is perfect for 35's. And yes we use our JK alot off road in the big rocks. So i feel it is safe to say that the chart is misleading customers........
but your claim of 64 RWHP i think might be off a little too
2007 JK Unlimited 6 Speed 4.10 Gears
3 Inch BDS Lift
35x12.5x16 Yokohama Geolander AT/S
16x8 Cragar Soft 8 Black Steel Wheels
Custom front Winch Bumper from RoundStar OffRoad
Mopar Offroad Rear Bumper
Oilpan/Tranny skid Plate by Skid Row
JKS Quicker Disconnects
Skyjacker Brake line extenders
Skyjacker Adj Rear track bar
High Clearance Adj Front Lower Control Arms by RocKrawler
RocKrawler Front Lower Control Arm Mounting Bracket/Skid Plates
Warrior Products Rear Safari Doors
Plenty of ROCKRASH
but your claim of 64 RWHP i think might be off a little too
2007 JK Unlimited 6 Speed 4.10 Gears
3 Inch BDS Lift
35x12.5x16 Yokohama Geolander AT/S
16x8 Cragar Soft 8 Black Steel Wheels
Custom front Winch Bumper from RoundStar OffRoad
Mopar Offroad Rear Bumper
Oilpan/Tranny skid Plate by Skid Row
JKS Quicker Disconnects
Skyjacker Brake line extenders
Skyjacker Adj Rear track bar
High Clearance Adj Front Lower Control Arms by RocKrawler
RocKrawler Front Lower Control Arm Mounting Bracket/Skid Plates
Warrior Products Rear Safari Doors
Plenty of ROCKRASH
08-22-2009, 04:11 AM
#6
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I absolutely LOVE when someone can defend their position with facts and numbers........hell, you even did it with graphs and quotes! You are my new hero planman! 
08-22-2009, 06:18 AM
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JK Junkie
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The table ignores the torque and horsepower curves of different engine designs. It ignores types of use--towing, elevation above sea level, driving steep mountain passes, etc. It ignores the difference between a manual and an automatic in that automatics have some slippage due to the torque converter.
It's very much conceivable that with changes in elevation and altitude that your power requirements are 20-30% higher than what mine and some others are. You can also probably get away with burning a lower octane because of elevation.
What you would encounter in your every day driving, 3,000+ feet and grades of 3% or more requires twice the power of what I need on a drive from home to minneapolis over 700 miles away.
So here's a little comparison of the power needed for planman and I to run our jeeps in our own backyards at highway speeds of 70mph.
planman at 3,000 feet elevation, dealing with lets say 3% grades on the highway which is probably on the low side.
The power needed to maintain a 70 mph speed is 85 whp, which presents itself at about 2500 rpm.
jpop (I love talking about myself in third person) at 600 feet elevation, primarily ungraded flat highways.
The power needed to maintain a 70 mph speed is 40 whp, which presents itself at about 1500 rpm.
Obviously other factors come into play such as temperature, wind and humidity which would, as a percentage of additional power needed, more greatly effect someone closer to sea level. Therefore you need a lot more overhead to cope with maintaining speed. Even so, there is a vast difference in what it takes to move our vehicles through their existing environments.
I think the biggest caveat in all of this is the premise that spinning at higher rpm ranges is going to adversely effect fuel economy or engine wear. The need to produce less power per stroke minimizes additional engine wear and controlling manifold pressure by the throttle blade doesn't make fuel consumption increase by rpm range alone. On my vehicle and under my driving conditions I can run in 5th or 6th with a couple percent difference in economy despite there being nearly a 20% difference in driveline ratio. That is why when it does come time to move to a steeper gear set I totally subscribe to planman's personal experience and theory of "don't fear the gear" and you are far better off being over geared than under geared.
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08-22-2009, 06:47 AM
#8
JK Junkie
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Always love to hear replies from an engineer.
Wow! More than 2x as much whp needed at 2400 feet higher elevation, with only a 3% grade...
So, what whp do I need to maintain 70 mph at 4500 feet above sea level on a 6% grade? (Very common on I-90 between Billings, Bozeman, Butte, & Missoula.)
Wow! More than 2x as much whp needed at 2400 feet higher elevation, with only a 3% grade...
So, what whp do I need to maintain 70 mph at 4500 feet above sea level on a 6% grade? (Very common on I-90 between Billings, Bozeman, Butte, & Missoula.)
Now you need to tell me if your real world experience matches that.
08-22-2009, 08:10 AM
#9
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Gearing with 35s or 37s
That chart is very misleading because it is based on a manual transmission gear ratio of 1.0. It leads people to under gear their rigs.
Quote: These calculations are assuming a manual transmission with a 1:1 ratio
Automatics have a 4th gear (overdrive) ratio of 0.69.
6 speeds have a 6th gear ratio of 0.84.
The experienced jeepers (who have driven different setups with different gear ratios) nearly always give unanimous answers:
With a non-supercharged engine:
An automatic on 35s or larger should run 5.38s if they drive mountain passes, live at higher elevations, tow anything, or ever plan to upgrade to 37s--especially if they drive a 4 door.
An automatic on 35s that lives and wheels at low elevations, doesn't drive steep grades, or doesn't tow anything should run 5.13s.
A 6 speed on 37s should run 5.13s, and maybe 5.38s if they don't spend much time over 65 mph.
A 6 speed on 35s that is either a 4 dr, or drives at high elevations, tows, or drives steep grades should run 5.13s.
A 6 speed on 35s that is a 2 door and will never upgrade to 37s, or a 4 door that lives and wheels at low elevations and almost never tows should run 4.88s.
There is very minimal debate about this among guys who have had the experience of driving different setups with different gear ratios. They guys who suggest otherwise usually have never driven or experienced different gear ratios.
The shops discourage the 5.13 and 5.38 gears because they don't understand our engines only produce 64 rear wheel horsepower 169 torque at 2000 rpm, at 2500 rpm they produce 88 horsepower and 184 torque, and at 3000 rpm they produce 107 horsepower and 188 ft lbs of torque.
They don't understand that automatics have a 4th gear ratio of 0.69. These mini-van engines need higher rpms to produce enough horsepower and torque to turn heavy 35"+ tires--especially up steep freeway grades or at higher elevations.
Okay, rant over. It is just that every time I see that table on quadratec, 4wd, and other websites, it reminds me of all the folks who wasted $1000-$1500 to gear to the wrong gear ratio--then they believe they need to spend more money on engine upgrades (superchargers, cold air intakes, headers, etc.) because they are not satisfied with the weak performance of our engines at rpms under 2500-3000. They don't even get that the table is based on a 1.0 transmission gear ratio for a manual transmission. They could have almost doubled their rear wheel horsepower if they had just properly geared their rigs to run 3k rpm at freeway speeds.
Quote: These calculations are assuming a manual transmission with a 1:1 ratio
Automatics have a 4th gear (overdrive) ratio of 0.69.
6 speeds have a 6th gear ratio of 0.84.
The experienced jeepers (who have driven different setups with different gear ratios) nearly always give unanimous answers:
With a non-supercharged engine:
An automatic on 35s or larger should run 5.38s if they drive mountain passes, live at higher elevations, tow anything, or ever plan to upgrade to 37s--especially if they drive a 4 door.
An automatic on 35s that lives and wheels at low elevations, doesn't drive steep grades, or doesn't tow anything should run 5.13s.
A 6 speed on 37s should run 5.13s, and maybe 5.38s if they don't spend much time over 65 mph.
A 6 speed on 35s that is either a 4 dr, or drives at high elevations, tows, or drives steep grades should run 5.13s.
A 6 speed on 35s that is a 2 door and will never upgrade to 37s, or a 4 door that lives and wheels at low elevations and almost never tows should run 4.88s.
There is very minimal debate about this among guys who have had the experience of driving different setups with different gear ratios. They guys who suggest otherwise usually have never driven or experienced different gear ratios.
The shops discourage the 5.13 and 5.38 gears because they don't understand our engines only produce 64 rear wheel horsepower 169 torque at 2000 rpm, at 2500 rpm they produce 88 horsepower and 184 torque, and at 3000 rpm they produce 107 horsepower and 188 ft lbs of torque.
They don't understand that automatics have a 4th gear ratio of 0.69. These mini-van engines need higher rpms to produce enough horsepower and torque to turn heavy 35"+ tires--especially up steep freeway grades or at higher elevations.
Okay, rant over. It is just that every time I see that table on quadratec, 4wd, and other websites, it reminds me of all the folks who wasted $1000-$1500 to gear to the wrong gear ratio--then they believe they need to spend more money on engine upgrades (superchargers, cold air intakes, headers, etc.) because they are not satisfied with the weak performance of our engines at rpms under 2500-3000. They don't even get that the table is based on a 1.0 transmission gear ratio for a manual transmission. They could have almost doubled their rear wheel horsepower if they had just properly geared their rigs to run 3k rpm at freeway speeds.
For me that's one of the best summaries I've read on this subject. The rest of this thread adds even more.
08-22-2009, 08:33 AM
#10
JK Super Freak
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Just wanted to say, glad to see some informative responses to this thread. I personally don't know much about gears. So I can admit that the graph may be a little misleading as the more experienced guys claim it to be. But it does give me a good idea of what I should be running around for my set up.