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Topic Review (Newest First) 
05012013 02:38 PM  
SuicideSaints  Yeah, that 4th gear is key. I messed up the calculation when I first was trying to figure my rig out. I am pretty sure you are sitting on the stock 3.73 gears.  
05012013 02:27 PM  
turnbull  OHHH. That explains everything. I have been using the RPM value from 5th gear, but I was using the correct speed (74 MPH reads as 60 on my speedo). I don't know the RPMs at 4th gear. But my guess is that the my gears are 3.73, possibly higher. That is fine by me, and so I do not plan on regearing anymore.  
05012013 02:08 PM  
SuicideSaints  Sorry one more thing. This equation only works if you are in 4th gear when you take the rpm reading. In 4th gear the ratio is 1:1  
05012013 02:06 PM  
SuicideSaints  Ok, I see the equation you used, it is the correct equation. But, your speedometer is off on your jeep and that is not the true speed your jeep is traveling at that rpm. So that is throwing your calculation off. You will need to know true speed using GPS.  
05012013 02:03 PM  
SuicideSaints  I am not sure how you came up with that gear ratio? How did you do it, with the math equation? If you are using the (rpm x tire diameter) / (mph x 336) you have to make sure you are reading your true speedo on the gauge. Unless you have recalibrated the gauge or using gps speed that equation is going to be off and you will incorrectly calculate the gear ratio. I would say there is no way you have that gear ratio. I would say you have 3.73 gears. I would agree with everyone else saying that get a 33 in tire and not two, the difference between 3035 is huge. I only lost about 12 mpg when I regeared and went to a 35 in tire. I was pulling in about 17 now with 6+ in lift and 35 in KM2s I am averaging 15. I regeared to 4.56 and love it, 4.88 would be a good choice for 35, if you go with 33s 4.56 is a good choice.  
05012013 02:01 PM  
kyjeep 
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05012013 01:59 PM  
turnbull 
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05012013 01:53 PM  
Jerry Bransford  I believe you would be disappointed with performance no matter what ratio you choose to try to work with both 30" and 35" tires. Those tire sizes are just too far apart for any ratio to be even a good compromise. I'd pick one tire size to live with & gear for that. Or at least two tire sizes that are closer together.  
05012013 01:51 PM  
turnbull 
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RPM * Tire Diameter/(MPH * 336) So the RPM is ~2150, MPH is ~74, and Tire Diameter is 35. You can check the numbers yourself but I'm pretty sure I did it correctly. Unless this is the wrong equation of course. And yea, 30" tires will look funny, but I am still keeping the 35s so I need the lift still. 

05012013 01:49 PM  
turnbull 
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I don't see why I would need such a high gear ratio for offroading. It's not like i'm gunna be driving in 5th gear offroad. Plus I already have plenty of power in lower gears. Quote:


05012013 01:43 PM  
PiePuncher  3.07 turning 35's.... U sure u have 3.07. Your jeep would be a slug with 35's. A smaller tire, less lift, would increase gas mileage... Also, if u r running 35's, won't little tires with lift look funny? Reading 530ktm post got me thinking and there is lots wrong w the whole picture..  
05012013 01:30 PM  
530ktm  You can not possibly know what your gas mileage is with out having the speedometer calibrated accurately and you already said it is a mile off. Also, going from 35 to 30 inch tires is a huge difference. If you do any kind of off road driving you will not be very happy with anything but 4.88 gearing running 35 inch tires. And forget driving on 30 inch tires with that gearing. Not sure what you are trying to accomplish here but have you thought about going somewhere in the middle and run 33 inch tires and gear properly for that set up, like 4.56 gearing. This will run great on road and off road. I do not see the benefit of changing from 35's to 30's for any reason.  
05012013 01:22 PM  
PiePuncher  I would get 4.10/4.11. It will increase your acceleration and you will still have a good top speed. It will also allow you to increase your tire size quite a bit if wanted. There will b a big difference in 3.07 and 4.10/4.11.... Is there not a tag on your differential that states what your gearing is??  
05012013 12:36 PM  
turnbull 
I thought the same. That's one reason why I am confused. I wish I could just check, but I can't so I just did the math and came up with ~3.07. So that is the optimal gas mileage range? 

05012013 12:13 PM  
SinfulDragon  I thought the D44 came with 3.73 or better gears...  
05012013 12:04 PM  
Gunner  My guess is your going to want to be some where in the 2250 to 2400 rpm cruise range on your 30 inch tires. Pick the speed you drive and gear accordingly.  
05012013 11:52 AM  
turnbull 
advice on gearing So first let me start off with what I know for certain: I have an '04 Wrangler with the 4.0L, 5speed manual, D44 rear, and 35" tires. And here is what I think I know: I am running this on a 3.07 gear ratio. I don't have my Jeep right now and I won't have access to it for about 2 more weeks, so I can't check the rear diff. However, judging by the RPMs vs. MPH I got, I figured it must have 3.07 gear ratio. By the way, I bought it like this, so no hatin At around 2150 RPMs, the speedometer reads 60 MPH, but since the speedometer is synced to stock tires, I am actually driving around 74 MPH. Honestly though, I can maintain speed pretty well in 5th gear, even on slight grades. So I was thinking about regearing, since I have seen suggestions for 4.88 gears for 35s which is significantly higher than what I have. But one thing to note is that I will be getting 30" tires for highway driving, and most of my driving will be done on those tires, so 4.88 gears wouldn't really make sense. I was taking a look at this chart to get an idea of what gear ratios to go with: Tire to RPM Ratio Chart  jeepfan.com I was thinking about 3.73 gears, since I figured that would be a good balance between 30" and 35" (with more favor towards 30" since they will be used more), and I know that was a stock option for Jeeps anyway. So my question is, how will increasing my gear ratio to 3.73 affect my mileage for both sets of tires (30" and 35")? Will it increase or decrease? Right now I am getting ~1516 MPGs with the 35s (I don't have 30s yet). According to the chart I posted, the yellowhighlighted RPMs indicate "better gas mileage," but does this mean optimal gas mileage or just better than "factory ratio"? Because if it were optimal gas mileage, I don't know why 3.07 gears would even be an option since it is not even close to the optimal mileage. 
