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Old 11-01-2018
HandPants  HandPants is offline
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Hi Guys,

I'm running 31 inch tires with what i'm assuming is the standard diff gear.

i'm lucky to get over 300k's a tank.

What would you suggest as a ratio? the majority of my driving is local and highway.

Thanks.

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Old 12-01-2018
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I run 31's and still get better than 400 to a tank. Your speedo will not be reading correctly unless you have changed the speedo gear or fitted a speedo calibration device. This too will not be helping and make your figures look worse than they are. One thing I picked up a while ago was to periodically reset the ECU. disconnect both battery terminals and short the pos and neg together, make sure they are both disconnected from the battery. This will reset the ECU and it will relearn your driving habits and the tyre size effect. Sounds weird but it works. The other thing I fitted was a yellow box speedo calibrator, grate Aussie made device, that way the ECU will be seeing the correct speed and can factor that in with other inputs to manage injector duration. 31's generally don't warrant a regear and unless you can do the work yourself you are looking at a fair bit of cash. Hope this helps.
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Old 13-01-2018
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Quote:
Originally Posted by HandPants View Post
Hi Guys,

I'm running 31 inch tires with what i'm assuming is the standard diff gear.

i'm lucky to get over 300k's a tank.

What would you suggest as a ratio? the majority of my driving is local and highway.

Thanks.
depends what gearbox you have, auto, six speed, five speed, as the ratios are different

for example a 6 speed has similar rpm's at 100kph as an auto even though the stock diff ratio for a 6 speed is 3.07 and the auto is 3.73

and as pointed out, probably the speedo gear wasn't upgraded with the increased tyre size so you maybe travelling further than whats indicated on the odometer
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Old 13-01-2018
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Didn't the early TJ's from 97 till about 00 come out, (auto & manuals) with a 3.07 final drive?

If it helps, my TJ with a nv3550, running 33x10x15 KM2 and 4:10 final drive, sits at about 2100 rpm at 100 kph in overdrive - it drives well and I get good eco (upward of 500k on the open road) but I would like to go to 4:56 because the nv3550 has the tallest overdrive available in a TJ and I want more power... as you always do

Pretty sure this is based on 1 to 1 (fourth gear)


As well said by bonza, unless you can do most of the work yourself and pick up the parts cheap, changing ratios to save fuel is a bit like Jeep and economy in the same sentence.

Choosing a skinny wheel and tire combination that weighs as little as possible when needing new tyers can help, be fastidious! research the actual diameter, width, and weight from as many different manufacturers of 31" tyers as you can because it can vary a lot! - you'll get better eco from lightweight skinny and obviously, the smallest diameters 31" tyers available but how you use and drive you TJ should influence what you purchase.

Frequent servicing, driving under 100 on the freeway, quick shifting the manual, together with lightweight skinny alloy wheel and tire combinations make a noticeable difference for me.
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Old 14-01-2018
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Yup wouldn't waste the cash on a regear for 31s. My brother on 31s on a 2000 tj (manual) was getting well over 400 on the highway. He did drive it for econ, when not on the traccks. i.e. keep revs down, stay under 100 (basically what above have been saying).

Id adjust driving style or look to other issues. you'll not get eco back from a regear at 31s given the cost.



Spend the cash on some better mods Or go 33s and bang 4.56 in it (or 4.11 if you're fuel conscious )
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