Avatar of pebbo

pebbo

Better Fuel Economy through Re-Gearing

G'day folks.

I've put bigger tyres on (35-inch Micky Thompson) and ever since my fuel economy is horrible. Do you guys think if I put my Patrol to the mechanic and get my diffs re-geared I would gain better fuel economy? It's quiet sluggish on the road and I haven't used the 5th gear for quite a while. Re-gearing would cost me about 1500 aud and I only get that through my financial adviser (my wify, lol) if this comes with an improved fuel economoy.
HillsForThrills

This is a slightly touchy subject, depending on which camp you're in... Bigger tyres, on the highway, WILL give better fuel economy at highway speeds due to the bigger rolling diameter... around town you may (or obviously have...) noticed a slight reduction in economy, due to the need for more power to turn the bigger wheels from stop/start driving... Personally, I run 35's on my GQ and I barely noticed a difference in my economy around town, but highways I can certainly see the increase (easily .5km/L possibly more...) so for me, I'm not going to bother changing ratios, as the effect on highway driving will outweigh the increase around town... By the sounds though (you say you haven't used 5th for a while...) your engine power is probably not enough to actually benefit from the larger diameter, in which case, lower gears would benefit your vehicle, for both increased economy and better torque around town, and a slower crawl speed in low-range (which is the only benefit I would get in mine... however the TD42 has enough torque that I can pretty much idle everywhere anyway, and don't really need the ultra-slow ratios...). You must bear in mind, that lowering your ratios, will actually increase the engine revs at a given speed...
Oh, and gotta ask... Where can you get your diffs re-geared for $1500...? GQ's are $1200 per end, and that's just for the actual gears, not installation... I would have thought GU's would be similar if not more...? I need a better parts shop... hehe...
ARGS

As far as I'm aware it should, it should bring your revs closer to stock so the motor won't have to run as hard pushing the bigger rubber etc
HillsForThrills

Args, mate, not arguing with ya or bein smart, but lowering diff ratios, actually brings the SPEEDO back to factory... ie: if for example (in my GQ) the speedo now reads 90 and the tacho says 2500, (assuming this is with the larger diameter tyres... the ACTUAL speed with the factory diff gears will be close to 100km/hr...)... now, lower the diff ratios and the speedo will STILL read 90km/hr and 2500rpm, but the ACTUAL speed will be back to 90... so to do 100km/hr, the revs will actually INCREASE to say, 2900rpm with the speedo now reading 100km/hr... However, the vehicle will actually have more torque at the rear wheels due to the lower gears, meaning it isn't working as hard to maintain the speed... It's a tricky subject/scenario because to LOWER diff gears, the number is higher (ie. 4.6:1 is LOWER than 4.11:1), and while the revs increase, so does the torque, and that actually helps the engine turn the wheels easier... Drag racers will attest to the difference a diff ratio can make... And it can make ALL the difference... Not sure I've explained it properly, but hopefully you can understand it a little better...
john

I have recently bought a Pajero 2800 1996 diesel I notice that I often am looking for another gear change from 5th up but not available , The revs at 110 kl limit Tas or even when at 100 are about 2600~3000 and I can see a benefit in economy and relieving the engine by keeping on hgw speed at lower revs that the engine would feel happier and my fuel economy, with and on fairly flat highway sections I can see no reason to have revs over say 2300. But naturally the gear ratios disallow this outcome
Any suggestions / comment ( current tyres Pirelli Scorpion Atr - 275/65 R17)

More from our Forum


noahjames78901234 in Members Introduction
Introduction

Hi all I'm Gry Kimlin. My first 4 wheeler was a Jeep, an ex-airforce follow me cj5 as I remember....

jendyjk in General 4WD
Road Of Fury Racing Game

Play Road of Fury for free online at While driving along the Road of Fury heavily armed hostile...

jendyjk in Members Introduction
Forum Newby

Hi AllMy name is Lea and I have a 09 JK Rubicon Unlimited and 03 TJ.  Love the Jeeps!I live on...

hasser in Members Introduction
Hi

Hi Guys, Im Adam. Id be keen on some experienced 4x4er opinions as I am in the market.Where should...

Aaron1010 in News and Updates
Which Car Can Navigate Narrow Paths And Wide Deserts With Ease?

Off-road vehicles made by Polaris consistently perform well, whether they are used on wide desert...

hasser in General 4WD
River Crossing - Do You Need A Snorkel?

I came upon this video and it really made me realise just how important a snorkel can be and just...

James227 in Feedback and Compliments
Site Is Coming Along Nicely!

What a great idea to be able to search for 'like minded' cars.. also love the clean simple...

rosydam in Do-It-Yourself
Your Latest Modifications

Hey guys, just browsing for some ideas what to do next on my truck what was your most recent...