Lower Gear ratio better mpg?

[l.groves]

OK. Thats it! I'm getting a new ring and pinion set. Yes I know I will need two sets but mine is only 2wd unless put into 4wd manually. I get 15-17 mpg city. I'm thinking down to 3.20's any suggestions?

[Triathlete]

First off you will find that there are only a couple options when it comes to R&P's for the VX. Secondly these gear sets are very rare and hard to find. Unless you are running a different size tire I doubt if you will see a significant change in MPG.
You say you are only 2 wheel drive? Have you disconected the TOD? Removed your front drive shaft? Manual front hubs? If none of this has been, then you are not 2 wheel drive (unless you have an imported JDM model). When not in 4lo the TOD splits torque between rear and front as needed when wheel slippage is sensed.

[PK]

Welcome to the forum.
That is an interesting first post there my friend.

Couple of points -
First up - 15 - 17 MPG city is damn good for one of these.
You don't mention what size tyres you run, or what you use the VX for, but if you are going higher gearing, then I guess you don't offroad, and you run standard tyres??

Second - if you only change one diff, don't ever put it in 4wd, because you will break something.

As for ratios, sorry but I don't know of any higher gear sets for our diffs. Others might, and I am sure they will chime in.

You could try searching the forum for "diff ratios" etc.

Regards

PK

[l.groves]

I drive on 255/55 18's. I dont know exactly why I drive in 2wd only since it was that way when purchased. I jumped the check wires a while back and it indicated a problem with a control switch or unit or something under the tranny lever in the middle. I tested it in the dirt and sure enough that is exactly how it works. 2wd in 4H and 2 rear wheels lit up on the TOD display. 4LOW and I get 4LOW with all four wheels lit up on the TOD display. I've been driving it this way for a year or two and seems to have had no problems other than that dang blinking light. So I refinanced the house and now I can do some other things like put a turbo kit on my MR2 and try some new gears for the VX. I checked some sites and found that the ring/pinion is a 8.5 10 bolt as used on some other Jeep models and GM models. Man you guys ask alot of questions.

[Triathlete]

You actually have a 12 bolt on the rear, 10 bolt on the front.

[PK]

I drive on 255/55 18's. I dont know exactly why I drive in 2wd only since it was that way when purchased. I jumped the check wires a while back and it indicated a problem with a control switch or unit or something under the tranny lever in the middle. I tested it in the dirt and sure enough that is exactly how it works. 2wd in 4H and 2 rear wheels lit up on the TOD display. 4LOW and I get 4LOW with all four wheels lit up on the TOD display. I've been driving it this way for a year or two and seems to have had no problems other than that dang blinking light. So I refinanced the house and now I can do some other things like put a turbo kit on my MR2 and try some new gears for the VX. I checked some sites and found that the ring/pinion is a 8.5 10 bolt as used on some other Jeep models and GM models. Man you guys ask alot of questions.

Don't worry about the questions.
Remember, on this site you are a newbie, and we have no idea of your mechanical expertise, driving habits, long term goals etc.
So when you ask for our advice, we need to ask questions so that the advice we give you is accurate and relevant.

For instance, we now know you are driving on one of the smallest diameters tyres that could be fitted to the VX, and possibly the easiest, cheapest options for you would be to buy larger tyres. Especially if your tyres are getting worn anyway.
Your tyres are about 29" diameter.
Most of the people here run 31 - 35" dia.
Is this a feasible solution??

FWIW anything over about 32" you have to do a little bit of trimming to the front wheel wells.

Anyways, sounds like you know what you are doing.

PK

[Ascinder]

I hate to burst your bubble, but I think what you are referring to is the GM "corp" 10 bolt. It is not the same as the isuzu Corp 10 bolt. They aren't interchangeable. Also, our 10 bolt is up front, so you'd be trying to hook up 4wd in that case to save gas mileage..... As Triathlete posted, our rear is a 12 bolt isuzu. You really won't save a ton of money(mileage) going to lower gears, unless you have either excess torque or horsepower either. If you could get used to the VX driving like an anemic shadow of itself, I'd say go for it, but you'd be pulling it out of the powerband it was designed for. To get the same speed using higher gearing, you'd be lugging the engine. It was mentioned earlier in this thread that we don't know your specifics, so maybe you've already thought all this out, so if I were you, I'd see what gears were made for ISUZU Corp 10 and 12 bolts and then take a look at both the pros and cons before I went and did it. It was also mentioned that we don't know your degree of mechanical skill, but I'll just throw out there that setting up a ring and pinion isn't done with a set of wrenches and a lazy Sunday afternoon. Shops charge a decent amount of coin to set them up because they require some special equipment. As I said, you may already know all this, but then agian, maybe you don't. Just throwing in my two cents.

[Riff Raff]

Thanx PK, you're right on target. The main problem is the tires-- you're running 255/55R18 (29" O.D.) which are smaller in diameter than the OEM tire of 245/60R18 (29.5" O.D.). Thus, your current smaller diameter tires are rotating 1.8% more than OEM causing your VX to consume more fuel (less MPG) for the same distance traveled.

Instead of changing the differential ratios, a better solution for more Highway MPG is to go to a tire that meets three(3) criteria:

1. Must be "tall" in O.D. between 32" -- 35" O.D. to act like a transmission Overdrive thereby reducing engine RPM's (saving fuel) for the same given forward speed of travel.
2. Must be "narrow" in width to create less drag/rolling resistance. The skinnier, the better.
3. Must be "lightweight" to reduce unsprung weight and use less fuel from standing start/launch.

Here are some optional tire sizes that meet the above criteria (tall, narrow, lightweight):

P255/70R18 (32.1" O.D./35 lbs) - bolt-on perfect with OEM rims.
P265/70R18 (32.6" O.D./44 lbs) - slight trimming required.
P275/70R18 (33.0" O.D./46 lbs) - more trimming required. (recommended tire: BFG - Rugged Trail)

To minimize fitment problems, utilize your stock OEM 18x7 rims for the above listed tires. Use only "P"-series tires (aka Passenger/P-Metric) which are lighter in overall weight, and stay away from heavy "LT"-series (Light-Truck) tires.

For the absolute extreme gas saving tire, you could use:
35/10.0-15 (35" O.D./48 lbs) - lifting required. (recommended tire: MickeyThompson - Baja Pro, which is a Sand-Rail tire and not DOT approved for the street. Use 15" super lightweight CenterLine brand wheels to keep weight to a minimum)

Focus on changing to a taller O.D. of your tires, not the gearing in your differentials. Then drive your VX like you are hauling very fragile eggs; be featherlight on the gas pedal, and let off the gas pedal early before coming to a stop. You'll be amazed at how much your MPG will improve.

[Triathlete]

(recommended tire: BFG - Rugged Trail)

Everyone I know that has bought these tires has complained about how quickly they wear. Just a FYI.

[Ldub]

OK. Thats it! I'm getting a new ring and pinion set. Yes I know I will need two sets but mine is only 2wd unless put into 4wd manually. I get 15-17 mpg city. I'm thinking down to 3.20's any suggestions?

Thanx PK, you're right on target. The main problem is the tires-- you're running 255/55R18 (29" O.D.) which are smaller in diameter than the OEM tire of 245/60R18 (29.5" O.D.). Thus, your current smaller diameter tires are rotating 1.8% more than OEM causing your VX to consume more fuel (less MPG) for the same distance traveled.

AND...

Unless you're already factoring in 1.8 - 2% less miles on the number of miles driven per tank, you're not getting 15-17 mpg...

[l.groves]

Finally a non bash the new guy information. Thanks Riff Raff I apreciate your knowledge. I must say I am still a little stooped on the 12 bolt rear gears. Non of the listings I found mentioned this and I am now having a very hard time finding any fitment for 12 bolt. My tires are pretty new and in great shape so tire change to me would not be beneficial in the long run since I will still end up with the same stock specs. I want to overcome the norm and work towards the modified so that when I do get new tires I will see even more benefit. I'm sure the torque of the 3.5 will not let me down with the change in ratio to reek the benefits of say driving a car instead using the granny gear ratio's this thing was made for. I don't creap up rocks or climb hills. My original purchase concerns were for pulling jet ski's in comfort and style. Which the VX does extremely well. I fell in love with the model when it was released and always dreamed of owning one. Now I just want to modify to my liking. This is something I have always done to whatever I have owned. One thing I've noticed is there is alot of couch potato's out there that think too much instead of getting off their keester and taking action to find a real outcome, since there are generally too many variables to fathum an end result. Ok enough of the deep thoughts by Randy. I need a beer to come back to reality.

[Ldub]

I don't think anyone has "bashed the new guy"...yet.

You may not like the info you've been given, but there are a lot of us "couch potatos that think too much" that happen to know a thing or two about these vehicles...and the Isuzu corp 10 & 12 bolt front & rear axles they came with.

Getting your panties in a wad & alienating those who have tried to splain what's what to you, is not what I'd call conducive to receiving further help...

[l.groves]

Actually it feels more like getting a wedgy. Like if you want to EXplain yourself you should actually spell it right. After reading that you should understand what I mean. People look for researched information. Not "you idiot you don't spell explain -splain". Its e-x-p-l-a-i-n... Of course you don't put in a new ring and pinion without setting the backlash. Of course you don't drive in 4wheel drive if the ratio's are different. So Ldud go back and correct your spelling and give some information that counts. Hey, If you want to feel like the smart guy prove it don't state the obvious. Then praise almighty Ldud is a genious. All hale Ldud!!! Oh yea did you go back and correct your spelling yet.

Anyways, enough caffeine venting. I found out the the rear size ring gear is 220mm (8.66"). I did find a kit that changes Isuzu to a DANA 44 which would give more options on ratio's. Only It may only be for smaller gear sets. I'll have to call and find out for sure.

[Scott Harness]

Actually it feels more like getting a wedgy. Like if you want to EXplain yourself you should actually spell it right. After reading that you should understand what I mean. People look for researched information. Not "you idiot you don't spell explain -splain". Its e-x-p-l-a-i-n... Of course you don't put in a new ring and pinion without setting the backlash. Of course you don't drive in 4wheel drive if the ratio's are different. So Ldud go back and correct your spelling and give some information that counts. Hey, If you want to feel like the smart guy prove it don't state the obvious. Then praise almighty Ldud is a genious. All hale

Ldud!!! Oh yea did you go back and correct your spelling yet.

Anyways, enough caffeine venting. I found out the the rear size ring gear is 220mm (8.66"). I did find a kit that changes Isuzu to a DANA 44 which would give more options on ratio's. Only It may only be for smaller gear sets. I'll have to call and find out for sure.

Dude! Let me splain somin to you. You are drownding yourself and not making any friends...ps you spelt genius incorrrectly

[Ascinder]

Look, I'm going to lay this out for you pretty clearly. We are all a bunch of layed back, nice, friendly, mature people over here. And I'm not saying you're not, but if I were you, I'd take a look at Ldubs previous posts and know full well that if he misspells something, it's (usually) on purpose to illustrate emphasis or satire in the situation. I'd also take a step back and a deep breath and examine this thread for yourself again. No one is trying to get hostile with you, so take the good advice with a grain of salt and if you don't like it, ignore it. There's a lot of good information on this site and everyone here is happy to give it out freely, provided it is asked for and recieved in a reasonable and kind manner. Respect is gotten when it's given. We aren't like a lot of other forums that have giant flame threads. It's not how we do business over here. We are a family oriented and tight knit group that in my own opinion get along very well together because of that mutual respect I mentioned. All I'm saying is you may want to rethink your methods in future posts. I think if you give this forum a chance and don't come in on the offensive, then you'll find it a great place and a wealth of information and friendship.