AstroMath 3.42 + 31"= ?

[blinkibus]

HI,

I am sure some of you are currently or have spent time running larger tires with 3.42 gears.
I understand technically what happens when you mess with gear ratios like that, but my question is what does this really feel like?
Super sluggish, no hill climbing, high revs at highway speeds, reduced fuel economy, no big change, etc.? (please be specific about your set-up: ratio, tire size, engine, tranny mods)

According to my calcs those with 4.1 's are not coming back into the normal stock range, but going somewhere else entirely. What does that feel like?

I have 33" tires on an old suburban with 3.73 gears, and that seems to work (OEM tire was 235 75/15). But the 350 just chugs along.
I was also running 185 70/14's on 14" peugot rims on an '85 subaru with only maybe 70hp, that worked fine. But I had a low range if needed.

I would just run it myself and see, but my rear end is about to give out, and needs to be rebuilt ASAP. I am going to lift my van but haven't decided how high yet!?! Mostly because of this gearing issue. Redoing both the front and rear (with an LSD) is probably going to cost in the neighborhood of $2000 locally, but I'm in for the rear diff already. So I could choke up and re-gear all around, although I'd rather not spend the $$$. But damn those 4-5" lifted vans look so good!!!

Yours Truly

[97CargoCrawler]

I too have the GU6 gears and I'm running 31" BFG Mudders with no problems whatsoever. I pass everyone uphill no problem without redlining or feeling like I'm killing my van. BUT, I have a cargo van and I never have any passengers. I do have a bench seat, recliner and a lot of tools that add some weight. My drivetrain is all stock.

In my opinion the stock ratio and tire setup were sort of overkill. I remember spinning the tires everytime I punched the accelerator, and while that was fun sometimes it was dangerous in wet conditions. I have only tried to spin my 31's once and it worked great but I don't think I'll be doing that again any time soon! I thought I would have to spend the $800 (parts only one axle) for 4.10 gears but since I won't be towing anything or climbing any intense grades with a van-load of passengers it just isn't necessary. I was pleasantly surprised it worked out this way.

My gas mileage is only slightly less than with my previous tires (235/75's) and I have no trouble passing folks in the fast lane uphill. Sometimes I like to leave people in my dust just to prove I can. My van is a 1997, and it was very well maintained by the previous owner. I would imagine a neglected vehicle might not perform as well under these conditions.

With 235/75's I doubt you will notice much difference in gas mileage or torque, I didn't. I went from stock tires to 235's to 31's. If you go straight from stock to 31's I guarantee you will be driving a completely different van. Nothing will feel the same to you. It took me a month to feel safe driving my van after increasing to 31's. Those are some big ass tires! Now that I have gotten used to the big tires I would NEVER go back.

I should also mention that I first went with the 2" lift and 235/75's and while it looked awesome and felt more manly, it just didn't meet my expectations. So ultimately I had to save up the cash and go bigger!

Comparison of stock to 235/75 to 31x10.5:


Comparison of stock to 31x10.5:

[astrozam]

Heres my original thoughts when I switched from 3.42's to 4.10's viewtopic.php?f=5&t=961
I still like them and when/if I ever do my lift/bigger tires it will be all the more worth it. Its def improved towing.

[kings-x59]

here's a link if you'd like to play around with gear ratio calculations.
http://www.angelfire.com/fl/procrastination/rear.html

[lockdoc]

97CargoCrawler is the first person I EVER heard that has been OK with 3.42 gears with 31" tires. I would be inclined to say that the gears are not 3.42 with the rave review given. Otherwise the van's V6 is just a freak of nature like a 95 I had for a bit. I run 3.42's in mine with a V8 and it still sucks. I live in an area with a lot of hills. Mostly hills actually. I basically have to floor it to go anywhere and my mileage sucks. You just can't keep it going when you hit a hill. It has to downshift to third to keep up to speed. I should be able to stay in fourth while cruising. When my van was stock with the 27" tires it was nice so I know it is the tires. 3.73 would be nice with 235 tires and 4.10 is nice with 31". IMO 3.42 is good up to the 235's. Anymore and it sucks.

[97CargoCrawler]

My van has 178,000 miles on it, has had trans rebuilt once, engine never, diff gears are GU6 unless GM f 'ed up when printing the label on the door and has been a daily driver since '97. Up until July 2007 it carted around a load of contractor tools and materials everyday. Aside from being well maintained there is nothing special about it. I live in a very hilly area of California, my drive to work consists of highway driving at speeds averaging 75mph, winding mountain roads and nasty compacted bumper to bumper traffic. I'm dead serious when I say I have no problem keeping up with traffic. I'm sure if I had the 4.10 gears I would notice a major increase in low end torque but I just don't think I need it. I have yet to be in a situation where I felt like the van was laboring. Granted I'm not towing anything or trying to pull up tree stumps either. But for a daily driver I have no complaints.

[astrozam]

No one is saying its impossible just very unusual, I'm sure the fact that its a cargo and lighter has alot to do with it,Do you pull the hills in OD or D ? anyhoo its a cool van

[lockdoc]

I believe you Crawler. Like Zam said, it is just rare. I had a 95 I put a transmission in and the engine had a gazillion miles on it. But it ran like a raped ape. Never did figure out why it was so different than others.

[97CargoCrawler]

As far as I know I only have drive "D" and no overdrive. I'm not a wealthy guy, and I have never bought or inherited a vehicle with less than 160,000 miles on it. At 17 I took over my fathers '82 FJ40 LandCruiser with 160K miles or so on it, 33x12.5 tires and 10 years of everyday driving. I then drove it for another 11 years everyday. While I have no gauge whatsoever what a nice shiny new truck would feel like when you stomp the pedal or climb a nasty mountain, I do know what a tired old truck feels like. My van puts a nice smug smile on my face. With 178k miles on her I'm certain a transplant will be in order soon, but so far she is giving me everything she's got.

[ihatemybike]

As far as I know I only have drive "D" and no overdrive.

FYI, on our vans
D = .7 (overdrive)
3 = 1
2 = 1.63
1 = 3.06

[LaGrasta]

You wouldn't believe what I did!

I have 30" BFG KOs and 3.23 gears! My pursuit for better mpg had me searching in crazy directions with absolutely no increase in mpg. I think I'm too far out of the power band now to appreciate any added mpg. UGH!

With that said, it climbs just fine and has enough torque for anything and everything I do.

[97CargoCrawler]

FYI, on our vans
D = .7 (overdrive)
3 = 1
2 = 1.63
1 = 3.06

That's good info. Couldn't find that in my manual. I have never driven in 3rd, but I have used 1st and 2nd a few times. I tried 3rd today and it seemed to be holding me back a bit when coasting. The manual says 3rd if for driving with heavy loads or on steep hills. While I didn't use it the few times I have driven with a load or on a steep hill at least I put my worries to rest when I read "D" is for normal driving and normal towing.

[blinkibus]

Hi,

So that's two who say 3.42's and big tires work and two who say no way. Any tie breakers out there?

But I think we can all agree that with anything bigger than 235 75/15 tires a gear swap is a good idea, even if not necessary, in most cases, in regards to these particular vehicles, under normal conditions, or maybe not.

But then again I was talking to a guy today who had 3.73's (up from 3.08) put into his old chevy truck so he could run 35" tires, and he says the gearing is "just about perfect". Go figure?

[GEJ]

Ok-I have read this thread from the beginning and hear is what I think. and then there was the point made so I thought .So in conclusion I hope it has helped you out some.

Look-some times you just got to try it to see if it is what you want.

[blinkibus]

Howdy,

I also wanted to add that the info provided by 97CargoCrawler was great. The photos with the tire size comparison are a great reference. Thanks!