Chevy & GMC Vans

I hoped the title would get your attention. I have replied in several different topics on tire size, and lift and how it affects gas mileage and never really got much of an answer. With the cost of gas going to $4.00 gallon and higher it's getting very expensive to take a trip these days.

Before I lifted the van and added the 29" BFG AT's I was getting 20+ MPG on the highway. After the lift and installing the BFG AT's, I was lucky to get 15 MPG.

Before the lift (Pretty Sad Looking) with the BFG 225-75-15 Long Trails 20 MPG


Lifted with the Long Trails still installed. (Looks Pretty Good) Unfortunatly these were only on for a week before I upgraded to the BFG AT's and I didn't check my mileage


And now with the BFG 235-75-15 AT's installed. (Looks Even Better) 15MPG


I am very happy with the lift and will never consider going back but I am considering less aggressive tires.

I still have my BFG Long Trail 225-75-15's with less then 5K miles on them. These tires performed well on the road, in the snow and rain, and on the fire roads I frequent in the National Forests of VA and WV.

On my list of things to do is get a full size spare. So I am thinking about buying 5 new rims and one more BFG Long Trail 225-75-15 and going back to the Long Trails to save on gas. Of course, if the difference is minimal then I will keep the AT's on the van and buy a rim and tire for the full size spare and be done with it. The cost of the wheels then mounting and balancing is another factor.

Pic of the wheels I am considering


Link:
http://store.summitracing.com/partdetai ... RR-3105750

I really like the look of the white spoke wheels and may get them either way.

So my question is, which is worse for MPG, the aggressive tires or the lift?

Opinions and discussion are most appreciated!

What is killing you is the larger diameter, wider and more aggressive tires. If you want your mileage back you can either run the long trails or swap 4.10 gears in. The lift probably makes mileage slightly lower but I doubt much. With the SPB, I ran 30" tires and had 3.42 gears with the 4" lift and struggled to get 15. I then swapped in 4.11 gears and immediately went to around 20 mpg highway and easily 15 in town or towing. Before I was lucky to get 9.5 towing the same loads.

Dean,
I was hoping to hear from you and thanks for your reply. You tried to talk me into 4:10 gears back in October when I had the ring and pinion gear replaced. I should have listened to you then and got 'er done. As you may remember, the cost of doing the front diffy as well is what kept me from the upgrade. I regret not making the move then. No way can I afford to do it now since I already spent $700 repairing the rear end. Should have bit the bullet and got it done then. I figure it would cost at least $1000 to do both now, so there you have it.

I can always mount the 29" BFG's on my AWD '06 Escape and make it more rough road capable. It has a 4 cyclinder and gets 28MPG HWY. Hopefully they won't kill the mileage too much there.

What do you think of the Cragar wheels?

Here's a pic of how they might look

The throttle response with my 4:10's is excellent. It seems like it takes no effort at all to move the van. Fiancee drives a 250hp Nissan Murano and she even commented of how effortless the Astro stood up and accelerated on the freeway on-ramp when she drove it the other day.

I haven't re-calibrated my speedo/odo yet, so I've not done a lot of mpg calculations since the gear change-over. The one trip I did log and calculate (the Weekend following Sportsmobile trip that you have seen posted) included a lot of varied driving all on one tank and a half, including;

-freeway at posted speeds.
-over a 5000 ft. mountain pass on the highway with very steep grades, at posted speeds
-more mountain pass on fire roads and gravel
-crawling around canyons and thru water crossings
-more freeway at 70-80 mph

and I think my observation was 15.2mpg.

Consider this too:
Some guys I used to work with now work at the local Discount tire. They are very impressed with the knowledge and judgement of thier manager ( who himself has built a nice Ram 4x4 and a gnarly rock crawlin jeep). I told the manager that I think I may need a more heavy duty LT 5-6 ply tire, and have a buyer for my new Kelly Pathfinder AT's and maybe I should get BFG AT's or MT's. I am worried about sidewall slices (again, based on the same type of trip as the Sportsmobile thread).

He could have sold me an $800 set of tires right then and there ( he himself was actually mounting $1100 tires on Brian's SPortsmobile at the time of this conversation). His reply made a lot of sense: Even though the Pathfinder's are only 4 ply, P rated, they have a strong/lightweight nylon sidewall ply, plenty strong relative to the vans weight. The tread is agressive enough ( i agree so far) and the softer tire gives a great foot print off road with out airing down nearly as much as the stiffer tires need to do. And the lighter tire gives beter throttle response and fuel economy. My buddy looked it up, and my tire is 15 pounds lighter than a BFG AT and the MT's are even heavier.

Sorry for being so long winded, but you know by now thats what get from a T.Low reply.

T. Low...not long winded at all..I wish I had done the 4:10 gear change over when I had my ring and pinion gear replaced due to the two broken teeth on the pinion gear. I kick myself everyday for not following Deans advice. But what's done is done. Looks like I'll be switching back to the Long Trails...Gas is killing me and it's made me rethink some of my longer trips, closing in on $100 to fill the van up and only getting 350 miles.... And 4+ miles to the gallon would be worth it I believe.

I could sure use some advice here too. I'm putting on BFG 31x10.5 mudders in a few days I will definitely need to upgrade from 3.42 to 4.10 gears. I have a RWD, so what do you guys approximate that will cost to have done? How difficult is it to do yourself? And how do I know what type of axle I have, bolt# spline# etc.?

97...the gear swap for just the rear axle will be in the $550 - $750 range for a shop to do. That is with all new parts and labor. If you can get a used set of 4.10/4.11 gears and a master install kit, you could do it yourself. You will need some specialized tools like bearing pullers, a hydraulic press, inch-pound torque wrench, and dial indicators.

Your van being a 97 has a GM 7.625" 10 bolt with 28 spline axles. If you decide to tackle it yourself and want used gears, you can use gears from a 7.5" 10 bolt from an S-10, Astro or Camaro.

Just make sure you are comparing apples to apples. You mentioned worse mileage with the larger tires... which is going to happen... but I didn't see you acknowledge the needed correction factor to properly figure your mpg.

I'm not sure what (if anything) is available, but you might consider looking for a narrower tire at the same height. It will be lighter and offer less rolling resistance, yet still give the right stance and provide the same ground clearance.

Just for a comparison, I have neither the lift OR the tires,but with Dean's help I went from 3.42's to 4.10's,with the same size tires (just under 28" 215/75r/15's ) I noticed a slight decrease in mpg, but I have great power for hills or towing.If I were to enlarge my tires to say
( 29" 235/75R15 ) I would be reducing my engine rpm's and the engine would be thanking me with a slight increase in mpg, but I would lose just a little of that gained power for hills or towing.Tire size and gearing go hand in hand whether you want good mpg OR power for towing /hill climbing,you cannot change 1 without sacrificing the other.

Here you will find conversion charts for RPM,gear ratios,tire size.Hope this helps you pre plan your next move.Just tab down and take a look at which chart(s) works for your needs.

http://www.csgnetwork.com/automotiveconverters.html

This is how I figure my gas mileage:

I get paid every two weeks on Friday. I pretty much only drive my van to work and back. I have my driving style down to where I'm hitting empty at about 5:30 p.m. every other Friday, or Payday! If I don't make it to Friday, then I either drove like a dumb @ss, or I had some detour along the way. Very scientific. I try my best to stick to the schedule because I am dirt poor between paychecks.

Now let me tell ye all this: With my stock pee wee tires I filled up every two weeks, or about every 300 miles. Then I put on 235/75's and I still fill up every two weeks or 300 miles. How so? I stopped driving like a dumb @ss! I shut off the A/C when driving up hills, I try not to chase after people who cut me off anymore, and I no longer speed up to check out the hot girls that pass by........2% of the time. So there it is. I get the same gas milage with bigger, wider tires because I now drive like a grandma.

Somehow I will have to make it work with the 31X10.5's for a while. If you happen to see a massive white Safari cargo going 20mph on the freeway, that'd be me!

97CargoCrawler wrote:I could sure use some advice here too. I'm putting on BFG 31x10.5 mudders in a few days I will definitely need to upgrade from 3.42 to 4.10 gears. I have a RWD, so what do you guys approximate that will cost to have done? How difficult is it to do yourself? And how do I know what type of axle I have, bolt# spline# etc.?

Do you already have a posi? If you don't, consider this the time to install that too.

But of course! It's gonna be a long time before I can afford it though. I just spent about $2500 on parts for my new lift. Tires, new spindles, brakes, shocks, etc. I only spent $2800 for the van! Here's a little tip in case you're thinking of going the spindle lift route and you want all new parts: For 2 spindle nuts and two washers....it cost $40. It gets worse from there.

97CargoCrawler wrote:But of course! It's gonna be a long time before I can afford it though. I just spent about $2500 on parts for my new lift. Tires, new spindles, brakes, shocks, etc. I only spent $2800 for the van! Here's a little tip in case you're thinking of going the spindle lift route and you want all new parts: For 2 spindle nuts and two washers....it cost $40. It gets worse from there.

In the words of my amigo Hefe Martinez, "Daaaang, Dawg!"


But yur gonna luv it! Its gonna be bad ass.

Tire weigh and tire rolling resistance, (aka friction or tread traction) of the TA KO tires does have a big effect on mileage. I may swap out my 225/70-16 TA KO's for a set of Long Trail 215/75-16's .

I am still waiting to see if pulling the ATC underhood fuse to disable my AWD will make any difference in mileage.

I usually drive slow. but I put a K& N filter in last week and have been testing it for any new power.