I want my mileage back

April 9, 2004

I recently put new chromed 20's and goodyear forteras on my '03 Yukon. I was getting about 16.7 mpg and now get about 15.4,,,,,,,,ouch. A guy at a truck mod shop said it was my wheels. He said the added weight ws like towing a jet-ski. What do you think? Has it happened to anyone else here?

I was looking for ways to boost my mpg anyway, got some suggestions?

I think I heard here that TB spacers don't work, is that true? The "truck-guy" said HP - no, mpg - yes.

I'm also wondering if a Westers will boost my mpg? I don't race, but I'd spend the money if it helped my mileage.

How about electric fans and under-drive pulleys? Anybody tried these? Do they work?

Thanks in advance.

Shaners · April 9, 2004

If the overall diameter of your new tires is bigger than the stock tires, then your speedo/odo will be off and that will make it "appear" that your MPG's have dropped (on paper).

Also a wider tire equals more rolling resistance and that can decrease your fuel economy.

chevy4x4trucks · April 9, 2004

Am I reading your sig right? You have a yukon lt w/ a v6?

Ditto what shaners said about the tire size.

If you want to boost your mpgs get an aftermarket intake and exhaust, but then you can't hammer down the throttle.

Tucson_02Silverado · April 9, 2004

larger wheels are more mass unless some exotic materials are used...Chrome plating is not exotic. Most larger wheel diameter tires are actually heavier than the 16/17" versions as the shorter sidewalls of the 20/22/24 need more tensile strength to hold the weight.

April 9, 2004

chevy4x4 - thanks, I fixed the sig.

I measured the rollout on the new and old tires, it's only half an inch different. That's less than 1% so my odo is ok.

The shipping weight on the new wheels is 40lb. I have no idea what the stock aluminum wheels weigh. I figure the tires are about the same since the 20's are wider but have less inner mass. I plan on weighing them both this weekend (just to satisfy my curiosity).

I have a magnaflow muffler but am afraid of going full ctback low retriction because I don't want to lose my torque. Since this is a driver not a racer I'm more concerned with 0 - 45 than I am with ET.

2001 HD · April 9, 2004

Go to one of these sites for tire calculators. 245's to 285's=almost 6mph difference at 70 mph.and .078% odometer error.

http://www.dakota-truck.net/TIRECALC/tirecalc.html

http://www.discountpartcenter.com/tirecalc.html

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

I agree with everyone else. Bigger tires will hurt you milage a little due to more weight. Hope this helps.

03z71 · April 9, 2004

When I went from P rated tires to LT rated tires, I noticed a drop in mileage. The new tires were exactly the same size as the old but they were obviously heavier (more plys). I think increased weight of the wheel/tire combo could definitely be what did it.

Schwag · April 9, 2004

Put the old set back on for a while and see what happens...

-steve

Bob G. · April 9, 2004

The cheapest way to keep the mpg that you had is to keep it stock! THE HORROR!!! LOL!!

Bob G.

redvett · April 9, 2004

When you change speedo input you MUST change your calibrations so the PCM,BCM & ABS systems are at the right speed calibrations. Look at it this way, The change in input changes the data for engine= air fuel and transmission speed for shifting. The ABS needs the correct cal's, for the brakes. Taller tires slow down the drive line speed and change all data. Change the speedo input and you should be O.K. but going much larger in tire size will slow down the engine andd make it lug and be out of the power band.

willfxp · April 9, 2004

Brought up in another thread, but is $2000 worth of mods (PCM, intake, exhaust, ec.) worth the extra 1-2MPG gain?

redvett · April 9, 2004

Its the whole package and engine performance is one of them. If you can spend $2000 on tires & wheels dont you think you need to recalibrate for those tires. You can reprogram with a Prediator for less than $500 and tweek it for fuel mileage or performance. I did it to my 01 Corvette A4 and ran the 1/4 mile at 12:98 @ 109mph and still can average 26mpg. Now if they will just get the predator out for 04 trucks i will be happy.

April 9, 2004

I have a Hypertech PP III and adjusted the tire size as soon as I put the tires/wheels on. I put it back to stock program to see and there was no difference in mileage. I'm sure the odo is right.

I weighed my stock tire/wheel and it was 58 lb. My 20" wheel, by spec, weighs 40lb. I can't find any data on the weight of the tire. I think I'll take one off this weekend and weight the whole thing just to see.

I thought about switching back to the stock wheels/tires to see but they get uglier every time I look at the 20's.

Maybe I just need to suck it up amd move on. There are ways to regain my mileage, and heck, its only money. I do put a lot of miles on it and if the payback is 12 months or less I can justify it.

redvett · April 9, 2004

Its going to take the fuel & timing tables time to change if you just change the speed signal and if you unhook the battery about the same. You will have to wait and take a trip with both settings under similar conditions.