37s and 3:73s

[Ehall8702]

I second the mileage. Stock they didn't get that high. I had a 99 Tahoe that was lifted a total of 9". had 35s when I got it, with 3.73s. Wasn't horrible, but wasn't great either. Motor ran strong, tranny would snap your head back. I put 38s on it, and couldn't use OD inless going down hill bout 90. Regear to 4.56s, you will have more pulling power, not to mention save your tranny.

That was what I was worried about is driving rpm beIN too low and kicking back and forth in and out of OD . Idk if the 35s do that since I only have 1st and 3rd at the moment but think next weekend I'll be putting new trans in and I'll know then. Still have my 33s , some roughly 34s , these 35s and sum 37s on the way so regardless I'll have tires that'll be ok, but truck will definantly look stupid with 5 1/2 " lift ( 2.5 suspension and 3bl) with 33s on it lol. Look ok with 35s with just 2.5 on it right now, when I get around to the bl I think it'll sit perfect.

 

[Ehall8702]

And I'm running 20" rims, which if my back remembers correctly are ALOT lighter with a 35 vs a 16" rim with a 35 on it...again maybe one more factor giving me good number? And I run my tires at 50psi so less rolling resistance too? Not trying to justify my claim I'm just adding info

 

[GreenZ98]

I would imagine those 37s are gonna scrub frame like nobodys business when you get close to full lock on a oem wheel, my 35s on stockers would.

My 98 with 3:73s and 285s and a blackbear tune on a perfect day ain't gonna get but 15 and that's also with a new engine and fuel injectors. Heck a brand new reg cab 4x4 Silverado barely gets 20mpg on the highway.

 

[Ehall8702]

I would imagine those 37s are gonna scrub frame like nobodys business when you get close to full lock on a oem wheel, my 35s on stockers would.

My 98 with 3:73s and 285s and a blackbear tune on a perfect day ain't gonna get but 15 and that's also with a new engine and fuel injectors. Heck a brand new reg cab 4x4 Silverado barely gets 20mpg on the highway.

My 35s on boss wheels scrub at full lock, the 33s on stock Denali 20s didn't touch at all. I hate these boss wheels and they r only temporary till my oem ones get powder coated. Haven't tried the 35s on them yet as u can see the backspacing is alot different between the oem and the aftermarket wheels. I have a tire machine so I'm just gonna have to swap and see what it does I guess. As for the mileage 255 miles from door to door and just under half tank on a 21 gallon tank, 90% of that running 80-85mph on freeway. I figured about 12 gallons used to cover 255 miles is 21.25 mpg, unless my math is totally wrong or my tank has a mysterious resivoir in it lol! Was almost dead empty when I filled up and I force fed 21 gallons into it before we left. As for tires front two were bfg at 315/50r20s and rear were mileking mk868 33x12.50r20s. do those tires runs small or something I'm missing here?

 

[Hipster]

I would imagine those 37s are gonna scrub frame like nobodys business when you get close to full lock on a oem wheel, my 35s on stockers would.

My 98 with 3:73s and 285s and a blackbear tune on a perfect day ain't gonna get but 15 and that's also with a new engine and fuel injectors. Heck a brand new reg cab 4x4 Silverado barely gets 20mpg on the highway.

15mpg is approximately just about darn near exactly what I get with the same exact set-up less the super tune. Maybe even over optimistic for me.

 

[L31MaxExpress]

I didn't believe it either , why I did the math a handfull of times just because I figured there was no way that was right. Now I left out that was straight interstate riding from the UP to Rockford Illinois and then back. I don't keep track around town or on my daily travels as I honestly don't care about those numbers. As for the power issue, I could hardly pass a car going uphill with the stock tires on it (265/75r16 roughly a 31x10.50) untill I pulled my throttle plate and ground off the aluminum "baffle" on it, removes the vortec box at the same time so idk which made the difference but man did it make a HUGE difference. I stand by my highway claim of 22 mpg tho, a buddy of mine has a standard can long box with 3:42 on 305s ( 33s) and claims 21-22mpg. We don't really have anything but long open roads here with 55+ mph speed limits, not alot of "town" driving so that may help the mileage numbers some. I got two sets of rims so I'll put the 37s on and see what it feels like and if it's a dog they will come off and wait till I get sum gears for it. The option of SAS is there to but all I really have access to is 3/4 and 1 ton axles and damn sure don't think that'd be good daily driver setup.

268 Cammed 305 Tahoe with 305/50R20s and 3.42 gears. 22-23 mpg highway running 70 mph @ 1,700 rpm. Cammed 8.1/4L80E same Tahoe same wheels/tires/gears gets 18 mpg on long trips.

Cammed 350/4L85E/3.73 14 bolt Express conversion van on 31.5" tall tires. 18-19 mpg highway.

With the weight and height of the 37s you will want gears. 4.56 minimum, 5.12 would be better. A coworker had a lifted 99 Tahoe with Lunati's version of the hotcam. Truck was on 37s. 5.12 gear was perfect. ~2,500 rpm @ 70. It would smoke the 37s all the way through 1st gear.

 

[Ehall8702]

268 Cammed 305 Tahoe with 305/50R20s and 3.42 gears. 22-23 mpg highway running 70 mph. Cammed 8.1/4L80E same Tahoe samw wheels/tires/gears 18 mpg on long trips.



Cammed 350/4L85E/3.73 14 bolt Express conversion van on 31.5" tall tires. 18-19 mpg highway.

With the weight and height of the 37s you will want gears. 4.56 minimum, 5.12 would be better. A coworker had a lifted 99 with Lunati's version of the hotcam. Truck was on 37s. 5.12 gear was perfect. ~2,500 rpm @ 70.

Im glad I'm not the only one getting good highway numbers then, and I'm not sure if I'm gonna run the 37s or not yet, wanna eat BL on and see how they look and if and how bad they run on both the oem and the aftermarket wheels. May stick with the 35s but I see gears in my future for sure. Thanks for the info

 

[L31MaxExpress]

15mpg is approximately just about darn near exactly what I get with the same exact set-up less the super tune. Maybe even over optimistic for me.

Is your PCM calibrated for the tire size? If you have oversize tires the odometer will read falsely and read lower than actual. Just 3" of height change from factory is about 10% error. Going from a 29" tall tire to a 32" tall tire threw my speedometer and odometer off 10%. 100 miles traveled on the odemeter was really 110 miles. That would make your MPG 16.5 rather than 15 if not taken into account or the tune changed to reflect the new tire size.

If a truck with 29" tall tires and 3.73 gears were swapped to 32" tall tires. 4.10s would make it read almost correct.

 

[Ehall8702]

Is your PCM calibrated for the tire size? If you have oversize tires the odometer will read falsely and read lower than actual. Just 3" of height change from factory is about 10% error. Going from a 29" tall tire to a 32" tall tire threw my speedometer and odometer off 10%. 100 miles traveled on the odemeter was really 110 miles. That would make your MPG 16.5 rather than 15 if not taken into account or the tune changed to reflect the new tire size.

If a truck with 29" tall tires and 3.73 gears were swapped to 32" tall tires. 4.10s would make it read almost correct.

You know I didn't account for the size difference! My speedo is off a few mph but I used GPS for speedo. But I know I was just under half a tank, and distance was 255 miles so numbers r still on. My speedo is off 5mph right now ( going faster than speedo reads) so when I get the 0411 swap done I'll get it adjusted then.

 

[shorepatrol]

My 98 with 3:73s and 285s and a blackbear tune on a perfect day ain't gonna get but 15 and that's also with a new engine and fuel injectors. Heck a brand new reg cab 4x4 Silverado barely gets 20mpg on the highway.

All of the above. I run the exact same setup.