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Gearing Question Moving to 34" Tires

2K views 4 replies 3 participants last post by  DaJokr 
#1 ·
New member here. Have a 15 GMC Denali LML CCSB with stock 265/60/20 tires/wheels. Looking at leveling the front and moving to 275/65/20 tires and 9" wheels. I have 3.73 gearing and when I tow a 11,000 lb. fifth wheel or my enclosed car trailing the shift points and rpm ranges are spot on. The calculator says the tire change will move me to an effective 3.50 gearing. I am a bit concerned that I will not like my towing performance. Can a few comment on their real life experience?
 
#2 ·
Most don't bother with a regear until running a 35 or larger tire.

All dmax trucks run 3.73 gearing unless specially modified by the owner. There may be an exception in older models with the zf6, but I'm 99% confident in my answer here.

You might be on the teetering point depending on if you tow a lot or a little. If you tow a little then no, if you pull a trailer several times a month then might be worth considering.

Try without regearing and see if it's a noticeable difference. I don't think it would be worth it personally though.
 
#3 ·
I've been running 25/65/18 (34.6"×12.8") for a while. I tow often, it's not too bad. I keep it in manual mode, then if the truck seems to be lugging, or you see a hill approaching, just tap it down to a lower gear. It's always easy to shift down lower, and it's nice having the rpm lower when you're empty and cruising fast on the hwy.

I have thought about changing gearing, but held off as I might go to a bigger tire still.
Basically if you do mostly hwy you're probably fine. If you do more city, switch to a 4.10 or maybe 4.44
4.56 might be a bit much for your tire size. (Most guys go 4.56 with 37"s)
 
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#5 ·
Adding to what kev said, 35's are when guys start thinking about gearing, 37's it becomes necessary only if you tow. I'm planning on 37's down the road but won't be regearing as I tow only a couple times a year or not at all. The taller tires help improve mileage when unloaded.

The other side to that is I have a built trans and tuning so it kinda becomes a moot point regearing with extra power, despite the shift points moving around a bit :D
 
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