3.42 Gears / 33" Tires / Towing

[CHEVY86CANADA]

Hi guys,

Over the winter i bought some 33"tires (275/60R20) to go along my 2016 Sierra Elevation.. this truck has a 5.3L and 3.42 gears ...during summer time i usually pull my TT that weights 6350lbs dry so knowing myself it is usually at 7500lbs full so lets make it 8000lbs for worst case scenarios ... I have a 6L-80 Trans 6 Speed ... So my question is; will it be that much of a power loss with the 33's on ... I mean this truck can pull 9200lbs as per the dealer specs .. but that is on the dealer tires i had last summer ...i didnt even think about the loss of power it may cause ... But i had so much of a deal on the BFG KO2 tires ... I couldnt pass on ... Now im uncertain of what i have done as the tires and installed on my rims and just waiting to bolted on ... Thanks for your help ! 

[Pearl2017]

the stock 20" tires are 655 revs per mile the tires you got are 612 revs per mile. So if we divide 612/655 we get .934. If we multiply that by our rear 3.42 gear we get 3.19. So basically the tires you have are like changing the gears to 3.19 about 7% taller. I used the revs per mile I found online so recalc if you find they are different. I think the Michelin defender in that size is 622 RPm.

 

So if your towing up a hill and the rpms would have been 3500 they will now be 3220 ...not a huge difference for TOWING.

 

Of course those rear tires are probably and extra 30 lbs of rotating mass so acceleration wont be as good but so what if you're talking about towing. Use the magic of torque multiplication and gear selection and the engine will never know what is behind it. Just keep an eye on your trans temp with the heavy loads and as long as you dont overheat it you should be OK

Edited March 6, 2018 by Pearl2017

[CHEVY86CANADA]

Wow thank you this is very informative !! Yeah i thought about the trans heating up.. i decoded my truck rpo codes and i have a HD Trans cooling system .. but i will keep a close eye on it .. maybe add a better cooling system ... Thanks for the info ! Very much appreciated 

[Pearl2017]

i just looked up that BFG 275/60/20 and it is 630 revs per mile so not a very big difference at all. ~4%  :-)

[CHEVY86CANADA]

5 minutes ago, Pearl2017 said:

i just looked up that BFG 275/60/20 and it is 630 revs per mile so not a very big difference at all. ~4%  :-)

Even better ;) thanks for your time on searching that data i wouldnt even know how to calculate that stuff

[ksfarmdude]

3.73's would be much better ratio with the taller tires 

[Kenrbass]

7 minutes ago, GMCanadian said:

Even better ;) thanks for your time on searching that data i wouldnt even know how to calculate that stuff

It will be a struggle. My son did the same thing. Then he sold the truck because it struggled pulling his boat.  

[CHEVY86CANADA]

3.73's would be much better ratio with the taller tires 

I thought of that but wouldnt that involve me swapping my rear axle and i believe id have to change gears up front too no?

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[CHEVY86CANADA]

It will be a struggle. My son did the same thing. Then he sold the truck because it struggled pulling his boat.  

Struggled much ? How much weight was he pulling ?

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[Kenrbass]

struggled enough to where he sold the truck. boat was 5k pounds.  I don't buy the 4% notion. On paper maybe, but it's a leverage thing.  He should have just went back to stock.  It would have been much cheaper. lol

[CHEVY86CANADA]

Yeah ..you are making me worried now ... Lol i kept all my stock parts so if i have to go back to it i will however i will have to try ii at least ... I know for a fact that 3.73 would be ok as i have a friend with that ratio and he has no problens whatsoever ...but swapping to 3.73 i dont know what id need ..

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[CDNSS]

Your gonna need alot of throttle to move that load with 3:42 and 33” tires  cruising rpm not that big a diff but the starting gear ratio is not great I towed 7000 lbs with a 5.3 cc 4wd and a 6 spd with 33” tires but changed to 4.11,gears towed in 5 th at 2200 at 68 mph  if you dont have alot of hills or headwinds might be ok but for 33” you need min 3:73  to perform decent IMO. KEEP  THAT 5.3 above 2k  when towing 

find an online gear ratio / rpm  / speed calculator and plug in you actual trans ratios by each gear then you will see the difference with 33’s 

 

 

[CHEVY86CANADA]

Your gonna need alot of throttle to move that load with 3:42 and 33” tires  cruising rpm not that big a diff but the starting gear ratio is not great I towed 7000 lbs with a 5.3 cc 4wd and a 6 spd with 33” tires but changed to 4.11,gears towed in 5 th at 2200 at 68 mph  if you dont have alot of hills or headwinds might be ok but for 33” you need min 3:73  to perform decent IMO. KEEP  THAT 5.3 above 2k  when towing 
find an online gear ratio / rpm  / speed calculator and plug in you actual trans ratios by each gear then you will see the difference with 33’s 
 
 

What was involved in the gear swap if i might asked .. i might want to do that ...thanks

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[CDNSS]

You need to  change ring and pinion in both front and rear diff not a big deal but  you need to have the ecm reprogrammed for the new ratio not sure if a 2016 can be done by dealer  you may need to find a custom tuner I already had a custom tune in my old truck so easy to do when I installed 4:11 

 

now have a 2017 6.2 so not that easy to reprogram  so sticking to stock tire ht as I tow my car trailer alot  

[CHEVY86CANADA]

You need to  change ring and pinion in both front and rear diff not a big deal but  you need to have the ecm reprogrammed for the new ratio not sure if a 2016 can be done by dealer  you may need to find a custom tuner I already had a custom tune in my old truck so easy to do when I installed 4:11 
 
now have a 2017 6.2 so not that easy to reprogram  so sticking to stock tire ht as I tow my car trailer alot  

I dont want to trade in .. but id love a duramax if id change .. but i was looking at the Kodiak as it has a max tow package and it is geared with 3.73 but the deal that the dealerships are giving out is killing my trade in a lot .. it horrible .. the rebates they have it better buying new now than having to by used .. i will consider ring and pinions once i try my new setup .. thanks for all the info !!

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