tire size and gearing??? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

'89Z71 · 07-14-2003, 02:05 AM

I was just wondering what gears i should be running with 33" tires. Also if i upgrade to 35" tires what should i use for gears? How to i tell what gears are in my diffs right now? I know they are stock. My truck is an '89 GMC Sierra Z71(5 spd). If you know what gears I have do tell please. Thanx in advance!!!! DK

wildwood · 07-14-2003, 11:09 AM

I'm running 35s with .373 gears. It's a little less powerful than it was with 33s but OK. I've got a 4 speed transmission with Bull low so There's no prob. If your truck is auto trans, you might want .410s with 35s but .373s would probably be OK for 33s. If your going to be putting them on anyway, I'd just try them and see, if it's too sluggish then change the gears. If you call a chev deaaler with your VIN, they should know the factory setup.

Mudder · 07-14-2003, 01:21 PM

Get one of the rear tires off the ground. take your tranny out of gear. turn the tire 1 complete revolution (be precise). Count the number of times the drive shaft turn in relation to the 1 revolution of the tire. If it turns 3 times and a 3/4 you have 3.73's. If it turns just a bit over 4 you have 4.11's and so on. Good to mark the drive shaft and tire.

There is also a tag on some rear ends that will give u the number of teeth on the ring gear and pinion gear. Divide them and that will give you your ratio.

I am running 35's with 4.11's and they are great IMO.

'89Z71 · 07-15-2003, 01:35 AM

Thanx for all the info so far!

As soon as I get a free day in the near future I'll be sure to check it all out.

07-14-2003, 02:05 AM	#1
'89Z71 Registered User Join Date: Jan 2003 Location: Star Prairie WI Posts: 392	tire size and gearing??? I was just wondering what gears i should be running with 33" tires. Also if i upgrade to 35" tires what should i use for gears? How to i tell what gears are in my diffs right now? I know they are stock. My truck is an '89 GMC Sierra Z71(5 spd). If you know what gears I have do tell please. Thanx in advance!!!! DK __________________ '89 GMC Sierra Z71 -"Scream'n Demon" * LOUD PIPES SAVE LIVES * My Truck

07-14-2003, 11:09 AM	#2
wildwood Registered User Join Date: Jun 2003 Location: Calgary AB Posts: 110	I'm running 35s with .373 gears. It's a little less powerful than it was with 33s but OK. I've got a 4 speed transmission with Bull low so There's no prob. If your truck is auto trans, you might want .410s with 35s but .373s would probably be OK for 33s. If your going to be putting them on anyway, I'd just try them and see, if it's too sluggish then change the gears. If you call a chev deaaler with your VIN, they should know the factory setup. __________________ You can't get out if ya don't get in

07-14-2003, 01:21 PM	#3
Mudder Registered User Join Date: Feb 2001 Location: East Central, MO Posts: 11,336	Get one of the rear tires off the ground. take your tranny out of gear. turn the tire 1 complete revolution (be precise). Count the number of times the drive shaft turn in relation to the 1 revolution of the tire. If it turns 3 times and a 3/4 you have 3.73's. If it turns just a bit over 4 you have 4.11's and so on. Good to mark the drive shaft and tire. There is also a tag on some rear ends that will give u the number of teeth on the ring gear and pinion gear. Divide them and that will give you your ratio. I am running 35's with 4.11's and they are great IMO. Last edited by Mudder; 07-14-2003 at 01:23 PM.

07-15-2003, 01:35 AM	#4
'89Z71 Registered User Join Date: Jan 2003 Location: Star Prairie WI Posts: 392	Thanx for all the info so far! As soon as I get a free day in the near future I'll be sure to check it all out. __________________ '89 GMC Sierra Z71 -"Scream'n Demon" * LOUD PIPES SAVE LIVES * My Truck

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