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· Premium Member
'05 TB 4.2 EXT
6,631 Posts
I lifted 2 inches of the 2009 Trailblazer LS last year to install bigger tires 265/65/R17 (rare size tires) for off-roading.

Recently after experiencing a puncture, I changed both the rear tires to 265/70/R17 (easily available size).

I know this minute difference is fine for 2W and 4 Auto but will it cause any issues while off-roading in 4 High or 4 Lo?

Does the 2009 Trailblazer LS with a 4.2 engine have 50/50 lock at the central differential?

Thanks in advance.

View attachment 61206
"Does the 2009 Trailblazer LS with a 4.2 engine have 50/50 lock at the central differential?"

You apparently don't understand that there is no actual direct hookup through the transfer case to both front and rear differentials in AWD .... the rear is "IN" physically but the front differential is "FLOATING" on a variable clutch that is controlled by modulating the amount of pressure on it to send up to 50% of the engine output power to the front axle.

In AWD the clutch is very active constantly hunting and slipping --- more or less --- to compensate for the values the wheelspeed sensors are reporting.
This "hunting activity" is why it is not a good idea to use AWD - because of the inherant damage and heavy wear to the internal parts of the transfer case.​
It's a very poor design - but not as bad as a semi-viscous intermediate drive like Subaru.​
But know this --- the GM 4WD unit on our TBs is not just gears and shafts coupled by a HiVo chain --- there is that silly clutch, evere seeking to do the will of an actuator that is never in the same transitional profile when operating in AWD.​

So -- at all times ... the rear axle receives engine power <unless the transfer case is in neutral> --- but the front axle can be in a "share-the-power" mode when the transfer case is in either 4WD-High or 4WD-Low.
This is physically ... real 4WD but with an asterisk (*)​

Here's the asterisk---> In AWD, the clutch - which has been locked as far as it could be locked when it was in 4WD - (depending on how much of it is not worn away) --- and had sent equal power (50% / 50%) to both differentials --- now will still send less power to the rear because it has to send varying power to the front, subtracting from the overall available power.

IOW --- when you send power to the front differential, you cannot get it for free and the rear differential loses whatever amount it has to share with the front - minus the asterisk!

This AWD asterisk causes a lot of power assignment/reassignment activity --- and it never really achieves a real power assignment balance - always losing power in both the (A) transition of power front or rear ... and then (B) the time it takes to make that change.

It may feel seamless because from the driver's seat, the vehicle never feels like it loses nor gains speed nor momentum --- but the shuttling of power to-and-from the rear differential to the front differential through a slipping clutchpack - is rife with losses that show up as wear on the clutches and heat generation.

IOW ---> don't use AWD.
This is the official AWD Warning/Rule #2 and you obviously know Rule #1 about the battery.
There will be other rules.

· Premium Member
'05 TB 4.2 EXT
6,631 Posts
Can’t mix tire sizes on 4wd vehicles.
even with all 4 the exact same , they are not exactly same from factory
have to set air pressures with a stager guage so the circumference truly match . A 1/4” diff can destroy
Especially anything AWD .
Same thing applies to 2wd on drive axle/transaxle. Different circumference ‘s melt the diff spider gears , burns up limited slip clutches
Using donut spare on AWD is death
Using donut spare on drive axle kills diffs in axle or transaxle
There's a lot of old fart theories there.
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