What's the SHORTEST tire GM fitted to 4-door Grand Blazers / Tahoes between '91 & '07?

[Marky Dissod]

Specifically, what are smallest diameters GM ever OE fitted for 4-door Tahoes between 1991 & 2007 (GMT400 & GMT800)?
(Please ignore 2-door Blazers.)

My Z71 presently wears 255/70R18 (32.05") - thank previous owner for 18" wheels.
Want to lower it a wee lil bit, but not with shorter springs at this time.
Must keep 18" wheels - planning on upgrading front brakes to either GMT930 or GMTK2Y.

Wondering if 255/55R18 (29.04") or 235/60R18 (29.10") would be safely workable?
What passes for 'roads' in the 5boros of NYC can become 'off-road' at a moment's notice.
I can live with the pointing fingers and the laughing behind my back - it's mine, no one else's.

 

[Marky Dissod]

Managed to find some stuff y'all may find interesting - unless it's already common knowledge.

GMT900 Police Pursuit Tahoes used 265/60R17, 29.51" tall. Is this correct?
GMT900 Special Service Tahoes used 255/70R17, 31.05" tall. Is this correct?

Wayback Machine

GMT800 Special Service Tahoes (5W4?) used 245/75R16, 30.46" tall.
But what tire size did GMT800 Police Pursuit Tahoes use? I prefer not to guess.

Wayback Machine

GMT400 Police Pursuit Tahoes (Z56?) used the same tires as '90s Caprice 9C1s:
235/70VR15, which are 27.95" tall. Had I not seen this in writing, I'd not believe it.

I do not yet know the tire size of the 2000 (GMT400) Tahoe Limited.

 

[iamdub]

Managed to find some stuff y'all may find interesting - unless it's already common knowledge.

GMT900 Police Pursuit Tahoes used 265/60R17, 29.51" tall. Is this correct?
GMT900 Special Service Tahoes used 255/70R17, 31.05" tall. Is this correct?

Wayback Machine

GMT800 Special Service Tahoes (5W4?) used 245/75R16, 30.46" tall.
But what tire size did GMT800 Police Pursuit Tahoes use? I prefer not to guess.

Wayback Machine

GMT400 Police Pursuit Tahoes (Z56?) used the same tires as '90s Caprice 9C1s:
235/70VR15, which are 27.95" tall. Had I not seen this in writing, I'd not believe it.

I do not yet know the tire size of the 2000 (GMT400) Tahoe Limited.

You beat me to it. I was gonna mention the PPV as having the shortest factory-spec'ed tire size. It's common knowledge that they're smaller, but all the specific sizes probably aren't memorized.

I did a little digging and ran across something saying the 2003 Tahoe PPV tire size was a 255/70R16. This calculates a 30.1" height. Most of the relevant tires you've listed are right in the 30" range. I wouldn't count that 28" tire on the GMT400 since that platform is much smaller in most every aspect than the GMT800+.

 

[Marky Dissod]

I wouldn't count that 28" tire on the GMT400 since that platform is much smaller in most every aspect than the GMT800+.

How much does a GMT420 - Tahoe weigh?
How much does a GMT820 - Tahoe weigh?

 

[iamdub]

How much does a GMT420 - Tahoe weigh?
How much does a GMT820 - Tahoe weigh?

According to info my ten seconds of Googling returned:

GMT420: 2,312kg = 5,097lbs.
GMT820: 2,250kg = 4,960lbs.

 

[MassHoe04]

From my experience the ride with PPV tires sucks!
In case Y'all might be wondering... It was driver's seat experience, not back in the cage.

The low sidewall profile, very stiff sidewalls (for speed and cornering) and high speed-rated belts make for a kidney-busting, tooth-breaking ride!

I understand you are looking to go lower in height, but PPV tires would not be my recommendation. Especially, in NYC! As you say, the roads go to hell in the matter of several feet. You might have more options if you had 17" or even 16" rims. But I would definitely not recommend PPV tires. Because the PPV tires have to really perform and hold up at high speed, they come with a hefty price tag too.

Someone here will have some good suggestions for you, but stay away from PPV tires. IMHO

 

[Marky Dissod]

T- is PLENTY of speed rating for me. No plans to EVER exceed 90MpH.
Although making my Z71 handle somewhat more like a PPV would be appreciated - keeping the 18" wheels for room to fit larger brakes - I'm not willing to sacrifice much of its Z71-ness.

If I wanted a vehicle that handled THAT much like a PPV, either a mid-'90s Caprice 9C1, or a Holden Caprice 9C1.
I got a Tahoe Z71 instead. How much better can a Z71 dance on the highway without ruining its Z71ness anyway?

Will I ruin the vast majority of its Z71ness by going from 255/70R18 to 255/55R18, regardless of which tire I choose?
Most important thing is to be able to press 4Hi in wintry road conditions and keep going anyway (may never press 4Lo).

 

[Alex_M]

From my experience the ride with PPV tires sucks!
In case Y'all might be wondering... It was driver's seat experience, not back in the cage.

Probably sucks from back in the cage, too

OP, is it looks that is leading you to wanting smaller tires? Generally larger tires are more appropriate for more rugged terrain.

To answer your question, shorter sidewall and smaller tire will always lead to a harsher ride. Some tires and load ratings will be worse than others depending on compound and construction, but smaller will always be harsher than larger.

For winter traction, narrower is better than wider. More point pressure so your tires sink down thru the snow to the hard pack or asphalt below better.

Tread also, obviously, makes a big difference. If this is for looks you won't want an off road or winter tire, but I would look at all season tires. Look for something with lots of siping (pronounced sipe-ing) and grooves perpendicular to the direction of rotation.

 

[Marky Dissod]

Not sure what you mean by 'looks'. I care about aesthetics far less than most people.
Maybe I'm crazy, but I cannot presently afford to lower my Z71 using more conventionally acceptable means.
Was thinking, if GMT400 Tahoes weigh roughly about as much as my GMT821 Tahoe, then tires of similar diameter / height are also safe.
Am I right or wrong?

My thinking so far:
235/75R15 (28.87") was OE on many if not most GMT430 bubbas, right?
Not willing to go under 255/55R18 (29.04") or 235/60R18 (29.10").
No such tire size as 275/50R18 (28.82"), but the extra width would likely cost more than 255/55R18 or 235/60R18.
Basically an tire between 29" & 32" tall, between 235mm & 265mm.
235/65R18 (30.03") would also be under consideration of course.

Year-round grip in rain, and to a lesser extent snow & ice, are paramount crucial tire characteristics.
True winter-snow&ice tires that are only useful 14 days or less a year are not worth it though.
I'm not opposed to offroad-ish tires if they also handle rain/snow/ice better than other options.
Snow is a higher priority than hardcore offroading.
Example:
If I still had a Caprice today, I'd choose between Falken WildPeak A/T Trail or A/T3W, Cooper Discoverer AT3 4S, and Vredestein Pinza AT - they all are superior in rain and snow to Michelin Defender LTX M/S, they also have offroad ability, and they're all cheaper too.

 

[Alex_M]

Sure, size has little effect on safety as long as you are keeping within safe load/speed ranges. It's just a bit unconventional to look at smaller tires when also trying to increase ride quality on rougher terrain. Only attempting to understand your desire so I can offer a better recommendation.

Since you specifically brought it up, and since you are not going specifically for a "street truck" look, the Falken AT3W is a great choice. I've had 3 sets and love em. Price has gone up a bit in the last few years, but what hasn't.

Lots of folks also give the Coopers rave reviews. I have limited experience with them. Only a couple half used sets. Under half tread, I was unimpressed with their rain handling.

 

[Marky Dissod]

Think I have to go to the tire store I've been loyal to for 30 years, and ask them if I may TEMPORARILY try on a set of used 255/55R18 or 235/60R18 tires (29" tall).
Used, because I want to know how bad things will eventually get.
Tires don't handle rough roads as they age ... do they?

I'll drive around for 20min-30min, see how much rougher the road gets compared to 255/70R18.

If 29" tall tires are too rough, I'll step up to 245/60R18 (29.6" tall) and try again.

Once I find an acceptable bumpy road ride, I'll buy a new set of tires in that size.

I've til winter '23 to find a year-round all-weather tire that handles rain, snow, and unpaved roads, be they paved roads that got unpaved to be repaved, or naturally unpaved roads that never will be paved.

 

[iamdub]

I just don't get the logic here. You want and need as much tire as possible due to the roads, but also want as little as tire as possible to lower it.

You say you can't afford lowering components, but you're gonna buy a set of tires with a "built-in drop". Tires far exceed the cost of drop components. But, if you need tires, then that's the primary goal here and I understand that.

Smaller tires will disrupt so much else in addition to having less sidewall. IMO, the losses far outweigh the gains.

Get the tires you need for use in your planned environments, for your comfort, etc. Get stock size (mostly adhering to overall diameter here) or slightly smaller if that's how it falls out.

If you would be satisfied getting anywhere from a fraction of an inch of drop to maybe 1.5" of drop at most (per the sizes you've questioned), then you're not looking for much drop. This means you can drop it for very little cost while maintaining or improving the original handling, load capacity, speedometer and odometer accuracy, ride quality, durability, etc. with new and proper tires.

For such a small drop, maybe an inch +/-, you can lower the front for free by de-cranking the torsion bars. Technically, you can lower the rear for free by trimming a coil or so off the factory coils (the RIGHT way- with a hack saw or slowly with a cut-off disc). These rigs tend to be squishy so the minimal increase in firmness might be welcomed, if it's even noticed. Or, you can swap in 1"-2" coils if you run across a deal.

 

[Marky Dissod]

Anything more than a 2.0" drop would force me to upgrade the side mirrors with power folding.

Wait a sec: the front torsion bars are adjustable for height? Do I need to change this thread's title?
Schidt! How do I go about adjusting the front torsion bars to lower the front?

As for the rear coil springs:
Are they mounted metal-to-metal? Or are there rubber spring cups or something like that?
Hoping for the latter.

Tossed out my Caprice 9C1s front & rear spring cups (all 8 of them).
Forgot what I sprayed on the contact points to keep it from squeaking.
No one else noticed the subtle lowering, except me and my ex.

 

[iamdub]

Anything more than a 2.0" drop would force me to upgrade the side mirrors with power folding.

Wait a sec: the front torsion bars are adjustable for height? Do I need to change this thread's title?
Schidt! How do I go about adjusting the front torsion bars to lower the front?

As for the rear coil springs:
Are they mounted metal-to-metal? Or are there rubber spring cups or something like that?
Hoping for the latter.

Tossed out my Caprice 9C1s front & rear spring cups (all 8 of them).
Forgot what I sprayed on the contact points to keep it from squeaking.
No one else noticed the subtle lowering, except me and my ex.

You're fortunate to not be wanting to slam it. The lesser the drop, the cheaper it is.

They are adjustable. That's why I was wondering why someone would subject themselves to the cons of tiny tires just to get such little drop. Have your cake and eat it- mild drop and normal, sensible tires. First, ensure all tires are inflated evenly. Park on a level surface and measure each corner from the center of the wheel to the underside of the fender lip, going straight up. Record your measurements. Raise the front at least until the tires are hanging and set it on jack stands. Draw a mark on the torsion bar adjusting bolts with a permanent marker or paint pen. A dot or line facing the front of parallel with the cross member will work. You just need a reference point. Back each bolt out between 3-5 turns each. Keep accurate count and record how many turns you adjust each. I forget what it is, but there's a generalized formula where X turns equals X inches of drop (or lift). My rough guess is two turns equals .25". It actually will vary between trucks. Anyway, my point is that, when you measured it before you started, you probably found that the left (driver) side was lower than the right side. You can back out the RH bolt a little more or back out the LH side less to even it out. Remove the jack stands and set the front down and assess. I recommend you take it for a spin around the block to cycle and settle the suspension before measuring to see how much drop you achieved based on your X number of turns. Again, all trucks vary. But, you should be able to get a solid inch of drop and level it side-to-side with this. If they're even still in place, your jounce stops (they look like and are often called "bump stops") will need to be trimmed a little. They should be just barely touching the control arm and not hovering over it nor squashed.

The rear is supposed to have isolators. They're probably squashed and not adding much thickness at this point. Actually, this is another area to gain a small amount of drop, equal to the thickness of the rubber. Remove the isolators and slip a piece of 5/8" heater hose over the coil (cut or not). This will eliminate the coil from being metal-on-metal with the chassis and axle perch while only adding the thickness of the hose on top and bottom.

 

[Marky Dissod]

No need to slam it. 2.0" lower is low enough.
I stay out of some NY / NJ / CT garages 'cause I can't peek my head far enough out of the roof for my comfort.

On one of my Caprice 9C1-LT1s, I sprayed something on the part of the springs that rubbed.
Forgot what it was 'cause it was over a decade ago.
It may be like the stuff some spray on the frame and the rear trailing arms so they can safely rub (after trimming those thingies off)?
Can I spray that stuff on the springs and the spring seat pockets, instead of heater hose?

 

[MassHoe04]

Sure, size has little effect on safety as long as you are keeping within safe load/speed ranges. It's just a bit unconventional to look at smaller tires when also trying to increase ride quality on rougher terrain. Only attempting to understand your desire so I can offer a better recommendation.

Since you specifically brought it up, and since you are not going specifically for a "street truck" look, the Falken AT3W is a great choice. I've had 3 sets and love em. Price has gone up a bit in the last few years, but what hasn't.

Lots of folks also give the Coopers rave reviews. I have limited experience with them. Only a couple half used sets. Under half tread, I was unimpressed with their rain handling.

Just about a month on Cooper AT3 4S on my Z71. Amazing on wet roads, snow & slush. Very grippy and confident ride. Quiet on the road too.

Mine are 265/70 R17, but just wanted to confirm this particular line of Coopers seems to be a really good tire in all conditions.

 

[iamdub]

No need to slam it. 2.0" lower is low enough.
I stay out of some NY / NJ / CT garages 'cause I can't peek my head far enough out of the roof for my comfort.

On one of my Caprice 9C1-LT1s, I sprayed something on the part of the springs that rubbed.
Forgot what it was 'cause it was over a decade ago.
It may be like the stuff some spray on the frame and the rear trailing arms so they can safely rub (after trimming those thingies off)?
Can I spray that stuff on the springs and the spring seat pockets, instead of heater hose?

I have no idea what this spray is that you speak of. Can you post a product name or link? To my knowledge, there is nothing that can be sprayed out of a can that will withstand two metal parts rubbing each other under thousands of pounds of pressure for years. If there was such a magic lubricant, I'm sure GM would've just sprayed that on the spring pockets and perches and not invested in having isolators made and installed. I'm not saying to not use it. But, while you're spraying lubricants, spray a little on the coil ends and slip some heater hose over them. If you're concerned about the thickness of the heater hose reducing your drop, you're splitting hairs and putting way too much thought into it. The resting height of these things vary from drive to drive and season to season so you'll never see the ~1/16" effect from the heater hose. Wanna make up for that 1/16" drop loss? Measure it in winter. Or add a few gallons of gas to the tank.

I'm one of those that measured each corner multiple times, to the 1/16", before lowering and during the various stages of lowering to closely document each result. Recently, I let the air out of my load bags and noted a precise 1/4" drop. So, I understand maximizing your efforts. But, risking suspension noises to keep 1/16" of a drop exceeds the risk vs. reward threshold.

 

[Marky Dissod]

After one does the rear axle free travel mod, what would one spray on the recently exposed metal, in case one managed to bottom out and make metal to metal contact again even after doing the rear axle free travel mod?

 

[iamdub]

After one does the rear axle free travel mod, what would one spray on the recently exposed metal, in case one managed to bottom out and make metal to metal contact again even after doing the rear axle free travel mod?

You'd eff up a bunch of stuff before the axle hits the frame, such as the pumpkin smashing the EVAP box. The panhard mount on the axle would hit the cross member above it, too.

But, just spray on some quality spray paint. I like the paint/primer combo stuff. If you want more protection, cover that with some undercoating. The frame is bare metal when it's built and they spray on some kind of thick, rubbery coating that seems to stick pretty well for a long time. You'd be doing the same, if not better with something that actually adheres to the metal, like spray paint.