Dialing In Tire Pressure After Upsizing to LT285/75R18 (ZR2 Case Study)

Truck: 2024 Chevrolet Silverado 1500 ZR2Stock tire: Goodyear Territory MT, 275/70R18 (≈33.1")New tire: Goodyear Wrangler Territory AT/S, LT285/75R18, Load Range E (≈34.8–35") — same exact tire as equipped on the Silverado EV Trail Boss (these are EV Trail Boss Factory Equipped Tires).Wheels: OEM ZR2 18"

Why this article

I upsized my ZR2 from the factory 275/70R18 to a 35"-class LT285/75R18 E‑rated tire (the same size used on the Silverado EV Trail Boss). The goal here isn’t just to show the fitment (it does fit with a minor trim), but to get tire pressures right after the swap. This write‑up pairs real‑world notes from my road test with the fundamentals behind PSI selection so you can avoid harsh ride, center wear, or—worse—heat build‑up from under‑inflation.

TL;DR (If you just want numbers to start with)

• Do not copy the Silverado EV Trail Boss placard (~56 psi front shown). It’s ~2,500–3,000 lb heavier; that PSI will be too high for a 1500.

• Do not keep stock ZR2 pressures either (set for P‑metric/C‑load construction).

• Safe starting point (empty daily driving) for LT285/75R18 Load Range E on a Silverado 1500: 46–48 psi cold front & rear. Tune from there with the “hot‑rise” and tread tests below.

• Towing/hauling: raise the rears to ~58–62 psi (fronts ~48–50), staying under wheel/tire limits.

Principle: LT tires carry load as a function of pressure. Heavier‑duty (E‑load) tires generally need more PSI than P/C tires to carry the same weight, but you shouldn’t inflate them to an EV’s heavier‑vehicle placard.

Baseline: Stock ZR2 vs. the New Setup

What changed

• Diameter: ~33.1" → ~34.8–35" (effective gearing slightly taller)

• Width/profile: went with a narrower, street‑biased 35 for low noise/rolling resistance

• Weight: ~50 lb (stock) → ~56 lb (new), +6 lb per corner

• Construction: P/C‑type → LT Load Range E (much stiffer carcass, different load‑inflation curve)

Road notes from the swap (65–73 mph GPS check)

• Speedometer now reads ~2–3 mph slow relative to GPS at highway speeds.

• Ride is quieter and smoother; bumps are better absorbed.

• Engine works slightly harder off the line (taller effective gearing + added rotational mass).

• Fitment: at full‑lock while reversing into a driveway there was a very slight rub only as the suspension compressed over the bump; no trimming performed yet. (ZR2 sits just under a 2" lift from a standard 1500.)

Why you can’t use the Silverado EV Trail Boss placard PSI

The EV Trail Boss is a different animal: it carries much higher axle loads. Its placard pressures (one front reading observed: 56 psi) are tuned for that curb weight and GVWR—not for the tire itself. If you put EV placard PSI into a much lighter 1500:

• You’ll get a harsh ride, longer braking distances on imperfect pavement, and center‑tread wear.

• TPMS and handling tuning won’t match your truck’s actual axle loads.

Conclusion: The EV’s higher PSI is not a target—it’s a red flag that your 1500 doesn’t need that much pressure when empty.

Why you shouldn’t stick with stock ZR2 PSI either

Your ZR2 placard was engineered around the original tire construction (P‑metric/C‑load). An LT Load Range E tire is stiffer and is designed to carry load as PSI increases up its load curve. At the same cold PSI, an E‑load tire typically carries less load than a P‑metric/C at that same pressure. That’s why many 1500 owners feel squirm/heat if they try to run E‑loads down near 35–38 psi.

Rule of thumb: Upsizing to LT Load Range E usually warrants a bump into the mid‑40s psi for empty daily use on a 1500, then up into the high‑50s/low‑60s when you add real payload or tongue weight—within wheel limits.

The simple, no‑scale method to dial it in

1. Start: 46–48 psi cold (all around).

2. Drive 30–60 minutes at highway speed. Measure hot PSI rise:

   • +4 to +6 psi hot = sweet spot.

   • >+8 psi rise = under‑inflated → add 2–3 psi next cold.

   • <+3 psi rise & harsh ride/center wear = over‑inflated → bleed 2–3 psi.

3. Tread/temperature check:

   • Center hotter/more wear = too much PSI.

   • Shoulders hotter/more wear = too little PSI.

   • Even across = keep it.

4. Load days: For towing/hauling, bump rears to ~58–62 psi, fronts ~48–50. Re‑check hot rise.

5. Respect limits: never exceed the wheel’s max PSI (many 1500 OE wheels are ~50–60 psi) or the tire’s rating.

Real‑world context: What GM manuals say (and why)

GM’s guidance emphasizes matching replacements to OE TPC Spec tires and sticking to placard PSI because TPC integrates braking, handling, TPMS, etc. That’s the right advice for a stock‑size, stock‑type tire—on the same vehicle. Once you change both size and construction (P/C → LT‑E) and you’re not on the EV, you have to use load‑based logic rather than copying either placard blindly.

Bottom line: Placards are vehicle‑specific, not tire‑specific. When the vehicle changes (EV vs. 1500) or the tire construction changes (P vs. LT‑E), you set PSI by required load, then confirm with hot‑rise and tread.

Quick reference table (this build)

Item	Stock ZR2	New Setup
Size	275/70R18 (≈33.1")	LT285/75R18 (≈34.8–35")
Load Range	P/C	LT‑E (80 psi max)
Weight (tire)	~50 lb	~56 lb
Baseline cold PSI (empty)	~38 psi placard	46–48 psi start
Towing/Hauling (rear)	42–50 psi typical	~58–62 psi (within wheel rating)
EV Trail Boss placard seen	n/a	~56 psi front (on EV; do not mimic on 1500)

Notes: Always verify your wheel’s pressure rating; do not exceed.

FAQ

Will the taller tire hurt MPG?  Mixed. Lower RPM at cruise and a more road‑biased tread can help; added mass and taller gearing hurt in city driving. I’m logging results on long freeway runs to quantify it.

Why not just inflate to the max printed on the sidewall? That’s the tire’s maximum at its rated load, not your truck’s need. Running “max cold” empty kills comfort and grip and accelerates center wear.

What about TPMS thresholds? If you’re running mid‑40s cold, your TPMS low threshold on a 1500 should be fine. If you routinely see warnings, re‑learn after setting a stable cold PSI.

Do I need an alignment after upsizing? I did one at install. It’s cheap insurance, especially with a different tire profile and any trimming.

Sources & Attributions

• GM Owner’s Manual & Service Info: Tire Inflation Description; TPC Spec guidance; vehicle‑specific placard logic.

• Silverado EV Trail Boss reviews: observed front tire pressure screen around 56 psi (EV platform—heavier curb/GVWR).

• Industry standard practice: LT load‑inflation tables (consult your specific tire manufacturer for exact load vs. PSI values).

What I’d do (summary)

• Start at 46–48 psi cold on LT285/75R18 E for empty driving.

• Use hot‑rise (+4–6 psi target) and tread temperature/wear to tune.

• For towing/hauling, raise rear to ~58–62 psi, front ~48–50, while respecting wheel/tire limits.

• Do not copy the EV Trail Boss placard on a much lighter 1500.

This article reflects measurements and observations from my ZR2 build and general best practices for LT tires on half‑ton trucks.