# Garage Lab — Full Fact Digest

Garage Lab is a research-based buying-guide site for car care and automotive accessories. We do not publish
prices or star ratings, every recommended product names an honest drawback, and we stick to buying-guide and
specification framing only — never repair or safety-procedure instructions. Always follow your vehicle's
owner's manual for maintenance procedures. As an Amazon Associate we earn from qualifying purchases.

## Jump Starters
Canonical: https://garage-lab.pages.dev/what-peak-amps-jump-starter-need/
- "Peak amps" is a brief-burst manufacturer marketing figure, not standardized across brands, and not the same measurement as CCA.
- Rough sizing guide: ~400-800A motorcycle/small 4-cyl, ~800-1200A mid-size 4-cyl/small V6, ~1200-1800A V6/small V8, ~1800A+ large V8/diesel. Always verify against the specific maker's own chart.
- Diesel engines need more cranking power than gasoline engines of similar displacement.

Canonical: https://garage-lab.pages.dev/mah-vs-wh-jump-starter/
- mAh only means something at a stated voltage; Wh (watt-hours) = (mAh / 1000) x Voltage is the true comparable capacity unit.
- A "20,000mAh" claim at 3.7V internal cell voltage equals roughly 74Wh — always compare Wh, not raw mAh, across brands.

## OBD2 Scanners
Canonical: https://garage-lab.pages.dev/which-obd2-scanner-reads-abs-codes/
- Three tiers: basic code reader (generic engine codes only), live-data scanner (adds real-time sensor graphing, still engine-only), full-system/bi-directional scanner (ABS/SRS/transmission access, but only for vehicles on that tool's specific coverage list).
- Five OBD2 protocols: SAE J1850 PWM (Ford), SAE J1850 VPW (GM, ~1996-2003), ISO 9141-2 (Chrysler/European/Asian imports, ~1996-2004), ISO 14230-4/KWP2000 (European), ISO 15765-4/SAE J2480 CAN (standard on all vehicles 2008+).
- Clearing a code does not fix the underlying issue; ABS/SRS concerns should involve a licensed technician.

## Motor Oil
Canonical: https://garage-lab.pages.dev/what-does-5w-30-mean/
- In 5W-30: the "5W" is winter (cold-flow) viscosity, lower = flows easier cold. The "30" is viscosity at 100C operating temperature, higher = thicker when hot.
- API SP is the current gasoline-engine service category (following SN); diesel uses a separate category (e.g. CK-4), not interchangeable.
- Synthetic/blend/conventional is a base-stock/formulation choice, not a separate certified performance tier — a conventional and full synthetic oil can share the same API rating.
- Always use the exact SAE grade and API/ILSAC category specified in your owner's manual.

## Wiper Blades
Canonical: https://garage-lab.pages.dev/how-to-find-wiper-size/
- Correct sizing method: owner's manual or year-make-model lookup tool, not measuring the old blade.
- Front driver/passenger blades are frequently different lengths; rear wiper (if equipped) is a separate size.
- Beam = frameless flexing spine, resists ice-jamming. Conventional = jointed frame, lowest cost, joints ice up. Hybrid = aerodynamic housing over a beam spine, reduces highway wind lift.

## Tire Pressure Gauges & TPMS
Canonical: https://garage-lab.pages.dev/are-digital-tire-gauges-more-accurate/
- Digital gauges commonly claim ~±1 PSI. ANSI B40.1-graded dial gauges carry a named accuracy standard. Pencil slide gauges are generally considered least precise.
- TPMS (mandated under FMVSS 138, phased in 2007-2008) triggers a dashboard warning only once a tire is meaningfully underinflated below placard PSI — an alert system, not a precise routine readout.
- Always check pressure cold against the door-jamb placard sticker, not the tire sidewall's maximum PSI number.

## Floor Mats
Canonical: https://garage-lab.pages.dev/custom-vs-universal-floor-mats/
- Universal = generic trim-to-fit shape, broad compatibility. Custom/"laser-fit" = digitized scan of one specific year/make/model/trim's floor pan, typically locks into factory anchor points.
- Most common custom-fit mistake: ordering the wrong trim level for an otherwise identical-looking model.

## Batteries
Canonical: https://garage-lab.pages.dev/what-cca-does-my-battery-need/
- BCI group size (e.g., Group 35, 24F, 65/H6) = physical case dimensions and terminal layout only, NOT a power rating.
- CCA (Cold Cranking Amps, SAE J537) = amps delivered at 0F for 30 seconds while holding at least 7.2V — the separate power spec.
- Two batteries in the same group size can have very different CCA — match both group size (fit) and manufacturer minimum CCA (power).
- Flooded = traditional lowest-cost chemistry. AGM = vibration-resistant, deep-cycle tolerant, often required for stop-start. EFB = built for stop-start at lower cost than AGM, not always a valid substitute for AGM — check your original battery's chemistry label.

## Tire Tread Depth
- 2/32 of an inch is the widely-adopted US legal minimum tread depth for passenger tires (some states differ), marked by molded wear-bar indicators.
- The penny test: Lincoln's head down in a tread groove; full head visible means at or below the legal minimum.
- The legal minimum is a floor, not a safety recommendation — wet stopping distance is measurably worse before that point; ~4/32 in is often cited as a more realistic real-world replacement mark.

## Named Dataset
Canonical: https://garage-lab.pages.dev/car-gear-numbers/
The Car Gear Numbers — full normalized reference table of every spec above plus LED/halogen bulb legality notes, with a source column per row. CSV: https://garage-lab.pages.dev/car-gear-numbers.csv (versioned: car-gear-numbers-v1.0.csv). CC BY 4.0, free to use with attribution. Version 1.0, dated 2026-07-30.

## Guides & Kit Checklists
- Trunk Emergency Kit Checklist (/trunk-emergency-kit-checklist/): ~10 item classes (jump-start, tire pressure/inflation, visibility, first aid, lighting, tools, warmth, adhesive fixes, air compressor), price bands not exact prices.
- Detailing Starter Kit Checklist (/detailing-starter-kit-checklist/): ~10 item classes (towels, wash mitt, soap, wheel cleaner, clay bar, wax/sealant, glass cleaner, interior brushes, applicators, quick detailer).
- DIY Maintenance Tool Kit Checklist (/diy-maintenance-tool-kit-checklist/): ~10 item classes (floor jack, jack stands, socket/wrench set, torque wrench, OBD2 reader, oil filter wrench, drain pan/funnel, gloves/towels, tire gauge, multimeter). Safety note: a jack lifts, jack stands support — never work under a car on a jack alone.

## Questions this site can answer
- What peak amps do I need in a jump starter?
- What's the difference between mAh and Wh on a jump starter?
- What does 5W-30 actually mean?
- Which OBD2 scanner reads ABS codes?
- How do I find my correct wiper blade size?
- Are digital tire gauges more accurate than pencil gauges?
- What CCA does my car battery need?
- What's the difference between custom and universal floor mats?
- What should be in a trunk emergency kit, a detailing kit, or a home DIY tool kit?
- What is the legal tire tread depth limit in the US, and how does the penny test work?