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315/30R21 upsize, downsize & alternatives

Every safe alternative tire size for 315/30R21 within the ETRTO ±3% overall-diameter tolerance. Grouped by upgrade intent. Speedometer impact and catalog availability shown for each.

By Mark Bishop · Last verified 2026-05-17 · What does 315/30R21 mean?

Plus-1 (next rim size up)

Plus-1 keeps overall diameter constant while bumping rim diameter by one inch and dropping aspect ratio by ten points. The standard daily-driver upgrade — sharper steering response, mild ride penalty, modest tire-cost premium.

SizeOD (mm)%ΔTrue @ 60 mphVerdictIn catalog
325/25R22 721 -0.15% 59.91 mph Safe —
335/25R22 726 0.54% 60.32 mph Safe —
315/25R22 716 -0.84% 59.49 mph Safe —
285/30R22 730 1.02% 60.61 mph Within tolerance —
345/25R22 731 1.23% 60.74 mph Within tolerance —
305/25R22 711 -1.54% 59.08 mph Within tolerance —
295/30R22 736 1.85% 61.11 mph Within tolerance —
295/25R22 706 -2.23% 58.66 mph Within tolerance —
305/30R22 742 2.69% 61.61 mph Within tolerance —
285/25R22 701 -2.92% 58.25 mph Within tolerance —

Same rim, wider footprint

Same rim diameter as your OEM, just a wider footprint. Increases grip and footprint contact at the cost of fuel economy and steering effort. Confirm fender clearance at full lock before purchase.

SizeOD (mm)%ΔTrue @ 60 mphVerdictIn catalog
325/30R21 728 0.83% 60.50 mph Safe Yes
335/30R21 734 1.66% 61.00 mph Within tolerance —
345/25R21 706 -2.28% 58.63 mph Within tolerance —
345/30R21 740 2.49% 61.50 mph Within tolerance —
335/25R21 701 -2.98% 58.21 mph Within tolerance —

Winter / narrower contact

Narrower than OEM, aspect ratio raised to preserve overall diameter. Higher contact pressure improves snow and slush bite — the Nokian-style rule of one width step down for winter on the same overall diameter.

SizeOD (mm)%ΔTrue @ 60 mphVerdictIn catalog
305/35R20 722 -0.12% 59.93 mph Safe —
305/30R21 716 -0.83% 59.50 mph Safe Yes
295/35R20 715 -1.09% 59.34 mph Within tolerance —
285/35R21 733 1.45% 60.87 mph Within tolerance —
295/30R21 710 -1.66% 59.00 mph Within tolerance Yes
285/40R20 736 1.88% 61.13 mph Within tolerance —
285/35R20 708 -2.06% 58.76 mph Within tolerance —
295/35R21 740 2.42% 61.45 mph Within tolerance —
285/30R21 704 -2.49% 58.50 mph Within tolerance —
295/40R20 744 2.99% 61.79 mph Within tolerance —

Other geometric alternatives

Geometrically valid alternatives that don't fit a named category. Often combinations of rim and aspect change that happen to land in tolerance.

SizeOD (mm)%ΔTrue @ 60 mphVerdictIn catalog
345/35R19 724 0.24% 60.14 mph Safe —
295/40R19 719 -0.53% 59.68 mph Safe —
305/40R19 727 0.58% 60.35 mph Safe —
335/35R19 717 -0.73% 59.56 mph Safe —
315/35R20 729 0.84% 60.51 mph Safe —
345/30R20 715 -1.02% 59.39 mph Within tolerance —
285/40R19 711 -1.63% 59.02 mph Within tolerance —
315/40R19 735 1.69% 61.01 mph Within tolerance —
325/35R19 710 -1.70% 58.98 mph Within tolerance —
325/35R20 736 1.81% 61.09 mph Within tolerance —
335/30R20 709 -1.85% 58.89 mph Within tolerance —
285/45R19 739 2.31% 61.39 mph Within tolerance —
315/35R19 703 -2.67% 58.40 mph Within tolerance —
325/30R20 703 -2.69% 58.39 mph Within tolerance —
335/35R20 743 2.78% 61.67 mph Within tolerance —
325/40R19 743 2.80% 61.68 mph Within tolerance —

Try another alternative

Type any size below — we will compute its overall-diameter delta against 315/30R21 and verdict using the same ±3% rule.

For full results across all common alternatives, use the tire compatibility calculator.

What this page tells you

Every alternative listed above falls inside the ±3% overall-diameter tolerance defined by ETRTO 2024 Standards Manual §2.3 — the universal safe-fit threshold that keeps speedometer accuracy (SAE J1349), TPMS calibration (NHTSA FMVSS 138), ABS reference, and AWD viscous-coupling temperature inside their factory programming. Sizes outside that envelope are excluded from this table; if you want to see them anyway, use the compatibility calculator.

315/30R21 has an overall diameter of 722.4 mm (28.44 inches), a sidewall height of 94.5 mm, and turns 709 revolutions per mile. We surface 41 realistic alternatives across the categories above; 3 of them are currently sold in tire models we catalog. The remaining alternatives are geometrically valid but uncommon — they fit a vehicle perfectly but you may need to special-order the tire.

How to read the verdict column

"Safe" means the alternative is within ±1% overall diameter — indistinguishable from OEM in everyday driving, no recalibration recommended. "Within tolerance" means 1–3% — fitable per ETRTO, but you may notice mild speedometer drift and should consider a one-time OBD-II calibration if you drive an AWD or EV. Anything beyond ±3% is excluded from this list per the safe-fit threshold.

Categories explained

Each category corresponds to a different driving-priority trade-off. Plus-1 and Plus-2 trade ride comfort for sharper steering and a more filled-out wheel-fender opening. Wider sizes on the same rim trade fuel economy for grip. Winter narrower sizes increase contact pressure on snow (more downforce per unit of footprint area), which is why every European winter-tire engineering bulletin recommends a one-width-step-down policy for winter. Narrower same-rim sizes trade dry grip for fuel economy. OEM-equivalent sizes are useful when your favorite tire model is no longer made in your exact size — find the under-half-percent OD match here and you have an effective drop-in replacement.

What this page does not cover

Geometry only. Wheel offset, bolt pattern, brake-caliper clearance, fender clearance at full lock, and TPMS sensor compatibility are mechanical fitment constraints that depend on your chassis and wheel choice — those need a vehicle-specific check. Cross-reference your vehicle fitment page for OEM offset and bolt pattern, the wheel manufacturer's fitment guide, or your vehicle owner's manual before purchase.

Vehicles currently using 315/30R21

See the full reverse-lookup of vehicles for 315/30R21, including approved-alternative fitments that don't appear above.

Sources & methodology

Last verified 2026-05-17 against the standards below.

  1. ETRTO 2024 Standards Manual §2.3 (section width, aspect ratio, overall diameter formula). European Tyre and Rim Technical Organisation, Brussels.
  2. Tire & Rim Association 2025 Yearbook, Table 1-2 (load index → maximum load equivalence). T&RA, Copley OH.
  3. SAE J1349 (Engine Power Test Code / speedometer accuracy reference).
  4. NHTSA FMVSS 138 Tire Pressure Monitoring Systems — rev/mile calibration requirements.
  5. Tire Industry Association Technical Bulletin TB-2019-04 (plus-sizing guidance).
  6. Nokian Tyres "Why winter tyres should be narrower" technical bulletin, 2019.

FAQ

What is the safest alternative tire size for 315/30R21?
The safest alternative is any size listed above as "Safe" verdict — these are within ±1% overall diameter and require no recalibration. The OEM-equivalent category contains the closest matches; the Plus-1 category contains the most commonly used aftermarket upgrade.
Will any of these alternatives change my speedometer reading?
All listed alternatives are within ±3% overall diameter, which falls inside the SAE J1349 ±4% speedometer envelope. Sizes within ±1% (Safe verdict) produce sub-1 mph error at 60 mph indicated. Sizes within 1–3% (Within Tolerance) produce 1–2 mph error at 60 mph — measurable but inside the factory tolerance.
Why are some alternatives marked "In catalog: yes" and others not?
"In catalog" means at least one tire model in our database is sold in that exact size. Sizes without an "In catalog" mark are geometrically valid alternatives — they fit your vehicle — but you may need to special-order the tire from the manufacturer or expand your tire-shopping radius.
Can I mix two of these alternatives across axles?
Don't. Mixing different overall diameters across an axle creates a permanent rev mismatch that the ABS module can read as constant slip, sometimes throwing warning lights, sometimes degrading anti-lock response. On AWD vehicles the viscous coupling absorbs that mismatch as heat. Fit four matching tires (or at minimum, matching tires per axle for staggered setups).
Where do these tolerance rules come from?
The ±3% overall-diameter tolerance is documented in ETRTO 2024 Standards Manual §2.3 and the Tire & Rim Association 2025 Yearbook, and is adopted by every passenger-vehicle OEM tire-fitment guide we have reviewed. The standard derives from the maximum diameter change that preserves speedometer accuracy (SAE J1349), TPMS rev/mile tracking (FMVSS 138), ABS reference (FMVSS 135), and adaptive-transmission shift calibration in one envelope.