OEM Safe
Within ±3%
Inside factory tolerance — ABS, ESP and cruise control stay calibrated.
Fitment comparison
285/30 R20versus305/30 R20
Δ Ø +12.0 mmSpeedo +1.77%OEM-safe
305/30 R20 stands taller than 285/30 R20 — bigger rolling diameter, slightly more clearance, calmer cruise revs.
305/30 R20 is a wider variation of 285/30 R20 on the same 20-inch rim, adding 20 mm of tread footprint. This sizing approach trims or stretches rolling diameter by a small margin.
The speedometer offset is small but measurable; worth keeping in mind if you watch the dash closely. The wider section adds contact patch and lateral stability, while eating into fender and suspension clearance. Diameter change stays inside the conservative ±3% safety window — an OEM-safe fitment on most vehicles.
TakeUseful when extra dry grip and stance matter more than a small fuel-economy hit.
Quick fitment verdict
285/30 R20 → 305/30 R20 at a glance
Fender Clearance
Check at lock
Wider or taller setup — verify clearance at full steering lock and over bumps.
Speedometer Impact
+1.77%
At a true 100 km/h the dash reads 101.8 km/h — negligible.
Daily Driving
Livable
Daily use is fine; expect a slightly different ride and cruise rev count.
Side-by-side telemetry
Dimensional read-out
Current
285/30 R20
- Diameter
- 679.0 mm
- Sidewall
- 85.5 mm
- Wheel
- 20″
- Width
- 285 mm
Δ delta
Ø +12.0 mm
SW +6.0 mm
RH +6.0 mm
NewNew
305/30 R20
- Diameter
- 691.0 mm
- Sidewall
- 91.5 mm
- Wheel
- 20″
- Width
- 305 mm
Real-world effects
How this swap actually feels
- Steering response47/100 · Softer turn-in
- Ride comfort73/100 · More cushion
- Fuel economy42/100 · Slightly higher drag
- Highway cruising67/100 · Lower cruise revs
- Pothole resistance69/100 · More wheel protection
Shareable card
Generate fitment card
Export a garage-grade telemetry card of this comparison — perfect for forums, Reddit and Discord.
Ride height
Lifted stance
Chassis sits higher — slightly more clearance, wheel-gap visually grows.
New tire lifts the chassis by ~6.0 mm — more clearance, slightly more wheel-gap.
Suspension travel · arch clearance
Wheel gap
Wheel gap visually increases
How the arch-to-tire gap reads from across the parking lot — the visual stance change everyone notices first.
285/30 R20
305/30 R20
Wheel-gap Δ+6.0 mm
Static · unloaded chassis
Fender relationship
Tucked · Flush · Poke
The visual relationship between the tire's outer edge and the fender lip — the lens enthusiasts use to judge a fitment.
Tucked
Inside fender
Flush
Lip-aligned
Poke
Outside fender
Width & offset dependent
Speedometer reality
Dash reads 101.8 km/h
Taller rubber: at a true 100 km/h your dashboard reads optimistically high.
ABS · ESP · cruise control
Setup telemetry
How this setup changes the car
Driver-perspective read-out of the 285/30 R20 → 305/30 R20 swap — steering, comfort, stance and dash behavior in plain enthusiast language.
Steering feel
+6.0 mm sidewallSofter, more relaxed turn-in
Taller sidewall flexes a touch more before loading the contact patch — calmer, comfort-tuned.
Ride firmness
30% → 30%Softer over potholes and joints
Bumps and expansion joints are absorbed better — a comfort win for daily driving.
Fender relationship
+20 mm widthWheel sits closer to the fender
Wider tire pushes the contact patch outboard — flusher stance, but verify fender lip clearance at full lock.
Speedometer behavior
+1.77%OEM-safe speedometer reading
Inside the factory ±3% tolerance — ABS, ESP and cruise control behave as designed.
Daily drivability
Ø +12.0 mmLivable upgrade with minor trade-offs
Daily use is fine; expect a slightly different cruise rev count and a touch more road feel.
Direct answer
Is 305/30 R20 OEM-safe?
Yes. Overall diameter changes by +1.77% versus 285/30 R20. OEM-safe. Speedometer, ABS, ESP and gearing remain inside the factory tolerance.
Direct answer
Will 305/30 R20 rub?
Borderline. Width changes by +20 mm and diameter by +12.0 mm. Borderline — check fender lip and inner strut clearance under load.
Direct answer
Does the speedometer change?
Yes — by +1.77%. Swapping 285/30 R20 for 305/30 R20 changes overall diameter, so at an indicated 100 km/h your true speed becomes 101.8 km/h. That's within the ±3% OEM tolerance — no recalibration needed.
Direct answer
Does lower sidewall affect comfort?
Yes — softer ride. Sidewall changes by +6.0 mm (30% → 30%). Ride softens and absorbs bumps better, with slightly less precise turn-in.
Current Tire
285/30R20
New Tire
305/30R20
Fitment · Scaled comparison
● Excellent fit
285/30 R20
Diameter
+12.0 mm
+1.77%
Sidewall
+6.0 mm
Speedometer
101.8 km/h
at true 100
Clearance
Excellent fit
305/30 R20
Ground line · Scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+12.0 mm
1.77%
Speedometer at 100
101.8 km/h
+1.77% error
Ground clearance
+6.0 mm
ride height delta
Sidewall change
+6.0 mm
revs/km: 460.7
Permalink for this comparison:
/compare/285-30-r20-vs-305-30-r20Detailed comparison
| Metric | 285/30 R20 | 305/30 R20 | Difference |
|---|---|---|---|
| Overall diameter | 679.0 mm | 691.0 mm | +12.0 mm (+1.77%) |
| Sidewall height | 85.5 mm | 91.5 mm | +6.0 mm |
| Circumference | 2.133 m | 2.171 m | +37.7 mm |
| Revs / km | 468.8 | 460.7 | -8.1 |
| Ground clearance | reference | +6.0 mm | +6.0 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 101.8 km/h | +1.77 km/h |
Verdict: excellent
Within ±3% — speedometer, ABS and traction control should behave normally.
Dimensional comparison
Side-by-sideScaled engineering side-profile of both tires. Width, sidewall and overall diameter are dimensioned so you can see the change at a glance — without parsing the numbers.
Current
285/30 R20- Profile
- 30%
- Circumference
- 2.133 m
New
305/30 R20- Profile
- 30%
- Circumference
- 2.171 m
Side-by-side fitment
GeometryCurrent
285/30 R20- Section width
- 285 mm
- Aspect ratio
- 30%
- Sidewall
- 85.5 mm
- Wheel diameter
- 20″(508 mm)
- Overall diameter
- 679.0 mm(26.73″)
- Circumference
- 2.133 m
- Revs / km
- 468.8
New
305/30 R20- Section width
- 305 mm
- Aspect ratio
- 30%
- Sidewall
- 91.5 mm
- Wheel diameter
- 20″(508 mm)
- Overall diameter
- 691.0 mm(27.20″)
- Circumference
- 2.171 m
- Revs / km
- 460.7
Real-world consequences
Pros / consWider tire (+20 mm)
Section width- More dry grip and cornering bite
- Sharper steering response on initial turn-in
- Bigger contact patch under braking
- More road noise on coarse asphalt
- Worse aquaplaning resistance in standing water
- Higher rolling resistance, small MPG hit
- Possible fender or strut contact at full lock
Taller overall (+12.0 mm)
Rolling diameter- Higher ground clearance and approach angle
- Longer effective gearing — calmer highway revs
- Bigger contact patch lengthwise
- Speedometer reads low by ~1.8%
- Reduced fender, strut and bumpstop clearance
- Slower 0-60, more downshifts under load
How it changes driving feel
Seat-of-the-pantsSteering response
Sharper turn-in
Ride comfort
Comparable
Road noise
Louder on coarse asphalt
Wet / aquaplaning
Reduced standing-water margin
Fuel economy
Small MPG penalty likely
Curb / pothole protection
About the same
Fitment risk check
Verify before installFender rubbing
Width jump >20 mm — verify fender lip and inner liner clearance at full lock.
Suspension clearance
Wider tire may contact strut or control arm on full compression.
Cluster preview
Within toleranceSpeedometer impact
At a true 100 km/h, your dashboard will read 101.8 km/h after switching to 305/30 R20 — a +1.77% offset. Use the speedometer error calculator for any indicated speed, and the speedometer error guide for the full background.
Ground clearance change
The new tire's half-diameter changes ride height by +6.0 mm. Small differences are absorbed by suspension travel, but anything beyond ±10 mm can affect headlight aim, fender clearance and bump-stop margin. See the plus-sizing guide before committing.
Back to
285/30 R20
Back to
305/30 R20
Drivers also compare
Closely-related fitments and plus-size swaps for 285/30 R20 and 305/30 R20.
245/35 R20 vs 285/30 R20
Wider variation on the same rim — more grip, less clearance.
Δ 0.07%
265/35 R20 vs 305/30 R20
Wider variation on the same rim — more grip, less clearance.
Δ 0.36%
255/35 R20 vs 305/30 R20
Wider variation on the same rim — more grip, less clearance.
Δ 0.66%
255/35 R20 vs 285/30 R20
Wider variation on the same rim — more grip, less clearance.
Δ 1.09%
275/35 R20 vs 305/30 R20
Wider variation on the same rim — more grip, less clearance.
Δ 1.36%
245/35 R20 vs 305/30 R20
Wider variation on the same rim — more grip, less clearance.
Δ 1.69%
245/40 R20 vs 305/30 R20
Wider variation on the same rim — more grip, less clearance.
Δ 1.85%
265/35 R20 vs 285/30 R20
Wider variation on the same rim — more grip, less clearance.
Δ 2.09%
Related topics
Comparison hub
Back to the tire size comparison calculator
Browse every wheel and tire fitment comparison, by rim size or popularity.