OEM Safe
Within ±3%
Inside factory tolerance — ABS, ESP and cruise control stay calibrated.
Fitment comparison
245/40 R20versus305/30 R20
Δ Ø -13.0 mmSpeedo -1.85%OEM-safe
305/30 R20 is shorter than 245/40 R20 — quicker gearing feel, tighter arch gap, livelier throttle response.
305/30 R20 is a lower-profile take on 245/40 R20 — same 20-inch wheel, shorter sidewall. This wheel and tire pairing shifts overall diameter slightly from OEM.
Expect a slight but noticeable shift in indicated speed compared to the original tires. The shorter sidewall gives the tire a firmer, more responsive feel and sharpens steering input. More tread on the ground tends to improve dry grip and stance, with a small fuel-economy and clearance tradeoff. Diameter change stays inside the conservative ±3% safety window — an OEM-safe fitment on most vehicles.
TakeSuits drivers who value sharper steering and appearance over outright ride softness.
Quick fitment verdict
245/40 R20 → 305/30 R20 at a glance
Fender Clearance
Likely rubs
Significantly wider/taller — rubbing risk on liners or fender lip is real.
Speedometer Impact
-1.85%
At a true 100 km/h the dash reads 98.2 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
245/40 R20
- Diameter
- 704.0 mm
- Sidewall
- 98.0 mm
- Wheel
- 20″
- Width
- 245 mm
Δ delta
Ø -13.0 mm
SW -6.5 mm
RH -6.5 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 response72/100 · Sharper turn-in
- Ride comfort48/100 · Firmer ride
- Fuel economy4/100 · Slightly higher drag
- Highway cruising52/100 · Higher cruise revs
- Pothole resistance42/100 · Less wheel protection
Shareable card
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Ride height
Lower stance
Chassis drops — tighter arch gap, more aggressive stance.
New tire drops ride height by ~6.5 mm — tighter arch gap, lower stance.
Suspension travel · arch clearance
Wheel gap
Wheel sits closer to the fender
How the arch-to-tire gap reads from across the parking lot — the visual stance change everyone notices first.
245/40 R20
305/30 R20
Wheel-gap Δ-6.5 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 98.2 km/h
Shorter rubber: dashboard reads conservatively low — you're slower than it claims.
ABS · ESP · cruise control
Setup telemetry
How this setup changes the car
Driver-perspective read-out of the 245/40 R20 → 305/30 R20 swap — steering, comfort, stance and dash behavior in plain enthusiast language.
Steering feel
-6.5 mm sidewallSharper steering response
Shorter sidewall transmits inputs faster — quicker turn-in, more confident on-center feel.
Ride firmness
40% → 30%Slightly firmer over rough pavement
Expect more chatter on broken tarmac and a sharper pothole strike — keep an eye on wheel damage risk.
Fender relationship
+60 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
-1.85%OEM-safe speedometer reading
Inside the factory ±3% tolerance — ABS, ESP and cruise control behave as designed.
Daily drivability
Ø -13.0 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 -1.85% versus 245/40 R20. OEM-safe. Speedometer, ABS, ESP and gearing remain inside the factory tolerance.
Direct answer
Will 305/30 R20 rub?
Possibly. Width changes by +60 mm and diameter by -13.0 mm. Possible rub at full lock or full suspension compression — verify fender lip and inner strut clearance before committing.
Direct answer
Does the speedometer change?
Yes — by -1.85%. Swapping 245/40 R20 for 305/30 R20 changes overall diameter, so at an indicated 100 km/h your true speed becomes 98.2 km/h. That's within the ±3% OEM tolerance — no recalibration needed.
Direct answer
Does lower sidewall affect comfort?
Yes — firmer ride. Sidewall changes by -6.5 mm (40% → 30%). Ride becomes firmer and steering sharper, but potholes and expansion joints hit harder and wheel damage risk rises.
Current Tire
245/40R20
New Tire
305/30R20
Fitment · Scaled comparison
● Excellent fit
245/40 R20
Diameter
-13.0 mm
-1.85%
Sidewall
-6.5 mm
Speedometer
98.2 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
-13.0 mm
-1.85%
Speedometer at 100
98.2 km/h
-1.85% error
Ground clearance
-6.5 mm
ride height delta
Sidewall change
-6.5 mm
revs/km: 460.7
Permalink for this comparison:
/compare/245-40-r20-vs-305-30-r20Detailed comparison
| Metric | 245/40 R20 | 305/30 R20 | Difference |
|---|---|---|---|
| Overall diameter | 704.0 mm | 691.0 mm | -13.0 mm (-1.85%) |
| Sidewall height | 98.0 mm | 91.5 mm | -6.5 mm |
| Circumference | 2.212 m | 2.171 m | -40.8 mm |
| Revs / km | 452.1 | 460.7 | +8.5 |
| Ground clearance | reference | -6.5 mm | -6.5 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 98.2 km/h | -1.85 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
245/40 R20- Profile
- 40%
- Circumference
- 2.212 m
New
305/30 R20- Profile
- 30%
- Circumference
- 2.171 m
Side-by-side fitment
GeometryCurrent
245/40 R20- Section width
- 245 mm
- Aspect ratio
- 40%
- Sidewall
- 98.0 mm
- Wheel diameter
- 20″(508 mm)
- Overall diameter
- 704.0 mm(27.72″)
- Circumference
- 2.212 m
- Revs / km
- 452.1
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 (+60 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
Lower profile (-10% aspect)
Sidewall- Sharper turn-in and less sidewall roll
- More planted on smooth tarmac
- Bigger brake / caliper visual real estate
- Harsher ride over expansion joints and potholes
- Higher wheel-damage risk on impacts
- Less curb protection for the rim lip
- More sensitive to correct tire pressure
Shorter overall (-13.0 mm)
Rolling diameter- Shorter effective gearing — perkier acceleration
- Lower center of gravity, sharper transitions
- More fender and arch clearance
- Speedometer reads high by ~1.8%
- Engine spins higher at cruise, small MPG hit
- ABS / ESP recalibration may be advisable
How it changes driving feel
Seat-of-the-pantsSteering response
Sharper turn-in
Ride comfort
Harsher impacts
Road noise
Louder on coarse asphalt
Wet / aquaplaning
Reduced standing-water margin
Fuel economy
Small MPG penalty likely
Curb / pothole protection
Higher wheel-damage risk
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 98.2 km/h after switching to 305/30 R20 — a -1.85% 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 -6.5 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
245/40 R20
Back to
305/30 R20
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