OEM Safe
Within ±3%
Inside factory tolerance — ABS, ESP and cruise control stay calibrated.
Fitment comparison
245/40 R17versus225/40 R18
Δ Ø +9.4 mmSpeedo +1.50%OEM-safe
225/40 R18 stands taller than 245/40 R17 — bigger rolling diameter, slightly more clearance, calmer cruise revs.
Plus-sizing from 245/40 R17 to 225/40 R18 keeps overall diameter close to factory while opening room for a larger 18-inch wheel. This swap lands within OEM rolling-diameter tolerance. Speedometer drift stays small enough that most drivers won't notice it day to day. A narrower footprint can help in deep snow and frees up extra clearance for suspension travel. Diameter change stays inside the conservative ±3% safety window — an OEM-safe fitment on most vehicles.
TakeCommon upgrade for sportier handling and a tighter wheel-gap look on the same vehicle.
Quick fitment verdict
245/40 R17 → 225/40 R18 at a glance
Fender Clearance
Check at lock
Wider or taller setup — verify clearance at full steering lock and over bumps.
Speedometer Impact
+1.50%
At a true 100 km/h the dash reads 101.5 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 R17
- Diameter
- 627.8 mm
- Sidewall
- 98.0 mm
- Wheel
- 17″
- Width
- 245 mm
Δ delta
Ø +9.4 mm
SW -8.0 mm
RH +4.7 mm
NewNew
225/40 R18
- Diameter
- 637.2 mm
- Sidewall
- 90.0 mm
- Wheel
- 18″
- Width
- 225 mm
Real-world effects
How this swap actually feels
- Steering response75/100 · Sharper turn-in
- Ride comfort45/100 · Firmer ride
- Fuel economy43/100 · Slightly lower drag
- Highway cruising66/100 · Lower cruise revs
- Pothole resistance39/100 · Less 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 ~4.7 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.
245/40 R17
225/40 R18
Wheel-gap Δ+4.7 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 101.5 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 245/40 R17 → 225/40 R18 swap — steering, comfort, stance and dash behavior in plain enthusiast language.
Steering feel
-8.0 mm sidewallSharper steering response
Shorter sidewall transmits inputs faster — quicker turn-in, more confident on-center feel.
Ride firmness
40% → 40%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
-20 mm widthMore tuck under the arch
Narrower contact patch tucks slightly inboard — cleaner look from the rear three-quarter.
Speedometer behavior
+1.50%OEM-safe speedometer reading
Inside the factory ±3% tolerance — ABS, ESP and cruise control behave as designed.
Daily drivability
Ø +9.4 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 225/40 R18 OEM-safe?
Yes. Overall diameter changes by +1.50% versus 245/40 R17. OEM-safe. Speedometer, ABS, ESP and gearing remain inside the factory tolerance.
Direct answer
Will 225/40 R18 rub?
Borderline. Width changes by -20 mm and diameter by +9.4 mm. Borderline — check fender lip and inner strut clearance under load.
Direct answer
Does the speedometer change?
Yes — by +1.50%. Swapping 245/40 R17 for 225/40 R18 changes overall diameter, so at an indicated 100 km/h your true speed becomes 101.5 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 -8.0 mm (40% → 40%). Ride becomes firmer and steering sharper, but potholes and expansion joints hit harder and wheel damage risk rises.
Current Tire
245/40R17
New Tire
225/40R18
Fitment · Scaled comparison
● Excellent fit
245/40 R17
Diameter
+9.4 mm
+1.50%
Sidewall
-8.0 mm
Speedometer
101.5 km/h
at true 100
Clearance
Excellent fit
225/40 R18
Ground line · Scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+9.4 mm
1.50%
Speedometer at 100
101.5 km/h
+1.50% error
Ground clearance
+4.7 mm
ride height delta
Sidewall change
-8.0 mm
revs/km: 499.5
Permalink for this comparison:
/compare/245-40-r17-vs-225-40-r18Detailed comparison
| Metric | 245/40 R17 | 225/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 627.8 mm | 637.2 mm | +9.4 mm (+1.50%) |
| Sidewall height | 98.0 mm | 90.0 mm | -8.0 mm |
| Circumference | 1.972 m | 2.002 m | +29.5 mm |
| Revs / km | 507.0 | 499.5 | -7.5 |
| Ground clearance | reference | +4.7 mm | +4.7 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 101.5 km/h | +1.50 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 R17- Profile
- 40%
- Circumference
- 1.972 m
New
225/40 R18- Profile
- 40%
- Circumference
- 2.002 m
Side-by-side fitment
GeometryCurrent
245/40 R17- Section width
- 245 mm
- Aspect ratio
- 40%
- Sidewall
- 98.0 mm
- Wheel diameter
- 17″(432 mm)
- Overall diameter
- 627.8 mm(24.72″)
- Circumference
- 1.972 m
- Revs / km
- 507.0
New
225/40 R18- Section width
- 225 mm
- Aspect ratio
- 40%
- Sidewall
- 90.0 mm
- Wheel diameter
- 18″(457 mm)
- Overall diameter
- 637.2 mm(25.09″)
- Circumference
- 2.002 m
- Revs / km
- 499.5
Real-world consequences
Pros / consNarrower tire (-20 mm)
Section width- Better aquaplaning resistance
- Lower rolling resistance and slightly better MPG
- Quieter ride, less tramlining
- Lighter unsprung mass on the corner
- Less dry grip at the limit
- Smaller contact patch under hard braking
- Stance can look tucked or undersized
+1″ rim upsize
Wheel diameter- OEM+ look, fills the arch better
- Sharper response with matching low-profile rubber
- Bigger brake clearance for upgrades
- Heavier wheel, more unsprung mass
- Harsher ride, more wheel-damage risk
- Tire and wheel cost both go up
How it changes driving feel
Seat-of-the-pantsSteering response
Softer, slower
Ride comfort
Comparable
Road noise
Similar cabin noise
Wet / aquaplaning
Comparable wet behavior
Fuel economy
Negligible change
Curb / pothole protection
About the same
Cluster preview
Within toleranceSpeedometer impact
At a true 100 km/h, your dashboard will read 101.5 km/h after switching to 225/40 R18 — a +1.50% 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 +4.7 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 R17
Back to
225/40 R18
Drivers also compare
Closely-related fitments and plus-size swaps for 245/40 R17 and 225/40 R18.
225/40 R18 vs 255/35 R18
Wider variation on the same rim — more grip, less clearance.
Δ 0.24%
215/45 R17 vs 245/40 R17
Wider variation on the same rim — more grip, less clearance.
Δ 0.40%
225/45 R17 vs 245/40 R17
Wider variation on the same rim — more grip, less clearance.
Δ 1.02%
225/40 R18 vs 235/40 R18
Wider variation on the same rim — more grip, less clearance.
Δ 1.26%
215/40 R18 vs 225/40 R18
Wider variation on the same rim — more grip, less clearance.
Δ 1.27%
245/40 R17 vs 255/40 R17
Wider variation on the same rim — more grip, less clearance.
Δ 1.27%
225/40 R18 vs 245/35 R18
Wider variation on the same rim — more grip, less clearance.
Δ 1.33%
205/50 R17 vs 245/40 R17
Wider variation on the same rim — more grip, less clearance.
Δ 1.41%
Related topics
Comparison hub
Back to the tire size comparison calculator
Browse every wheel and tire fitment comparison, by rim size or popularity.