OEM Safe
Out of spec
Beyond OEM tolerance — speedometer and ABS need professional review.
Fitment comparison
245/35 R18versus255/40 R18
Δ Ø +32.5 mmSpeedo +5.17%Aggressive
255/40 R18 stands taller than 245/35 R18 — bigger rolling diameter, slightly more clearance, calmer cruise revs.
255/40 R18 is a wider variation of 245/35 R18 on the same 18-inch rim, adding 10 mm of tread footprint. This wheel and tire pairing moves rolling diameter well outside the usual OEM tolerance.
The dashboard speed will be significantly off — plan on recalibration before daily use. More sidewall typically improves comfort and curb protection, especially on city streets. The wider section adds contact patch and lateral stability, while eating into fender and suspension clearance. A diameter change beyond 5% is aggressive enough to influence ABS, traction control and gearing; treat it as a serious modification.
TakeTreat as a serious modification — verify clearance, recalibrate the speedometer and reassess load capacity.
Quick fitment verdict
245/35 R18 → 255/40 R18 at a glance
Fender Clearance
Likely rubs
Significantly wider/taller — rubbing risk on liners or fender lip is real.
Speedometer Impact
+5.17%
Dash reads 105.2 km/h at a true 100 km/h — recalibrate.
Daily Driving
Aggressive
Geometry deviates enough to matter — confirm clearance before daily use.
Side-by-side telemetry
Dimensional read-out
Current
245/35 R18
- Diameter
- 628.7 mm
- Sidewall
- 85.8 mm
- Wheel
- 18″
- Width
- 245 mm
Δ delta
Ø +32.5 mm
SW +16.3 mm
RH +16.3 mm
NewNew
255/40 R18
- Diameter
- 661.2 mm
- Sidewall
- 102.0 mm
- Wheel
- 18″
- Width
- 255 mm
Real-world effects
How this swap actually feels
- Steering response26/100 · Softer turn-in
- Ride comfort94/100 · More cushion
- Fuel economy48/100 · Slightly higher drag
- Highway cruising80/100 · Lower cruise revs
- Pothole resistance93/100 · 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 ~16.3 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.
245/35 R18
255/40 R18
Wheel-gap Δ+16.3 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 105.2 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 245/35 R18 → 255/40 R18 swap — steering, comfort, stance and dash behavior in plain enthusiast language.
Steering feel
+16.3 mm sidewallSofter, more relaxed turn-in
Taller sidewall flexes a touch more before loading the contact patch — calmer, comfort-tuned.
Ride firmness
35% → 40%Softer over potholes and joints
Bumps and expansion joints are absorbed better — a comfort win for daily driving.
Fender relationship
+10 mm widthFender gap reads near-identical
Width delta is too small to change stance — same visual signature as OEM.
Speedometer behavior
+5.17%Out of tolerance — recalibrate
Beyond ±5% — speedometer, gearing and ABS calibration all need a professional review.
Daily drivability
Ø +32.5 mmAggressive setup — verify before daily use
Geometry deviates enough to matter — check clearance, recalibrate the dash, then re-evaluate.
Direct answer
Is 255/40 R18 OEM-safe?
No. Overall diameter changes by +5.17% versus 245/35 R18. Not OEM-safe. Overall diameter strays beyond ±5% — recalibration and clearance review are required.
Direct answer
Will 255/40 R18 rub?
Possibly. Width changes by +10 mm and diameter by +32.5 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 +5.17%. Swapping 245/35 R18 for 255/40 R18 changes overall diameter, so at an indicated 100 km/h your true speed becomes 105.2 km/h. That's outside safe tolerance — recalibrate.
Direct answer
Does lower sidewall affect comfort?
Yes — softer ride. Sidewall changes by +16.3 mm (35% → 40%). Ride softens and absorbs bumps better, with slightly less precise turn-in.
Current Tire
245/35R18
New Tire
255/40R18
Fitment · Scaled comparison
● Not recommended
245/35 R18
Diameter
+32.5 mm
+5.17%
Sidewall
+16.3 mm
Speedometer
105.2 km/h
at true 100
Clearance
Not recommended
255/40 R18
Ground line · Scaled comparison
Not Recommended
Over 5% — speedometer & ABS may misread
Diameter change
+32.5 mm
5.17%
Speedometer at 100
105.2 km/h
+5.17% error
Ground clearance
+16.3 mm
ride height delta
Sidewall change
+16.3 mm
revs/km: 481.4
Permalink for this comparison:
/compare/245-35-r18-vs-255-40-r18Detailed comparison
| Metric | 245/35 R18 | 255/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 628.7 mm | 661.2 mm | +32.5 mm (+5.17%) |
| Sidewall height | 85.8 mm | 102.0 mm | +16.3 mm |
| Circumference | 1.975 m | 2.077 m | +102.1 mm |
| Revs / km | 506.3 | 481.4 | -24.9 |
| Ground clearance | reference | +16.3 mm | +16.3 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 105.2 km/h | +5.17 km/h |
Verdict: danger
Over 5% diameter difference — likely to affect speedometer accuracy, ABS calibration and gearing. Not recommended without professional review.
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
245/35 R18- Profile
- 35%
- Circumference
- 1.975 m
New
255/40 R18- Profile
- 40%
- Circumference
- 2.077 m
Side-by-side fitment
GeometryCurrent
245/35 R18- Section width
- 245 mm
- Aspect ratio
- 35%
- Sidewall
- 85.8 mm
- Wheel diameter
- 18″(457 mm)
- Overall diameter
- 628.7 mm(24.75″)
- Circumference
- 1.975 m
- Revs / km
- 506.3
New
255/40 R18- Section width
- 255 mm
- Aspect ratio
- 40%
- Sidewall
- 102.0 mm
- Wheel diameter
- 18″(457 mm)
- Overall diameter
- 661.2 mm(26.03″)
- Circumference
- 2.077 m
- Revs / km
- 481.4
Real-world consequences
Pros / consWider tire (+10 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 sidewall (+5% aspect)
Sidewall- Plusher ride, better pothole and curb protection
- More forgiving on bad roads and trails
- Lower wheel-damage risk on impacts
- More sidewall flex, softer steering feel
- Slightly delayed turn-in response
Taller overall (+32.5 mm)
Rolling diameter- Higher ground clearance and approach angle
- Longer effective gearing — calmer highway revs
- Bigger contact patch lengthwise
- Speedometer reads low by ~5.2%
- Reduced fender, strut and bumpstop clearance
- Slower 0-60, more downshifts under load
How it changes driving feel
Seat-of-the-pantsSteering response
Similar feel
Ride comfort
Comparable
Road noise
Similar cabin noise
Wet / aquaplaning
Comparable wet behavior
Fuel economy
Small MPG penalty likely
Curb / pothole protection
About the same
Fitment risk check
Verify before installFender rubbing
Check fender clearance, especially with lower offset wheels.
Suspension clearance
Wider tire may contact strut or control arm on full compression.
Speedometer drift
~5.2% diameter delta — speedo and ABS calibration likely affected.
ABS / ESP calibration
Outside factory tolerance — recalibration may be required for safety systems.
Cluster preview
Excessive driftSpeedometer impact
At a true 100 km/h, your dashboard will read 105.2 km/h after switching to 255/40 R18 — a +5.17% 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 +16.3 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
245/35 R18
Back to
255/40 R18
Drivers also compare
Closely-related fitments and plus-size swaps for 245/35 R18 and 255/40 R18.
215/40 R18 vs 245/35 R18
Wider variation on the same rim — more grip, less clearance.
Δ 0.08%
225/45 R18 vs 255/40 R18
Wider variation on the same rim — more grip, less clearance.
Δ 0.23%
245/35 R18 vs 255/35 R18
Wider variation on the same rim — more grip, less clearance.
Δ 1.11%
235/45 R18 vs 255/40 R18
Wider variation on the same rim — more grip, less clearance.
Δ 1.12%
255/40 R18 vs 265/40 R18
Wider variation on the same rim — more grip, less clearance.
Δ 1.21%
245/40 R18 vs 255/40 R18
Wider variation on the same rim — more grip, less clearance.
Δ 1.22%
225/40 R18 vs 245/35 R18
Wider variation on the same rim — more grip, less clearance.
Δ 1.33%
215/45 R18 vs 255/40 R18
Wider variation on the same rim — more grip, less clearance.
Δ 1.61%
Related topics
Comparison hub
Back to the tire size comparison calculator
Browse every wheel and tire fitment comparison, by rim size or popularity.