Which tire is taller, 245/40 R20 or 245/45 R20?

245/45 R20 is taller by 24.5 mm (3.48%) compared with 245/40 R20.

What is the diameter difference between 245/40 R20 and 245/45 R20?

245/40 R20 measures 704 mm overall diameter, 245/45 R20 measures 729 mm — a difference of 24.5 mm (3.48%).

How much speedometer error does this change create?

Switching from 245/40 R20 to 245/45 R20 changes the speedometer reading by +3.48%. At an indicated 100 km/h, your true speed becomes about 103.5 km/h.

Is 245/45 R20 a safe replacement for 245/40 R20?

Between 3% and 5% diameter difference — speedometer drift is noticeable. Consider recalibration and confirm clearance with your vehicle's manufacturer specification.

What else should I check before changing tire size?

Beyond diameter and speedometer error, verify wheel offset (ET), rim width, hub bore, load index, brake and suspension clearance, and your vehicle's manufacturer specification. Local regulations may also limit how far you can deviate from OEM.

Fitment comparison

245/40 R20versus245/45 R20

Δ Ø +24.5 mmSpeedo +3.48%Borderline

245/45 R20 stands taller than 245/40 R20 — bigger rolling diameter, slightly more clearance, calmer cruise revs.

Switching from 245/40 R20 to 245/45 R20 keeps the wheel but adds sidewall for extra cushioning. This alternative fitment noticeably changes overall diameter compared to OEM. More sidewall typically improves comfort and curb protection, especially on city streets.

The speedometer error is noticeable and may warrant a recalibration if you rely on indicated speed. The 3–5% diameter gap puts this in caution territory: doable on many cars, but verify clearance and consider recalibration.

TakeA comfort-leaning direction that's easier on wheels and suspension over rough surfaces.

Quick fitment verdict

245/40 R20 → 245/45 R20 at a glance

OEM Safe

Borderline

Noticeable drift from OEM — drivable, but recalibration is wise.

Fender Clearance

Likely rubs

Significantly wider/taller — rubbing risk on liners or fender lip is real.

Speedometer Impact

+3.48%

Dash reads 103.5 km/h at a true 100 km/h — visible drift.

Daily Driving

Aggressive

Geometry deviates enough to matter — confirm clearance before daily use.

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 +24.5 mm

SW +12.3 mm

RH +12.3 mm

NewNew

245/45 R20

Diameter: 728.5 mm
Sidewall: 110.3 mm
Wheel: 20″
Width: 245 mm

Real-world effects

How this swap actually feels

Steering response
38/100 · Softer turn-in
Ride comfort
83/100 · More cushion
Fuel economy
63/100 · Slightly lower drag
Highway cruising
75/100 · Lower cruise revs
Pothole resistance
80/100 · 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

+12.3 mm

Chassis sits higher — slightly more clearance, wheel-gap visually grows.

New tire lifts the chassis by ~12.3 mm — more clearance, slightly more wheel-gap.

Suspension travel · arch clearance

Wheel gap

Wheel gap visually increases

+12.3 mm

How the arch-to-tire gap reads from across the parking lot — the visual stance change everyone notices first.

245/40 R20

245/45 R20

Wheel-gap Δ+12.3 mm

Static · unloaded chassis

Fender relationship

Tucked · Flush · Poke

Stance language

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 103.5 km/h

+3.48%

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 R20 → 245/45 R20 swap — steering, comfort, stance and dash behavior in plain enthusiast language.

Steering feel

+12.3 mm sidewall

Softer, more relaxed turn-in

Taller sidewall flexes a touch more before loading the contact patch — calmer, comfort-tuned.

Ride firmness

40% → 45%

Softer over potholes and joints

Bumps and expansion joints are absorbed better — a comfort win for daily driving.

Fender relationship

+0 mm width

Fender gap reads near-identical

Width delta is too small to change stance — same visual signature as OEM.

Speedometer behavior

+3.48%

Noticeable speedo drift

Drift is visible at highway speeds; ABS still works but loses a sliver of precision.

Daily drivability

Ø +24.5 mm

Aggressive setup — verify before daily use

Geometry deviates enough to matter — check clearance, recalibrate the dash, then re-evaluate.

Direct answer

Is 245/45 R20 OEM-safe?

Borderline. Overall diameter changes by +3.48% versus 245/40 R20. Borderline. Drivable, but speedometer drift becomes noticeable and ABS calibration is affected.

Direct answer

Will 245/45 R20 rub?

Possibly. Width changes by +0 mm and diameter by +24.5 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 +3.48%. Swapping 245/40 R20 for 245/45 R20 changes overall diameter, so at an indicated 100 km/h your true speed becomes 103.5 km/h. That's noticeable drift but usually safe.

Direct answer

Does lower sidewall affect comfort?

Yes — softer ride. Sidewall changes by +12.3 mm (40% → 45%). Ride softens and absorbs bumps better, with slightly less precise turn-in.

Current Tire

245/40R20

Width

Ratio

Rim

New Tire

245/45R20

Width

Ratio

Rim

Fitment · Scaled comparison

● Borderline

245/40 R20

Diameter

+24.5 mm

+3.48%

Sidewall

+12.3 mm

Speedometer

103.5 km/h

at true 100

Clearance

Borderline

245/45 R20

Ground line · Scaled comparison

Slight Difference

Within ±5% — usable, recalibration recommended

Diameter change

+24.5 mm

3.48%

Speedometer at 100

103.5 km/h

+3.48% error

Ground clearance

+12.3 mm

ride height delta

Sidewall change

+12.3 mm

revs/km: 436.9

Open visual comparisonCompare visually

Permalink for this comparison:

/compare/245-40-r20-vs-245-45-r20

Detailed comparison

Metric	245/40 R20	245/45 R20	Difference
Overall diameter	704.0 mm	728.5 mm	+24.5 mm (+3.48%)
Sidewall height	98.0 mm	110.3 mm	+12.3 mm
Circumference	2.212 m	2.289 m	+77.0 mm
Revs / km	452.1	436.9	-15.2
Ground clearance	reference	+12.3 mm	+12.3 mm
Speedometer @ 100 km/h	100.0 km/h	103.5 km/h	+3.48 km/h

Verdict: warning

Between 3% and 5% — noticeable speedometer drift; recalibration may be advisable.

Dimensional comparison

Side-by-side

Scaled 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

245/45 R20

Profile: 45%
Circumference: 2.289 m

Side-by-side fitment

Geometry

Current

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

245/45 R20

Section width: 245 mm
Aspect ratio: 45%
Sidewall: 110.3 mm
Wheel diameter: 20″(508 mm)
Overall diameter: 728.5 mm(28.68″)
Circumference: 2.289 m
Revs / km: 436.9

Real-world consequences

Pros / cons

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 (+24.5 mm)

Rolling diameter

Higher ground clearance and approach angle
Longer effective gearing — calmer highway revs
Bigger contact patch lengthwise
Speedometer reads low by ~3.5%
Reduced fender, strut and bumpstop clearance
Slower 0-60, more downshifts under load

How it changes driving feel

Seat-of-the-pants

Steering 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 install

Speedometer drift

~3.5% — borderline; recalibration recommended.

Cluster preview

Borderline

Speedometer impact

At a true 100 km/h, your dashboard will read 103.5 km/h after switching to 245/45 R20 — a +3.48% 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 +12.3 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

245/40 R20

Back to

245/45 R20