This is a modification rather than a substitution. Check clearance at full steering lock and full suspension compression, confirm the load rating meets the placard, and expect the speedometer to read high by about 3.3% unless it can be recalibrated for the new size.
Want to try other sizes against these? Open this comparison in the interactive tool.
A step down in height on the same rim
275/65R18 sits 1.08 inches shorter than 275/70R18 on the same 18-inch rim. That lowers the vehicle by 0.54 inches at the axle and frees the same amount of space in the arch.
People arrive at this comparison for two reasons: recovering clearance after a fitment problem, or reducing cost, since smaller sizes are generally cheaper and more widely stocked.
Be careful about load rating. A smaller tire encloses less air, and the load index on 275/65R18 must still meet the figure on the vehicle's tire placard — particularly on anything that tows or carries weight.
275/70R18 and 275/65R18 measured against each other
Both sizes reduced to the same units. The diameter row is the one that drives everything else on this page — ride height, gearing, speedometer accuracy and odometer readings all follow from it.
| Measurement | 275/70R18 | 275/65R18 | Difference |
|---|---|---|---|
| Overall diameter | 33.16" | 32.07" | −1.08" (−3.3%) |
| Section width | 10.83" (275 mm) | 10.83" (275 mm) | +0" |
| Sidewall height | 7.58" | 7.04" | −0.54" |
| Rim diameter | 18" | 18" | +0" |
| Circumference | 104.17" | 100.77" | −3.4" |
| Revolutions per mile | 608 | 629 | +21 |
| Ride height at axle | Baseline | −0.54" | −0.54" |
What the dial shows against how fast you are going
Your speedometer was calibrated to 275/70R18, which turns about 608 times per mile. Fit 275/65R18 at about 629 revolutions per mile and the same wheel speed now represents a smaller road speed than the instrument assumes. The error is 3.3% at every speed, so it grows in absolute terms the faster you go.
| Speedometer reads | You are actually doing | Difference |
|---|---|---|
| 30 mph | 29 mph | −1 mph |
| 45 mph | 43.5 mph | −1.5 mph |
| 60 mph | 58 mph | −2 mph |
| 75 mph | 72.6 mph | −2.4 mph |
Over distance the same proportion applies to the odometer. Every indicated 1,000 miles on 275/65R18 is really about 967 miles covered — so the vehicle accumulates recorded mileage faster than it actually travels.
What this particular change asks you to check
- Section width grows by 0 inches, so the tire sits closer to the strut and the inner liner on both sides.
- Overall height drops by 1.08 inches, lowering the vehicle 0.54 inches at the axle.
- Both sizes use a 18-inch rim, so the existing wheels carry over if their width suits the new section.
- Speedometer error of 3.3% — check whether your vehicle supports recalibrating for a new tire size.
- Confirm the load index on 275/65R18meets or exceeds the figure on the vehicle's tire placard, particularly if the vehicle tows or carries load.
- On all-wheel-drive and four-wheel-drive vehicles, change all four together — mismatched rolling circumferences load the differentials and transfer case continuously.
275/70R18 vs 275/65R18 FAQ
Is 275/65R18 bigger than 275/70R18?+
275/65R18 measures 32.07 inches in overall diameter against 33.16 inches for 275/70R18. That makes it 1.08 inches shorter, a change of −3.3%. It is also 0 inches wider in section width.
Will 275/65R18 fit in place of 275/70R18?+
The diameter change is −3.3%, which is outside the 3% envelope usually treated as a routine substitution. Treat this as a modification: verify clearance at full steering lock and full suspension compression, confirm the load rating meets the vehicle placard, and expect the speedometer to read incorrectly unless it can be recalibrated.
How much lift does 275/65R18 give over 275/70R18?+
0.54 inches at the axle — half the diameter difference. The other half of the change goes upward into the wheel arch, which is where fitment problems usually appear.
How far off will my speedometer be?+
The speedometer will read high by about 3.3%. At an indicated 60 mph you would actually be travelling about 58 mph, so the vehicle covers less ground than the dial claims.
Do I need to regear for 275/65R18?+
A −3.3% change shifts the effective gearing noticeably. To restore the original engine speed you would multiply the current axle ratio by 0.967. Whether that is worth doing depends on how the vehicle is used — towing and heavily loaded driving make the case sooner than commuting does.
What is the revolutions-per-mile difference?+
275/70R18 turns about 608 times per mile and 275/65R18 about 629 — a difference of +21 revolutions. That figure is what the speedometer and odometer are calibrated against, which is why both readings shift.
These are nominal figures. Every number above is calculated from the marked size. Real tires vary from nominal by a few millimetres between manufacturers, and by more as tread wears or pressure changes. Use this to plan and to check a quote — measure the actual tire before committing to a tight fitment.