Data sheet TS-C13 · Comparison
285/65R18 vs 275/70R18
275/70R18 is 1.8% taller than 285/65R18 by the formula, adding 0.57 in of diameter. It is also 10 mm narrower, with a taller sidewall and fewer revolutions per mile.
Fig. 1 — Cross-section, size 2
Table 1 — Data
275/70R18 is 33.16″ tall, +1.75% against 285/65R18. At 60 mph on the dial you drive 61.1 mph.
| Item | 285/65R18 | 275/70R18 | Change |
|---|---|---|---|
| DOverall diameter | 32.59″ | 33.16″ | +1.75% |
| ASection width | 11.22″ | 10.83″ | −0.39″ |
| BSidewall | 7.29″ | 7.58″ | +0.29″ |
| CRim | 18″ | 18″ | same |
| Revs per mile | 619 | 608 | −11 |
| Dial 60 mph = | 60.0 | 61.1 | +1.8% |
| Axle height | 16.29″ | 16.58″ | +0.29″ |
+1.75% — within the ±3% rule of thumb tire shops use. The speedometer and gearing stay close to stock.
Where to buy 275/70R18 ↓Fig. 2
Side view and width, to scale
Size 1 dashed, size 2 solid, on one ground line.
285/65R18275/70R18
Table 2 — Speedometer
| Dial shows | True speed | Difference |
|---|---|---|
| 30 mph | 30.5 mph | +0.5 |
| 45 mph | 45.8 mph | +0.8 |
| 60 mph | 61.1 mph | +1.1 |
| 70 mph | 71.2 mph | +1.2 |
| 80 mph | 81.4 mph | +1.4 |
Engine RPM at the same road speed: −1.7%. Gear ratio calculator
Table 3
Published dimensions
From each maker’s size table. A tire is listed only with a source.
The math says 33.16″. 20 tires from 5 makers measure 33.19″–33.62″. Tallest here: Nitto Trail Grappler M/T (mud-terrain), 33.62″. Check the maker’s number before you buy for a tight fit.
| Tire | Type | Diameter | Width | Rims, in | Weight | Tread | Max load |
|---|---|---|---|---|---|---|---|
| Firestone Winterforce LTfirestonetire.com · Oct 15, 2026 | LT · E 125R | 33.19″ | — | 7.0–8.5 | 53.8 lb | 19.0/32″ | — |
| Nitto Ridge Grapplernittotire.com · Oct 15, 2026 | LT · E 125/122Q | 33.19″ | 10.98″ | 7.0–9.0 | 58.5 lb | 16.4/32″ | 3,640 lb @ 80 psi |
| Nitto Recon Grappler A/Tnittotire.com · Oct 15, 2026 | LT · E 125/122S | 33.19″ | 10.98″ | 7.0–9.0 | 54.3 lb | 15.9/32″ | 3,640 lb @ 80 psi |
| Firestone Destination X/Tfirestonetire.com · Oct 15, 2026 | LT · E 125S | 33.20″ | — | 7.0–8.5 | 50.3 lb | 16.0/32″ | — |
| Firestone Destination M/T2firestonetire.com · Oct 15, 2026 | LT · E 125Q | 33.20″ | — | 7.0–8.5 | 59.9 lb | 20.0/32″ | — |
| Firestone Transforce HT3firestonetire.com · Oct 15, 2026 | LT · E 125S | 33.20″ | — | 7.0–9.0 | 48.9 lb | 15.0/32″ | — |
| Firestone Transforce AT2firestonetire.com · Oct 15, 2026 | LT · E 125R | 33.20″ | — | 7.0–8.5 | 51.2 lb | 18.0/32″ | — |
| Kumho Road Venture AT52kumhotireusa.com · Oct 15, 2026 | LT · E 125/122S | 33.20″ | 11.00″ | 7.0–9.0 | 55.1 lb | 16.0/32″ | 3,640 lb @ 80 psi |
| Kumho Road Venture RTkumhotireusa.com · Oct 15, 2026 | LT · E 125/122R | 33.20″ | 11.00″ | 7.0–9.0 | 59.3 lb | 17.3/32″ | 3,640 lb @ 80 psi |
| Kumho Crugen HT51kumhotireusa.com · Oct 15, 2026 | LT · E 125/122R | 33.20″ | 10.50″ | 7.0–8.0 | 56.2 lb | 14.5/32″ | 3,640 lb @ 80 psi |
§ 1
How do the dimensions differ?
By the formula, diameter increases from 32.6 in (828 mm) to 33.2 in (842 mm). Section width decreases from 11.2 in (285 mm) to 10.8 in (275 mm). Sidewall height increases from 7.3 in to 7.6 in.
Nominal revolutions per mile fall from 619 to 608. Ground clearance at the axle increases by 0.29 in (7 mm). The scale drawing and differences table show these unloaded nominal dimensions, not measurements of a specific tire.
§ 2
How do speed and gearing change?
By the formula, changing to 275/70R18 makes 60 mph indicated equal 61.1 mph true, assuming calibration for 285/65R18. At 100 km/h indicated, true speed is 101.8 km/h. Actual distance traveled is also 1.8% greater than the odometer indicates.
At 65 mph with a 3.73 axle ratio and a 1.00 transmission gear, calculated engine speed drops from 2,501 rpm to 2,458 rpm, a 1.7% reduction. The formula-only axle ratio for restoring the original engine speed is 3.80: 3.73 × 33.16 / 32.59. The speedometer table shows the calculated speed changes.
§ 3
What do the makers publish?
The Nitto, Firestone, Kumho, Toyo and Mickey Thompson size tables list 17 tires in 285/65R18 and 20 in 275/70R18. Published diameters span 32.56–33.4 in for 285/65R18 and 33.19–33.62 in for 275/70R18. Listed load ranges are SL, XL and E for 285/65R18, versus SL and E for 275/70R18.
Toyo lists its Open Country A/T III at 32.6 in and 638 revs per mile in LT285/65R18, versus 33.2 in and 626 revs per mile in LT275/70R18. These maker-published figures differ from the nominal calculations. The measured-model tables show individual listings checked October 15, 2026.
§ 4
Which dimensions matter for your comparison?
For more nominal axle ground clearance and lower calculated cruising rpm, 275/70R18 supplies the taller diameter. For less overall height and more nominal section width, 285/65R18 supplies the shorter, wider dimensions. Neither comparison establishes vehicle fit; fit depends on the vehicle, wheels and suspension.
Compare the exact tire model as well as the size code. Maker dimensions and approved rim widths vary, and the available load ranges are not identical.
Table 4
Sizes within 3% of 275/70R18
Same rim or ±1″, diameter within 3%. A shop rule of thumb, not a law.
| Size | Diameter | Width | vs 275/70R18 | At 60 mph | Clearance |
|---|---|---|---|---|---|
| 255/80R17 | 33.06″ | 10.0″ | −0.3% | 59.8 | −0.05″ |
| 295/70R17 | 33.26″ | 11.6″ | +0.3% | 60.2 | +0.05″ |
| 33x11.50R17 | 33.00″ | 11.5″ | −0.5% | 59.7 | −0.08″ |
| 33x11.50R18 | 33.00″ | 11.5″ | −0.5% | 59.7 | −0.08″ |
| 33x12.50R17 | 33.00″ | 12.5″ | −0.5% | 59.7 | −0.08″ |
| 33x12.50R18 | 33.00″ | 12.5″ | −0.5% | 59.7 | −0.08″ |
| 325/60R18 | 33.35″ | 12.8″ | +0.6% | 60.4 | +0.10″ |
| 235/80R18 | 32.80″ | 9.3″ | −1.1% | 59.4 | −0.18″ |
| 285/70R17 | 32.71″ | 11.2″ | −1.4% | 59.2 | −0.22″ |
| 305/65R18 | 33.61″ | 12.0″ | +1.4% | 60.8 | +0.23″ |
Size sheets
Q&A
Common questions
Is 275/70R18 wider than 285/65R18?
No. By the formula, it is 10 mm narrower: 275 mm versus 285 mm.
Is the diameter change within 3%?
Yes. The nominal increase is 1.8%, inside the ±3% window. That window is a tire-shop rule of thumb, not a law or vehicle maker specification.
Do both sizes have load range E options?
Yes. Toyo lists load range E versions of the Open Country A/T III in both sizes.
Notes
Method and sources
Each number and rule comes from a source with the date it was checked.
- Sidewall = width × aspect ratio ÷ 100
- Diameter = rim × 25.4 + 2 × sidewall (mm)
- Revs per mile = 63,360 ÷ (π × diameter, in)
- True speed = dial × new diameter ÷ old diameter
- Clearance change = half the diameter change
Numbers are nominal: the tire unloaded, on its measuring rim. Revs per mile published by makers run higher than the formula. “Within 3%” is a rule of thumb tire shops use, not a law. Tire pressure: the placard on your door jamb.
- Toyo: size table (toyotires.com)checked Oct 15, 2026
- 49 CFR 571.139 (FMVSS No. 139), S4.1ecfr.gov · checked Oct 15, 2026
Related
Calculators and size classes
- Tire size calculatorTwo sizes: diameter, sidewall, revs and speedometer.
- Compare up to 4 sizesUp to four sizes side by side, drawn to scale.
- Metric ↔ inchesMetric to inches, and 33x12.50R20 to metric.
- Speedometer errorTrue speed after a size change.
- Gear ratio and RPMEngine RPM and the ratio to regear to.
- Wheel offset and pokeBackspacing, poke and inner clearance.
- DOT date codeHow old a tire is, from the DOT number.
- Load index chartLoad index in pounds and kilograms.
- Bolt patternMeasure it, convert inches to mm.
- Rim size and tire fitWhat 17x8 ET35 means, which sizes go on it.
- What fits my carStart from the placard on the door.
- Tire size chartCommon sizes in inches, by rim.