305/70R17 vs 35x11.50R17 — the narrow-35 question
A metric size that reaches for 35 inches and lands at 34, against the narrow flotation tire that names itself one.
35x11.50R17 is 1.19 in taller than 305/70R17 (3.52%) and 0.51 in narrower. A speedometer calibrated for 305/70R17 would under-read by 3.52%.
Measured against each other
Overall diameter
33.81 in35.00 in+1.19 in (+3.52%)Section width
12.01 in / 305 mm11.50 in / 292 mm-0.51 in (-4.23%)Sidewall height
8.41 in9.00 in+0.59 inCircumference
106.2 in110.0 in+3.7 inRevolutions per mile
596.5576.2-20.3Ride height at the axle
——+0.59 inSpeedometer reading
——+3.52% under-read
| Dimension | 305/70R17 | 35x11.50R17 | Change |
|---|---|---|---|
| Overall diameter | 33.81 in | 35.00 in | +1.19 in (+3.52%) |
| Section width | 12.01 in / 305 mm | 11.50 in / 292 mm | -0.51 in (-4.23%) |
| Sidewall height | 8.41 in | 9.00 in | +0.59 in |
| Circumference | 106.2 in | 110.0 in | +3.7 in |
| Revolutions per mile | 596.5 | 576.2 | -20.3 |
| Ride height at the axle | — | — | +0.59 in |
| Speedometer reading | — | — | +3.52% under-read |
Calibrated for 305/70R17, running 35x11.50R17
- Dial reads 30
- 31.1 mph
- Dial reads 50
- 51.8 mph
- Dial reads 70
- 72.5 mph
- Odometer counts 100
- 103.5 mi covered
Change either size in the comparison tool, or see the full speed table in the speedometer error calculator.
305/70R17 gets to 33.81 in. It is routinely described as a 34 and occasionally as a 35. It is neither, quite.
The shortfall
1.19 in, or 3.52%, against a genuine 35. Rounded to the nearest half inch the metric size is a 34, and that is the honest label for it.
The flotation size, meanwhile, is 35.00 in by definition and 0.51 in narrower — 11.50 in of casing against 12.01 in. So the metric tire is the wider one and the imperial tire is the taller one, which is the reverse of the usual arrangement in this family of comparisons.
Sidewalls, and the shapes behind them
Just over half an inch apart, 8.41 in and 9.00 in. The metric size states a 70-series profile; the flotation size works out to a 78-series, because it reaches 35 inches on a comparatively narrow casing.
That difference in proportion is the whole reason the narrow 35 exists. Height on a narrow casing can only be bought with profile, and 78 is what it takes.
What the gap costs
Very little, and that is the point of running the numbers at all: a size argued about as though it were a whole class apart is worth two and a half miles an hour at 70. In gearing terms 3.73:1 converts to 3.86:1, with 3.91:1 the nearest set sold, and nobody re-gears for three and a half per cent.
What separates the two, then, is not anything a calculator produces.
Why the metric ladder stops here
305/70R17 and 315/70R17 are the top of the metric range on a 17-inch wheel, and both fall short of 35 inches. There is no metric size that reaches it, because a casing wide enough to produce a 9-inch sidewall at a 70-series profile would have to be around 325 mm — and that is wider than almost any vehicle with 17-inch wheels can accommodate. The flotation notation takes over at this height for structural reasons, not marketing ones.
Availability, which decides it
Both are minority sizes. 35x11.50R17 is offered in a modest number of aggressive patterns for people whose limit is width; 305/70R17 is offered in a modest number of mostly all-terrain patterns for people who want a metric size. Neither is a shelf item, and the practical choice is usually made by which one exists in the tread wanted.
The wide alternative
315/70R17 against 35x12.50R17 is the same question with both tires an inch wider, and with a much smaller height gap between them.