255/40R19 — what a wheel size costs when diameter is held
The middle of a three-wheel stack where the rolling diameter agrees to a hundredth of an inch.
Metric notation · Performance and ultra-high performance
- Overall diameter
- 27.03 in
- 687 mm
- Section width
- 10.04 in
- 255 mm
- Sidewall height
- 4.02 in
- 102 mm
- Aspect ratio
- 40%
- sidewall as a share of width
- Wheel diameter
- 19 in
- the hole in the middle
- Circumference
- 84.9 in
- 2157 mm
- Revolutions per mile
- 746.1
- geometric, not measured
- Revolutions per km
- 463.6
- geometric, not measured
- Typical load index
- 88–104
- 1235–1984 lb per tire
Low-profile sizes hold less air for their width, so the same vehicle weight needs a higher reference inflation. Extra Load construction is common in this class, and that is what lifts the index band — not any change in the casing size.
The load-index range shown is the band this CLASS of size is typically produced in — not a list of what is in stock for this exact size today. Load index and speed symbol are printed on the sidewall of the specific tire you are holding, and the required minimum is on the placard of the specific vehicle you are fitting. Read both.
Nearest real sizes in imperial notation, same wheel
Compare any two sizes, including ones this site has no page for, in the comparison tool.
Platforms recorded with this size
Premium and performance saloons on 19-inch wheels, often as a rear size in a staggered set.
Three wheels, one diameter
| Size | Wheel | Sidewall | Diameter |
|---|---|---|---|
| 255/45R18 | 18 in | 4.52 in | 27.04 in |
| 255/40R19 | 19 in | 4.02 in | 27.03 in |
| 255/35R20 | 20 in | 3.51 in | 27.03 in |
The three agree to 0.03%. Section width is 10.04 in throughout. Sidewall falls by almost exactly half an inch at each step, which is what absorbs the inch of extra wheel diameter.
What actually changes
Not the speedometer, the odometer, the axle ratio or the ride height. Those all follow from the rolling diameter, and the rolling diameter is fixed.
What changes is the split between a rigid component and a compliant one. An inch of wheel diameter adds rim material at the largest radius, where it has the most effect on rotational inertia, and removes half an inch of sidewall from each end, where the tire does its work absorbing surface irregularities. That is a real mechanical difference and none of it appears in any figure on this page.
The figures on this page describe geometry. They are exact and they are also incomplete, which is worth saying plainly on a page whose whole point is that three different tires measure the same.
Its nearest match outside the stack
215/65R16 measures 27.00 in — 0.10% below this size, from a crossover fitment on a 16-inch wheel with 5.50 in of sidewall. 235/55R17 is 0.15 in above at 27.18 in.
Rim width
4.02 in of sidewall puts this size in the middle of the sensitivity range: more casing than a 35-series has to take up a difference in wheel width, less than a 55-series. It is enough that staggered sets built on this code — a common arrangement on the saloons and coupés that wear it — can end up with front and rear tires whose measured widths differ by more than the codes suggest, because the rear wheel is wider as well as the rear tire. The rim width to tire width reference puts numbers on the effect, and the staggered fitments reference on the arrangement.
Speed symbols in this size run high; the speed rating table lists them.
Related
Class: Performance and ultra-high performance. Every figure above is computed from the size code, not stored — see how these numbers are calculated.