Ram 1500 (DS): three factory sizes, the 20-inch one tallest

An unusually long production life

This generation was introduced in 2009 and continued in production for years after its successor arrived, sold in parallel as the lower-cost option in the same showroom. That matters for tire arithmetic in one specific way: the recorded fitments span a very long stretch of model years, and a 2010 truck and a late one can be looking at different starting points.

The three sizes recorded are 265/70R17 at 31.61 in, 285/45R22 at 32.10 in and 275/60R20 at 32.99 in.

The order is not the order you expect

Read those in wheel-diameter order and the pattern breaks. The 17-inch tire is the shortest, the 20-inch is the tallest, and the 22-inch sits between them — 0.89 in shorter than the 20.

So the largest wheel does not carry the largest tire here, and the spread from the 17-inch fitment to the 20-inch one is 1.39 in, or 4.38%. Two trucks of the same generation, at the same indicated speed, are 4% apart in true road speed.

What that does to upgrade arithmetic

35x12.50R20 at 35.00 in, from each starting point:

• From 265/70R17: +3.39 in, 10.74%. An indicated 70 mph is 77.5, and 100 miles of odometer is 110.7 travelled.
• From 285/45R22: +2.90 in, 9.04%.
• From 275/60R20: +2.01 in, 6.09%.

The 17-inch truck is making a change nearly twice the proportional size of the 20-inch truck's, to the same tire. Anyone quoting a speedometer error for "a DS on 35s" has to say which DS.

Two sizes that barely move anything

Against that, 285/70R17 from 285/45R22 is +0.61 in — 1.90% — with zero change in section width. Both are 285 mm casings. It is a pure sidewall trade: 5.05 in becomes 7.85 in, on a wheel five inches smaller in diameter, at essentially the same rolling height.

For a truck bought on 22-inch wheels and used somewhere the roads are bad, that is the most consequential change available with the least arithmetic attached to it.

33x12.50R20 from the 20-inch fitment is a 0.01 in change — the rolling diameter does not move at all — and adds 1.67 in of width. What it delivers is tread pattern and stance, not height, and it is worth being clear about which of those you are buying.

A moving specification, and an empty ratio field

The ratio column is blank for this generation, and the reason is bound up with what makes the DS unusual in the first place. A truck that continued in production alongside its own replacement, sold in a narrowing range of configurations over those extra years, does not have one settled specification to record — it has a moving one, and the year matters as much as the model.

Nothing above needs one. Diameter, width, sidewall and speedometer error are functions of geometry alone. Engine speed is the exception, and the gear ratio calculator takes the ratio from your own differential tag or build sheet.

The used-wheel market on this platform

A long production run and high volumes mean take-off wheels from this generation are abundant and cheap, and moving between the three factory packages is a common way to change tires without buying new wheels.

The arithmetic makes some of those swaps nearly free and others not. Between the 20-inch and 22-inch fitments the rolling diameter changes by 2.71%, which is inside most substitution tolerances. Between the 17-inch and 20-inch fitments it is 4.38%, which is not — the speedometer would begin to read noticeably low, and every downstream system reading wheel speed inherits the same error.

Checking that figure before buying a set is thirty seconds of work in the comparison tool and it is the step most often skipped.

Geometry ends where the wheel well starts

None of this says a tire fits. Cab and bed configuration, suspension, ride height and wheel offset decide contact, and on a platform sold across this many model years the configurations vary more than the tire sizes do. The upgrade sizes recorded here are observations of what owners run.