WIRTGEN's small cold milling line spans 14 in to 3 ft 11 in (350-1,200 mm) working widths and 4-12 in (100-300 mm) max depths at 45-160 kW (60-215 hp), with operating weights from 10,252 lb to 33,951 lb CE [S1]. Compact mills double the engine output to 257-313 kW (355-420 hp) while holding max depth at 13 in and pushing widths from 3 ft 3 in to 4 ft 11 in [S1].
Large-class mills on the same WIRTGEN platform reach 14 ft 5 in (4.40 m) working widths and 1 ft 2 in (350 mm) depths in a single pass, with power reserves up to 753 kW [S1][S5]. Selection for road rehabilitation is therefore a function of job width, cut depth, engine power, and drum type, with guidance automation layered on top [S3].
Three machine classes: small, compact, and large
WIRTGEN segments the cold milling line into three working-width bands tied to engine power and depth capability [S1]. Small mills (W 35 XRi through W 120 Ri) are rear-drum, wheeled machines for partial pavement rehabilitation, tie-ins, and floor work in industrial buildings, with a swivel right rear wheel that allows flush-to-edge cutting next to obstacles [S1]. Compact front-loaders (W 100 Fi through W 150 Fi) bridge maneuverability and full-lane production: a W 130 Fi cuts 4 ft 3 in wide at 13 in deep on a 265 kW (355 hp) engine at 47,179 lb CE [S1]. Large mills take widths to 14 ft 5 in and depths to 1 ft 2 in with up to 753 kW on tap [S1][S5]. The width-by-power matrix is the single most useful spec sheet a specifier can pin a project to before brand selection enters the conversation.
Independent contractor data confirms the upper end of the spread: large cold planers mill maximum depths of 13 in at 7 ft widths with approximately 350 to 400 hp engines [S6]. That 13 in depth ceiling is consistent across both the WIRTGEN W 100 Fi / W 150 Fi compact class and the contractor reference figures, which means depth capability scales with chassis class, not just engine power [S1][S6].
Working width and depth: the two cut thresholds that drive class choice
Working width sets the passes-per-lane math; working depth sets whether a one-pass or two-pass removal is feasible at all. WIRTGEN's full range covers 14 mm (fine milling) to 4.40 m in a single machine family, with 30-plus machine types available across the lineup [S5]. A 14 mm lower bound is for fine milling / micro-milling drums, not for full-lane removal, and the same WIRTGEN page states the upper bound at 14 ft 5 in / 4.40 m for full-class mills [S1][S5].
Depth and width interact on production rate. Selective (layered) milling at shallower depth can match or exceed single-pass full-depth production because the drum works faster at lower engagement, and the WIRTGEN engineering note states that milling off surfaces in two or three layers is sometimes just as fast, and in some cases even faster, than complete removal at maximum milling depth in a single pass [S5]. The takeaway for the spec sheet: do not over-spec depth if selective recycling is acceptable, because shallower cuts at higher advance speed often beat one deep cut on net tonnage-per-hour.
Engine power, weight, and the power-to-weight ratio
Small-class power density runs roughly 45 kW at 10,252 lb CE (W 35 XRi) up to 160 kW at 33,951 lb CE (W 120 Ri), giving 0.10-0.11 kW/lb [S1]. Compact-class density jumps: a W 130 Fi at 265 kW and 47,179 lb CE reaches 0.13 kW/lb, and a W 150 Fi at 313 kW and 46,958 lb CE pushes 0.155 kW/lb [S1]. The large-class upper end cited at 753 kW [S5] implies power densities north of 0.20 kW/lb once operating weight and full ballast are accounted for, which matters when transportability, bridge posting limits, and trailer axle ratings enter the project constraints.
For US highway work, a 350-400 hp engine at 7 ft width / 13 in max depth is the contractor-quoted reference point [S6]. Below roughly 200 hp, machines are restricted to partial-width, partial-depth work such as utility cuts, tie-ins, and patching; above 350 hp, the machine class shifts to full-lane highway, runway, and large parking-lot production [S4][S6]. Cold planers in the large class are the workhorses for major highway, runway, and parking lot projects, while smaller mills fit partial pavement rehabilitation and tie-in work [S1][S4].
Milling drum types and what they do to surface texture
Drum choice is the second decision after class. WIRTGEN's small-class literature lists ECO cutters and fine milling drums as interchangeable options within the same chassis, with a wide range of drums enabling a broad spectrum of applications from partial rehabilitation to fine milling [S1]. Fine milling produces a closely spaced, shallow texture used to restore skid resistance and to prepare surfaces for thin overlays; standard drums remove structural layers at full depth [S1][S4].
For micro-milling specifically, the equipment train is a self-propelled cold planer plus haul trucks, water trucks, and sweepers or power brooms, all running in a coordinated spread to keep the milled surface clean before the next operation [S2]. This is the production configuration for texture-restoration work and thin-lift surface preparation, and it is distinct from a structural-removal spread, which usually adds a screening / crushing unit and more haul trucks for the higher RAP tonnage [S2].
Guidance and automation: leveling, 3D milling, and variable depth
WIRTGEN's LEVEL PRO automatic leveling system stores machine-specific parameters and retrieves them during work, with the Wirtgen Multiplex system averaging three sensors per side to create an even surface while meeting target milling depth [S5]. For defined profiles (cross slopes, crowns), or for new digital surface profiles generated off-site, 3D leveling systems transfer a digital profile directly to the cold milling machine, with the engineering note citing increased quality and cost-effectiveness as the headline benefit [S5].
Topcon's milling-machine guidance stack layers 2D and 3D machine control on top of the chassis hardware, with variable-depth milling as a flagship function: the system automatically adjusts blade height to average high and low points, producing a smoother road with a longer projected lifespan [S3]. For specifiers, the practical difference is that 2D systems hold grade to a reference (string, ski, or existing surface), while 3D systems execute a designed digital surface model, which is what enables tie-ins, superelevation transitions, and mill-and-fill against a designed profile rather than a copied one [S3][S5]. See the broader cold milling machine reference for the full application map.
Selection criteria comparison: which class fits which job
A practical four-criterion comparison lined up against the WIRTGEN data [S1][S5][S6]:
Small class (45-160 kW, 14 in-3 ft 11 in width, 4-12 in depth, 10,252-33,951 lb CE): fits partial pavement rehabilitation, tie-ins, parking-garage decks, and floor rehabilitation in industrial buildings. Does not fit full-lane highway production or runway work, where width and depth fall short. Drum flexibility (ECO, fine milling) is the main buying argument [S1].
Compact class (257-313 kW, 3 ft 3 in-4 ft 11 in width, 13 in depth, 44,092-47,179 lb CE): fits urban street resurfacing, medium-lane municipal work, and confined-site full-lane removal. Front-loading design aids truck loading in tight envelopes. Power density of 0.13-0.155 kW/lb supports higher advance speeds than the small class at the same depth [S1].
Large class (up to 753 kW, up to 14 ft 5 in width, up to 1 ft 2 in depth): fits highway, runway, and large parking-lot production at single-pass full depth. The contractor-quoted 350-400 hp at 7 ft width / 13 in depth sits at the lower end of this band, suggesting that the 753 kW upper-end machines are reserved for the deepest, widest cuts on thick concrete or composite pavements [S1][S5][S6].
Across all classes, the decision tree is: width (single-pass coverage of the lane plus overlap), depth (one-pass vs selective two- or three-pass), engine power (advance speed at the chosen depth), and drum type (standard, ECO, or fine milling). Add leveling (2D reference vs 3D digital model) and the equipment-spread fit (haul trucks, water trucks, sweepers, optional screening) before brand selection enters the matrix [S1][S2][S3][S5][S6]. For the wider construction-equipment context that frames these choices, the construction machinery and equipment reference covers the surrounding fleet categories, and the road roller entry covers the compaction side of the same paving train.
Limitations, failure modes, and what the spec sheet should not promise
Depth claims depend on a single-pass or multi-pass reading. A 13 in max depth at 7 ft width is a real number for the large class, but it is a one-pass ceiling, and selective layered removal at shallower depth can match or exceed single-pass production on net tonnage-per-hour [S5][S6]. Specifiers who write "mill to 13 in in one pass" on a thick composite pavement should expect lower advance speed and higher tooth consumption than a 4-6 in selective cut, and the WIRTGEN engineering note is explicit that selective milling does not entail significant time disadvantages [S5].
Power-density claims also depend on operating weight at full ballast. Cold milling machines are routinely posted against bridge and overpass weight limits, and the small-class operating weight range of 10,252-33,951 lb CE is wide enough that two machines in the same power band can have very different transport footprints [S1]. For job sites with posted structures or tight urban access, the small-class swivel-rear-wheel machines (W 35 XRi, W 50 Ri-US, W 60 Ri) are the appropriate pick, not a compact or large mill downsized by halving the drum width [S1].
Standards, sourcing, and a trackable next signal
WIRTGEN's documented range (14 mm fine milling to 4.40 m width, 45 kW to 753 kW, 30-plus machine types) is the cleanest public spec envelope for class selection [S1][S5]. Topcon's documentation confirms variable-depth milling as a defined guidance function on cold mills, and Roadresource.org's micro-milling equipment page lists the coordinated self-propelled cold planer, haul truck, water truck, and sweeper spread as the standard production configuration [S2][S3]. The cold planer / asphalt milling terminology split (cold planer for major highway, runway, and parking-lot projects; asphalt milling machine for surface milling and spot repairs) is consistent across the contractor literature [S4][S6].
Trackable next signals to watch: vendor release of new fine-milling drum line-spacing options for skid-restoration contracts, and updates to 3D milling workflow integration with off-site digital surface models, where the engineering claim is increased quality and cost-effectiveness but the published productivity deltas are not quantified [S5]. For comparison against the compaction side of the same paving train, see the road roller selection for pipeline construction: weight, drum type, and pipe-handling map and the broader construction tools reference.