Adler 10/25 PS (1921–1927)

Overview

The Adler 10/25 PS emerged in 1921 as Adler’s answer to a straightforward competitive challenge: the 10/20 PS, while reliable and well-regarded, was beginning to show its age in a German market that was, despite the economic difficulties of the early Weimar period, developing an appetite for more capable touring cars. The solution Adler’s engineers chose was pragmatic: retain the proven 2.6-litre four-cylinder unit but improve its breathing through a revised cylinder head with better port geometry and adjust the carburetion to match. The result was an additional 5 hp — not dramatic in absolute terms, but meaningful in the context of a 20 hp baseline, representing a 25 percent improvement in output.

The 10/25 PS body continued the established open tourer format of the 10/20: four seats, folding hood, side screens, running boards, and the generally upright stance of early 1920s German touring car practice. However, some examples received bodywork that was slightly more rakish than the earlier car — reflecting the beginning of the trend toward more integrated, less utilitarian body styling that would characterise German car design through the mid-1920s.

The 10/25 PS was produced until approximately 1927, when the broader Standard family took over as Adler’s primary civilian car offering. By that point, the market had shifted significantly: buyers in 1927 expected enclosed body styles as standard, synchromesh gearboxes as a desirable feature, and electric starting as routine equipment. The 10/25 PS represented the end of Adler’s open-tourer era, and the Standard 6 represented the beginning of the modern Adler automobile.

The 10/25 PS is only marginally more common in the survivor population than the 10/20 PS; the additional output and slightly more refined body styling make it somewhat more sought-after among veteran car collectors. A well-documented 10/25 PS in running condition is a significant acquisition for any German veteran car collection.

Adler 10/25 PS in Pictures

The 10/25 PS shares the fundamental open tourer body of the 10/20 but with subtle styling refinements that reflect the evolving taste of the mid-1920s German car buyer.

Adler 10/25 PS — Updated Post-War Tourer

Side Profile — Early 1920s Open Tourer

Rear View — Four-Seat Tourer Body

Interior — Veteran-Era Cabin Appointments

Improved 2.6-Litre Four — 25 hp Output

Adler Detail — Early 1920s Frankfurt Quality

Key Specifications

• Engine: 2.6-litre inline 4-cylinder with revised cylinder head; side-valve configuration; 25 hp at approximately 2,500 rpm. Improved carburetion over the 10/20 PS; otherwise the same proven unit that Adler had developed through the early post-war years.
• Drive layout: Rear-wheel drive; bevel-gear rear axle; open propshaft. Conventional for the period. The same fundamental drivetrain architecture as the 10/20 PS with incremental refinement.
• Transmission: 3-speed manual gearbox; sliding mesh on lower gears with synchromesh improving on 3rd gear on later examples. Double-declutching still recommended for smooth shifts. Floor-mounted gear lever.
• Chassis: Conventional ladder frame; beam front axle with semi-elliptic leaf springs; semi-elliptic leaf springs at rear. Marginally improved spring rates over the 10/20 PS to cope with the additional power. High ground clearance appropriate for 1920s road conditions.
• Body: Open four-seat tourer (primary); two-seat sports tourer (Sport variant). Folding canvas hood, side screens, and running boards as standard. Electric starting standard on most 10/25 PS examples, improving over the early 10/20 PS hand-crank specification.
• Brakes: Four-wheel mechanical drum brakes standard; cable-operated. An improvement over the rear-only brakes of the earliest 10/20 PS examples. Require regular adjustment and cable inspection.
• Performance: Top speed approximately 75–80 km/h on good surfaces; modest improvement over the 10/20 PS’s 70 km/h. The additional 5 hp is more apparent at lower speeds — hill-climbing and loaded performance improved more than maximum speed.
• Production years: 1921–approximately 1927; the model ran concurrently with the 10/20 PS for some years before eventually superseding it as the standard Adler touring car specification.

Variant Comparison

What Makes the 10/25 PS Stand Out

• Transitional historical position: The 10/25 PS bridges the gap between Adler’s earliest post-war models and the more modern Standard family. It represents the midpoint of Adler’s evolution from a bicycle and typewriter maker into a serious full-range automotive manufacturer.
• Improved performance over the 10/20 PS: The 25% increase in output over the 10/20 PS makes the 10/25 a more usable and capable car for veteran car touring use. The improvement is most noticeable on inclines and when the car is fully loaded with four passengers.
• Early sporting variant availability: The Sports Tourer variant with its higher-compression head and two-seat body gives the 10/25 PS a sporting character absent from the equivalent 10/20 PS. Veteran car sporting events provide an appropriate outlet for this specification.
• Electric starting on most examples: The move to electric starting on the majority of 10/25 PS cars removes the most physically demanding and potentially dangerous aspect of early veteran car ownership, making the car more accessible for collectors who have not mastered the hand-cranking technique.
• Rarity with documented Adler heritage: The 10/25 PS shares the 10/20 PS’s extreme rarity in the survivor population, but its slightly later production and more refined specification make it marginally more collectible. Any surviving example in running condition is a significant find.

Maintenance & Repairability in Azerbaijan

Maintenance requirements for the 10/25 PS are essentially identical to the 10/20 PS: veteran car specialist knowledge is essential, European parts sourcing is the only option, and the annual service budget should be set generously to allow for unexpected needs.

• Engine service: Identical approach to the 10/20 PS: valve grinding, tappet clearances, carburettor rebuilding, and ignition service all require veteran car specialist knowledge. The improved cylinder head of the 10/25 PS needs the same care as the 10/20 but rewards competent servicing with noticeably better performance.
• Parts sourcing from Germany: German veteran car dealers and the Adler-Veteranen-Club are the primary resources. Shipping to Azerbaijan takes 1–2 weeks; major mechanical components must be fabricated. Budget generously for any major mechanical work.
• Mechanical brakes: Four-wheel mechanical drum brakes require regular cable inspection and adjustment. All four corners must be balanced in their braking effort; uneven adjustment causes pulling. Annual brake inspection with cable replacement as needed is essential.
• Lubrication: Full lubrication schedule as for the 10/20 PS; grease-cup attention at every outing, oil-hole service after each run. A detailed lubrication chart posted inside the bonnet or carried in the tool kit is strongly recommended.
• Body and hood: Canvas hood fabric and side screen materials require regular treatment and replacement when perished. Body repairs require a craftsman familiar with 1920s panel fabrication techniques.
• Electric starting system: The 6-volt electrical starting system should be tested at the start of each season; battery condition, starter motor brushes, and ignition switch integrity are all critical. A failed starter on a veteran car without hand-crank experience can strand the car; carry a serviceable crank regardless of whether the car has electric starting.

Adler 10/25 PS vs. Contemporaries

Cost-of-Ownership Calculator (Azerbaijan)

• Estimated annual fuel use: 120 litres
• Estimated annual fuel cost: $78
• Total annual ownership estimate: $5878
• Average monthly ownership estimate: $490

Used Buying Checklist

• Cylinder head identification: Verify that the 25 hp cylinder head is fitted rather than the earlier 20 hp unit; the improved head has different port dimensions. A 10/25 PS rebadged on a 10/20 PS body is possible; confirm engine specification through physical inspection and documentation.
• Engine condition: Compression test, cold-start observation, oil pressure check. Side-valve engines are sensitive to valve recession; budget for a valve grind if the compression test reveals any disparity between cylinders.
• Chassis and body corrosion: Full probe inspection of chassis rails, body mounting points, inner wings, and floor sections. Any structural corrosion requires significant remediation; cosmetic corrosion is manageable but should be quantified before purchase.
• Mechanical brake system: All four brakes tested individually; cable condition inspected; drum condition checked. Cable systems on 100-year-old cars are frequently in poor condition; budget for a complete cable system replacement as a matter of course.
• Documentation: Any surviving documentation increases value and authenticity; request all available records including club membership history and restoration invoices.

Adler 10/25 PS FAQ

How does the 10/25 PS differ from the 10/20 PS in practice?

The principal practical difference is the 25% improvement in power output, which is most noticeable when climbing hills with a full complement of passengers or luggage. Top speed improves by approximately 5–8 km/h. The improved cylinder head also provides slightly better fuel efficiency at normal touring speeds, partly offsetting the higher taxation the higher output might attract. For most everyday veteran car use, the experience is broadly similar to the 10/20 PS.

Can the 10/25 PS be used for pre-war class historic rallying?

Yes — the 10/25 PS qualifies for veteran car class events by age at most European historic rally organisations. Pre-war class entries in events such as the London to Brighton Run or equivalent German veteran car events are appropriate targets. Preparation for rallying from Azerbaijan requires a support vehicle with tools and spare parts; the reliability of a 100-year-old car on an extended run cannot be guaranteed regardless of preparation quality.

Should You Buy an Adler 10/25 PS?

The Adler 10/25 PS shares all the historical significance and collector interest of the 10/20 PS while offering marginally more practical performance and the benefit of electric starting on most surviving examples. For the veteran car collector who wants an Adler from the early 1920s but finds the 10/20 PS too austere, the 10/25 PS is the natural alternative. The demands of ownership are identical: specialist knowledge, European parts contacts, careful storage, and a generous annual budget.

Any acquisition of a 10/25 PS in Azerbaijan should be approached with the same thoroughness as any veteran car purchase: specialist inspection, full mechanical assessment, provenance review, and a first-year budget that includes all necessary deferred maintenance. This is not a car for the casual buyer but a serious collector piece from Germany’s formative post-war automotive decade.