Although a further development of the T-55, the TR-85M1 uses a T-block powerpack (similar to the one used in the Leopard 1) based on a V8 German 830 hp (620 kW) diesel engine, an improved turret, a locally-designed "Ciclop" fire control system (with cross-wind sensor, laser rangefinder and night vision), new 100 mm BM-412 Sg armour-piercing fin-stabilized discarding sabot (APFSDS-T) projectiles and a fully redesigned suspension with 6 road wheels on each side, protected by metal side skirts.

After the Warsaw Pact invasion of Czechoslovakia, Communist Romania adopted a new national defense doctrine.

The new vehicle would have a weight of approximately 40 tons, a 100 mm main gun and a 500 horse power engine.

It is often alleged that TR-77 was a copy of T-55 but only a very small portion of its equipment were carried over from the Soviet tank: night vision gunner's periscope, ammo, coax MG and probably the main guns sight, the general shape of the turret and temporarily the engine.

Also, the hydromechanic transmission was designed by the ICSITEM research institute from Bucharest based on an available model and produced by Hidromecanica Brașov factory, thus completing the T-block powerpack.

[5] Ion Mihai Pacepa, a two-star Romanian Securitate general and the highest-ranking intelligence official ever to have defected from the former Eastern Bloc, later asserted in his book Red Horizons: Chronicles of a Communist Spy Chief that the engine technology was obtained using spy rings and confidential assistance from the Federal Republic of Germany.

The laser rangefinder was not integrated with the daylight aiming system and only a limited number of corrections could be inserted in the ballistic fire-control computer.

Problems were made worse when Nicolae Ceaușescu decided to cancel in July 1982 all imports of special equipment for the arms industry.

[8] At one point, Ceaușescu threatened to stop tank production altogether because of the poor manufacturing quality.

The initial teething problems were not corrected until after the fall of communism in Romania when the Romanian engineers used foreign parts to improve TR-85's reliability.

On 14 April 1994, the upgrade program was approved by the Supreme Council of National Defense and development of the new tank, officially designated TR-85M1 Bizonul (The Bison), began in 1996 when two prototypes were built.

[10] The modernization program involved both foreign companies (most of them from France), such as Aerospatiale Matra, Sagem, Kollmorgen-Artus, Racal, and local defense companies such as the ROMARM military consortium, METRA (Military Equipment and Technologies Research Agency), Electromagnetica, FAUR, Elprof, Aeroteh, IOR, Prooptica, Artego, Arsenal Reșița, Metav, Forsev, Anticorozivul, IEMI, Rolast, Aerostar and IOEL.

The TR-85M1 is equipped with laser illumination warning sensors that can automatically trigger the GFM-76 smoke grenades and flares, thus disrupting the guidance systems of thermal and infrared guided missiles.

The metal side skirts have three holes each that form steps for the crew to reach the roof hatches.

The TR-85M1 tank also has NBC protection and an improved, rapid fire suppression system using non-toxic agents.

Also, the older TR-85 tanks have a conventional driver's seat bolted on the floor, whereas the M1 version has a parachute-harness like arrangement.

In this way, the driver has no contact with the hull except on the pedals and is out of the shockwave area of exploding land mines or IEDs.

[12] The gun can fire APFSDS-T (BM-421 Sg), shaped charge (BK-412R and BK-5M), high explosive (OF-412), armour piercing with tracer (ballistic-capped BR-412B and BR-412D) and target practice (PBR-412 and PBR-421B) rounds.

[14] To increase the firepower of the TR-85 tank, the BM-421 Sg round (known internationally as the M309 cartridge) was developed in cooperation with Israel as part of the modernizing program begun in 1996.

[9] The new stabilization system improves the accuracy of the main gun and reduces the target engagement time, turret temperature, noise, fire hazard and maintenance.

The gunner's day sight telescopic periscope features an integrated laser rangefinder (200 m to 5.000 m measurement distance) and an electronic reticle.

Above the gun barrel there is a SAGEM MATIS thermal viewer designed to operate at wavelengths between 3 and 5 μm in the spectral band.

Initially, the TR-85 M1 tanks had an inferior SAGEM ALIS thermal viewer (8-12 μm in the spectral band) for the gunner, now present in export configurations.

[18][19] The commander has a Société Française des Instruments de Mesure (SFIM) EC2−55R panoramic sight with a second generation SAGEM image intensification system that can be independently directed to the target.

In 2024, a modernized variant designated TR-85M1R was unveiled at the Black Sea Defense & Aerospace [ro] exposition.