Honda ST90 Specs and Review (TrailSport Minibike)

For sure, the Honda ST90 is among the most underrated fashions of the Honda CT collection. Produced for under three years, this bike, fondly referred to as the May Dax (marketed within the U.S. because the TrailSport™), succeeded the extremely acclaimed CT70 lineup. Portability, reliability, and off-road enjoyable are simply a few of the excellent qualities you’ll uncover concerning the ST90 on this information.

The Honda ST90 was an 89-cc minibike produced from 1973 to 1975. Successor to the celebrated Path 70 collection, this two-wheeler featured the identical Dachshund-like chassis, retro styling, foldable handlebars, and provided a 3-speed semi-automatic transmission.

Regardless of its second-fiddle reputation, the Honda ST90 is well-loved for its non-discriminating measurement and beginner-friendly performance greater than its Dax likeness. These attributes could not have made the pocket bike an enormous hit again within the day. However they’ve efficiently earned the ST90 its loyal, rock-solid following that also raves concerning the bike’s easy choices.

Round Motorcycle Headlight and Handlebars

In regards to the Honda ST90 TrailSport™

The Honda ST 90 is a barely greater model of the CT minibike collection launched by Honda in August 1969. The 89-cc Dax descendant, particularly, was produced from 1973 to 1975 and was not given a CT designation regardless of the lineage. As a substitute, it was offered solely in North America because the TrailSport – fairly totally different from what most shoppers assumed to be the that means of the letters “ST” (Sport Touring) within the bike’s nomenclature.

Typically, the ST90 pocket bike has a bench-style saddle, Dachshund-like body, and folding handlebars attribute of the CT collection. Likewise, it shares the identical air-cooled 4-stroke OHC engine and a 3-speed semi-auto gearbox with an automated centrifugal clutch meeting because the DAX system. The 2-wheeler’s distinct T-bone body assist distinguish it from the extra widespread Honda minis such because the Z50 Monkey & Gorilla and the CF/CY Nautydax bikes.

Its 14-inch wheels and barely greater energy mill make the ST90 seem like an older brother of the Path 70. Extra importantly, these large-diameter wire-spoke wheels (paired with the bike’s cradle-down tube) make the Honda ST90 a correctly proportioned bike with an aggressive look and novice-friendly mannerisms – good for in-training younger riders and older youngsters approaching off-roading proficiency, and incomes it the moniker the “Mighty Dax.”

1973 Honda ST90 Specs & Options


The ST90 is dropped at life by a single-cylinder, 89 cm³ (5.4 in³) air-cooled OHC energy mill. Bore-stroke ratio is 50 x 45.6 mm (1.969 x 1.795 inches), whereas compression ratio is 8.2:1. A 17-mm Keihin carb with a 40-mm air filter mount handles air-fuel combination and may improve to a PZ22 aftermarket carburetor for higher top-end efficiency. General, this engine configuration lends to a bone-stock high pace score of 35 mph or 56 km/h (low-speed move with limiter) and 50-80 mph or 80-129 km/h (high-speed move sans limiter).

Gas & Lubrication

Gas tank capability is 2.6 L/0.7 USgal (inclusive of 0.1-USgal reserve) of normal gasoline with a minimal PON 86/RON 91 score. Lubrication-wise, the producer recommends high-detergent, premium-quality 4-stroke oil or its equal. Engine oil needs to be an SAE 10W-30 or 10W-40 and have at the very least an API-grade of SJ assembly JASO T903 MA requirements. Different viscosity grades resembling SAE 30, 20/20W, or 10W are permitted following ambient temperature.


A semi-automatic, 3-speed transmission (with a left-foot-operated return system, N-1-2-3 shift sequence) and an automated centrifugal clutch meeting ship energy to the wheels. A 428H O-ring chain (view on Amazon) with 94 hyperlinks plus joint handles wheel spin. The pocket bike’s wide-ratio transmission makes for predictable dealing with and stability.

For reference, listed below are the inventory gear ratios for the 1973 ST90:

Main Discount Ratio 3.722
Transmission Gear Ratio – I 2.538
Transmission Gear Ratio – II 1.647
Transmission Gear Ratio – III 1.045
Ultimate Discount Ratio 2.666 (15/40T)


It has a Contact Breaker Level ignition system requiring an NGK D-6HS/Nippon Denso X20 FS spark plug (with a niche of 0.6-0.7 mm or 0.024-0.028 inch). It’s wired for six volts, is fitted with a 6V 5.5 AH/(10 HR) battery, and has an A.C. generator with a rated output of 0.049 kW @ 8,000 RPM serving as its charging system. The handbook doesn’t specify the precise battery format required for the ST90 to run.

Convert its wiring harness to help a 12V electrical system with a corresponding regulator/rectifier and stator improve. Doing so will allow you to make use of a ten HR YTZ7S battery with 113 x 70 x 105 mm dimensions. A CTEK 12-Volt Battery Charger (view on Amazon) can even assist prolong the longevity of your new 12V battery.

Tires & Brakes

Inventory tires consist of three.00-14 (4PR) entrance and rear tires mounted on wire-spoke rims. Advisable cold-tire stress for the entrance and rear are 124 kPa (1.27 kgf/cm2, 18 psi) and 165 kPa (1.69 kgf/cm2, 24 psi), respectively. Brake kind and specs are additionally unspecified within the handbook, however photographs present the ST90 makes use of drum brakes at the back and front to finish its tire-and-wheel meeting.


The entrance suspension consists of Ceriani forks, whereas the rear has a swingarm, and the wheelbase is 1,170 mm (46.1 inches) – virtually six (6) inches longer than the CT70s. There aren’t any particulars of minimal floor clearance or turning radius within the service handbook. However on condition that the ST70 and ST90 share the identical design, it will be secure to say floor clearance is at the very least 165 mm (6.5 inches) whereas turning radius is at the very least 1.6 meters (5.2 ft).

Red 1973 Honda ST90 Minibike


 General dimensions are 1,755 x 760 x 1,030 mm (69.1 x 29.9 x 40.6 inches – L x W x H), making the pocket bike longer however narrower than its counterpart, the Polaris Outlaw 90. Seat top is roughly 813 mm or 32 inches. Dry weight is 86 Kg (190 lbs.), whereas load restrict capability is 100 Kg (220 lbs.). Not solely can the ST90 carry heavier youngsters, however it may possibly additionally accommodate older riders. General, the TrailSport is moveable and extra strong than most of its opponents.


Enclosed in a cradle-down tubular metal body (62° caster angle, 67 mm path) are the ST90’s crankcase, inside Honda ST90 elements, and plastic physique panels in a colour scheme that takes after the CT70 K0-K3 variations. All fashions had a black saddle, 6V headlights, flip alerts, and tail/brake lights. Additionally they include rearview mirrors and a speedometer (view on Amazon). Manufacturing unit hand grips, serrated footpegs, and up-type fenders add to the rugged enchantment of the bike.

Honda ST90 Worth

Here’s a full rundown of resale values for all 89-cc Honda ST90 fashions launched between 1973 and 1975:

Yr – Trim – Mannequin Quantity Listing Value Retail/Commerce-In Values
1973 Honda ST90 N/A $480 – $1,990
1974 Honda ST90 $480 – $2,500
1975 Honda ST90 $475 – $1,945
(Supply: Nada Guides)

Pre-owned TrailSports preserve their worth fairly effectively, with resale pricing starting from $1,200 to $4,000. A number of of those items can be found on Craigslist and different well-known dealer websites. Count on little to no beauty and mechanical injury for items priced over $1,500, and a few of them could even include just a few aftermarket upgrades, a transformed electrical system, and new lighting. In the meantime, machines offered for elements are uncommon. In case you are searching for a near-mint Sweet Yellow Particular trim (fondly referred to as the Large Chicken), be ready to pay a good-looking value.

Ache Factors of the TrailSport™

Beginning Issues

The kick-starter for secondhand ST90s is reportedly problematic. It kicks with the spring stress however doesn’t essentially flip the engine over. A number of elements may trigger this to occur:

  • Gas hunger
  • Congested traces/filter/drain system
  • Bone-dry or maladjusted clutch plates
  • A fouled spark plug

Examine the spark first by visually inspecting the adjuster and inventory flywheel/stator meeting. The latter is a moist setup, so count on oil to leak out when eradicating the flywheel cowl.

As for the plug, there are circumstances the place even new plugs prove crammed out with soot even after just some minutes of check driving. When this occurs, you want to look into accompanying signs like smoke, as these indicators will make a distinction in how your analysis seems. You’ll have a weak spark attributed to unhealthy factors/condenser, worn rings/blow-by, an excessive amount of oil within the system, weak coils, or an incorrect plug hole.

Different suggestions to deal with beginning issues embody a clutch adjustment and engine oil change to a variant appropriate with moist clutch engines that meets JASO T903 MA requirements. By no means use engine oil labeled as Vitality Conservation or Useful resource Conservation I/II. Or it’s possible you’ll solely must steadiness the air-fuel combination and use hotter plugs in your two-wheeler.

Lack of Transmission Choices

Many fanatics felt it was a disgrace that the ST90 solely provided a 3-speed gearbox, on condition that it rides easily and supplies good steadiness. Good factor mechanics these days have gotten more proficient with transmission rebuilds.

Based on these specialists, you’ll be able to add a sub-transmission to an ST90 – a technique is utilizing the ATC90 energy mill as a donor and doing a little bit of machining. These steps enable the ST90 to have a sub-transmission whereas maintaining its auto clutch setup. Using a CT90 engine is an alternative choice. Nonetheless, its motor mount has a distinct bolt sample than the ST90’s so changing the transmission might not be easy.

Rarity of Components

For probably the most half, the Honda ST90 has all the fundamental parts you want to construct on. The most important problem it poses is, maybe, the non-interchangeability of elements with a CT70 or CT90. This makes performing restomods extra sophisticated than it already is. Expectedly, this is among the causes some fanatics veer away from proudly owning this traditional mini bike.

About Honda

An establishment within the motorcycling panorama, the Honda Motor Firm Ltd. is one in all in the present day’s most profitable world automotive producers. The Japanese agency developed from automotive elements and motorized bicycles with surplus engines to mass-production of automated army plane propellers and race automobiles, alongside venturing into different industries. The maker of the Honda ST90 is acknowledged worldwide for spearheading improvements in electrical cars, motorsport automobiles, and vitality options.

Conclusion – Honda ST90 Overview

The Honda ST90 might not be the creme de la creme of collectible, classic pocket bikes, however it’s getting there – and quick. Its sensible options, simplified transmission, and nostalgic exterior proceed to develop on each common shoppers and fanatics. Positive, there are newer, extra tech-advanced minibikes the place children can observe on. However for critical, in-training off-roaders, nothing beats studying methods to journey on this traditional, 3-speed two-wheeler.

Leave a Comment