HPI Savage Bearing Sizes for Accurate Rebuilds

A Savage that feels heavy when rolled, sounds gritty through the drivetrain or develops wheel play rarely needs guesswork. It needs the correct bearing in the correct position. HPI Savage bearing sizes vary across the long-running Savage range, so ordering a full set based on the word “Savage” alone can leave you with parts that do not fit.

The original nitro Savage, Savage X, XL, Flux and later platform revisions share some common dimensions, but they are not identical vehicles. Wheel hub design, transmission layout, centre driveline hardware and optional conversion parts can all affect the bearing count and size. The dependable approach is to identify your exact model, inspect what is fitted and use bearing measurements to confirm every replacement.

How RC bearing sizes are written

RC bearings are normally described as three measurements in millimetres: inner diameter x outer diameter x width. A bearing listed as 8 x 16 x 5 mm has an 8 mm bore for the shaft or axle, a 16 mm outside diameter for the hub or case, and is 5 mm wide.

This format matters because two bearings can look almost identical on the workbench while having a different bore or width. A 5 x 10 x 4 mm bearing and a 6 x 10 x 3 mm bearing are not interchangeable, even if both appear to fit inside a similar housing. Forcing the wrong bearing into place can damage the bearing seat, create side load or leave the assembly loose.

If the old bearing is still readable, its size may be stamped on the shield. If it is not, measure it with digital callipers after cleaning away dirt and grease. Measure the bore first, then the outer diameter and width. Take the bearing out of the housing before measuring where possible, as plastic suspension parts and dirt around the seal can make an installed bearing difficult to read accurately.

Common HPI Savage bearing sizes

Across many HPI Savage nitro and early Savage-based drivetrains, several bearing sizes appear repeatedly. These are useful reference dimensions, not a universal kit list for every version.

| Common size | Typical Savage locations |
|---|---|
| 5 x 10 x 4 mm | Differential cases, gearbox and transmission assemblies |
| 6 x 12 x 4 mm | Selected transmission and driveline locations |
| 8 x 16 x 5 mm | Wheel hubs and larger rotating assemblies |
| 10 x 16 x 5 mm | Gearbox, clutch or driveline positions on certain versions |
| 12 x 18 x 4 mm | Larger support positions on selected Savage configurations |

The 8 x 16 x 5 mm size is one many Savage owners will recognise from wheel-bearing work. It is a common dimension in monster lorry hubs, but its use should still be confirmed against your specific axle and hub arrangement. Savage models have been produced with different uprights, wheel axles and conversion components over the years.

Likewise, the smaller 5 x 10 x 4 mm and 6 x 12 x 4 mm bearings are frequently found in enclosed drivetrain assemblies. They may look clean from the outside while running rough internally, particularly when a vehicle has been used in wet grass, loose sand or deep dust. A differential that feels smooth by hand without load can still become notchy once the drivetrain is under power.

Why model identification comes first

“HPI Savage” covers a substantial family of vehicles. A nitro Savage 25 is not simply a Savage Flux with a different engine. Their power systems, transmission components and centre drivetrain arrangements differ, and later models may have revised parts even where the model name looks familiar.

Before building an order, check the chassis plate, original box information or exploded diagram for the full vehicle designation. Look for details such as Savage X, X 4.6, XL, XL 5.9, Flux HP, Flux 2350 or XS. The Savage XS is especially worth separating from the full-size Savage family, as it is a different-scale platform and should not be treated as a full-size Savage parts match.

It also pays to account for upgrades. Aluminium hubs, aftermarket bulkheads, upgraded transmission cases and conversion kits sometimes use a bearing size different from the original HPI part. If the vehicle was bought second-hand, assume nothing until the existing parts have been checked.

Checking HPI Savage bearing sizes before ordering

A methodical strip-down is quicker than placing a second order for one missing bearing. Start with the areas showing symptoms rather than removing every bearing at once. Wheel bearings are usually the first place to look if there is lateral wheel movement, a rough rolling feel or visible rust around the axle.

Remove the wheel, inspect the hex and axle, then rotate the hub bearings slowly with a fingertip. A good bearing turns freely without a gritty sensation, tight spot or noticeable side-to-side movement. Do not judge it only by whether it spins for a long time. A sealed bearing packed with good grease may not free-spin dramatically, but it should feel consistent and smooth.

For gearbox and differential bearings, inspect the parts during a rebuild or whenever you have access to the housings. Check for brown staining, damaged shields, loose inner races and bearings that stay behind on a shaft rather than sitting securely in their bore. A loose bearing in a plastic case can indicate a worn housing, not just a failed bearing. Replacing the bearing without addressing an enlarged seat may only delay the problem.

Keep removed bearings organised by location. A simple labelled tray prevents a common rebuild error: mixing similarly sized bearings and reinstalling a wider bearing where a narrow one belongs. It is particularly helpful when working through a centre gearbox, where several dimensions can be used within a compact assembly.

Rubber-sealed or metal-shielded bearings?

For a Savage used as a basher, rubber-sealed bearings are generally the sensible choice. They offer better protection from wet ground, dust and fine grit, which are exactly the conditions that shorten bearing life in a monster lorry. Quality rubber seals also make routine cleaning less risky because less contamination reaches the race.

Metal-shielded bearings can have a place in cleaner, dry conditions where low drag is the priority, but they are less tolerant of dirty running. They are not automatically a performance upgrade for an off-road Savage. The real gain comes from a correctly sized, good-quality bearing that remains smooth after several packs or tanks, rather than a lightly protected bearing that feels fast only when new.

Ceramic-hybrid options are another consideration, but they are not essential for every rebuild. They can reduce friction and resist corrosion in some applications, yet they cost more and still need correct installation and sensible maintenance. On a heavy monster lorry that lands hard and runs in poor conditions, bearing fitment, seal quality and regular inspection often matter more than choosing the most exotic material.

Fitment details that prevent early failure

Clean the bearing seat and shaft before fitting new parts. Dirt trapped behind a bearing can stop it sitting squarely, while burrs on an axle can damage the seal during installation. Press on the outer race when fitting a bearing into a hub or case, and press on the inner race when fitting it onto a shaft. Loading the wrong race transfers force through the balls and can damage a new bearing before the vehicle has run.

Do not use a hammer directly on a bearing. A suitable driver, socket or bearing tool that contacts the correct race gives controlled pressure and reduces the risk of cracking plastic components. If a bearing needs excessive force, stop and check the size, housing condition and alignment.

Once assembled, rotate the drivetrain before applying power. It should turn freely with no binding, although a complete Savage drivetrain will naturally have more resistance than a bare bearing. Check wheel play, gear mesh and driveline alignment at the same time. A new bearing cannot compensate for a bent axle, damaged stub shaft or overtightened wheel nut.

When to replace a full bearing set

Replacing only the failed bearing is sensible when the rest of the vehicle is clean, recently rebuilt and known to have low running time. Replacing a complete set makes more sense when a used Savage has an unknown history, multiple bearings feel rough, or the lorry has seen repeated wet running. Bearings tend to wear in groups because they have been exposed to the same conditions.

A full rebuild also gives you the chance to clean the transmission, inspect differential gears and replace worn hardware before a small bearing issue becomes a more expensive driveline repair. For a lorry that sees regular bashing, this preventative work is usually better value than waiting for a seized bearing to damage an axle, hub or gearbox case.

The correct HPI Savage bearing sizes are not just a specification to tick off. They determine how accurately the hubs, gearbox and driveline are supported under load. Confirm the model, measure any uncertain bearings and build the rebuild around fitment rather than assumption - it is the simplest way to keep a Savage running smooth, straight and reliable.