The Identification Problem
Most MGB rubber bumper parts look nearly identical to chrome bumper equivalents from a distance. The overriders look similar. The subframe looks similar. The anti-roll bar looks similar. But they are different — and fitting a chrome bumper part to a rubber bumper car, or vice versa, causes fitment problems, handling issues, or outright failure to locate.
The problem is compounded by the number of cars that have been converted in both directions. Rubber bumper cars were converted to chrome bumper appearance (the most common); chrome bumper cars were fitted with rubber bumper front ends (less common but not rare). When buying parts for a car of uncertain history, the identification problem is not just "is this the right part for the car" but also "is this car actually what the seller says it is".
The good news: the key differences are measurable and observable. You do not need specialist knowledge — you need a tape measure, a torch, and a willingness to look before you order.
The Rubber Bumper System as a Whole
The rubber bumper MGB is not defined by a single component — it is defined by a system of components that work together. These changes were introduced in 1974½ to meet US bumper impact regulations, and they touched the front and rear override assemblies, the suspension geometry (specifically the front anti-roll bar), the body mounting points, and the valence panel configuration.
Front overriders
Rubber bumper overriders are taller and more pronounced than chrome bumper units. The US version has a flat vertical face with a slight bulge at the top; the UK version is taller and more rounded. Both are wider in section than chrome bumper overriders and mount to different brackets on the front subframe.
Rear overriders
Same logic as the front: rubber bumper rear overriders are taller and shaped differently from chrome bumper equivalents. The rear valence panel mounting points also differ — US and UK rear configurations are not identical.
Raised ride height suspension
The rubber bumper cars sit higher — approximately 83mm higher at the front, 51mm higher at the rear — due to different spring rates and a revised suspension geometry. The raised ride height is the single most important identification signal (see below).
US vs UK specification differences
US-market rubber bumper MGBs were built to Federal bumper impact standards. UK-market cars retained a slightly different override profile and different valence panel configuration. When sourcing parts, always confirm the market specification of the car, not just the bumper type.
Common incorrect fits
- Chrome bumper overriders fitted to rubber bumper bodies — common in reverse conversions; visually similar but won't mount correctly
- Chrome bumper ARB fitted to rubber bumper cars — changes handling characteristics and is a clear indicator of conversion
- Rubber bumper overriders fitted to chrome bumper cars — may look right but the mounting brackets don't align
- Wrong-market valence panels (US vs UK) — will not sit correctly in the mounting points
Key Identification Point — Ride Height
Ride height is the single most reliable indicator of rubber bumper vs chrome bumper specification. It does not require specialist tools. It does not require removing anything from the car. It is unambiguous and measurable.
Measure ride height with the car on level ground, unladen, with standard fuel load. Measure from the ground to the centre of the wheel arch at each corner. If the measurements are below the rubber bumper specification, the suspension has been altered — do not assume the car has rubber bumper specification parts.
| Measurement point | Rubber bumper (1974½+) | Chrome bumper (1962–1974) | Difference |
|---|---|---|---|
| Front (ground to arch centre) | ~622mm (24.5 in) | ~539mm (21.2 in) | ~83mm higher (rubber) |
| Rear (ground to arch centre) | ~616mm (24.3 in) | ~565mm (22.2 in) | ~51mm higher (rubber) |
What ride height tells you
If a "rubber bumper" car sits at chrome bumper ride height, the suspension has been altered. This could mean: the original rubber bumper springs have been replaced with chrome bumper units (uncommon); the car was originally a chrome bumper that has been fitted with rubber bumper body panels (increasingly common as the rubber bumper look falls out of favour); or the rubber bumper springs have sagged (possible on cars of this age, but sag of this magnitude would be unusual).
Before ordering rubber bumper parts for a car that sits low, check the other signals below. The combination of ride height, ARB diameter, and overrunner profile will tell you what the car actually has — not what the seller says it has.
The ride height check is non-negotiable before you buy anything for one of these cars. It takes two minutes and a tape measure and it tells you more than any visual inspection of the bumper components themselves. A rubber bumper car sitting at chrome bumper height has had its suspension altered — and once that's happened you can't assume anything else about the car's specification is original either.
The ARB diameter check is the second thing I'd do, and it's the one most people skip. You're looking for a 3/4 inch bar on a rubber bumper car. If it's 7/8 inch, someone has fitted chrome bumper suspension components — either during a partial conversion or because they preferred the handling characteristics. Neither is a disaster on a driver-quality car but both matter if you're trying to restore to correct specification.
Part number prefixes are your friend once you're into the detail. GHK for rubber bumper body panels, GHF for chrome bumper. If a seller can't tell you the prefix and won't let you look, that's worth noting. The good news is that both Moss Motors and Rimmer Bros catalogue these cars thoroughly enough that cross-referencing is straightforward — give them the chassis number and they'll confirm the correct specification.
Decision Tree — Is This Part Correct?
Work through these checks in order. Each one narrows the answer.
1. What is the car's ride height?
If the car sits at chrome bumper height (~540mm front): The suspension has been modified or replaced. Do not assume the car has rubber bumper specification parts. Continue to step 2 to determine what the car actually has.
If the car sits at rubber bumper height (~620mm front): The car is likely a genuine rubber bumper or a careful restoration. Continue to step 2 to confirm part-level specification.
2. What diameter is the front anti-roll bar?
If the ARB is 3/4 inch: The car has rubber bumper suspension specification — consistent with rubber bumper body.
If the ARB is 7/8 inch: The car has chrome bumper suspension — a reverse conversion if the body panels are rubber bumper style. Do not order rubber bumper suspension parts assuming they will fit the current configuration.
3. Do the overriders match the market specification?
If US-market car with tall, rounded overriders: Likely UK-spec overriders fitted in error. UK overriders on a US car may fail a state inspection in states with bumper height rules.
If UK-market car with flat-face overriders: Likely US-spec overriders fitted — cosmetic difference only; functionally acceptable.
If overriders are short and shallow: Chrome bumper overriders on a rubber bumper car — the overrunner has been swapped, likely during a reverse conversion. Check other signals before ordering rubber bumper parts.
4. Does the part number prefix match rubber bumper catalogue?
If prefix is GHF: Chrome bumper specification part — not correct for a rubber bumper car unless it is a shared part used across both ranges (some mechanicals like brake calipers do interchange).
If prefix is GHK: Rubber bumper body panel specification — correct for rubber bumper range.
If you cannot identify the prefix: Describe the part to a specialist (Moss Motors, Rimmer Bros) and give them the vehicle's year, model, and market — they will cross-reference the correct part number.
Not sure what you've got? Tell Geoff the year, model, and what parts you're looking for — he'll confirm the right specification.
Ask Geoff →What Vehicles Does This Fit?
- MGB — 1974½ through 1980 (rubber bumper range, from chassis number 410001 onwards)
- MGB GT — 1974½ through 1980 (rubber bumper range, same chassis number threshold as the roadster)
The 1974½ threshold is the key date. Cars built before this date are chrome bumper specification regardless of calendar year — the production changeover from chrome to rubber bumper happened partway through the 1974 model year. Always check the chassis number, not just the year.
For a full overview of the MGB range including the chrome bumper years and GT variants, see the MGB marque page.
Original vs Replacement — How to Tell
With overriders and body panels, the visual differences between original and replacement are subtle — which matters when you're evaluating a part or a car.
Overriders
Original rubber overriders show age in their surface finish: slight discolouration, minor surface checking, and rubber that has hardened slightly but remains intact. Replacement overriders (quality reproduction from Moss Motors or Rimmer Bros) have a smoother, more uniform surface finish and retain the original flexibility. Cheap pattern overriders may have flash lines from the mould, slightly incorrect profiles, or a surface that cracks under light flexing.
Valence panels
Rubber bumper valence panels were originally zinc-dipped and primer-coated before painting. Rust on a valence panel that has not been stripped is a good indicator of a genuine original part that has been repainted. A too-perfect panel under old paint is likely a reproduction. Check the mounting flange edges — original parts have a slightly rounded edge from the dipping process; laser-cut reproduction edges are sharp.
Anti-roll bar
Original ARBs show surface corrosion in the centre section (the part not exposed to road dirt but not protected either). A very clean ARB on an older car suggests it has been replaced. The diameter stamp is usually on the flat end of the bar — look for a stamped number that should read something like 18G 1234 for rubber bumper specification. If in doubt, measure the diameter and compare against the specification table above.
Where to Source Rubber Bumper Parts
Rubber bumper MGB parts are well supported by the two main MG specialists. Both carry full rubber bumper range catalogues and can cross-reference from chassis number to confirmed specification.
Moss Motors
The largest MG parts supplier with the most complete rubber bumper range. Overriders, valence panels, subframe components, and suspension parts are all catalogued with clear rubber bumper vs chrome bumper designation. Their online catalogue is searchable by chassis number range.
Moss Motors — MGB rubber bumper parts →
Rimmer Bros
Strong rubber bumper coverage with clear part number cross-referencing. Good for mechanicals and suspension components. Their telephone and online support is experienced with MG range specification questions.
For original and NOS overriders
The MG Car Club and MG Owners Club are the best sources for NOS overriders and rare body panel parts that no longer appear in the standard catalogues. Club forums and classifieds occasionally surface parts from private sellers who have acquired old dealer stocks.
For original vs reproduction identification on overriders and valence panels, see our OEM vs NOS vs Reproduction guide.