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Strut bump stop 31336857729 is a polyurethane suspension cushion made in China by Bonpora for BMW front strut assemblies and supplied to wholesale buyers, importers and workshop groups worldwide. The part carries Bonpora reference 4110206 and cross-references OE number 31336857729, a front axle jounce bumper catalogued under the BMW suspension numbering system. This page explains the function of the component inside a MacPherson strut, presents the complete technical data for the reference, and sets out the commercial terms that matter to trade buyers - volume pricing, OEM support, packaging, warranty and lead time - so a first inquiry can be prepared accurately and answered without unnecessary back and forth.
A strut bump stop, also described as a jounce bumper, bump rubber or auxiliary spring, is the progressive elastomer element fitted on the piston rod of a MacPherson strut. It becomes active in the last part of the suspension stroke: when a wheel drops into a pothole, crosses a sharp ridge or the car carries more load than usual, the stop compresses and stiffens progressively, absorbing the remaining travel before the damper reaches metal-to-metal bottoming. The part therefore protects the damper, the top mount and the surrounding body structure from shock loads. Once it has flattened, cracked or crumbled away, comfort at full compression deteriorates and the damper wears faster, which is why professional workshops treat this inexpensive component as a routine consumable rather than an optional extra.
On the front axle the bump stop slides over the damper piston rod between the top mount and the dust boot. On many BMW struts the stop is combined with the dust cover and the protective sleeve as a single assembly, so replacement is usually handled together with the dust boot. The 31336857729 reference reproduces the original geometry: a bore of roughly 26 mm seats over the damper rod, the 70.5 mm outer diameter forms the contact surface inside the strut housing, and the 85 mm free height provides a long usable compression stroke. Those proportions point to a larger-diameter rod and a tall cushion, a layout typical of the struts this reference was specified for. When cross-referencing between related numbers it is safer to confirm all three dimensions against the removed part than to rely on outward appearance alone.
Polyurethane bump stops tend to fail gradually rather than without warning. Recognised workshop symptoms include knocking or thudding over sharp impacts, a noticeably harsher ride whenever the suspension reaches full compression, and visible cracking, powdering or permanent flattening discovered once the strut is opened for service. Because the part is hidden inside the assembly, most workshops inspect or renew it whenever a strut, top mount or dust boot is being replaced anyway. Fitting stops in pairs on the same axle keeps both sides of the suspension balanced, and the low unit cost makes renewal the simplest way to protect a new damper from repeated bottoming damage.
The published parameters for Bonpora reference 4110206 are summarised in the table below.
| Parameter | Value |
|---|---|
| Product Name | Strut Bump Stop |
| OE Number | 31336857729 |
| Bonpora Nos | 4110206 |
| Fitment | BMW |
| Size | Φ26 × Φ70.5 × 85 mm |
| Material | Polyurethane (micro-cellular) |
| Country of Origin | China |
| Warranty | 1 year |
| Delivery Time | 15-30 days |
| Packaging | Neutral export packaging |
| Custom Service | OEM & custom design support |
In the BMW part numbering system a front suspension reference typically opens with the 31 group, which identifies the front axle assembly, followed by a digit pair that describes the component family, and closes with additional digits that indicate the specific variant and revision. The 3133 sequence in this reference points to the front axle shock absorber and strut family, and numbers in this range are commonly listed for BMW front strut and damper assemblies. Because applications vary between model series, production years, suspension options and market versions, the complete number printed on the original part remains the decisive identification detail. When the markings on a removed sample have worn away, send the three measurements together with any surviving partial digits, or a photograph of the strut, so the correct reference can be verified before production is scheduled.
A large share of professional buyers source suspension elastomer parts by type and measurement rather than by vehicle model - for example a strut bump stop with a 26 mm bore and a 70.5 mm outer diameter, or a tall polyurethane cushion with a free height near 85 mm. Specification-based sourcing suits bump stops well, because the three dimensions largely decide whether a replacement seats on the rod and engages at the intended point of travel. Measure the inner diameter, outer diameter and free height of the removed component, record the material and Shore hardness where a datasheet is available, then compare the values with catalogue data. The polyurethane bump stop catalogue lists references together with dimensions and OE numbers, so a cross-check can be completed in a few minutes before an inquiry is sent.
OE-number sourcing remains the most dependable route for imported replacement parts, because part numbers are specific while vehicle descriptions are often ambiguous across markets. The workflow below keeps an inquiry efficient and reduces the risk of mismatched stock.
Send the full OE number together with the inner diameter, outer diameter and free height of the old part. For this reference the expected values are approximately 26 mm, 70.5 mm and 85 mm. When all three agree, the stop will seat on the rod and engage at the intended point of the suspension travel.
Micro-cellular polyurethane is the prevailing material for current-generation bump stops because of its progressive compression curve and low permanent set. Buyers switching from an original rubber stop may notice a slightly firmer response in the last stage of travel; supplying the Shore hardness and free height of a reference sample lets the factory match the formulation to the application instead of working from appearance alone.
For first-time cooperation, dimensional inspection and material verification on samples are the most practical risk controls. Bonpora supports sample approval before batch production, and volume supply runs under IATF 16949-based process control, so inspection records can accompany shipment documents when required.
Every batch passes through a controlled production chain: raw polymer and curing-agent batching, metered mixing, moulding under controlled temperature and dwell time, then demoulding, trimming and final inspection. Key checks include outer diameter, bore and free height measured against the drawing, compression force behaviour sampled per batch, and density verification of the micro-cellular structure. These characteristics decide how the stop behaves during suspension travel, so they are tracked on records rather than assessed by eye. Buyers with a technical requirement can request a dimension report or a compression test summary with their shipment, which keeps incoming inspection straightforward on the receiving side.
Factory-direct purchasing removes intermediary margins and gives buyers visibility over the factors that decide batch consistency: tooling condition, material batching and process parameters. Bonpora moulds the shock absorber parts range in-house, from rubber and polyurethane compounding through to finished-component testing, so dimension reports can be issued per batch and mould maintenance is planned internally instead of being outsourced. Direct supply also simplifies commercial handling for wholesale buyers: volume pricing by order quantity, repeat-order scheduling against stock levels, and neutral export packaging that leaves goods unbranded for re-packing under the distributor label. For importers building a BMW suspension programme across several OE references, one factory covering multiple part families means fewer suppliers to qualify and audit.
Beyond catalogue references, the factory develops bump stops and related custom parts from customer drawings, 3D data or physical samples. A typical project covers dimension confirmation, material formulation, hardness matching, pilot moulding and sample approval before mass production begins. Custom service extends to colour, branding and packaging as well, which suits importers building their own ranges and fleet programmes that need batch documentation with every delivery.
Standard shipments use neutral export packaging marked with the Bonpora number 4110206 for traceability, so goods arrive unbranded and can be re-packed under the distributor label at destination. Delivery time is 15-30 days depending on order quantity and the production schedule, and a 1-year warranty covers manufacturing defects. Batch traceability information travels with each shipment, so any delivery can be traced back to production records if a quality question arises during the warranty period.
Most buyers assembling a complete front-end programme combine bump stops with dust boots, top mounts and related rubber-to-metal components. Sourcing several suspension references from one supplier reduces freight consolidation work and keeps material and hardness specifications consistent across the range, which matters when a distributor services a single vehicle family in volume. Use the site navigation to review related catalogue groups, or send a mixed list of OE numbers for a combined quotation covering several part families in one shipment.
For wholesale pricing on the 31336857729 strut bump stop, send the OE number, target quantity and destination port through the contact form on this site. A standard quotation lists unit pricing by volume break, packaging specification and the earliest available production slot, so total landed cost can be compared rather than unit price alone.
The reference belongs to the BMW front axle suspension catalogue, and numbers opening with the 31 group are commonly listed for front strut and damper assemblies. Fitment should be confirmed against the complete OE number on the original part or through a parts-catalogue lookup before ordering, because applications can differ between model series, production years and market versions.
Measure the inner diameter, outer diameter and free height. For this reference the approximate values are 26 mm, 70.5 mm and 85 mm. Significant deviations usually point to a different variant, so the OE number should be re-checked before an order is placed.
Polyurethane provides a progressive compression curve, lower permanent set and better resistance to the cracking and powdering that affect rubber parts exposed to ozone and road chemicals. The firmer final-stage feel is generally mild, and matching the Shore hardness to a reference sample keeps the ride character close to the original.
Yes. OEM and custom design support covers product dimensions, material and hardness, plus colour and branding options on the packaging. Standard shipments stay neutral and unbranded unless custom packaging has been agreed in advance.
