Wheel and Tyre Fitment: Bead Security Features
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Bead Security Features
03.55
| 00:00 | The final performance related features we'll discuss are both concerned with the security of the bead on the wheel, although for different purposes and applications. |
| 00:08 | Let's start with something we've already discussed briefly in the earlier wheel structures module, bead locks. |
| 00:15 | As you might recall, for most wheels, it's the tyre pressure that's a primary means of holding the bead of the tyre against the outer flanges of the wheel, creating a seal. |
| 00:26 | The issue here is that certain applications benefit from running very low tyre pressure, like drag racing or off roading, say below 10 psi or so. |
| 00:36 | With this low pressure, the bead will be less secure on the wheel and the tyre can de-bead, which is where the beads are no longer in contact with the flange of the wheel and essentially fall into the drop centre, causing the tyre to deflate and lose all its structure. |
| 00:53 | With a double bead lock wheel, the retaining hump is replaced with a flange and another outer flange is then bolted to the barrel to clamp the tyre bead and hold it in place. |
| 01:03 | This can be used on just the outboard bead or both beads for a double bead lock. |
| 01:08 | This also solves another problem where the tyre rotates relative to the wheel. |
| 01:13 | If this only happens a small amount, then it's not really an issue and the effects are negligible. |
| 01:18 | In the worst case, this can make significant reductions on our drive under acceleration and braking performance. |
| 01:26 | This situation is most common in drag racing where the longitudinal grip between the tyre and the road and the acceleration are generally both very high. |
| 01:35 | And this, along with safety, are the key reasons bead locks are used in drag racing. |
| 01:41 | When bead locks are out of the budget though and not allowed by the sanctioning body, some racers turn to adhesives to essentially glue the bead to the wheel or even screws that are drilled through the flange of the wheel and into the tyre bead, although hopefully you can understand why both of these are less than ideal solutions. |
| 02:00 | With that said, this can still be an issue even in applications that run relatively normal tyre pressures like the different forms of circuit racing. |
| 02:09 | If we were to mark the wheel and tyre in alignment before the session, we'd be able to see that the marks moved out of alignment after the session. |
| 02:17 | As we already discussed, this is where we often forego balancing wheels with balancing weights for motorsport. |
| 02:24 | However, bead locks aren't commonly used in these applications as the extra weight is more detrimental to grip and performance. |
| 02:31 | This is where bead knurling comes in as an alternative option featured in some wheels. |
| 02:37 | Knurling involves straight grooves rolled into the surface of the bead seat, essentially making the surface rougher, increasing the friction between the tyre bead and wheel to prevent relative motion. |
| 02:49 | While absolutely not as secure as a bead lock, there are not really any other downsides to knurling and the extra cost to have it is minimal compared to bead locks. |
| 02:59 | As a final note, the same idea is why lubricating the surfaces of the wheel that will be in contact with the bead of the tyre when the tyre is fitted is ideally avoided as this can lower the friction between the tyre and the wheel, making relative motion easier. |
| 03:15 | The key points to remember here are that tyres can de-bead when running low pressures and demanding applications. |
| 03:21 | And this will not only end our race but could be a serious safety risk. |
| 03:26 | Bead locks are used to secure the bead to the wheel so that this can't happen and can also prevent the tyre from rotating relative to the wheel, which is detrimental to acceleration and braking. |
| 03:39 | In applications where lowering unsprung weight is critical or bead locks aren't allowed or really justified, bead knurling can help increase the friction between the tyre and wheel to limit this relative movement. |
