Wheel and Tyre Fitment: Checking Clearance
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Checking Clearance
03.45
| 00:00 | Contact between the rotating wheel and the suspension, chassis or bodywork at speed can not only cause some really serious damage to any of the parts involved, but unsettle the car and cause the driver to lose control, leading to a serious accident. |
| 00:14 | For this reason, it's critical whenever we're making changes to the wheel and tyre fitment that could cause clearance issues, we need to check for this. |
| 00:23 | This is a very similar process to what we discussed when measuring a vehicle for wheel and tyre fitment. |
| 00:28 | So, everything going to plan, there shouldn't be an issue. |
| 00:31 | But we still need to check, even if we've done this work already or not, to avoid any risk. |
| 00:37 | We'll work through an example of this, looking at the wheels we chose for our GT86 in the previous example since we now have them on hand. |
| 00:45 | To refresh our memory, these wheels are Enkei Raijins, an 18x9 ET45 in the front and rear and run a 27-65-18 Michelin slick. |
| 00:57 | The wheels and tyres are much wider than the factory option, although a very similar offset. |
| 01:02 | Just over an inch was added to the outer flange and just under an inch was added to the inner flange compared to the largest factory option. |
| 01:10 | The overall diameter of the tyre is also 20mm or so larger and the guards are more or less unchanged. |
| 01:17 | Just a small roll of the lip, but the suspension components, like the aftermarket coilovers, will give us some more space. |
| 01:24 | This adds up to a relatively significant change on this vehicle. |
| 01:28 | And even though we've done our due diligence in the previous module to ensure they'll fit, we still need to check to be sure. |
| 01:35 | The first step with the vehicle supported safely on a hoist or axle stands is to remove the spring and bump stop from the front suspension. |
| 01:43 | Then assemble the suspension again without these parts and fit the wheel, with the tyre mounted of course. |
| 01:49 | We can then use a jack under the lower control arm to cycle the suspension through its full travel, while also steering from lock to lock, checking for any unwanted interference. |
| 02:00 | Rotating the wheel while we do this can help highlight any issues that we might not be able to see. |
| 02:06 | In this case we can see that there's plenty of clearance in all areas through the full suspension and steering travel, so there's nothing to worry about. |
| 02:14 | If the clearance is tight, it's worth checking this on each side of the car. |
| 02:18 | Ideally each side will have the same amount of clearance, but this is not always the case, and unfortunately some well used motorsport vehicles aren't always symmetrical. |
| 02:27 | It should also be noted that this method doesn't take into account compliance with suspension bushings and chassis stiffness. |
| 02:35 | Depending on the car, this could result in significant movement of the wheel compared to what we just checked. |
| 02:41 | The same process should be repeated on the rear of the car, but of course without any steering involved. |
| 02:47 | In saying this, many vehicles have some form of rear steering, so if possible we need to cycle this as well. |
| 02:54 | Rear steering and compliance are why it's best to leave at least a few millimetres of clearance everywhere to allow for some extra movement. |
| 03:02 | Naturally, if we find any interference, it needs to be addressed to ensure that it won't cause an issue. |
| 03:07 | In the best cases this might just be a light roll of the guards, but in the worst case we might find that our wheels just won't work at all. |
| 03:15 | Which is exactly why we do all our measurements and checks in the first place. |
| 03:20 | The key points here are that whenever wheel and tyre fitment changes are made that could affect clearance, we need to do a double check with a physical test. |
| 03:29 | To do this we need to remove the spring and bump stop so we can cycle the suspension and steering throughout some tyre travel while rotating the wheel to check for clearance at the limits. |
| 03:38 | Be sure to allow for some extra movement with compliance. |
