Side-Slip/Alignment Test - Discussion

Auld Jim Halpin

Hello, I have tried to research this test from the NCT and not having found much concrete information I thought we might discuss same here.

My situation: This year, 2016, car failed on REAR axle side slip test with figure of -20.0m/km. Some of my prev results are -12,-16,-11 and last year -20.(Limit is +/-18) Last year also got "Ball Joints Worn" on rear axle so got relevant parts replaced (good mechanic with great reputation)and on the retest I got -1.0m/km. As I said this year I get -20, no mention of ball joints or other failing parts. Car is RWD. Mileage is 114k miles with just 4000 miles since last years NCT. Front axle has been fine over the years, around +1 to +4. Tester used two lanes and got the fail result on both lanes.

In my research I noted these points.

In the NCT for the side-slip test they only use the RH wheels.(Can anyone confirm this) Should it not be both sides and what might be the ramifications of not testing both sides?

In the NCT, car has to be straight on to the pad, with no steering input, steering straight ahead and no braking - is this a bit much for the tester to achieve consistently?

There does not appear to be any mechanics in Ireland that have a side-slip tester in their workshops so it makes accurate diagnosis and repair a bit hit and miss? (And very costly)

The side-slip test is done by driving the wheel over a pad which has sensors to detect sideways movement/pressure - in contrast to 4 wheel laser/infrared alignment which is done with the vehicle stationary. Is it possible to do 4 wheel alignment on a rolling road?

I have read of people getting full 4 wheel laser/infrared alignment done and still failing side-slip test? - In those cases it was suggested that suspension parts, bushes etc were worn and the alignment was undone by driving it after the adjustments were made?

This in turn suggests that a fail on side-slip is rectified by having suspension components and bushes inspected for wear, replaced if necessary and then 4 wheel alignment carried out?

I also read with suspension and bushes passed ok and alignment done you might still fail side-slip if bearings are worn, any thoughts? (Presumably tester in NCT would have flagged bearings?)

Do you think the NCT should give more information on why a particular item has failed and thus help owners to more quickly get problem diagnosed and save money on diagnosis. Should NCT offer more info in return for the E55 you are paying them? - In my case a non mechanical person could end up getting alignment done and fail, get suspension parts replaced and no alignment and fail, get alignment done and possibly still fail side-slip for some other reason.

Lastly anyone got suggestions for getting alignment done in Dublin, for me, or other locations. One place I asked they said they charged the labour rate of 85 per hour plus VAT! That suggests to me that it could be a long day and a very expensive day!

Also is it required to have 4 brand new tyres when getting 4 wheel alignment, I am sure it helps but how crucial is it, many places try to sell you tyres or they won't do the alignment?

Thanks for reading and here are some links to YT vids of the side slip test plate in action.

https://www.youtube.com/watch?v=S2cku5nibvc
First square blue plate that wheel goes over, both wheels

https://www.youtube.com/watch?v=UcNOj8DmgRI
Skip to 2:50, plate in ground, both wheels

https://www.youtube.com/watch?v=DpjT4lMB4w8
First plate, both wheels

https://www.youtube.com/watch?v=5OF9TJ5vuRE
Both wheels tested