MK Indy front bump steer measuring and adjustment

[Swampy]

Generally everyone is always looking to get the best for their cars set up. Having been involved in motorsport for a while the desire to get all components as good as possible (within budget and realistic boundaries) on my car has been in my thoughts from the begging of my build.

Having used unusual nissan 200sx as a donor car adapting the suspension components to suit the MK indy (normally based around ford components) was always going to be a challenge if i was going to make the car handle well.

It took a bit of back reading through books from Uni and consulting friends in the industry about which method to take on some of the geometry adaptations i had to make to fit the nissan units to good effect.

So bump steer.
Basically when i built the car i needed to make everything fit. If you have at least one start point then you can always work forwards or indeed backwards from there. In my case the fine tuning of bump steer wasn't really considered in the initial stages. I knew the car needed a Rack and uprights and then something to connect the pair.

Now the car is complete the modifications or fine tuning can begin.
I had used extended track rod end pins which i had previously made to suit the travel of the suspension and the max rotation of the rose joint. It seemed that the spacing between the upright and the rose joint was not quite high enough to give a neutral or zero bump steer (without changing the steering rack located where was necessary and the arc of the wishbones, which i wanted to leave as MK had designed).

So i had some secondary "bump steer pins" made to allow for more spacing adjustment and whilst i was at it i strengthened the material used (en24t steel) for the pins and the spacers fattened out to accept the sandwich load going through them but changed from a steel material to aluminium for lightness.

Original Pin setup


New Pin setup


So how I measured the bump steer.
Possibly not the most conventional way of doing it and i will no doubt gather some further knowledge from comments on here after people gasp in shock or maybe aww to what i have done.

I bought a flat sided laser pen from ebay and attached it to the flat disc side of the hub right

I measured the distance from the centre of the hub pin to a board on which i projected the light in this case 1210mm
I removed the lower damper bolt and supported the lower wish bone at its full droop position.
Made sure the chassis was as level as i could with a bubble then locked the steering wheel straight (using a ratchet strap)

I marked the laser light on a board at this position and then jacked the lower wishbone (without damper) upward to a full maximum squat position. It's to be noted that this is probably further then the wishbones will actually travel in real world use.

With a start position and finish position marked i could then change to the new pin (with larger spacing between the hub and the rose joint) and repeat the measuring.

The first time i did the process i forgot to level the chassis. When i did so i found a 5mm difference over a 100mm travel with calculated to 0.7mm of toe or 0.23 degree of difference over full travel.


This is a lot better then before and fairly neutral so i will leave it at this until i am able to use a proper setup on a flat patch. Also with the Pins being made of the stronger en24t steel and the new style of spacer i can adjust the hight between the hub and rose joint easier in the future.

Any way a cheap way of checking your bump steer and getting some idea of which way it needs to go to become neutral

[Iancider]

Swampy - this is beyond my pay-grade.  I can't but I know a man who can...

Dave Gallop at Track developments 07977 948883

http://trackdevelopments.com/

[Facial Hair Optional]

Swampy - this is beyond my pay-grade.  I can't but I know a man who can...

Dave Gallop at Track developments 07977 948883

http://trackdevelopments.com/

Yeah DG has top level black-ops security clearance, he's your man.