Untitled Document
  • 8 July 2017 – Suspension Set up – Introduction

    The next job for us was to look at setting up the suspension including, the Ride height, Toe and Camber. This was a job that we had been putting off as we both weren’t too confident about how to get the best set up for this. Fortunately Richard, Mark’s colleague at JLR had some experience doing this in racing teams and helped us out.

    The suspension set up can take some time and involve a lot of trial and error before you achieve the setting up you want. Often by adjusting one setting then changed something else, so it is important to measure and re-measure every time you make an adjustment. As we thought, this became quite fiddly job and took us a full day to get right. Eventually we got a base set up as we wanted it. This might be something that we will have to readdress later once we have done a few miles and the suspension settles properly.

    I hope the next few posts will best describe the process we went through.


  • 8 July 2017 – Suspension Set Up – Ride height set up

    Before we started doing any setting up it is important to first check the tyre pressures are all consistent. We set this to 30psi all round. We also placed the 4 wheels on to grease plates which are essentially just two circles of aluminium sheet metal with grease painted between them. This was important so we could remove any friction between tyre and ground and allow the wheels to move freely. This would then let suspension to sit without tension on it and would then give us a true measurements from the wheels.

    Ride Height

    We decided the obvious place to start would be to set the ride height. Initially we contacted Stuart Clarke to ask him the ride height measurements on his 289 build to give us a rough idea what to aim for. He confirmed measurement from centre of the wheel to top of the wheel arch were rear: 375mm front: 365mm. We had the jaguar XJS rear axle as opposed to the MG back axle set up on Stuarts build and we had been told previously that the Jaguar rear axle can often ride slightly higher than the MG equivalent.

    We firstly used a Plum line (string with a weight on the end) and used a sharp to mark the centre point of the wheel and wheel arch which gave us a consistent position to measure from.

    We could visually see the rear was riding way higher than the front and the first measurement confirmed this; O/S/F: 349mm, N/S/F: 355mm, O/S/R: 410mm, N/S/R: 410mm.

    Rear Ride Height

    We started by adjusting the rear. Firstly we marked a position on the platform adjusters to count the number of turns we made when adjusting the height. We knew the thread on the shock absorber had a 3mm pitch so each turn would reduce the ride height by 3mm.

    We set the platform adjusters to one thread from the bottom of the shock absorber which we worked out would give us a rear height of approximately 375mm. We soon realised that when the shocker was at maximum extension the strings moved slightly so we discussed whether we might need to add additional helper springs to keep spring location when at full droop. This is something we will add later. This is assuming that we ever drive so fast that we get air!

    Front Ride Height

    We wanted to achieve a ride height set up with an approximate 10mm rake. Knowing that we had a ride height of 375mm at the rear this would set the ride height at the front of 365mm. The front shocker absorbers also had a 3mm thread pitch so we adjusted them accordingly to achieve the 365mm measurement at the front. This meant adding height to both front nearside and offside.

    Once adjusted we lowered off the jack to confirm the measurements. We bounced the car on the turn plates and also rolled the car backwards and forwards several times to allow the suspension, tyre and chassis to settle before re-measuring.

    We went through this process a few times before we got the ride height set up correctly, eventually getting a 10mm rake with Rear: 375mm Front 365mm,


  • 8 July 2017 – Toe set up

    Toe

    Next was to set up the wheel toe, Richard had some poles with grooves cut into them. These were based on the ‘Smart String 4 Wheel Toe Alignment System’ that he had previously used when working for some racing teams. The Smart strings works by attaching brackets to the vehicle, supporting transverse pole on the front and rear of the vehicle. Then parallel lines are ran from the front to back to measure from. As we only had the poles we supported the poles on 4 axle stands 2 at the front to at the back. This really helped us set up a string box around the car to take measurements from. We didn’t have any geometry settings for the car so talking with Richard we decided a good base to start from was to have the front and rear toe in 1mm each side. This would give an overall toe of -2mm on the front and -2mm on the rear. By doing this the car would drive straighter and the back end would not kick out as easy on corners.

    You can read more about the Smart Strings system here.

    Front Toe

    We firstly we had to find the centre on the steering rack and set the steering wheel straight. Next we set up the box around the car using the poles, one pole at the front one pole at the rear. We then ran weighted fishing line from the front pole to the rear pole creating a box around the car to measure from. Firstly we measured from the centre of the hub to the line on all 4 hubs, this was to get the same measurement from the hub to the line on all 4 hubs to make sure the lines parallel.

    Once the lines were exactly parallel this allowed us to get a precise measurement from the front and rear of the wheel to the line to work out the toe in millimetres. The front toe was a reasonably straight forward to set up. With the steering rack set centrally it was a case of shortening the track rods either side until we got the front wheels to toe in by 1mm on each side with an overall toe of -2mm. One issue we had was that the track rod was too long and bottomed out in the track rod end. As there was plenty of thread on the rod we took 10mm of thread off the end of the track rod on both sides with a hacksaw. This stopped the track rod bottoming out in the track rod end and we could get the toe to measure correctly.

    Rear Toe

    The first measurement of the rear toe showed we had -4mm on N/S and -1mm of the O/S. Unfortunately the rear toe set up was more difficult to sort out. With the Jaguar XJS rear axle this meant adding or removing shims between the front and rear mounting points of the lower suspension arms to the solid mounted Jaguar rear diff. We ended up adding some shims to the front mounting and removing them front the rear mounting point of the N/S lower suspension arm. This was to push out the toe on the N/S rear to give us -1mm on each side.


  • 8 July 2017 – Camber Set Up

    Camber

    After setting the toe front and rear we looked at setting the camber. To measure this we used a bar with 2 bolts sticking out, each bolt measured the same distance off the bar. Placing the bar with the bolts up against the wheel with one bolt on the top of the wheel rim and the other bolt on the bottom of the rim. This then gave us a flat surface to measure the camber on.

    We had a magnetic angle gauge that we stuck to the bar this gave us the number of degrees camber that the wheel was set to.

    We were aiming for -1 degree camber on each wheel this would give us better cornering.

    Rear Camber

    For the rear the camber is set by adding or removing shims between the drive shaft and the diff. There are 2 sets of shims between the diff and the drive shaft on each side. One set between the inboard brake discs, this is for centralising the disc with the calliper. The other is between the outside of the disc and the drive shaft, these are to set the camber.

    So as the drive shaft also acts as the top suspension arm the more shims you add the less camber you get and the more shims you remove the more camber you get.

    The N/S/R had -2.5 degrees and the O/S/R had -1.5 degrees so we add some shims to both side to get the -1 degree on both sides.

    Front Camber

    The front camber was a lot easier to set this used a cam bolt off set the position. So by loosening off the nut of the bolt then turning the bolt this ether made the lower mounting closer or further away from the chassis altering the camber. Once we got the correct setting we tightened the bolts.

    Once the camber was set front and rear we knew this could affect the rest of the suspension set up so we rolled the car forward and backwards bouncing the suspension to settle it.

    We rechecked all the suspension measurements again and just had to adjust the front toe correctly again.