Dave's Loose Rear End

[sanzomat]

I've been thinking some more about the rear suspension on my Spyder. My problems began on the drive home when I picked it up last November and I managed to spin on the exit of a roundabout - luckily nobody else around. Things improved a lot when I found the tyre pressures were set way too high but there remained a question mark over the 12 year old tyres and I still managed a spin at Combe on the June action day and the car has never really felt right. As I've now changed the tyres I was hoping it would cure everything but I found it was still weird on last Thursday's pub meet. It has gradually improved as the tyres have scrubbed in but I was still left feeling something isn't right in the rear suspension. There is a lot of published info on the net on Libra/Spyder suspension issues and it is noted that the unusual long double trailing arms pivoting on Land Rover track rod ends can cause issues when the the TRE's wear as the length of the trailing arms puts a lot of leverage on the joints and amplifies any slack to a bigger movement at the wheel.

I've been pushing and pulling the rear wheels around but no significant play could be found.

There was a clue though in the pictures taken by the pro at the June Combe day (posted on here in the event post) as you can see the rear wheel is showing positive camber (relative to the car body so even more given a bit of body roll) under load in the pics.

I've measured the camber at rest and the nearside was at -0.5 degrees and the offside was very slightly positive at rest. This doesn't seem right and explains why I'd perceived a better feel on right handers than left handers
The pictures at Combe appear to show (at a guess) around 1.0 degree positive on the nearside so it would seem that the camber changes from rest to under load by around 1.5 degrees. That would have meant my offside would have been at 2.0 positive which would give me a great excuse for spinning on the left hander through the esses.

According to GTMOC it should be set to 2 degrees negative (at rest) so my car was clearly wrong. Yesterday evening I had a play and found out its really easy to adjust so I set both rears to 2 degrees negative. I also adjusted the ride height as GTM recommend 140mm front and 150mm rear (measured from underside of sill to the ground) and mine was set with the front at 145 and the rear at 135.

I took it out for a spin and it feels like a massive improvement although by then it was dark so maybe wasn't pushing  all that hard.

I still need to check the toe in. It looks like the fronts are parallel. There is some debate on GTM forums as some prefer toe in some prefer parallel and some prefer toe out so I'll leave that for now (especially as I'm changing the steering rack soon). The rear was parallel but adjusting the camber seems to have left it toeing out slightly so I need to tweak that as it is supposed to be set toeing in very slightly (about 2mm at the rim seems to be the consensus). I'll try to do that before Combe on Monday. I think I'll take some tools with me and make some adjustments on the day, maybe go for even more rear camber for the track... As Dave G will be there I'll be hoping for a bit of advice!

['The Gaffer']

It is amazing what a degree can do here and there, interesting read. Maybe Dave can do a full setup for you including corner weighting?

[Lucky Ed]

Nice one Dave. Toe out on the rear would explain you problems, I had it on my car and whilst it wasn't too bad in the dry, it was nearly undriveable in the wet and would try and throw itself into a spin at every opportunity. I would have thought getting the toe correct was more important than the camber, but I'm sure Camber Dave would know best.

[Facial Hair Optional]

I'm taking mine to Camber Dave as soon as I can now the R888s are on it. From what I hear he uses black magic or witchcraft or sumfin but everyone raves about how their car is massively better afterwards. I'd take it to Dave, Dave if I were you!!

I hear someone is starting the DKCC (Dave Kit Car Club) we are gonna lose half our members!!!! 

[YellaBelly]

Another vote for Camber Dave

[sanzomat]

I'm sure that having it all set up by Dave would give great results but I'm actually enjoying learning about all this stuff and for me its a part of the whole kit car ownership experience to have a dabble and play, research how to do things, get a bit of advice/opinions from the forums and just learn by a bit of trial and error. I'd like to get myself to a point where i understand what all the settings do sufficiently to know what to try/change. It would also be good, now I know how easy it is to make the adjustments, to maybe have a track set up and a road set up, and maybe different track set up for different types of track. It seems the main compromise with track biased set ups is the tyre wear when on the road so if I can make my own changes I can enjoy the track and dial it back to minimum wear rate for the road...

[Iancider]

Sanzomat,

I still recommend a visit to Dave Gallop - Dave does a double service.  Not only will he set it up perfectly for you but he will give you an incredible tutorial on the art of it all.  His deep knowledge also means he can tell you much more than you might expect and he has to my knowledge several times improved on poor suspension designs by kit manufacturers.  He will analyse why it is problematic and if there is a way he will design a solution for you.

Regards
Ian

[Moleman]

Well we will see how well you do this Monday then?   

[Camber Dave]

Setting up your own car.
The priority for the drivers perception of the settings is listed in order of importance.

Do your adjustments in the reverse order to my list so that early settings remain unaltered by subsequent changes

1)   Dampers – Play around with these. Start with about 1/3 of the adjustment range for a quick start. Keep adjusting until you find a compromise between soggy comfort and quick response to driver inputs. If you can't find this point – change the springs.

2)   (most important) Front tracking
EVERYBODY including your granny will feel tracking errors
Always do this last so you don't compromise it with other adjustments

3)   Cornerweights – there are tricks to setting up weights that don't need scales.
Always set the front ride height level (in the configuration you most use the car –driver only or empty –this does for 2 people). Also set the front spring perches to the same height. These two ensure the suspension presents the tyre to the road equally to both right and right turns.
Set the rear ride height 20mm (+ - 10mm) higher than the front.
Adjust the driver's side rear spring perch higher than the left.  I can't tell you how much as it depends on the spring rate. BUT by adjusting it you WILL get the front level and the perches equal height.

4)   Camber - Unless you have better advice, set the rear to ½ the value of the front. The static camber is set to an amount so as the car rolls in a corner the outer wheel is still leaning in at the top (Dynamic Neg Camber).  For Road touring use up 1 to 2 deg max to avoid tramlining and white lines turning the front wheels. Track use - 3 to 4 degrees – check hot tyres with a tyre temp. gauge and reset to give 5 deg hotter on the inside band of tread.

5)   Rear tracking – set to 10' to 30' toe IN for rear end stability. Camber and later setting won't normally upset this setting so can be done first.


6)   Spring rates – These merit an hours lecture on their own. Briefly, the spring rate sets the handling and comfort level of the car. Dampers control the speed of wheel movement, and how the sprung mass responds to road and driver inputs. See above.

I hope this helps those who wish, in the best spirit of the kitcar world, to do it at home.

[jmad]

Sanzomat,

I still recommend a visit to Dave Gallop - Dave does a double service.  Not only will he set it up perfectly for you but he will give you an incredible tutorial on the art of it all.  His deep knowledge also means he can tell you much more than you might expect and he has to my knowledge several times improved on poor suspension designs by kit manufacturers.  He will analyse why it is problematic and if there is a way he will design a solution for you.

Regards
Ian

I would second this. It was really interesting to learn what Dave was doing and why.

[Moleman]

Dave is the man for this sort of thing Dave. 

[YellaBelly]

Dave's miniature front suspension/steering model is cool too