|Topic Review (Newest First)|
|07-12-2019 02:33 AM|
thanks. that pretty much mirrors my thoughts and experiences from working on lots of race cars over almost 5 decades
i assume you are aware the Ohlins dont need bump stops to prevent internal damage...all you get is a bashing noise!!. i have very thick o rings
at this time i have no aero. the car has a cup type rear wing but i can find no supportable data on its performance and Lotus cars have not replied to messages re this.
i would be interested if you have some downforce data
i run a Motec ECU so i can log almost anything, but i dont have suspension sensors
|07-11-2019 03:14 PM|
I have the Ohlins so I have not been worried about hitting the bump stops on the shocks. I have software that will let me record the actual suspension travel and play back in to the suspension geometry so that you can watch where the roll centers, toe, camber, etc. is doing. I just do not have shock travel sensors or the geometry of the Lotus mapped.
As far as being worried about the upper control arms, the real problem is the angle of the lower control arms. Typically, you want to keep the lowers close to parallel to the ground, give or take a couple of degrees. Getting the angle of the lowers such that they are pointing down can cause some strange behavior with respect to the roll center. It can force the roll center below the ground which is normally a bad thing but I was told by one F1 team that their suspension was actually setup this way. Couldn't get anymore theory as to why because it was considered a secret.
Now, if you a lot of aero on your car, there is actually a reason to use the bump stops on the shocks. On our circle track cars we would actually tune the handling of the car by how much force was being transmitted to the tire via the bump stop. Think of it as having a spring changing it's rate at certain ride height.
So, my suggestion would be to get the drop ball joints and if you are concerned about the rear then get another set for the rear. If you decide to go to lowered spindles later, you could also lower the car even more with the drop ball joints, too.
|07-11-2019 02:34 PM|
thanks Eldon. every time you lower the car via the springs (rather than via drop spindle hubs) , the available bump stroke in the shock reduces and you are then more likely to strike the bump stop . my measurements at the front tell me that at 120mm front ride height, the stock bilstein shocks only have 28mm of bump travel remaining which corresponds to 38mm of upward wheel movement. this is simply not enough on anything other than a billiard table
various other shocks give more travel by virtue of their design. The Ohlins for example have 35mm of bump travel at that height. Nitrons slightly more i believe. I have freshly re-valved Ohlins double adjsutables, so i dont plan to change to anything else unless i get a compelling argument to do so
of course, the stronger the spring, the less movement you get for any given input force. this appears to be the main reason why a lot of racers have gone to very high spring rates
the next issue, and my main concern, is the changing wishbone angles and therefore roll centre when you lower the car via the springs. other racers have also told me the rear is less sensitive than the front but very few seem to do anything much about it, yet they seem to get around the track OK.
no-one else is offering a suspension model, so i guess either its secret business they wont share, or no-one has bothered (which i doubt).
so , my plan at this stage is to make some different ball joints to return the upper arms to their original angles and that will solve the worst of the problem.
|07-11-2019 05:10 AM|
I have not set down and mapped the front and rear geometry, which is something I want to do. I have talked to a couple of people that have been playing with this chassis longer than I have and this is their recommendations. Not quite sure why you cannot get any lower 125 mm. I went to 120 mm front and 125 mm rear and the car's handling was fine. Not sure what you mean by "unacceptable travel in the dampers". One thing that I learned that is a lot different with this chassis than others that I have played with is that the suspension travel is very limited. I'm use to cars having around 75 mm of travel but the Lotus appears to be more like less than 25 mm. Once you stiffen the springs, the chassis basically become a gokart so you have to start changing your thought patterns.
I've been told that the rear geometry is not as sensitive as the front so you do not need to be as concerned there. I put the drop ball joints in the front and lowered the car to 110 mm front and 115 mm rear. The car picked up a slight mid to corner exit push but I believe that is because I'm now carrying the inside front tire off the ground. Driving wise it just required a little more steering input. Thinking about slightly stiffening the rear springs a little since the car does not have a rear sway bar.
|07-10-2019 09:42 PM|
yes, the extended pin ball joints are clearly the cheaper option. Am i correct in assuming you just fitted them to the lower arms F &R ??
are your height numbers just an educated guess, or do you have some data to support them??
at present the car is 125mm at front and 130mm at rear, laden with fuel and driver and the arm angles have changed a lot so the roll centre has changed also. I cant go any lower without getting into the realm of unacceptable travel in the dampers so i'm considering the drop spindle option
|07-10-2019 04:22 PM|
Originally Posted by terryob View Post
|07-10-2019 03:00 PM|
Sorry guys,, i have a S2 car that i've retrofitted with a V6. So, my interest is only in S2 stuff. I'll amend the initial post to make it clear.
so, i'm still chasing a "model" of the suspension
|07-10-2019 10:26 AM|
Originally Posted by TedR View Post
Elise Parts might have S3 suspension or might be worth a call regarding this.
|07-10-2019 08:38 AM|
Does an S3 Exige run their own upright? Or is it common with S2 cars? There are a lot of options for aftermarket aluminum drop spindle uprights for S2 cars that keep wishbone and steering arm geometry while lowering the car.
Black Watch Racing sells extended ball joints (not sure of compatibility.
|07-10-2019 03:51 AM|
roll centre query
i am investigating roll centres for my Series 2 Exige race car (now V6 powered) and particularly the impact of lowering the car via the springs/dampers and therefore altering the arm angles and roll centre
this is an old article, but it seems the issues raised in it never got resolved
has anyone got an update or a dimensional "model" that is correct??
is anyone working on long pin ball joints or other solutions to rectify roll centre changes caused by lowering?
has anyone found a need to alter the steering rack height ?
can anyone using drop centre uprights comment on how they worked out