Strut braces
06-07-2010, 07:46 PM
#31
Drifting
no not really, 5mm each way,(0.19 inches) this is actually more room then most aftermarket strut bars out there. the dynatech touched both the hood and rail on Rods car.
I just dont like the idea of putting an already bend bar as a strut brace. i would think it would bend easier then one that is straight.
I just dont like the idea of putting an already bend bar as a strut brace. i would think it would bend easier then one that is straight.
06-07-2010, 09:31 PM
#32
Rennlist Member
no not really, 5mm each way,(0.19 inches) this is actually more room then most aftermarket strut bars out there. the dynatech touched both the hood and rail on Rods car.
I just dont like the idea of putting an already bend bar as a strut brace. i would think it would bend easier then one that is straight.
I just dont like the idea of putting an already bend bar as a strut brace. i would think it would bend easier then one that is straight.
Yes, I agree, depending on design and loading, pre-bent bars are less stiff than a straight bar. The sharper the bend, the more the rigidity is reduced. For example, the cup bars do have 4 vertical bends and 2 horizontal. The bends are very large radius, so that does maintain much of the bar's integrity, but in a straight compression or straight tension test, it will deflect slightly more than a straight bar with identical cross section, given the same load. Most of the aftermarket bars have bends to help clearance: weltmeister, racing dynamics, brey kraus, etc...
06-07-2010, 09:37 PM
#33
Rennlist Member
06-07-2010, 09:40 PM
#34
Rennlist Member
I wouldn't have thought so either, but the frame rails move more than you might think.When I put a lower brace on my 968 it made a lot of difference on the track, like a 50lbs spring increase.I was very surprised.The chassis is a little different, but still I think everything is moving around up there, you want to minimise as much as you can.
06-07-2010, 09:46 PM
#35
Drifting
All this talk about strut braces has me asking one question, is their such a thing as too stiff a chassis. At what point does it not matter or become detrimental to the handling of the car. Obviously by adding braces here and there, cages, seam welded bodies the vehicle becomes heavier. In which case our objective(at least for us) is to be as quick as possible around a race track. Weight will slow us down.
06-08-2010, 01:15 AM
#36
Rennlist Member
sorry Jim, i made a mistake in my first post, it was meant to say 5mm. thanks for correcting me on that one.
All this talk about strut braces has me asking one question, is their such a thing as too stiff a chassis. At what point does it not matter or become detrimental to the handling of the car. Obviously by adding braces here and there, cages, seam welded bodies the vehicle becomes heavier. In which case our objective(at least for us) is to be as quick as possible around a race track. Weight will slow us down.
All this talk about strut braces has me asking one question, is their such a thing as too stiff a chassis. At what point does it not matter or become detrimental to the handling of the car. Obviously by adding braces here and there, cages, seam welded bodies the vehicle becomes heavier. In which case our objective(at least for us) is to be as quick as possible around a race track. Weight will slow us down.
Thats the big question, right? My initial thought is that ideally you want the tub infinitely stiff, which allows all designed springing and dampening to be limited to the bolt on suspension parts. If you have a lot of flex in the tub, it will act somewhat as part of the suspension, so it will have a spring rate and a dampening rate, but its an unknown and maybe unpredictable. So its hard to setup and dial in a car that has significant body flex because of the unknown variables.
Infinitely stiff is impossible in reality. So how stiff is too stiff, just right, or not stiff enough? Is it ok if the shock towers move 1/2" when loaded in a corner - probably not. What about 1/8" - maybe. What about 1/64th - probably pretty good, but too good?
Would be interesting to hear from a real race team chassis designer on something like this. Do they attempt to design a tub to be as rigid as possible in all areas, or do they intentionally design some flex into the body. The full factory race cars sure have an awful lot of cage tubing in them, and will tie in to the shock towers when allowed. Looking at the factory 968TRS roll cages gives a good idea of what the factory thought was worthwhile to stiffen up on the 944 tub.
06-08-2010, 01:24 AM
#37
Rennlist Member
Good info Jim. What about the concept that strut bars are possibly useless if there is no triangulation? If view from the front of the car and the struts move sideways under load, that the whole assembly of two uprights with a horizontal bar across the top will just shift into a rhombus type shape. I know that some 911 guys believe that in regards to their front strut bars and hence they triangulate. With us, it's much more difficult of course with that motor thing in the way...
I agree that there is some probability that the shock towers can move together if tied in by a bar along the top. But instead of a single shock tower moving under load, now two have to move together. So in a very simplified model (too simple), the distortion would be half as much given the same load.
I would also say that any of the bars that have fixed ends, instead of a pivot or simple supported end connection, would be more rigid and would resist the rectangle from distorting into a parallelogram (moreso than a bar that has a single bolt, heim joint, pivot joint connection).
