I'm working on a design for custom upper shock mounts for my Solstice - these will be one-piece aluminum units with spherical bearings pressed into them for locating the Koni damper shaft. I also intend that the upper spring perch will move with the bearing to keep the springs square to the direction of shock travel (similar in design to these), so that means that the entirety of the compression force at each corner will be acting on the spherical bearing.
I'm looking at using either Aurora PNB-12T (5,750lbs static axial load rating) or PNB-10T (4,720lb static axial load rating) bearings. I'd prefer to go with the -10T bearings as they are slightly smaller and will be easier to incorporate into the design (meaning a little more ultimate shock travel), but I don't know how much that extra ~1k of axial load rating is critical. Assume about 750lbs per corner at rest. Since I'm not an engineer by trade I don't know what I don't know about this. Should I just use the -12T?
Thanks!
Chris
Is this application at the front or rear of the car? Does this shock mount support the car weight at that corner? Or, is it supporting the shock forces only?
boulder_dweeb wrote:
Is this application at the front or rear of the car? Does this shock mount support the car weight at that corner? Or, is it supporting the shock forces only?
Both front and rear. The upper mounts are identical at all four corners. The suspension is double a-arm all around, and the coilover supports the full weight of the corner.
Pic of coilover unit (using stock upper mount):
In place:
One figure I have seen is to take the maximum expected load and triple it.
A question: How much load will be on the spring when the strut is at max compression? This would be your theoretical maximum static load. Dynamic loads will be higher because the strut damping adds a lot more load than static would have you think (thankfully, not MUCH more because compression damping tends to be relatively light), plus a fudge factor... 5000lb sounds pretty good for a strut car.
IIRC, the SOP for spherical bearings mounted axially as a strut top were 7/8"/22mm ID units. Your situation will put greater stresses on the bearing because of the ratio. Does the number correlate to sixteenths of an inch? Even a "12" seems a bit on the small side, then.
On the other hand, your application is perfect for just using a standard rod end. You don't have to accomodate for rotation.
@Knurled - the -12T is a .75" bore unit with a ball diameter of 1.187":
The -10T has a bore of .625" and a ball diameter of .968":
A rod end would work if it weren't for the need to be able to access the rebound adjuster on the top of the damper shaft 
I could guess at the load on the spring at max compression but I'd almost certainly be wrong. I need to read up more on suspension dynamics...
Street, or track only? You'd want overkill for a street car to take the abuse of bottoming out hard on potholes and whatnot every not and then.
Kenny_McCormic wrote:
Street, or track only? You'd want overkill for a street car to take the abuse of bottoming out hard on potholes and whatnot every not and then.
Street use is only for back/forth from venues and periodic transit to places like the shop where I get the alignment and corner-weighting done. The more I do to it the less enticing it is as a street machine...
Knurled wrote:
A question: How much load will be on the spring when the strut is at max compression? This would be your theoretical maximum static load.
Statically, all of the load will travel through the spring. The shock has zero load until it moves. Unless its gas-charged or something, but it would still be insignificant.
Read through this thread when you have a chance. There is some good info that might apply to you.
Spherical bearing info
Some real-world experience: we use a bearing in a very similar upper mount. Stainless, PFTE lined, etc. The bearing is an FK SS9XT. We've put hundreds out there over the past 10 years or so, thus a pretty good sample and mileage size. Our customers take them on the track as well as drive cross-country.
We found very quickly that we needed a very tight tolerance on the bearing, otherwise it would develop play almost immediately. We need an "F1 fit". I doubt this has anything to do with the race series 
With that F1 spec, it's good for years. I don't know exactly how many miles, but we get very few requests for replacement bearings. I'd guess at least 30,000 miles if not more. The bearings are so tight when we get them that you cannot rotate them by hand.
Other than a small number that have loosened up over the past decade or so, we've never had a bearing failure. It only has to deal with the shock loads in our application, bottoming loads are supported by the bumpstop. So what you're basically doing is shaking it constantly, but never truly pounding it.
Also... http://grassrootsmotorsports.com/forum/grm/spherical-bearing-source/25849/page1/
I could guess at the load on the spring at max compression but I'd almost certainly be wrong. I need to read up more on suspension dynamics...
= static load + (spring rate * remaining compressive stroke), excluding any bump stop compression.
But I guess in this type of application the more damaging load is the dynamic load from the damper.
Damper loading in compression won't be too high: bottoming out, and topping it out (depending on damper design and whether it has an end of stroke cushion) will typically result in much higher forces. If it were me, for my car: I'd use the heavier bearing, and also consider incorporating large diameter washers above and below that provided a fail safe in the very unlikely event that the bearing failed.
Thanks for all the info everyone! This gives me some good leads. I've also found that Hoerr Racing sells metric spherical bearings from Fluro that may be a good choice. Lots to think about.
Chris
I have purchased the metric bearings from Hoerr Racing and they have held up well to road racing conditions. They also are my source for Aurora brand bearings.
