Since no one wants to own up on a price. I was thinking probably a 100 a piece. These are more difficult to design, more expensive to manufacture, and use more proprietary parts the FM's unit. Probably the best I'm going to do. So who would buy a set of these for 200?

 

I don't see how you can have both. The fixed mount is what allows for the increased travel of the long shock. That's really an ***-backwards approach - you're supposed to use a shock length to fit your suspension. I'm actually running the ISC pieces on the rear because they work and they're cheap. I'd choose the bushing over the bearing for a street car any day in this circumstance.

My guess is IF somebody saw the need for these proper mounts/perches, they'd also want to build a shock to suit their needs. It's really a difference between perfect and close enough.

 

That is always the question, is close close enough? Personally, from a mechanical engineering standpoint. Not close enough increases your spring constant at the points around maximum shock travel, and very little around usual travel. Further this is just spring constant. I couldn't imagine it being anymore then 50 lb/in variance. That is a long torque arm. I might be able to make a cheaper FM version, but isn't that what ISC is?

 

Yes- ISC has filled that void. IMO this design would be on the other extreme.

My intent was to throw out a product idea, not request a product. I thought this seemed more feasible, marketable and attainable for more owners. But I'm not an engineer.

When we were doing a suspension for the race car, the engineer flat out said that what he did was the correct way to do the coil over, anything else was less than correct and anything less than correct was a waste of time. Those might not have been the exact words, but that's a good summary and delivers the point.

 

and i guess that's where keith at FM was going when he worked out the optimum shock length for a miata. you dont need adjustable length shocks, you just need enough droop travel that you dont lift a wheel but not so much that you hurt driveline angles or bind and you need to set bump travel so that you almost but dont quite rub the wheel in the fender well with the bumpstop removed. if that length allows enough room for the suspension setup with the floating perch, the work is done.

however....

even though rob's suspension guru says it's not worth it to do it any other way, how much does the spring REALLY bend? and what load does that put on the components? and how do those loads affect handling?

 

I'd be all for a set that has the normal spring setup, just taller for more travel. I don't plan on going out and winning Le Mans, I just want something I can use with a basic shock (Illumina's for example) to improve on track ability for a better price (the bearings are nice too).

 

100 a piece? never mind

 

I think his point behind what he built was that going with a known proper application means you don't have to go to all the trouble of figuring out all the "what ifs". It's a very similar scenario to building a miata turbo setup.

 

if we give two identical cars (EXCEPT for these perches) to the stig and have him do a double blind set of laps in each, would the lap times be different?

 

It is the proper way to do coilovers, as long as a doesn't compromise travel. One other thing to look at would be the springs twist as it is compressed.

 

in theory yes - I believe the approach in racing is to control the things you can to reduce lap times so you can compensate for the driver's mistakes.

 

I would HIGHLY recommend you grab the ISC mounts.

I had them on agx's and cheap sleeve coilovers and the entire package was very competitive, especially for the price.

For anything other than a hardcore track car I would say they are your best bet for price/performance.

 

I never discourage product suggestion thats for sure. I wasn't being condesending either I just wanted to make sure I was understanding everything correctly. We had alot of information flowing in, and I had to put in words what I was thinking so I could be corrected if I was wrong.

 

Clean sheet of paper, there is no reason not to do floating perches. There is a significant bending moment on the springs that has an effect on wheel rate and damper stiction. As you mentioned, if the damper is designed from the outset to give enough stroke with the floating perch, you have the best of both worlds. That's how I configured the double adjustables I'm developing.

I'm not good enough with the math but there is some data floating on the interweb and on Hyperco's site re: bending loads, before and after results with floating & fixed perches.

 

A dynamic lb/in spring factor yes, some trivial dynamic factor added. Damper static friction force... It adds side load to dampener, increasing the normal force, increasing the friction force and induces dampening characteristics based on theta of axis which is not intended? I could see that. The side load would be tremendous while the vertical load would not. I would bet the shocks life is significantly compromised without a full floating end.

 

Separate from the side loads that are geometry induced, a flat wound coil spring twists and generates side load when compressed. Additional reasons to isolate those spring forces from the damper shaft with floating perches. That's where hydraulic perches come in and where I stopped. The hydraulic perches take up too much room, require maintenenace and aren't cheap.

The Miata geometry isn't too bad, not as bad as some. What steered me towards floating perches was uncovering how much side load the spring itself generates. Combine that with the geometry and there was enough load to raise a flag. I go through so much effort with urethane bushings, spherical bearing shock mounts and all to reduce friction, and the fixed spring mounts are still introducing friction right at the damper shaft. Argh

Hyperco's OBD ( Optimum Barrel Diameter) springs are designed to reduce the side loads while reducing overal spring mass. Our damper is designed around the Hyperco springs.

The OEM replacement floating perches M2 showed are a great idea but I don't think too many will be able to make use of them without custom damper bodies. Typical OEM replacement steel bodies like Koni, Bilstein and Tokico are far too long. Koni Race's would have to be built with custom long shafts and I don't know if the valve body is short enough to actualy increase stroke and they're already only 72mm in rear.

Maybe the guys with 28/30 series Koni's, Penske's et.al would use them but that's a really small market.

 

Sorry for the necro-post,

Could you not use a torrington (aka needle) bearing to allow the springs to spin? capturing it may be a little tricky though.

 

We could chrome treat the springs and mesmerize the competition.

It is a good point, I'd be worried there there would be complications with doing this. I don't know what effect building up angular momentum in your spring has.