The Ultimate Performance Mazda RX7 JRi coilovers are motorsport monotube dampers that are race-proven, nitrogen-charged, and double-adjustable.
The JRi valve is Jeff Ryan’s latest shim over piston and bleed design, which is an evolution of the world-renowned Penske valve. UP custom valves the JRi shocks specifically for the RX-7, with their years of supporting RX-7s in the Optima Ultimate Street Car Challenge series, road racing, and autocross.
For our street/track usage on a set of non-staggered (‘square’) tires, Ultimate Performance recommended 700/500lb spring rates (12.5kg / 9kg).
The separate compression and rebound adjustment knobs are stacked on top of the damper for easy access and adjustability from under the hood (for the front shocks) and from opening the rear hatch (for the rear shocks).
The top adjustment knob is for Rebound, while Compression is adjusted by the doweled sleeve under the knob, and requires the use of a pick or tool. Compression is adjusted the same as rebound (clockwise = stiffer, counter-clockwise = softer).
The top hats are in the shape of a rotary, which is kind of cool.
The top spring sits on a spring mount that pivots on the upper bearing. This removes the bending moment that acts on a spring in a more typical (and cheaper) design where the spring sits on the top hat itself.
17 comments
How come nobody makes sealed roller thrust bearings for automotive coilover applications? There are sealed options for mountain bikes… sure the rubber cover here helps, and its prolly fine for race use where you replace them every race weekend. But for a street car dirt and sand and road grime will get in there…
I’m sorry, but the how to adjust height on the Ohlins style coilovers section is wrong. the whole just enough preload to seat the spring thing leaves you with a tiny amount of droop travel. I mean if you have really soft springs I guess that would work. But the kinda spring rates a car that sees track days you really need helper springs. And use the damper length adjustment the same way you’d pick shock length for a non-adjustable style damper (like the JRi here). You set it one time at the correct length and leave it there, and use the other perches to adjust height (like you would on the JRi here)
Race cars go years without replacing roller thrust bearings in spring perches. If dirt and road grime got past the rubber cover and clogged up the bearing, it would still have less friction than no bearing at all.
If you set the spring collar with excessive droop travel to allow the main spring to rattle around under full droop, it can cause damage to the damper body and threads as well as potentially not ‘seat’ on the collar in a full droop condition. Helper springs allow for more droop than the length of the uncompressed spring, which is not how the Ohlins are configured. The recommendation was to maximize droop travel in the Ohlins when many people frequently add a bunch of preload to further reduce or completely eliminate droop travel, which is bad in most cases.
my concern for a clogged up roller bearing in a street car application would be noise. that being said, I’ve never run them. Do they get noisy when all dirty and clogged up?
Thats why I suggested to add helper springs. I added helper springs to the Ohlins I had on the rear of my NC (cheaped out on the front). And yes I agree eliminating all droop travel is a bad thing, I disagree with how you explained to get there. In my experience what you describe (preload just enough to seat the spring and then adjust the height with the damper length) is exactly how you end up with no droop travel. Unless you run soft springs… Even if you don’t run helper springs, doing the math or trial and error to find a happy medium between compression and droop is a much better choice than just make the spring snug and hope it all works out.
and just to avoid confusion, I’m a different person than the Bob below complaining about the aluminum shock mount.
Anyone who has ever adjusted the ride height of an older or dirty coilover is familiar with the loud creaking/groaning/chattering as you rotate the perch against the spring. Since you never hear this during normal usage while in the car (well, sometimes you can hear it on a front strut as you turn the wheel lock to lock and are standing next to the tire), you won’t hear any more noise from a dirty roller bearing. Helper springs serve a completely different function than roller bearings.
If you set the spring perch to the base of the spring with zero preload (or maybe ~5lbs) as recommended, the droop travel will be determined by your spring rates. The only way you would end up with zero droop travel is if you run extremely high spring rates where your wheel rates = your corner weights. The problem is the vast majority of people who run coilovers with a separate upper and lower ride height perches are they crank way too much preload into the spring with the upper perch and reduce or eliminate their droop travel. The problem with lowering the spring perch and allowing the spring to rattle around under full droop (without a helper spring) is that it can cause damage and get jammed at an angle when compressing after a full droop moment. Short of adding aftermarket helper springs, my recommendation is the best option of the two and is a common practice since you’ll never see a coilover like Ohlins delivered or recommended to run with unseated springs under full droop.
That’s a good point. I’m planning on going to stiffer springs soon, I’ll add the bearings at the same time. Any idea where one might buy that rubber cover? Think UPSS would sell that separately? I tried googling for something like that and wasn’t able to find anything. Does it matter if I put it at the top or bottom? Ideally I’d like it at the top further away from dirt, would that impact functionality in anyway that I can’t think of at the moment?
The helper spring comments were only in relation to droop, not anything to do with the bearing.
But yes, agree that having the spring just snug is best case scenario for that type of coilover without a helper spring, just in most cases it’s still very little droop… unless the springs are really soft. And yes, definitely don’t run it where the springs can become unseated.
Honestly, that’s pretty thin aluminum on that front shock mount. Remember aluminum does not have an infinite fatigue life. It will eventually fail. I would check it for cracks every year.
And it’s billet and not forged.
It saved like what, a few grams?
Bad design decision.
Sorry, it’s the rear, so I guess it makes it even worse?
I would rather have a steel tubed damper.
Yes the ‘fork’ lower damper mount you are referring to is for the rear damper. It’s a more than adequate design that is consistent with, if not more robust than most aluminum damper bodies on professional race cars, street cars, and even entry-level coilovers. If steel bodied dampers give you peace of mind, then make your purchases accordingly (which will greatly limit your options).
There are many high end dampers that use aluminum in this location. Aluminum has advantages, lighter weight and better thermal conductivity. Not a problem, especially in an RX7 where the damper isn’t subjected to side loads.
No material has an infinite fatigue life, but a properly engineered component will be designed to outlast its intended use. The billet aluminum lower damper mount is well-designed and more than adequate for the loads and longevity of a damper.
“For a shock the design limit of the lower mount is not damping – it’s the load seen when the shock limits the extension of the suspension. ( Unless of course you have a provision such as axle straps to limit the travel which is separate from the shock ). As Greg mentioned, this is a rare “overload” type event and hence is usually specified as a one time load rather than a fatigue validation. Load range 20-30kN is typical.”
Car weight is approx. 1300 kg
Dampers can see loads of 100g
So, 1300/4 = 325 kg
F = ma
F = 32500 N
Ballpark part strength (1/4″ PLATE 6061-T651 ASTM B209 · Tensile Strength = 45,000 PSI · Yield Strength = 40,000 PSI min)
Cross sectional area = 5 mm x (2x10mm) = 1e-4 m^2
Max load = 2.758e+8 N/m^2 x 1e-4 m^2
Max load = 27580 Newtons
So, the part has a safety factor of 27580/32500 = 0.85
Provide some numbers on cross sectional area and I can update this, but otherwise, this part is not strong enough as designed. If you can do a better analysis, I would love to read it.
Cheers!
The unsprung weight of a corner of the car is nowhere near 325 kg. The spring does not have enough energy to generate 100 G of rebound acceleration to that unsprung weight. Therefore, you are greatly and erroneously overstating the tensile loads on the damper forks, which are indeed designed sufficiently strong.
Most any damper internals would fail at forces far lower than the tensile limit of the aluminum fork arms (which are 7075, not 6061).
Just incase anyone was wondering, here is the full, 15 year old, original conversation/quote from above…including the arguably important parts that were omitted.
https://www.eng-tips.com/threads/load-on-lower-shock-mount.274851/
Modern search engines are amazing…
I would smoke that with FEA to prove it’s strong enough but I am busy on similar things that make me money. It is strong enough belive me.
“… the load seen when the shock limits the extension of the suspension…”
…
I beg you to sit and think for a minute about where the energy to extend the suspension is coming from and what combination of mechanisms and real world situations are going to limit how fast the suspension will extend. Or, as has been pointed out, a halfway realistic estimate of unsprung weight.
Data logging shows it is less than 20 g’s
Hey guys, do the rear JRi coil over top hats have a small circular relief machined in on the top-side?? The reason I ask is the rear shock tower mount in the FD has a small protrusion that may prevent the top hats from mounting totally flat with the shock tower mount if this is not done.