View Single Post
      06-30-2012, 08:15 PM   #1
Brigadier General
CJ421's Avatar

Drives: 2017 F30 340i
Join Date: Feb 2011
Location: Blue Bell PA

iTrader: (1)

Garage List
JRZ RS1 Damper My Thoughts

These are my *initial* thoughts on the JRZ RS1 damper kit. I ordered the following through and had it installed at VAC Motorsports.
  • JRZ RS1 dampers (non-height adjustable; M3 style rear)
  • M3 rear lower camber links
  • AC Schnitzer M3 sport spring kit
  • Ground Control Street camber plates (M3 version)
AC Schnitzer unfortunately doesn’t publish their spring rates but this combo is recommended by JRZ and VAC. VAC performed an advanced alignment on my car as well which is more than just “within specs”. I ended up with -1.9* rear and -1.6* front camber and zero toe in the front. The car is NOT lower than stock. The rear is actually a bit higher (about two fingers' worth now) and the front ever so slightly lower, perhaps 1.5-1.75 fingers total. It looks more aggressive though due to more front camber and more of a rake towards the front like the M3. I like the stance a lot.

These items were added to my existing setup:
  • Quaife LSD
  • OEM M3 components:
  • --Front control arms
  • --Front tension struts
  • --Rear guide rods
  • --Rear wishbones
  • --Rear subframe bushings x4;
  • --Strut tower brace;
  • --Front and rear sway bars;
  • Rogue Engineering adjustable toe arms;
  • Powergrid adjustable sway bar end-links;
The only differences I’m seeing now are a direct result of the items in the JRZ setup.

Why upgrade springs and dampers? The suspension’s purpose is to keep the tires in proper contact with the road and therefore maximize their grip; the goal of suspension modification is to make the car better at doing that (at least for those of us who value function over form). The springs and dampers are the primary agents responsible for maintaining this contact.
The 335i needed more damping force altogether to keep the car settled and quicker to react plus stiffer springs. I found a monotube damper design with high gas pressure would provide faster reaction times than a twin-tube. VAC was more than helpful during the selection process and was ultimately responsible for introducing me to JRZ. Unlike most ‘tuner’ shops, VAC is both a race shop and a machine shop and has an international reputation in high-performance motorsports. The advice I got from them wasn’t marketing fluff or “here’s what the guy with the race exhaust down the street uses”, but drawn from their motorsports experience. I was never shown a product brochure. VAC Motorsports is professional through and through and use JRZ in their race cars.

The JRZ RS1 Damper

The RS1 is a monotube damper with a large piston rod and 24 clicks of adjustment (one knob controls compression and rebound). It has adjustable gas pressure – a feature very few non-full race dampers have. The RS1 is a powerful damper; it can work with a huge range of spring rates, even very low rates such as stock springs if you’re in a class that requires such. Cheaper dampers are only designed to work with a narrow range of spring rates. Finally the RS1 can be fully rebuilt and re-valved if necessary. It is a damper worth rebuilding.

JRZ dampers are well known in European racing circuits. As a matter of fact the RS1 internals are no different than their full racing dampers and are built on the same assembly line. JRZ builds its dampers in the Netherlands.

The Driving Experience

These are my initial impressions ONLY. I had four 25 minute sessions at NJMP Lightning Raceway on a 100*F+ day; my tires overheated about halfway through each session. I was not able to explore the JRZ setup as much as I wanted. These impressions are an exclusive comparison to the stock springs and dampers. The JRZ dampers’ adjustment knob was set to halfway at all four corners.

There is no longer a lack of damping with the JRZs; my brief runs on the track shows they are capable of creating exponentially more force. Their react-and-settle time for transient maneuvers – hitting bumps, turning, acceleration and braking – is immediate. Quick corners slalom turns and lateral acceleration in general is beautifully controlled; the car is poised and ready as soon as the steering wheel is centered. The damping happens so quickly and uneventfully that I had a lot of “wait – we did turn 5 right? I don’t remember it” moments. Yes, the damping is that well executed. Not having to wait for the car to react is one less thing my brain has to process and compensate for.
The RS1’s superb reaction times are thanks to many things especially the large piston; it can displace a lot of fluid quickly and its design goes beyond just being a big piston; it has a special tapered shape and … well, I’m not a physics expert. However JRZ figured this out, it works well.

This setup loads up in corners with room to spare and holds the car there like it is on rails; it’s a feeling that must be experienced. The stock spring and damper combo by comparison keels over to full compression on one side and stays there; in other words, the damping force is exhausted quickly and the soft springs didn’t help matters. At no point did I approach full compression on the RS1; I always had room in turns. My tires simply lacked the grip to maximize this setup’s power especially given the blistering conditions.

I noticed a difference in the 335i’s tendency to ‘squat’; the front end tends to lift up like a speedboat under full acceleration with the stock springs and dampers – it wasn’t pleasant as I had to correct it via steering. It’s gone with the stiffer springs and RS1 combo; the car tracks 100 percent straight and feels rock solid.

Nose dive under heavy braking is also better controlled. There is much more resistance and less of a “tip forward” feeling when going from 135MPH on the front straight to 65. Letting off the brakes and going into a turn is more confidence inspiring as well since the JRZ dampers are so much more effective at controlling the forces acting on the car.

Ride and Road Feel
The ride is referring to the spring’s and damper’s control of the car over bumps. This is high-speed compression and rebound of the damper – transient maneuvers that cause the piston rod to move in excess of a certain velocity (for example, five inches per second). This is opposed to handling which is low speed compression and rebound – the damper’s piston rod doesn’t move as fast when compressing gradually for a turn as it does when hitting a sharp bump. The force created by the damper increases exponentially with the piston velocity and there lies the compromise; a stiff damper with a lot of compression force is great on a smooth track but is going to be unpleasantly rough on the street. Not so with the JRZ RS1.

The RS1’s ride is no harsher than stock. The damper curve (a graph of how a damper generates force relative to piston velocity) of the RS1 is such that despite their ability to produce far more force than the stock dampers, the compression and rebound movements have a natural feel. These forces are remarkably well controlled. JRZ’s philosophy is to make the fluid transfers inside the damper body as smooth as possible and those efforts are certainly appreciated here. I don’t have an RS1 dyno but I imagine the damper curve is super smooth. A not-so-good damper by contrast will have a rougher graph – inconsistency, in other words.

Continuing, the ride is also more compliant thanks to almost infinitely better reaction times. Thinking of the road surface as a book, this setup reads it word for word including the punctuation marks without adding opinions or paraphrasing. Just the facts, ma’am. JRZ from experience concentrates R&D on the small compression movements – these comprise the majority of damper travel movements. Going over small bumps, cracks in the road, tar strips, and even highway rumble strips is effortless; bumps will happen and they’re over just as fast. The chassis feels “alive” and in sync with the road surface. This was a strange sensation at first. Previously I was only getting communication through the steering wheel and “oh that must have been a bump” from the chassis. It’s reassuring to know what’s going on under your car as it happens.


I’m pleased with what the JRZ dampers and AC Schnitzer sport springs have done for my 335i. Had I known the difference they would make I’d have done them initially instead of other items (control arms and so on). Good dampers and springs made 80%+ of the overall difference versus stock.
I have some Michelin PSS on order which should let me explore the setup a bit further. I'll probably end up posting a new thread later on with updated thoughts/impressions.

2017 BMW 340i (F30) - M Sport, Mineral Gray/Coral Red, 6MT; Dinan exhaust
Past: 2011 335i (E92) - M Sport, Le Mans Blue/Black, 6MT

Last edited by CJ421; 06-30-2012 at 10:23 PM.