Shock refresh

[Pete_vB]

My daily driver 1M has just ticked over 50k miles (I know). I've been noticing increased harshness and decreased poise over bumps, and I strongly suspect my shocks are going- not exactly unexpected given the age. Thus it seems time for a refresh, and I'm hoping to gather wisdom here. I understand and value high quality shocks- I run Ohlins and 2x JRZs on my other cars. This is my street car, however, so my priorities are:

• Low maintenance- ~50k mile rebuild frequency.
• Roughly stock ride height is required- significant lowering is not an option.
• Stock or near stock springs rates are good- I'm not trying to stiffen the car up.
• No adjustment is prefered as long as the valving is correct. I autocross the car and if the valving is off I will pull what's left of my hair out.

With this in mind I'm looking into options, which seem to include:

• OEM replacements (I don't think OEM is rebuildable?).
• Bilstein HD or Sport (or mix and match). I know bilstein quality and valving is good, my main concern is that they are valved for the M3 rather than the 1M- probably not a good thing.
• Ohlins Road and Track- adjustments, valved for stiffer springs, and 20mm lower than stock all count against these. The step up in quality from the bilsteins is a plus.
• KW V1 skips the adjustments but is again valved for the M3, stiffer springs and lower ride height.

Am I missing anything? My ideal doesn't seem to exist- Bilsteins, KW or Ohlins, custom valved perhaps slightly stiffer than stock to work with stock or near stock springs on the 1M. Anyone heard of such a thing, or know of something that could be modified to be a suitable substitute?

Gathering knowledge here before I dig in...

[One///Em]

Unless changing springs too, probably best to stick with OEM. OEM shocks are great IMO

[TXmtrhed]

JRZ RS-1's valving is very good, adjustable (single) and can be used with stock springs. A few 1Addicts including Advevo have used a similar setup. I'm only using a 15mm drop with Swift springs but I could easily put it to stock height. I think the ride quality is exceptional at street settings. Not sure about the lifespan of these shocks though.

[HP Autosport]

Most aftermarkets are far superior than OE.

OE dampers have too much compression damping and not enough rebound damping, thus the harsh ride over bumps and not enough control.

[Pete_vB]

Originally Posted by HP Autosport

Most aftermarkets are far superior than OE.

OE dampers have too much compression damping and not enough rebound damping, thus the harsh ride over bumps and not enough control.

Why do you feel the factory chose the strategy of high compression/ low rebound damping?

[scotth944]

Originally Posted by HP Autosport

Most aftermarkets are far superior than OE.

OE dampers have too much compression damping and not enough rebound damping, thus the harsh ride over bumps and not enough control.

I would have thought it was the other way around with OEM setups for daily driver issues with speed bumps and pot holes??

[One///Em]

Originally Posted by scotth944

I would have thought it was the other way around with OEM setups for daily driver issues with speed bumps and pot holes??

+1

[Pete_vB]

That's usually correct- generally race cars move towards a greater compression to rebound ratio when ride comfort is a lower priority. Eyeballing it the compression damping on the 1M doesn't look terrible high, assuming these graphs originally posted by eeghie are correct. Note they are upside down compared to what you'd expect, looks like about a 3:1 ratio front and rear at the knee.

[lcrain]

My butt tells me the stock shocks were not developed with daily driving on crap streets in mind. I am no expert, but the 1m seems to handle low speed bumps and undulations poorly. My pothole dodgin skills are in expert mode with the 1m.

Fwiw I really like the user reviews of the ohlins r/t. Users describe the ohlins "soaking" up bumps, IMO the stock 1m shocks do the opposite of that and there is room for improvement for a car that sees mixed driving with an emphasis on street. I am in no hurry to upgrade as I don't really care about the ride and find the stock suspension fine for my skill level at the track. When(if) I upgrade it will likely be the ohlins. I, like you, don't think I will benefit from too much adjustability, so the single adjustable category is very appealing to me (ohlins r/t, jrz rs1 and the MCS singles). ~$3000 is nothing to sneeze at though.

Pete, you are such a great resource for us. I look forward to following this thread and seeing which route you go.

[HP Autosport]

Originally Posted by Pete_vB

Why do you feel the factory chose the strategy of high compression/ low rebound damping?

That may be a question for the BMW 1M chassis engineers, but my guess is that they developed the 1M dampers on very smooth roads. Our roads here in the US is not nearly as good as it is in Germany.

[eeghie]

Originally Posted by Pete_vB

Why do you feel the factory chose the strategy of high compression/ low rebound damping?

The reply on the specific height of the rebound curve was that for the 1M it was needed to stabilize movements of the body and wheels after a bump. The curves as they are, were specifically engineered for the 1M and my speculation is that they were tuned spending a dis proportioned (many would say the right) amount of time on a relatively smooth track.

Would love for this thread to analyze different damper behaviors vs what we see in the curves, but in my experience, as confident and gracious as ///M was to provide the OEM curves, no competitive damper supplier approached since was willing to.

[Pete_vB]

So I'm beginning to dig in here, I'll post what I'm finding as I go along. If someone spots an error please jump in and let me know.

It's interesting to see how BMW altered our cars vs the M3.

This is based on googling so I'm not sure of the source, but I'm seeing M3 spring rates quoted around 167 F and 550 R- they are progressive like most modern setups, so in reality this would be an average. Motion ratios are quoted at .96 and .57, so wheel rates would work out to 154 F / 177 R. It's a little unusual for the rear to be higher than the front.

The 1M, on the other hand, was quoted at 230 F / 550 R, wheel rates of 212 F and 177 R. So it appears BMW stiffened the front spring rate up significantly for the 1M. I think they left the swaybars alone? So that would result in more mid corner understeer, but ability to put a little more power down out of the corners.

On the shocks, it looks like they went the opposite direction. The front shocks look like they are similar to the M3s despite the stiffer springs, while the rear shocks have been stiffened up to be on the stiff side. Compression to rebound ratio looks very similar to the M3.

If we assume the above is true and take the changes as a package, we might hypothesize that BMW was trying to add stability- the higher front spring rates would promote understeer and hence stability mid corner. On corner entry, however, that would result in poor turn-in, so higher rear bump and rebound forces transfer weight faster at the back, counteracting this and promoting quick turn-in. The increased rear bump might also help put a little power down on corner exit, a good thing given the 1M's torque.

I wonder, however, how this strategy, which depends on the rear running more damped than the front, would work over bumps?

It's a work in progress, but interesting. I don't have much of the data I'd need to do a proper analysis- I'm leaving bump stops out, assuming linear springs, guessing at swaybars, toe curves, roll center heights, etc. I still hope some trends pop out, we'll see.

[scotth944]

"so higher rear bump and rebound forces transfer weight faster at the back, counteracting this and promoting quick turn-in"

Pete, are you saying that this increases front end traction or is it due to the rear end losing traction faster than the front and thus, resulting in a turn-in (trail braking effect)??

[TXmtrhed]

The swaybars for the M3 and 1M are the same.

[Pete_vB]

Originally Posted by scotth944

"so higher rear bump and rebound forces transfer weight faster at the back, counteracting this and promoting quick turn-in"

Pete, are you saying that this increases front end traction or is it due to the rear end losing traction faster than the front and thus, resulting in a turn-in (trail braking effect)??

Both, effectively.

A car is fastest when it's neutral, meaning the front and rear wheels are sharing the load. If the front wheels take too much load they lose traction first- we feel this as understeer, and the rate we can turn the car becomes limited by the front end.

By adding ~35% more spring rate in the front vs the M3 BMW made the front take more of the load as the car rolls in a turn, which we would expect to see as corner entry understeer. However stiffer low speed damping at the rear works a bit like a spring to increase the load the rear takes as well: consider an infinitely stiff shock at the rear would have the same effect as an infinitely stiff spring.

So the stiffer shock takes load off of the outside front tire and moves it to the outside rear. This both increases the amount grip the front tire has, and decreases grip at the back. If done correctly, though, the net effect is that you're neutral and can enter a corner faster.

Now we get to mid-corner: If it's smooth shocks no longer come into play, so we have just the springs, and more front spring rate will add understeer.

Finally corner exit, and possibly part of the reason BMW chose somewhat high compression forces: At mid corner the outside rear tire is already compressed, so as you unwind the steering and add power it's really the inside rear that moves- in compression. By increasing compression damping you can get the inside rear to take some of the load off of the outside rear, hence balancing the load to get more power down. However they actually increased rear rebound much more than compression (essentially doubling it at the knee vs the M3) suggesting they were much more concerned with the corner entry behaviour above.

This combination may explain the 1M the handling characteristics we know and love (or not). Get aggressive with the throttle and you'll pop the the tail out, but once the car has taken a set it's understeery on the springs alone, making it easier to catch the tail. The shock tuning promotes sharp turn-in. However mid corner bumps bring the shocks into play, and since the rear shocks are relatively stiffer than the front this can provoke mid-corner oversteer. At least that's my current read.

[scotth944]

Thanks Pete,
This would seem to fit some of the corning situations I have seen where a nice flat turn keeps the car firmly planted through all 3 phases but in the one's with elevation/camber changes after turn-in, the front does not have an issue but the back end gives up relatively easy even though I was not giving it very much "gas". I find this makes the car feel unpredictable since I'm not sensing any feedback with the steering as traction becomes marginal in this type of condition.

I myself find a predictable car will turn quicker lap times than a "fast car" but that is probably due to my balls of steal starting to get tarnished.

[M3 Adjuster]

nice summary thus far... ... just trying to follow along without being dragged!

[Pete_vB]

Originally Posted by scotth944

This would seem to fit some of the corning situations I have seen where a nice flat turn keeps the car firmly planted through all 3 phases but in the one's with elevation/camber changes after turn-in, the front does not have an issue but the back end gives up relatively easy even though I was not giving it very much "gas". I find this makes the car feel unpredictable since I'm not sensing any feedback with the steering as traction becomes marginal in this type of condition.

I myself find a predictable car will turn quicker lap times than a "fast car" but that is probably due to my balls of steal starting to get tarnished.

This would seem somewhat in line with others results. The 1M was very quick on the smooth Hockenheim ring, for example, but relatively slower at the Nurburgring, which is bumpier and puts a premium on high speed stability. Sport Auto commented that it was actually "too stiff" for the 'Ring (on the stock tires), but fun for the most advanced drivers.

Looking at the damping curves it seems probable that a number of adjustable shocks designed for the M3 could work well if preset correctly. In fact the 1M's damping looks very similar to the M3 DCT EDC (electronic damper control) set to medium (front) and hard (rear). This makes we wonder if for example the Bilstein HD and Sport high pressure monotubes designed for the M3 could be set to work well with the 1M.

Scott, it might be interesting to try increasing front shock damping to try and gain a little confidence/ stability, and there may be an inexpensive way to test this using some front M3 struts. I know MDORPHN recently swapped his front JRZs and had positive results, perhaps he can comment on what he's done with damping and what the effect was?

As a point of comparison the Ohlins R&T system goes significantly stiffer still, increasing front rate ~50% and the rear ~25%. It seems likely you'd want either very sticky tires or smoother surfaces to make those work well with the springs that come with the package, though it'd be interesting to see how they set the damping.

[timbo_3101]

I never really thought about this, since it was (and still is) too technical for me to understand.

However, I had a recent event on circuit where my results were disappointing.

In fact, there were considerably poorer than my previous attendance in 2012 when I was entirely stock. It was also considerably poorer than my fellow (stock) 1M racer. At present my vehicle is at 13000km (8000miles), running a firm KW Clubsport setup and competition tyres.

This circuit has been poorly maintained over the years and has a bumpy surface (unlike the better known circuits in my region), and I was subsequently advised by one of the M3 racers to soften my suspension setup. When reviewing notes from 2012, I did not have such issues with traction, etc

[Pete_vB]

Originally Posted by timbo_3101

I never really thought about this, since it was (and still is) too technical for me to understand.

However, I had a recent event on circuit where my results were disappointing.

In fact, there were considerably poorer than my previous attendance in 2012 when I was entirely stock. It was also considerably poorer than my fellow (stock) 1M racer. At present my vehicle is at 13000km (8000miles), running a firm KW Clubsport setup and competition tyres.

This circuit has been poorly maintained over the years and has a bumpy surface (unlike the better known circuits in my region), and I was subsequently advised by one of the M3 racers to soften my suspension setup. When reviewing notes from 2012, I did not have such issues with traction, etc

It's certainly fairly easy to set up a car too stiff, and the more bumps the softer you'd want to go. Nissan softened their lap record Nismo GT-R when setting it up for the Nurburgring: shocks, springs and swaybars. A car also tends to get more difficult to drive as it gets stiffer, requiring more and faster driver inputs. If you're having traction issues it sounds likely you do need to soften it up for that track...

[scotth944]

"it might be interesting to try increasing front shock damping to try and gain a little confidence/ stability, and there may be an inexpensive way to test this using some front M3 struts."

Pete, are you suggesting going towards increasing the front dampening instead of decreasing the front spring rate because of high speed or just to get power down at turnout faster (if I am understanding the dynamics correctly)? I was wondering if less front spring with more rear bar wouldn't make for a more stable setup as long as I'm not overly aggressive with the gas on turnouts?

[Em/1]

Originally Posted by Pete_vB

That's usually correct- generally race cars move towards a greater compression to rebound ratio when ride comfort is a lower priority. Eyeballing it the compression damping on the 1M doesn't look terrible high, assuming these graphs originally posted by eeghie are correct. Note they are upside down compared to what you'd expect, looks like about a 3:1 ratio front and rear at the knee.

Pardon my ignorance, but pronouns are leaving me confused. What is upside down? Are graphs reversed re rebound and compression; my read says compression:rebound is 1:3 instead of 3:1...