**TC Kline Racing - Performance Suspension 101 (PS101)

[TC Kline Racing]

We recently ran an advertisement with our 'philosophy' on 'tuning' the suspension for a BMW/Mini/Porsche

In case you missed it, we wanted to share it with you (it is also attached for downloading):




Performance Suspension 101

Through our 26 years of racing BMW’s, and acquiring 11 National Championships along the way, we have learned a lot about suspension and how to maximize performance from it. Because there is a tremendous amount of misinformation out there, we are offering this document to help you make a more informed decision on what performance suspension to put on your car. Here are some facts to consider:

#1 - The overriding purpose of a performance suspension is to maximize the tire contact with the pavement. A tire has a set of parameters which need to be satisfied in order to perform at its maximum. These include; pressure, camber angle, operating temperature, spring rate, damper characteristics and load capacity. Some of these factors can be dealt with through intelligent choices of tire brand, size and compound. However, the things which are much harder to control are the suspension design and the ability of the dampers to keep the tire in contact the pavement the maximum amount of time. BMW has an excellent suspension design on their cars, so the parts we can look to improve are the damper and spring package, suspension bushings, and alignment settings, all engineered to optimize performance.

#2 – The suspension and sub-frame bushings are part of, and play an important role in the performance of a suspension. OE suspensions are designed to work in concert with the bushings on the car. Raising the spring/shock rate too much will reduce handling and feel, unless the bushings are upgraded as well. There are several levels of bushing flexibility available depending on the objective. Harder rubber bushings like BMW M brand, are best for street where ride quality is important. Urethane and delrin bushings are desired for very aggressive street, or in racing where spherical ball joint bushings are not legal. Ball joint bushings offer the most control, but can be harsh riding and will make noise as they wear.

#3 – A tire likes to have load applied to it in a progressive manner – load the tire too quickly, and it will just give up, (slide). Too much spring and/or too high a shock rate will materially reduce the performance. So will a shock that ramps up the damping too quickly. High spring rates can improve the lap time on fresh tires, but as the session/race progresses, too stiff a spring will prematurely wear out the tire from too high peak loads. If you are finding the handling deteriorates quickly, try a lower spring rate to see how it improves tire grip later in a session. We see this even in F1. The teams which have figured out to get the tires to work longer usually win. There is a constant battle between chassis stiffness and tire traction at every level of motorsport. Finding the balance is the key to success.

#4 – The higher the traction potential of a tire, the more spring and damper load it can take. R-compound tires can take on a firmer suspension than street tires, and race tires can take on a firmer suspension than R compound tires. However, as stated above, if you have too firm a suspension on your car, it will actually reduce the performance potential, because the tire can’t deal with the loads and just gives up.

#5 – Damper construction: Whether twin tube or mono-tube, high pressure gas, low pressure gas or no gas at all, single adjustable or multi-adjustable, with remote reservoir or not – Valve technology, durability and low flex of the parts are what matter. For example, the dampers which come on BMW’s are twin tube, and have excellent durability characteristics. “Twin tube shocks” are a design in which a second tube inside the main housing contains the valves which control the damping. “Monotube shocks” have the valves contact directly to the inside wall of the damper housing. There is a constant debate as to which is better, and in reality both are capable of excellent results, so the proper choice is the ones which accomplish the desired goals in the most durable way.

Common Misconceptions:

#1 – More damping and higher springs rates offer more performance:

#2 –If it costs more, then it must be better: Not necessarily so. Although it is true it costs more to build a sophisticated suspension, there is no guarantee it will offer the optimum performance for the car you are driving.

#4 – High pressure gas is better than low pressure gas: Nitrogen is used in high pressure gas dampers to control foaming of the fluid. However, if you are using a shock fluid which doesn’t foam, then gas pressure is not required. Also, high gas pressure introduces the need to control the additional damper movement for the gas as it compresses, while a low pressure damper has all of its damping in the fluid. And last, high pressure dampers ride more firmly on low deflections like road seams because it take more force to displace them. The advantage of high pressure dampers is the gas pressure can be used to make small changes in effective spring rates, and they can be mounted upside down.

#5 – A lower ride height is better – Over lowering a suspension will take it beyond it optimum working range, and will actually reduce the traction, feel and performance. It is a common practice to increase spring rate in overly lowered suspensions as a ‘band aid’ way to increase performance and feel by limiting suspension movement. Once a suspension has dropped below its working range, the suspension ‘falls away’, which in reduces the effective spring rate. A suspension works its best when as it is loaded, the suspension arms go through the path where they are parallel to the ground.

#6 – Remote reservoir dampers are better than self contained units: The need for remote reservoirs comes from when then damper housing can’t carry enough fluid throughout its travel. This happens when the valves are larger and require more fluid for a given displacement. Using larger valves are desirable to have more control for a shorter amount of travel. This is great for suspensions with very limited movement like formula cars and/or cars with ground effects. (Because down force is way more valuable than spring rate, cars with high down force constantly battle between mechanical grip and the need for a stiff chassis to keep the aero package at it optimum level). However, small, high quality precision parts can do an excellent job of controlling damping inside the main housing.

#7 – You need a higher spring rate on a race car than a street car: Optimum spring rate for a given traction level never changes. The only reason for higher spring rates on a race car is because the chosen tires have a higher level of traction. However, on a race car, more damping rate is desirable to better control the speed at which the body rolls, and this also offers better feedback to the driver. Great race damping is usually too firm for most street cars – the cure is to have adjustable dampers which have their adjustment range accommodate the best of both worlds.

#8 – A go-cart feel is faster. Body roll is not an undesirable characteristic. When the body rolls, it softens the transition of load to the tire and can dramatically improve its long term traction and durability, as well as offer the ability to trail brake more, and get on the power earlier. – However, many drivers like the go-cart feel for the responsiveness, and they are willing to trade long term maximum traction for it.

#9 – Higher spring rates make a car ride more harshly: Actually shock settings have more impact on ride quality than springs. In fact, reducing the actual weight of a spring improves ride quality as well. So a coil over conversion to a lighter springs allow an increase in spring rate while maintaining good ride quality.

Final Note: It would be truly helpful if all of the participants on the forums and chat rooms had to a résumé attached to their comments, because there is a tremendous amount of misinformation out there. However well-intentioned these people may be, if the knowledge and experiences aren't there, the suggestions offered and products endorsed are based on their personal experience, which many times does not represent the best advice.

For example: If a new to BMW enthusiast purchases brand 'x' suspension because his friend or someone on line recommended it, he may feel the change to the car and appreciate that there is a performance improvement, but, because he has no other BMW experiences to compare it to, how can he/she know their new suspension is the best option?

[c_ozanich]

vote for MOD to sticky this. Great read--Thanks TC KLINE

[TwinTurboed]

Sticky this please. Thank you so much for posting this info!

[MAddict]

Thank you for sharing this, hoping there are future updates to come.

[135Pats]

This is outstanding…and displays exactly why I tend to keep out of the suspension arguments. My knowledge is elementary on that front…

[135iam]

Good Stuff!

I spent some time chatting with TC on the phone back when I first bought my 135 and I asked him "Why does BMW have close to 2.5-3X the rear spring rate as the front?" as this didnt make sense to me based on my previous S2000 setup experience.

His response was excellent, and I would love to see that explained on here for others as well.

[128Convertibleguy]

Great stuff.

One omission is the links between ride height, center of gravity, weight transfer, and spring (better yet, wheel) rate. Admittedly a quite complex subject, but it's a major reason why race cars are pretty low, with somewhat stiff springs to avoid bottoming. There is such brilliant simplification in the material, maybe they could simplify this?

[FactorX81]

This info is good, I would love to see some more 1series specific info. They have or had a project one series so they should have some insight.

[TC Kline Racing]

If you have any specific questions, please feel free to ask here or email.

[maddman]

Excellent info!.....Thx!

[fe1rx]

Originally Posted by TC Kline Racing

If you have any specific questions, please feel free to ask here or email.

What is the rear roll center height as a function of ride height?

The front is relatively easy to figure out (as a function of ride height and static camber). Close to ground level, closer as static negative camber is increased.

Adding roll angle into the equation adds another level of complication. Can you give any insight into how the roll centers migrate front and rear as a function of roll angle?

Thanks!

[TC Kline Racing]

Originally Posted by fe1rx

What is the rear roll center height as a function of ride height?

The front is relatively easy to figure out (as a function of ride height and static camber). Close to ground level, closer as static negative camber is increased.

Adding roll angle into the equation adds another level of complication. Can you give any insight into how the roll centers migrate front and rear as a function of roll angle?

Thanks!

As you lower the rear ride height, the roll center goes down....as you raise the rear ride height the roll center goes up.

If you continued to lower the car, you would run out of suspension performance before roll center becomes an issue.

[TheSt|G]

And as always, never a question in my mind where I'm buying my coilovers from.

[fe1rx]

This deserves to by a sticky? It is an advertisement plain and simple. It could not be any plainer - "We recently ran an advertisement ..."

What, dear moderator, is stickyworthy about this (or any) advertisement?

[Ginger_Extract]

Originally Posted by fe1rx

This deserves to by a sticky? It is an advertisement plain and simple. It could not be any plainer - "We recently ran an advertisement ..."

What, dear moderator, is stickyworthy about this (or any) advertisement?

x2.

[Kgolf31]

Originally Posted by fe1rx

This deserves to by a sticky? It is an advertisement plain and simple. It could not be any plainer - "We recently ran an advertisement ..."

What, dear moderator, is stickyworthy about this (or any) advertisement?

Let me know when Ohlins, or any other suspension provider is active on every BMW forum answering specific questions about specific vehicle setup.

Oh wait...they don't


Regardless, I don't see anywhere in the article that states...Buy a Coilover Kit for $XXXX Shipped!

Just simple, plain advice they have been offering for a while.

[TheSt|G]

Originally Posted by fe1rx

This deserves to by a sticky? It is an advertisement plain and simple. It could not be any plainer - "We recently ran an advertisement ..."

What, dear moderator, is stickyworthy about this (or any) advertisement?

Aside from that line(which is a tenuous connection at best), nothing in the writeup pushes their products.

Otherwise it serves as quite a good primer for the uninitiated.

[fe1rx]

Originally Posted by TC Kline Racing

Final Note: It would be truly helpful if all of the participants on the forums and chat rooms had to a résumé attached to their comments, because there is a tremendous amount of misinformation out there. However well-intentioned these people may be, if the knowledge and experiences aren't there, the suggestions offered and products endorsed are based on their personal experience, which many times does not represent the best advice.

I was at the local BMW dealership today picking up some parts and there was a new 335i outside waiting for delivery. It was all tarted up with "M Performance" stuff. In fact "M Performance" was proudly emblazoned on the side skirts. I have been wondering if maybe "performance" doesn't translate from the German, but seeing that car there I finally realized that when BMW says "performance", they mean it in the sense of a theatrical performance.

Similarly, the word "upgrade" has lost its traditional meaning and now simply means "change" and one is wise to suspect that the established wisdom is merely a lie told often enough.

The challenge is to find advice from like-minded individuals, whether it be fashion advice for your boulevard posing, or advice that will measurably improve (lap) time, speed or acceleration (in all directions). If the latter, competition certainly improves the breed (and of course TC Kline has appropriate credentials). And as for the driver, here is a cynical view a "friend" sent me. It should offend just about everyone!

[Suprgnat]

Originally Posted by fe1rx

I was at the local BMW dealership today picking up some parts and there was a new 335i outside waiting for delivery. It was all tarted up with "M Performance" stuff. In fact "M Performance" was proudly emblazoned on the side skirts. I have been wondering if maybe "performance" doesn't translate from the German, but seeing that car there I finally realized that when BMW says "performance", they mean it in the sense of a theatrical performance.

Similarly, the word "upgrade" has lost its traditional meaning and now simply means "change" and one is wise to suspect that the established wisdom is merely a lie told often enough.

The challenge is to find advice from like-minded individuals, whether it be fashion advice for your boulevard posing, or advice that will measurably improve (lap) time, speed or acceleration (in all directions). If the latter, competition certainly improves the breed (and of course TC Kline has appropriate credentials). And as for the driver, here is a cynical view a "friend" sent me. It should offend just about everyone!

Attachment 1039666

That graphic should be a "sticky", too.

[Ginger_Extract]

Originally Posted by fe1rx

I was at the local BMW dealership today picking up some parts and there was a new 335i outside waiting for delivery. It was all tarted up with "M Performance" stuff. In fact "M Performance" was proudly emblazoned on the side skirts. I have been wondering if maybe "performance" doesn't translate from the German, but seeing that car there I finally realized that when BMW says "performance", they mean it in the sense of a theatrical performance.

Similarly, the word "upgrade" has lost its traditional meaning and now simply means "change" and one is wise to suspect that the established wisdom is merely a lie told often enough.

The challenge is to find advice from like-minded individuals, whether it be fashion advice for your boulevard posing, or advice that will measurably improve (lap) time, speed or acceleration (in all directions). If the latter, competition certainly improves the breed (and of course TC Kline has appropriate credentials). And as for the driver, here is a cynical view a "friend" sent me. It should offend just about everyone!

Attachment 1039666

Saving this for future use. Surprisingly sharp, and accurate. Also, it brought the lols.

[one30five]

Originally Posted by fe1rx

This deserves to by a sticky? It is an advertisement plain and simple. It could not be any plainer - "We recently ran an advertisement ..."

What, dear moderator, is stickyworthy about this (or any) advertisement?

Originally Posted by Ginger_Extract

x2.

[QUOTE=Kgolf31;16009654]Let me know when Ohlins, or any other suspension provider is active on every BMW forum answering specific questions about specific vehicle setup.

Oh wait...they don't

I know i'm late to this. but I had to say something. I don't see a SINGLE product mentioned in that post. I don't see anything said about their products or anyone elses

I don't know these guys personally, but i was in business with a guy and we bought a semi truck from them. One they had used to pull their car trailer. I got to ride in the VW Passat to go to the bank. They couldn't have been a nicer group of people. showed us their shop and cars. They know what rhey are talking about and they don't need to sell you shocks. they WIN. They are highly respected in the motorsports community.

So stop being ignorant jerks and read it again. you might learn something

[TC Kline Racing]