Suspension update and upgrades

[fatbillybob]

I don't agree, but it really depends on the application. You shoot for a target roll gradient ratio and do your best to keep flat ride while doing so (tune roll stiffness with bars). .

I only deal with racecars. I have had to develop a couple of chassis from no data. I always start with a target chassis frequency and a flat ride concept. My thinking is it is a good place to empirically start. I know enough to be dangerous.

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[TeeLew]

That's only to balance the throttle steering because the faster driver is more abusive to the rear of the car. I don't really think that car understeers but neutral or oversteers to point the car around the corner and down the track. The slower driver would feel that the car understeers because his rearend is planted.

Yes & No.

When I said the pro driver wants an 'understeer' car, I was speaking in terms of a mathematical analysis. Abusive isn't really the right word, but they will drive the car in a manner which challenges the rear, and it starts from the beginning of the brake zone. They have higher brake pressures which puts more pitch into the car & will time the brake release/steering input in a manner which keeps the front tires loaded. They don't underachieve the corner entry, so they're never picking up maintenance throttle keep rolling speed. They're patient in the middle. They tend to apply throttle from 0 to 100% in one motion as opposed to putzing around in the middle. They drive the right line and hit their apexes (amateurs don't, at least not consistently). To do most of this requires a rear end which is nailed to the ground. No one is fast driving with their fingertips.

I have a saying: Once you find a setup which is 'balanced' for a given driver, a 1% increase in oversteer will slow them down 10% & a 10% increase in understeer will slow them 1%. (It's a rule of thumb, the units are arbitrary)

Most drivers want a 'balanced' car, but there are very, very good drivers who want, if not require, actual understeer. The reason is simple. Most laptime is made by being able to carry entry speed & get to early full throttle. If the car has a good steady-state skidpad balance, then it will be entirely too loose on entry to be able to attack the front side of the corner, mid-corner will be balanced with front & rear tires equally saturated and then at exit there will be no extra rear grip capacity to apply throttle.

The alternative is a car which has the rear stuck early in the corner, so the driver can attack. Mid-corner, the fronts will be saturated & the car will understeer. Once turned, the driver is then able to chase the throttle so the excess rear capacity is used to accelerate the car. The trick is minimizing the middle loss while maintaining the entry & exit advantage.

You have to make compromises no matter how you do it. These are the compromises I've found which makes the cars I work on go the fastest. I've never been able to achieve this with a car which has reasonable power with anything close to a flat ride spring lash up. I'm not trying to mislead. I'm just sharing my thoughts.

 

[TeeLew]

I always start with a target chassis frequency and a flat ride concept. My thinking is it is a good place to empirically start. I know enough to be dangerous.

Can you explain why you think this is a good place to start?

 

[TeeLew]

It is amazing the go to is do what others before you have done but those things are actually often wrong in the sense that they don't reflect your compromises. The real racers will let you go down the headfake path because they want to beat you.

We think completely opposite. I start with as much previous information as I can find to try to understand what got them to where they were and then use what I've learned to find the shortest path to the compomises I want to make. Those who don't know their history...

If someone is providing a setup, the vast majority of people will refuse to just put it on the car without making modifications because they "know better". I'll duplicate it to the absolute best of my ability and try to understand it before making changes. I've had plenty of times where I've been given no information. A few times I've been given old information. I've rarely been given blatantly false or misleading information.

 

[Norm Peterson]

Fixed budgets and conversations like these really make for difficult chassis development. It is amazing the go to is do what others before you have done but those things are actually often wrong in the sense that they don't reflect your compromises. The real racers will let you go down the headfake path because they want to beat you. When racing vettes we had a unique situation where about 10 of us racing the same chassis kind of co-developed together and what we discovered was fast was not the conventional wisdom. Right or wrong my tendency is to go my own way but development is slow and painful.

It's not much different when you're an individual trying to make thoughtful changes to your street-driver or dual-purpose street/HPDE car. Except that since the budget for pure testing tends to be even smaller, you have to try to be a little smarter about your choices before you commit the $.

That's only to balance the throttle steering because the faster driver is more abusive to the rear of the car. I don't really think that car understeers but neutral or oversteers to point the car around the corner and down the track. The slower driver would feel that the car understeers because his rearend is planted.

Understeer is something that can be defined mathematically from variables that determine what the front and rear ends of the car are doing and compiled into an understeer budget (front minus rear axle cornering compliance in terms of degrees/g). Oversteer can be considered "negative understeer", or an understeer budget number with a negative sign.

Your faster/more aggressive driver is adding a traction effect to the rear slip angles, which goes directly to the rear axle cornering compliance effectively making it greater (think looser). The resulting understeer budget number ends up somewhere between less positive and somewhat negative. The better driver can keep this in balance and reliably 'catch it' when he oversteps the balance point with a little too much throttle; the less experienced/less skilled driver cannot consistently do so and is likely to leave himself a little more cushion.


Norm

 

[IPOGT]

Both excellent. Bilstein just a little better at everything, and is reflected in the price (~$750 vs ~$600). You won't go wrong either way.

Faced with having one of my PP shocks suddenly leaking a puddle of oil in my garage, I decided to replace with a full set of Bilstein all around on my Ford Performance X springs. Should be an awesome street combo that shouldn't be too shy on the track either.
Looking forward to it.

 

[IPOGT]

I was quite happy with the street pack until the shock crapped out. Had a nice balance. I'm sure with the Bilstein I'll probably like it more than with the OEM shock and strut combo.

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