Bump Steer remediation

Agnelli

True Classic
Agnelli,

Which arms did you get and how do you like them? That will be on my list soon.

Chris
Chris-

The reinforced stamped steel arms. Three options from memory 1) stock 2) reinforced steel 3) fully adjustable exhorbitant.

I like them. Got the long fasteners at the same time also good.

I’ve seen the 128 rear coil over solution which allows eliminating the heavy leaf spring but don’t know as to efficacy for handling. That would be interesting to learn.

Jim
 
Last edited:

Longitudinal

True Classic
excuse the 30 second kindergarten drawing... but I've seen somehing similar done in a series production car (not fiat) and it was machined steel items, bolted together a little bit like the drawing below.

View attachment 38044
SteveC

That's pretty clever. I might make the bolt portion a two piece assembly with separate bolt and taper. It would be cheaper to machine, and it seems to me that it would torque more accurately if the taper were not rotating in its bore.
 

Longitudinal

True Classic
The modified upright was intended to bring the camber gain curve closer to stock and raise the front roll center.

Ah. From the title, I assumed that this was to correct bump steer. From a camber gain standpoint on a street car with street car tires doing street car things, it's probably not worth the effort/cost/risk. But the idea that Steve shared is a good one for sure.
 

Rupunzell

Bernice Loui
Raising the roll center often reduces mechanical grip.. ~reducing mechanical grip at the front of a FWD chassis could result in more understeer.~

Camber gain is interactive with the entire dynamics of the chassis-suspension.

Know one variant of the Lancia Stratos chassis used struts to gain wheel travel over the other Stratos chassis that used double A-arms all around.

Spring rate-damping/suspension travel/ride/control and all that are a complete system. Alter one item, the entire system dynamic will change all demands to be set up / tuned up as a system. Do you know precisely what the specific dynamics and suspension/chassis interactions were as the folks at Fiat designed in and why they were designed the way it was?


Bernice



Longitudinal,

The modified upright was intended to bring the camber gain curve closer to stock and raise the front roll center. Macpherson strut suspensions have very limited camber gain and do not work well when lowered. In a race car, you can compensate with very stiff springs to limit suspension travel and set static alignment where you want it. On Gus, I want good geometry with reasonable suspension travel. The 225 lb/in springs I am currently using are at the edge of reasonable for a street car, IMHO.The steering geometry will have to be corrected separately.

I think someone could use finite element analysis and cad to design a part that could be machined from billet, but I don't know THAT guy. If any of you do, I'd love to talk to him.

Chris
 
Last edited:

Rupunzell

Bernice Loui
"Macpherson strut suspensions have very limited camber gain and do not work well when lowered."

~Could be correct when the dynamic roll center is lowered below road surface level, this causes the cornering forces to be applied below the tire to road contact area. This is one of the many reasons why simply lowering a suspension/chassis does not always improve suspension/chassis performance. There is a similar effect with wider rims on a strut suspension... It's all interactive folks and no one item can be changed without having the entire suspension/chassis system being affected.
This was part of the rational behind PBS lowering the body around the suspension, their race results tell how effective this PBS modification prove to be.

There is zero wrong with a Mcpherson strut suspension, it's performance is dependent on how it was designed and what it was designed to do.

Question remains, what are the goals for any given suspension/chassis? There are no absolutes, just a set of trade-offs that must be accepted for what they are.


Bernice
 

Chris Taunton

Daily Driver
Chris-

The reinforced stamped steel arms. Three options from memory 1) stock 2) reinforced steel 3) fully adjustable exhorbitant.

I like them. Got the long fasteners at the same time also good.

I’ve seen the 128 rear coil over solution which allows eliminating the heavy leaf spring but don’t know as to efficacy for handling. That would be interesting to learn.

Jim
Hey Jim,

I am researching now. I may go with coilovers if there is room, just so I have options for spring rates. it looks like 175 lbs/in. is a good starting point. I will try to determine the rate of the existing spring.

Are the standard arms known to be weak? Maybe it is important because improvement in tires... Did you stick with rubber bushings or go with nylon?

Chris
 

Chris Taunton

Daily Driver
excuse the 30 second kindergarten drawing... but I've seen somehing similar done in a series production car (not fiat) and it was machined steel items, bolted together a little bit like the drawing below.

View attachment 38044
SteveC
Hey Steve,

This approach in a little like the Autodelta knuckle risers we discussed earlier. There is not room inside the wheel for that type of shenanigan.

Chris
 

Chris Taunton

Daily Driver
Raising the roll center often reduces mechanical grip.. ~reducing mechanical grip at the front of a FWD chassis could result in more understeer.~

Camber gain is interactive with the entire dynamics of the chassis-suspension.

Know one variant of the Lancia Stratos chassis used struts to gain wheel travel over the other Stratos chassis that used double A-arms all around.

Spring rate-damping/suspension travel/ride/control and all that are a complete system. Alter one item, the entire system dynamic will change all demands to be set up / tuned up as a system. Do you know precisely what the specific dynamics and suspension/chassis interactions were as the folks at Fiat designed in and why they were designed the way it was?


Bernice

You are correct in assuming that I do not know the specific suspension design criteria for the Fiat 128. I was 5 years old, do not speak Italian, and am not an engineer.

Therefore, my approach, like PBS, was to return the car to geometry closer to originally designed at a reduced ride height.

Considering the advance in tire technology and my desire for improved performance, what changes would you recommend?

Chris
 

Agnelli

True Classic
Hey Jim,

I am researching now. I may go with coilovers if there is room, just so I have options for spring rates. it looks like 175 lbs/in. is a good starting point. I will try to determine the rate of the existing spring.

Are the standard arms known to be weak? Maybe it is important because improvement in tires... Did you stick with rubber bushings or go with nylon?

Chris
To your question having read a lot here and on Mirafiori on the rear arms. I think the stock arms are prone to bending / disfiguring. On my car, the prior owner must have somehow hit something. The left arm had been replaced, but not the right, which exhibits minor deformation. I am definitely keeping the new OE style rubber bushings. Don't want to compromise ride quality or increase noise or rattles which of course is already existing in spades. Pretty certain you can do coilovers, based on looking at Instagram posts that seem to emerge primarily from South America and Europe.
 

Dr.Jeff

True Classic
Sorry to intrude, because I know nothing about the 128. But this all sounds very exciting to me, I'm enjoying the read. However I'd love to see some pics of the items you guys are discussing. And converting to coilovers sounds really good to me. Very cool projects - I love oddball old cars with designs like these, and modifying them to give increased performance while maintaining decent drivability for the road. ;)
 

Rupunzell

Bernice Loui
The US of A spec 128 was "Jacked up" in the front using taller springs. Installing the original stock 128 front springs should cure that problem. The rear has a single leaf spring which can be lowered with the usual leaf spring lowering blocks. There were higher rate rear leaf springs available at some point. With some measurements and help from the local moto spring shop it is possible to modify or have made a rear lea spring as needed.

If the goal is simply lower the front, going back to the OEM stock suspension is a good start.

BTW, the practice of upping the ride height at the front was a very common method for import cars to meet US of A bumper height requirements. That coupled with the 5mph bumpers completely altered the suspension/feel/dynamics of these non US of A cars.
Much of all that was a silent import barrier.

Bernice
 
Last edited:

Dr.Jeff

True Classic
BTW, the practice or upping the ride height at the front was a very common method for import cars to meet US of A bumper height requirements.
Indeed, lots of import vehicles of the era were equipped that way for our market. There were also some very odd approaches to meeting the "impact bumper" requirements when that first appeared. Yet another difference for our market was engine components to meet various smog (pollution control) requirements, which lowered their output considerably. I recall it was a very common "custom" mod to obtain the Euro spec (or similar) components to eliminate all of this. A full-time business for some shops, often at highly inflated prices for the parts coming from Europe.
 

Chris Taunton

Daily Driver
Sorry to intrude, because I know nothing about the 128. But this all sounds very exciting to me, I'm enjoying the read. However I'd love to see some pics of the items you guys are discussing. And converting to coilovers sounds really good to me. Very cool projects - I love oddball old cars with designs like these, and modifying them to give increased performance while maintaining decent drivability for the road. ;)

Hey Dr. Jeff,

When I start on the rear suspension I post pictures. There is not a lot of clearance between the strut and the tire, or tire and inner fender, depending on wheel offset. There may not be room for the spring without changing the offset and adding flares, which I don't want to do.

We will see. I have not looked seriously at this yet.


Chris
 

Dr.Jeff

True Classic
There may not be room for the spring without changing the offset and adding flares
That's always an option :p

Fiat 128 2.png
 

fiatfactory

Steve Cecchele
The biggest issue with the 128 chassis, and tuning it to get the tyres to work, is chassis flex.

No matter what you want to do with camber curves and setting the car up while it is static, this all goes out the window in the real world, especially if you also have an engine that produces considerable torque.

The front ends flex, adding a bigger / stiffer front bar just makes it flex more. There are guys in eastern europe that make a "kit" to reinforce the Zastava, but with all the bolted in attachment, I seriously see only little benefit from most of it. My rally 128 had considerable plating and undercar re-inforcement. The standard chassis will flex enough to eventually develop serious chassis cracks when you improve the engine output considerably.

same with the rear roll stiffness, the lower inner bushes of the control arms have sufficient flex under hard cornering loads to alter the rear toe. I also had the issue (in rally) of bending the rear lower arms and the attaching spindle bolts. My solution to both issues was to add a forward brake reaction rod (a shortened 128 coupe unit) with the forward pickup point mounted so it was aligned the other two mount points (on the lower arm) so as to not cause rear steer with suspension travel.

All the well prepped racing / hill climb 128's in Europe I have seen mount a lighter , slimmer bar solidly mounted on the firewall (more or less under the steering rack) with adjustable driving links for attachment as close to outboard as possible on the lower arm.

2ikdufr.jpg
this is one of the kits available from eastern europe, I don't know what they did with the sway bar in this pic, but looks likethe replaced it with some forward reaction rods with a ball joint / knuckle at the forward end.
2d0ns08.jpg
this it the kit... as I said with all the bolt in attachment, I don't see a lot of addition stifness, but it would do something.


SteveC
 
Last edited:

Chris Taunton

Daily Driver
The biggest issue with the 128 chassis, and tuning it to get the tyres to work, is chassis flex.

No matter what you want to do with camber curves and setting the car up while it is static, this all goes out the window in the real world, especially if you also have an engine that produces considerable torque.

The front ends flex, adding a bigger / stiffer front bar just makes it flex more. There are guys in eastern europe that make a "kit" to reinforce the Zastava, but with all the bolted in attachment, I seriously see only little benefit from most of it. My rally 128 had considerable plating and undercar re-inforcement. The standard chassis will flex enough to eventually develop serious chassis cracks when you improve the engine output considerably.

same with the rear roll stiffness, the lower inner bushes of the control arms have sufficient flex under hard cornering loads to alter the rear toe. I also had the issue (in rally) of bending the rear lower arms and the attaching spindle bolts. My solution to both issues was to add a forward brake reaction rod (a shortened 128 coupe unit) with the forward pickup point mounted so it was aligned the other two mount points (on the lower arm) so as to not cause rear steer with suspension travel.

All the well prepped racing / hill climb 128's in Europe I have seen mount a lighter , slimmer bar solidly mounted on the firewall (more or less under the steering rack) with adjustable driving links for attachment as close to outboard as possible on the lower arm.

View attachment 40095
this is one of the kits available from eastern europe, I don't know what they did with the sway bar in this pic, but looks likethe replaced it with some forward reaction rods with a ball joint / knuckle at the forward end.
View attachment 40096
this it the kit... as I said with all the bolt in attachment, I don't see a lot of addition stifness, but it would do something.


SteveC

Steve,

That is very interesting. I wounder how it would feel with street friendly spring rates and no front anti-roll bar. A front bar mounted to the firewall or front floor could be added if needed. That is a popular solution with Alfa 105 racers for the same reason - the radiator support area is not very stiff.

I bought some Braces from Classic Performance that go from the lower control arm mount on the body to the front anti-roll bar mounts. The idea is similar - feed braking loads into the firewall structure. I also bought the strut tower brace, but none of it fits. I will modify the lower braces to fit, but the strut brace isn't even close. I will start over and make my own down the road.

What is the source for the kit pictured?

Chris
 

Lowtechprime

True Classic
I drilled mine out.. Used a Heim joint with a boot around it filled with grease to make it last longer and an airframe bolt with a mechanical locking nut on the bottom (+ thread lock!) This was how I had it at first (pic) because the car is really low, but after driving it felt really odd so I moved it to the top and got the alignment. The Heim is a good deal slimmer so it lowered it enough to make a difference. It's really good now, not any noticable bump steer.. Even with the boot though, Heims don't last very long on the street...
 

Attachments

  • IMG_20150703_175121_152.jpg
    IMG_20150703_175121_152.jpg
    110.1 KB · Views: 62
Last edited:

Dr.Jeff

True Classic
That is a neat kit for the front end/suspension. There are a wide range of things like this available for other (more common) vintage cars - for example the Mk1 VW Golf. For those applications some of the reinforcements have been developed to also support areas that tend to weaken, in addition to stiffen the chassis for handling. Lots of good ideas among them to inspire some creative designing.

I seem to recall several years ago one of the Fiat specialists that built a lot of racing components for the X1/9 offered tubular/heim joint suspension components? But I realize that doesn't help for your 128. How about the companies in Croatia that make a lot of 128 racing stuff, any of them have something like this?
 
Top