Impoving handling of Fiat 128 / Yugo / Ritmo

Non-engine, eg: aerodynamics, gearboxes, brakes, suspension
NickRP
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Impoving handling of Fiat 128 / Yugo / Ritmo

Post by NickRP »

Hello,

this winter I was planning to do some improvements of suspension on my Yugo (for those who don't know Yugo shares 99% of suspension with Fiat 128, and also many with Ritmo). The Yugo is a daily driver, it has 1.6 SOHC engine with 80bhp which moves it around acceptably, but handling is not as good as I would like it to be. A few times I was in very unpleasent situation to expirience understeer while just following the car (of newer generation) ahead of me, that was holding the line perfectly. Torque steer is also present (i.e. detectable) from the moment the car got 1.6 engine.

It is worth saying that the car is well mantained, tyres (165/65R14), shock absorbers, springs, rubber bushes etc are all in good condition.

A few improvements already done:
1) The car was lowered by 30mm on both ends.
2) Leaf spring with 3 leaves is used on the rear end (stock had two).
3) Longitudal reinforcements are installed between point where wishbone is connected to the chasis and point where anti-roll bar is fixed on the front.

I have plan to do the following:
1) Use 8mm longer lower wishbones to increase front wheel base (I'd have to check if the driveshafts will be long enough, or those will have to be replaced as well).
2) Reset the front wheel camber (-.5 to -1 deg).
3) Upgrade to shorter (F-127 like) uni-directional (unsure about wording here) "gas" shock absorbers.
4) Fit strut tower brace.

This all should help handling a bit. But I am afraid that the torque steer will remain, as in the actions listed nothing is actually improving longitudal stability of the front wheels.

The problem with Fiat 128 type front suspension (for those unfamiliar) is that anti sway bar is actually acting as single longitudal supporting point of the front suspension. And sway bar is laid in rubber bushes everywhere, so it does a poor job. If needed, I can provide photos of how this all looks like.

I would be interested to hear some advices on improving handling on this type of front end suspension. As I said, the car is used on every day basis and I wouldn't like to compromise comfort unless ABSOLUTELY neccessary (comfort is already terrible). Furthermore, all the improvements should be robust and reliable (so that I do not have to change parts every now and then, as I simply do not have time for that). I would like to avoid any drilling and especially welding on the chasis. Apart from that, I am ready to undertake any other reasonable actions.

Many thanks,
Nikola Radenkovic
sumplug
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Post by sumplug »

Yugo chassis will flex alot i bet, so fit a top strut brace and a bottom one if you can. Fit one at the back. Engines on these rock about a lot, so an engine brace would be ideal. Polyester bushes should replace as many rubber bushes as possible. The sway bar[anti roll bar], should be first on list. Maybe fit a thicker Sway Bar. Look at fitting wider wheels and lower profile tyres. Say, 185x60x13 tyres on a 5.5 or 6 inch rim. More positive camber will improve turn in for sure. This will improve things greatly.

Andy.
NickRP
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Post by NickRP »

Hello Andy, thanks for the answer.

Fitting bottom brace would be very complicated, as it would have to clear twin exhaust pipe and gear selector bar. I found one photo, it's not the best one, but you'll get a picture.

I'll put extra engine brace on my list, there is an easy way to add one on cambox (where 128 had brace originally).

The problem with bushes on the front of the sway bar is that they have to be slided over the sway bar in order to mount them where they are supposed to go. This process is a headache even with relatively soft rubber bushes. With polyester items, this would be hardly even possible, as the bush has to pass a few curved parts of the bar... Furthermore, I do not know if there is any source of the polyester bushes for 128 or Yugo. :(

I already have the thickest possible sway bar available for Yugo. I think is is 22mm DIA, but I'll check that.

All the best,
Nikola
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sumplug
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Post by sumplug »

What about running a bottom Struct Brace from the front edge of the inner wing so it runs close to the radiator? Polyester bushes can be made to measure by the way. Looking at your picture, those suspension bushes can be upgraded.

Andy.
Guy Croft
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Post by Guy Croft »

Have you seen member Huw Davies calculators Nick?

http://racingaspirations.com/suspensiongeometry.php

GC
TR-Spider
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Post by TR-Spider »

[quote: The problem with bushes on the front of the sway bar is that they have to be slided over the sway bar in order to mount them where they are supposed to go. This process is a headache even with relatively soft rubber bushes. With polyester items, this would be hardly even possible, as the bush has to pass a few curved parts of the bar... Furthermore, I do not know if there is any source of the polyester bushes for 128 or Yugo]

I would try polyurethane bushes, especially on the swaybar, which has a strong role on locating the wheels on your setup. Don't worry about the mounting, the front ones are usually slotted, so it's an easy exchange...
for parts try http://www.superflex.chriswitor.co.uk/S ... Prices.pdf

Thomas[/quote]
NickRP
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Post by NickRP »

Guy Croft wrote:Have you seen member Huw Davies calculators Nick?
Excellent tool... but how should I configure it for Mac Pherson suspension?
TR-Spider wrote:I would try polyurethane bushes, especially on the swaybar, which has a strong role on locating the wheels on your setup...

Thomas, thank you for the link, that's really helpful, I'll email them for furhter info.
Best regards,
Nikola Radenkovic
Guy Croft
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Post by Guy Croft »

Sorry Nick,

I'm not 'into' handling, my knowledge pretty well stops at lowered and stiffened! I studied it all at university but 5 years in the armed forces after graduation and I could not remember anything except the bits that interested me (engines)..

Maybe Huw can offer a software upgrade on Macpherson struts? Write and ask.

GC
NickRP
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Post by NickRP »

Hi Guy,

unfortunatelly, handling is also my weak point. I've never studied it, and most of the things I tried to deduce myself. Good as brain gymnastics, though.

Sure, I'll write to Huw. Hopefully that upgrade will not take too much of his time.

I still didn't get answer from Superflex, but looking more detailed in their price list, it looks like they do not stock PU bushings for front sway bar clamps (the ones at the very front of the car). I will make a photo to be clear to which I refer.

Over here it is quite popular mod to instal unibal's in wishbones and clamp sway bar using two profiled steel plates. However, this is making the whole front suspension acting direct on the chasis (i.e. lot of noise, vibrations and limited life). Furthermore, swaybar is not perfectly round (it is made of forged rod, I believe), so significant wear occurs where the clamping plates are holding it... So, that's definetely not something I am after.

Many thanks,
Nikola Radenkovic
p.s. sorry for my English, it is rusty and I miss many words (esp. car tech. terms), but hopefully what I write is still understandable.
sumplug
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Post by sumplug »

Nick.
Try these people. They make universal bushes
http://www.powerflex.co.uk/

Andy.
NickRP
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Post by NickRP »

Hello Andy,

thanks, I've just written to them... When/if they reply, I'll copy and paste what they wrote here.

All the best,
Nikola Radenkovic
hcd
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Post by hcd »

Hi Nikola,

A few ideas...

Strut brace will definately help reduce chassis flex around the strut towers and has to be the number 1 mod. You could probably just weld in some braces - maybe not - just read your original post again.

Increasing front toe out may reduce the understeer.

Adding an anti roll bar to the rear suspension will also help with understeer working on the theory that the axle with less roll loses grip first. A friend of mine did this on his Volvo S70 race car with great results.

If you just increase the front antiroll bar tortional stiffness (however you do it) you may actually increase the understeer.

My racecar (2006 set-up) only has a front antiroll bar (rear is live axle) and - yes it does understeer, lift off oversteer is almost impossible to achieve. I'll be adding a rear anti roll bar next season to balance it out a bit.

Huw
NickRP
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Post by NickRP »

Hello Huw, thanks for the advice.

I could bolt a brace between the towers on front, so no welding is neccessary. I will go for that mod. I am in process of self designing it. Could you tell me, is the brace going to be loaded only by forces acting axially, or there will be torque acting on it? This is very important design consideration, as I'd like to do it right from the first try...

I do not have rear anti roll bar, however, leaf spring is acting as a roll bar to certain extent and I can't do much there. I used harder leaf spring, to help understeer, but with front end in far from perfect shape, it didn't help much.

All the best,
Nikola Radenkovic
hcd
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Post by hcd »

Hi Nikola,

I guess the forces acting on the suspension mounting point could come from any direction - braking, accelerating?? Here's an idea I haven't seen before, I only hope the bulkhead can take the load at that point.

Image

Here's an excellent easy to read analysis of LOCOST cars and tortional rigidy, gives some great examples of triangulation that could be put to use designing the brace.
http://www.locost7.info/files/chassis/k ... alysis.doc

all docs - http://www.locost7.info/mirror/chassis.php

Huw
Guy Croft
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Post by Guy Croft »

I just remembered an 'aide-memoire' for suspension and chassis.

1. Any increase in front-end stiffness (including engine/chassis strut braces -suprisingly, dampers, springs, tyres, tyre pressures, anti-roll bars, joints and bushes, chassis welding) increases the tendency to understeer (car tries to go 'straight on and won't turn corners easily).

2. Any increase in rear end stiffness increases tendency to oversteer.

I've experimented with many of these, it's all true. The best mods are front and rear alterations to keep the vehicle dynamics balanced for given weight distribution, tampering with one end independently can be potentially catastrophic, done that too.

For stiffness I think you can also read 'weight' (mass), not so sure about that one though.

GC
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