850 Stabilizer bars.

On the rear, the suspension will tend to go more toed in under driven load as the various tolerances and the bushings bottom out. By that same token it will return to a less toed in state as you brake or let off the gas.

In the front the toed in state will lessen towards 0 toe as the wheels are driven forward and pull the tolerances out of the various tie rod ends that make up the steering mechanism.
 
Hillclimb yesterday. Six runs. First run I had the front sway bar attached but that freaked me out and felt decidedly unsafe! Second run with out it was much better. I started the day with just a touch of front toe in and after each run I adjusted the toe out and the last run of the day was OK. General consensus amongst the other competitors is the tyres. Running Avon formula Ford cross plies and they don't like any camber so I will be switching to radials. Will try the front sway bar again but connect to the top wishbones like the Abarth unit.
 

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Quick check on the front toe today. Back to toe out. The rear is out to the edge of the bolt holes so I will be elongating the holes in the next couple of days so I can run zero toe in at loaded weight.
 
Have been getting some technical advice from Hegen Speed in Germany re suspension. Hegen has some excellent Youtube videos under the Schuergers channel. https://www.youtube.com/channel/UCLwLVvPJJ4_UZj0PFIhMp9g
On the 1000 OTS they have a 20mm front bar and the stock 16mm on the rear. The Abarth bar is not available but I picked up a Hyundia I30 bar at the wreckers that is almost a direct fit. It is 21mm but that's as close as I could find. Have to make up rose joint links to the top wishbones.
 
Test day at the track yesterday. first run with the Hyundai anti rollbar fitted. Also swapped the Avon crossply race tyres for Yokohama 048's and had as little rear toe in as I could get. Car was transformed! The antiroll bar just makes the car chuckable! The radial R spec tyres can handle higher tyre pressures and I started the day with 15 psi at the front and 25 at the rear cold and left them there! The Avons had to stay around 20 psi hot and that does not suit this car on the rear. Now to get the toe set accurately at an alignment place.
 
I think it might be time to resurrect this thread. For the past couple of years, I have been running Nankang AR1's, 185 x 60 on the front and 205 x 60 on the rear and these have been excellent. The front settings are just a small amount of negative camber and toe in and with the 21mm roll bar the handling is excellent. The rear has a fair bit of negative camber and the toe in is the minimum I can get even opening up the holes a bit. Normally the handling is excellent but I'm thinking the rear toe in might be too much for the very fast circuits. Monday at the Sydney Motorsport park main circuit there is a long straight with a very fast first corner. I could probably take it full bore but generally just lift off and a tap on the brakes bring the nose in and I accelerate. The rear tyres just jump sideways in a jerky motion and the soft rubber marbles up in the centre of the tyre. Blokes following behind reckon the tyres have too much grip! Now I don't want to give up grip but I'm thinking going to zero toe in in the rear might help. Any thoughts are appreciated.
 
ramona300 said:
I think it might be time to resurrect this thread. For the past couple of years, I have been running Nankang AR1's, 185 x 60 on the front and 205 x 60 on the rear and these have been excellent. The front settings are just a small amount of negative camber and toe in and with the 21mm roll bar the handling is excellent. The rear has a fair bit of negative camber and the toe in is the minimum I can get even opening up the holes a bit. Normally the handling is excellent but I'm thinking the rear toe in might be too much for the very fast circuits. Monday at the Sydney Motorsport park main circuit there is a long straight with a very fast first corner. I could probably take it full bore but generally just lift off and a tap on the brakes bring the nose in and I accelerate. The rear tyres just jump sideways in a jerky motion and the soft rubber marbles up in the centre of the tyre. Blokes following behind reckon the tyres have too much grip! Now I don't want to give up grip but I'm thinking going to zero toe in in the rear might help. Any thoughts are appreciated.
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I doubt there is quite such a thing as too much grip… is this behavior of stepping out on all turns or just that one turn at the end of the straight? Are there any roadway discontinuities or changes in the surface: macadam to concrete, expansion joint, a ridge where they stopped for the day and picked up the next morning? Or were you just in the marbles that build up on turns which your tires slid across?

Are there any strange bits of wear of late on the tires? Are you getting unusual wear in the middle of the tire, you mention the soft rubber making marbles in the center of the tread.

Could you refresh our memory on how you lowered the rear suspension beyond just lower springs. At one point we had talked about moving the suspension points upward in the body which I don’t recall you doing.

What are your current suspension settings?
 
The rear is just 1300tc coils with out the caps so it sits lower with a fair amount of negative camber. Toe in is about 2mm. The rear is similar to stock apart from gas shocks and dyneema strops. In the video I will post in a couple of days it's easy to see the rear jumping around. I had this Canadian bloke tell me after how he was stuck behind me in his Alfa and he reckoned the car was jumping sideways and it was he who mentioned the tyres had too much grip. Only notice at this circuit which is very fast with flowing corners. I think the tyres on the rear have too much slip and I think corner one on this circuit loads up the tyres for a lot longer. So if the toe in increases on the outside tyre for a few seconds it's the cause of the problem. Tyres are much different now to what they were in the seventies. The photo is back in the pits and a lot of the rubber is gone by then!
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ramona300 said:
The rear is just 1300tc coils with out the caps so it sits lower with a fair amount of negative camber. Toe in is about 2mm. The rear is similar to stock apart from gas shocks and dyneema strops. In the video I will post in a couple of days it's easy to see the rear jumping around. I had this Canadian bloke tell me after how he was stuck behind me in his Alfa and he reckoned the car was jumping sideways and it was he who mentioned the tyres had too much grip. Only notice at this circuit which is very fast with flowing corners. I think the tyres on the rear have too much slip and I think corner one on this circuit loads up the tyres for a lot longer. So if the toe in increases on the outside tyre for a few seconds it's the cause of the problem. Tyres are much different now to what they were in the seventies. The photo is back in the pits and a lot of the rubber is gone by then!View attachment 79451
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I'm only guessing, but I wonder if the high cornering loads in turn one are compressing the suspension bushes so much that they eventually spring back quickly and overload the tyre grip, making them skip. I don't know if that's even possible? Or maybe something not working properly with the dampers. Sounds scary, good luck.
 
You are definitely overloading the outside of the tire. I would start by adjusting your tire pressures to try to engage more of the tread. You can see the feathering of the rubber which seems to trail off in the inner third of the thread.

Are you sure its not ‘jacking’ where the outside tire is digging in, the body lifting to the extent of the limiting straps and then ‘jumping/skipping’ across?

Does anyone have a video of the behavior?
 
GregS said:
I'm only guessing, but I wonder if the high cornering loads in turn one are compressing the suspension bushes so much that they eventually spring back quickly and overload the tyre grip, making them skip. I don't know if that's even possible? Or maybe something not working properly with the dampers. Sounds scary, good luck.
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I was just reviewing the video. The problem is heat as well. The first lap is OK but after that the problem starts. Corner one is long and the car corners flat but there is a fair amount of load for a long time. I noticed too that corner 3 which is a slower right hand corner the car does the same. I think I have set up the rear toe incorrectly. I think the answer is to make a bracket with a bolt set up to winch the adjustable part of the arm out. open out the hole further and get out to zero to 1mm of toe. Take off the wheel and use my frame on rollers I used on the front set up and measure to an accurate centreline.
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kmead said:
You are definitely overloading the outside of the tire. I would start by adjusting your tire pressures to try to engage more of the tread. You can see the feathering of the rubber which seems to trail off in the inner third of the thread.

Are you sure its not ‘jacking’ where the outside tire is digging in, the body lifting to the extent of the limiting straps and then ‘jumping/skipping’ across?

Does anyone have a video of the behavior?
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The problem I can't fix on the rear is the camber. These tyres prefer to be vertical and if they were vertical they would not fit under the guards! The outside of the tyre does not really touch the road. The outside still has the brand name untouched. The only evidence so far is verbal from people following behind and my backside which feels the whole thing. There are other cameras out there in my group but getting stuff from them is a problem. When I post the next video I shall be asking for stuff in return. The tyre pressures are pretty well spot on for all the circuits and the car handles and brakes very well. Even the fronts get a build up of the rolled rubber and the car will wander down the straight till it drops off! Hegen Speed in Germany runs zero toe on the rear of his coupe. I figure if I start with zero to 1mm on the straight it will increase the negative toe as it loads up.
 
Hmm, the rear tire does have wear on the outside tread, perhaps not in your 'normal' but it is showing it is getting used. Clearly not rolling over at all.

Rear toe on an 850 is normally pretty minor at .02-.18".

A characteristic of a semi trailing arm suspension is increased toe in as the suspension compresses and yours is already 'compressed', so to your point, less toe in statically will give you a reduction under load. Did you set the toe in after the lowering of the rear?
 
The rear toe is what the professionals did at the shop after I installed the new shocks and coils. I did a rough check yesterday underneath measuring across the rims as close as I could get to the centre. The difference between the rear rim and the front of the rim was 10mm, car unloaded. That's a lot of toe in! I have 3 manuals and they all vary a lot is what the specifications are and how to get there. The workshop manual I would say is the best after some careful reading! I don't have any of the Fiat tools but I can winch down the car on the trailer to get to the specified load position, 155mm between the rubber bump stop face and the centreline of the axle. It's well above that empty on the trailer. The toe in there should be zero 12 minutes plus or minus 6. Or in simple terms a bar across the face and measure 2.03m from the centre and make the toe in 3.5mm from the centre line will give 0 degrees 6 minutes. I reckon I have something like 35mm at the moment! Even down the main straight the resistance must be affecting the top speed. Hegen Speed in Germany runs 0 toe in on the rear and it probably makes sense as the toe would go negative under load under cornering.
 
ramona300 said:
The rear toe is what the professionals did at the shop after I installed the new shocks and coils. I did a rough check yesterday underneath measuring across the rims as close as I could get to the centre. The difference between the rear rim and the front of the rim was 10mm, car unloaded. That's a lot of toe in! I have 3 manuals and they all vary a lot is what the specifications are and how to get there. The workshop manual I would say is the best after some careful reading! I don't have any of the Fiat tools but I can winch down the car on the trailer to get to the specified load position, 155mm between the rubber bump stop face and the centreline of the axle. It's well above that empty on the trailer. The toe in there should be zero 12 minutes plus or minus 6. Or in simple terms a bar across the face and measure 2.03m from the centre and make the toe in 3.5mm from the centre line will give 0 degrees 6 minutes. I reckon I have something like 35mm at the moment! Even down the main straight the resistance must be affecting the top speed. Hegen Speed in Germany runs 0 toe in on the rear and it probably makes sense as the toe would go negative under load under cornering.
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Yeah that is a lot. Even the 3.5mm seems a bit much each side, though it does lend some stability to the car which you may need.

I would definitely want to do some testing before being at full chat in a fast corner.
 
kmead said:
Yeah that is a lot. Even the 3.5mm seems a bit much each side, though it does lend some stability to the car which you may need.

I would definitely want to do some testing before being at full chat in a fast corner.
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That 3.5mm is 2.03 metres from the centre of the wheel. The 1973 850 has the rear toe as 0.5mm in which is probably the same as the 3.5mm above. Using the normal race car set up with string and having the correct ballast weight in the car that 0.5mm makes a lot of sense.
 
I have made up a model of the Fiat 850 rear suspension out of paddle pop sticks. I used the page in the workshop manual and simply overlaid the sticks. The wheel hub is not to scale, I made it longer so it's easier to see what's happening. I presume the diagram shows the suspension in the loaded position for a wheel alignment. That is the distance from the centre of the shaft to the bolt hole of the rubber mount is 155mm. Toe in this position is zero plus or minus 12 minutes. Note the angle of the pivot points of the rubber bushes! The black line shows them as being very different!
In the second photo, there is a pen top holding the suspension up in an exaggerated position to show what happens. The red line shows the suspension going to a very noticeable toe-out. Toe-out is not good. Toe out and some distortion of the rubber bushes could be my problem. At the moment I'm making up the brackets to hand string lines to do a full check on the front and rear toe. This time I will load my seat up with 85 kilos and when I'm happy I will pull down one side to a fully loaded position to check as well. I think having a light car and doing the alignment without the driver in the car is giving the wrong rear toe.
Suspension rear a .jpg
Suspension rear.jpg
 
mmm ice cream.... The problem is that your model does not reflect forces or compliance. Yes, the bushes do not fall on the same axis and that was deliberate. The angles and bush stiffnesses were chosen to deliver a range of responses under various load and travel conditions. You can't plot angles without the relative stiffness/compliance of those bushes. But, this is a pure race car so none of that matters anymore. I assume you have changed the bushes and maybe even gone to rod end/uniball? That will give you a single simple axis with no bush compliance [which would have been introducing random toe effects as load varied].

It is also possible that you are simply trying to carry too much tyre.
 
It does not show the effect of camber either. I have been doing a lot of research into other cars that have similar rear suspensions that have the same problem. In particular, for the Porsche 914, the first thing they do is install steel bushes instead of rubber. I still have the rubber. I have one more event at Sydney Motor Sport Park Druitt circuit in a couple of months time where this problem really occurs at the turn one. After that it's mainly back to the refurbished Wakefield circuit where I don't have a problem.
 
ramona300 said:
It does not show the effect of camber either. I have been doing a lot of research into other cars that have similar rear suspensions that have the same problem. In particular, for the Porsche 914, the first thing they do is install steel bushes instead of rubber. I still have the rubber. I have one more event at Sydney Motor Sport Park Druitt circuit in a couple of months time where this problem really occurs at the turn one. After that it's mainly back to the refurbished Wakefield circuit where I don't have a problem.
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The 914 doesn’t have a semi trailing arm, it has a straight trailing arm, it has a notably different suspension. It has a small angle in its axis of rotation but nothing like the 850 semi trailing arm which enjoys a compound motion. The 914 sees body roll induced camber change but doesn’t have the same toe change a semi trailing arm has.

The 911, 1968 and later model Beetle (shared with the 924/944) and BMW 2002, 320 through 1992 all had the semi trailing arm as an 850. I would be looking at those vehicles and how the camber and toe change have been managed over time.

By lowering the car you have moved from the base static position and into the start of the extreme motion change part of the arm’s travel.

One of the solutions to your problem is one we talked about some years ago. Moving the suspension arm up higher into the body to lower the car and keep the arm during the expected motion closer to the standard car’s base position or reconfigure the arm so the wheel bearing is raised higher in the assembly to have the wheel geometry starting from the ‘standard’ neutral position but raised higher to lower the body independent of the arm. Doing this would allow you to preset the base static negative camber independent of the arm position which is one of the elements you are facing. There will be a limit to this as the bottom of the arm arrives at the barrel of the rim…
 
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