850 Stabilizer bars.

[GregS]

I was having some rear toe change problems with my track X1/9, rear suspension design is a bit different to the 850, but similar in that the pivot points are not in a straight line. Common thoughts are to not use poly bushes as it relies on the rubber being able to deform with suspension movement. I made up a rig to measure the toe change with suspension movement on the car, and lowered the tie rod end connection outer point to correct it. Here's a link to discussion, post #14.

Suspension pickups - race build 1978 X1/9

I am moving to an x1/9 full track build after a break from building my last 128 - it’s been a long time since I looked at x1/9 chassis set-ups - can somebody bring me up to speed with best practice on relocating suspension pickups (or not) for the front? I and assuming the HP racers out there...

xwebforums.com

 

[ramona300]

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.

I have read all their various forums and had intended to make the toe in adjustment arm they sell for silly money. The car is not much lower than stock in the rear it just has the stiffer coils from the OT1300 with the plastic cap removed. Probably 25mm lower. It's still well above the workshop manuals loaded position of 155mm. I'm not going to shift mounting points upwards. I will get on with the string wheel alignment and check the angles fully loaded with the weight in the drivers seat and winch down from the rear lift point to the trailer to what I think the car does in a corner. Just make sure it's still toeing in still at the limit.

 

[ramona300]

I was having some rear toe change problems with my track X1/9, rear suspension design is a bit different to the 850, but similar in that the pivot points are not in a straight line. Common thoughts are to not use poly bushes as it relies on the rubber being able to deform with suspension movement. I made up a rig to measure the toe change with suspension movement on the car, and lowered the tie rod end connection outer point to correct it. Here's a link to discussion, post #14.

Suspension pickups - race build 1978 X1/9

I am moving to an x1/9 full track build after a break from building my last 128 - it’s been a long time since I looked at x1/9 chassis set-ups - can somebody bring me up to speed with best practice on relocating suspension pickups (or not) for the front? I and assuming the HP racers out there...

xwebforums.com

View attachment 80454View attachment 80455

That's an interesting discussion but I don't think mine is bump steer. And your right the toe definitely toes out as the suspension loads up! I thought about changing the bushes but I'm guessing abarth-online.de does not have any bushings on their site for a reason. They have all sorts of other suspension parts so I guess they stick with the stock stuff. In the top photo are you loading up the rear suspension to set the toe? I have your settings noted down and thought you had a lot of rear toe in. Loaded up it might be coming down to zero!

 

[Steve Thomas]

The car looks very nose down. I assume both ends are lowered but the rear tyre diameter is up? The nose down stance will be giving you another steer effect from the rear - wheelbase length change. If the inclination of a line through the two rear arm pivots when seen from the side is pointing down toward the front [as I suspect], then as the wheel rises it will move forward. Even in a stock semi-trailing arm setup, this happens a little depending on the inclination of the axis in plan. At the extremes there is no wheelbase change [swing axles] or lots [trailing arm]. FIAT use a middling angle plus the bush angles and stiffnesses to get the balance they saw as correct.

But the inclination of the axis in side elevation is another matter. I don't have the detail on an 850, but I know that an X has this axis angle set at zero. If the axis is tipped nose down, then as the car rolls, the inside wheelbase will shorten and the outside will lengthen - promoting turn in or oversteer. This will also give bonus [relative] toe in for the inside wheel and out for the outside.

But although I am talking "as seen in plan or side elevation" - that is a simplification. A semi-trailing arm moves the wheel in camber, castor, track, toe and wheelbase simultaneously. Best bet is not to have one

Second best bet is keep the travel as short as is compatible with the tracks you use and the amount of kerb you grab. Aside from that, I would do something at the rear to get the arm horizontal and changing the tyre is probably easiest - yes, I know, gearing etc...

 

[GregS]

That's an interesting discussion but I don't think mine is bump steer. And your right the toe definitely toes out as the suspension loads up! I thought about changing the bushes but I'm guessing abarth-online.de does not have any bushings on their site for a reason. They have all sorts of other suspension parts so I guess they stick with the stock stuff. In the top photo are you loading up the rear suspension to set the toe? I have your settings noted down and thought you had a lot of rear toe in. Loaded up it might be coming down to zero!

A moderate amount of toe in (1 or 2mm from memory) was set at static loaded ride height, then the hub jacked up and down to measure the toe change at full compression and droop.

 

[ramona300]

The car looks very nose down. I assume both ends are lowered but the rear tyre diameter is up? The nose down stance will be giving you another steer effect from the rear - wheelbase length change. If the inclination of a line through the two rear arm pivots when seen from the side is pointing down toward the front [as I suspect], then as the wheel rises it will move forward. Even in a stock semi-trailing arm setup, this happens a little depending on the inclination of the axis in plan. At the extremes there is no wheelbase change [swing axles] or lots [trailing arm]. FIAT use a middling angle plus the bush angles and stiffnesses to get the balance they saw as correct.

The nose is down slightly. The rear tyre is 205 x60 x 13 Nankang AR1's which have very similar rolling diameter to the original tyre but enormous grip. Fronts are 185 x 60 so that helps give the nose down attitude. The handling is excellent but always slight understeer. Yes the wheelbase does shorten in hard cornering but no idea if it's the outside or inside. I had to bend some tin on both sides after the last event. I rolled the arches but obviously did not go down far enough! The suspension is limited in droop by Dyneema rope but I don't have the rubber bump stops in place and I'm thinking they should go back in! I can only go by other peoples photos of how far the car rolls. Seems flat to me but might be beneficial limiting the travel by bump stop.

 

[Steve Thomas]

Too hard - too hard to give decent advice without spending a couple of hours crawling all over the car and shooting the breeze with you Regardless, a very pretty baby and very well presented.

 

[ramona300]

When I previously set toe in I used the plates and measured with steel bars extended well clear of the car to a centreline. I have made my string line framework set up now that sets up an accurate rectangle around the car. Plenty of YouTube videos out there that show how. I did a quick check today with the car unloaded and I think I have solved the puzzle. The rear right has 1mm toe out unloaded! Left has 2mm in. The big surprise was the front with 5mm toe in on the left and zero on the right. Measuring to a centreline obviously not a good idea!
The yellow string is just for the photo. I have 0.5mm stainless wire for when I get serious.