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  #1  
Old 11th September 2012, 07:40 PM
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alga alga is offline
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Default Self centering

My car does not self-center at all. The mushroom inserts are with their hole forward, Toyo R888 tyres inflated to 1.5 bar (tried 1.8, too, no effect), 1 degree toe in, -2 degrees camber. The wishbones are built to book dimensions, there is a visible caster angle in the kingpin axis. It does seem to self-center in reverse, though. Any pointers, ideas?
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Old 11th September 2012, 07:48 PM
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Bit of toe out for IVA sorted out self centre issue
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Old 12th September 2012, 12:29 AM
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*sigh* Thanks, I'll try that. But there's a reason why self-centering is a required for IVA, it's a safety feature.

I'm considering several ways to increase the caster angle. One is slotting out the holes on one of the front suspension brackets and fitting some eccentric washers, much like this: http://www.jegs.com/i/Specialty-Prod...23765/10002/-1

Another idea is shortening the four bushes on the top wishbones by some 2.5 mm (bush tube and crush tube) and packing with washers to increase the caster angle by about 1 degree.
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Old 12th September 2012, 07:29 AM
DRCorsa DRCorsa is offline
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Quote:
Originally Posted by alga View Post
*sigh* Thanks, I'll try that. But there's a reason why self-centering is a required for IVA, it's a safety feature.

I'm considering several ways to increase the caster angle. One is slotting out the holes on one of the front suspension brackets and fitting some eccentric washers, much like this: http://www.jegs.com/i/Specialty-Prod...23765/10002/-1

Another idea is shortening the four bushes on the top wishbones by some 2.5 mm (bush tube and crush tube) and packing with washers to increase the caster angle by about 1 degree.
That's what i was thinking of doing some time when i finish my project as it seems every car with Sierra uprights has the same issue.
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Old 12th September 2012, 08:20 AM
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If you have a dig about on here someone did an explanation of all this. The mushrooms dont add caster they give you trail. Its this trail that helps with the self centering, a bodge is a better word for it. There is not enough caster in the front suspension set up and no way to alter it.Thats why I am making my upper bones with adjusters on the inner joints. When they are on the car I will take some measurements of them in the corrected adjusted position then perhaps someone can do an ammended top wishbone drawing so they are built to include the caster without the need for adjusters. Caster is an important must have for straight line stability not just self centering. I am no expert on trig but i bet its only a few mm added to the front top wishbone tubes to sort it.

================... KPI ......... caster

Lotus Elise........................ 12 ......... 3.8 caster
Corvette C5, C6................. 8.8 ...... 6.5 caster
Pinto/MustangII/Wilwood... 11
Ferrari 512BB............... 9 or 13
ATS AFX Tall..................... 8
Triumph Spitfire................ 7 ..........4.7 caster
Lotus Seven..................... 9 .......... 5 caster
Mazda Miata................... 11.3 ........ 5 caster
Ferrari F355................... 13.16
McLaren F1...................... 9 ........... 6 caster ...... 16.25mm scrub

Bob
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Last edited by robo : 12th September 2012 at 09:24 AM.
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Old 12th September 2012, 08:33 AM
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I would suggest that you lower the tyre pressures to 1.1 bar as a starting point,
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Old 12th September 2012, 09:42 AM
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set the toe to 0deg and try it. if that fails then 0.5deg toe out will get it self centering but it will feel twitchy at high speed.
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Old 12th September 2012, 05:56 PM
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Quote:
Originally Posted by robo View Post
If you have a dig about on here someone did an explanation of all this. The mushrooms dont add caster they give you trail.
One is as good as the other:



Fixing the Sierra's trail inceases positive caster distance, too. It's the distance between the kingpin axis' projection intersection with ground and the centre of the contact patch, and it is precisely the lever that does self-centering.
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Old 12th September 2012, 06:04 PM
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Quote:
Originally Posted by TSM Locost View Post
I would suggest that you lower the tyre pressures to 1.1 bar as a starting point,
I thought so. But now I have 1.5 bar in the rear tyres, zero camber, and the marks left on the asphalt when spinning wheels are just narrow stripes along the edges.
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Old 12th September 2012, 06:06 PM
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Not quite the same thing because the trail wont become effictive untill you move where as the caster will be effiective at all times. Hence the lack of self centering when stationary. That castor like on a shopping trolley could be kicked arround 360 degrees and it will only straighten if you move forward. Also the inside wheel on turn in on the proper set up is forced downwards whereas the trail set up remains static. That in turn makes the steering feel vague, thats the reason all decent suspesion systems have caster built in. The mushrooms help but its only a patch up fix for an inherent problem, they do infact make the set up act as scrub which most would regard as undesirable.

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Last edited by robo : 12th September 2012 at 06:18 PM.
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