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Old 10-03-2006, 02:26 PM
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Alignment Specs; orig bias vs radials

'61 Bonneville

Orig specs call for:

Camber = -1.5* (note that it is negative)
Caster = +0.25*
Toe-In = 1/16"

But, this is right out of my 1961 service manual.

Car came with skinny rims and old tech tires. I now have brand new BFG KDW 245's all around.

Any suggestions on how to adjust the original specs for new tires/rims?

Thanks, Scott.

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Old 10-04-2006, 12:22 PM
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Your best bet will be to set it to factory and drive it a bit. Inspect the treads closely for wear indications. THEN adjust accordingly.

Some times the stock specs work OK. If your rims are the same ratio back spacing as the stock skinnies, you might not have issues. That is, they clear everything during turning.
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Old 10-07-2006, 05:59 PM
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alignment specs

Quote:
Originally Posted by TheMonkey
'61 Bonneville

Orig specs call for:

Camber = -1.5* (note that it is negative)
Caster = +0.25*
Toe-In = 1/16"

But, this is right out of my 1961 service manual.

Car came with skinny rims and old tech tires. I now have brand new BFG KDW 245's all around.

Any suggestions on how to adjust the original specs for new tires/rims?

Thanks, Scott.
When I first read your specs the other day I thought you might have had the caster and camber specs mixed up,but when I went to work I checked the 1961 tru-way frame book,and sure enough the specs were close to yours. I would personally set the camber closer to 0* and the caster around 1* positive if possible.toe should be good at1/16 .I am sure those tires are quite a bit wider than the originals,and with 1 1/2* negative camber you will probably get serious inside tire wear.
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Old 10-07-2006, 07:39 PM
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Yup yup...

I agree with 39 Chevy, the caster should be closer to a degree or even 2 degrees (helps with straight-line stability, and that long wheelbase is'nt gonna corner fast like a sports car anyways), and with wider radials you will see inside shoulder wear increases with your neg camber as stock. Better to set it up with zero or even a hair positive. Tire wear is the ultimate judge, as mentioned previously.

Bias tires needed specs a little closer to neg when new, as bias tires don't 'turn in' at the start of a cornering maneuver as well as modern radials do. The radial with it's stiffer carcass transmits steering motions to the tread surface a lot more predictably. Also with the specs on the neg side when new, as the springs would wear in and sag, the camber would get closer to positive as the suspension drops...


Doc
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Old 10-08-2006, 12:37 PM
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Great information, thanks.

I'm set up with -1.5* caster, 0 camber, and 1/16" toe-in right now. Front end is entirely new, and it's disappointing how it drives (stops great with new discs though ).

What I am finding, is that on the highway, on a flat surface it feels straight, and I can go no handed, but feels like it's ready to start pulling to one side at any moment, and would continue to pull.

It is very very sensitive to road crown. I'm adjusted totally even left & right, so flat surface it drives straight. Add just a little crown in either direction, and I really have to compensate for it.

Little imperfections in the road feel like they are going to send me in a new direction.

I think I'm going to try the positive caster. I'm getting good feedback from a friend that went with +1.5* caster, 0 camber, & 0 toe. He has radials on the same chassis, but not as wide of tread.

My upper control arm shaft is kind of interesting. It is not pressed bushings. The bushings are steel and thread into the UCA with an unconventional thread, and they have threads on the inside where the shaft rotates on the threads, and they get greased. So, *if* I do not have enough room to shim the UCA, I can drop the spring, and spin the UCA shaft a couple times to move the upper ball joint rearward along the shaft. I can maybe get an 1/8" off this, which would maybe be 1.5* worth (I think), So I should be able to get to positive.

You guys think 1.5* positive should be my next stop?

Do you think the poor handling that I'm describing is from the neg caster?

Thanks, Scott.
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Old 10-08-2006, 03:45 PM
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Yes

You HAVE to have caster in the positive side of the range. Caster is what adds straight-line stability. Think of the caster wheel on a shopping cart, the pivot point is ahead of the actual tire's contact point, so the tire 'follows' the cart. With cars you have to dial in positive caster, so the upper balljoint is 'behind' the lower one, this puts the pivot point ahead of the contact patch when the tire is rolling, so the tire 'follows' along, If caster is negative it will be very twitchy rolling forward. It will feel a lot smoother backing the car up, because in Reverse, the caster being negative is 'correct' to add stability.

Doc
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Old 10-09-2006, 08:50 AM
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Quote:
Originally Posted by DrChop
You HAVE to have caster in the positive side of the range. Caster is what adds straight-line stability. Think of the caster wheel on a shopping cart, the pivot point is ahead of the actual tire's contact point, so the tire 'follows' the cart. With cars you have to dial in positive caster, so the upper balljoint is 'behind' the lower one, this puts the pivot point ahead of the contact patch when the tire is rolling, so the tire 'follows' along, If caster is negative it will be very twitchy rolling forward. It will feel a lot smoother backing the car up, because in Reverse, the caster being negative is 'correct' to add stability.

Doc
I'm officially about to say something that I'm unqualified to say....

I had read that some old cars have negative caster because the 'steering axis inclination' is big enough to keep forward stability.

My new wheels have the same offset that the original wheels had, so the center of the wheels are the same but they are a lot wider. That is before the adjustment from the disc brakes. I think the disc brake conversion pushed my wheel out about 3/8" which would have changed my scrub radius, which might have taken away my forward stability.

Regardless, I want to give + caster a whirl. Based on my shim table, I won't be able to get +1* caster with 0 camber. I am going to have to unload my suspension & move my UCA shaft. Ugh....
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