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Old 04-08-2003, 22:54   #1 (permalink)
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The best handling mod and help to understand wheel allignment jargon

Ok - just had my front wheel allignment changed to 4 degrees positive castor, 1 degree negative camber and about 1mm toe. Bob Jane said that sounded like a good idea, so they spent 2hrs alligning them and doing an on car balance on my farking stupid mags (can't balance them, except on car which costs $20 a wheel!!)

So I get her back, only to find out a front bearing is loose. So I go get that tightened and make sure the wheel goes on the same way to preserve the balance.

ANd now, she goes round corners like she is on rails! Its awesome how much grip she has. I recommend it to anyone who has had there car lowered and has a camber/castor kit installed.

Now I need help understanding some jargon:

1. What is Front setback?
2. What is S.A.I.and Included Angle?
3. Thrust angle? On the rear I think.
4. What is castor?

I know toe and camber. Not sure about the others.
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Old 04-08-2003, 23:45   #2 (permalink)
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Re: The best handling mod and help to understand wheel allignment jargon

Quote:
Originally posted by 94ED_Fairmont
...Now I need help understanding some jargon:

1. What is Front setback?
2. What is S.A.I.and Included Angle?
3. Thrust angle? On the rear I think.
4. What is castor?

I know toe and camber. Not sure about the others.
I'll have a guess but if anyone knows for sure please correct me.

1) Front setback - I reckon your RH front wheel is setback slightly further in the wheelwell than the left.

2) SAI - Steering Axis Inclination. This is the designed in offset between the upper and lower balljoints when viewed from straight ahead at zero camber. An imaginary line drawn between the balljoints should intersect the road close to the centre of the tyre. Included angle means the end result after camber is taken into consideration.
(Included Angle = SAI + Camber)
(eg IA = +6.30 = +7.30 -1.00)

3) Thrust angle - I think this is telling you that the rear axle isn't pushing 100% down the centreline of the car but is slightly offset. Note how the right rear has +ve toe and the left rear has -ve toe, this means the axle is slightly offset to the cars centreline.

4) Castor is the angle (compared to vertical) of another imaginary line drawn between the balljoints, this time viewed side on. The rear balljoint should be slightly behind (more rearward) the front balljoint. This helps the steering to return to centre after turning and provides a more stable straight ahead feel.

It's interesting that you have some negative camber on the rears with a live axle. Just like the V8Supercars!
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Old 04-09-2003, 00:16   #3 (permalink)
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Yeah whats the go with the negative camber on the rear?
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Old 04-09-2003, 03:47   #4 (permalink)
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Spot on Raptor. To add the Thrust Angle is the angle between the geometric centreline and the rear axle thrust line (diff centre line). If the thrust line deviates to the right of the vehicles as seen from the top the thrust angle is positive.
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Old 04-09-2003, 04:07   #5 (permalink)
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Quote:
Originally posted by 94ED_Fairmont
Yeah whats the go with the negative camber on the rear?
Live axles deflect or bend under the weight of the car. Don't worry it'll help the cornering. If it gets too bad the bearings will sieze.

Back when live axles where more commonplace racers would get a bend pressed into the housing for some extra neg camber on the rear. Modern V8 Supercars have CV joints fitted at the outer end of the axles and camber adjusting plates engineered in.

It's amazing what a difference a wheel alignment can make isn't it 94ED_Fairmont.
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Old 04-09-2003, 04:27   #6 (permalink)
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Yeah - it makes the car feel like new. I just wish it didn't cost $20 a wheel to get them flippin mags balanced.
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Old 04-09-2003, 07:51   #7 (permalink)
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how can they do an accurate wheel alignment with a loose bearing. They are supposed to check all that first. ?
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Old 04-09-2003, 14:42   #8 (permalink)
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Thats what I was thinking. I also found it rude that they take $75 off me for getting the allignment and oncar wheel balance, then tell my to stuff it all up getting my whel bearing adjusted.

3 weeks ago, I was in the shop getting my front wheels balanced again, because by mechanic serviced my car and machined my front rotors, which threw the balance out. I had to go back to Bob Jane and get it re balanced.

Two days later I warped my front left rotor by over heating it, and had to get the rotor taken off and machined it was that bad. Thus throwing out my allignment again.

So far I have weasted $200 on wheel alligments and balancing to end up with a car that will probably still shudder at high speed.

When I take the car to Denmac Ford to claim teh ABS fault on the last month of my warrenty, I bet you $200 that it will come back with a shudder in the steering becaust they took the wheels off and ****ed with the wheel allignment.

If I am lucky I may get a discount getting them done again...
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Old 04-09-2003, 15:48   #9 (permalink)
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They definitely should have checked the mechanicals of your front end before they adjusted anything.

Take a look here to answer all your questions :
http://www.familycar.com/alignment.htm

Rick.
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