Author Topic: Bending Steering Arms to Reduce Bump Steer.  (Read 18361 times)

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Duk

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Bending Steering Arms to Reduce Bump Steer.
« on: April 07, 2010, 03:36:11 PM »
I'm looking to bend the steering arms to reduce the bump steer characteristics of my 75. I have Pace Engineering knuckle risers, and these seem to exacerbate the already pretty ordinary bump steer of the Alfa.
Does anybody know what I should get done do the spindles after I've heated and bent the arms? Crack testing? Stress relieving (what form)? Shot peening?

MD

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Re: Bending Steering Arms to Reduce Bump Steer.
« Reply #1 on: April 07, 2010, 08:42:16 PM »
Hey Dukster,

Don't bend anything! Drop a solid connector from the spindle arm down to the balljoint in the tie rod long enough to ensure a parallel movement of the tie rods to the ground.You will have to make something up for it and I know you can do it.

Transaxle Alfas Haul More Arse.

Duk

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Re: Bending Steering Arms to Reduce Bump Steer.
« Reply #2 on: April 08, 2010, 08:46:06 AM »
Hey Mischievous D!
Yeah, I already thought of and discarded that approach because I couldn't find a spherical rod end with enough articulation. Even using a standard tie rod end and some form of spacer wouldn't work because of the angle the tie rod end boss (on the spindle) is at. At full droop, snap!
It's a shame, because R32 Skyline outer tie rod ends come very close to matching, but the tapered section is a touch large in diameter http://www.otomoto.com.au/kkr/alignment/index.html.

My coil over set up uses a lower shock mount similar to the RS suspension design, and it gives the suspension that extra 2(ish) inches of droop travel.

It was actually Vin Sharp who suggested I bend the steering arms. He said just heat and bend them slowly and cool them slowly. I did ask him about any additional treatments, but he has never bothered with them. I'm only asking if people have done post steering arm treatments just in case.

jimnielsen

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Re: Bending Steering Arms to Reduce Bump Steer.
« Reply #3 on: April 08, 2010, 09:27:23 AM »
Here is an example of the sort of thing that MD is talking about. This is on a Giulietta, using a standard 75 upright. I would have needed to bend the steering arms 6" to get the level I needed. So instead, I just used a 12mm grade 12 bolt of the correct length straight into the steering arm (welded in place), and a rod end with reasonable articulation on the steering arm. The thread on the bolt gives easy bump steer adjustment. I also used a brace from the upright to near the lower end of the bolt, but this probably wasn't really necessary. And if the bolt had only been (say) 4" would not have been needed.

jim.
'95 Alfa Romeo 155 Q4
'90 Alfa Romeo 33 1.7 IE - my god! I can compete in Trofeo class!! -

Duk

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Re: Bending Steering Arms to Reduce Bump Steer.
« Reply #4 on: April 08, 2010, 02:17:47 PM »
Cheers Jim, that's was the initial idea that I moved away from.
That is some nice suspension work. It must have a nice height roll center and camber curve. It always baffles me as to why Alfa Romeo did their design like they did. Probably to fit the outer ball joints inside 13/14" rims  ???

I forgot to mention that this is for a road car.

MD

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Re: Bending Steering Arms to Reduce Bump Steer.
« Reply #5 on: April 08, 2010, 05:48:12 PM »
That's the one Jim..
Transaxle Alfas Haul More Arse.

Duk

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Re: Bending Steering Arms to Reduce Bump Steer.
« Reply #6 on: April 08, 2010, 07:09:06 PM »
1 additional advantage is a slight shortening of the steering arm and a slight increase in steering rate  ;D.

Eddy Bidese

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Re: Bending Steering Arms to Reduce Bump Steer.
« Reply #7 on: April 08, 2010, 08:55:28 PM »
Hi Guys. I went down the route of bending the arms on my GTV6. Cooling slowly as Vin says is important...meaning air cool, do not quench in oil or water. I welded up a jig to bolt to the upright to ensure I did both sides identically, and didn't unintentionally alter any other angles in the process. The limitaion, in a standard chassis, as to  how far you can lower the arm, is contact between the chassis and the steering link on full droop, I lowered about 40mm and no noticeable bump steer. The car is road registered and used for Road Rally and Club sprints and has done 2-3000Kms with no problem to date. Cheers.  Eddy

Duk

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Re: Bending Steering Arms to Reduce Bump Steer.
« Reply #8 on: April 09, 2010, 08:18:25 AM »
Cheers Eddy  8)
Are you using any method of improving the roll center and camber curve? You could really see the toe angle change with the knuckle risers when you worked the suspension thought it's travel.

Eddy Bidese

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Re: Bending Steering Arms to Reduce Bump Steer.
« Reply #9 on: April 09, 2010, 05:59:48 PM »
Other changes include lenghtening the uprights below the axle line and using long shanked upper ball joint ( in lieu of knuckle riser). All designed to fit within 15 in rims. As I am now using 16's to take larger brakes , both could be extended.
The front roll centre is still not high enough and would benefit from an extra 20mm extension of the top pivot point.
The comment on little or no bump steer is based on driving observation rather than speific measurement of the toe angle during suspension travel. However as the steering link is nearly horizontal in the rest position, geometrically I would not expect any significant toe change. Good luck.  Eddy

scott.venables

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Re: Bending Steering Arms to Reduce Bump Steer.
« Reply #10 on: April 09, 2010, 06:54:33 PM »
Eddy, where did you get the long shank upper ball joints?

Cheers, Scott

Eddy Bidese

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Re: Bending Steering Arms to Reduce Bump Steer.
« Reply #11 on: April 09, 2010, 09:30:29 PM »
Not sure Scott , They were in the car when I bought it From Tony Hawker about 4 years ago. As far as I know Hugh Harrison has done most of the work on it.

MD

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Re: Bending Steering Arms to Reduce Bump Steer.
« Reply #12 on: April 09, 2010, 09:35:30 PM »
I believe Vin Sharp has them
Transaxle Alfas Haul More Arse.

oz3litre

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Re: Bending Steering Arms to Reduce Bump Steer.
« Reply #13 on: August 22, 2010, 04:26:24 AM »
I'm looking to bend the steering arms to reduce the bump steer characteristics of my 75. I have Pace Engineering knuckle risers, and these seem to exacerbate the already pretty ordinary bump steer of the Alfa.
Does anybody know what I should get done do the spindles after I've heated and bent the arms? Crack testing? Stress relieving (what form)? Shot peening?
I have three 3 litre 75s, including two Potenziatas and have never detected any bump steer in any of them. They track through bumps just fine. In all my years of reading the AlfaBB I have never heard anyone mention it there either. What do you call bump steer?
2008 159 TI 2.4 JTDM Sportwagon. Stromboli Grey. Wife's daily driver.
2004 GT 3.2 V6, Stromboli Grey. My daily driver.
1989 75 3 litre, black.
1988 75 3 litre V6. Red. Son's daily driver.
2000 156 Twinspark manual. Cosmo Blue. Daughter's daily driver.

Duk

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Re: Bending Steering Arms to Reduce Bump Steer.
« Reply #14 on: August 22, 2010, 12:45:55 PM »
I'm looking to bend the steering arms to reduce the bump steer characteristics of my 75. I have Pace Engineering knuckle risers, and these seem to exacerbate the already pretty ordinary bump steer of the Alfa.
Does anybody know what I should get done do the spindles after I've heated and bent the arms? Crack testing? Stress relieving (what form)? Shot peening?
I have three 3 litre 75s, including two Potenziatas and have never detected any bump steer in any of them. They track through bumps just fine. In all my years of reading the AlfaBB I have never heard anyone mention it there either. What do you call bump steer?

Take a torsion bar out and work the suspension thru its travel, you will see bump steer. Then fit a set of Vince's knuckle risers (I should probably be referring to them as long shank upper ball joints tho  :)) and do the same test. Bump steer is worse again.
Where bump steer correction can be a real plus is when the car suffers from 'bump understeer'. As the suspension is compressed the wheels toe out. So when the outside front suspension is compressed during a turn, the wheel straightens to a degree. This means you have to turn the steering wheel more and gives the feeling of even slower steering. http://www.youtube.com/watch?v=LO07qmJ9zkk