Bump steer and roll center correction....

Suspension and other discussion

Bump steer and roll center correction....

Postby gtfour77 » Thu Oct 18, 2007 4:45 pm

I am currently working on a roll center adjusters, I will post pictures once it's done.
The next step is to correct bump steer via rods that will mount the outer tie rod end on the bottom of the steering knuckle mounting location instead of the stok top location... Does nayone know what size thread and pitch the stock tie rods have? I am getting ready to order a couple of these spherical bearing tie rod ends but wanted to confirm the thread size before I do so... I am guessing 14mm 1.5 pitch? Anyone know for sure? Here is what is needed.
http://www.pegasusautoracing.com/produc ... oduct=3067

Here is what it will look like...
http://members.cox.net/2bav8photo/granada05_baer.jpg

I will have more info after this weekend. There is an autocross I will be attending and I am planning on using at least the roll center adjusters...inless I come up with something that will allow me to mount the outer tie rod end on the bottom as a temp fix...
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Martin V.
Toyota Celica Alltrac 561 SM
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Postby CMS-GT4 » Thu Oct 18, 2007 6:05 pm

How does installing the rod below correct bump steer?

I think the polly tie rod ends alone will yeild better steering.

Also, not sure if your interested, but there is a guy with a st205 steering rack in the FS sextion. The rack is supposed to have a shorter lock to lock ratio. It might be idea to get the gear from the rack and use them in the 185. Maybe to add to your projects.
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Postby gtfour77 » Thu Oct 18, 2007 6:22 pm

Josh, mounting the outer tie rod end lower will improve bump steer on a lowered vehicle. If the rod end stays up high while the rest of body (including the steering rack) sits lower the angles are all off... the steering arms should be at the smae angle as the lower control arm for proper alignemt while under load and steering. If not moved o correct location ot will actually cause toe out on turns due to the steering knuckle moving upwards and tugging on the steering arm and not allowing it to stretch as much as it needs to. I know I am not really expaining this very clearly... :D

Here is a quote from http://www.mgf.ultimatemg.com/group2/su ... acking.htm

Cornering

When cornering, the wheels are being steered into the corner. The outside suspension is compressed, whilst the inside is decompressed. At the front wheels, this means that both the inside and outside wheel, through 'roll steer,' is turning out of the corner; the inside wheel is toe-in (opposite direction of steer) whilst the outside wheel is toe-out (opposite direction of steer). Thus the front geometry is promoting some degree of stabilising opposite 'wheel lock' in cornering (although let's not over emphasise this effect - the toe-angle change is very small in comparison to the steering angle).

Let meknow if any of this doesn't make sense...


Polly tie rod ends???? Can you elaborate?

Thanks for the st205 rack info, I'll look into it...
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Toyota MR2 Turbo 35 SSM
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Postby CMS-GT4 » Thu Oct 18, 2007 6:31 pm

Are the bearings in the pic you posted not polly?
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Postby gtfour77 » Thu Oct 18, 2007 6:49 pm

You mean polyurethane? If so then no, they are teflon lined spherical bearings... no give whatsoever... I am actually getting ready to do a full spherical bearing replacement of all poly and rubber joints on the celica over the winter...and correct the front and rear roll centers while upgrading to radius rods and spherical bearing joints especially in the rear.... I know it's a lot but hey, I have 5 months before the car needs to be back on the road...
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Postby CMS-GT4 » Thu Oct 18, 2007 6:55 pm

I meant teflon. Not sure what I was thinking.

I am real curious how your car turns out be next year. Post up some pics when you get a chance. Did you ever do the fenders?
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Postby gtfour77 » Thu Oct 18, 2007 7:02 pm

I will take pictures when I get to finish at least part of it... Like I said the roll center adjusters should be done by this weekend, I got one completed about 80%...it's tough to cut 1.5 thick aluminum without a band saw :doh: I bought a drill press so I just keep drilling and drilling for now... :D
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Postby ion_four » Thu Oct 18, 2007 8:40 pm

I hope you have good dental insurance...you'll probably lose some fillings after replacing all your bushings ;)

I haven't looked at my suspension in a couple weeks...could one just flip the stock tie-rod upside-down in order to correct bump steer?
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Postby RedCelicaTRD » Thu Oct 18, 2007 8:41 pm

Area RCA's legal in the SCCA? I might be a little bit behind but I thought you couldn't use them in the street classes.
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Postby ion_four » Thu Oct 18, 2007 9:16 pm

I'm pretty sure all suspension mods are legal, in SM, as long as they use the original body mounting points.

I think our local region has a "don't ask, don't tell policy" until someone raises a complaint, anyway ;)
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Postby gtfour77 » Thu Oct 18, 2007 9:59 pm

Haha, yes I work for the state so I do have a nice dental plan... :D But it should not be that bad at all, heck Mark Daddio has all spherical joints and he drives his car to every event... he drove to Topeka Kansas for the Nationals so it should not be that bad... As far as leagality, it is in fact leagal, like ion-four said as long original unmodified attachment points are used... Anything that moves vertically when cornering is a fair game... heck i could run custom spindles, a arms, struts...
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Postby CMS-GT4 » Thu Oct 18, 2007 10:04 pm

gtfour77 wrote:heck i could run custom spindles, a arms, struts...


Do it then. :D
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92 st185 (205 swap) | 03 350Z Track (sold) | 13 Pilot | 17 Mazda3
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Postby gtfour77 » Thu Oct 18, 2007 10:07 pm

Yeah right, not for now...that's getting a little deeper than necessary for now... :lol: Maybe some day when I am really really bored... heck one could do a custom conversion from nascar...they have some cool wheels with many widths available...heh
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Postby etantshi » Thu Oct 18, 2007 11:03 pm

You guys are really putting in work when it comes to these suspension mods. Hats off to all of you because I would be too lazy to do it. But when you do get it done I will def buy if there are made for others.
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Postby ion_four » Thu Oct 18, 2007 11:14 pm

A little research and some quality time on http://www.mcmaster.com can yield a lot of ideas, as far as custom spherical bearing suspensions and such ;)
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