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  '88 GT Castor: How much is possible and how much advisable????

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'88 GT Castor: How much is possible and how much advisable???? by imacflier
Started on: 07-14-2020 06:21 PM
Replies: 10 (188 views)
Last post by: Rickady88GT on 07-16-2020 12:03 PM
imacflier
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Report this Post07-14-2020 06:21 PM Click Here to See the Profile for imacflierClick Here to Email imacflierSend a Private Message to imacflierEdit/Delete MessageReply w/QuoteDirect Link to This Post
G'Evening, All,

Well for todays dive into odd tech let's consider caster settings with fast ratio power steering!

I am installing hydraulic power steering using an MR2 Spyder Electric Pump and a fast ratio Camaro rack and pinion....I may be using a steering quickener to get it down to two turns lock to lock.

From research on the Forum, it seems the "correct" castor is 5*. With a fast ratio self-centering is reduced. What happens as castor is increased over "correct"?

So: what do y'all suggest I use for a castor setting. How much castor is even possible?

At two turns lock to lock, manually returning to center doesn't sound like it would be much trouble....but I would love to hear what you think....and mebbe have even tried!

As always,

TIA for your opinions and discussion,

Larry
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Raydar
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Report this Post07-14-2020 06:39 PM Click Here to See the Profile for RaydarClick Here to Email RaydarSend a Private Message to RaydarEdit/Delete MessageReply w/QuoteDirect Link to This Post
This is gonna be interesting. I have a T/A WS6 rack that is - at some point - going into my 88 coupe.
I'll be watching.
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fieroguru
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Report this Post07-14-2020 07:46 PM Click Here to See the Profile for fieroguruSend a Private Message to fieroguruEdit/Delete MessageReply w/QuoteDirect Link to This Post
I elongated the adjustment slots in the upper a-arm and have the caster set to about 7 degrees. No power steering yet.
I had a 2.0 lock to lock in my C4 vette back in the day and really liked it.
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pmbrunelle
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Report this Post07-14-2020 08:00 PM Click Here to See the Profile for pmbrunelleClick Here to Email pmbrunelleSend a Private Message to pmbrunelleEdit/Delete MessageReply w/QuoteDirect Link to This Post
The more caster you have, the greater the distance between the contact patch and the steering axis.

Therefore, cornering force from the road has more leverage on the steering knuckle, and more cornering force is transmitted to the tie-rods, and ultimately the steering wheel.

This can be considered the "good" kind of information to convey to the driver. For instance, if you turn the steering wheel, but the torque felt stops increasing, that means you're plowing the front end.

Torque transmitted to the steering wheel that is unrelated to cornering force can be considered "noise" that is unhelpful to the driver, so by increasing the amount of good information, you drown out the undesirable information.

It is possible to increase the required steering effort such that the vehicle is unsafe to drive without the power steering. I suggest you do some test drives with the power steering disabled to make sure that you can still control the car in case of failure. Having a passenger cut out the assist mid-corner without telling you would be a worst-case test.

I think that with a lot of caster (sorry, I don't have a number), the camber would change as you approach full lock. I don't know if this could cause a bizarre difference in behaviour between high speed and low speed corners.

Mercedes cars have a lot of caster:
https://www.driving.co.uk/s...ongest-car-drift.jpg

Also, note that there's a difference between having the wheels self-center with respect to the chassis, vs. align themselves with the vehicle's direction of travel. In a drift, the chassis is not aligned with the direction of travel.

[This message has been edited by pmbrunelle (edited 07-14-2020).]

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Rickady88GT
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Report this Post07-14-2020 08:19 PM Click Here to See the Profile for Rickady88GTClick Here to Email Rickady88GTSend a Private Message to Rickady88GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
The alignment shops have specs for a power steering Fiero. Try it first and see what you think.
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imacflier
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Report this Post07-14-2020 08:34 PM Click Here to See the Profile for imacflierClick Here to Email imacflierSend a Private Message to imacflierEdit/Delete MessageReply w/QuoteDirect Link to This Post
Thanks, guys,

LOTS of good input and ideas....I especially like testing with a passenger turning on/off the power.

Also the potential for change in camber with increasing castor.

Lots and lots to think about and probably to test.

Warm regards to all, and,

Thanks again!

Larry
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Blacktree
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Report this Post07-14-2020 09:31 PM Click Here to See the Profile for BlacktreeClick Here to visit Blacktree's HomePageClick Here to Email BlacktreeSend a Private Message to BlacktreeEdit/Delete MessageReply w/QuoteDirect Link to This Post
IMO, the sweet spot for caster in a Fiero is 5-7 degrees. Less than 5 degrees will make the steering twitchy. More than 7 will give excessive steering feedback. Of course, personal preference factors in.
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Zac88GT
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Report this Post07-14-2020 10:35 PM Click Here to See the Profile for Zac88GTClick Here to visit Zac88GT's HomePageClick Here to Email Zac88GTSend a Private Message to Zac88GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
I had the ws6 fbody rack in my 88 and had the caster maxed out at ~9.5. The steering feel was great.
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Will
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Report this Post07-16-2020 10:16 AM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post
"Caster induced camber gain" is a thing as long as your caster is greater than your kingpin inclination... which I *think* is 5.5 degrees for an '88. That gives you greater camber--and theoretically greater grip--at low speed high steering angle turns.
When I turn the wheel and dump the clutch, my Formula has the tendency to unload the front and plow... not sure if extra caster/camber will help with that or not.

Steven Snyder has converted to power steering and fully adjustable upper control arms. He's running 12 degrees and said it gives great grip and feel, but the outer tie rod end is high enough relative to design that it's giving some bump steer problems.

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Will
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Report this Post07-16-2020 10:18 AM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post

Will

13353 posts
Member since Jun 2000
 
quote
Originally posted by pmbrunelle:

The more caster you have, the greater the distance between the contact patch and the steering axis.


*Longitudinal* distance... the lateral distance is scrub radius. The longitudinal component is called caster trail.


 
quote
Originally posted by pmbrunelle:
I think that with a lot of caster (sorry, I don't have a number), the camber would change as you approach full lock. I don't know if this could cause a bizarre difference in behaviour between high speed and low speed corners.

Mercedes cars have a lot of caster:
https://www.driving.co.uk/s...ongest-car-drift.jpg

Also, note that there's a difference between having the wheels self-center with respect to the chassis, vs. align themselves with the vehicle's direction of travel. In a drift, the chassis is not aligned with the direction of travel.



That's not a lot of caster... that's pretty normal across the industry for a RWD car. FWD cars have different needs.
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Rickady88GT
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Report this Post07-16-2020 12:03 PM Click Here to See the Profile for Rickady88GTClick Here to Email Rickady88GTSend a Private Message to Rickady88GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Will:

Steven Snyder has converted to power steering and fully adjustable upper control arms. He's running 12 degrees and said it gives great grip and feel, but the outer tie rod end is high enough relative to design that it's giving some bump steer problems.


Steven took me around Buttonwillow raceway few couple laps. A lot of fun.
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