Steering rack mods

Norm Peterson

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I have heard that the oem ford toe alignment was toed slightly inwards...to reduce tramlining. Then I hear that drag racers want the toe set to zero. Then the track folks sometimes set the toe slightly outwards. What's optimum for various applications ? Right now I'm toed slightly outwards..along with aprx -1.7 deg of camber on both fronts. What's worse for tire wear? I'm lost with all the conflicting info.
Toe in is more to eliminate twitchiness. Tramlining is a different phenomenon.

At -1.7° you could even run minimal toe in without sacrificing much peak lateral grip.

Zero toe on the machine could end up either 'in' or 'out' in operation depending on bushing compliances (how much and where).


Norm
 

buster

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Check your alignment, specifically toe.

Ok will do. Ive been meaning to do it for a while. Ive just changed a shit load of suspension ( well all of it apart from roll bars) so it's bound to need doing.
It was just as twitchy before I swapped out the suspension though.
 

Dreadknought

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Good refresher on the toe settings. It had been a minute since thought about it. As far as my particular needs, I'm currently running a 275 square set up and will be moving to a 305 or 315 square. I'm on MM caster camber plates running approx -1.5 camber and maxed out castor. Something like -7 to 8 degrees. May have the (neg) part backward. A while back I found a shop in the Dallas Texas area that rebuilds ford steering racks for performance applications, but I have not been able to find them recently.

I'll have my old rack rebuilt, and see about their opinion as to the scale of the torsion bar mod and potentially a quicker ratio.
 

SoundGuyDave

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To add to what Kerry said, IN GENERAL toe-in helps with stability, but toe-out helps with turn-in... The drag guys usually go zero toe strictly to minimize rolling resistance. I run factory toe-in on my daily driver, but the race car? 1/8" toe-out with -2.75* camber. Turns in nicely, with only a hint of instability at braking threshold.
 

01yellerCobra

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Good to know. I always thought the toe in was to help take up the slack of the bushings when the car started moving forward. So essentially when the car is moving it's at zero toe. Made me wonder if set ups running parts with less deflection (poly bushings, bump steer kit, etc) would be better off running less toe.
 
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Norm Peterson

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Good to know. I always thought the toe in waa to help take up the slack of the bushings when the car started moving forward. So essentially when the car is moving it's at zero toe. Made me wonder if set ups running parts with less deflection (poly bushings, bump steer kit, etc) would be better off running less toe.
You could run less because of the poly bushings, but I don't think the bumpsteer kit would be any reason (if anything, the greater distance between the pivot ball and the steering arm would suggest that a tiny bit more deflection would exist, for which you'd set a tiny bit more toe-in).


Norm
 

kerrynzl

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Good to know. I always thought the toe in was to help take up the slack of the bushings when the car started moving forward. So essentially when the car is moving it's at zero toe. Made me wonder if set ups running parts with less deflection (poly bushings, bump steer kit, etc) would be better off running less toe.

Scrub Radius and Backspacing is the best way to control any slack in any bushings. A wheel with a small scrub radius and a lot of back spacing will have drag on the inside [and want to toe-in]

When you increase the overall wheel diameter the scrub radius will get smaller and sometimes become negative scrub radius. This sometimes requires more negative offset to counteract increased drag on the inside.
 

Norm Peterson

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Norm, what is your toe + camber set at ?
-1.9°-ish camber, small amount of toe-in (don't remember the exact value any more).

Camber is not too much for my street driving, not quite enough for the track time. Definitely not enough to ride the inside curb through T10 at NJMP/Thunderbolt (a 55-ish mph 180° left) because the curb's height takes a degree or more out of what the right front tire actually runs at through there.


Norm
 

Sky Render

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Scrub Radius and Backspacing is the best way to control any slack in any bushings. A wheel with a small scrub radius and a lot of back spacing will have drag on the inside [and want to toe-in]

When you increase the overall wheel diameter the scrub radius will get smaller and sometimes become negative scrub radius. This sometimes requires more negative offset to counteract increased drag on the inside.

Scrub radius changes with tire width and wheel offset/backspacing, not wheel diameter.

http://www.motoiq.com/MagazineArtic...ur-Caster-King-Pin-Inclination-and-Scrub.aspx
 

kerrynzl

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I suspect that 'tire diameter' was intended, else "overall" is redundant.


Norm

Correct!
Whenever we do calculations we always refer to the overall measurement of the wheels [being a tyre and rim combo]

Scrub radius is the major cause of "death wobble" on old Ford Hotrods. The first thing they do is put smaller diameter and wider wheels on the car.[with the same percentage offset]

By doing that they increase the scrub radius [all it takes is one bump to start the death wobble]
 

kerrynzl

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↑↑↑ so what you're telling me is that "bigs 'n' littles" on hotrods wasn't just for appearance sake. Never knew that.


Norm

No..... What I'm really saying is some people should never touch cars [with tools] 90% of their improvements are usually a step backwards.

On the subject of "death wobble" ,the standard knee-jerk fix is to add more +caster.
But because these Rat-mobiles are lightweight ,the caster will try to lift the vehicle instead of self aligning the steering.
This causes the cross-leaf shackles to try and correct the height difference by shifting the axle sideways [making it worse]
Then to aggravate the situation, a lot of hotrodders will split the "A" frame wishbone and use them as parallel 2-links
During death wobble these links will parallelogram themselves because there is no lateral control.
 

syberspace

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You might consider the FR500S rack. Kohr Motorsports is selling them for $450. Supposed to give better feedback due to less assist and different ratio. I just ordered one.
 

Speedboosted

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You might consider the FR500S rack. Kohr Motorsports is selling them for $450. Supposed to give better feedback due to less assist and different ratio. I just ordered one.

One place I read that the ratio is different, but another place I read listed them as the same ratio. I guess I need to email Dean directly and ask.
 

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