Steering Rack Ratios

Lynn · 11-28-04, 09:42 AM

All,

The post about power steering in the "All" section got me to thinking (I know, uh-ohhh.) I am not sure this has been discussed in a while (if at all) and would be something a new builder would be very interested in, I would think.

When I was selecting components, there were two ratios available with the Flaming River Mutang II style racks. I chose to go with the standard ratio rather than the "quick" ratio. My reasoning was that I thought the quick ratio would make the car to twitchy in addition to making the steering a little heavier.

The standard Mustang II rack is 4.15 turns lock-to-lock and the quick rack is 3.75. I am curious what others rack ratios are being used with other racks?

Lynn

Phil · 11-28-04, 12:53 PM

Lynn
I have used the Pinto rack, the ratio is close to the 3.75 rack you mentioned, the only problem being that it is approx .100 shorter in width, easily fixed with a shim on one end. Also, the Pinto rack mounts vertically with a clamp in one end, and two bolts in the geared side, this is especially helpful when trying to resolve bump-steer, the Mustang rack is more difficult to move because of the mounting arrangement. Flaming River also sells new Pinto racks.
Phil

Ross Nicol · 11-29-04, 08:00 AM

Lynn I've spent some time on this one. I was going to use a quick rack but found the Ford Escort unit I bought wasn't the same as what's in the RF, which turns out to be a cortina unit.I kept the original rack with a 13" wheel and it's not easy to determine the ratio as with wide slick tyres on I've had to limit turn to turn lock.However I found I could almost leave my hands at 10 & 2 oclock when taking sharp corners on the track.The only thing that has bugged me for over a year now is the heavy steering as the corner loads the steering.Before the last race meeting I adjusted the castor back from 5.75 degrees to 4.5 degrees and the steering heaviness has gone.The car turns into a corner beautifully and is light.My opinion is power steering shouldn't be required in these cars.After all the motors in the back.
Ross

Gary Gibbs · 11-29-04, 08:22 AM

I think the factor one should look at is the overall steering ratio (steering wheel to tire rotation). This will take into account variables like the length of the tie rod end attachment from the ball joint pivot axis. Otherwise one is just looking at a piece of the pie.

Keith Hardy · 11-29-04, 10:45 AM

Phil, I just wonder how it now handles on the straight? I had a similar problem with the Penske Camaro and when I reduced castor to aid turn in, it worked a treat but became a handful on the straight especially on bumpy tracks where it tended to follow every line and groove in the asphalt. Found I couldn't roll a fag on the Hangar straight at Silverstone any more, and I missed my nap as well. Bugger! [img]/ubbthreads/images/graemlins/crazy.gif[/img]

Keith Hardy · 11-29-04, 10:50 AM

PS Penske IROC Camaro "resting" at Goodwood together with Trans Am.

Keith Hardy · 11-29-04, 03:18 PM

I meant Ross of course, silly me. [img]/ubbthreads/images/graemlins/crazy.gif[/img]

Ross Nicol · 11-30-04, 06:50 AM

Ken oh sorry Keith (only joking)straight line stability is
fine on my car.Maybe you took the castor back too far on the Camaro."Most racing cars are designed with between 2.5 and 4.5 degrees of positive castor" Carroll Smith (prepare to win)Mine is set to 4.5 degrees.
Ross

Keith Hardy · 11-30-04, 08:12 AM

Russ, (stop it [img]/ubbthreads/images/graemlins/mad.gif[/img] ) You may be right, I believe the castor came in at a shade over 2 1/2 degrees, but before, it was well over 5!! (previous owner who sold it to me cheap said "it wouldn't go around corners") heh heh. [img]/ubbthreads/images/graemlins/wink.gif[/img]

Kalun D · 11-30-04, 12:36 PM

FWIW

I had a pinto rack in my Cobra with about 4 turns and it seemed way too slow to me. The steering was easy but cumbersome especially in parking situations.

Running a 240Z rack in my GT40, it's 2.1 turns. 3 degrees caster.

Craig White · 12-01-04, 02:04 AM

Most, if not all, right-hand drive GT40 Australia cars, including mine, use local Holden Torana LH/LX model steering racks. These are also popular fitment to local Cobra replicas.

Seem to work well and have a 3.75 turns lock-to-lock.

My GT40 runs 4 degrees caster LH, 3degrees40 RH.

Ross Nicol · 12-01-04, 03:20 AM

Craig Might be a good idea to get castor even on both sides.Heres another quote from the great man Carroll Smith"Getting the castor even from left to right is more important than getting it exact" (prepare to win).

Lynn · 12-01-04, 05:57 PM

Here are the alignment specs for the Sabre:

WHEELBASE 95”

FRONT
Camber.........½ deg neg.
Castor..........4 deg pos.
Toe-in..........1/8” (30 min) in.

REAR
Castor..........0 deg
Camber.........¾ deg neg.
Toe-in..........1/16” in each side. (Total 1/8”)

Whatchathank?

Lynn

Craig White · 12-01-04, 06:31 PM

[ QUOTE ]
Craig Might be a good idea to get castor even on both sides...

[/ QUOTE ]

Ross, yeah, it's on my list of things to look into.

Craig White · 12-01-04, 06:45 PM

Lynn, this is what my GT40 Australia(DRB) was set up for originally.

Here are the alignment specs for the DRB:

WHEELBASE 95.3”

FRONT
Camber......... LH -1.22, RH -1.30 deg.
Castor..........LH 4.0, RH 3.40 deg.
Toe-in..........LH 1.1, RH 1.1 (total 2.2) mm.

REAR
Castor..........0 deg
Camber.........LH -1.03, RH -1.01 deg.
Toe-in..........LH 1.5, RH 1.5 (total 3) mm.

Chassis to floor - front 115/115mm, rear 135/135mm
Corner weight total 1148kg, front 43.1%, rear 56.9%