R&P 15:1 or 20:1 question

[Russ T Nut]

I'm ordering a front clip for my 56 Nomad and have a choice of steering ratios. The rack is a AGR power rack and I will be switching to a smaller dia. steering wheel. I have no idea which ratio would work best. 15:1 is advertised as high preformance, while 20:1 is for touring comfort. My car is to be used as an all around driver with some long road trips (if gas prices permit).
If you have real world experience with either ratio please give me your opinions.
Thanks
Russ

[J&Jhotrods]

Your steering will have a more modern car feel with the 15:1 ratio. I would only go with the 20:1 if it doesn't have power steering. You'll practically have to turn the steering wheel 1/2-3/4 turn just to make a right or left turn at an intersection, whereas the quicker ratio will be like a quarter turn. Not sure whether your motor will be stock or not, but If you like stabbing the go-pedal and getting sideways every now and again to get your heart pumping, but that is where you'll really notice the benefits of 15:1 steering. With 20:1 you'll feel like your swatting flies!:D:D
Jay.

[Russ T Nut]

Thanks Jay. I have no experience with either, my thoughts are I don't what to be heading down the hwy with 15:1 steering and blink and run off the road, nor do I want to be in town with 20:1 and take 3 turns of the wheel to pull into a parking space. As for power Im running a BB and I do like to get on it once in awhile. I think I'll opt for the 15:1 and give it a try.
Thanks for your insight.
Russ

[Chevynut]

Just for reference, if you've ever had the chance to drive a C4 Corvette the ratio of the later ones (88-96) was 13:1 or 15.7:1. Lock to lock turns was 1.96 or 2.36. The earlier C4's had 13.0:1 or 15.1:1 and 1.96 or 2.36 turns respectively. I think the difference in ratios from early to late was due to the slight difference in length of the steering arms.

I learned some time ago what "steering ratio" really means. I thought it was the ratio of the turns of the steering wheel versus the number of turns of the pitman arm shaft when using a conventional steering box, but that's not true. Steering ratio is the ratio between the turn of the steering wheel (in degrees) and the turn of the wheels (in degrees). So you can't specify steering ratio for a rack alone, without the other steering components. ;)

[Russ T Nut]

Thanks Cnut. I owned a 87 Corvette and was impressed with the steering response, but I never knew what the ratio was. With this info I now feel comfortable ordering the 15:1.
Russ

[Chevynut]

Russ, keep in mind also that with the longer wheelbase of the tri-5 the ratio won't feel as quick as with the C4. So your choice of the 15:1 ratio is probably the best one.

[J&Jhotrods]

I have had a good understanding of what steering ratio was for some time, but understanding what the effects the steering ratio has in conjunction with the rest of the steering system has finally sunk in-in a way that has helped me more thoroughly understand front end geometry and other suspension angles(anti-dive, anti-squat, camber curves, etc...). I've been aligning both production and race vehicles for about 20 years now, and have 6 years working on a circle track touring team, which is really what helped me understand how changes to steering and suspension affect vehicle handling. When measuring caster on an alignment machine(or hand held gauge), the wheels must be turned in and out 20 degrees for an accurate measurement. You can see the difference of steering ratio on different vehicles(stock 57 chevy or 90 corvette, just for example) by how far the steering wheel has to turn to reach 20 degrees at the wheel. Old car-half turn of strg. wheel. Newer perf. vehicle-less than 1/4 turn. I don't know if I'm adding more confusion as I'm just scratching the surface of the steering/suspension topic. Keep in mind that there is a direct correlation (when making changes to the steering/suspension system)between the caster angle and steering ratio. By just changing the strg. ratio alone to a quicker ratio, you might notice that the steering will be"twitchy"(for lack of better words) because it requires less input at the strg. wheel for turning angle and not want to return to center as easy as it did before,because now you've increased the turning input. By adding caster, it takes more effort to turn the wheels(from center) and thereby enhancing the added quicker ratio. I wish it was as easy as adding shims at the upper a-arm and you're good to go, but it requires several degrees more caster to achieve the desired effect. My personal opinion is to add the global west offset upper a-arms to your gearbox grocery list. They have(I believe) 5 or 6 degrees of added caster which should work quite nicely with the quick ratio gearbox. I am unsure what the stock box ratio is, I know it's no less than 20:1. I think it might actually be around 22-25:1(but don't quote me on that:D), so if you're only wanting to change the gearbox, even the 20:1 might be a good choice. I'll look in my factory manuals to verify the stock steering ratio tonight and get back to you.
Jay.

[Chevynut]

By just changing the strg. ratio alone to a quicker ratio, you might notice that the steering will be"twitchy"(for lack of better words) because it requires less input at the strg. wheel for turning angle and not want to return to center as easy as it did before,because now you've increased the turning input.

I think just the opposite would happen. With a given caster, there is a fixed amount of force trying to keep the wheels centered. A low numerical ratio steering box (i.e. 15:1) takes MORE effort to turn one degree than a high numerical ratio box (i.e. 20:1) with the same load on the wheels. The wheels turn FASTER with the 15:1 but the force is higher too. So it seems like it would want to center better with the 15:1 than the 20:1 ratio.

Is my thinking off? :D

By adding caster, it takes more effort to turn the wheels(from center) and thereby enhancing the added quicker ratio. ...... They have(I believe) 5 or 6 degrees of added caster which should work quite nicely with the quick ratio gearbox.

The C4 corvette front end has 6 degrees of caster.;)

[J&Jhotrods]

What I mean by "twitchy", is that, say you're driving along, and you go to avoid a pothole in the road, at highway speeds for example, with the increased turning angle of a quick(er) ratio gearbox, and caster staying at factory specs(somewhere around 0 degrees+ or- 1.00 degree), the steering won't want to come back to center as easily, making you feel like the car is now "darting" or "wandering" by barely turning the steering wheel. By increasing the caster, you'll now have that "feel of the road" that today's cars have. B.t.w., a newer dodge magnum came into the shop recently. Caster specs. are 11.00 degrees!:eek: Judging by how little I had to turn the steering wheel(less than 1/4 turn) to get the wheels to 20 degrees turning angle for the measurement, I'm guessing the ratio is around 12:1. I guess the moral of the story is, it wouldn't hurt to increase the caster angle as you increase(numerically lower) the steering gearbox ratio to achieve optimum road feel.

[J&Jhotrods]

A low numerical ratio steering box (i.e. 15:1) takes MORE effort to turn one degree than a high numerical ratio box (i.e. 20:1) with the same load on the wheels. The wheels turn FASTER with the 15:1 but the force is higher too..
CHevynut, it's caster that makes the effort more or less. More caster-more effort. Take a stock 57chevy resting on the ground with no tie rods hooked up and turn the wheel/tire by hand-it turns easy. Think of a shopping cart wheel-0 caster. It doesn't know which way to turn, flopping around even though you're forcing it in a certain direction. Now think of a chopper motorcycle with lots of rake and a stretched front end(LOTS of caster). If you've ever ridden one, when you get up to speed, you find yourself leaning to turn because of the force required to turn the handle bars is more difficult. It's confusing because sitting still the chopper front end wants to do anything but stay straight. Remember, caster angle is an imaginary line drawn from the top ball joint to the bottom ball joint, and measured from true vertical.
Jay.

[Chevynut]

.
CHevynut, it's caster that makes the effort more or less. More caster-more effort.

I agree that increased caster causes more turning effort. But there is a certain amount of effort required to turn the wheel at a fixed caster. That amount of effort is INCREASED by changing the streering ratio from 20:1 to 15:1. You have more leverage on the tire with the 20:1 ratio because the tire doesn't turn as far for a given rotation of the steering wheel. However, the 15:1 will increase the amount the wheels turn for a given rotation of the steering wheel.

Said another way, you have to apply more force at the steering wheel with the 15:1 to turn the tire 5 degrees than you would with the 20:1 ratio. But you don't have to turn the 15:1 as far to get 5 degrees of tire movement.

A higher numerical ratio provides more leverage to turn the wheels. ;)

[J&Jhotrods]

You are correct. It does require more effort at the steering wheel. That's why the quicker ratio is usually accompanied with power assist, unless you've got forearms like popeye!:D I might not be able to explain things very well sometimes, and I was worried I was going to stir up a bees' nest with this one. Knowing what you're doing and being able to explain it in a way that people can understand are two different things. I thank my dad for that, as he was a G.M. training instructor and he had a very unique way of breaking things down to their simplest elements so everybody understood what he was teaching. I struggle with it sometimes as I have to explain things to my customers about the problems with their vehicles and why it drives the way it drives, etc... How far away are you from being done with your wagon? I'll bet that C4 suspension is going to work very nicely for you. Can't wait to see it completed!
Jay

[Rick_L]

Caster adds stability to the steering. It tends to keep the car going in a straight line without wandering, and when you turn and release the wheel it tends to return the steering to center.

Caster also does this when you hit a bump, the road surface has caused a change in steering angle, and caster returns the steering to center. Here though the car may have a new direction of travel, so it's up to you to steer the car back in the intended direction.

When a car's suspension hits a bump and steers itself due to suspension travel (not due to the bump or pothole actually turning the tire) - that's "bump steer" and it is not a function of caster, or helped by extra caster, it's a function of toe-in (or out). This is caused by the steering tie rod not moving through the same arc as the lower control arm, and it is a huge problem with many rack and pinion installations.

[J&Jhotrods]

Speaking of bumpsteer, I have been giving this alot of thought in regards to what rack I will be using. My initial thought was to find a rack where the distance from one inner tie rod ball socket to ball socket would be equal to the length of the original steering's inner tie rod to inner tie rod pivot points. But, without actually measuring the bumpsteer on the stock steering linkage, I can guarantee that the factory steering linkage would have around 1/2 an inch of bumpsteer throughout it's suspension travel. I doubt there is a production car out there(even some newer sports cars) with less than a 3/8ths inch of bumpsteer. It's all a compromise to pass N.V.H. standards. In a perfect world, there is a steering rack out there for these cars where the tie rods travel in the same arc as the lower control arms and believe me, I'm searching(every time I'm under a newer car/truck setting the toe for alignments, I'm measuring these dimensions)! It's not a race car, so there really is no need to get down to "zero" bumpsteer. Something around 1/4 to 3/8ths is acceptable IMO. I just want to make sure I have not compromised turning angle and minimized bumpsteer enough before I plunk down the bucks on a rack conversion kit, which seems to be alot of the complaints from guys who have purchased these kits. Good input everyone! I think it's a topic worth discussing so we all can have a tri five that drives as good as it should!
Jay

[Russ T Nut]

Wow, alot of good info, much of it is over my head, but I do appreciate the input. Jay, Art Morrison advertises that they have designed their front IFS with the AGR rack and pinion to have no bumpsteer. The AGR r&p is a front mount that is a design take off of the old SCCA race design. This all sounds impressive ,but should I read into this that it does have bumpsteer but not as much as stock steering. It sounds like you do alignment work and you've researched the subject so do you think someone can design the geomerty to eliminate bumpsteer.
Thanks
Russ

[Rick_L]

"It's all a compromise to pass N.V.H. standards."

Tell me how having zero bump steer or close to it compromises NVH. I don't see a correlation. Or how having good NVH means you have bump steer.

NVH standards are arbitrary anyway aren't they?

When you say 1/2" of bump steer what do you mean? What are you measuring? Are you saying that the wheels toe in or out 1/2"? I haven't measured it but I don't think the 55-57 stock geometry is all that bad for bump steer. Have you measured a stock front end?

[J&Jhotrods]

I was just saying that overall ride quality is more of a concern to the auto manufacturers than having "close to zero bumpsteer". And, Rick, I meant to say 1/2 inch of toe change. The manufacturers built passenger cars to ride good and comfy, not so much being concerned about optimal handling abilities. It used to be that if you built a car to handle and corner good, chances are it is going to suffer in the comfort department. Luckily, we are living in a time where we can almost have our cake and eat it too, with all of the advancements in the aftermarket. Maybe the aftermarket chassis manufacturers could divulge some info on this, but if they were to share their secrets with us they may not sell as many chassis because we'll be building them ourselves! No, I have not measured the bumpsteer on a stock tri-five, but to satisfy my curiosity, and if I can borrow someones bumpsteer gauge, I plan on measuring it before and after the rack and pinion install and will post the results. Be patient though, because I'm starting at the rear of the chassis with the spring relocation, etc...
And Russ, I'm pretty sure you'll be happy with that Morrison Chassis, I think you definitely be having your cake and eating it too. Just don't spill any on the upholstery:D

Jay

[Rick_L]

I have a 67 Nova and they are notorious for bump steer from the factory. With toe-in set correctly at ride height, the front wheels toe in about 1" each when you jack under the crossmember and let the wheels drop through the suspension. It's very easy to see without any measuring equipment. This is caused by the tie rods being over 1" longer than the control arms. The reason they did this is there was a packaging problem with the power steering center link and power steering valve. They chose to make a one size fits all drag link (same for manual and power steering) and to make the error on both sides.

On a 55-57 the manual steering linkage is visually pretty close to the correct geometry. If you jack the car up as I described earlier you can't see the change, you need to measure the change in toe in.

On a 55-57 with factory power steering the left side tie rod is too long just like on the Nova. But the right side one is same as manual. Again you should be able to see the wheel/tire move as you jack the car.

Most factory front suspensions don't have this kind of problem.

Since most racks are too long (short tie rods), the problem is opposite to the Nova. As you jack up the car and let the suspension drop, the wheels will toe out if the tie rods are too short. It is very difficult if not impossible to get the tie rod long enough with a stock lower control arm. That's why replacing the front suspension with a clip (like a C4) or different control arms (like Jim Meyer does) is a better solution if you insist on a rack.

[J&Jhotrods]

Good point Rick on the chevyII. Everything on those cars were tight fitting. I'm sure you've seen an early chevyII yank the front wheels at the dragstrip without susp. travel limiters, and come down with the front wheels flailing about as the front susp. settles. Looks like a handful.
I don't know where I'll be able to come across a bumpsteer gauge to check the 57 steering, but I think a good test for the before/after rack and pinion install would be to remove coil springs, put frame/crossmember at ride height, and and observe toe changes 3" up and 3" down(in 1" increments) from actual ride height. Probably not as accurate, but it will certainly provide some baseline information.
Jay

[Rick_L]

Any way that you can come up with to measure toe in will work - obviously some will be more accurate and repeatable than others.

The bump steer gauge that the racers use is just a plate with two 1" travel dial indicators mounted. And you could do it with one.

[J&Jhotrods]

Ya know Rick, I was thinking about the bumpsteer gauge that the old race team I was working with had, and now that I think about it, it barely extends a few inches past the rotor for measuring. My thinking is, the farther away from the spindle center I get, the more accurate the measurement will be. I think I'll pull the springs, bolt the wheels/tires back on, put them on my alignment turnplates, and measure with toe plates. I do think you're right about the tri fives-they don't seem to have as much toe change through travel as even a mid 90's mustang with the macpherson strut type susp.
Jay.