Make it handle

[turbobuick1]

I don't mean to hijack the thread or take the discussion in a different direction, but I've got a question on the anti-squat characteristics for the rear trailing arm suspension.

I've got a '72 C20 that I am lowering to the ground with air suspension, and I am using a very different approach for the rear, that is, I 'Z'ed the rear frame 6" and added a 2" C-notch to the frame to allow the truck to lay frame on 30.5" diameter tires.

Before I gave any thought to anti-squat, I fabricated a K-member in an effort to increase torsional rigidity and keep the frame square in the area where I did a 6" 'Z'. At this time, I planned on using the stock trailing arm pivot point.

Now I am in the mindset that I should raise the trailing arm pivot points as high as I reasonable can, at the very least, flip the mounting brackets. This would mean altering the K-member, which is fine, but I'm wondering, is it neccessary?

Bear in mind I am building this as a practical everyday driver, not a performance-oriented truck at all. Should I be worrying about the anti-squat at all?

Appreciate any of your thoughts on this! You seem the be one of the most knowledgable people in terms of suspension design/geometry for GM trucks, hence why I am asking for your opinion.

[68GMCCustom]

I'm confused....how would trailing arms work around that tubing you have tacked in?

[robnolimit]

Looks good. I would flip the mounts, evev if it means replacing the two diagonal tubes with bent tubes. It will be worth it in the long run.

[turbobuick1]

Originally Posted by 68GMCCustom

I'm confused....how would trailing arms work around that tubing you have tacked in?

They actually clear with room to spare as it is right now. With the rear axle bolted to the trailing arms, the axle swings all the way up into the 2" C-notch without the control arms getting close to the tubing I have tacked in. It also clears the two-piece driveshaft, no problem. As it sits, I can raise the front pivot point of the trailing arms 1.25" without hitting anything, but I feel I will need to raise it more than that to gain more anti-squat.

Originally Posted by robnolimit

Looks good. I would flip the mounts, evev if it means replacing the two diagonal tubes with bent tubes. It will be worth it in the long run.

Thanks Rob, I appreciate your input. I think I'm going to do just that; flip the trailing arm brackets and raise the diagonal tubes to clear the control arms.

[robnolimit]

I'm doing a little research for my next article, and that took me out to Energy suspension. I have used Energy products for many years, but this was cool to see the place. I had an informative talk with some of the suspension tech's and learned a few things. Most of this will be in the next Street Trucks, but I wanted to share some here.
The goal of upgrading from rubber to urathane is to gain control over some of the forces that are pushing and pulling parts of your truck. With cab, bed, and core support mounts, the goal is to get the cab to help add strength to the chassis, and reduce flexing from bumps and corners. This may make the truck feel rigid and bumpy, but what is really happening is that you now feel the true suspension action. Engine and trans mounts will hold the drivetrain better, and deliver power to the axle with less loss. Torking the motor up takes power. Single rotation bushings, such as A-arms, sway bars and, leafs springs and trailing arms, are designed to limit any other motion, and act more like a bushing or bearing.
Then we discussed different suspensions, and came up with a few surprising conclusions. We agreed that for any performance build there would be gains in using urathane cab, bed, core support and motor and trans mounts. I even tossed in the concept of a urathane 'coupler' that would bolt in between the cab and bed (more on that later). Again, we thought that the front suspension, and both front and rear swaybars should get the upgrade. Here was the surprise. We did agree that for a 'drag' oriented project, urathane in the rear leafs or trailing arms would be a plus, but after some thought, that this may not be the ticket for going around corners. The idea is that urathane would additionally restrict the axle from articulating in a corner. We would want the springs/shocks/sway bars to control that, and/or, let it happen. But, we do both think that urathane in a 4 bar is the way to go. Just some food for thought.

[aggie91]

Originally Posted by robnolimit

...We agreed that for any performance build there would be gains in using urathane cab, bed, core support and motor and trans mounts. I even tossed in the concept of a urathane 'coupler' that would bolt in between the cab and bed (more on that later). Again, we thought that the front suspension, and both front and rear swaybars should get the upgrade. Here was the surprise. We did agree that for a 'drag' oriented project, urathane in the rear leafs or trailing arms would be a plus, but after some thought, that this may not be the ticket for going around corners. The idea is that urathane would additionally restrict the axle from articulating in a corner. We would want the springs/shocks/sway bars to control that, and/or, let it happen. But, we do both think that urathane in a 4 bar is the way to go. Just some food for thought.

With this last part in mind, what would you recommend for the rear leaf springs if it was going to be a Daily Driver/Occational Drag Racer/Occational AutoCrosser type of Truck? I have already done the cab/core support mounts in urethane and will be doing the front control arms and swaybars also once we get the parts back from sandblasting/painting...

I read your first two articles and looking forward to the next one.

[robnolimit]

some guys in the circle track and road race groups havetried spherical bearings in the front leaf eye instead of bushings. This allows for spring articulation and full transfer of torque to the chassis. Urathane in the leafs will help at the drag strip, but will cost you on the street and autocross. I'm going to look for some poly-lined bearing inserts. - give me a few days.

[69gmcc10]

How about polly bushings for shocks? are they a worthwhile upgrade or an upgrade at all?

[Rstone1]

I asked this question earlier and got no responce so I will ask again.

Inclination between the lower and the upper ball joint in the spindle. Is this needed, what is it used for and where is a good range to be in if it is needed?

[GMC Canuck]

Please correct me if I'm wrong but I will try and answer.
The axis between the lower and upper ball joint that the spindle turns on if moved out or in is camber (moving the top of the tire out or in, out for positive in for negative). This sets the angle of the tire when you go into a corner. You want a little negative camber, like a motor cycle leaning into a corner.
If you move the axis forward or back (you won't see any change on the tire) you're changing caster. Move the top back you have positive caster, forward for negative. Positive caster will pull the steering back to centre (like a shopping cart caster has massive positive caster and will always snap back to centre)

[Rstone1]

Thank for responding. I understand why it there and what it's for. I guess I should have been clearer. I'm wondering what's the least amount of degrees diference between the upper and lower ball joint you can get away with.
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[oldspowered67C10]

Rstone1, The inclination your speaking of is there to control camber change through steering arc of movement. This is also influenced by ball joint offset fore and aft.

I don't really under stand what you mean but minimum allowable though. Do you mean in the design of the spindle or in the position of the ball joints relative to the frame?

[Rstone1]

Yes in the design of the spindle. If you were to build your own. Factory spindles at all on the conservative side.
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[Mechanic77]

Rob can correct me if I'm wrong, but I believe you're referring to what they call the king-pin inclination angle.....the angle you get when you draw a line through the upper and lower ball joints to the ground....if you're making your own spindles, and know your wheel and tire size, you can determine the ideal king-pin angle. Ideally, you want the imaginary line drawn through the ball joints to hit the ground at the center of the tread on the tire, that reduces the scrub angle when you turn and will also reduce steering effort.....clear as mud?
Rob might be able to explain it better than I can

[Rstone1]

This what I'm wondering how small an incline can you have and not loose all of your steering feel?
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[oldspowered67C10]

Rstone1, alot of variables to think about there. KPI(king pin inclination), included angle and scrub radius.

If you decrease KPI the car tends to lose stability and the steering has a harder time returning to center, great for low speed parking lot type stuff but not so great for a performance car. But keep in mind, caster also has a effect on this.

The more you decrease KPI the more wheel back spacing you'll need to keep scrub radius in check. Of course the position of the spindle on the upright in or outboard effects this.

The more you decrease KPI the the closer together the lengths of the upper and lower control arms become which effects camber curve. The position of the control arm mounts relative to the frame in or outboard influences this as well.

Anyways, it seems you already are aware of the principals of KPI but are wondering what effects too little would have and at what point would you encounter driveability problems. Since you would have to incorrectly engineer a part to find out, cant say for sure but typical KPI is around 5-6 degrees so if I had to guess Id say at half that spec you start to run into issues. I suppose you could put vehicles with wildly varying purposes, say a WW2 era Jeep and a new corvette on a modern alignment machine to get the numbers so you'd have a way to relate the numbers to how a vehicle drives but even then there are other variable in play there also so while it may give you a idea its not exactly a sound scientific method.

Just out or curiosity, why are you asking this?

[Rstone1]

Well I'm concidering building my own spindles. I've seen a camaro built recently that didn't had like 2 or 3 degrease of KPI. And also alot of prototype cars don't seam to have much. I would like to get as close to 0 scrub as possible. I've talked to the camaro owner a little bit and he says that his car handles real well. He's going to the autocross nationals. just looking to do something different than normal. There has to be a better way to make these trucks handle.
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[robnolimit]

Originally Posted by 69gmcc10

How about polly bushings for shocks? are they a worthwhile upgrade or an upgrade at all?

Shocks only work when the shaft moves. So, anything that soaks up the transfer of suspension movement from the shock shaft is bad. shocks are one of the components that when it comes to performance, I'd go straight to bearing mount. But, urathane bushings are a big + from stock rubber.

[robnolimit]

KPI Hey, you guys did great sorting that out. Rstone1, if you are serious about fabbing your own set up, get a copy of "suspension geometry pro" from "autoware", it's way cheaper than buying extra steel. My HellBoy C10 has 7* KPA in the spindle. Just so you know. I wouldn't go much less than 5*. When it comes to scrub radius, there is a common belief that '0' is the goal. In this case, however, '0' is a comparison number that everyone can compare to and understand. Like a strarting point. In practical application, as you close in on '0' scrub, you start to loose all steering feel. Now add in power steering and you have no feel at all. In a performance build, I would aim for 2" scrub radius with a 10"+ wide front tire.

[hotrod1]

I dont think that this thread ever discussed braking systems, more specifically vacuum assist, hydroboost, manual master cylinders (dual and tandem).

Most of our trucks on this thread are maybe for autocross/protouring, handling, and do see street time as well. A play vehicle maybe? The majority would tend to have disc all the way around as well.

There seems to be a trend towards getting rid of the assist braking systems and going towards the manual systems; lack of vacuum, available space, not as safe as manual, etc. Are manual systems feasible on a vehicle that sees street time, a hot rod show, autocross?

If manual is the way to go, the question then becomes dual or tandem? What about the dual cylinder with balance bar vs tandem cylinder with a proportioning valve? How about pedal set ups? 6 1/4 to 1 or 7 to 1? Can manuals be placed on the frame using the stock pedal, or would putting it on the firewall better? If firewall, masters inside the cab or on the outside in the engine compartment. I would think masters inside is nothing but a pain in the neck. I maybe wrong.

Is all this worth considering, or leave the vacuum master alone and choose another thing to tinker with?

[Rstone1]

Just wanted to thank everyone for there input. It really helped. Rob thank again for your input. I drew it up in CAD and with a scrub right arount 1.25" I was at 5 degrees of KPI. I'm a parapaligic so I end up having to drive one handed all the time so I was going to go with a 16 to 1 box with a 2 to 1 quickiner on it so I was thinking I could get by with a little less than normal becasue of the faster ratio on the steering. I could be mistaken though. trying to get close to 1 turn lock to lock.

[robnolimit]

Originally Posted by Rstone1

Just wanted to thank everyone for there input. It really helped. Rob thank again for your input. I drew it up in CAD and with a scrub right arount 1.25" I was at 5 degrees of KPI. I'm a parapaligic so I end up having to drive one handed all the time so I was going to go with a 16 to 1 box with a 2 to 1 quickiner on it so I was thinking I could get by with a little less than normal becasue of the faster ratio on the steering. I could be mistaken though. trying to get close to 1 turn lock to lock.

It would be worth a few phone calls. I would call Lee engineering and talk with them about steering boxes, then I would call KRC and have a chat about pumps. These guys are at the top of their game, and very helpfull.

[robnolimit]

Brakes more specifically, the delivery system. That being the pedal, booster and master. If you have ever read about "the pogo incident" from my younger days, you know I have spent some time on brakes. The goal, for me anyway, is to create 1000 to 1250 psi of line pressure at the top end with the type of pedal feel that you want to match you intended driving style.
I have a great three car comparison. Three that are currently in my garage.
1. My trusty sled, 1946 ford convert. Has a 5.5-1 pedal ratio, hydro-boost and a 1 1/8" master. (4wd, oem type 11"ft, 11"rr) This car weighs in at 3400 lbs, and stops on a freekin dime with three cents to spare. I once put a set of really agreesive pads on it, and with Falken tires it stopped from 60-0 in 92 feet, out braking a Porsche! The pedal is very soft and smooth, BUT, in a track setting, or the roads up to Big Bear, the pedal feel is so light its hard to feel the pad contact.
2. The Bullit, 55 F-100, has big 14" 6 piston Baer brakes, the pedal is 6-1, and uses an 8" dual diapham booset and 1" master. This is a standard street/perf set-up. The motor makes good vacuum and it is very comfortable to drive. Stop and go is no problem. Pedal feel is great. It does take a bit more effort than my '46, but much less than a stocker old p/u. I like it. When the Bullit was fresh build, I had got a hold of a bad master right from the start, the fading master cost me three points at the first Truckin Throwdown. Had it not failed, I would have won by two points. Aaargh!!!, but, its an easy fix and now works perfect every time.
3. HellBoy. My goal was to eliminate anything that could fail, and to have lots of adjustment for tuning. I used a Wilwood hanging pedal at 6.5-1 with tandem masters. The front is a 3/4"bore, and the rear is 13/16". The diffenerce in bore size puts a lille more pressure to the front brakes. The balance bar assembly allows adjustment to the front and rear brake without a proportioning valve. It's a pain to bleed. It looks really cool. Yes, it works very well, and the pedal feel on the track is consistant. It is easy to feel the brakes, and modulate pedal input. But, it takes a firm push to stop it, so on the street you have to be used to it. Most of us are not used to manual brakes any more. It takes some getting used to.
I'll put together some info on this for you.

[robnolimit]

Those in So Cal, the So Cal challenge is this weekend. A car show area has been added. Come check it out, in Riverside at Adams Motorsports Park. if your not local, follow the action on facebook at No limit Engineering.

[MrBlue]

Rob,
First thanks for all the information. I know that I read this somewhere between page 1 and this last page, BUT What shocks do you recommend. I am going to lower with springs, this is a street driver, not a racer. Thinking of 3-inch front and 4-5-inch in the rear
Thanks,
Victor