Make it handle

[SCOTI]

Originally Posted by robnolimit

there is a slight change, but it actually reduces some of the factory bump-steer. More than the front/back position, when you 'tip' the spindle back to gain caster, it raises the steering arm slightly, and this also helps the factory steering geometry a bit.

This is where my thoughts were going.... slight improvement on the bump-steer.

[theastronaut]

I've skimmed over most the thread and there's a ton of great info here!! As much info there is on the suspension though, I didn't see as much discussion about modifications to the frame to decrease torsional flex/twisting. Having a rigid structure that the suspension is bolted to will help tremendously to get the suspension to work as it should instead of the frame twisting and absorbing the cornering loads, and tweaking the relative suspension mounting points front to rear- altering the four wheel alignment.

Since so many of us have stock frames, could we talk some about what could be done to the original frames to increase their rigidity? I'm going to be boxing the frame on my '66 C10 and would like to add an X member while I've got the body off. I started a topic on this but thought this would be a good place for discussion also. If it would be more appropriate to use a separate topic, the one I started is here:

http://67-72chevytrucks.com/vboard/s...d.php?t=495785


My biggest questions at this point are:

What would be a good design for an X member? I've seen a few that seemingly didn't have much bracing that would transfer twisting forces from side to side, instead it looked like the center cross supports themselves would flex/twist easily. I've also seen one with about a 1.5 foot long round tube center support design that looked really strong, since round tubing doesn't like to twist. Your thoughts on this?

Do I need to fully box the frame rails front to rear, or do I need to leave some area open around the crossmembers to allow some flex so the frame doesn't crack? Or is that a myth?

Here's where I'm at now, making patterns for boxing the frame. The first pic show how much flex there is with just one rear bag aired up. I'm planning on boxing all the way up to the steering box up front, and back past the C notchs in the rear. Also planning on welding the crossmember rivets.







And here's the pics I found of an X member with a tubular center design.

[jmlcolorado]

Originally Posted by theastronaut

I've skimmed over most the thread and there's a ton of great info here!! As much info there is on the suspension though, I didn't see as much discussion about modifications to the frame to decrease torsional flex/twisting. Having a rigid structure that the suspension is bolted to will help tremendously to get the suspension to work as it should instead of the frame twisting and absorbing the cornering loads, and tweaking the relative suspension mounting points front to rear- altering the four wheel alignment.

Since so many of us have stock frames, could we talk some about what could be done to the original frames to increase their rigidity? I'm going to be boxing the frame on my '66 C10 and would like to add an X member while I've got the body off. I started a topic on this but thought this would be a good place for discussion also. If it would be more appropriate to use a separate topic, the one I started is here:

http://67-72chevytrucks.com/vboard/s...d.php?t=495785


My biggest questions at this point are:

What would be a good design for an X member? I've seen a few that seemingly didn't have much bracing that would transfer twisting forces from side to side, instead it looked like the center cross supports themselves would flex/twist easily. I've also seen one with about a 1.5 foot long round tube center support design that looked really strong, since round tubing doesn't like to twist. Your thoughts on this?

Do I need to fully box the frame rails front to rear, or do I need to leave some area open around the crossmembers to allow some flex so the frame doesn't crack? Or is that a myth?

Here's where I'm at now, making patterns for boxing the frame. The first pic show how much flex there is with just one rear bag aired up. I'm planning on boxing all the way up to the steering box up front, and back past the C notchs in the rear. Also planning on welding the crossmember rivets.

I think i read, on this thread actually, that your supposed to box fully, but only run 2" beads of weld, then leave 2" open alternating between. This keeps some flex there to prevent cracking in the areas of high stress.
Someone correct me if im wrong.

Id like to see how much flex you have after boxing the frame. Maybe a comparison photo once completed?

Im not building an all out track machine like some of the guys here, but rather, a rat rod. Im using a 68 C10 frame that i zeed under the cab. I have bags in the same location as you and have a bunch of flex.
Im kinda thinking that having the zee will lower the truck CG but then again, i know nothing about this science other then what ive read on this thread over the past 3 days

Im hoping that boxing will tighten this truck up and make it handle better. Im also thinking of adding an X section on the lowest part of the zee to tie at all together. I know this frame does NOT want to flip over. I had it all stripped down to flip upside down to do some work and it took everything i had to keep it from righting itself while it was on its side.

[hotrod1]

We kind of went a little overboard. We have three jackstands under the frame and it stays level in every direction.

[theastronaut]

Originally Posted by hotrod1

We kind of went a little overboard. We have three jackstands under the frame and it stays level in every direction.

Do you have pics of your frame?
Posted via Mobile Device

[hotrod1]

You can see the build - 56 pro-touring - under the 1956 category.

I listened to Rob from No Limit on the cross brace (like an X). He knows his stuff. The rest of the craziness was our idea. We even added a cage, but the frame is that stiff without it. Big dilemma. Some say that it needs to flex, other say not. After its done (don't hold your breath, wont be done anytime soon), I will be able to tell you about the not flexing frame. We have spent way too much time on the frame, but it is a class on welding and fab work.

[killerpickup]

Originally Posted by killerpickup

Here are a few shots of my project.

Stll trying to figure out pic inserting.

[robnolimit]

This is a good topic. I am asked all the time, " How much stiffer is it ? " How do you quantify that, there is no 'industry standard' for testing old or modified chassis. Here's what we do. Place three stands under the chassis, Two in the front, under the frame rails, just in front of the IFS crossmember/front CL. One in the back appx 10" fronm the rear of the rail. It helps over time to be consistent. The front needs to be stabilized, we use hooks in the floor, a pallet over the top, and a few hunder pounds over the front CL will work. The chassis should be level. Measure from the end of the un-suported rail to the floor. Next, place apxx 200 lbs (it would be nice if everybody used the same weight) on the end ov the un-suported rail, and measure the 'sag'. Do all of your chassis work, and re-check to see where your at.

[robnolimit]

When it comes to actual boxing/bracing, remember that material thicknes is second to structural design. Triangles are stronger than squares. If you box the frame, 1/8" is fine, 3/16" is OK too. I do weld the full plate. Gaps lead to cracks. I don't usually box the intire frame. If you build a good center section/X-member, boxing under the cab is of little use.

[BMERDOC]

FWIW, The industrial term is "Torsional Rigidity". I'm at work right now so I don't have extra time to add more info, sorry.

[theastronaut]

Originally Posted by robnolimit

This is a good topic. I am asked all the time, " How much stiffer is it ? " How do you quantify that, there is no 'industry standard' for testing old or modified chassis. Here's what we do. Place three stands under the chassis, Two in the front, under the frame rails, just in front of the IFS crossmember/front CL. One in the back appx 10" fronm the rear of the rail. It helps over time to be consistent. The front needs to be stabilized, we use hooks in the floor, a pallet over the top, and a few hunder pounds over the front CL will work. The chassis should be level. Measure from the end of the un-suported rail to the floor. Next, place apxx 200 lbs (it would be nice if everybody used the same weight) on the end ov the un-suported rail, and measure the 'sag'. Do all of your chassis work, and re-check to see where your at.

I have been thinking about coming up with a way to check the amount of twist before and after bracing the frame, and your way of checking reminded me of a post I found while I was looking around at different X member designs. I found a couple companies that had a fairly standardized test to measure frame flex. They set the frame up on three of the suspension mounting points, then see how many ft-lbs it took to make the frame twist one degree.

This guy's Cobra frame takes 11,122 ft-lb to make it twist one degree.




I'll bolt my front crossmember back in and set the frame up the same way, but I think even without adding any weight the frame will sag under it's own weight at least a few degrees, so it will be hard to get a baseline this way. I guess I could use that as the baseline, and then add weight to get it to twist one more degree. Rob's way will work great to get a baseline of how much it twist now vs after bracing it, but doesn't tell how much force it takes to twist the frame a given amount.

[theastronaut]

Originally Posted by robnolimit

When it comes to actual boxing/bracing, remember that material thicknes is second to structural design. Triangles are stronger than squares. If you box the frame, 1/8" is fine, 3/16" is OK too. I do weld the full plate. Gaps lead to cracks. I don't usually box the intire frame. If you build a good center section/X-member, boxing under the cab is of little use.

I'm planning on boxing the frame full length with 1/8" plate and adding a double (upper and lower level) X member with a large diameter round tube center section. The upper level X brace will weld to the upper flange of the frame rail, and the lower X brace will weld to the lower flange of the frame rail. I'll tie the upper and lower X members together with vertial triangulated bracing between the upper and lower X members. The solid round tube center section shouldn't allow any twisting front to rear, since round tube is very resistant to twisting down it's length.

The reason I want a double layered X member is that the distance between the upper and lower sections of the frame C channels changes as the frame twist. An upper and lower X member will tie the top and bottom flanges of the C channel together and won't let the distance between them change. If I just made a single layer X member and welded it in the frame rails, it wouldn't hold the frame rails from spreading top-to-bottom.


I made this drawing in paint to show how the distance between the frame rails change as they twist. Notice how distance "A" is shorter than distance "B". Just one brace in the center would still allow the frame to pivot around that one brace, no matter how strong the brace is. Upper and lower X members with triangulated vertical bracing in between should lock down the distance of the rails, keeping them from twisting.

[theastronaut]

I drew up a rough sketch of my idea of a double layered X member using MS Paint. My paint skills suck but I wanted yall to see what's going on in my head and see if yall approve. Don't stare at it too long or you'll get disoriented and fall out of your chair.

[Greywolf200]

Greetings folks, sorry to interrupt the discussion on frame boxing, but I think I discovered my level of ignorance today. I had the frame straightened on my '70 C10 last week and had it aligned today. Rob was wanting +8 caster, -1 camber and I was going to try 1/8 toe out. I asked the tech for max caster, -1 camber and 1/8 toe out. He was saying these dimensions were a combined number. Is this correct, and the trick is to balance it half per side? 4+4=8?

FYI-I don't know how it will be in the long run, but the 1/8 toe out seems to yield a better turn-in. It takes a set better now. Really want some more caster though.

Thanks,

[Spla'nin]

Originally Posted by Greywolf200

Greetings folks, sorry to interrupt the discussion on frame boxing, but I think I discovered my level of ignorance today. I had the frame straightened on my '70 C10 last week and had it aligned today. Rob was wanting +8 caster, -1 camber and I was going to try 1/8 toe out. I asked the tech for max caster, -1 camber and 1/8 toe out. He was saying these dimensions were a combined number. Is this correct, and the trick is to balance it half per side? 4+4=8?

FYI-I don't know how it will be in the long run, but the 1/8 toe out seems to yield a better turn-in. It takes a set better now. Really want some more caster though.

Thanks,

Caster should be matched side to side for street calibration but the 8 to 9 degrees on each side is the hot ticket...

If you are still stock...you will need some help / additional work to get to +8* caster because it is not possible unless you alter stock or go aftermarket to tilt the spindle...
these include modifying / changing to different A arms
modifying attachment points via rewelding
and/or crossmember moving or replacement...

I am considering the dropmember & move forward route currently...

[BMERDOC]

Originally Posted by Greywolf200

Greetings folks, sorry to interrupt the discussion on frame boxing, but I think I discovered my level of ignorance today. I had the frame straightened on my '70 C10 last week and had it aligned today. Rob was wanting +8 caster, -1 camber and I was going to try 1/8 toe out. I asked the tech for max caster, -1 camber and 1/8 toe out. He was saying these dimensions were a combined number. Is this correct, and the trick is to balance it half per side? 4+4=8?

FYI-I don't know how it will be in the long run, but the 1/8 toe out seems to yield a better turn-in. It takes a set better now. Really want some more caster though.

Thanks,

Too add...He may have been refering to the Toe as combined (total toe). 1/16 per side is fine, 1/8" is a bit agressive. The caster is not combined, it is per side. On a stock suspension, don't feel bad if he could only get 4 degrees caster. 8 and 9 degrees is pretty hot but caster is not a tire wearing angle. On a street truck 4-7 degrees is fine. Just make them equal.

[robnolimit]

I have ta agree with DOC, stock front ends, or even stock dimension components will only get you about +4* caster. Even so, I'd bet your truck dives a lot better now.

A question for ya DOC, with 'normal' thought, I would say that really wide front tires will create a wander, I'm talking about 305 or bigger. Now, do you think that big caster numbers, 8* to 9*, would correct this? I'm considering larger front tires, more to the inside, -1* camber, with a 2.36" scrub radius.

[BMERDOC]

Rob, That much caster will cure just about any abnormal tendancy. I think your biggest problem would be what I call "trameling", bumpsteers ugly little sister. A wide/low profile (or just wide or low profile tire) has a tendancy to follow defects in the road surface. The wider or lower a tire the greater the chance of this occuring. I think that a greater amount of caster would help in correction but wouldn't help in the initial response of the tire to the defect in the road.
With that much tire and caster, even with power steering, I hope your gym membership is still in effect
Are you concerned about unsprung weight?

[Ackattack]

If someone in the "crowd" was an engineer that was good with FEA (finite element analysis) programs, they could figure out how best to box and strengthen the frames. I'm an engineer, but don't work with FEA.

[Greywolf200]

Originally Posted by Spla'nin

Caster should be matched side to side for street calibration but the 8 to 9 degrees on each side is the hot ticket...

If you are still stock...you will need some help / additional work to get to +8* caster because it is not possible unless you alter stock or go aftermarket to tilt the spindle...
these include modifying / changing to different A arms
modifying attachment points via rewelding
and/or crossmember moving or replacement...

I am considering the dropmember & move forward route currently...

Thanks for clearing this up for me. This is what I thought, but he's the tech with 5 years experience? I ended up with .6 camber (.4 and .2) total, 1.9 caster (1 and .9) total and 1/8 toe out total. It does drive much better though. He took 13/32 out of one screw on the driver side. I think I'll go back and talk to him again.

I'm looking at a crossmember mod also if Rob ever has time to check out the modification I came up with.

Thanks again,

[Spla'nin]

Originally Posted by Greywolf200

Thanks for clearing this up for me. This is what I thought, but he's the tech with 5 years experience? I ended up with .6 camber (.4 and .2) total, 1.9 caster (1 and .9) total and 1/8 toe out total. It does drive much better though. He took 13/32 out of one screw on the driver side. I think I'll go back and talk to him again.

I'm looking at a crossmember mod also if Rob ever has time to check out the modification I came up with.

Thanks again,

Here is a good link for your info FYI...

http://www.aligncraft.com/terms/terms.html

The two "issues" listed with increased positive caster listed here are increased road/impact "feel" (watch those pot holes) and less tolerance to unmatched alignment...neither one is a deal breaker for me. YMMV

Rob and or others, I was wondering if there is a good target range for SLA scrub radius for autocross/road course...amazing how many factors come into play with tires, hubs, SAI, etc...!

[robnolimit]

Originally Posted by Spla'nin

Here is a good link for your info FYI...

http://www.aligncraft.com/terms/terms.html

The two "issues" listed with increased positive caster listed here are increased road/impact "feel" (watch those pot holes) and less tolerance to unmatched alignment...neither one is a deal breaker for me. YMMV

Rob and or others, I was wondering if there is a good target range for SLA scrub radius for autocross/road course...amazing how many factors come into play with tires, hubs, SAI, etc...!

Thats a great description on the link. I'm guesing it's about 25 yrs old. Tire, whhel and steering/suspension developement have changed ideas a bit. Many production cars now come with 8* to 10* caster, a number that would heve seamed crazy 20 yrs ago. A 285 ft tire (BMW, Audi, Vette) would be another crazy thought. Tire diameter and wheel offset can be used to tune scrub. 2 1/2 to 3" is in range for our tastes.

[ItsRandy]

Hey Rob...Got any of those rear sway bars for sale like the one on JT yet?

[robnolimit]

Had a good question today. "would'nt it be best to mount the rear shocks straight up and down?" Well, maybe, not. First thing to remember/or understand, is that most shock companies make one valve set (usually a front valve), so most shocks are valved the same. Example, if you buy Brand-X lowering shocks for your truck, and you get front and rear shocks, they may be different lengths/mounting, but they have the same valving. - This does change when you get into higher quality, more performance shocks. The front of your truck weighs appx 2300 lbs., 1150 per side. Lets say the A-arm has a 2 to 1 ratio, so there is appx 2300 lbs of force to act on the shock. Out back, there is appx 1200 lbs, 600 per side. If the shock is straight up on the axle, it moves at 1-1. It sees 600 lbs force to control. Now factor in unsprung wieght. This should be thought of as a % of total, not just a number. The front unsprung wt. I'll guess to be appx 220 lbs, or 9% of the total front wt. the rear unspung is appx 270lbs, or appx 23%. What does all this mean? The front shock deals with alomst 4x the force as the rear, but it does move at a slower rate due to the leverage effect, but this still tells you that the front shock valving should be stiffer than the rear. Next, apply the unspung wt. %, The rear is almost 2 1/2 times higher, higher unspung % = softer compression. It is a safe bet to say that we in truckland need softer rear valving. - but remember, most shocks are valved the same. So, if you lean the rear shock, you can reduce some of its valving effects. I'll look for a chart to post up. Have a great day.

[robnolimit]

Originally Posted by ItsRandy

Hey Rob...Got any of those rear sway bars for sale like the one on JT yet?

should be in stock to ship by the 15th.