Clean Sheet Front End - Lateral-g Forums

ccracin · #1 10-23-2006, 11:48 AM

Well folks here is my issue. I am designing the chassis for my 68 C-10 pickup. I have several 2 D layouts done and I am going back and forth on the direction I want to go. I am from a circle track racing back ground that says aggresive neg. camber gain is good. About 1.5-2 deg. per inch of travel. This has a RCH aroung 5" above the ground and will not move more than an inch in dive and roll. It also does not move r to l excessively.This is using a 60" track width with 18" lower arms and approx. 8" uppers at abot 15deg angle up to the ball joint. I set this up so far using a circle track pinto spindle with 10 KPI. Then I read some more about street and road race stuff and it seems that .5-1deg. per inch is what I am finding that arena. When I set things up to do that, my RCH is around 2" off the ground and moves all over the place up and down and right to left. I know from experiance that when the roll center moves alot left to right the handling becomes very unpredictable. I also am looking at the AFX spindles after seeing them on this site. I am going to be talking with ATS soon. Any comments on a clean sheet front end. I have seen posts in the past but I am hoping to guide this discussion towards my goals. I know there are a million things to look at and I am willing to give any imput I can. I am hoping through discussion to make some decisions. Thanks alot.

novanutcase · #2 10-23-2006, 07:50 PM

CCracin:

As qualified as many people on this site are you may want to point this question at the jolly old souls over at Cornercarvers.com. They seem to thrive on this type of thing and I think they probably have more people over their that can answer this question with more certainty. Can it be done here? Certainly! but I just thought I would give you another avenue in case you weren't aware!

John

ccracin · #3 10-24-2006, 07:23 AM

Thanks John. I'll try over there. I agree that I've seen some good stuff here as well. Hopefully someone will be willing to spout some opinions. Thanks again.

Chad

ccracin · #4 10-26-2006, 03:57 PM

Wow 129 views and no replies other than one telling me to look somewhere else. I know the knowledge and opinions are there, come on folks.

**camcojb** · #5 10-26-2006, 04:50 PM

Quote:

Originally Posted by ccracin

Wow 129 views and no replies other than one telling me to look somewhere else. I know the knowledge and opinions are there, come on folks.

Well, the advice to go to CornerCarvers is very good. Just buckle down and do a LOT of searching before asking any questions. If you ask about something that has been asked many times before they will blast you.

However, with all that said, they have some extremely good suspension guys there, that's what they do.

Jody

Mean 69 · #6 10-26-2006, 05:31 PM

There are clearly a ton of factors that go into a front suspension setup, it's way harder thanthe rear setup due to the need to steer as well. To make things really interesting, virtually everything is coupled to something else, in a negative way: push this paramter a bit, something else blows up. It is REALLY a big exercise in compromises, and because you can't have it all, you need to pick your battles. Sounds like you already have a huge headstart in terms of the circle track experience, just learning the lingo takes forever.

A few things to keep in mind, at the forefront, are things like the amount of suspension travel you will be looking at, it'll typically be a lot more than a high speed oval track setup, so insuring things don't go whacky in terms of travel is very, very important. As you noted, the circle track cars can and do run very high camber gains, but in general, this is WAY too much for a road course/street car (by the way, the two are about as closely related in terms of design requirements as there are, if you design for road course, you can detune the setup by softening up rates, etc, and it will almost always work exceedingly well on the street, which is why we take this as a design approach basis for our goodies. It's also the hardest of the suspension "biases" to solve, unfortunately).

I can give general pointers for the priority list, as I see/design things, but I am sure that others might do things differently. You have to start somewhere, or you'll go nuts, the first thing I do is to insure that the lower control arm is parallel to the ground at ride height. At some point you will run into packaging issues, but if you think you can run an 18" lower, that is really good, plenty long enough for a 60" track width. You already figured out that the main thing that affects camber gain is the ratio of the upper arm length to lower, this is also very important in terms of the roll center migration, though not the only contributor. Make the upper, and it's mounting as a start to get the camber gain somewhere around .7 degrees per inch of bump, over the first two inches, and start playing. A suspension program is extremely useful. Alter the upper pickup points up and down, play with the length of the arms, and see how it all affects the roll center height in bump/droop, and also pay very close attention to lateral migration in roll (2 degrees of roll is about all you need to consider). Then you get to start picking your battles.

It's all really complex, as I noted, but it is super cool to play with and learn about. You won't get too much specifics other than general pointers from folks that have it "figured out" because it likley took them a long time to do so, and they will probably be reluctant to share the secrets they found. I know I won't! One dude that di, is Herb Adams, grab his book called Suspension Engineering, it is an easy read, and has a lot of good info in it. Warning, don't copy his front suspension design that is listed in the book, I am not sure if he put it there to throw people off, but it's not terribly impressive and can be greatly improved.

One more point to your specific application, anti-dive. Trucks have a notoriously long polar moment, high center of gravity, and usually have a high front weight bias (static), in braking there is a good amount of weight transfer, exaggerates the whole deal.

Have fun, good luck!
Mark

ccracin · #7 10-26-2006, 08:25 PM

Jody,
You are quickly becoming my favorite on this site. Anyway I have already applied for membership to the almighty corner-carvers. I'm not rying to be a smart a**, but I know alot more about suspension geometry than super charging and I am intimidated just from reading the rules. I do admit from browsing the forum they know what they are talking about. I'll see how long it takes me to get blasted.

Mark,
Thanks alot for the info. I do have a suspension program and I have read the book several times. I even have it highlighted and tabbed. That's pathetic. Packaging may be an issue, but since I am building the chassis from scratch I have a bit of freedom. I felt the same way about his example.

One od the biggest down falls for me so far is the scrub radius. Since this is essentially a street machine we want some dish to the wheels and with a 10deg KPI its tough. I was thinking of running a 2" dropped heidts spindle to help with scrub radius. I can correct the bump with the placement of the rack.

I am only designing for 2 deg roll. But when I try to get the camber gain down to where you suggest the roll center migration right to left is terrible. I am still crunching, but it is challenging. To get this my upper arm is almost 50% of the lower and it is at about 5 deg. Is the .7/inch in the first 2 inches really adequate for the flat corners that street driving gives? I guess it is or you wouldn't have said it. With this set up when I am at 1 deg roll the roll center moves 7 inches. At 2 deg it is 15 inches. That to me is unacceptable. If I maintain the same arm lengths and change upper arm angle to 15 deg I get about 1.7 deg -camber gain per inch. But when I roll 1 deg the roll center only migrates 1.9 inches and at 2 deg. it's only 3.9". To me that is pretty good. With the latter setup the roll center is at 5.2" above ground and only moves .375" in dive and roll. This helps with the taller polar moment that you spoke of allowing me to run softer springs with less roll. With the first example the RC is 1.8" and moves down 1" in dive and roll. What do you think or am I missing something? The problem I do see with the aggresive camber gain is tractive effort under hard braking. I could have up to -6 deg under full dive.

I will have some anti-dive built into the front, especially running a big block with power adder.

Any comments based on the above are appreciated.

By the way, I am also considering the ATS AFX spindles, but I need to call and get some dimensions I can layout. Any thoughts on these for a clean sheet application?

Thanks,
Chad