I'd be a little cautious with this as a general statement. What is good for a circle track car might not be good for a road race car, and typically, this is indeed the case. Ideally, adjustable Ackerman would be the best so one could alter dynamically to see the effects. I recall reading Carroll Smith's book, engineer to win, and he had the opposite comment on Ackerman that was derived in real world testing (open wheel car, road race....). For decades, the thought was that Ackerman wasn't a big deal, due to loading of the inside tire on turns (small) and therefore the anticipated effect was negligible. Turned out not to be the case after a few decades of assuming this, increasing Ackerman in particular helped intial turn-in, etc.

I too have the short Pitman arm and Howe link, and the measurements I took a few years back were all over the map left to right, independent of Ackerman (which in turn would be all over the map too as a result!). With Brian's work straightening the drag link out, using a stock style Pitman, it seems that this might work after all. I like the outer tie rods you are using with the adjustment threaded adjustments, and have thought about using them on the inners as well (space permitting) in order to facilitate adjustable Ackerman, assuming the left-right stuff gets sorted!

Then there's bump steer.... "ASSuming" the design of the Howe link to adjust bump really works......

With a rat motor and additional weight over the nose of an already nose-heavy car, I'd think long and hard about the steering...... By the way, I agree with the gallery, that is one cool looking machine. Have you measured scrub radius using the ATS spindles? Lots of tire on that car (mine will ahve the same....), you steering gear might not be too happy if it has to fight scrub.....

Mark

Thanks for your input Mark.
I talked to some guys that specialize in race car alignments and they told me the Howe center link, tie rod end adjusting and adjustable idler arm will make the bumpsteer relatively quick and easy. They have used it many times before.
I have been doing lots of research and had lots of help from Mark Savitske over the phone. When the car is finished and has all the weight in it, it will go to a proper race car alignment shop and have it done properly before I start making any changes to it. Between there experience and me learning as much about what I need for this specific car, I think we can make it work well. If the ackermann becomes an issue, at least we know where to start for a fix.
I would say roughly scrub radius would be about 2 1/2 inches maybe more... I can measure it more accurately if you wanted to know for yourself if you plan on using those spindles. I put a very safe fitting offset in the wheels knowing I can change the inner and outer shells after to move things around. I can also add an inch or so to the wheel width. The plan was to use these tires for some initial testing and fine tune from there.
Hopefully the nose weight won't be as high as it would have been, with my engine set back so far. It looks closer to the front then it is because of the blower belt. I'll be working hard to balance it out as well as I can, but I have been thinking a lot about steering, thats why I have my crazy questions.
All the input is greatly appreciated, it makes my brain work harder. :)

we need a build thread that is an awesome car! we need some details :thumbsup:

I joined this website for one reason -- great dialog from smart people on the one thing that is important here -- lateral g. Mark makes some excellent points regarding Ackerman, especially regarding "adjustability". Ackerman is very vehicle and use dependant, and is therefore dependant on dynamic, not static situations. Ackerman is slow to build (needs lot of wheel turn to be significant), so it is generally more useful for slow speed, high steering angle turns such as in autocross or high wheel angle turns that dirt sprint cars employ. It is less of a player in low steering angle, high speed turns -- like a 160 mph sweeper -- especially with today's tire technology. Carroll Smith's "Tune to Win" was published in 1978 (I can barely spell bias ply). His follow-on publication, "Engineer in Your Pocket", 1998, makes no mention of Ackerman as a tuning tool. Today's tires, especially race tires, operate at very high slip angles that tend to mask small Ackerman effects (at high speed/high g). Positive scrub radius can produce the same effect as pro-Ackerman -- increased "drag" on the inside tire promoting turn-in. Of note, dynamically, scrub radius of the heavily loaded (and deflecting) outside tire in a turn decreases while the inside tire's scrub radius increases as the effective center of the contact patches move laterally. Running zero scrub radius could actually give you negative scrub under heavy loading. As Mark points out, the better balanced your car is and the more the inside tire is contributing to the turn, the more this dynamic is altered. I guess my point is that there is no one textbook answer that applies across the board. Each vehicle's suspension characteristics are generally unique and a balance of compromises, and it takes real word testing and "adjustments" to optimize them for the particualr dynamics to which the vehicle is exposed. Just an opinion, and food for thought.

Pappy

Very nice, Pappy! I like the threads that address things that make me think, so this is one that I like a lot!

Carroll mentioned the Ackerman "thing" in the book called Engineer to Win, which was the last of his three main books (Prepare, Tune and Engineer to Win). I don't have the "Engineer in your Pocket" book, I'll have to grab a copy because I have mearned a lot from all of his books, as well as many others by other smart folks. As you implied, no one answer, many opinions and strategies on any given theme. That's what makes it so interesting.

Agreed on the low speed implied "benefit" of the Ackerman, at higher speeds/smaller turn angles it won't be nearly as noticeable, unfortunately I don't have enough time or money to live most of my life in a pure race car on fast tracks, so this is an important aspect for my current cars which I drive on the street and limited track time. I am really glad that others are working this steering issue on the second gens, I am pretty confident I could "solve" the issue, but I just don't have the time so stealing shamelessly from other smart folks before is a fine strategy as well! We all learn faster together.

I am not too concerned about the scrub radius for my own second gen using the ATS spindles, I have a set of these that I am currently installing on my 69 convert and compared to the factory second gen setup. No question it will increase scrub, so that's not a direction I personally want to go with my own project, as I am going to run a lot of rubber up front and wish to keep it lower rather than higher. If it comes out at 2 1/2 inches, that doesn't seem too bad to me at all, maybe a little higher than I'd start a paper design after but not as bad as I thought it would be. I am a glutten for punishment sometimes, and I am jones'n to make my own spindles, and probably will for this car....

Great work and input guys, thanks a million!
Mark

ATS Spindles
 

Mark,

Thanks for the kind words. Measurement info for you and Speedjohnston -- I have ATS spindles on my car (C4 Vette lower control arms and Lefthander uppers w/roller bearings and Torrington thrust bearings. At 13 inches below the hub center (the radius of a 26 inch tire), the scrub radius from the spindle ball joint line (looks to be about an 8 degree kingpin inclination angle) to the wheel mounting flange is 2.875 inch. I am running a 10.5 in. wide wheel with 6 in. backspacing, which gives a tire scrub radius of 2.125 in.

Pappy

Pictures of said car, please.... And yes, I believe the KPI is 8 degrees for those spindles if my (failing) memory serves me.

Cheers,
Mark

Mark,

Don't want to hijack Speedjohnston's thread. The link below has some pictures. I will take pictures of the front suspension for a project update.

Pappy


https://lateral-g.net/forums/show...t=20865&page=3