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Looks like I have a lot to catch up on in this thread. I had a baby on Monday so I've been a little busy, and I won't get back to the subframe work for a while. I'm almost done with the fabrication though, and after moving the subframe back 1" I preserved all the original FB subframe mounting points, so if I ever feel like going back all I have to do is pull the engine and swap it. That said, I've read a lot about the swap here and decided long ago to do it anyway. A lot of people seem happy with it and I can keep tinkering with the roll center.
I'm still looking for advice on coilovers. I'd like to have those on hand for when I finish the subframe install. The BC Gold set are an option, but they're pricey especially when I don't need rears.
I also heard a rumor that an NA Miata intermediate steering column is the right length between the rack and the GSL-SE power steering upper column when you move the subframe back? Can anyone confirm before I buy a used one?
Peejay, do you think if you'd relocated your subframe back you would be happier with the swap? It should help caster a little although I guess it shouldn't impact roll center
1/4" steel support plates with new tubes
3/4" angle iron spacer, welder to the frame, then coated in POR-15
Last edited by derSchwamm; 05-10-19 at 10:17 AM.
Reason: forum broke
well if the earth is round, then if you lower the roll center enough, it'll pop up again at the top of the screen right?
I haven't sat down with a tape and a CAD program and plotted things out recently so it may be possible the FB roll center moves around to somewhere weird... but the disadvantage to roll center getting closer to CG is not only the jacking effects but that the weight transfer is taken up by inelastic stuff rather than stuff that's tunable.
I also heard a rumor that an NA Miata intermediate steering column is the right length between the rack and the GSL-SE power steering upper column when you move the subframe back? Can anyone confirm before I buy a used one?
Peejay, do you think if you'd relocated your subframe back you would be happier with the swap? It should help caster a little although I guess it shouldn't impact roll center
I'm the one who started that 'rumor' after I acquired an NA6 column and steering shaft. The steering shaft is almost identical in length to the FC shaft that I extended for my car. Note my car has the 1" axle shift. The Miata shaft is slightly longer, but only just. One should be able to make it work, especially if the FB power steering column (AHEM) is shifted back a bit. I am tall and use a 2" extended steering wheel with a stock column position...
Part of the reason why I liked the idea of a wheelbase shift was to get weight off the nose. Moving the axle centerlines forward is the same as moving weight back. I am at 1200 front/1330 rear with me in it and a half tank of fuel. That is 47.4/52.6. Riley's "ideal" is 44/56, and stock untouched FBs are around 53/47.
I haven't sat down with a tape and a CAD program and plotted things out recently so it may be possible the FB roll center moves around to somewhere weird... but the disadvantage to roll center getting closer to CG is not only the jacking effects but that the weight transfer is taken up by inelastic stuff rather than stuff that's tunable.
Oh , I agree. But if you make it too low, the suspension ends up having to be so stiff that it can't follow the road.
The prime rule of fast driving is to have smooth inputs. The reason for that is so the tires stay happy. Softer suspension means the chassis has smooth response. Yeah, having high "antis" makes things stiffer anyway, but only in proportion to the amount of braking or acceleration or cornering requested. It's not "on" all the time.
The thing with the FC stuff is that the arms are so short that the RC moves all over the place. SA/FB have much longer arms that pivot almost under the engine. I think Mazda made the FC arms short to compensate for the wideness of a rack and pinion. Me, on the other hand... I want to use a center takeoff rack, and mount the control arms in the center of the car. A chassis with a stable roll center will take a "set" in a corner much more readily, and will thus feel more secure and confidence-inspiring.
Oh , I agree. But if you make it too low, the suspension ends up having to be so stiff that it can't follow the road.
The prime rule of fast driving is to have smooth inputs. The reason for that is so the tires stay happy. Softer suspension means the chassis has smooth response. Yeah, having high "antis" makes things stiffer anyway, but only in proportion to the amount of braking or acceleration or cornering requested. It's not "on" all the time.
The thing with the FC stuff is that the arms are so short that the RC moves all over the place. SA/FB have much longer arms that pivot almost under the engine. I think Mazda made the FC arms short to compensate for the wideness of a rack and pinion. Me, on the other hand... I want to use a center takeoff rack, and mount the control arms in the center of the car. A chassis with a stable roll center will take a "set" in a corner much more readily, and will thus feel more secure and confidence-inspiring.
It's more complicated than that. First off, it's not so much about the tires wanting things smooth, as not overwhelming them before load transfer happens... which is a lot faster than a lot of people think. Next, think back to the active suspension days in F1 when you could make the suspension do whatever you want. One of the things that they found was that the solutions that seemed like they'd work best... didn't generate heat in the tires, so they deliberately started inducing vertical load variation. And in fact with modern (hard surface, race) tires, the same still works with passive springs and all the rest - running wheel frequencies a lot higher than traditionally thought useful works the tires and gets heat into them, which is more important.
I'm not a fan of antis at all, honestly... looking at something different to try to get anti out of the rear suspension.
The whole thing with the FB is like... I kind of feel like a lot of the existing solutions end up oriented around the fact that there's no decent shocks and struts.
(I don't know if any of this works on soft surfaces)
- running wheel frequencies a lot higher than traditionally thought useful works the tires and gets heat into them, which is more important.
i was looking through a really old Japanese Rx7 magazine last night and they were running 12k/10k (670/560) springs in the FC's, if you move forward in time, they seem to soften things up, default is like 450/350 (8k/6k).
not sure what my point is, other than running really stiff on an FC has been done, although it doesn't seem to be the best way. (plus on a US road your head would fall right off)
It's more complicated than that. First off, it's not so much about the tires wanting things smooth, as not overwhelming them before load transfer happens... which is a lot faster than a lot of people think. Next, think back to the active suspension days in F1 when you could make the suspension do whatever you want. One of the things that they found was that the solutions that seemed like they'd work best... didn't generate heat in the tires, so they deliberately started inducing vertical load variation. And in fact with modern (hard surface, race) tires, the same still works with passive springs and all the rest - running wheel frequencies a lot higher than traditionally thought useful works the tires and gets heat into them, which is more important.
I'm not a fan of antis at all, honestly... looking at something different to try to get anti out of the rear suspension.
...This is all getting beyond the scope of the thread, so all I can really comment is: It's okay to be wrong.
F1 can immediately be thrown out as a topic of discussion because F1 is the ultimate in delicate-flowerism in that they have to curate the tracks they run on so that their so-called "high tech" overblown go-karts don't have to suffer widdle biddy bumps. That is fine if you like having a "perfect" place to operate because your delicate sensibilites cannot handle a less than pool table smooth surface.
This is what Real Man top-level **** is:
This is AWD, sure, but you see that? The lower control arm is mounted at a heavily raked axis for a lot of anti-lift (I guess) on acceleration, so longitudinal thrust forward will drive those front tires into the ground, so that the steering wheel can do more than just give the driver a place to hang his arms And notice how the strut is decidedly off-axis? That is entirely intentional. Graph the angle of the upright as the suspension cycles up and down. It will become clear that the upright rotates in side view, and that braking torque will ALSO drive the front tires into the ground. (Ford's been doing this on Fox bodies since 1978, but they screwed the pooch with horrendously bad Ackerman and other issues)
Note that this is also the tarmac suspension setups...
This is getting pretty far off topic but what the heck, it's fun.
I'm bringing up F1 more just in the sense of "they had the tools to discover what the tires liked and it wasn't exactly what they expected" Most of what I'm cribbing from is professional level circuit cars.
WRC stuff is deceptive. Look at http://www.zercustoms.com/news/image...o-R-WRC-26.jpg where you can see the control arm better; the angled strut axis causes a lot of people confusion and from everything I've seen is more about packaging adequate length around the halfshafts and stuff than geometry in the conventional sense.
I was thinking about bumpsteer issues and remembered that ride height did not affect toe on the SA/FB but toe does change markedly with bump on the FC. This has a nice negative feedback loop, with body roll causing the outside tire to toe out, steering away from the corner, but it gives a loose sloppy feel to the suspension.
SA/FB have the opposite problem - because they are rear steer, bushing compliance makes the outside wheel toe in under lateral loads, which can feel spooky.
I did that on my rearend. That lasted exactly one trip around the block before I took it back under the knife and replaced half the rod-ends with bushing ends I made out of a cut up suspension link and some left hand thread 3/4-16 allthread I had kicking around. (You don't have left hand thread allthread kicking around? )
Granted, it was FUN when I went to back the car out of the garage and, when putting the trans into gear took up all of the drivetrain lash, you could hear and feel a deep "ka-THUNK!" like when Petter Solberg shifts into gear when Phil Mills tells him to get ready. Then I got on the road and it stopped being fun. The weird part was, all the mechanical thunk-clank-bang made me instinctively think I was driving a dogbox and I kept trying to shift quickly without the clutch.
this one time we were the sideshow for the WTCC cars, and i got to peek under the fastest, the Chevy Cruise (first time i'd seen one) and it was really WEIRD. it was a KW setup, but it didn't make any sense at all, the shock was in a really strange place, not sure why, but it was fast.
it was a fun race, Sears Point/Infineon/Sonoma turned into a corner of Italy for a day, the pits smelled like perfume and the language was Italian...
we put NSX brakes on the Intergra, and learned that there is more to it than that, it was so bad, the driver had to start braking at corner exit... we also got T boned by a guy with one of those ricer tow hooks, and those things are like can openers, it sliced the door right open, and was ~6" from the drivers knees
As far as I can tell from the very few pictures I've found of the Chevy WTCC stuff, it's just putting the strut tube in a weird place... probably partially for tire clearance, partially to make the strut more vertical and get the virtual swing arm length longer.
05-09-19, 11:42 AM
