Making "Dubs" work

[Steve Chryssos]

The Alloway Hemi Challenger employs a "Caricature" rake and wheel selection accomplished by raising the rear axle centerline and suspension pickup points. What effect does this have on vehicle (I said vehicle) dynamics?

https://static1.pt-content.com/images/pt/2005/07/DSC02712vi-1.jpg
https://static1.pt-content.com/images/pt/2005/07/DSC02616vi-1.jpg

[Damn True]

Oh man! IMO that looks awful.

Kinda reminds me of the '69 that was in the same issue of PHR as your car.

Seems like it would be a butt-load of unsprung weight, and that front end......driveways and speedbumps are out of the question eh?

[parsonsj]

Hmmm. OK.

1. It reduces caster. Perhaps the front suspension was designed for such a rake, but I doubt it based on Craig Morrison's comment about show and go wheel and tire combos.
2. It reduces the effectiveness of the rear brakes, by accentuating the weight transfer forward during braking.
3. If the rear links are not parallel to the ground, the car will have roll oversteer. Some drivers like that, but most find the behavior "darty" and hard to control.

That's good for a starter list.

jp

[Mean 69]

I'd personally think that all of the nasties with such a steeply inclined car will never be felt, because A: the car will never be driven hard, if at all, and B: the darned wheels and tires on that thing would mask/supercede any specific compromises that the suspension would have.

My goodness, what were they thinking? There really is such a thing as taking it "too far." I hate to be a smart a$$, well, actually I don't hate it, but is this car a "Pro Touring" car??!?!

Mark

[kmcanally]

but is this car a "Pro Touring" car??!?!Mark
not IMO....all form and no function...thats ok though as there is always a place for a car like this...back in the hey day of the pro street rage it was called a "fairground car"...

[yody]

i like the way it looks. those must be bigger than 20's. Nice to look at, amazing undercarriage, probably not the best car to take to the track....................

[Ralph LoGrasso]

Are those 22s or 24s? Looks like they may be 24s?

[BRIAN]

I would have to say I love his work but those wheel are just too big in my opinion. Last years TBird looked on the edge but come on those are a little funny looking besides the lack of performance issues. To each is own but I have to say after seeing that I may go smaller than my planned 18's as that trend has come and is on it's way gone. WOW!!! am I alone on this???

[F70t/a]

I love it. it looks really clean. It makes a nice cruiser and strip car :geek:

[YoungGun]

Those are def bigger than 20's...they can make 20s work (Sometimes) but those dont.
My question is did they have to extend the wheel well opening? I only ask because I have a pro-street buddy whose 68 Camaro has an extra couple inches to lengthen the quarter panel and fit the bigger wheel. Is tubbing that enough?

You could put those on an Escalade and the still might be out of place and too big!!!

Tim

[Steve Chryssos]

Well, you had to see it in person. It just OOOZED attitude--even with a simple black on black color combo. I wouldn't mind parking this hot rod NEXT to my full on P-T car. (65 Riviera?) And Craig Morrison has stated in another thread that the car has two sets of wheels & tires.

So back to th questions: Can it work? Can you compensate for a set of 22's and 18's by stepping the rear suspension and adjusting the suspension geometry i.e. extra static caster up front, extra spring rate up front??
-On this car the four bar's lower links were parallel to the frame rails which have a lot of rake--not the ground. Is this an improvement or a detriment
-As the pic at bottom shows, the car has plenty of caster.
-But, if I wanted less rake, the four bar would have to be raised (stepped) further to compensate for the mondo wheels (which I think were 22's with a lot of sidewall). This would move the rear suspension above the cars cg, No? How then do you position the rear links to compensate for the stepped chassis? Down in front? Up in front?
https://static1.pt-content.com/images/pt/2005/07/DSC02746vi-1.jpg

Take a smart pill or something. I'm asking youziz guys to help design this theoretical stepped chassis so that it works well (not perfect). The only limitation is bump clearance to the top of the rear fenders. Car would have less rake than the Alloway car

-Compensatory caster up front
-60% static rear weight bias??
-Compensatory anti-dive characteristics??

Let's see your thoughts.

[parsonsj]

A 4 bar needs to have the control arms llevel to the ground at ride height, or roll oversteer will occur because as the body rolls to right in a left hand turn, the right side bars get closer to parallel to ground, lengthening the wheel base on the outside tires; the opposite happens on the inside tires (the bars rotate even farther from parallel), shortening the wheelbase. A 4 bar level at ride height will tend to shorten the wheelbase on both side of the car the same amount as the tire goes up on one side about as much as the tire goes down on the other side.

The way to "fix" the rear suspension is to push the frame attach points up into the car. Probably several inches for such a huge tire. Mebbe go to a 3 link (assuming it has a rear seat) to save the rear seats. With a 3 link you can tune in less anti-squat so there is more rear brake leverage (anti-lift) to help with the inherent weight transfer disadvatanges. I'd swap over to a more tunable rear sway bar too.

More static caster, sure. I forgot about anti-dive before, so that would need some work too.

I dunno. Mark is right: that's a lot of work just to put a very heavy wheel and tire under the car.

jp

[Steve Chryssos]

Okay. So maybe rear rotors need to be larger than fronts? Like they are on my Hemi Ram. Add that to the wish list. What else?

[steemin]

I certainly can appreciate the work that went into this car.
Beautiful craftsmanship!
But to be candid. I don't understand ones desire to put wheels of that size under a car. The only reason I can come up with is to prove that it can be done.
I must be an old fogey..(45) just does not work for me.
Scott

[BRIAN]

Do not really see how the different tires alone are going to make a difference as the rear arms have to sit the same with both sets so they will have to be of the same diameter. I can't see in the pics but is there several equally spaced sets of mtg for the 4 bar to be lowered and raised within that set up without changing the bars relation to each other? Obviously the remaining suspension components would have to be equally adjustable. That lower arm as you said sits level with the frame which means there has to be some serious limitation of the backseat and rear pan?? I would think the breaking may be the easier problem to resolve. I am curious to see a write up on the car and what they designed. AM killed with that 55 so I am sure this one will also perform. Still not into the wheel thing though which is surprising because some of the 69's with the 20's don't look bad.

[Steve Chryssos]

The 2nd set of wheels just subtract rake--level the car out, which in turn levels out the lower links. The part I'm having trouble with is if you step the frame, the rear suspension swings thru an arc that is many inches too high. Wanna get the lower links level with the ground? Then you have to raise the suspension pickup points a little more. What affect does this increase in height have on handling?

[sinned]

Haven't heard much about the effects raising the rear subframe has on RRCH. With the front end that low I'm sure the FRCH is on the ground at least and by raising the rear frame rails they have raised all the points that determine RRCH, kind of backwards thinking.

I disagree that because the 55 handled so well this will too, that car was built totally different than this one and no car running "dubs" can possibly handle well. It is simply not possible due to side wall compliance issues. Might make a nice "drift" car though. I doubt simply chaging tires will make a difference as the front end is really too low to have any travel, I imagine it as having "mini truck" type handling (just bounce off the stops through the turns).

[CAMAROBOY69]

I think it looks awesome!!!! I would have to assume it would ride a little rough and not handle as well as if he had smaller wheels in the rear. But who cares when a car looks that good!! :drool:
If nothing else you could drive the car like that as daily driver then when you get to the track throw on some smaller diameter wheels in the rear.
THAT would be creative engineering. Compensate for large wheels for daily driver and shows, then still have the ability to just throw on smaller wheels for the track without having any clearance issues like dragging exhaust or suspension components dragging. :look:

[Mean 69]

There are quite a number of things happening when you lift the end of the car up this far that might not be so obvious, but are really important.

As John stated, roll steer is certainly one aspect that you'd really need to be aware of, with the special case of a parallel (plan view) four link setup, or three link, or torque arm, the roll axis is defined to be parallel to the inclination of the lower links. There was discussion about the lateral restriants in one of the archive threads, I think the three link one. You can cheat this tendancy by better defining the roll axis, through a convergent lower link arrangement, again, see archive. Anyway, as this one is exectued, the LCA's should be made to be parallel to the ground in order to mitigate roll steer characteristics with the big boy tires. I suppose this could be done either at the frame, or at the axle, with multiple link mounting points, it feels to me that you'd want to do it at the axle (or both locations, really).

One issue that I would be really, really concerned about in terms of basic ride quality is the fact that the LCA's are pointing down-to-front, and the impact on pure bump-ride quality. If you look at this in side view, well, when virtually all suspensions rise due to bumps, the path of the wheel either moves purely up, or moves towards the rear. This is important. Nature really wants a trailing type of linkage for wheels going over bumps, the easiest analogy I have is the front wheels of a shopping cart. In normal operation, they handle little bumps pretty good, but every once in a while, you get one turned around such that the wheel part is actually in front of the pivot. When you hit a bump in this fashion, you REALLY feel it. Same deal here, with the big tires it certainly looks to me that the path of the wheel over bumps moves it FORWARD, this will really increase the harshness of just basic ride.

When you jack a car up so far like this relative to a decent static setup, the "Anti's" get crazy really fast, due to two different but simultaneous things. One, the center of gravity will raise, even with a big rake, I can't see it going anywhere but up. As a result, the CG height which is fundamental in defining the Anti-squat and Anti-lift of the rear setup, changes. From that specific difference, it might not be terribly different, but it could be. What will really throw things out of whack is the location and angles of the control arms, not only the lowers as were discussed above and in previous posts, but the uppers too. Depending upon how they are arranged, virtually all other important aspects of the geometry will likely change, and in these cases, DRAMATICALLY, unless there is sufficient allowable adjustment to bring things back into line with the new setup. Roll center height, side view swing arm, aye-aye-aye, all of these aspects are really sensitive to even tiny changes.

For the front, well, there'd be a bunch of stuff happening there too, caster is certainly going to be affected, but I would, at least at first thought, think all of that would be secondary to the really radical roll couple between the front and rear roll centers. I suppose you could use different stabilizer bars to calm things down a bit.

I think the real key for this type of setup is to have significant adjustment points for the rear control arms. Certainly, a three link or the parallel UCA type four link would make things quite a lot easier than the convergent UCA arrangment. I think most folks here know how much admiration I have for Katz' abilities, and though we haven't discussed this one, I can virtually guarantee that the approach here was to make a good handling car with the "go" rubber, and have something "acceptable" for the "show" rubber. Katz, perhaps better than anyone understands the word "compromise." Nothing is free.

Good mental exercise, eh?
Mark

[MuscleRodz]

Kicking or "Z"ing the frame will lower the CG of the car and help in cornering. With such a large wheel, there should also be a equally large brake to stop the huge amount of rotating inertia. Therefore you would expect to see a larger brake on the rear of this car with a lot of bias to the rear. However, those wheels are for show, so performance with that set is not an issue.

This car was built to perform. Alloway knows how to build them. I will have to find the magazine, but I remember this car was going to compete in the 0-200-0 shoot out, but was not finished on time.

I think once all has been diclosed about the car, it could be one of the baddest out there.

Mike

[BRIAN]

What I was saying in regards to the AM 55 was that they made that set up work so well I am sure they would pull it off with this one. Just as everyone else does I buy every magazine out there and that 55 has pulled off what I believe to be bench mark numbers for a STREET driven car with NO adjustments made to it. I have not seen the Challenger so I assumed that the lower arms were level with the larger set up. If this were true it obviously would throw off the vehicle on the smaller diameter tires without some form of adjustability. What it comes down to is the chassis had to be designed at a specific ride height to perform as a handling machine. If they go beyond this and jack it up to stick large tires under it for show purposes that doesn't mean it will handle well under those adjustments. Hey you can take any car with an adjustable suspension and raise and lower it all you want but it only performs well at a specific height. The first measurement you take when setting up a chassis is ride height. If it is designed to sit level with say a 26" tall 18 and they just jack it up at the show then no it isn't going to handle well at all at that level. Kind of like a mechanical air bag system?? I am interesteed is seeing a write up on the car as to what they intended it to do and in what configuration.

[Steve Chryssos]

This car will not offer optimum handling at any ride height because of the radically different roll center heights. But it looks like all the geometry was set up for the GO wheels and tires which supposedly just reduce the cars rake thereby bringing the rear LCA's parallel to the ground.
Back to the mental exercise. Let's apply all this to my Rivi as follows.
-22's/19's with 45 or 50 series rubber (plenty of sidewall--probably sporty SUV tires)
-Almost level chassis (no crazy rake) Low CG
-To accomodate the big rubber without a crazy rake, rear suspension must be stepped--probably more so than on the Challenger.
-So the problem is: RRCH is way higher than FRCH. Rear axle centerline might be 5" higher than front axle centerline
Questions:
1) From what I've read so far, rear LCA's should still be parallel to ground. What about the rear UCA(s)?
2) Can I compensate for RRCH/FRCH differential with an atypical panhard bar location?
3) Will spring rate FR/RR vary as opposed to build with balanced wheel/tire selection?
Remember, this is a hot rod build. Furthermore, I believe the trend towards tall rubber is growing. As Mark said, it's a mental exercise. May as well explore the subject.
Then if someone serious shows up to ask questions (maybe me), we can say: "Knock yourself out, but...." or "If you must, do it like this..."

And we haven't even looked at drivetrain alignment issues. If you raise the rear clip, do you raise the engine and trans? Rotate the rear axle a bunch? Yeesh!

[MarkM66]

This car was built to perform. Alloway knows how to build them. I will have to find the magazine, but I remember this car was going to compete in the 0-200-0 shoot out, but was not finished on time.Mike

Wrong car. You're thinking of the Mopar Alan Johnson is building.

[MuscleRodz]

My bad. Too many magazines and cars to keep up with. :guilty:

Mike

[Mean 69]

This car will not offer optimum handling at any ride height because of the radically different roll center heights. But it looks like all the geometry was set up for the GO wheels and tires which supposedly just reduce the cars rake thereby bringing the rear LCA's parallel to the ground.

While simultaneously bringing the upper arms back into a reasonable angle, which will lower the RRCH (big time), and "correct" the geometry for the anti's etc. Keep in mind on this car that the UCA's define the roll center height, because they are the sole lateral locating device(s) on this setup (convergent four link). (The way you find it is to find the imaginary intersection point of the UCA's, which will be behind the axle. Then, you project this point along the roll axis of the rear, and find where it intersects the rear axle centerline.) Because in this case, the UCA's are asked to do two things simultaneously (locate rear laterally, AND longitudinaly), things are a bit more complex to optimize than a non-converging UCA arrangement. In this latter case, the roll center height is largely determined by the PHB, or Watt's, so you can do a heck of a lot more to determine a "better" roll couple between the front and rear suspension systems.

The short answer, in my opinion, is that you will want a decent amount of vertical liberty for adjusting the PHB/Watt's when you dramatically raise the car as such. It should scale bascially linearly with the amount of axle lift. Then, you will want to drop the LCA's, at the axle. You'd likely want to do the same with the UCA(s), but the darned axle would get in the way, so you'd have to be able to raise the front of it(them) instead. It is actually an easy (and very educational) exercise to draw this out on paper to find the "envelope." Of course, it is even easier to do with the really good programs available, but I think you learn more doing it old school, and then use the computer to verify math, etc. Too many folks are quick to spit out answers el;ectronically without understanding what they are telling them (I always get a kick out of cashiers that can't count out change from a transaction because the register doesn't pop up the exact answer for them).

Again, there is a lot less going on in the front that would be really nasty in such a case, you could just live with what the changes are in the pimp example, and leave them set for the functional case.

Your mileage may vary.
Mark

[Steve Chryssos]

Thanks for all the info guys. Now if I can somehow combine Alloway's caricature formula with Frank Serafine's Caddy SRX AWD conversion idea, I'll have one hell of a hot rod.

[Ralph LoGrasso]

Steevo,

If you're keeping the 'riv black (which you should!) you should maybe think about some black centers with polished lips on the wheels. It would look absolutely sinister and go great with the black/chrome accents the riv already has.