Re: large torsion bars on a convertible
[Re: burdar]
#2356389
08/19/17 02:44 AM
08/19/17 02:44 AM
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Joined: Jan 2003
Posts: 27,474 So Cal
autoxcuda
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I have 1.14 MP bars in my 68 Barracuda coupe with welded subframe connectors. 245/50/15 sidewall tires. Bilstein shocks
I've run .99" T-bars before that. 245/50/15 sidewall tires. And 225/60/15 before that. KYB shocks. Still softer and less harsh that 1.14" w/bilsteins
I also have a 68 Dart GT conv. So Cal car no frame or trunk rust whatsoever. No subframe connectors. It has .87" Tbars. KYBs. All rubber bushings. 245/60/15 sidewall tires.
I can certainly tell the difference in frame regidiity and cowl rattle/flex on the conv.
Tires sidewall is a big part of the harshness equation. What tire size are you running?
I would not run bigger than 1" in a convertible. I'd want to run subframe connectors too.. And I'd run rubber bushings. Paint tends to crack between trunk corner and convertible rear corner molding. Ebody verts seem even worse.
I would certainly not run 1.12" Tbars on a conv. Even with the subframe connectors. That's like putting stiff ends on a wet noodle.
Last edited by autoxcuda; 08/19/17 02:45 AM.
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Re: large torsion bars on a convertible
[Re: burdar]
#2356539
08/19/17 01:20 PM
08/19/17 01:20 PM
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Joined: Jan 2003
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autoxcuda
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That was exactly my concern. I thought a really large bar would tear up the car. The top of the quarters are not cracked...and I don't want them to. I'm planning on running a 225-40 tire up front. So you think the 1.06 is even too big... I'll look at some more options. I know there is a 1.03 out there too.
I want the car to feel tight and not spongy. I just put a caliper on the stock bars and they measure .88". So how big of a difference is there between .88 and 1"?
When I went from .88 (.87) stock a/c-340 bars to .99" there was a very noticeable reduction of roll, brake dive, responsiveness. Its more than double the spring rate. Of course there is increase road feel harshness. When I jumped to 1.14" there is a huge difference than stock. With really low profile tires not only will you notice driving over coins on the road, but you'll be able to make out the dimes from the nickels! That 225/40 series tire will feedback lots of road imperfections. That's a VERY low/narrow profile. That will magnify everything. With the .99", Ive ran 225/60, then 225/50 (got a good deal) and back to 225/60. Noticeable difference in road feel. I would: -1 1/8 front and solid rear sway bars. That will reduce the roll and help responsiveness. -Stock rubber LCA bushings, rubber offset uppers and strut bushings. And rubber leaf bushings -bilstein RCD shocks -max 1.03" t-bars. MP years ago made a .92" bar, BTW -And keep your .87 bars. You can swap T-bars w/o re-alignment. Just measure ride height, unbolt one shock end, back t-bar adj all the way out, then slide T-bar out.
Last edited by autoxcuda; 08/19/17 01:41 PM.
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Re: large torsion bars on a convertible
[Re: burdar]
#2356551
08/19/17 01:38 PM
08/19/17 01:38 PM
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Joined: Jan 2003
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autoxcuda
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I'm trying to match the stance of this car. It has a complete RMS suspension on it though. If I found out the front spring rates of that suspension, would that translate over to torsion bars? Do you have a measurement from ground to top of fender for that car? That would really help get an idea of clearances. Also the RMS crossbar sits lower than stock Kmember. So you'll have more clearance than that car. Smart choosing the TTI shorties! Bottom line is something will become the bump stop: 1) LCA bump stop 2) bottom of Kmember 3) head pipe 4) H-pipe (probably will high center on tall speed bumps) 5) torsion bar via LCA pivot and rear T-bar anchor 6) shock I've successfully, err unsuccessfully, used ALLLL those things as bump stops at some time. . Sometimes more than one at a time!
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Re: large torsion bars on a convertible
[Re: burdar]
#2356578
08/19/17 02:27 PM
08/19/17 02:27 PM
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Joined: Dec 2003
Posts: 22,697 Bitopia
jcc
If you can't dazzle em with diamonds..
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If you can't dazzle em with diamonds..
Joined: Dec 2003
Posts: 22,697
Bitopia
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I just need a torsion bar to be stiff enough so I don't bottom out but not be so stiff that it puts wear and tear on the body. This is your conundrum, because any bottoming out now, is like having a 6?" diameter TB at that point, and the impact loads the chassis sees, and any TB of smaller diameter, softens the impact loads the chassis sees. The actual forces don't change, just the rate they get to the chassis does, if everything else stays the same. Seems like everyone has different bottoming out thresholds, so no one answer fits all IMO. Pick your poison. Me, I go big.
Last edited by jcc; 08/19/17 02:31 PM.
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
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Re: large torsion bars on a convertible
[Re: burdar]
#2356595
08/19/17 02:58 PM
08/19/17 02:58 PM
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Joined: Jan 2003
Posts: 27,474 So Cal
autoxcuda
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The 225-40s should have three inches of sidewall visible beyond the wheel lip. I had a Stratus that I dropped 2" and ran those sized tires. It was a stiffer ride but nothing excessive. I know comparing the two cars is apples verse oranges.
I don't have a fender to ground measurement. I was just going to eyeball the fender to wheel gap and then see what my clearance is to the top of the inner fender. Even with the RMS suspension, that car has stock inner fenders. He's working with the same clearance As I will be.
I knew caster/camber would be an issue so I bought SPC double adjustable UCAs. Those should work great to get the best alignment. I have rubber bushings on the car with a stock sway bar. I can upgrade that once the car is on the road. I've got the MP 0 arch road race springs on the back. They might be a little too low. It depends on how low the front can go.
I appreciate the input. It looks like I'll get some 1.03 bars and see how they work. But the bottom of the K-member should be what bottoms out first on your car. The other stuff can/has been manipulated more. Like, aren't you running dropped spindles? The bottom of an RMS crossover will bottom out before a stock K-member because the RMS sits lower. Do you know the rim diameter and tire size of that Red Dart Conv? If you did, I think I could figure out your K-member ground clearance. The larger diameter rim and less sidewall give an optical allusion of being low. We naturally see these cars with a lot of black tire between the rim edge and top fender lip. Ride height being constant: as the rim diameter goes up with sidewall thinning, that rim edge to top fender lip gets smaller. There is less black between the rim and fender.
Last edited by autoxcuda; 08/19/17 03:08 PM.
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Re: large torsion bars on a convertible
[Re: burdar]
#2357057
08/20/17 12:29 PM
08/20/17 12:29 PM
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Joined: Jan 2003
Posts: 27,474 So Cal
autoxcuda
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Yes, I asked him what he was running for wheel/tire sizes. He has 18x8s up front with 225-40s. I have 2" drop spindles. I quickly mocked up a 225-50 and put it where it looked good. I only had 1 5/8" from the top of tire to the bottom of inner fender. I thought that's what I would hit first...not K-member to ground. A 225/40 will have some more clearance then the one I tested.
I've got another picture of the car that is a closeup of the wheel lip to fender distance. It doesn't even look like there is an inch between them. When you say "bottom of inner fender" is that the same thing I'm calling "top of fender lip" ?? I'm going to assume it is, but please correct me if I'm wrong. So let's just make that 1 5/8 rounded to 1 1/2 for easy math. The sidewall on a 225/40/18 is 3 9/16"...3 1/2" That would make it 2" to the rim bead. Then 18" rim diameter bead to bead. Then assume tire compresses 1/2" with weight of car. So that would leave 3" from ground to tire bead. 2" + 18" + 3" = 23" from ground to top wheel lip is my guesstimate for the red dart convertible. Now I'll go out and measure my car...
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