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Racing a Post or Hardtop, is one better ?

tubalcain

tubalcain

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I raced Mopar's many years ago and sometimes wondered why the post body seemed to be preferred. I often chose odd combinations. The convert got me in some better class brackets. Maybe some of you will satisfy my curiosity about the advantage of choosing a post over a hardtop. Searching the net about curb weights of the two is a mixed bag at best. Was it a structural thing?
 
The post car is structurally stronger and has a very slight advantage in weight distribution. When you add frame connectors you add weight, but eliminate some body flex. I wouldn't race a convertible without frame connectors and the advantage would be in weight distribution if you are allowed to run with the top down.
 
Post cars are (generally) more structurally rigid and lighter. The B pillar is what provides the rigidity - it's literally a vertical support column (a post!) that spans the the height of the car from the rocker to the roof and ties it all together. Because of that, they require less peripheral support bracing around the door and window openings which reduces weight. Hard tops often had roll-up quarter windows and larger back lights which add to the mass.

Also, post cars were usually bare-bones models for budget-minded buyers so they were sparsely equipped to keep costs down - rubber floor mats with basic interiors, radio/heater delete, single mirror, no undercoating, etc.
 
Probably doesn't really matter much if you are racing seriously, because if you are, you likely have at least the frames tied and a full cage.

When I raced my '65 in the early years it used to lift one wheel about 6"s higher than the other, cracked a few windshields, and worse, popped out the back window a couple times. Over the years in the late '70s / early '80s, tying the frames helped, then upgraded to narrowed full frames, link suspension and 12 point cage. The biggest change in the later years that made a big difference was the front cage bars and motor plate; the car was much easier to drive at faster speeds.
 
I ran hardtops and 4 door sedan b bodies in the 12’s with no bar or frame ties and slicks. The 4 door was definitely more rigid.
 
Thanks gents, that clears it up for me. I kinda figured that it was the high HP- big slicks thing. I raced lower stock class and the only way that I could flex the chassis was with a bumper jack. Did lots of winning with my 361, closer to 400 inches. Got caught in tech once and was put in SS/JA. That was an eye opener!
 
tubalcain said:
I raced Mopar's many years ago and sometimes wondered why the post body seemed to be preferred. I often chose odd combinations. The convert got me in some better class brackets. Maybe some of you will satisfy my curiosity about the advantage of choosing a post over a hardtop. Searching the net about curb weights of the two is a mixed bag at best. Was it a structural thing?
Click to expand...
Post is stiffer because of the b pillar, hardtops don't have the b pillar, more subject to twisting....no?
 
Jerry Hall said:
The post car is structurally stronger and has a very slight advantage in weight distribution. When you add frame connectors you add weight, but eliminate some body flex. I wouldn't race a convertible without frame connectors and the advantage would be in weight distribution if you are allowed to run with the top down.
Click to expand...

Gus chiggins said:
Post is stiffer because of the b pillar, hardtops don't have the b pillar, more subject to twisting....no?
Click to expand...

See what this guy chose.......should answer the question

1963 43 Plymouth at Daytona.jpg
 
That dart was Chrysler's decision. If I had been asked, they'd have built it on the post coupe.
 
33 IMP said:
That dart was Chrysler's decision. If I had been asked, they'd have built it on the post coupe.
Click to expand...
I've always been curious as to why Hemi Darts were hard tops and not post sedans. There wasn't really a 'Cuda post-type car either so Plymouth would have had to field a Valiant. And despite hard tops having somewhat less overall rigidity, they didn't come with frame connectors either. It really was a curious choice.

My belief is that it was a marketing decision based on the "Win on Sunday, sell on Monday" adage. Let's be honest, '68 Dart post sedans and Valiants are not the sexiest cars out there so I imagine they made the concession to use the hard tops and fast back 'Cudas for that reason. In 1968, the 'youth market' was just getting established as a viable consumer base. I'd wager that in 1965, a 'racy' appearance probably didn't matter as much to people like it might have three years later. A lot changed in a short time.

Sure the post cars are cool now but back then my guess is the general buying public viewed them as cheap, throwaway transportation and wouldn't be caught dead in one. Either way, the '68 Hemi Dart might be one of the coolest vehicles ever produced by the Big Three so I'm glad it came to be regardless of what platform was chosen.
 
If you are going fast enough to run a roll bar or cage, the stiffness added by a post becomes meaningless. IMO, post cars are usually cheaper to obtain and they are more likely to have light-weight options like manual steering or (or lack of options), etc. and that is why they are preferred race car bodies.
 
It’s a moot point since they were so compromised by the acid dip, but the ‘65 AWB hardtops had B pillars
IMG_2224.jpeg
 
Jerry Hall said:
The post car is structurally stronger and has a very slight advantage in weight distribution. When you add frame connectors you add weight, but eliminate some body flex. I wouldn't race a convertible without frame connectors and the advantage would be in weight distribution if you are allowed to run with the top down.
Click to expand...
If you are racing a ragtop "legally" I believe faster than 13.49 (was 12.99) it must have a 6pt bar in it which eliminates any body flex and if it is slower than that I wouldn't bother unless it was a stick shift.
 
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