Hardtop or Soft-top for track days?

deviant · Postby **deviant** » Thu Dec 08, 2011 9:18 pm

I think one thing that we are all forgetting here is that....

.....It is 100% more fun being on track with the roof down :mrgreen:

davekmoore · Postby **davekmoore** » Fri Dec 09, 2011 12:36 am

FWIW after having the soft top up last time at PI, despite the clips being very well adjusted and fully engaged, at the end of the straight the clips still popped leaving the front of the roof 4 inches open and threatening to open all the way. This was not fun especially as the end of the straight is a good place to be concentrating on driving, not on sailing.

For the rest of the day the roof was down. No doubt this was slower. But it was much more fun hearing and seeing what was going on around me. And whereas the roof being down and creating more drag might have cost me 2 seconds a lap, the lack of driver expertise was probably worth -10 seconds. Still had fun though.

davekmoore · Postby **davekmoore** » Fri Dec 09, 2011 12:38 am

deviant wrote:I think one thing that we are all forgetting here is that....

.....It is 100% more fun being on track with the roof down

+1

lightyear · Postby **lightyear** » Fri Dec 09, 2011 7:42 am

With the softtop down at phillip island it is in no way more fun. The buffeting, and your head wobbling does nothing to help concentrate, and the less wind noise, the easier it is to listen to the revs, etc.... I have more fun keeping up with faster cars, something you can't do with the softtop down. And i agree that the hardtop does help with stiffening the car. The softtop has no diagonal bracing, the hardtop does as it is a solid structure. With a hardtop on the car it will even stop the 100km/h wobble.

Lokiel · Postby **Lokiel** » Fri Dec 09, 2011 10:24 am

Guran wrote:
Lokiel wrote:
16bit wrote:only stiffness you will get will be if you have bolted plates instead of the latches.

I disagree. Prior to fitting my roll bar, the chassis felt firmer with the hartop+latches.

http://forum.miata.net/vb/showpost.php? ... stcount=14
Like the soft top, the hardtop is an unstressed component. If the hardtop were carrying structural loads, the rear window would pop out of its mountings as the bodystructure flexed by any degree.

The top is able to dampen (slightly) some of the lateral movement of the windscreen header, but the primary reason behind this is that with the top up the visual contrast between header and sky is diminished. With the convertible top raised, the multi-component aspects of the top induce rattles which the single-piece hardtop doesn't have, thereby creating the impression that the hardtop has stiffened the car vis-a-vis the erected convertible top or with the top down.

The car's torsional rigidity was measured in all three planes (as a body-in-white as well as a completed car) with the top down, top up and the hardtop on and there were no appreciable differences in the figures.

I don't question that it may feel stiffer, but this is much more an example of the placebo effect than one actually reducing the bending moment of the car, I'm afraid.

bwob

This sounds quite reasonable and MAYBE my perceived additional stiffness was more due to the fact that the padded roof made the ride MUCH quieter but one of the MAZDA head honchos way back in the early days was claiming it added 15% rigidity (which is a lot) - marketing hype to sell more hardtops maybe?

jonosx · Postby **jonosx** » Fri Dec 09, 2011 2:13 pm

My car definitely feels stiffer with the hardtop on. Without it there is a "shimmy" (for a lack of a better term) through the chassis that you feel through the seat when hitting bumps etc. Hardtop on and its gone.

plohl · Postby **plohl** » Thu Dec 15, 2011 10:45 am

Soooo, when people are running hard tops, do you have the windows down? And when running the soft top, do you have the windows down and the rear window lying down?

evil_weevil · Postby **evil_weevil** » Thu Dec 15, 2011 12:00 pm

I always have my windows up. I havent got a window net, until then for me windows up

Guran · Postby **Guran** » Thu Dec 15, 2011 1:00 pm

Always have my windows up. You'll learn why when you have your first spin off the track onto dirt / mud / puddles. :lol:

It's also a lot less noisy with the windows up and I've already lost enough hearing range in my right ear as it is.

plohl · Postby **plohl** » Thu Dec 15, 2011 2:24 pm

interesting. Never thought about what happens where you have an "off"

Cal · Postby **Cal** » Fri Dec 16, 2011 5:14 pm

murph wrote:I know with the top down is a LOT slower

Yeah nah. I run a hardtop on my race car, but take it off at different circuits. I back to backed it at Morgan Park with and without. It's a whole second quicker without it. That is on a tight circuit though, where the polar momentum of 23kgs of weight (in about the worst place possible) moving left to right. At Phillip Island, Bathurst or Eastern Creek I run with it on for the aero advantage it offers at speed.

Guran · Postby **Guran** » Mon Feb 27, 2012 3:11 pm

In the name of good science, I experimented with this at Wakefield Park on Sunday 19th Feb. You can read the details here. In summary, running with the hardtop fitted was about half a second per lap slower than running without the softtop raised. The main reason for the difference was the hardtop added about 20kg to the vehicle weight, which resulted in lower speeds at the ends of the shorter straights - in other words, slower acceleration. Note that I was running the hardtop with the softtop still installed but folded down, because this is a requirement for the "standard" class that I compete in.