Sunroof Pros and Cons

[Guest]

:bs: My Festiva never handled any different with or without the sunroof... It's a good THEORY.. But experience says it just isn't so. The amount of normal Festiva bodyflex is not exaggerated by a sunroof..

Next you guys will be telling us we all need rear strut bars or we're doomed from the dreaded bodyflex. Please!!

[Safety Guy]

The sunroof is for Luxstiva. For practice I may put one in Muttstiva.

For a performance Festiva I don't want one.

Luxstiva will get a mild B6 and the Aspire suspension and brakes. The "theme" will be a nice daily driver automatic with A/C. The sunroof will be nice for my "luxury Festiva."

I don't expect the tip up sunroof to add much weight up top. I will weigh things if and when I do it though, so folks will know.

As far as reducing structural rigidity, if the cut goes into a roof reinforcement support, I'd expect some more flex. If not, I'd expect it to not be so noticeable. Remember, this is a small 'roof, not a large one!

No way would I put a sunroof (or A/C) on that future project I call "Speedstiva!"

Oh, and if my Aries ever gets back on the road with that V-6, it won't have a sunroof either. I'll only have one Aries, and it will be as light as possible (within reason).

Karl

[Rich Norman]

Someone asked me this before, the person having been told sunroofs will hold back the Festiva in the dark ages of handling :

My reply:

Unless you have proof positive, from results of test rigging for static torsional rigidity, you have nothing but aimless speculation.

At any rate, there is so much more related to analyzing and optimizing chassis and suspension dynamics, that the mere concern of the installation of a sun roof is made quite trivial.

[SimonTuffGuy]

I wouldn't take my ragtop out for anything. I couldn't tell last year because of the air suspension, however I'll be sure to post up my feelings once I get my Teins installed (if it feels different then when I had both of my previous Festivas without and with a stock sunroof)

Simon

[Rich Norman]

:bs: My Festiva never handled any different with or without the sunroof... It's a good THEORY.. But experience says it just isn't so. The amount of normal Festiva bodyflex is not exaggerated by a sunroof..

Next you guys will be telling us we all need rear strut bars or we're doomed from the dreaded bodyflex. Please!!

Lateral rear suspension loads are primarily handled at the trailing arm attachments. This lessens the lateral forces at the top of the rear shock considerably, making a rear horizontal brace not as critical as on a rear strut car.

But bracing the towers for vertical / negative 3? 4? degree ( forgot the angle ) spring loads is beneficial ( especially if you are racing ). Rear braces from roll cage and strengthening plates work wonders for this.

[Guest]

I agree, bracing is a must for proprietary race cars like Tim's Deronne's WHRRI car or your V8 monster. But IMHO, for a regular street car that is sub-150hp, FWD and has rear struts, it's just a conversation starter.

[strat81]

I wouldn't take my ragtop out for anything. I couldn't tell last year because of the air suspension, however I'll be sure to post up my feelings once I get my Teins installed (if it feels different then when I had both of my previous Festivas without and with a stock sunroof)

Simon

^kind of a moot point since you haven't had the same suspension setup on a non-sunroofed car...

granted it is in theory... but you can't cut a hole out of the roof of a car and expect it to be just as rigid as it would be as one solid piece. the difference may not be noticeable... but it is still there...

[Guest]

but you can't cut a hole out of the roof of a car and expect it to be just as rigid as it would be as one solid piece. the difference may not be noticeable... but it is still there...

That is true unless the hole was reinforced like the 121 Funtops that came that way stock.

[Rich Norman]

granted it is in theory... but you can't cut a hole out of the roof of a car and expect it to be just as rigid as it would be as one solid piece. the difference may not be noticeable... but it is still there...

If you are talking about the OEM sunroof, I doubt it's installation will be noticeable for most people.

Weight for the oem part won't be too much of an issue unless you are obsessed with freeing up the last couple of pounds for a race car. The weight of the assembly is 10 lbs. 20 oz. For a racing application, it's often just not worth having one out of safety concerns alone. Many track regulations want the sunroofs positively restrained or allow removal/substitution. Just one less thing to worry about.

The assertion that a sunroof will be too heavy and will noticeably detract from "performance" street handling holds true for some cars. But making a case about it's weight and it's perceived impact on handling while other aspects of the car remain unoptimized is just flat-out ridiculous.

An oem-type sunroof in the Festiva is unlikely to cause a rigidity problem. The hole that is cut out for it is on the small side ( as sunroofs go ), but more importantly, it is made in an area between roof reinforcements. Thanks to good engineering ( Mazda ), the sunroof frame is very rigid ( thanks to an extruded aluminum profile ) and is adhesive bonded to the roof skin. I can tell by it's engineering that it is a sunroof designed for function and concern for strength. Mounted properly in place, it is giving back a sizable amount of the original strength.

People tend to believe that the roof's contribution to chassis rigidity is just based on the flat sheetmetal. Hardly. You also do have box sections at the windshield and liftgate headers, above the side doors, and roof reinforcements to assist in keeping the bodyshell rigid, and they play no small part in that.

The worries are not unfounded, because the roof sheetmetal does act as a large stressed panel. Obviously removing too much of this skin, or cutting into these reinforcements, such as an opening for a canvas sliding roof ( a cut that involves far more area and roof supports ), or adding T-Tops ( cutting out the box sections above the doors ) has potential to reduce the stiffness of the roof module ( and hence body ) rigidity considerably.

Want a simple experiment, take a stiff cardboard box ( rectangular shape works ), cut a small rectangular hole on the longest and widest side, twist ( torsion ). Then cut out the majority of this same side, leaving a perimeter. Twist. Note the difference.

[Silv3rBull3t]

Yes, most OEM sunroof's are built with rigidy in mind but all I am saying is that MOST especially since most people will not be buying OEM equipment are NOT.. From what I have seen they serve almost no purpose other than to put a foam/rubber seal around a hole cut in a roof along with a piece of glass. And yes you are right most of the time you would never be able to tell, but in my instance I race my Festiva and I know the loads I put on it would prove that a sunroof reduces structural rigidy to some degree.

Also, when a car is a convertible or ragtop it is usually substantially heavier than the coupe or sedan version because they do add bracing to strengthen it from lateral loads and flexing which proves to be heavier and sometimes even worse still than the lighter, sedan/coupe versions, so for a race application people do not tend to look for either.

In your car DJ, you have 100+ lbs of audio/visual stuff in the back so IMO you would never tell to begin with. What's another 10lbs in the worst location possible for COG? Probably not much for you, but for people who are trying to get the most out of the car it is. Every lb counts! For me, I even swapped from the shitty auto seatbelts and all their horrible wiring/tracks for the old style manual belts. I saved almost 30lbs right there... But anyway my point is that you have to decide what you want your car to do well and head in that direction. -Kyle