Advantage Of Non-sunroof Model?

[funkymofo 0]

As per title really.

I notice most people building track day cars opt for a non-sunroof model if possible,but why?

Are there structural advantages or is it to do with roll-cage fitment,or is it something completely different?

 

Thanks in advance.

Edited November 27, 2006 by funkymofo

[aeinstein 0]

having a sunroof is nice in the summer, but cutting a square of metal out of your roof will reduce strength.

 

i've only known the sunny models to have suffered rust in the corner of the screen as that is the weak point and it flexes enough to fatigue the metal.

 

never seen it on a non sunny.

 

if i had a sunroofed track 205, i'd plate the sunroof.

 

and if you tip a car on track, you really don't want a glass shower, do you?

 

al

[ashley peddle 3]

its more motasport innit

 

i think a lot of the worry is rolling the car with glass above you as instinct is to put your hands up... its easily fixable with something like this... (what i have fitted to my car )

 

[aeinstein 0]

its more motasport innit

 

i think a lot of the worry is rolling the car with glass above you as instinct is to put your hands up... its easily fixable with something like this... (what i have fitted to my car )

 

 

ashley

 

i assume your gti has/had a flip up, rather than a vac roof? although it has the screen trim off a vac roofed car?

 

al

[ashley peddle 3]

no it wasnt a flip up... it was a full sliding back one from factory...

[Baz 421]

As Ashley says Motorsport regs state that any shatterable material in the roof is not allowed, and has to be replaced with something adequate or plated.

[smckeown 1]

strength, looks beter, doesn't leak

[Alastairh 47]

If i was to build a track car from scratch. I personally start off with a sunroof shell and do exactly what ash has done.

 

Put Ashleys car side by side to a non sunroof shell, and press the roof in...

 

Alastair

[ashley peddle 3]

what alister is trying to get at is that supposedly sunroof models have more strength in the roof because (like with convertables) they are built with the flimsy glass roof in mind... rivet in place a nice piece of aluminium and you have added strength so *in theory* its stronger than a non-sunny dunno if thats tru or not though, lol...

 

my roof still leaks a bit, but only 1 lil drip and its stored inside anyways so i dont care

[funkymofo 0]

cheers guys, I actually figured it would be along those lines but just wanted to make sure there was nothing glaringly obvious that I had overlooked!

 

I actually really like the look of the aluminium plate riveted on!

 

Will be going to view a few of the little critters this week so now I know sunroof is one less to thing to worry about!

Edited November 27, 2006 by funkymofo

[ashley peddle 3]

i still have 2 of them plates left over from the group buy if you need

[j_turnell 134 3 Cars]

Can't see how a non sunny shell can be stronger tbh. For pug to cut a hole in the shell obv they had to strengthen that area which they did on the factory sunroofs. So removing it and putting a plate on it surely has to have more strength than a thin bit of metal all the way accross with no strengthening????

As Alastair says try pressing on the roof of both.

[Rob Thomson 6]

Can't believe that nobody's mentioned weight... the sliding sunroof weighs a load, something like 15kgs? And it's obviously in absolutely the worst possible place for that weight...

 

I've never seen a pneumatic sliding sunroof that's worked properly. Either the latch is knackered, the pneumatic bit doesn't work properly, or the sliders are f***ed. Or in the case of my old 309, all three.

 

Regarding the strength thing, how much a panel deflects up and down has bugger all relation to how effective it is in a car monocoque, because that isn't how it's loaded. If you're bored, go find an old shoebox with a lid. Open the lid and try flexing the main part of the box, holding it at it's ends. Flexes like a bastard, doesn't it? Now shut the lid, and twist the box again but holding it shut. Oh look, suddenly it's infinitely stiffer... That flat bit of card makes all the difference. Same with cars.

[funkymofo 0]

i still have 2 of them plates left over from the group buy if you need

 

 

 

let me get the car first and then I might be in touch lol

Edited November 27, 2006 by funkymofo

[j_turnell 134 3 Cars]

Regarding the strength thing, how much a panel deflects up and down has bugger all relation to how effective it is in a car monocoque, because that isn't how it's loaded. If you're bored, go find an old shoebox with a lid. Open the lid and try flexing the main part of the box, holding it at it's ends. Flexes like a bastard, doesn't it? Now shut the lid, and twist the box again but holding it shut. Oh look, suddenly it's infinitely stiffer... That flat bit of card makes all the difference. Same with cars.

 

 

So using your shoe box example if the lid has folds and strenghtening within it then surely its going to provide even more strength against flex than a single skin lid?

Edited November 27, 2006 by j_turnell

[Paintguy 0]

I'm with JT on this one.

 

I've changed many roof skins (although no 205's - yet ) and models with factory sunroofs always have extra strengthening in them. I recently did 2 non-sunroofed cars (307 & Punto) and they were literally just a metal skin welded around the edges, with no real reinforcement at all. In fact the Punto had absolutely nothing inside the roof 'framework', and the 307 only had a couple of thin bits of tin sikaflexed on to reduce resonance.

 

Whether the sunroof reinforcement adds to the strength of the shell is another matter. As Rob says above, the roof skin really only prevents lozengeing of that area, but if I were going this route, I'd still rather plate over a sunroofed shell. Or replace the whole skin with a non-holey one. If the car goes tits up, I'd rather know there was a bit more than just a flat metal plate above my head.

 

Clearly whatever method is used, the weight and safety advantages of not having the glass roof are a given IMO.

[Rob Thomson 6]

So using your shoe box example if the lid has folds and strenghtening within it then surely its going to provide even more strength against flex than a single skin lid?

Clearly folds and strengthening gives the panel extra rigidity, but in terms of that giving the shell extra torsional rigidity (which is what matters in terms of handling etc) it'll have absolutely bugger all effect.

 

If you were to roll a car and it landed on it's roof, the strength of the roof panel is practically irrelevent because it'll fold up however stiff it is. The box sections around the edges and the pillars are what take the forces.

 

The rigidity of the roof panel is important if you're worried about wind noise or you stack big boxes of s*it on top of your car when you're not using it, but a flat panel is going to be just as effective at keeping the shell stiff as a flat panel with a hole and strengthening.

 

Trust me, I'm an engineer...

[ashley peddle 3]

sunroofs weigh 15.5kg's, my panels weigh 3kg's so there is quite a weight saving... plus its off the top of the car so lowers the centre of gravity (only by a small margin but every little helps right?)

[pdd144c 0]

Weight is the main reason. As for non sunroofs being stronger, has anyone actually seen what holds the roof skins on? 6 spot welds and some filler... Hardly structule.

[Alastairh 47]

Rob take one flate piece of metal and do a Ralf haris shake it side to side, quite alot of movement wouldn't you say?

 

Then take a baking tray, that has scrimped ends (just like a 205 sunny roof) and do the same action.

 

Which one moves more?

 

Oooh snap, im an engineer aswell...

Edited November 28, 2006 by Alastairh

[Emmy Seize 8]

To sum it up :

 

Better torsional rigidity ? - YES

Lower center of gravity ? - YES

Less weight ? - YES

Less aerodynamic drag ? - YES

Not bumping your head against the headlining every 2 seconds ? - YES

Nice to have a piece of metal between your head an the tarmac once you overdid it ? - YES

 

And after all : The stupid sunroof is just damn UGLY !

[taylorspug 7]

Weight is the main reason. As for non sunroofs being stronger, has anyone actually seen what holds the roof skins on? 6 spot welds and some filler... Hardly structule.

 

Thats more the reason than anything. The roof really doesnt do alot in terms of strength, and if it is making a big difference then you've made a hash of installing your cage and tieing it in to the shell. Currently have the roof skin off of my Golf, and the shell doesnt deflect at all or need any bracing, mainly because the cage is properly tied in to the shell and supports it.

[Rob Thomson 6]

Rob take one flate piece of metal and do a Ralf haris shake it side to side, quite alot of movement wouldn't you say?

 

Then take a baking tray, that has scrimped ends (just like a 205 sunny roof) and do the same action.

 

Which one moves more?

 

Oooh snap, im an engineer aswell...

A structural engineer....?!

 

You've completely missed my point, which is that it doesn't matter how much the roof panel flaps about (like Rolf's wobble board) because that isn't how the panel works as a structural element of the car. When the roof panel is loaded as the shell twists the forces try to make the square roof diamond shape. It's the panel's resistance to that loading that gives the car additional strength, not its resistance to up-and-down movement. Additional strengthening to the panel will have bugger all effect to the torsional rigidy of the car.

 

(Anyway, aren't the edges of a baking tray like the box sections around the edge of the roof....?)

[Daxed 7]

On any day that it isn't raining (bit few and far between at the moment), it is a joy to open a roof as big as the factory fitted one and get a free hair dry.

 

My last 3 205's have all had the factory roof and all have been completely leak and trouble free.

 

Do you guys end up upside down a lot?

[Henry Yorke 269 3 Cars]

My 205 is a non sun roof!

 

The main reason people want a non sunroof is because it feels more motorsporty and if you want to compete you have to do something about it anyway. In a similar way, a white non sunroof is the most desirable as white is a motorsport colour!

 

If i was worried about being upside down, then I would be thinking more along the lines of a decent helment and a roll cage as opposed to whether there is a piece of tin foil above my head.

 

Also a rollcage fits better with no sunroof too.