Why No 17" with Moon Roof?

[Space_Cowboy]

Now, I know that this topic has been discussed before. I think the jist of it is that the extra grip with the 17's would cause too much chassis flex and would actually "shatter"? moonroofs due to the stress on the roof? (I've contacted GM about this, but so far to no avail) but here's my question, does anyone have 17's (or bigger) on their car with a moonroof? Have you guys been covered in glass at all? Also, let's say I installed sway bars and strut braces and such to help stiffen up the car, would this still be an issue?

[MA-VIBE-FAN]

Pontiac's only comment to dealers has been that the 17" speed rated rain tire and the Sunroof combination raises the center of gravity and excceds an internal GM number for roll over cararistics. (Vibe inital order broadcast 9/25/01)

[Space_Cowboy]

oh okay, so there's really no issue with chassis flex or anything? I thought that was kind of a stretch anyway....strut braces and sway bars and dropping the car should help with the rollover issue yes?

[NovaResource]

quote:Pontiac's only comment to dealers has been that the 17" speed rated rain tire and the Sunroof combination raises the center of gravity and excceds an internal GM number for roll over cararistics. (Vibe inital order broadcast 9/25/01)I think that's a bunch of bunk.The 16" tires are 205/55-16 and are 24.9" in diameter.The 17" tires are 215/50-17 and are 25.5" in diameter.That makes the tire .6" taller and moves the center of gravity up .3"You're telling me a height increase of .3" makes the Vibe a greater risk to roll over? You could probably get .3" of lift by over-inflating the 16" wheels to 40+ psi (which is how many Vibes came from the dealer).

[MA-VIBE-FAN]

You are forgeting the weight of the sunroof package being added at the top of the car. And I am not telling you anything, I am just passing along the infomation that Pontiac has told their dealers.

[NovaResource]

quote:You are forgeting the weight of the sunroof package being added at the top of the car.The weight of the moonroof is not really significant in this. A Vibe with a moonroof and 17" wheels is only .3" taller than a Vibe with a moonroof and 16" wheels. Moonroof or not, I can't see how a height increase of .3" will make the Vibe a higher roll-over risk. Is Pontiac saying that a Vibe with a moonroof and 16" wheels is so close to being a roll-over threat that a .3" height increase puts it over it's limits? That's like saying a Vibe with a moonroof and 16" wheels is not very safe and just barely under their limits. If that was true, why did it get a 4-star roll-over rating by the NHTSA?quote:And I am not telling you anything, I am just passing along the infomation that Pontiac has told their dealers.I know. I'm not blaming you or saying you made it up.

[MA-VIBE-FAN]

Nova, not sure we can overlook the weight of the roof. Looked at sunroof sites but didn't find any weights. So called over to the dealership, they quickly checked the shipping weights of two recently sold Vibes. Base w/Auto (2416 lbs) and Base w/Auto & Moon/Tunes (2780 lbs). Thats a 15% difference, most of which is at the top of the car. As far as actual rollover, I will head over to NHTSA to check up, but my recollection is that the current rollover test is called a"table test". They compare based on the angle that a table would be tipped before the car would roll off. Any testing GM would do would be actual testing so tire adhession and other real world variables would come into play. I am sure every manufacturer has standards for every thing (air thru a vent, fluid thru a hose, drain on battery, center of gravity, etc), and I am sure it involves math I have dedicated my life to avoiding.

[NovaResource]

You think the moonroof weighs 364 pounds?! I don't think so.

[JayAyeEm]

quote:You think the moonroof weighs 364 pounds?! I don't think so.Seems high to me too, but I guess that in addition to the weight of the glass there is the additional reinforcing that has to be done to a roof with a hole in it, plus the mechanism to open the roof. And, don't forget, it is Moon and TUNES. That amplifier under the seat has got to be a pound and a half. And the 2 extra speakers, maybe 10 ounces each.

[a58vette]

Got my GT with 17s on it and told the dealer to install a sunroof and they did. Being an aftermarket sunroof i was very suprised that it goes inside the roof not pop out like some sunroofs do. I have not noticed anything different with the handling of the car. Havent shattered the sunroof and I definatley havent rolled it. From my perspective I cannot see anyreason why GM doesnt offer the two options together.

[d_m_kolb]

I was told many months ago and wote this in another post, the reason GM didn't make the 17s with the sun roof a option was because of a safty issue. During testing phaze the 17" tires grip so well when they did extremely hard cornering there was so much body flex that the sun roofs were shatering because of it. The 16" don't grip as well so the bosy flex wasn't enough to cause a problem. This is why there is no sun roof offered with the 17"

[Moreorles]

My Matrix came with 17" wheels and a moonroof. The dealer never said a word about it. I didn't even know it was an issue until I saw it online. This was all factory, not aftermarket. I guess I lucked out.

[Space_Cowboy]

okay, although it sounds like toyota is offering these two options together and pontiac isn't, let's just say there is an issue with chassis flex. Should I seriously be worried about it? I want to put some bigger rims on my Vibe now, just because the 16's in such a tall car with a large wheel well kinda look whimpy. So if I invest in things like sway bars or a strut brace should i still be worried about my sunroof?

[d_m_kolb]

If you invest in the aftermarkets parts you said I wouldn't be worried at all. Plus you'll love the way it handles.

[ragingfish]

Perhaps toyota uses different 17 tires that don't grip as well? I dunno anything about this shtuff.

[MA-VIBE-FAN]

quote:You think the moonroof weighs 364 pounds?! I don't think so.I didn't say I think the sunroof weighs 364 pounds, I said that the examination of Pontiac Invocies for two cars where the only difference was the Moon & Tunes package was 364. I then continued research by emailing http://www.sunroof.org and asking them. The reply was along the lines of " there are many variables but the weight should be between 30 and 60 lbs". He also requeted 25% of any funds that exchanged hands over his answer. I had to inform his it was a cashless transaction.So with that in play, it now leaves us wondering about the shipping weights on Pontiac Invoices. Ex. Nova's Base/Auto/Power has a shipping weight of 2780 lbs , as does NSimkins' Base/Auto/Power/Moon & Tunes/Aluminum Wheels/6-disc. as does Ullbergm's Base/Power/Moon&Tunes.(PS Nova, like the new signature additions).Happy Holidays and New Year to all.

[CaCathy13]

Well if I put 18's on my Vibe would I need to worry about my Sunroof shattering? I find this kinda scary...I have never heard of a sunroof shattering because of the way tires grip the road....

[d_m_kolb]

The tires don't really make the sun roof shater. It the body flex that was causing the problem. When you take a corner very fast at high speed the vehicle will lean into the curve. The better the tires the better they hold the road and the more the body of the vehicle will flex because of this. Most owners I wouldn't think would have a problem. Remember when a manufacture tests it's vehicle they are on the verge of flipping it in a conner to see what it can do and what it can handle. Most owners will never drive like this. (I probably will from time to time)A strut bar and rear sway bar I would think would make sure this would never happen since it will help keep the vehicle body flex to a minimum and the vehicle will handle better anyway.

[ourvibe]

Here's a good one.If anyone has a copy of the Canadian brochure for the Vibe take a close look. On front cover is a Lava GT with 17 inchers and you can see outline of sunroof and on page 5 is a Satellite GT 17 inchers and you can just see the sunroof. Guess the marketing guys don't talk to the engineering folks.

[ragingfish]

So, let's say for sake of argument that the body flex with the better gripping tires does, in fact, make the sunroof shatter in extreme conditions. Why, then, wouldn't the windshield shatter too? I'm confuddled.Perhaps, BTW, the heavier vibe in the two you asked about had alloy wheels or something? Just a thought...

[CaCathy13]

17's or not, if I put on better gripping tires on my stock 16's, wouldn't I face the same problem??This whole sunroof shattering deal is very confusing...

[Moreorles]

I wouldn't worry about it. I havn't heard of anyone breaking a sunroof. I did however develop a crack in my windshield, and had no idea where it came from. It is possible that something hit it without my noticing. Anyway, it's since been replaced and good as new.