I see what you are getting at now. You recon. that the door itself adds stiffness? It will, only if you weld it solidly into the main body. The door is on two hinges, a pin at the catch and rubber seals. The rubber seals transmit no load, I can press them in with my little finger!
lol, more the shape of the pressed metal that the door goes into, the way it curves around the rear wheel profile means its nothing like the front door. If I really was to try and explain my theory behind it Id need to write a long post, cant do that right now as I really dont feel normal.
I'd assume what you can gain from not having the rear door you could lose somewhat from having a larger front door. The ideal for chassis stiffness is probably a 5 door with the backs welded up, that's how I'd play it with a full on cage. Of course I'm not building a track car, I want a road car and not really wanting to give up my leather seats either. Once you move all the factors around both chassis are probably the same amount of stiffness due to the advantages and disadvantages of each shell. I think to truly calculate the difference you'd need more than an A4 diagram aswell, dozen other factors. Most of them discounted with a cage by the track fellas who weld in and get it all nice and stiff anyway. In theory wouldn't a larger hole be allowing more flex than two smaller holes though? I still prefer the 5 door for whatever reason, probably because it's way more convenient than a 3 door for the amount of stuff I chuck in the back.
same as me and my pug 205, it might have been just a 250quid scrapper but i still hated the 5dr look, just doesnt suit small cars.
All design engineers undertake basic structural design on A4 sheets. And, that's all this is a basic look at the relative merits of 2 and 4 door car structures, in the same body shell type. Fistly, I am only considering 'Torsional Rigidity' in the basic body. Roll cages, that add stiffness are another topic entirely, and will only confuse more, what is obviously a confusing topic already. Bending stiffness is a different matter. And, when it comes to bending, two small holes are better than one larger hole only if the total length of the two holes is the same as the length of the one the single hole. In this case it is are not. Torsion is transmitted through the peripheral skin of the structure. So, the more skin you leave in the periphery, the better torsion is transmitted. As, the angle of twist is proportional to the area of metal left in the skin, multiplied by the length of the total metal cut out, no matter where along the length you cut it out, then, as the total metal cut out in a four door body is more than in a two door body, it will twist more. Extra metal in the rear door sills, and at the wheel arch will do little to help torsional stiffness as it is not running around the periphery of the structure. (It will help bending stiffness). The quater panel of the two door will transmit torsional loads, as it is on the periphery of the structure, and it helps more towards bending stiffness as well, as it is tall, and is thus dificult to bend. Welding up rear doors would increase torsional stiffness above that of the two door body, but it would weigh more. Thus, the loads to be transmitted would be higher. It is all a trade off between weight and stifness. Convertables have a lot of extra steel shoved in them to increase stiffness, but they still end up a lot less stiff than tin tops! Some figures I found on the net: Ford Focus 3d 19.600 Nm/deg Ford Focus 5d 17.900 Nm/deg
It wasn't a dig at using an A4 sheet, it was that it was on a single sheet when the full amount of it would be obviously alot more. Not discounting your calculations, merely stating a point. We could spend years debating this, I propose a more fun test, get one of each and rag them around a track for a few hours. Anyone want to submit their car for this testing?
I appear to have missed another one of these debates... 5 door, although more practical if you want to use a GTI as a family car (which kind of defeats the point of having a GTI) looks sh*t. 3 door mk2's look the best. Argument settled and lets move on!
There's nought really wrong with the look of the 5 door, it's certainly easier to find a good deal on them aswell. I paid 270 for one with pretty much no rust, can't exactly complain for that price.
Not dead, just resting. Iv just found some more figures that seem to show more doors being stiffer in the case of BMWs: BMW E46 Sedan (w/o folding seats) 18,000 Nm/deg BMW E46 Sedan (w/folding seats) 13,000 Nm/deg BMW E46 Wagon (w/folding seats) 14,000 Nm/deg BMW E46 Coupe (w/folding seats) 12,500 Nm/deg BMW E46 Convertible 10,500 Nm/deg Sedan is 4dr, wagon is 4dr, coupe is 2dr. Biggest difference is just the folding rear seats but BMW's are braced like crazy behind the rear seats on the non folding rear seat models.
My 3dr was awesome, but the reason I went for the 5dr was for practicality. From this - To this - Also there isn't many 5drs being done these days, and this one has nearly every option from VW, and after 20yrs they still work!!
Sorry, you are not quoting like for like. The coupe is 2" lower than the 'sedan'. More like a convertible hard top. So, it is a bit stiffer than the convertible, which makes sense. Need figures for two and four door 'sedans', from previous incarnations of BMs
Sorry you've lost me on the E46 thing, the coupe is 2" lower so its more like a convertible? To be honest from what I read on that thread (suspect same thread you got your focus figures from?) some 5dr cars are very stiff due to manufacturers designing them to be stiffer, and some are just bendy POS. Dont know for sure about 5dr golf mk2s but they are pretty chunky compared to others, my 5dr pug 205 here looks seriously weak. Did you see the figures for the Phaeton? Crazy for a car with such large doors.
Looks like it was the same thread. I hunted for ages to find figures that compared two door and four door cars from the same manufacturer. I discounted the BM figures for the reasons below. Because it is lower, the body won't generate the same 'polar moment of inertia', because, the distance around the periphery will be less and the enclosed area will be less. You have to compare like with like. Two door with four door - with otherwise identical bodies in cross section. When searching, did you notice how many manufacturers, including VW were, quoting higher torsional rigidy for new models compared with previous? Some saying 80% more. They seem to have realised, at last, how important rigidity is. Some people have known for years. Perhaps it's the only part of the body that the stylists let the engineers have their say on? Back in the day, Saab produced uber stiff bodies, with built in extruded steel tubes in the A and B pillars. I tried to find figures for the Saab 99, which was available in 2 and 4 door forms. As Lotus Engineering said, "the Saab 99 was the best handling FWD car".
Gotya on the BM stuff now, and yea the new stuff is crazily stiff I thought some of the figures where misprints! While searching on the subject I do remember reading something on Saabs being one of the stiffer makes or cars for its time but cannot remember what forum it was on. I really hunted for any old golf figure (Mk1-3) just to compare with modern day stuff but nothing seems to be out there.
maybe it's rose tinted spectacles bit my first mk2 gti (5dr) always felt very stiff and handled superbly...
