You would need to consult the AACA or similar European institution. Some classifications by year include Antique (may include Brass Era), Vintage, Classic really pertains to those luxury marques such as Pierce-Arrow, Cadillac, La Salle, Packard, Dusenberg, Auburn, Cord, Chrysler Imperial, or the high-end model lines of general manufacturers such as Hudson, Studebaker, Buick, Nash, etc.
I would wish this site to be as credible as possible, as there is a wealth of knowledge among its users in a broad range of vehicles, so assigning an arbitrary "cut-off" year would be too much for everyone to remember, I think.

Excuse the American references, there would of course be Bentley, Rolls Royce, Mercedes-Benz, among the Classic category.

I know in the States the postwar thru 1965 is sometimes referred to as classic, but standard definitions do exist, if you talk to the right people. I can work on this if you're interested. I am a member of the Buick Club of America, there may be senior members from whom this info can be requested.

Quite a hard subject this one, lots of different names used for the same type vehicles and also some odd vehicles that don't quite fit into the same catagory!
Convertibles,cabriolets,soft tops, roadsters,t-tops,t-roof,laundaulet etc...
'Vintage'(up to 1925) as wrenchhead suggests, I think would be an option.

I agree that many old cars can fit into current categories. I also think that it wouldn't matter a great deal if they are all assigned to a vintage category or if we just eliminated the classification system altogether.

However, if we are going to assign a class then we should be accurate.

As you know I favor a few broad classes and would eliminate most of the current categories. That would do more to solve the problem then adding more categories.

I do not think that it is good to put all the old cars together, especially with a so big range. Some of these old sedan or convertible are enough similar to current car to be in the same category I think.
"ground conveyor" is for the forklifts and other vehicles usually used in warehouses, airports, etc. to "move things".

That is a pretty good idea. We could just be arbitrary and say anything made before 1925 to 1930 or so is vintage. That could include everything: open cars, roadsters, covertibles, saloons, limousines, etc. Most everything that I am aware of after about 1930 or so fits in one of the existing classes.

I have no problem with being arbitrary since, in my opinion, the classes are a little arbitrary anyway, ground conveyer seems to be for anything that can't be placed anywhere else, pickup trucks in cars, chasis cab (whatever that is), etc.

One time I suggested that we'd have a class for vintage vehicles, since they do not have roofs and are not really convertibles. But I think we ended up saying that it'd be difficult to distinguish the years of a vintage vehicle. Like, what would the cutoff year be?

It is my to-do list since some time: explain clearly all categories

I really don't have a good idea. I asked the question with hopes that some admin would have a good idea. I guess the a term that is not to confusing might be runabout as many of them were called that when they were just a chassis and no top.

While on this subject, we might could make some definitions as used on the site and post a link or something. I get a little confused sometime with things like ground conveyer.

I think that a roofless car is called a "roadster" ? But it does not fit well these ones.
For these very old cars (i.e. at the time when none had roof), they often had different category names, or no category at all, as cars were rare.
How should we list such cars actually?

A convertible is generally a car that has provision to 'convert' it from a closed car to an open car by putting the top down.

I noticed while looking at some of the old cars that they are not really convertibles because they have no top at all. Should we continue to list these open cars as convertibles?

examples are:

http://www.imcdb.org/vehicle_49307-Whitney-1900.html
http://www.imcdb.org/vehicle_20470-Stanley-EX.html
http://www.imcdb.org/vehicle_11847-Stutz-Bearcat-1914.html