I understand you only described one feature, and this is a good example of the level of detail required to pitch an idea to someone else. I can't tell if there's anything wrong with what's written because you only described a single feature. In a way I kind of expected you were describing the entire game in one document, but this is a nice surprise.
Good
Visuals, some people like me would prefer most of the description to be in pseudocode and pictures. So if you have a bit of a flare for drawing don't hold back.
Bad
The details are mostly written, so you'll only gain an understanding from someone who's already in a world of cars. I know what a transmission is, manual, automatic, and semi-automatic, and I've seen it in enough games that you could have probably said, this is a picture of how it looks. You must choose these transmissions. Programmed with these restrictions.
If this were completely alien, entirely new to me, I'd be excited about it and confused. Seriously though I can't properly imagine not knowing how a car works, even an imaginary one.
Some of the Pros and Cons were redundant because of this very thing.
Suggestion
The title of the document is too vague, seen at top-left in the browser, it would be a good idea to name the document by the feature, if you only describe that one feature.
Transmission Systems, is a lot more clearer to you and anyone looking for a specific feature than just (Game Design Document). If you view from the google folders it's the first thing you'd see.
I don't know how your folders are organized, but this would be my only gripe.
Document complexity
You have a document that you can show to someone else to get the idea across, it's granular enough, but if they don't understand the terms you use they might not understand how it fits. "Lighter (Less taxes on some models)" this kind of sounds like I'll be getting taxed.
And I notice you went overboard, describing exact strategy with a player's guide motif. It doesn't need changing, but it may have been unnecessary.
First impression here on the forum
Considering the way you presented it here, on the forum, this is pretty much a beginner project and a very generic drag-racing simulation, so you'll be attempting to emulate a set of standard details found in driving. You shouldn't want help unless you encounter major difficulty and require a morale boost.
In this forum, mostly, I see and hear people want to work on their own games. Do you have a team of people already helping you with this? If not, consider you don't need a very complicated design document for a do-it-yourself project. You'll want a broad description, and in the features, you can make lists. Mostly a list is useful only for yourself so you can prime your brain right before you start writing pseud-code.
