There's already a ton of touring cars on the market, so I assume a lot of people in development departments and the team racers have been trying and thinking what would work best on a touring car chassis. There is already a lot of experience out there that I would like to tap into.

A number of specs are already defined by the IFMAR/ROAR/EFRA rules, like maximum length, width, height and minimum weight etc. There are a couple of things that you can choose freely but can impact performance quite significantly like wheelbase and internal drive ratio.

Hot Bodies Cyclone S

To get a base line of the specifications of other cars I made a list of successful touring cars with their respective specs for comparison. It is by no means an attempt to make a complete list of all touring cars that have been available on the market at some point in time. I just picked a couple that are or were popular, have won many races, or just look interesting. I threw in a couple of older cars to see if there’s a difference with the newer cars and where the development is heading. Some of the cars I looked at dropped off the list because their data was not available. It’s amazing how bad some manufacturers websites are and how little information they have on there for their products.

By doing this comparison I don't have to reinvent stuff that's already figured out by others. All manufacturers have team drivers and do a lot of testing. There are some things they have figured out over the years that work best. You still have to look at this data with an open mind of course: something that a lot of people are doing isn't necessarily right!

Here’s the comparison table I came up with after some searching the web:

Car, Length, Width, Height, Wheel Base, Weight, Type of Drive, internal Drive Ratio

There seem to be some differences in how the cars are measured. It is mostly not stated what is measured. I couldn’t imagine anybody building a car not 190mm wide, so the cars that are narrower are probably measured without wheels, or they stated width when they really meant track width.

The wheelbase on most cars is adjustable. The middle positions all come in around 255-260mm so it looks like everyone agrees on this. I’ll keep that as a guideline for my car in development.

What kind of surprised me is the big difference in internal gear ratio’s. This probably depends on what kind of maximum spur gear size is used. If the main shaft is low in the car, you limit the maximum size of the spur gear and you need a bigger internal gear ratio. Corally seems to be the only manufacturer who gives you the possibility to use a whole range of pullies to adjust the internal ratio. 

The weight is hard to compare. One company states the weight race ready, the other one only the chassis without tires and body. It doesn't really matter I guess, you just want it to be as low as possible anyways, but it would be nice to know if you're in the ball park.

As a reference, also to see in how much the cars are true to scale, the specs for BMW’s racing car for the World Touring Car Championship:

BMW 3-Series WTCC :

Length: 4,535 mm
Width: 1,845 mm
Height: approx. 1,350 mm
Wheel base: 2,763 mm
Vehicle weight: 1,140 kg (with driver)

As you can tell, not far off! The wheelbase is quite a bit longer than it’s 1:10^th scale brothers  though.