Any thoughts on the Trackwidth vs. Wheelbase ratio argument?

[97ekdude]

Figured if there was anywhere to ask this would be the place, the argument is 1.6:1 is the golden spot, seen both sides and not sure where to stand? I'm at 1.78:1 with probably close to 70% front weight. Not overly concerned but it's worth a topic 🤷

[Stuart]

I think you may have your ratio flipped as your wheelbase should be larger than your track.  Having said that, I would argue that the ideal ratio would be a function of the specific course layout you are competing on.  Tight Chicago Boxes would dictate as short of a wheelbase as practical while sweepers and less transition intensive elements would favour a longer wheelbase.

[PedalFaster]

I saw a good response elsewhere on the internet:

As always, "it depends".

Wider track width is better for maximizing cornering G-force without rolling over. Narrow track width is better for fitting between obstacles. If the criterion involves negotiating a slalom, the increased cornering G's allowed by a wide track width may be negated by the vehicle having to go much further side to side in order to negotiate the slalom.

Long wheelbase is better for ride quality and stability in general, worse for tight-parking-lot maneuvering, worse for the above-mentioned slalom course. If the overall length of the vehicle is defined, it's usually not wrong to make the wheelbase as long as you can within reason, because weight hanging out beyond the axles is generally bad. But urban transit buses have relatively short wheelbases and long overhangs (with the engine usually hanging out way beyond the rear axle!), because maneuverability in tight quarters takes priority over how quickly the bus can negotiate an autocross course.

I'm not aware of any "ratio" that is "optimum" between the track width and the wheelbase. Production vehicles cover a pretty wide range.

TL;DR: A problem as complex as designing or optimizing a vehicle platform for performance generally can't be accurately distilled down to a single simple guideline. Look at Formula 1 -- even though the rules place very tight constraints on the car designs, and the teams all have annual budgets in the hundreds of millions of dollars (so their cars are very heavily optimized), the cars still have varying wheelbases because their designers have different design philosophies.

Based on your short blurb, I think you're focusing on the wrong thing -- I think you'd derive more benefit for less effort by moving as much of that 70% weight off of the front axle and towards the rear axle than you would by attempting to modify the track (or wheelbase!) of an already-existing car.

[PedalFaster]

I think you'd derive more benefit for less effort by moving as much of that 70% weight off of the front axle and towards the rear axle than you would by attempting to modify the track (or wheelbase!) of an already-existing car.

A few quotes from elsewhere by Andy Hollis, a multi-time national champion who's built a number of winning ST-class cars, about weight distribution in FWD cars (which I assume you have, given your stated weight distribution):

if you can physically move weight to the rear, do so. Put it in the RR.

By the time PWC was done with us, we had 350lbs of ballast in the TOMO TCA car. That's because we were super-careful as to placement. Our weight distribution got better and better the more they gave us ("Please don't throw me in the briar patch!!"). Sure, it affected accel and decel, as expected. But our handling actually got better up until the final 50 lbs or so. Behind the rear axle jacks weight off the nose.

My first clue on this idea was a number of years ago driving my FWD autocross cars to events...they actually handled in a more neutral fashion when the rear was loaded up with race gear.

I've yet to see a FWD production car that wasn't nose-heavy, especially on the LF. So they steady-state understeer badly to the left and even worse to the right. And power application is always a problem, even with a good LSD. So equal side weight on the nose helps there, too.

Even on a short-wheelbase CRX, that RR weight placement just works.