RWD vs. FWD: Part 4 – Ballasting

In the last experiment, I discovered something rather shocking: on equal footing, a FWD vehicle can be faster than a RWD of the same Miata-ish specifications if the FWD vehicle has a static weight distribution more like a RWD vehicle than a FWD vehicle. That got me wondering about adding weight to rear of a FWD vehicle to improve performance. My Yaris is probably something like 65/35. Could I make it faster by adding weight to the rear to give it a more balanced center of gravity? Or would the extra weight be just dead weight?

Let’s see if I can improve the 65/35 FWD Miata by adding weight to the rear axle. The stock weight is 1080 kg, so I’ll add just enough weight to make 60/40 and 55/45 vehicles.

  • +90 kg (1170 total) -> 60/40
  • +196 kb (1276 total) -> 55/45

Lap Times

Last time I ran 20 laps and chose the best 10, so I did that again. My laps this time weren’t as consistent. It seemed performance was dropping from tire wear. Maybe I should have turned off tire wear and fuel usage. Well, I didn’t and this is the result.

Vehicle Best Average Std Dev
RWD 63.020 63.188 0.127
FWD 65 63.619 63.741 0.076
FWD 60 62.930 63.129 0.085
FWD 55 62.689 62.819 0.080
FWD 60 1170 63.529 63.816 0.167
FWD 55 1276 63.880 64.198 0.206

Again, we are focusing on the FWD 65 CoG which has been converted to 60 and 55 by adding ballast to the rear. As you can see, the 60/40 ballasted car set the fastest lap by about a tenth, but it was also slower on average by about a tenth. It was also harder to drive consistently. I got one really good lap on it, but I couldn’t match it again.

Squiggles

In the speed graph below, red is RWD, blue is 65/35, brown is 60/40, and magenta is 55/45. Looking at isolated laps isn’t all that useful to show trends but showing lots of laps on top of each other is cluttered. So I’m just going to put the fastest laps up because it looks better.

Conclusions and Thoughts

If you have a FWD vehicle with 65/35 weight distribution, crappy tires, and low power, you can add 70 kg to the rear to make it 60/40 and it might not change performance much. Your ballasted vehicle will hold corner speed a little better. It will also rotate more willingly. However, you’ll pay for that better handling in lower acceleration. On some tracks, like Brands Hatch Indy, those forces will equal out in lap time.

Am I going to add ballast to my Yaris? Probably not. I want my consumables as low as possible. However, it would be fun to do this test in the real world to see if I get the same results.

4 thoughts on “RWD vs. FWD: Part 4 – Ballasting

  1. Very interesting set of experiments. Adding weight to a race car feels inherently wrong, but it seems there is some benefit here. Is this all down to setup?

    Like

    1. Adding weight would make the car slower in any kind of drag race. But if you were going around a circle, what matters is grip, and the more even the static weight distribution, the better the overall grip. I think it comes down to this: is the racetrack you’re on more like a drag strip or a circle?

      As far as setup goes, it’s identical for the FWD vehicles.

      Like

    2. What you’re supposed to do is move the battery around.
      Take that 40lbs out of the front and find the best place to put it while on the corner scales, then run the wires.

      Like

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s