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.

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.