RWD vs. FWD: Part 7 – RR

There are a lot of high performance cars with a MR or RR layout. Porsche 911, Boxster, and Cayman come to mind as well as Toyota MR2. I don’t think about exotics since I would never own one. MR and RR vehicles have more weight in the rear, which might amount to as much as 40/60. Compared to something like 50/50, the 40/60 wins on a drag strip or 0-100-0 type of test. 40/60 has a lot of weight on the drive wheels during acceleration, and when stopping it has a more equal weight distribution on all tires. But what happens in corners? Let’s find out.

Driving Impressions

The RR layout was the most difficult for me to drive. This may because I’m not used to it. So, instead of collecting the top 10 laps among 20 total, I took the top 10 from 29. What made RR so difficult to drive is that RR really wants to swing out if you trail brake a lot, and it’s easy to get it to a point where it’s hard to recover. You can read this as Ian crashed a few times in the beginning, and that’s why he did 29 laps. I found I had to drive it in a much more point-n-shoot manner. By that I mean that I didn’t try to blend the inputs as much. Instead, I drove it thinking “square off the corners”.

Squiggles

I’m using pretty much the same setup as the last test. Red is a 200% power FR Miata in its usual 51.5/48.5 balance. Blue is a 200% FF “Miata” in 60/40 balance. Black is a 200% RR Miata in a 40/60 balance (because most Porsches I see are black). In the graph below, the same red and blue laps are shown from the previous post, and the top 5 laps are shown from the RR vehicle.

You can see in the brake trace that my brake release in the RR vehicle is more abrupt. I’m not using much trail-braking. Also, I’m much later to throttle because I’m waiting for the car to straighten up a bit. But once it is pointed in the right direction, I get to full throttle pretty quickly. BTW, squaring off corners like this is one strategy for driving in the rain (regardless of layout).

Lap Times

Well this ain’t no dragstrip and the RR configuration got its bit butt handed to it. Well, not that much. It’s less than a second.

Conclusions and Thoughts

Most RR vehicles have wider tires in the rear than front. I didn’t make that change or a host of others one might make when changing from 51.5/48.5 to 40/60. So there may be some good reasons why RR was slower than FR or FF. Had we started with a 911 and modified it for FR or FF, we might get different results. Let’s revisit some caveats.

• This is a simulation, not the real world
• I’m the only driver (so far anyway), and I have my biases
• There is one testing venue: Brands Hatch Indy
• The vehicle is relatively light weight (1080kg) and has moderate power (250hp)
• The tires are modeled as street tires, not racing slicks
• The base vehicle is a Miata, which is neither FF nor RR

That wraps up some of the easy tests I had planned. Aero is probably next, but I’ll be taking a break from sim experiments for a little while as my focus turns to racing in the real world in about 11 days.