FWD vs. RWD rain: part 2 (thanks Paul)

I have to thank YSAR reader Paul for sending me down this path, because it’s been really fun. I truly appreciate feedback that makes me look critically at a problem. In this part 2, I do some testing in Assetto Corsa, and come away with some surprise.

Testing scenario

To do the fwd vs. rwd and dry vs. wet experiments, I had to choose a track, two cars, and two grip levels. I like to use Brands Hatch Indy and the NA Miata as a baseline. Sometimes I use the Street 90s tire and sometimes the Street tire. The Street 90s are a couple seconds slower. When you have the AI drive the car, both tires have the same lap times. I think it uses the default (Street 90s) tire. So that’s what I did too.

For the FWD car, I chose the Chevy Monza Classic 500EF. This model is a free download. One reason I chose it is because the dry lap times are very similar to the NA Miata when both cars are on their default tires.

For the wet grip, I reduced traction from the default 0.98 to 0.75. That figure is a little bit arbitrary, but I’ve seen various tables that show a reduction of about that much.

  • Track: Brands Hatch Indy
  • RWD: NA Miata
  • FWD: Chevy Monza
  • Dry – 0.98 grip
  • Wet – 0.75 grip

How to modify Assetto Corsa grip

There are three ways to modify the grip of cars in AC that I know of: run a server, change tires, change track surface. The easiest is the last, but for completeness, I’ll describe the other two first.

If you set up your own server, you can set the grip level of the track. This requires a separate program running as the server. That’s why I’m not recommending it. But on the plus side, it’s just one line of one file.

If the cars are developed in the legacy way, they have editable text files for individual components like tyres (yes, that’s spelled with a ‘y’ because AC uses the British English spelling rather than American English). Most cars these days have binary files that aren’t easily edited. Both the Miata and Monza use binary files. This is why I’m not recommending this way.

If you look in a track folder, you will find a surfaces.ini text file that you can edit. A track may have several surfaces. For example the Brands Hatch Indy file has 11 surfaces. Before you go editing this file, first make a backup copy so that you can restore it to its original configuration later. The grip levels of the various parts of the track range from 0.98 on asphalt to 0.6 for grass. To simulate rain, I set everything to 0.75 because I was lazy and didn’t want to multiply everything by 0.75. But that would be a better way I suppose. However, I planned on driving on the track, not grass or curbs.

AI driver

The first thing I wanted to test was how much the AI driver was affected by reduced traction. Here are the values.

  • RWD -7.31% loss
  • FWD -6.95% loss

There is more loss in RWD than FWD. To put it into the perspective of a typical lap, if your dry time is 2:00 minutes, your RWD wet time will be 2:08.78 and your FWD wet time will be 2:08.34. 0.43 seconds is pretty significant in a sprint race, but we’re not talking about 10 seconds here. It’s just a little time. However, this is the AI driving. What about a human?

Human driver

Move over AI, it’s time for Ian to step into the car.

  • RWD -9.06% loss
  • FWD -6.92% loss

That looks a bit more significant. Let’s put this into perspective of my Toyota Yaris at Thunderhill last May. My fast dry time was 3:43. If we multiply these 223 seconds by 1.0906 and 1.0692 we find that the difference between RWD and FWD is nearly 5 seconds. That’s pretty significant! Given that my Yaris is heavier, higher, and less powerful, than a Miata, the Miata has all the advantages on a dry day, but given some rain, the advantage just might tip in my direction.

Here are the graphs for the simulation experiments.

However, this is a human driving a simulator, what about in real life?

More data diving

Let’s look at the actual laps from the race. On a dry track, I was averaging about 3:50 in traffic. Bring on the rain and that drops to 4:20. So about 30 seconds. I had to make a lot of passes, and when I had a clean lap, I got down to 4:03, which is a loss of just 9%. Driving around slow cars in the rain really kills your lap time.

Some of the fast RWD cars I passed included the Miata of Eyesore and the Celica of Uncle Joe’s. Eyesore’s fast lap was 3:29 but in traffic it was typically 3:35-3:40. They dropped to 4:35-4:40 in the rain, a loss of 60 seconds. Uncle Joe’s fast lap was a 3:34 and it’s traffic laps were in the 3:40-3:45 range. In the wet, they dropped to 4:25-4:30, or about 45 seconds.

Two of the fast FWD cars I passed were the Integra of Big Test Icicles and the Neon of Neon Pope. The Integra went from 3:50 dry to 4:25 wet. The Neon was 3:45 and 4:30.

The race winners, Shake and Break (E30), were typically lapping at the same speed as Eyesore in the dry (3:35) but much faster in the wet (4:10).

Let’s take a look at the relative losses of these cars.

  • Yaris -13%
  • Celica -20%
  • Miata -28%
  • Integra -15%
  • Neon -20%
  • E30 -16%

Summary

Given equal lap times on a dry track, a FWD car definitely has an advantage over a RWD on a wet track. How much? I think it depends a lot on the skill of the drivers. At the high end, maybe 0.5 sec per lap. At my level, a couple seconds. At the “you can’t drive for shit in the rain” level, I think it’s less about which wheels are connected to the engine and more about the driver lacking the skill and confidence to maximize traction in the rain. Pedal mashers who over-brake and then hammer the throttle are the ones most severely affected. A Miata doesn’t normally spin when you stomp on the throttle. But it does in the rain, and if one’s driving style isn’t very nuanced, rain will be very unkind to your lap times. However, in a FWD car, stomping on the throttle may cause a bit of understeer, which is easily mitigated by lifting. FWD cars are more noob friendly. I’m not a noob, so I don’t see that FWD and RWD are that much different. But to someone not used to sliding their car around, RWD could be a major disadvantage.

I just watched the “you suck at racing in the rain” video again asking myself “where does the Yaris have an advantage?” The expectation is under acceleration. But that’s not where I’m catching people. It’s under braking. There is no FWD braking advantage. If you’re thinking it’s because my car is newer than the others and has ABS, that’s a good idea. However, you can hear the tires sliding in some corners when they lock up because my ABS has been broken for a while.

So to sum it all up, the reason for Yaris Rain Domination (YRD) is a little bit of FWD advantage and a shit-load of “most people suck at racing in the rain”.

FWD vs. RWD in the rain?

A recent comment from an old post sent me down the path of attempting to quantify the difference between FWD and RWD in the rain. How much faster is FWD? A little? A lot? Here’s my first quasi-quantitative attempt at answering that question. I’ve taken a bunch of graphs from SpeedHive from the Lemons Thunderhill event in 2019 where it rained suddenly on Sunday. In the images below, you can see the lap times get slower as a “swell” in the graph. If there’s a big difference between FWD and RWD, the swell for FWD should be much smaller than RWD.

FWD Acura Integra

RWD Mazda Miata

RWD Lotus mongrel

FWD Hyundai Elantra

RWD Mazda Miata

RWD Porsche Boxster

RWD BMW E30

RWD BMW E30

FWD Dodge Neon

RWD BMW E30

RWD Mazda Miata

RWD Toyota Celica

AWD VW Vanagon

FWD VW GTI

FWD Hyundai Accent

RWD Mazda RX-7

I don’t see much difference between the swells of FWD, RWD, or the one case of AWD. This is just a random selection of graphs though, and maybe with a larger selection I’d see the trend. Here’s the last graph showing our Toyota Yaris. Note the Y-axis! We had a 35 minute stop, which has the effect of making our rain laps look better than they were. But of course we did rock in the rain, as evidenced by the video linked below.

Post-race analysis: drivers

Let’s take a look at some of the telemetry traces of the Triple Apex Racing drivers from the last race.

Danny vs. Danny

The first thing I want to discuss is Danny. I’m usually a couple seconds faster than Danny. I was on Saturday. Then we switched tires on Sunday and everyone went faster. But was it really the tires? In the speed trace below, Saturday is black and Sunday is red. I’ve displayed the top 3 laps each day. Saturday he was doing 3:39-3:40 while Sunday it was 3:36s. What I see here is that he’s driving differently. On Sunday (red) he started backing up the corners. He gets his braking done earlier and gets on gas earlier. Most of the time, his minimum corner speed is higher despite the change. The fresh tires may have contributed a little to his higher speed, but I think it’s mostly because he’s getting better at driving a low powered FWD car with an open diff. His usual car is 911 GT3, so yeah, it’s a little different!

 

Danny vs. Ian

Due to yellow flags, I didn’t get many fast laps. I did a 3:38 and 3:37 back to back. You can see these starting at the 10:00 mark in my video from the last post. In my 3:38 lap, I lose 1 second passing an E36 in T2 when it changes line mid-corner. Then I pass the yellow Miata in T5, messing up my T6 entry, causing another loss of a second on the run up to 9C. The 3:38 could easily have been a 3:36. On the 3:37 lap, I lose a little time making a pass in T2 and then 1 whole second in T3W while I wait for a fast E36 to get around me. So that too could have been a 3:36. Had I gotten a bunch of clean laps, I’m pretty sure I would have been doing a bunch of 3:36s. Could I have broken into the 3:35s? I don’t know. For the most part, Danny and I drive pretty similarly. Below, the red lines are Danny’s fast laps (as above). The black is my 3:37 and the blue is 3:38. This is a speed trace from 7W to the SF line. We have a slightly different way of doing 1W, but the rest is similar enough that you might think it was the same driver.

Randy vs. Danny

So I’m sure everyone wants to know how fast Randy was (green lines below). Faster than Danny (red lines). Where is he faster? You might expect it’s the fast corners, but it’s the slow ones. He gains nearly 1.5 seconds in T9C alone! And he was only 1.8 seconds faster than Danny. T9C is on the far left of the graph. But he’s also faster in T7W and T11. How? Mostly by running over curbs. As the car owner/builder, I don’t really approve of that.

Post-race analysis: aero

At the last Lemons race I did a lot of lightening, which is good, but I also turned the car into a parachute and destroyed our top speed. This race we made two aero improvements.

1. A-pillar deflectors

This is simply a piece of plastic that bulges out a bit. The intent is to have the air go around the window instead of into it. Randy Pobst signed it.

Let’s take a look at the top speed on the main straight before and after the new “aero package”. The top speed went up from 92.0 to 95.4. It’s even more dramatic when you look at the speed trace.

2. Rear wing

Normally, all you have to say is “wing” but I need to emphasize “rear” here because we made an aero joke at the last Lemons race.

Note that we didn’t actually run this on track.  It was just to give Mario and Daniel a laugh when they drove in and saw the wing on the wrong end of the car. Here’s a picture of the same wing installed on the roof. Also, there’s a note I wrote to try to persuade Randy to take a stint in the Yaris.

So what did the rear wing do? The #1 place I felt it did something was in T1. I usually have to brake in T1, but with the wing holding down the rear end, I was able to do a brief lift and then go right back to throttle. You can see how much faster I can do T1 in the graph below (blue is with wing).

The wing also turned T8 into a straight. It’s normally a corner that gives some people a fright, but with the wing on there was no drama at all.

Conclusions

I think the new aero worked. I guess the next question is if we can make it work better.

Sim racing holiday shopping guide

Sim racing represents a fantastic value as a training tool for your driver development program. The holiday shopping season often has the best prices for electronics, so in this Black Friday/Cyber Monday post I will offer up a few builds.

Software

I think the best way to get started is with Assetto Corsa and rFactor 2. Both are on sale right now on Steam for 75% and 50% off. Neither one has a subscription price, so you can get both for $20. After a couple months, if you decide you want to compete against other people, iRacing is the best platform for finding races at any time of the day. I don’t think you should jump right into iRacing because of the emphasis on competing. Whether you’re racing to win or racing not to lose you can pick up bad habits when you’re focused on placement instead of technique. Learn to drive, then learn to race.

Low Budget Build

Most PCs going back 5-10 years have enough CPU power and RAM to run sim racing titles like Assetto Corsa, iRacing, and rFactor 2. That means you can convert an old desktop into your sim rig. There are second hand PC stores that will sell you a decent machine for $50-100. 1080p monitors are as little as $100 new, so you might find those second hand for half that. Make sure you check the performance of the graphics card at the website below. You’ll want something with a Passmark score of at least 1000.

https://www.videocardbenchmark.net/gpu_list.php

If you have a little more money, you can upgrade the GPU. Check the best value chart and buy something near the top of the list that’s around $100. Sometimes you can find shockingly good deals.

https://www.videocardbenchmark.net/gpu_value.html

If you look at the RSR Live Timing site, which is  where many Assetto Corsa drivers log their lap times, you’ll find that most of the fastest lap times are set with Logitech G25, G27, DFGT, G29, and G920 hardware. The G25, G27, and DFGT were replaced by the G29 and G920 a couple years ago and yet fast times are still being set with older hardware. That’s because the Logitech gear is robust enough to last years and good enough to set world records. Don’t listen to the sim racing snobs who tell you that belt and direct drive are necessary. Logitech is good enough. You should be able to find a used one for $75-100.

The total price of the budget build is $225-400. That’s around the price of a track day.

Turn Key Build

You can get a decent gaming computer for $540 from Amazon. Instead of getting a 1080p monitor, you might rather get something with a wider field of view. A 2560×1080 monitor will let you look through the corners and see your mirrors better and some are as little as $150. I recently purchased a curved 2560×1080 and I highly recommend that over a typical 16:9 1080p. That ran me about $300 though. I think an extra wide monitor is a nice compromise between a single 1080p and a triple screen.

To simplify your life, get all the controllers from one company. That way you can use the pre-packaged presets in the sims and you don’t have to have more than one set of drivers. Whether you decide on Logitech, Thrustmaster, or Fanatec is mostly about your budget. I feel pretty strongly that brake pedals ought to have load cells, so I might prefer going with Fanatec from the get-go if I didn’t want to mod the brake.

  • Logitech G29 $199 – Total $900
  • Thrustmaster T300 RS $299 – Total $1000
  • Thrustmaster TX XW $649 – Total $1350
  • Fanatec $1000-1500 – Total $1700-2200

Cockpit

While you can clamp the wheel to a desk and throw the pedals beneath, you will have a better experience in a cockpit of some kind. I don’t think the simple wheel stands are a good idea because the force feedback of the wheel overwhelms their stability. If you’re trying to cut costs, use a desk. If you want a cockpit, get a cockpit. I don’t have any experience buying these though. As I mentioned in my post about why not to build a sim rig, space is the primary concern.

Randy Pobst is a sweetheart

The Lucky Dog race at Thunderhill was good fun. Ultimately, we didn’t place particularly well, but as we’ve found out over the years, it’s more fun racing for giggles than trying to win. So we were leisurely about pit stops and put some guest drivers in the car. One of those drivers was the Internet celebrity pro driver Randy Pobst. Randy has a reputation as a fast driver but there’s a lot more to the package. He’s very approachable and knowledgeable, and he listens as well as he talks.

FUUUCK. I only had one camera working on Sunday when Randy was driving and it was pointed to the rear.

When Randy got in the car I told him to “bring it back whenever”. Given that he drove it until the end of the race (~60 min), I think I believe him when he said he was having a lot of fun. Apparently the Yaris reminded him of his old 80s Golf. Randy wasn’t the only person who had a great time in the econobox of doom. Lemons veterans “Crazy Mike” and Steve “Chotus” Warwick also drove and loved it. Mike was an “official” Triple Apex Racing driver this race and Steve was a stud driver, piloting some 4 or 5 cars on the weekend. That reminds me of a quote.

I never had a 10, but one night I had five 2s… and that ought to count for something.

— George Carlin

Every time I race the Yaris, it reminds me of why I built it. I love driving and hate wrenching. Despite appearances, the Yaris is a great driving car. It’s also cheap to run and tougher than it looks. It got side swiped twice during the race and just shrugged them off. The one annoying feature of the car is inside wheel spin from the open diff. That’s something I may address in the off season.

Look for some video and telemetry posts in the near future.

Aero Thoughts

I haven’t looked at the data yet, but here’s my seat of the pants impression of what it did.

  • The wind deflectors on the A-pillars did something. There seemed to be less noise in the cockpit. Did they improve top speed? I think so. In the last Lemons race we lost a few mph on the main straight and I think we got that back.
  • The wing probably added useful downforce in T1 and T8. I always take T8 flat out, but this time it was a really boring flat out. In T1, I usually brake lightly, but this time I would just breathe the throttle off for a heartbeat and then go right back on. No brakes needed. That allowed me to make some passes on higher powered cars.
  • The interior of the car still smells a little of catalytic converter, so I think some fumes are getting in from the rear. I want to fix that somehow.

I won’t know if these impressions are correct until I check the data. I’m fully prepared to be wrong!