Hypothetical FWD Rallyx Build

Lets say you started with a production FWD car. What modifications would you do to make the car faster on a rallyx course, with no restrictions due to budget or classing?

Seems to me you want:
Rally tires
Limited slip
Increase wheel independence (remove front sway bar)
Increase travel? Not sure what methods there are of increasing travel over stock on traditional FWD car. The simplest one is to increase track, but that obviously has its downsides as well.
Make it lighter
What do you do with regard to weight bias? Is there a sweet spot?
More power (duh)

Before anything else, reliability. Being scored cumulatively means that a breakdown on one run can kill you for the whole event even if it's a five minute fix.

Tires, tires, tires.

The LSD helps a ton.

For FWD, I have had a lot of luck with a car that is 70/30 balanced as it helps the rear to rotate.

Also I like a FWD car that is a bit stiffer in the rear. Adding a sway bar to the back of my Neon made it like a whole new car and I could throw it in to corners much harder than before.

Suspension has eluded me so far. I'm going to try attacking the 2017 season with higher spring rates and better dampers. You need something that is a little bit stiffer, but probably about half of what someone would do with the same car built for stage rally.

Make use of the travel available as much as possible. Good bump stops, and spring rates that are soft enough to allow for the full range of the strut travel to be used, while still having just enough spring rate to avoid bottoming out. Ground Controls are good for this as you cam experiment with rates for about $50 for a new set of springs per an axle.

In addition to limited slip, if cracking the box open, see if there are more aggressive final drives available as well.

ProDarwin wrote: Lets say you started with a production FWD car. What modifications would you do to make the car faster on a rallyx course, with no restrictions due to budget or classing? Seems to me you want: Rally tires Limited slip Increase wheel independence (remove front sway bar) Increase travel? Not sure what methods there are of increasing travel over stock on traditional FWD car. The simplest one is to increase track, but that obviously has its downsides as well. Make it lighter What do you do with regard to weight bias? Is there a sweet spot? More power (duh)

Production?

Rally tires #1. Diff #2 if available for your car. A clutch diff will make turn in a whole lot worse, though.

I am NOT a fan of removing sway bars. You need to drastically increase spring rate to keep it off the bump stops and now the car stutters over rough things and you end up going slower. I increased spring rate and kept the sway bar on mine, it corners "near" the bump stops, which is as good as you can get.

Make the rear suspension lower, especially if you have a car that is tall in the back. This obviates the need for stiffening the front, lower rear means the front works better.

More power is kind of the opposite of what you want in a front drive car. You want "drivable" over "more".

Good motor mounts! You will break axles more frequently if you don't.

Adding some reality to this thread, the car is a 2003 Nissan Sentra SE-R SpecV

Tires are currently a sore point for me. The closest region down here uses silly tire rules that do not match SCCA. If you can fit 4 Quarters side by side in the tread, you are in "rally tire" class. This means our Altimax Arctic, which would be great for SCCA classing, has pushed us into a class where there are much better options. I am currently considering those options, depending on $$$$$$$$$$$$$$$

We have the factory diff (torsen).

Gearing down is possible (3.7x - 4.1x), but we would shift more. This weekend I hit 3rd twice during the course. With a 4.1 I would've definitely hit it at least one more time, maybe more. Not sure if we would gain time overall or not.

Alternatively, a rebuild using the newer QR25DE bottom end does yield and extra 900rpm (and 25more hp). Of course even then the gearing decision may be difficult.

What rates are strut cars typically running? What do you mean by "good" shocks? Is there rally-specific valving, or do you mean "not blown up"?

I love removing the sway bars but I am not experienced in FWD anything...

In reply to Knurled:

We ditched the front bar and I think it feels better. There is no rear bar.

This car has really E36 M3ty rear geometry, so that may be something we have to address to even get the back lower.

With ~175hp on tap I can A) see places where more low end power would be useful and B) where a longer RPM band would be more useful

Knurled wrote: More power is kind of the opposite of what you want in a front drive car. You want "drivable" over "more".

I disagree

ProDarwin wrote: What rates are strut cars typically running? What do you mean by "good" shocks? Is there rally-specific valving, or do you mean "not blown up"?

The research that I did led me to understand that street/track based coilover dampers are typically built with less suspension travel, higher spring rates, and thinner strut rods. You want to be able to keep the car up off the ground a little bit but still get several inches of travel.

My stock springs were 140 lbs/in in the front at 120 lbs/in in the rear and I'm going to 250/200 on an 8 inch 2.5" ID spring with adjustable collars. I'm totally guessing at that, though. I know that if I were building my car for track use or Autocross, I'd want 600-900 lbs/in springs, so I'm going to start with a 75% increase and see where that lands me. If it needs to be stiffer, I'll get 300s for the front and move the 250s to the rear. If it needs to be softer, I'll put the 200s on the front and get 175s for the rear.

The biggest difference that I can see is that you're going to spend more time at the ends of the travel of the strut, so a good bump stop is important and you need to make sure that there's enough travel when the wheel drops down that you're not banging the top of the valve.

Subbed for intrest.

wae wrote:

Knurled wrote: More power is kind of the opposite of what you want in a front drive car. You want "drivable" over "more".

I disagree

You would

I second the "reliability" part. I've won multiple regional/division-level championships not be being the guy with the fastest single runs, but being the guy who is "almost as fast, but more consistent and my car doesn't break" .

wae wrote: 250/200 on an 8 inch 2.5" ID spring with adjustable collars.

These are almost identical to the rates I run on the e30 (which probably weighs similar to your Neon, I'd guess), for what it's worth. I think I'm at 225 in the rear (but my car is near 50-50 on weight).

Sway bar/no sway bar is something that you'll get four opinions on if you ask three people. Personally, I think there is a LOT of "it depends", but as a general rule, I like a stiffer front suspension because then you can really drive the outside front into the ground when entering a corner. My FWD driving strategy is to enter corners hard and carry speed since you aren't going to be able to accelerate much exiting the corner, so you can see why I like a front suspension that won't bottom out when you're basically parking the whole weight of the car on one wheel.

This driving strategy also leads to debeads and rolled cars, but I didn't show up to be slow.

Suspension geometry also plays a huge role. If your front roll center's really low, you will need all the help you can get. This is where making the rear lower, if possible, helps. It helps keep the inside front more planted. I learned that years back from some IT guys when I was playing with my Golf, and sure enough, putting those Neuspeed Race mega-slam springs in the back made me able to accelerate out of corners a lot better. There are also some geometrical benefits that would make this post a massive text wall.

In reply to Knurled:

When I ran my mk3 vw I'd run a srs bilstein coilover in the rear and bilstein dunes in the front. So I can see where you're going with the stiff rear. Tim O'Neil setup my 323 based on his on BG chassis and the rear is shockingly soft, but the car is also over 500lb lighter than the mk3 was and though the horsepower is greater than the mk3, the torque isn't as broad.

I've thought about disconnecting the front sway bar on my Neon. With the Qaife, if I understand right, it needs both wheels on the ground to work properly. If so, I'd think having no front sway bar would help with that.

And, yeah, durability/reliability is key, or wae would have the trophies I brought home for last season instead

In reply to captdownshift:

Not stiff, low. The race springs weren't really all that stiff, and it doesn't much matter on an A2 because it lifts a tire no matter how stiff or soft the suspension is.

Until you lower the back a lot. Then the inside rear stays on/close to the ground because the car rolls less. The rear roll center is at ground level no matter what the ride height is, so making the whole rear end lower doesn't change the roll axis but it does change the roll couple, and it changes it in the direction you'd want it to go if you are otherwise cornering with the outside front on the bumpstop and the inside front topped out.

Which, incidentally, will make EVERYONE greet you by holding one hand about a foot over the other, when you get back into grid.

For those talking about gearing the event this weekend was at vir and they are known for higher speeds on their "rallyx" courses.

In reply to Knurled:

I'm trying to work with the suspension for my mkiv so I would love a text wall. Though not for rallyx, many of the principles might be the same. My understanding is that the front end of the golf gets into positive camber way to fast because the control arms are at a less than optimal angle, hence stiffening up the front inducess less travel and helps with grip. At the rear I thought being a solid beam the roll center would just be the middle of the beam. Lowering would bring the center of gravity closer to the beam, causing less body roll, but also make the rear more twitchy.

Camber is meaningless on dirt. Don't worry about alignment too much.

moxnix wrote: For those talking about gearing the event this weekend was at vir and they are known for higher speeds on their "rallyx" courses.

I'm pretty sure I'd have been into 3rd in this car at the last Summit event I went to. But yes, overall VIR avg speeds are higher.

I'm not familiar with VW rear ends, but I don't think our roll center is at the ground. There is a goofy locating link that people often replace with a panhard setup, which puts the roll center near the middle of the axle.

Knurled wrote: .. I like a stiffer front suspension because then you can really drive the outside front into the ground when entering a corner....

Rally tires, properly inflated, are required for this technique to be successful. Otherwise, you can add "AND DEBEAD IMMEDIATELY" after 'corner'.

If I had a B15 Spec-V for rallycross, I would put snow tires on it, make sure the struts were fresh, and maybe stiffen up the rear via a swaybar. Then drive it to its strengths and don't expect too much. Anything more than that is just going to lead to headaches. I have a B15 with the SR20 and automatic. I can tell that the rear suspension geometry sucks just driving it on the street.

Edit: the front sway bar issue depends as much on the course (surface, design, and roughness) as the car or the driver. I never tried a fwd with no bar (that I know of) but I liked Evan's miata better after removing the bars and adding stiffer springs. Gary's Legacy with STI springs and no bars was quite good as well.