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4-tec 2.0 spec racing has taken off at our track—here's my setup and info >

4-tec 2.0 spec racing has taken off at our track—here's my setup and info

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4-tec 2.0 spec racing has taken off at our track—here's my setup and info


Old 02-18-2019, 06:21 PM
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Default 4-tec 2.0 spec racing has taken off at our track—here's my setup and info

TLDR: Here's my black carpet indoor racing setup. We have a good turnout every week for 4-tec 2.0 indoor spec racing on black carpet—we tend to have two qualifiers and an A and B main. This is an amazing price controlled class that seasoned racers and noobs both run at our track—an excellent entry point into on-road racing. It's similar to what slash did for off-road, except that the car is actually stunningly good in comparison—we're not even a second behind 25.5 touring car lap times.

500cst shock oil
3k diff oil
red w/ black stripe springs
3mm ride height clips
66-80% traction compound inside to out (based on traction that day)
inside hole on tower (stock)

450cst shock oil
2k diff oil
red springs (stock)
NO ride height clips (as low as possible)
100% traction compound
inside hole on tower (stock)
Camper link in the upper position, inside hole on hub (stock on newer kits)

Droop screws front and rear tightened so when the car is on a stand, the shock springs have no play up and down but loose enough so you can spin them easily—ie, snugged up, but not tight.

Now for the book (details, and testing):

We do 4-tec 2.0 spec racing on black carpet at our track. Figured I'd share how I've been setting up cars for competitive close racing on carpet. We use this class to get folks into the on-road racing scene and a lot of us (me!) are seasoned racers. Our 4-tec 2.0 spec class is filled with actual fast guys, noobs, and everything in between. Everyone's welcome! It produces some of the closest intense racing for the lowest cost of entry.

For racing these things on black carpet, you really have to do very little. There are official 4-tec spec racing rules, which we basically follow, with a few modifications / interpretations. First off, we only allow 2s lipo batteries—if we allowed nimh like the spec rules state, the 7 cell packs would be faster and then to compete everyone would buy a pack for each race and do dangerous nimh charging things that are simply not good for a class you want noobs to start with. We also allow the use of traction compound (because otherwise its an ice rink,) and we basically allow any tuning that the manual shows such such as the addition of droop screws or moving the camber links (although we don't.)

In order of importance, my car has the following setup changes and modifications to work well on black carpet:

Droop screws: The chassis will not really let you use them with any pressure against them, so all you can do is tighten them to make sure the springs are snugged up and not flopping around. When I set them, I tighten them until when I compress the suspension while the car is on a stand, then let go, I can still spin the springs freely with a finger, but the collars and shims don't have any up or down play. This basically means your minimum down travel is limited by the spring length (because the chassis is too flexible to support droop screws with spring tension against them, but that's how it is. Remember to adjust droop screws to snug springs after any spring or ride height change. These basically make it possible to compete on carpet without CA gluing the tire sidewalls to prevent traction rolls, which is a real turn-off for new racers. NOBODY glues the sidewalls at our track, even those who do in other sedan classes, and we want it that way.

Rear Ride Height: Using the stock springs, I removed all the spacer shims from above the upper retainer, basically setting the rear as low as I can go. This dictates how the front end is setup in relation to this. Note that you cannot go to a softer rear spring without raising ride height because the softer springs are longer for some reason, and it basically disqualifies them from spec carpet racing. Using droop screws would make for preload at ride height and now you're at a stiffer spring again. Traxxas really jacked this up in our opinion.

Front Springs / Ride height: The car transfers too much weight forward in general, but especially when taking a high speed sweeper corner—a little rotation in the technical sections isn't all that bad, but good luck with any big flowing corner where you might have to lift a little... cause you will come around and back it out of the corner every time. With the stock springs, you can run 2mm of shims to make it pretty good, but you'll have to stay on top of it in some corners, especially with the brushed motor providing some noticeable drag brake compared to brushless. I found I could throttle trim forward a little and live with it, but the RIGHT solution is to go two springs stiffer to the black stripe springs. Since these are SHORTER than the stock springs, I ended up with 3mm (2+1) ride height shims. This REALLY locks the car in and provides really great steering response.

Traction compound: Full rear tire, 2/3 or more front, to preference. Never touch the side wall of the fronts or you'll traction roll in warm-up. I tend to do 2/3 when grip is good and more if grip is low.

The above things are the "must haves" for carpet in my opinion. The next are somewhat optional, but I think they're good choices:

Body: Most of us run VTA camaro or firebird bodies because they have proven themselves so capable in vintage trans am racing. The limitations on big wings basically makes these bodies the clear choice. Having said that, one of our top 3 guys runs an AMC javelin body, so don't be afraid to be different, just realize the body will make a difference. I'm a fan of the bodies that come with multiple nose cones (such as the protoform firebird) so you can swap it out once it's destroyed. The leading edge of these cars get abused because the class requires detailed real car replicas but those lexan details equate to cracking points. You would be surprised how decent a body can look and work with lots of board tape and shoe goo repairs—body repair is a great skill to pick up. Most of us have shoe goo all inside the front ends from repairs, and yes it weights a little, but HEY more steering!

Lipo selection: These cars are VERY heavy, but the weight of the big motor is so far inboard that it takes only a very light battery to balance the car left to right, so leave those big 7000+ batteries alone. In my testing, I was able to get .3s a lap by going from a 315g 7500 battery to a 215g 5500 shorty battery mounted middle. I prefer shorties, but let me be 100% clear, I drove a 7500 full size pack all the way forward, making the ride height 1mm lower on one side, and the car did fine, and I placed 2nd in the main with a tire coming off the wheel and stiff competition—driver is the key here, spend your money wisely on practice before batteries. We also allow people to run weights in the battery tray to balance the car left to right because the rules allow you to pick any lipo and thus any weight, and some lipos come with weights you can move in them, so restricting weights in the tray would just mean people who were set on balancing the car would have to spend more money for different batteries and this is NOT what you do for a class that is supposed to attract people to the sport. Don't be afraid to drive a cheap light 25c full size pack until you feel like you're car is actually slower down the straight after 5 minutes of racing and that is what is holding you back from finishing better. I can't stress this enough.

Shock oils: I haven't done any testing. I put in 500/450 as a starting point and I hold the fast lap at our track for this class, and I'm always in the top 3 for qualifying, but I get beat by people who haven't changed it from stock, so for my son's car, I didn't change it at all. I will when it's time to refill. Don't stress over this, and we don't even tell new folks to mess with it.

Diff oils: This one makes a difference, but until you're competitive at the track, it's not that important to change the stock stuff out. It's not something we tell new folks to even mess with. We've done everything from putty, 100k, 20 weight shock oil, to empty. Here's what we found: It's just like touring car except on a small track you want a light front diff. It might be because the speedo doesn't brake hard enough to ride that front outer tire around corner entry, it might be that the car just won't turn in hard enough, or it might just be because it's a big heavy traxxas... but the moment the traction goes down, a heavy front diff pushes so hard in the infield that all corner exit advantage is GONE. If you're on a big flowing track without a bunch of 180s, crank that front diff up. I turned a track record with 60k in my front diff, but I went to 5k for the remainder of the day because the traction went down and I simply couldn't compete. For the rear, 1-3k is where I like it, 2k is where I settled—it's all about corner exit stability and getting on power. I currently have 3k in the front as that worked well the week before. A thinner rear diff will let you diff out a little and exit smoother if you grab all the throttle, where as a thicker rear diff will be more apt to kick out but exit the corner faster if you're good.

Tires: Rotate the tires every track day and scrub them in during practice, otherwise they're done pretty quickly on one side. It doesn't matter what direction the water vanes are pointing—the track is dry.

Servo: The stock servo is slow and you will strip the gears out eventually with an impact. The metal gears are a cheap add. Invest in it as you can't run a non traxxas servo in the spec class, and the faster traxxas one isn't that much faster according to some—although I have yet to find specs for it. If your hobby shop stocks the gears, lucky you. You'll DNF one day when they go if you don't have access to them.
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Old 02-19-2019, 10:32 AM
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Well done!
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