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Last edit by: fenton06
This is a place to share knowledge related to 1/12th scale racing. It is not to be used for conversations.

Click links to go to manufacturer product page. If any are missing please add them!

Pre-mounted tires readily available in the US:
Gluing your own donuts:
https://www.youtube.com/watch?v=hm7z1rz-74s - Special thanks to Edward Pickering!
Truing tires:
https://www.youtube.com/watch?v=8wqHOLWq6Uc - Special thanks to Edward Pickering!

The following information came from HERE, with some editing and information added. Thanks Christian!


BSR, CRC, Jaco:
Pro One is no longer selling to the public, but it and the brands above are all mounted by BSR and use the same foam. The nomenclature of the BSR vs Jaco/CRC is a little different in a few instances but is otherwise the same. The BSR foam consists of three families, and can be identifed as synthetics, naturals, and blends.

Synthetics - The old school, light weight, easy to true "dry feeling" tires. These include tires like CRC/Jaco Yellow (BSR White), Black, Gray, etc. These tires offer the highest wear rate and lowest grip. Many racers continue to use these nder high bite conditions.

Naturals - These tires are usually the best alternative for low bite and asphalt. They include Pink, Magenta, Double Pink, Lilac (BSR Team Purple), Purple, and other tires. These tires provide a ton of grip, but tend to get sticky in high bite conditions. This rubber does not wear as easily, and the cars will pick up gunk and fibers from the carpet under most high bite conditions. This is especially bad if the humidity is high.

Blends - These are the tires most people run today. They were initially called "JFT foam" by some, as it was believed that the tires were the same as the JFT tires. We can divide the blends further into two groups: high rubber and low rubber content. The high rubber would be the new rear Orange and Red from the BSR family, and the low rubber would be the Green and Blue varieties. When, asked about the difference, John Foister from BSR Tires said they came from the same "family" of foam, but they offered different grip. According to John, the Green/Blue has more bite than Orange/Red, but from track testing Oranges offer more bite than Green (being equivalent to in hardness) when the grip is high and absolutely no grip when it is lower. The Orange foam has a denser pore structure and the tire is not as prone to chunking. It is also important to note is that BSR Blue rears are not the same as the BSR Blue fronts!

JFT stands for Japan Foam Tire. They started the new wave of foam tires we are all using now (Blue/Blu, Green/Greene, Dbl Blue, etc). These tires are a little different than the BSR tire family, but work in very similar conditions. They offers four varieties A (asphalt), C (carpet), S (???), and R (???). This does not mean that those types only work on that surface, but this is what they recommend.

JFT uses the same foam for fronts and rears if the color is the same.

A: Used on asphalt, considered close to the natural rubber variety and are named consistently with other natural tires.
C: Used on carpet, considered a blend.
S: Used on carpet?, tires are ???
R: Used on carpet?, tires are ???

For setup, the JFT foam seem to generate more bite than the BSR, therefore the car tends to be a little more aggressive.

Ulti is another Japanese brand that offers an array of compounds. They have their own way of rating tires, and are difficult to equate to other brands. They have 4 different varieties, each in varying degrees of hardness.

J: High rubber content tire, similar to Pink/ Magenta. Soft would be close to a pink. These offer the most bite and are great for asphalt/carpet front tire. (J hard being very popular)
X: "Balanced" blend, similar to JFT Blue/ Green. Soft is equivalent to Green, medium to Blue in hardness. Great for carpet!
Y: High synthetic blend with lower grip, and is not a very popular variety.
Z: A very expensive "special" foam that is supposed to be magic on asphalt. Only make it in soft shore.
European tires:
There are many great European foam tire brands that use their own types of foam, as well as traditional foams. SOmeone with more knowledge about them will need to fill this in!

Tire Diameter:
If you are racing on carpet, you have to evaluate how much grip your track has. If your track is low to medium grip, you can run bigger tires. If you are on higher bite you have to cut them smaller, there is simply no way around it. Bigger tires are needed for asphalt, especially in the rear. The larger tires provide much needed lateral bite.

Carpet (mm)
Low - Medium Bite
Front: 42.0 - 42.5
Rear: 42.5 - 43.00
Medium - High Bite
Front: 40.5 - 41.0
Rear: 41.5 - 42.0
Big Race
Front: 39.5 - 40.0
Rear: 40.5 - 41.0
Asphalt (mm)
Parking Lot
Front: 43.0 - 44.0
Rear: 44.0 - 45.0
Prepped High Bite
Front: 42.0 - 43.0
Rear: 43.0 - 44.0

Tire Saucing:
Most facilities have moved towards odorless traction additives such as SXT. Some of additives evaporate very quickly and some do not. This seems to be something that is also dependent on tire compound and ambient temperature. For example, saucing a Green compound seems like it never dries, especially when tjhe temperature is lower. We have found that wiping the tires off 15 minutes before we go run allows the sauce to cure, which makes the car come in much quicker with Green rears. Blue compounds on the other hand, do fine when wiped off right before hitting the track.

Saucing half front and full rear is a good initial starting point. If the front of the car is too agressive you can sauce les than half, or for a shorter amount of time.
Tire Fuzzing:
In conditions of increasing grip, foam tires will somewtimes get sticky and pick up fuzz and debris from the track. This is highly dependent on the rubber sedan tire that is being run at your local track and the compound/ type of foam you are running on you car. The softer the sedan tire and the harder/higher rubber content in your foam tire, trouble with fuzzing seems more likely to occur.

There are ways to get around fuzzing under most conditions, and usually involves the selection of the correct foam compound. The more fuzz you get, the softer/lower rubber content you want to run.

Problem: Car fuzzes with Lilac/Team Purple fronts and car starts pushing.
Solution: Use a softer front tire and or different family of foam. Replace it with Blue or Double Blue front.

Problem: Car loses rear bite 6 minutes into the run. Blue rear tires look almost clean but have small carpet hairs.
Solution: Use Green rear tires. The softer compound wears instead of getting sticky, minimizing fuzz.

Tire Selection:
Starting out, pick 2 tire compounds for the front and rear. The following should have you covered 99% of the time.

Front - Green and Blue (BSR) or Green and Light Blue (JFT)
Rear - Blue and Double Blue (BSR) or Blue and Dark Blue (JFT)

You may wonder about other compounds out there and if they might be better, trust me, they probably won't be. Even if there are other tires that can be as fast, the synthetic family wears out really fast and the high natural rubber will probably fuzz on you over an 8 minute run. The blends family seems to be the most versatile foam type available today. They last awhile, and sticking to them will make your process of tire selection simpler.
Tire Chart:

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Old 06-04-2003, 07:20 PM   #3091
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what is a good servo for 1/12?
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Old 06-04-2003, 07:23 PM   #3092
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Went to the track tonoght.
I was working on geting rid of the car's twitchyness, and I ended up doing something completely different. I ended up setting up the car based on how much foam dust was left on the body after the run. Initially, the fronts were wearing more, so I added caster, and it made the wear a lot more even. Not to mention laptimes were down.

Is this a decent way to set your car up, based on even tire wear?
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Old 06-04-2003, 07:27 PM   #3093
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Originally posted by CypressMidWest
Actually, the Six-Pack and CarpetKnife from CRC can also be ordered with the old front-end. They call it "retro"
my bad....maybe it's because all the kit i see at my LHS are Assoc. strut
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Old 06-04-2003, 07:40 PM   #3094
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This thread is busy tonight.

On the Dynamic strut front end, in order to free up the kingpins to make the steering block move freely, what sized reamer do you use?

And do you ahve to use a reamer, or could I just usae a drill bit? I understand you shouldnt use a power drill, but how about a drill bit in a tap handle? Would that work?

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Old 06-04-2003, 09:58 PM   #3095
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Default Re: Discharging 4-cell packs

Originally posted by mushu
I'm getting ready to do some 1/12 scale racing and I have a question. What's everyone using to discharge their 4-cell packs. There are plenty of choices for discharging 6 cell packs down to .9v per cell @20-30 amps, but what about 4-cell packs. The only things I've been able to find are the high-end Integy chargers and the Competition Electronic chargers.

I asked the same question about ten or twenty pages ago! And the same basic answer. Seems like Deans or somebody would make a 4-cell specific cut-off device. The one I use on my 6 cell packs don't seem to take the 4-cell packs down very far.

Think I'm off to the electronics store to see what I can build or come up with......I'll keep you posted.

By the way, a guy on here posted a home-made discharger diagram.....seems to me I saved it.... Hmmmm
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Old 06-04-2003, 10:01 PM   #3096
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Originally posted by dg8one

what is a good servo for 1/12?
I'm going to use the Airtronics 94145 servo in my 1/12 car. I think thats what the number is, it's metal geared and has good specs. You can get them from Hobby Ect. for 65 dollars. I've heard this is what a lot of people use, and since it's Airtronics you know it will last .

I think you could use any drill bit to ream it out, not sure what size though. Just put it in a pin vise or something, that's what I've used before. I'm going to order my car tonight and I was wondering if any 1/12 springs advertized on the CRC site would fit the old style and dynamic strut front end, there's not difference right? Thanks!
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Old 06-04-2003, 10:08 PM   #3097
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Hi Guys, A little off topic, but I was just cruising the net and I saw that SpeedMerchant has an online shop now. http://www.teamspeedmerchant.com/index1.html No more waiting for my LHS to order for me.
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Old 06-05-2003, 12:50 AM   #3098
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Mushu: I found it! Someone (sorry, can't remember the name to give you credit) posted this for me when I asked the 4-cell/discharge question. In reading it you will notice a resistor. Looks to me like the text at the end discussing how to size the resistor says that without a resistor it discharges to about 3.5 volts.....that sounds about right to me for 4 cells. There is a drawing and picture that go with this, but I can't seem to get it to copy from the file to this thread. If the guy who originally posted this could re-post the drawing, it would sure help out! Thanks! and good luck with your discharger project Mushu!

Auto Cut off

Once you have built a bulb discharger you should build an auto cut-off device to protect you cells from reversal which can be very damaging. The device simply switches the load off once it reaches a predetermined voltage (usually about .8 volts per cell). To build the device you will need:

1 x High current 12 volt relay (A 30 amp Bosch automotive horn relay is what I use but anything similar will do.)
1 x Momentary push on switch (where the switch is on only while you press it and is off at all other times)
1 x About 1 foot of battery wire
1 x Pair of battery connecters
1 x 1/4 watt or larger resistor approx 30 ohms (more about this later)
A few pieces of small hook up wire (any small wire will do)

The first step is to wire up the main current loop using standard battery wire, locate one of the coil terminals and solder two pieces of wire (black) to this (one to go to battery negative and one to go to the discharger load negative). Then locate the common terminal and the normally open terminal of the relay (these terminals are open circuit when the coil is not activated and short circuit when the coil is activated) and solder one piece of wire (red) to each of these. Each pair of red and black wires can now have their battery connectors attached.

To check the first stage of the circuit, first measure the resistance between the pair of wires that plug into the battery and the pair that plug into the load they should both be infinite (open circuit) if they are not recheck the circuit and fix any problems.

If this checks out ok the battery can be plugged in. At this stage nothing should happen (if there are flames explosions etc. something is wrong). By using short piece of small wire energise the coil by connecting the unused end of the coil to the positive of the battery (where the switch is on the diagram). When this wire is applied the relay should turn on and the load wires should have 7.2 volts across them, as soon as the wire is released the relay should go off and the voltage across the load wires should go to zero. Once again if the load voltage does not go to zero when the wire is removed check and fix the circuit before continuing. If this works ok the switch can be soldered into position between the two terminals just used.

The next step is to calculate the size of the resistor needed, to do this first measure the resistance of the coil (it should be about 100 ohms). Then the voltage at which the relay releases has to be found, this is done by soldering a temporary piece of wire in place of the resistor and discharging a battery while monitoring its voltage (press the switch to start discharging). The battery voltage at the moment the coil releases should be around 4 volts.

The resistor value can then be calculated using:

R = Rr(Vc/Vr) - Rr

R is the resistor value
Rr is the resistance of the relay coil (around 100 ohms)
Vc is the cut off voltage required (I use 5 volts for a six cell pack)
Vr is voltage at which the relay releases (around 3.5 - 4.5 volts)

This size resistor can then be placed in the position shown on the diagram in the place of the temporary wire used in the previous step. The discharger should now switch off at around the voltage calculated. All you have to do to use the device is plug in the load and battery and press the switch once to start discharging. Alternatively a variable resistor can be used in place of the resistor to trim the cut off voltage. If you have room in the case of the relay the resistor and switch wires can be placed inside (as I have done), this makes the devise much neater and less prone to damage. The switch can also be mounted on top of the relay.

The excess terminals on the relay can then also be removed leaving only three (negative, bat positive and load positive). Once the cut off trips the battery is completely isolated so it can be left connected for extended periods of time, however as always the load should not be left unattended while it is operating as it could set fire to something due to heat build up. I find mine very useful for racing as it only takes a few seconds to plug in after a race before going out to marshal the next race, when you get back the battery is dumped and ready to be recharged.

Last edited by Graphitedust; 06-05-2003 at 12:56 AM.
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Old 06-05-2003, 03:26 AM   #3099
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Cool I built one!

Instead of using all the formulas, I just bought a 1/2 watt pot, built the thing, and adjusted it and tried it until it cut off at my required voltage. Then I measured the resistance of the potentiometer and bought a resistor to match it. I then gave all the parts including the resistor to my son and he built him self another one. My son is 11. Different relays have different coils so this seemed the simplest way for me. It has to be a low resistance pot, like 500 Ohms or lower if you can find one. I think I ended up with like 150 ohms for 5.0 volt cut off.

I also used a digital meter with a min-max function so I could see exactly where the relay opened up. Made it easier than watching it.

By the way they both work flawlessly.

David Root
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Old 06-05-2003, 04:59 AM   #3100
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The website for that info is http://users.chariot.net.au/~samstain/howto.html

They also have all sorts of other good stuff, like tire warmers.
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Old 06-05-2003, 06:02 AM   #3101
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Originally posted by dg8one

what is a good servo for 1/12?
Call Mimi, she has the proper Airronics servo for $60..... Just let her know you need a 1/12th servo and she'll knw what you need......
G's RC Raceway- Best off-road track on the east coast...period!!!

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Old 06-05-2003, 06:04 AM   #3102
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Originally posted by racerdx6
. I'm going to order my car tonight and I was wondering if any 1/12 springs advertized on the CRC site would fit the old style and dynamic strut front end, there's not difference right? Thanks!

The springs work on both frontends.....They are all Associated frontend springs......
G's RC Raceway- Best off-road track on the east coast...period!!!

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Old 06-05-2003, 06:55 AM   #3103
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Originally posted by dg8one

what is a good servo for 1/12?
Airtronics 94145Z
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Old 06-05-2003, 07:25 AM   #3104
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The KO 947 is an excellent servo, as is the 3025 from JR. The Airtroncs referenced above is also great.
Team CRC, Access Race Place, US Indoor Champs, CD SUPERPRO, RK Designs, Cypress, Founder and lead instructor of the Ian Ruggles Negative Reinforcement Driver Training Program, enroll now.....
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Old 06-05-2003, 09:10 AM   #3105
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DavidRoot and RC Paperboy: Thanks for the assist!!!!

David: How low could you turn down the voltage? Could you get as low as 3.5 volts?
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