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I think that is where you will find yourself. The tire and wheel weight, as well as the total unsprung weight ratio to spring weight is what I think hampers going to a lightweight design, given the power capability and tire sizes and composition(softness).

the added weight slows the chassis down to a manageable level by adding inertia, it's tough to achieve the same effect with lighter parts because inertia is a mass derived function.

My problem with the argument though is that more and more sprung weight is not better and better. Where is the sweet spot? If a 4 lb car handles better than a 3 lbs car, a 6 or 12 lb car shouldn't be assumed to be better yet. We'd load them up with concrete if this were true. Is there a ratio that is near optimal?

It would be interesting to compare the unsprung mass of various cars to see the difference. Our old RC10's had some thicker arms whereas later cars have much more open area in their arms and are made with lighter but often more fragile components. I think in the end that it wouldn't be hard to design and build a very light suspension system that is decently strong. The biggest concern comes from the wheels and tires and these should be a bit smaller and lighter than the current offerings. This would hold other benefits as well such as less rotational mass to get moving.

I think you answered your own question right there. The sweet spot for the current tires/tracks/horsepower is around where you find the pro drivers running, ie, running weights to help fine tune the chassis.

if you change any of those variables, then you will dictate how much weight you need. I would bet you could run a lighter car all around if you narrowed the section width of the tires, giving a higher weight loading on the contact patch, and thusly, removing weight to get back to the current contact patch loading. that effect is two-fold because you lose weight in the unsprung mass in the process.

I think a narrower tread tire would be a good idea on hard dusty tracks but on high grip I don't think it would help. On loose dirt tracks I definitely wouldn't see a narrower tire helping. In that case I'd rather have a wide tire but with fewer yet longer spikes. Then again that takes us back to the tires of 25 years ago which were used on cars we got as light as possible and ran on loose dirt.

Jay Dub wrote: I recently stopped by my local track to watch the ROAR Off Road nats. The cars looked fast, handled well, and went through a set of tires EVERY run. The weight of the car, and the available power is why this is such an issue (I know tire compound has something to do with this btw). I think in the best intrest of the "racing" hobby, the cars should be much lighter, and have to use lower traction spec tires -smaller power plants will follow naturally. -Jeff

I thought that frequently Pro's changed tires between heats, and definitely for the main BITD also.. Of course the abrasiveness of the track could be a major factor here. It's been said before that offroad now is like hills and jumps on concrete or asphalt. Let's go back to racing in the dirt, and we won't have to have new tires for each heat and main. You could run a set for several race days with little to no difference.

Track design has evolved to be like that due to racer's wanting consistency. IMO if you want that, go race concrete oval, and touring cars...

Sorry to take up an off topic comment in the thread -

I agree. I miss the old tracks. These new hard packed clay tracks are car killers! I do less damage to the cars when they flip end over end on concrete! The old tracks really highlighted a well setup car vs a poorly setup one. The newer tracks are pretty easy to guess. Set it up stiff with heavy shock oil, soft tires, and make it heavy. It'll probably work! Modern "off road" is a joke. Especially in Europe where they have astroturf tracks with wooden jumps. That's not off road. Sorry. Dirt is off road!

Here is a motor you might want to take a look at:

http://www.hobbypartz.com/3650m-sl-4300kv-brushless-motor.html

It is a 380 size motor in a 540 can, so it will bolt right in without problem. I run this in 2wd mod buggy and it has alittle less on the bottom end but plenty up top.

It's interesting that they'd do that but if you look at the weight vs their 540 motors you'll see it's the same.

I looked at that motor vs a novak and its 165g V 187g.

http://www.teamnovak.com/products/brushless/motor_spec_chart.htm

28.34952 oz per gram.

I weighed my car in it's ready to run format minus battery. Keep in mind I haven't built the car for lightness. It's got Dubro heavy duty rod ends and all stainless screws. It does have a graphite chassis though. With a brushed motor, electronics, and body installed, again only lacking a battery, the weight came in at 2.79 lbs. I'm pretty sure if I could get it under 2.5 if I tried. You can get a fairly low mah lipo that weighs as little as .4 lbs. As you can see my car with the lightest battery out there is under the ROAR minimum but a heavier battery could potentially take it above. It wouldn't be very hard to build the car as light as possible as stay well under the minimum though and you could definitely keep a running car under 3 lbs.

Lightweight cars are ok, but I think that there is a point when the car doesn't work right. For example, the new Tamiya F104 cars on Tamiya rubber are faster with a lot of weight added on certain tracks. I raced the Tamiya nationals a couple weeks ago, and the guy who won F1 had like 6 oz. tacked onto his car. I wound up adding weight to my car, 4oz. and not only did I have to add 30% dual rate back into the car to get the steering back, the rear tire wear decreased due to the car not sliding. Now, the Tamiya USA track is pretty low traction. On a carpet track, with foams, I have no real reason to add weight to the car, unless it's a small amount (1/4-1/2 oz) over the nose to help on power steering. In fact, in that high traction situation, I have used a 98g 1800mah mini Revo pack (an average 4000 lipo weighs 200+ g). That does make the car considerably faster, in that situation. I have tried the little battery at the Tamiya track, and it is no good.

So it's horses for courses. In offroad, not only are the cars traction limited in a lot of cases, but removing a significant amount of weight from the car is going to alter the car's balance for jumping.

Charlie don't surf wrote:

kaiser wrote:won't the car need to be direct drive (or close to it like a trackmaster or something 2 gear instead of 3 gear) in order to make the most of the limited voltage/power, like a pan car?

Current roar rules state 3 gear reduction. You can have more but not less- you can however argue that the spur is the first reduction gear.

Actually, the only requirement is a single speed transmission.

8.10.1.4 Transmission: Single speed transmissions only

AscotConversion wrote:

Charlie don't surf wrote:

kaiser wrote:won't the car need to be direct drive (or close to it like a trackmaster or something 2 gear instead of 3 gear) in order to make the most of the limited voltage/power, like a pan car?

Current roar rules state 3 gear reduction. You can have more but not less- you can however argue that the spur is the first reduction gear.

Actually, the only requirement is a single speed transmission.

8.10.1.4 Transmission: Single speed transmissions only

Reduction, not speed

Charlie don't surf wrote: Actually, the only requirement is a single speed transmission.

8.10.1.4 Transmission: Single speed transmissions only
Reduction, not speed

http://www.roarracing.com/downloads/2010_ROAR_Rule_Book.pdf

8.10.1.2 Tire type: Rubber only
8.10.1.3 Battery Cells: Six cell maximum or 2s, 7.4v nominal lipo battery
8.10.1.4 Transmission: Single speed transmissions only
8.10.1.5 Rear suspension: Independent.
8.10.1.6 Body Style: Buggy or other off-road style body that resembles an actual offroad
racing non-truck type vehicle.

No mention of transmission other than single speed...so no limit on direct drives or 2 gear, 3 gear etc.

AscotConversion wrote: but removing a significant amount of weight from the car is going to alter the car's balance for jumping.

This is only true if you don't know how to tune a suspension for balance. You can't change weight in any way and not expect to retune the car. Then again most people don't know how to tune a suspension which is one reason why I've questioned the validity of adding weight. Most people don't know what they are doing yet most people today say that you need more weight. By default that implies they are wrong. I understand adding some weight for the sake of balance. What I don't understand is adding a half pound of weight just for the sake of making a car a half pound heavier.

No one would add weight to an F1 car in order to make it handle better. I know that someone is going to point out that the aerodynamics of an F1 car is such that with it's wings it has enough downforce to hold itself to the ground even if completely upside down. Yes that is equivalent to adding weight...in one plane. However if you were remove those wings and then add 2000 lbs of weight to the car, it wouldn't turn well or stop well, or accelerate well. The added weight will then resist acceleration forces, will try to remain moving at speed, and will try to move itself to the outside of a corner. But it will help push the tires down more. Admittedly an F1 car is a bit of a stretch when it comes to an example but the point is clear.

There has to be a valid reason why adding weight works better. Clearly it's to help the tires grip better but what if the problem lies with the tire rather than the weight on it? I keep hearing people say you need more weight on a looser track so that the tires grip better. I absolutely 100% guarantee that if you took a modern car that has been weighted down in the name of "performance", using modern tires, and were to run it on a loose dirt track from lets say the 80's against an old RC10 from that era, the new heavy car will absolutely get it's butt kicked. But why? It's heavy! The old cars were light. There are a number of reasons but I feel that a big one is tire design. The old tires were admittedly harder in compound and had no supporting foam inside. They also had very tall spikes but fewer of them. Modern tires are a soft grippy compound with foam inserts for support and have lots and lots of small spikes or something of the like.

I think the problem is obvious. I think it's all about weight per contact area and how that contact area interacts with the track based on it's material hardness. A modern soft but well internally supported tire with high contact area needs more weight to make it as effective. Modern tires have evolved over time with track design and lets face it, modern off road track design has hit a point of absurdity where it really isn't off road anymore. It's clayish concrete with a few large jumps. A very hard but dusty track is one that tread just can't grip into so it comes down to applying downward force to a tire to make it more resistant to sliding. So in essence while tire compound and design has a big role, it's been due to our present farce of a trend in offroad tracks as well. This by no means discounts the benefits of lightweight but suddenly as has already been pointed out make weight more of a situational tuning decision rather than a rule as many today treat it to be. It isn't always needed. Sometimes it can be beneficial and other times it won't be. This still completely ignores the many negatives of more weight regardless of situation.