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#21
19-08-2010
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Shy,
this is an interesting perspective... on low-grip tracks, more weight generates more grip - but is the incremental grip overproportional vs. the incremental weight, or is the better handling mostly coming from the car's reactions being slowed down and then becoming easier to drive overall? My understanding of tire adhesion is that more weight means more grip, but not enough to compensate for the extra inertia... hope I don't confuse you more with this  I really like the sprung vs. unsprung mass perspective too... I didn't think about that one initially... good stuff... Anyone without any commercial interest wanting to add to the "technical" part of the discussion?  Paul 
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#22
19-08-2010
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If you can add mass close to the centre of gravity you will not increase the inertia as much as if the mass was added further away. A normal 2wd byggy with rear motor will have quite high yaw and pitch inertia and very low roll inertia. But a X6 will have lower yaw and pitch inertia and a higher roll inertia, (battery placed from side to side).
Another benefit could also be that it also lowers the centre of gravity if the CG is originally positioned higher than the weight added.
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__________________________________________ Kyosho RB5 SP: RB5 Mid: ZX5 FS: Orion: Spektrum
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#23
19-08-2010
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The price ratio of such parts vs gains still is not me convinced...
You are still adding mass regardless and acting on 2% pc of the total car mass. It does have an impact i am sure, notable one you bet, must-have for the future.. not so sure. I m not talking about adding 15grms under the bulkhead to midly compensate for lipo weight.., but people are adding under pack weights, on servo, behind bulkhead, even on motor.. this is getting totally silly !! 2 years from now, i d be happy to bet that noone will add weights anymore to such extremes as today. it s like charging packs in ice, running the stiffest chassis possible, progressive springs, super long shocks in front.. It all faded out at some point.
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#24
19-08-2010
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Basic science says the lighter car will be faster. In all forms of motorsport there is a minimum weight, and teams spend a fortune lightening their cars to get to the weight limit. Reason being that more energy is required to move the greater mass, in any direction, and on top of this are inertial effects which increase the energy required to accelerate the mass, or to put this simply for the mass to change from one moving state to another. In practice it is not so simple as the car has to contend with bumps and make use of the grip available from the tyres. In a tractive and braking sense the tyre's grip is primarily controlled by the mass it's carrying, so a heavier car will have more traction, or a more rear weight biased car the same. So in a low grip scenario the extra energy needed to accelerate the higher mass could be much less significant than the improvement in available traction. In a cornering sense the tyre's grip is not a simple function of mass, infact carrying more mass could reduce it's capacity depending on it's properties. This is very long and complicated to explain but F=muR does not apply simply because the tyre is rolling and flexible. In a 1/10th sense different foam inserts will produce different cornering properties (as different tyres pressures do on the big stuff). A heavier car will need bigger/stiffer inserts to allow the tyre to produce more cornering force and these same inserts could then reduce cornering force on the lighter car. This is also the reason why high unsprung mass on a light car could not be desirable. As for the bumps well whether the car behaves itself or not is a function of mass, unsprung and sprung, spring rates, mass distribution, damping properties (at different damper speeds) and tyres. Mass is only part of it. 1/10th damper technology is archaic and this means that it is impossible to seperate the performance between large bumps at high speeds, or rough ground, or handling and so on. It may be that a heavier car has a larger window of performance and the dampers are better at dealing with the variety of what's thrown at them. My observation is that weight gets put on regardless at the moment but as the sport moves forward those that can find a way of making the set-up work with a lighter car are going to be faster, just basic physics.
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#25
19-08-2010
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I don't know if this apply's to anyone else but personally there are only 3 reason's I add weight to a car...
1 - Add weight at either end to change the weight distribution and balance of the car. 2 - To keep the front end of a 2wd down. 3 - To get up to the weight limit (  )I always prefer my cars to be lighter and need less motor for adequate straight line performance, making them like a brick and then going for the brute force method of adding more power seems a bit silly to me. It takes more effort to get the thing moving and change direction, all the electrics get hotter, tyre wear (and wear and tear in general) is worse. A lighter car will recover from bumps more quickly too as there's less weight to stop moving, also in my experience a lighter car is no less stable through bumps if your shocks are right... When I was running the B4 the only weight I had in it was the Trish front bulkhead (40g) to keep the front on the ground, move the weight forward a bit and get up to the weight limit. And the squat block (28g), to get up the the limit and balance the bulkhead which moved the weight a little too far forward, it was under 1500g...
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#27
19-08-2010
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Interestingly my B4.1 is so much better on the bumps I'm going to straight away start running it under 1500 grams. For whatever reason, whether it's the new shock angles or the new shocks, it has much less friction than the old one as well as more travel. Feels softer on the bench but just glides around the track. And being rear motor traction shouldn't ever be a problem. It needed 40 grams just to get it legal so plenty of scope to play with weight distribution.
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#28
19-08-2010
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I am shocked at some of your comments lads.
You are actually saying that the likes of Ellis Stafford, Lee Martin and so on don't know what they are doing and week after week they win major meetings.....these are some of the best drivers in Europe!!! Matt Benfield's B4.1 had weight in it at the last national and he finished 2nd only to Kev Lee in the last leg of the A and his car looked brilliant. How can you argue facts and facts. I hear the theories and yes they are right in principle but no one can argue with Ellis running loads of weight in his car and has dominated the last three years. 3 years lads, not one event.......come on that is a difficult one for anyone to argue with. Weight works - simples 
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#29
19-08-2010
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As it's your business to sell weight to RC car owners then that's an obvious post.
Weight works at the moment, the key to moving the game on is to understand why and how to get the car to work without it.
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#30
19-08-2010
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Like Tony says, you can't argue with the results.
Sometimes I run at a very small local indoor track thats all slippy polished floor with no jumps and Ive been playing with the weights in my X6. So far Ive found that putting more weight in the front makes the car push into the bends rather than giving it more grip but exit grip seems better. Weight on the rear improves traction and grip out of the bends but makes the tail a bit loose mid corner and hampers acceleration. This makes weight a valuable tuning aid to get the best out of the cars setup. The first thing I alter is spings, then its weight, then I move onto shock positions and the rest. When I ran my B4 I used sticky weights and never moved them but with the X6 Ive got the full brass kit so I can add or remove weights to suit the conditions  .
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Mark Dyson Clown
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#31
19-08-2010
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#32
19-08-2010
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Well done guys this is one of the most interesting threads I've read in ages. Everyone has valid points and their own experiences to share. What gets me though harks back to the original question - why?
When I started racing in the early 90's we did everything we could to make our buggies lighter (including drilling a silly amount of holes in the chassis of my XX!) so we could maximise the performance of our motors and cells. These two areas have developed at a staggering rate in our fine hobby, but has it simply shown that the cars themselves haven't kept up?! We've gone full circle, first we make them lighter, now we make them heavy. Who's going to be the first top racer to win right on the weight limit again?!
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#33
19-08-2010
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My theory on this is that back in the days with brushed motors and nimh/nicd batteries both power and amount of energy stored to finish 5min of racing was the main concern to make the cars go faster. The solution then was that lighter was faster as it put less strain on the motor and batteries. Now with brushless, lipo and power beyond, the limit now is how to get that power more effective to the ground. And if the tyres will produce more relative frictional force with a higher tyre load then heavier is faster.
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__________________________________________ Kyosho RB5 SP: RB5 Mid: ZX5 FS: Orion: Spektrum
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#34
19-08-2010
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Now now, come on! I doubt Tony is becoming a millionaire selling his little brass weights!
Ellis has done extensive testing, below and above what he currently uses. So of course this tree doesen't grow into heaven! When I earlier stated that in onroad a heavier car is faster in the wet, that is of course only to a certain extent. That's common reason! What the limit is will vary depending on conditions, but there will be a "sweet spot". And yes, all your physical theories are "correct". But you're forgetting that RC racing simply cannot be compared to 1:1 racing. The speed, low weight and power is simply way way too extreme here! Me and Elvo had a fantastic & VERY long discussion tread on myTSN (Serpent) many years ago. The topic was "fluid dynamics", more commonly known as aerodynamics. I learnt all about Bernoullis theorem, inverted aeroplane wings, diffusers, gurneys, vortexes and so on... which was so much fun & very interesting! But in the end the conclusion was: The speed relative to the scale is so high that more or less none of these principles apply! Firstly we don't have "drag penalty" as we're overpowered. Secondly it's just "pushing air" here and there, plus tons of turbulence! So it's very much down to experimenting! Keep in mind that also insects don't have "aerofoil" wings. They're just simple & flat, like RC wings. They just showe air around!  (fluid dynamics don't work in such a small scale, as the air molecules are always the same size)(Yeah, yeah.. the point comes now...)  The same is the truth for weight. Forget your schoolbooks! Go to the track and start testing - with laptimes! If you at a given track and the best setup you can come ut with - are faster with a very light car - nice! Go for it! But try also with more weight - at different places in your chassis! I'll do whatever is faster! F*** theory! Books have been rewritten throughout history! And look at F1! They're experimenting all the time! Motorsport is no "given science"! It's trials & errors & crazy stuff all the time! A given setup change may even have different results on different tracks! So TEST, TEST, TEST!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! That being said, we now see more and more tracks with astro turf. Which means high grip and a fairly flat surface. This caters for lighter cars. My guess is we will also see softer (yet durable) tire compounds in the future (maybe also lower profile). Again, easier to get a light car working well... In my crystal bowl I see OR getting closer to on-road...
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Life's too short to go slow! www.ymr.no Tech Tips, HopUps & Bling Xray 2014 XB4 4WD & 2WD | B4 FTW Night Fox XL | Mugen MRX-5 | RB | Futaba 3VCS FASST | Faskolor Visit my showroom
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#35
19-08-2010
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Weight is good because:
Adding weight low down lowers the cars centre of gravity = more stability + more corner speed + better acceleration out of corners. Adding weight improves the ratio of sprung to unsprung mass. Adding weight stops you're car from doing wheelies. When you hit a big bump the suspension always bottoms out so suspension settings are irrelevant , but a heavier car requires more energy to make it fly. A heavy car has more inertia so will be less responsive and easier to drive, especially in bumpy conditions. It's easier to get the correct weight distribution by adding weight than modifying the car. Weight is bad because: A heavy car needs more power to accelerate and uses more energy. A heavy car has more inertia so will be less responsive and will wear the tyres faster. A low centre of gravity can hurt straight line acceleration on a 2wd as there is less weight transfer to the rear. (Only applicable if the car won't wheely) Heavy cars break more wishbones. Lifting heavy objects can injure your back. BRCA insurance does not cover cars above 20kg.
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#36
19-08-2010
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I'm gonna comment too
There is a very important thing that more weight does, and that is it makes the car easier to drive. Especially on bumpy astro tracks, and in the UK that's all they got in the national series. There's no use for the super fast laptime if you crash twice in 5 mins. Anyone who has done a national in the UK knows these guys have 2 times 3 minutes of practise before qualifying starts. So you better get the car safe and easy, as the tracks they run on are VERY difficult. Of course the top guys also have to be super fast but I bet that even they make a trade off between fast laptimes and a car that is still driveable. Then there's always the personal feel you want for your car. Some people just don't like how a heavy car feels (like richard for example). Ellis does, but his driving style simply asks for heavier cars. I don't think Tom God runs his car at 1700-1800gr? And he won this year. Hitting bumps can indeed be solved with changing pistons etc, but one thing you don't change: weight of your wheels+tyres. So going extremely heavy or extremely light will not be good as this messes up the ratio between chassis weight and wheel weight. Only way to test that is by trial and error. Personally I also don't like super heavy cars, but I also never succeeded in running with very light cars. So I go for the medium solution (as with any setup change I make ). Smooth high grip I will use around 1550-1600gr (2wd) and on lower grip, or bumpier astro, more like 1650 - 1670 max. Depending on grip level, weight will also be moved fwd or back. As tony says, just try it for yourself, and if you get lost, do what the top guys do and start over again. Or even better, the subtop, as they will most likely have setups that suit the majority of the drivers. I've driven with some cars or seen people trying to drive cars from the top drivers, and usually they can't complete a single lap without crashing out twice in every corner
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#37
20-08-2010
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This is the best oOple discussion tread in 2010!!!
__________________
Life's too short to go slow! www.ymr.no Tech Tips, HopUps & Bling Xray 2014 XB4 4WD & 2WD | B4 FTW Night Fox XL | Mugen MRX-5 | RB | Futaba 3VCS FASST | Faskolor Visit my showroom
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#38
20-08-2010
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If you chose to run your car light then that's fine mate. You are a top driver, I respect that and you have to do what is right for you and how it all feels for you. I am simply saying for the majority (probably over 95%) a heavier (note heavier, not 3kg) car is easier to drive and this reduces errors and therefore the overall package is better and ultimately quicker. In fact a heavier car under test after test conditions is quicker on lap times as well. You can push the car more when heavier because like I said before it’s simply better over bumps and jumps. This is Off-Road – not touring cars where I would agree lighter should be better!! These are all facts from the best drivers in Europe and the club racer, under test conditions, by results, by Championships and every day racing. Maybe in the future we will learn, if it’s there, that we can run lighter and lighter but at the moment there cannot be arguments that a slightly heavier car is faster. Ellis runs a kit of some 310g of weight that he moves around to TUNE his car to the conditions. Lee has various weights from 70g upwards for under Lipo and under Servo for TUNING his car. Tom Cockerill recently realised running weight is an easier car and he is our 2010 Champion I posted here to help Paul (Lonestar) not to get into arguments lads. Everything I say has factual results and not hypothetical or theories or maybes, Facts!! Finally to those that have commented on this being a commercial interest and I sort of resent that comment ...... those who know me also know I certainly don't need to sell brass, it's not my living, it's my hobby ...... I can't keep up as it is with orders all over the world and certainly didn't post here for that reason but I suppose some people have assumed that....... never mind eh!!!!
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#39
20-08-2010
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Back-to-back testing on high grip found the car to be more stable and less reactive to direction changes. It may not be the perfect answer to getting the car's handling to my liking but it works. I dont do much racing outside of the Nationals and in the 4WD, this has really helped me without changing oils and pistons bu half weights, etc. Just for the record, Mike and Grant Williams (who came up with the idea in the CAT) tune their 4WD using different lead plates under the chassis.
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#40
20-08-2010
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But your 2wd was good as well - what weight you running on that Matt?
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