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  #1  
Old 09-08-2016
oldschooldriver oldschooldriver is offline
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Default When to add weight?

I'm running a B5m lite and my son is running a Centro C4.2. I know the main thing is practice to get our laptimes down and consistent, but I know getting the cars handling right makes this a bit easier. I've seen a few drivers adding weight low down on the chassis to improve/lower the centre of gravity.

We run with shorty batteries. What are peoples thoughts on adding weight and what do you run? and when should weight be added?

There seem to be different types of weight and different values, but Im guessing it should be added low and ideally at some point in the centre line of the car.

30G 50G 80G saddle size or shorty size?
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Old 11-08-2016
AntH AntH is offline
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Never. It's complete and utter nonsense and don't let anyone convince you otherwise. Adding mass low does lower the centre of gravity but crucially you are increasing the roll moment as the mass is still above ground level. Moving existing mass about in the car to get more traction or reduce wheelies is a good idea though.
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Old 11-08-2016
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Completely disagree weight is an excellent turning aid when we ran the b5m lite we lined the battery tray with weight I used 2 Yokomo saddle weights along side 50g we also lined under the servo with lead plus the brass bulkhead

This would make the car hold the track very well on the bumps and balance the car in the air it would also give the b5m better steering as the car generates massive rear traction too much on high grip.

Yes a light car can be quick but a heavier car will hold the track better and be more consistent on bumps etc

Just give it a go and see what you think.
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Old 11-08-2016
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heavier will make the car smoother, more docile and easier to drive consistently and is better on a rougher track, lighter will make it more lively and responsive, harder to drive but ultimately faster if you get it right. small amounts of weight placed in the right place on a 2wd, like in the front bulkhead can make a big difference. on my current 2wd i have 60g in between the motor and the battery, car weighs 1570g with this added
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Old 11-08-2016
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Quote:
Originally Posted by AntH View Post
Never. It's complete and utter nonsense and don't let anyone convince you otherwise.
And that's why virtually every top driver with every current buggy platform is using under-LiPo, under-servo, stick-on weights, bulkhead weights, why last year's Worlds winning car was specifically designed to incorporate pocketed brass weights all over the chassis, and why the off road aftermarket scene over the past 10 or so years has been dominated by weight products...

If you don't use weight properly you can negatively affect the handling of your car, but to say that weight is in no way beneficial under any circumstances is one of the most incredibly misinformed statements I've seen in a long time - professional engineers making championship winning platforms do tend to have a good grasp of physics! Weight is a huge part of balancing a car for the surface you're running on.

To the OP, sometimes the way you use weight is down to your own feeling of how the car is handling. For high grip, bumpy tracks, you'll tend to want to run a heavier car, as it helps keep the car a little more predictable. You can use under-LiPo weights in a similar way, if you're running in low grip with the shorty backwards, running an under-LiPo weight rearwards will help you get a little more traction - the car could become more prone to stepping out at the rear due to the pendulum effect though, so keep that in mind. In low grip you'd also want to think about removing any front weight you have to try and shift the weight bias rearwards as much as possible. If your car is jumping nose-up, adding some stick-on weights, or a brass bulkhead or similar will help greatly. Weight over the nose will make the car a little more lazy as mentioned, so it's a careful balancing act - you can end up with a car that jumps nicely but hooks suddenly mid-corner. It's all just trial and error to see what makes the car feel right for you, but it's definitely something that makes a big difference.
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  #6  
Old 12-08-2016
fivepointnine fivepointnine is offline
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When I ran 17.5 in the US we would never add weight as we were always trying to get the buggy to the minimum legal weight. Here on a bumpy, high grip track a 50g under lipo weight will help the buggy feel much more settled.
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Old 12-08-2016
AntH AntH is offline
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Here's some things you can do instead of adding weight.

Car unsettled on bumps / poor ride: Increase shock piston hole size and or number of holes and either keep oil the same or increase slightly. You can use a softer spring also. I run at or under minimum weight where I can, poor ride can be tuned out.

Car lacking on power steering and / pulling wheelies; Move lipo forward or use a different configuration car with a weight distribution further forward.

Car lacking traction: Opposite of above.

Car going nose high / rear high on jumps: Tune out using shock pistons. Use larger / more holes at end that is going high. This is the most flaky of all reasons to add weight.

Jared Tebo was easily the quickest at the worlds in every round in terms of lap times with a shaft car with a weight distribution that put probably over 45% over the front axle. No or very little weight added. Why were Associated adding lots of weight? not sure but probably because the B6 weight distribution might be more towards the rear than a shaft 2wd.

Here's a challenge for you. Name any other form of Motorsport apart from tractor pulling where adding weight is considered a good idea. You can include any other form of RC racing in that too. 1/8th OR, no , any on road class, no. Post up a list.
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Old 12-08-2016
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Never heard so much waffle in a long time.
I have worked with Champions driving many different chassis from all over the world and they ALL use weight to tune their cars.

Everyone has their own thoughts I suppose
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Old 12-08-2016
AntH AntH is offline
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Quote:
Originally Posted by RudeTony View Post
Never heard so much waffle in a long time.
I have worked with Champions driving many different chassis from all over the world and they ALL use weight to tune their cars.

Everyone has their own thoughts I suppose
Yep, we can agree on that! Over and out from me.
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Old 12-08-2016
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Quote:
Originally Posted by AntH View Post
Here's some things you can do instead of adding weight.

Car unsettled on bumps / poor ride: Increase shock piston hole size and or number of holes and either keep oil the same or increase slightly. You can use a softer spring also. I run at or under minimum weight where I can, poor ride can be tuned out.

Car lacking on power steering and / pulling wheelies; Move lipo forward or use a different configuration car with a weight distribution further forward.

Car lacking traction: Opposite of above.

Car going nose high / rear high on jumps: Tune out using shock pistons. Use larger / more holes at end that is going high. This is the most flaky of all reasons to add weight.

Jared Tebo was easily the quickest at the worlds in every round in terms of lap times with a shaft car with a weight distribution that put probably over 45% over the front axle. No or very little weight added. Why were Associated adding lots of weight? not sure but probably because the B6 weight distribution might be more towards the rear than a shaft 2wd.

Here's a challenge for you. Name any other form of Motorsport apart from tractor pulling where adding weight is considered a good idea. You can include any other form of RC racing in that too. 1/8th OR, no , any on road class, no. Post up a list.
http://events.redrc.net/2016/08/chas...nic-greiner-2/
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  #11  
Old 12-08-2016
oldschooldriver oldschooldriver is offline
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Default Fantastic discussion.... Keep it going....

F1 use weight. They all want a driver that is as light as possible, so they can use extra weight in whatever position to get the right balance and get them to the minimum weight limit.

I'm used to setting a car up, so no problem there. Well, I'd like to thi nK so.... Just I'm from an era in late 80s to 1995 where you did not add weight as batteries barely lasted 5.5mins and motors and speed controllers were less efficient and heavier so it wasn't an option to add weight. Now a tiny bit of carefully placed extra weight could make more of a difference to laptimes due to better handling, as the power and efficiency is soo much better.

Really interesting discussion, and helpful. I know people all have different view, and I'm sure we can all discuss thi gs without falling out over any differences of opinion.

My old futaba receiver that I'm still running is probably 40grams and the size of a matchbox. It's up on its end as I couldn't fit it in my b5m lite otherwise. For weight distribution in my RC10 I used to slide my receiver and novak esc back and forward as they were relatively heavy compared to modern day electronics and I had space in the chassis.
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  #12  
Old 12-08-2016
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When to add weight.

Well I add weight at a very critical time. When my Mrs will not shut up going on.

I add approx 200g brass RudeBits lipo weight to her top lip to close the mouth.....

I have thought of adding the same weight in her rubber verruca socks when she goes swimming but yet to try that weight distribution....
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  #13  
Old 12-08-2016
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Quote:
Originally Posted by AntH View Post
Here's a challenge for you. Name any other form of Motorsport apart from tractor pulling where adding weight is considered a good idea. You can include any other form of RC racing in that too. 1/8th OR, no , any on road class, no. Post up a list.
Can you name any other form of motorsport comparable to off road RC racing, or RC racing in general? I can't think of any series where a base chassis is produced that incorporates a multitude of layouts for various engines, gearboxes, steering layouts etc. Full size racing cars can be designed from the outset to have a perfect, or near enough perfect given the design limitations, weight distribution for the components involved. Imbalances from front to rear can be tuned out with aerodynamic adjustments. Stacking weight is a hindrance because the amount of weight required to make a difference to the weight distribution of the car would ruin the car's handling, and you're very right with your observation of increasing the roll moment.

However, your argument is very black and white, and I've seen you mention "flaky science" in several posts - but you don't seem to be applying the theory correctly. By the same logic, we should never use wings because of the drag they generate. You're right in pointing out the negative impacts adding weight can have from a physics standpoint, but with an RC car, the driver is never connected to the car physically. You drive through visual feel and the confidence you get from the car. Adding 50 grams might mean the car will lose 0.1 mid-corner in perfect conditions, but if it's the difference between a driver turning in and feeling the car float, and then a driver turning in and feeling his car much more planted and stable, the driver is going to be able to pull out more time over a 5 minute run than is lost with the added weight.

With regards to the idea that suspension tuning is the answer to all stability issues, you again seem to have a very black and white idea of how the car performs. 2wd buggies will never have perfect weight distributions out of the box. It would be nice if they all did, because it would mean that we could all install electronics of a specific weight in a specific place and end up with a perfectly balanced car, but that's not how cars are designed. If you go up in size on your front pistons to cope with one bump better, you might get the car riding the same over that bump as if you dropped 25 grams under the servo. Great - it handles that one bump better. What about the other 10 corners on the track that might be very high grip and smooth? You'd want a firmer front end for that, but you've just sacrificed a cumulative second or two by gaining a tiny bit of stability over one bump. You can't say there's one clear-cut solution that suits every car on every track, and in constantly trying to adjust your shock setup to find a better balance for the track and conditions you'd be chasing your tail. I understand why you're thinking what you're thinking - but you're thinking in terms of ideals, and that's just not how you can set up an RC car. A chassis has virtually infinite possibilities for weight distribution within the confines of the kit layout, with speedos, motors, batteries, receivers and servos of differing weights, but it's very rare that you can position them in such a manner that the left/right and front/rear distribution produces a nicely balanced car. Weight isn't just an option if you're wanting to be competitive on a wide variety of tracks, it's virtually a necessity.

With regards to the RZ6 and B5 differences, the motor and battery being transverse on the Associated already puts the two heaviest things on the chassis further back than the Kyosho. It's little surprise they decided to run more brass up front than Tebo did. You can't compare them directly though, because they had different geometry with different front shock setups, different electronics placements, different chassis shapes, different plastic grades, different CGs, different screw mounting points so different flex characteristics, different alignment... saying "one didn't run as much weight as the other and it was faster over a lap so weight is useless" is very much specious reasoning.

It's interesting to see people come up with different theories, but to try and claim one thing has no benefits using one incorrectly applied theory, and subsequently rubbishing anyone who thinks the opposite (which seems to be every other driver or professional engineer on the planet) is a bit daft, to say the least.
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  #14  
Old 12-08-2016
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The thing is the cars we are all racing have an incredible power to weight ratio for their scale (sometimes far to much power lol). In the states in the stock classes which have low power compared to what we race of course need to be as near to the limit as possible but they travel slower, generally have smoother tracks to race on and don't become as unsettled on bumps unlike cars raced in the uk for example.

7/8 years ago cars had batteries that would just about last the five minutes so any extra weight would impact your ability to finish the race irrespective of the handling of the car itself - to finish first, first you must finish as the saying goes..

Indoors I can see the need to not run as much if any weight where tracks are smoother and cars are more predictable around the circuit but outdoors on most tracks I regularly run my car over 1600g and I am no worse off relative to the people I race against.
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