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Old 03-17-2013, 05:25 PM   #1
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Default Unsprung weight on your 8th scale

So we've all seen the unsprung weight that's been added to all 4 corners of some of 8th scale buggys driven by the pros.
I'm sure there's reasons for it, but when I ask around I can only find theories about what it does and when to and when not to use it.
So what does it do? When do you use it? When do you take them off?

Based on my limited knowledge of 8th scale nitro geometry and tuning, here's what I have come up with (probably wrong):

I would think that you would use them to increase the pressure applied directly to the tire without affecting the tuning of the chassis. You could add them without having to respring, redo rideheight or camber angles. Not sure if you would have to rethink shock pack when landing (don't think so).

I would think that they would be effective in a situation where you need to increase traction, and would be detrimental in a situation where you have too much traction.

I would think that if the traction was low AND the track was smooth, this would be the ideal place to use them.

I would think that if the traction was low and the track was bumpy, that would not be the time to use them. My reasoning for this is that I think that the extra weight would send the wheel higher up into the air on each bump in the track, compress the spring further and disturb the chassis more.

But these are all theories. I'm looking to find out the real info. Anyone have the 'tuning rules' for these things?
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Old 03-17-2013, 06:14 PM   #2
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wud it not keep the wheel down in bumps?
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Old 03-17-2013, 07:31 PM   #3
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First off thank you for starting this off. I too have been thinking about this. I have a mugen mbx7 and I was thinking of buying the added weight to the front of my buggy. When too add it and when not to?
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Old 03-17-2013, 08:24 PM   #4
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I agree they will help on a dry dusty smooth track. During my tests with the Kyosho on a medium grip/ dusty, moderately bumpy track they actually slowed my qualifying times. If the track were smoother, I have no doubt they'd be dialed.
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Old 03-18-2013, 05:38 AM   #5
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Where, exactly, are these weights going?

To be "unsprung weight" they'd have to be put on the arms/shock lowers/tires etc. etc. I don't see any advantage of running weight there.
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Old 03-18-2013, 06:16 AM   #6
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The weights are added to hubs and caster blocks.


Some quotes from Jesse Robbers and Ty Tessman, 2012 IFMAR worlds warm up race posted in the D8 hara thread.

Quote:
Originally Posted by Jesse Robbers View Post
Mugen had weight on their front caster blocks/pillow balls, others followed. The weight mounted how and where it is does not act independently as a mass damper. The gain of one thing means the loss of another. The heavier caster blocks can prevent the tires from leaving the ground as easily, but once that is set in motion it takes longer to come back to the ground.

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Originally Posted by TYTESSMANN View Post
Since I was one of the few guys that actually tried the weight on the front caster blocks I can tell you what it did. The track that we ran on in Argentina was like nothing I have ever ran on before, the layout itself was relatively easy but the incredible high speed combined with all the bumps and rocks made this one of the most difficult tracks I have ever driven. At the beginning we really struggled for a setup, the new D812 is a car that is very nimble and has alot of steering on the track, perfect for US tracks but when we got on this track it was far too aggressive, driving my car on this track it felt like the car weighed nothing and bounced around, because of our lack of experience with this type of track we basically tried everything that we could to make the car easier to drive. The weight on the front was one of the things we tried, what it seemed to do was make the car react slower and feel lazier and easier to drive, the best way I can describe it maybe is that it made the car feel numb, luckily with more time on the track after the race we were able to come up with a setup that worked very well and the weight was no longer needed. I would consider putting the weight on the front as just a quick fix when needed.
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Old 03-18-2013, 09:47 AM   #7
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Quote:
Originally Posted by rfleck View Post
I agree they will help on a dry dusty smooth track. During my tests with the Kyosho on a medium grip/ dusty, moderately bumpy track they actually slowed my qualifying times. If the track were smoother, I have no doubt they'd be dialed.
Well that answers my question...
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Old 03-18-2013, 08:22 PM   #8
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Thanks for the quotes, nv529. Maybe I'm a bit on the right track after all.
I'd still like to nail down 'THE RULES' when it comes to these things.
Has anyone covered this in any of the tuning guides?
Regarding the car reacting slower and feeling lazier, those were the exact comments made by a friend of mine who bolted them on his MP9 last weekend at AMS in Michigan.
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Old 03-19-2013, 10:49 AM   #9
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Quote:
Originally Posted by TYTESSMANN
Since I was one of the few guys that actually tried the weight on the front caster blocks I can tell you what it did. The track that we ran on in Argentina was like nothing I have ever ran on before, the layout itself was relatively easy but the incredible high speed combined with all the bumps and rocks made this one of the most difficult tracks I have ever driven. At the beginning we really struggled for a setup, the new D812 is a car that is very nimble and has alot of steering on the track, perfect for US tracks but when we got on this track it was far too aggressive, driving my car on this track it felt like the car weighed nothing and bounced around, because of our lack of experience with this type of track we basically tried everything that we could to make the car easier to drive. The weight on the front was one of the things we tried, what it seemed to do was make the car react slower and feel lazier and easier to drive, the best way I can describe it maybe is that it made the car feel numb, luckily with more time on the track after the race we were able to come up with a setup that worked very well and the weight was no longer needed. I would consider putting the weight on the front as just a quick fix when needed.

So basicly, it sounds like adding unsprung weight hurt the cars front grip and handling making it easier to drive until they got the rest of thier setup dialed in and then they got rid of the weight.

Makes sense. More unsprung weight F's up the front suspension and costs you front grip. Less front grip, less oversteer, easier to drive.

More unsprung weight is not a good thing, but if it works......rock it. Not that I'll ever look at or use a Worlds setup sheet anyways.
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Old 03-20-2013, 12:33 PM   #10
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Coming from what I know of driving real cars on racetracks adding umsprung weight sounds so counter intuitive.

You should be trying to tune the suspension and dampers. Adding unsprung weight IMO is a 'if all else fails' approach. It's probably the easiest but certainly not the best.

But, I'm a noob so what do I know.
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Old 03-20-2013, 11:21 PM   #11
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Here's my take on the corner weights....

The weights are basically at the extreme corners of the buggies. These far corners are the best positions to add weight when you want to maximize the polar moment in all axis.(yaw/pitch/roll) At the corners this gives the greatest affect on how fast the car rotates. (slows it down) This probably is most noticeable when all 4 tires are off the ground or skipping across a rough surface.

The downside at these positions obviously is more un-sprung weight. Which hurts the ability of the tire to follow the track. Nevertheless, on rough tracks some prefer the tires to skip over the ruts instead of follow the contour of the track.

So its a compromise but on that track it was the best compromise for some setups.
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