Are links unsprung weight?

[makya]

Wam and I disagreed on this one in another thread, and in the past I've had this conversation and others similar to it concerning weight placement and it's effect on suspension, roll center, COG and ability of low speed vs. high speed capability, with no real reference to gather or source information from for scale purposes. although there is a lot of information on 1:1 rigs and suspension on places like the PBB, it doesn't always relate well to scale.

So I figured rather than just the two of us have the conversation in private, it might benefit all of us to discuss it that are interested.

Can't argue with that. Except I guess links are only 50% unsprung weight. Unlike knuckle weights @ 100%. I guess your argument applies even more to avoiding knuckle weights?

that's not true.

the links move with the suspension from a solid pivot point (the frame), so they are entirely unsprung weight.

It's true...but not worth arguing about here. I design, fab and race (real) race cars. Take it to PM if you want more discussion.

so WAM, I "think" I see what you mean about a link being %50 unsprung, since the end of the link close to the frame doesn't move as much as the other end, having less of an overall effect on the movement of the suspension, but to my understanding the entire link is pivoting off of the chassis and attached to the forces at work with the suspension, so wouldn't that make it entirely unsprung weight? or is there something that I'm not seeing (or understanding)?

if there's anyone else with input on this, i'd appreciate it as well. I think it's an interesting subject and overlooked too often.

 

[HyperMark]

I would say a percentage, not necessarily 50/50.
They are hanging from the chassis, therefore sprung weight.
They are also hanging from the axle housing, therefore unsprung weight.
If they could be removed, the chassis would rise an imperceptible amount.
Partially sprung weight.
My 2c

 

[WHITE-TRASH]

Whether it's sprung or unsprung weight is trivial in my thoughts. I use links with the best weight vs strength ratio I can find and add weight at the ends of the axles where it makes the biggest difference.


But for the sake of discussion I'll agree with hypermark. It's a variable ratio.

 

[OSRC]

Interesting question...I've always thought of them as unsprung weight since by definition they move when the suspension moves. ...similar to a control arm on a IS vehicle. Weight supported by the suspension - usually above the suspension which separates it from the road surface - is sprung weight.

However, I've also seen those parts call hybrid weight (also includes driveshafts, shocks, etc)...so technically I guess hybrid is correct.

 

[Ditchrat]

if there's anyone else with input on this, i'd appreciate it as well. I think it's an interesting subject and overlooked too often.

I'm about sick of meaningless discussions, this is interesting and a welcome change. Thanks.

Whether it's sprung or unsprung weight is trivial in my thoughts.

I wonder if it is trivial, I'm inclined to agree with you, but it certainly would be interesting to know.

 

[C*H*U*D]

...having less of an overall effect on the movement of the suspension,...

If a component is damped by the shocks, it's unsprung. As you get closer to the pivot on the chassis, like makya says, the effect it has on suspension is less but it's still unsprung.

I'm probably to blame for starting this because of my comment in the other thread. Like I said there, it probably has no noticeable effect on the crawlers we drive, but as speeds increase a good driver may notice.

I'm building a Mega right now, and it's going to be fast so some of these things have been on my mind lately. I won't be using brass links.

 

[QuesoDelDiablo]

They are both sprung and unsprung.

It's already been mentioned, but the weight will be carried partly by the frame (Sprung weight) and partly by the axle (unsprung). The ratio of those 2 will vary as the suspension moves through it's travel and it's angle changes.

I'll try and do some diagrams that clarify this relationship if I can find time.

 

[WAM]

I didn't want to burden that other thread with more detail...but it's fine over here. When I design racecar suspensions I use purchased suspension design software sold for that purpose. You have to input dozens and dozens of measurements and such. One thing is you have to help it describe what percentage of control arms and links are sprung/unsprung. On real cars, those links are often tapered and so the mass is not evenly distributed, so it's a chore. But a straight cylindrical link like our crawlers typically use are much simpler and will come out to 50% unsprung weight on the calculation. As you picked up on, this is because on average, the link only moves half way. One end moves the entire stroke and the other end doesn't move at all. Hence 50%.

Technically, a bent crawler link would not be exactly 50%, but I think the error would be in the noise. And this is all just a curiosity anyway since we don't actually use this for anything.

 

[QuesoDelDiablo]

Yup^^

He's right, when I drew it out and started looking at it I realized all the forces ion the Y direction balance. Because the mass of a straight link rod is evenly distributed, the centre of mass (where gravity acts) is dead centre on the rod. The forces acting in the other (X) direction will vary as the angle changes.

 

[makya]

I didn't want to burden that other thread with more detail...but it's fine over here. When I design racecar suspensions I use purchased suspension design software sold for that purpose. You have to input dozens and dozens of measurements and such. One thing is you have to help it describe what percentage of control arms and links are sprung/unsprung. On real cars, those links are often tapered and so the mass is not evenly distributed, so it's a chore. But a straight cylindrical link like our crawlers typically use are much simpler and will come out to 50% unsprung weight on the calculation. As you picked up on, this is because on average, the link only moves half way. One end moves the entire stroke and the other end doesn't move at all. Hence 50%.

Technically, a bent crawler link would not be exactly 50%, but I think the error would be in the noise. And this is all just a curiosity anyway since we don't actually use this for anything.

Thanks for explaining it better. White Trash also explained it fairly well when he said to put a link on a scale, then mount the link to the chassis, and set the axle end of the link on the scale. it weighs less, because (as you stated) some of the weight is supported by the chassis.

and you're right, at this point we don't use it, but I wonder if it will become more important later on. before brushless motors came around in buggy racing, we placed a huge emphasis on the minutiae in order to gain an advantage over the other racers. we used titanium links, carbon fiber chassis, smaller wire on the wing mounts, lightened the rotating mass as much as possible, etc... all to gain an edge cumulatively.

Maybe, as rock racing and trophy trucks become more popular these small issues will add up for racers to tune their rigs better.

 

[allanon1965]

its very refreshing to see an honest, intelligent and thoughtful discussion without someone bashing the idea or people into oblivion"thumbsup"

 

[durok]

^^^ meanwhile, I just ordered some of the heaviest links available - JEC Racing Stainless including the JEC/SuperShafty trailing arms.

Only concession to lightness was getting the drilled high clearance front lower links.

The front and rear lowers have frenched rod ends.

SO sweet.

Not racing, so weight gain is fine.... LOL

 

[hillbillyrc]

I think I just learned something.

 

[makya]

After reading back through this thread, am I the only one who's wondering how long it will be until we start seeing tapered links being marketed to Trophy Truck and U4RC?

 

[WHITE-TRASH]

Weight out at the wheels does more good than at the links so I don't think that will be the next big thing.

 

[JokersWild]

Where's dlux with a cad model? Lol