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Author Topic:   swing arm top bar
wingnut
Dirt Maniac

Total posts: 134
posted October 29, 2004 09:57 PM  
can anyone explain the job of the top bar on a swing arm {z} link ?, and what type of angle is a starting spot,higher, lower?

Is a z link and a watts suspension the same?

as you can tell this is new to me, so thank you for your help trying to understand it.

wingnut
Dirt Maniac

Total posts: 134
posted November 01, 2004 08:37 PM  
more specifically the top bar on the left rear. thank you

FlyNLoIMCA17
Dirt Forum Champ
Total posts: 753
posted November 01, 2004 09:49 PM  
zero should be able to help ya' on this one. He seems to be pretty swift on z-links.

Where you at ZERO???? LOL ! ! !

zeroracing
Dirt Forum Champ
Total posts: 1875
posted November 01, 2004 10:29 PM  
I have been doing hw. sorry.
ok so top bar on z link.
Are you familair with the upper bar on a 4 link? and how to figure its thrust? well the upper bar on the swing arm is very similar. To find the thrust think of the bars going on forever in each direction, now where they meet is your instant center, then draw a line from thier thru the center of the axle tube, that is your thrust. if you do this you can see the more angle downhill to back of the top bar the more thrust, therefore more drive, that wheel will have.
now if you draw this out a few times, as the car goes threw suspension movement, you notice that the rr gain angle downhill to back as the car rolls over.since the upper bar on a 4 link, and z link, is the main bar for thrust angle, the lower does have an effect on thrust but not as much. since your gaining downhill to back angle in the rr bar as the car hikes up your gaining drive on that wheel.
now to the lr, draw it out as the car rolls over. you will notice that the rear bar will loose its angle downhill to back, and many times go uphill to back. this means that the car is loosing thrust, and loosing drive on that side.
so if as the car rolls over on exit of the corner, the lr will loose bite, and rr will gain it, so loose exit car.
which brings me to starting points, since your gaining rr bite and loosing lr it will be loose.
so you will want more angle downhill to back in the lr to help balance the car on exit.
now angles. for lr you will want adjustment from 10 to 24 deg down to back(just like a 4 bar, only downhill to back). and rr adjustment 0-20 deg if you can get that much.
start out at 15 downhill on both for heavy heavy, so it will bite good but stay freed up off the corner, you dotn want to knock down the walls. As the track slicks off you can take some angle out of the rr bar, go like 5 deg and/or add some lr bar, go like 18-20. you will notice the car will hike up like a 4 bar also, but a z link both sideded car will not get nearly as tight and walk for the wall like a 4 bar will.

Is a z link and a watts suspension the same?
they can be, i mean a true watts link is 2 bars both level, equal in length, and mounted same exact distance from center of rotation, then it goes in a perfect straight line up and down, but the thrust on this is 0 so the tire will kinda skate over the dirt, some cars run similar on rr and to tighten it up.
a z link is a variation on a watts, they all have rearsteer, some have alot, some have a little, but unless you have some very advanced machining tools your not going to get everything perfect like i said above, so you get rearsteer, even if its only 1/16-1/8 its still rearsteer. but the z link is a similar design as watts, in that it looks similar, and you could turn your z link almost into a watts.
this works for works for any z link, swing arm, birdcaged springs, clamped up springs.
hope this helps and does not ramble too much.
later
jason

mod2_x
Dirt Full Roller

Total posts: 38
posted November 02, 2004 08:23 AM  
Zero,
I understand for the most part what you are saying, but correct me if I am wrong. I feel that it will have more of the loose effect on corner entry and in the middle then exit due to the chassis roll being at its greater point upon entry and in the middle of the turn. Does the car not want to roll back over to the left on exit which would put the downhill angle back in the left upper bar causing more drive of the left during exit. I understand the basic concept but think it works the other way on exit then what you say in your post. Maybe I read it wrong or am wrong in my thinking.I am kinda new at this and am trying to learn as much as possible. I would be interested in talking to you more. You can email me at rmohney@verizon.net

oldfordmod
Dirt Full Roller

Total posts: 46
posted November 02, 2004 10:26 AM  
Zero: thanks for reminding me about instant centers and equilivant links. I get to listening to racer talk and forget about basic concepts.

mod70
unregistered Total posts: 46
posted November 02, 2004 10:29 AM           send a private message to oldfordmod   Edit/Delete Message   Reply w/QuoteBBBBBB
Just to add a note, I believe that I read in Circle Track that the Watts link is primarialy used in road course racing. (For those guys that can't make up their minds which way they want to turn.)

oldfordmod
Dirt Full Roller

Total posts: 46
posted November 02, 2004 10:51 AM  
Try this site for definitation: http://www.spitzracing.com/watts_link.htm

zeroracing
Dirt Forum Champ
Total posts: 1875
posted November 02, 2004 11:15 AM  
I see what your saying about if the car hikes up on entry, and middle(from throwing it in hard), then as the car settles it will gain downhill to back angle and add bite.
but on most mods nowdays people run shorty bars or j bars to get the car to roll over alot, so on entry it will roll good, and threw the center, keeping the car freed up, but the major difference that i think you will notice will be the loose on the gas, because when you get back on it, the rr will have so much more thrust to it than the lr. also the car will not settle well usually, the car will have forces trying ot roll it over, and if you get any thrust on lr of the car, increase the bite angle, it makes the car hike up more and more, like a 4 bar with alot of angle, car jumps up. so when you get on the gas the lr will hike up, lessening the thrust of the lr tire.
i would conteract this with a little more starting angle in the lr than in the rr, then the car will hike up and keep angle in the lr, there will be a point that you run out of shock travel, or plain can not get any more rollover from spring rates, tracks.. etc.
I would also think of adding a rr brake floater. run it upside down(so the bar comes from the bottom of the rearend, then you can go under the spring if on a swing arm, also you can just use the regular lower link mounts. anyways, put like like 5 deg uphill in it, then you can tune the entry and middle with it, more angle to tighten less to loosen. a rr brake floater can greatly help your entry tuning. very simple.

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