Can someone explain to me what a 4 link, 2 link, Z link rear suspension is and what the differences are? What would be the best suspension if you were to buy a new mod for the dirt?

A 4 link is where the rear end has an upper and lower trailing arm (bar)that goes form the axle center line forward in the car. One is "above" the axle and one is "below" the axle. See picture below:


A z-link has one bar going forward in the car, this bar is on the bottom of the axle. It then has a bar going backwards in the car and is above the axle. See picture below (this is actaully a swing arm design):


A 2 link is more common on asphalt and I think that any Howe car illustrates the 2 link well (sorry no picture). Hope this has helped and pardon the dust and dirt on the car in the pics, I still haven't cleaned my car yet...

Oh and I would recommend a 4bar z-link combo car. Pretty much every builder has this set-up on their chassis now.

Scooters the man.. he even ran out and took ya some pics He knows his stuff too.

I'd agree Armond. Rob, unless you've moved big time, Todd lives just a few miles from you. PM him to talk. I think his car might be for sale... but I could be wrong.

Thanks Armond and Verwayne, your checks are in the mail

Yeah I think that "Rob" has commented on the car for sale on George's forum,here is the quote:


kbmotorsports17g
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Sounds like a nice mod for the price....too bad I have all my money wrapped up this year, I'd buy it and go back to dirt!!!

I'm still amazed we haven't sold it yet... And yes it is a 4 bar z-link combo.

Thanks Scooter.........my understanding is that a 2 link is more like what we on asphalt call a 3 link.....2 trailing arms(hence the 2 link name) a top link and a panhard bar...is that correct? Yes, I did comment on the car because I think it's a good deal for what's being offered and it looks fast lol. V, I live in Jenison now, not to far away from where I used to live. I'm asking questions for a few different reasons........I am going to run a modified in '09, that's for sure. Dirt or asphalt is the question. I am leaving Berlin obviously to do that. Kat and I are looking at buying a house north of GR, maybe Cedar Springs/Kent City area and it might be a good idea to go back to dirt and race Winston primarily. But, I'd like to not lock myself to one track either and a dirt mod is by far the best option at this point. We spend way to much money in the sportsman division at Berlin for very little return. I've always been fascinated with mods.....they are different here than on the east coast where I am from and much more economical! I'm sure as next season winds down you'll see my sporty for sale and me lookin for a mod! Hell, I'll drive one on Friday's if someone wants to put me in one...hint hint!

Thanks again for the info Scooter.

KBM17g said:

"I've always been fascinated with mods.....they are different...."

As have I Rob, as have I. Try it once and you won't look back.

have a good day,

schinde

Wish I saw this sooner...

I think it should be pointed out that the picture that Scooter has posted of a "Z-link" is actually a "Z-link Swingarm". A true Z-link does not have the spring mounted on the forward trailing arm, but rather a straight trailing arm like the upper control arm and the spring either on top of the housing, or set up as a coil-over on the front or rear of the bird cage.

The suspensions can be ran in any number of combinations. You can have a 4 link LR & 4 link RR... Z-link both sides... 4-link LR 3 link RR.... floated on birdcages or clamped up. The dirt cars are far more exotic than the asphalt cars and thats what I like about the challenge of setting a car up on dirt.

I believe that if you can get the set-up perfect a 4 link on both sides promotes the best traction and is the fastest, but it is an extremely touchy set-up and you have to have one smooth driver.

On top of the different style links you got your choice of short panhard bars, Jbars, or rear mounted pan hard bars. Different length pull bars, biscuit style, 2 way spring pull bar, etc etc. It goes on and on.

Damn...............it's alot to remember!!!!!!!!! I need a crew chief!

Its complicated and thats why you have to pay attention to what you are doing, but once you get used to it it isn't so bad.

I've spend the last 4 years working on different style dirt suspension on dirt mods and dirt late models and still don't have it all straight because there are just so many combinations you can run.

I prefer the 4-Z set up myself because it seems to work at just about every track you go to. While some guys with 3 links do just fine at other tracks for the reason they run at that 1 track all the time. The 4-Z just seems to work well everywhere when your traveling.

I'd like to add my 2 cents to this, now that I'm back.. If you are not going to to a lot of traveling or are going to stay on the same type of track (big/little,, flat/banked) and don't want to worry about all the adjusting (or maintenance) of a 4bar/4bar or any combination of that.. You may want to look into a leaf,split leaf or mono leaf rear.. much simpler,, a lot less week to week upkeep etc.. now granted you don't have the adjustability of the fancy rear setups but it is also a lot less chance to dial yourself out of the ball park as well.. We had a mono leaf Harris car that we ran at I-96,Hartford,Eldora and Terra Haute as well as other places and never really made any big changes other than maybe changing the RR spring for speed or banking.
I know that the 4bar is the hot setup and had it on my Jet,, but if I were going back to dirt (?) I think I'd really look at a mono leaf again and just adjust the rear setup with the right foot.
Just my 2 cents.

Kevin, good points. I'm not really sure what I'll be doing as far as if I'll travel or stay at one place. I do know after this season ('08) I'm not going to chase points and I'll go back to racing partial schedules so that kind of would open it up to explore new tracks if the urge arose. Most of the modifieds I've looked at are the 4bar/z link type..........seems the "in thing" so that may be what I'll go with.

Kevin,

What do you think of the leaf setup where the clamp one side to the axle and the other side is floated on the birdcage?

just curious.

I'm not real big on 1970's technology in dirt track racing... err I mean Leaf Springs because of the lack of adjustability. With that said having a composite leaf spring on the RR would be your only real option if your going to run leaf springs. I understand the leaf cars have incredible side bite, but some what lacking on forward bit (Of course that changes if your running 4bar LR and Mono RR etc etc).

Can you run a composite leaf on a mod?

Gavin,,, you can run anything until you get caught.. I'm not sure if UMP allows composite now or not.. The set up you mentioned (aka fast boy down south) is what most of the mono-leaf set ups are now.. then the LR spring is turned around and rearched.. Side bite is just like a 4 bar,, but like Jon stated not a lot of ability to adjust.. I agree if one understands or is willing to learn 4 bar,,, AND KEEP GOOD NOTES,,, that is the way to go these days.... If you are a weekend, I want to go racing and not spend all week doing maintainance,,, the leaf is a very simple option. I was working on a dirt car with a guy up until about a month ago when some serious issues put an end to the project... If you want the bite,are willing to do all the work, than by all means 4bar/4bar or 4bar/? is the way to go.

There is not a lot of regulation on suspension for UMP. You can run composite springs. In UMP you can have as many springs on the rear end as you want only as long as you have 1 functioning shock per corner only.

The Fast Boys set up is incredibly fast, but for short periods only. There is so much pinion angle and stress on the chassis that guys are sheering gears, U-joints, bending their chassis, etc etc that you better have a fat wallet to maintain a fast boys set up.

But then in UMP I only seen the inspectors 1 time all year up at Thunderbird and the only things they checked were the spoiler and body panel lengths. Didn't even bother with checking for any kind of traction control or whether the dummy shock we had on was a real shock or not etc etc.

Are leaf springs used much if any on asphalt? (Other than Camaro Street stocks)

Fast Boys Set-Up At Work:

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Jon,,, great picture,, brings back memories,,,, GOD I miss the dirt.... You are correct,,, we ended up with 3 or 4 yoke before we ever got things dialed in.. We got about 1/2 a season out of our springs, so yes they have to be replaced, if you want to go fast... Thanks again for the pic.

Did you by chance test the rate of the used spring you were replacing? I'm curious about the rate difference from beginning to end.

How did you correct the dynamic pinion angle issue? Run very little static angle to begin with?

WHOA! That thing is hiked up a lot more than I expected. I'm assuming that the left side is the one that is clamped and the right is the floating one. Wow. Has anyone floated both sides on the leafs and used a lift arm to keep the rear from winding up? Just trying to think of something that isn't going to hike the car up so hard. I would assume you could tune a 4-bar to act that way, but I'm not so familiar with the dirt mod stuff. I guess airing out the LF is cool and all, I just wonder how consistant one could be like that every lap.

I don't think that many cars use leafs other than camaros, like you mentioned. In the mods the 3 link is just way too simple and effective to get away from.

I don't know if I would want to be in that car once it let off the gas though, the unloading of the rear with that much travel has to make that thing wicked loose on entrance. Some guys can be real consistent hiking the LF 3 feet in the air. A friend of mine is notorious for running his LF high in the air and when he was racing it was hiked so much he couldn't see in front of him so he drove looking out the right side window to see where he was on track... craziness.

The lift arms only do something when you let off the gas or apply braking force. Your best bet if your going to have floated leafs is probably to have a spring loaded pull bar with a really stiff spring.. 1600-1800# to help tame the rear end down. Of course you could run a ladder bar and a pull bar at the same time on the car. Pierce is doing this now to his 2007/2008 chassis (yes its illegal in IMCA but not in UMP) and he isn't running leafs. Hmm.... something to think about.

Rob,, if you want to get even more confused/educated check out these web sites. 4M.net which is 95% dirt site or check out USMTS which is what we ran off and on and is like USA for dirt.

Gavin,,, it is cool to see and great for pictures,, but a real pain in the ass in traffic.. Always had to be second guessing how you come down. I think that is why the LM guys don't take it to this extreme anymore, and people like Schrader and Bloomquist have gone back to running a 4 wheels on the ground.. Schrader is still the only racers left out there,

Jon, yes pinion angles was almost neutral (which also caused issues) We did get them checked once and lost more than 1/2 the rate in the LR over 13 weeks. Schwartz had use check scale weights and heights weekly to know when to pitch them.. Again. I don't know that I would go to this extreme for a weekly want to be, because it can be costly, but it was a different option for running down south where there are real dirt tracks (Michigan has NONE). I think a simple mono leaf set up for a weekly dirt racer does give you a few more options than a simple 3 link.. You just need to learn how to adjust with the loud peddle.. I know a few guys that use to lift a good foot or maybe two all the way down the straights at Hartford to where they couldn't see out the front either, not naming names,, but it get to be a handful, and I think it makes things a lot more mentally challenging for the night.

i started modified with a 2 link switched to 4 link Z wow big dif more foreward bite yes at times i couldnt see in front cause left front was so high had to look out side window but you got to be on the gas on the wheel we broke yokes, shocks, springs unil we finally got it dialed in and then it was Whao Son i sold it after we got it dialed in 6 races with 4 link z after grenading a $17,000 diamond engine, bought a sprint car, i ran the mod @ www.Lakesidespeedway.net its a 1/2 mile high bank fast track real hard on engines rules are kinda there own cant be competitive there and run anywhere else,They call them A-Mods,i wasnt enjoying myself as much as i did in Open Wheel Sprint Cars

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Did you run the Z-link on a straight Z-link or on a swing arm?

We have never had a problem with the LF over hiking. Usually the most our LF hikes up is 6"

straight Z- link
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Not consistent at all. It sure looks impressive, and works for some...But they get crossed up easily and it ruins the lap.

I've read articles that preach against it and I've seen proof watching Speed channel.

Imagine if you had to check up a bit with the left front tire 4 feet in the air...

I'm not trying to say they are wrong necessarily, because if that setup works on that car with that driver...then don't change it. If that driver can make that work....Run it!

A lot of things that are technically incorrect seem to work really good.

Mike