Pre-runner type suspension stuff

Well, lets keep the thread alive......currently, I am running Rancho Pro Series in the front and they work awesome, have Superlift coils and daystar bumps...around 4" of lift. IN the rear, rough country springs, also daystar bumps with DPG Adjustable bump stop plates and Rancho RS9000 shocks (non res). They are the specific shocks for the TJ, and so the valving is setup for the weight of our rigs....I like it alot....I typically chase for a Jeepspeed guy so this truck is out on the whoops at least once a month. And it runs real good. I am limited to around 4-5" of uptravel though, and the rough country springs do not droop as much as I would like....any recomendations for rear leafs that will droop down 5-7"

I am running the full-traction 6in long arm on my 01, w/ 1.75in coil spacer and bump stop extension, no sway bars. fox 11in travel remote resi in the front and emulsions in the rear. the front handles awsome. i have 6.5in of uptravel on the shock and about 6in before the bumpstop hits. the rear bucks and bottoms a lot. it has about 4in of uptravel before the bump hits the extension off the spring plate. the rear shocks are a tad long. I was sold these shocks when i first got into prerunning from ORW and they said that these shocks would be perfect for my kit. turns out the fronts were way to long, thats why i have the extensions and coil spacer. I need shocks w/ a shorter compressed length in the front but the same extended length which is the problem. In the rear i just need to try to sell my 11in travel emulsions and buy some 10in travel resi's. I also need some ideas for bumps in the front because at full-compression the bump hits the left side of the pad because of the trackbar pulling the axle so far over to the right side. If you have any ideas let me know. I need to get this figured out before desert season this year.

why are long arms better for pre-running? i understand for rockcrawling how the flex is helpfull, but wouldnt it make you more likely to roll if going fast? keep in mind i dont know much about longarms

miketyson said:

why are long arms better for pre-running? i understand for rockcrawling how the flex is helpfull, but wouldnt it make you more likely to roll if going fast? keep in mind i dont know much about longarms

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Longarms flatten out the angle of the control arm to the ground surface, in a nutshell making for a smoother ride. I'm sure others can explain more fully.

karstic said:

Longarms flatten out the angle of the control arm to the ground surface, in a nutshell making for a smoother ride. I'm sure others can explain more fully.

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also the arc that the suspension travels is larger making for better angles during extreme travel, less caster change etc, more responsive steering, this is for 4-link long arms, not sure on the y-link long arms as I haven't really played with them, heard they have some strange "dive" issues

Skullvarian said:

also the arc that the suspension travels is larger making for better angles during extreme travel, less caster change etc, more responsive steering, this is for 4-link long arms, not sure on the y-link long arms as I haven't really played with them, heard they have some strange "dive" issues

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Told you some one smarter than me would chime in.

I'm planning on a prerunner style suspension on mine. I aslo have a HP D60 and a 14 bolt I could use but the axle wieght would ruin it I suspect. Anyone have any thought about using these axles. If I do I'll run 37's or so with about 6" of lift and lots of cutting. Otherwise I'll just stick with my 8.25 and D30 and truss them. I would run 33's with them. I'm really looking for a bulletproof set-up that hands good higher speed rides decently and general offroad use.. I need to regear my stock axles, add lockers and better brakes which would cost about the same as setting up my 1 tons... What to do...

Any opinions would be great. Thanks

I am new to this forum because I just bought a Cherokee, but I build design and fabricate tube chassis baja vehicles. They are on the smaller scale of single seaters. We put about 300 hours of design into each car before we build. I'd like to put my two cents in about desert blasting.

We pound and abuse our vehicles for many hours before each competition to obtain accurate data to make them lighter and faster. The biggest problem that we run into is the fatiguing the suspension tabs and breaking them off.

I read somewhere in this thread about someone taking their front swaybar off. We have tested and competed with and without, and the data shows that with the front sway bar, we are able to enter corners much faster and reduce the chance of rolling. The transfer of the spring through the sway bar keeps our inside tire planted and the body roll to a minimum, producing less energy lost and faster lap times.

We have also found that reducing the rotating mass helps increase our speed exponentially. We run modified CVT clutches (snowmobile clutches) with about a fourth of the weight machined out. We also run custom gearboxes, and the lightest wheels and tires we can find. We have found that a reduction of 10 pounds in our 700 pound vehicles equals a decrease of about .1 seconds in the 150 yard acceleration.

For suspension, we run any combination of double aarm, TTB, four link, or solid swing axle, the amount of travel is limited and adjusted according to each competition. But we have to run well designed bumpstops in order to limit the force transfered into the frame when we bottom out. We start breaing things when we bottom out.

Those are my two cents. If anyone has specific questions about this, please just ask and I will try to answer as best I can.

IHCJ9 said:

and the data shows that with the front sway bar, we are able to enter corners much faster and reduce the chance of rolling. The transfer of the spring through the sway bar keeps our inside tire planted and the body roll to a minimum, producing less energy lost and faster lap times.

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not quite right there. adding a front swaybar will increase your front roll moment or the amount of froce require to roll the front suspension about your roll center.

However your result are intersting as I would have thought that removing the front swaybar would have the opposite effect or make you handle better. The rear would not roll as much and not bit as hard and slide, ie induce a bit of oversteer to bring the rear end around.

What kind of vehicles are you building? How are they powered? Thanks for sharing, it's great to have test data to look at.

The vehicles we build are designed around a fairly strict set of rules to protect the driver. but here is a quick layout of the cars.

-Single seat, 1.25 4130 chromoly frame, TIG welded
-SAE rules require all teams to use 10hp Briggs and Stratton engines, a little under-powered but thats what we have to work with.
-Most are rear engine with CVT clutches going to either a CNC spur gearbox, Chaincase, or CNC planetary gearbox, all of which we design.
-The most common front suspension is a double aarm. Last year we tried a cross over long travel aram design. 21" of travel with 25" tires. Most front suspensions use cutsom spindles and 16" of travel at the wheel.
-Rear suspension is commonly double aarm with 12-15" of travel at the wheel with CNC half-shafts and bearing carriers. Right now we are running a three link solid axle setup with an modified axle out of a Polaris Ranger.
-Top speed of 35-45 mph with a two speed tranny.
-We routinely jump them 12-15 feet in the air and beat them fairly well.

In the sway bar design, we have found that a double aarm suspension reacts well to a sway bar setup. Our coilovers are set up fairly soft for most of their travel, this leads to quite a bit of body roll in some cars. with our 4 link solid axle car, the inside front wheel lifts off the ground during cornering. This comes from our front and rear roll centers not being in the same plane. the sway bar conteracts this in quick, fast turns, allowing us to keep both front wheels on the ground and keep the traction necessary to make the turn. As the inside springs go to full droop, the torsion bar transfers some of that force to the outside aarm, effectively stiffening that side. Without it, the body roll takes a lot of momentum out of the turn, causing us to understeer a little bit.

This program is sponsored by SAE and about 160 Universities accross the world compete. Feel freet o check out our site at www.baja.mtu.edu
Thanks for clarifying that, It is late here and I missed it.

None of these cars have their sway bars on in the photos. I need to upload the latest testing photos, It may be a while. But the website baja.mtu.edu also shows the Computer Aided Design we do on these cars.

I hope this can help some of the fullsize people wanting to baja their jeep. A lot of our technology goes into stadium trucks and Trophy tucks like Scott Taylor's truck.

Well, I know it's kinda worthless without pictures, but after alot of research I am finally in the middle of installing hydraulic bumpstops on my 93. Doesn't seem like many folks are running them in here so I couldn't find much info. or any photos here (there is some good info. on the Jeepspeed site though). Anyway, I will definitely post up some photos when I get more done.

Yeah hydraulic bumpstops are the latest fad in a lot of off road racing, but they are pricey! Post pictures when you can. I'd like to see them on a cherokee

Michigan Tech?

Is that 700 pounds loaded with a driver?

Ours are about 550 with me driving.



And we had fun at winter comp. I'm with SDSM&T baja racing.

TNT said:

I'm planning on a prerunner style suspension on mine. I aslo have a HP D60 and a 14 bolt I could use but the axle wieght would ruin it I suspect. Anyone have any thought about using these axles. If I do I'll run 37's or so with about 6" of lift and lots of cutting. Otherwise I'll just stick with my 8.25 and D30 and truss them. I would run 33's with them. I'm really looking for a bulletproof set-up that hands good higher speed rides decently and general offroad use.. I need to regear my stock axles, add lockers and better brakes which would cost about the same as setting up my 1 tons... What to do...

Any opinions would be great. Thanks

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I think I'll answer mine own question, since no one else did...:looney:

Stick with the stock axles and truss them. The extra unsprung weight would kill the ride and handling. Shocks would also be doing a ton more work and the added stress would be very hard on the unibody. Just sell the other axles and use the money to build the stock ones.

Hows that for an answer??? :wierd:

It all depends on your budget & expectations...

Depending how hard you plan to whale on the XJ, it'll take some coin and/or some fab skills. JeepSpeed gives some good points in the right direction, but remember that they are rules-limited with the 'intent' of keeping the class 17 'affordable'.

Keep in mind that those vehicles are pretty much "gone through" after each race. And what works well for serious 'pre-running' may not jive with making it the best low-speed crawler. Consider what your after.

I am with you on the stock axle deal, to a point. If one was hammering the XJ hard, consider a 'polished' D30 to be very expendable. The stock 8.25, 44 or common 8.8 rear swap maybe a little more long-lived, but also kinda expendable. Trusses, gussets & alloy shafts can't hurt... but still.

Focus a large bit on shock absorbers & bumpstops... Those components are the ones that'll make you the happiest IMO.

The 700 lbs is our heaviest car.. Dry weight of 450 lbs, add 150 to 200lbs driver, and then we add weight to simulate mud that gets packed into every nook and cranny of the car. We use 700 as a rough estimate.

So in reality it may only weigh 550 lbs at the beginning. But at the end we've weighed them at well over 850 lbs at this years UofW Stout competition.

TNT said:

I think I'll answer mine own question, since no one else did...:looney:

Stick with the stock axles and truss them. The extra unsprung weight would kill the ride and handling. Shocks would also be doing a ton more work and the added stress would be very hard on the unibody. Just sell the other axles and use the money to build the stock ones.

Hows that for an answer??? :wierd:

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I would agree with this. use trusses and geometry to add strength rather the jsut raw material is always better imo.

Just thought I'd post up some pics of the progress on the rear hydraulic bumpstops. It was all just tacked in place with the bumps in place to check for alignment at this point. More pics to follow when finished.







Sorry about this last one being sideways, I couldn't figure out how to rotate it with webshots, I guess I just wont take anymore like that!