Independent vs. Live Axle rear suspension

[RacerX]

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[blueovalz]

On a smooth surface the argument would be difficult between the two if one neglects the advantage of adjusting the negative camber into an IRS suspension. On a rougher surface, the argument favors the IRS because of the lessened unsprung weight. So I have to say the IRS wins in both cases.

[Lason]

Yep, autox=IRS, drag=straight axle

 

Just my $.02

[J__]

u can drift better with solid axle

[blueovalz]

performance handling on the street and autocross

 

So Ernie, does this guy want "handling" in the traditional sense (go fast in the corners)?

[JMortensen]

Live axle usually = no camber or toe adjustment in back, and lots of unsprung weight. Generally these are not going to be good features for autox. The live axle can handle a ton of power though, so if the guy is looking for a 90% drag car that he occasionally autoxes, then fine, but you don't normally see straight axle swaps as a mod for autoxing.

[grumpyvette]

the potential problem area with a basically stock independent rear suspension is its lack of ability to handle the heavier shock and torque loads, U-joints &half shafts generally don,t last to long once the power levels exceed about 1500-2000 ft lbs, that sounds like alot untill you do the math, put a 383 sbc on a healthy dose of nitrous putting out 650 ft lbs then run it thru a 4.11 rear gear, your now looking at about 2700 ft lbs of torque at the rear wheels in theory, thats why a DANA 60 live axle gets used in many serious drag cars

[boodlefoof]

Solid axle advantages:

 

1. Suspension designs allow more anti-squat = more traction out of a turn = can get on the gas more quickly. You can build some anti-squat with an IRS setup, but you will run into brake hop before you can get much.

 

2. More durable.

 

3. Less overall weight (due to extra frame bracing required for IRS).

 

Solid axle disadvantages:

 

1. More unsprung weight. - in a very light car, a higher proportion of total weight will be unsprung.

 

2. With a short wheelbase car like the Z, one needs to pay more attention to driveshaft angularity.

 

3. Not much (if any) camber - about 1* max. = less contact patch on uneven surfaces.

 

 

Anecdotally, aren't most of the cars winning auto-X events solid-axle cars? I've even heard of people making the switch to IRS when it became legal in their class and then switching back because they thought they did better with the stick axle.

[tube80z]

Solid axle advantages:

 

1. Suspension designs allow more anti-squat = more traction out of a turn = can get on the gas more quickly. You can build some anti-squat with an IRS setup, but you will run into brake hop before you can get much.

 

I'd be careful on that one. What you'll find is that you can quickly screw things up with antisquat and too much will make a car that puts power down well when going straight but oversteers when you press the throttle in a corner. The same is true of antidive and too much of that will make a car have terminal understeer.

 

The big one that you missed for an advantage is the a live axle is simple to setup. There are many pitfalls to be avoided with IRS and a poorly setup IRS will generally not functional as well.

 

Cary

[JMortensen]

Anecdotally, aren't most of the cars winning auto-X events solid-axle cars? I've even heard of people making the switch to IRS when it became legal in their class and then switching back because they thought they did better with the stick axle.

The only solid axle cars I've seen "win" at autox aren't really cars, but karts. Aside from that I can't recall a single autox I've been to where FTD was posted by a car with a solid axle. That doesn't mean they can't get FTD or that it's a "bad" idea to build an autoxer with a live axle, just my personal experience. I have, for the record, seen some really fast Mustangs at autox. Have yet to come across a really fast Camaro, but seen a bunch of really fast Mustangs. I suppose it helps that I used to autox with the Maximum Motorsports guys...

[tube80z]

Aside from that I can't recall a single autox I've been to where FTD was posted by a car with a solid axle. That doesn't mean they can't get FTD or that it's a "bad" idea to build an autoxer with a live axle, just my personal experience. I have, for the record, seen some really fast Mustangs at autox. Have yet to come across a really fast Camaro, but seen a bunch of really fast Mustangs. I suppose it helps that I used to autox with the Maximum Motorsports guys...

 

In Medford an ex-Griggs Mustang took TTOD when the Datsun guys didn't show up this year. Other than that I've seem a demon fast Toyota Starlet, a killer B210 (actually was a GT-5 car), another that had an L20B, and a few older RX-7s that all at one time or another took TTOD. So it can be done but it's not something typically seen.

 

I think you'll see more fast live axle cars at higher speed events. Autox generally seems to favor smaller cars and the deck is stacked.

 

Oh, I did forget some FWD cars that have live rear axles. Do those count?

 

Cary

[johnc]

There are lots of handling disadvantages to a live axle car in addition to what's already mentioned:

 

1. Anything that happens on one side has an affect on the other.

2. Wheel hop under braking.

3. Binding under compression.

4. Lateral location (panhard bar typically) is affected by sprung weight movement.

5. Wheelbase changes in roll.

6. Lack of compliance/suppleness due to unsprung wieght and the resulting shock valving needed to control that weight.

7. Asymentrical torque affects on the chassis under hard acceleration.

8. Engine torque loads affect suspension compliance.

9. Limited wheel travel due to the big punkin' banging on the floor of the car.

 

These can all be reduced significantly with proper tuning. But they just add a lot of work that isn't need with a proper IRS.

[boodlefoof]

The big one that you missed for an advantage is the a live axle is simple to setup. There are many pitfalls to be avoided with IRS and a poorly setup IRS will generally not functional as well.

 

Cary

 

Yes, I did forget to mention that one.

[mutantZ]

Dragging up an old thread, I recently watched a few rock crawler videos (those RC versions are awesome looking too) and they are overwhelmingly solid axle front and rear. Is there a particular advantage that a solid axle would have? At first glance, it seems an IFS and IRS would allow the vehicle more stability when going up and over extreme angles.

 

Sorry, I know rock crawling is about as far away from Z's as you can get.

[JMortensen]

Solid axle works better for rock crawling because it articulates and it's easy to get a strong solid front axle. Independent suspension goes more or less straight up and down and if you have 8 inches of travel, that's what you have, the axle can't twist under the chassis. Solid axles can droop and the axle can twist really far away from the chassis and so they can keep tires on the ground in places where no conventional IFS setup can (there are some freaky weird IFS setups that can do amazing things...)

 

Regular IFS articulation, watch how easily one wheel comes off the ground around 1:05:

 

Solid axle:

 

Insane independent suspension:

[mutantZ]

That last posting is pretty cool. It's like having a motorcycle swing arm at all four corners! Rock crawling makes going slow look like alot of fun.

[BlackdogNY]

I know this is old, but what about the advantages of wide rear tires that don't require flares. Large choice of wheels/tires, 315-345's would be nice under a s30. Also what about being able to use easy to find brake parts(Mustang)? Seems to be a good idea for drag and road course if it is set-up right. I am thinking about going this way in the future. It would be a backhalf or full tube car. All of the threads I have read it seems that the only real problem is the ladder bars/4link interfere with the seat mounts. Any pics/set-up ideas for a Z with solid axle that is for cruising/track days, not drag racing. Hay, first post. Don't even feel dirty....