A Arms in the Rear!

FABRICATOR

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There are two discussions going on here. Trailing arms have many advantages over A-arms in the rear, including strength and superior wheel movement. You are more likely to see variations on trailing arms than a shift to A-arms.

It’s just a matter of time before IRS overtakes solid axle setups, even on trucks. IRS travel is more effective than solid axle, so you don’t need as much.
 

zjohnson

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The ideal way to get the wheel travel, with the least amount of moving parts, is a trailing arm setup. Going super wide is the only way to get large travel numbers though, because the internal cv angle is what kills you. Running a non plunging CV allows for greater angulation. That in combination with a plunging axle, like the one from McKenzies will easily get you 25"+ of rear wheel travel w/out going to a super wide track width. If you don't mind going wide, 30"+ is easily possible with a wide trans.
In my opinion A arms aren't what you are looking for in Off road, to many parts to break, and the strength doesn't seem to be as good. Plus, with a raised torsion housing, you can get a good arc on your travel.
 

grantdcol

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I think a torsion setup would be a step in the wrong direction for a truck. Coilovers would be the way to go.

But yes, trailing arms can get you a great travel arc with a highly progressive motion ratio to the shocks, and most importantly, rearward travel.

-Colin
 

zjohnson

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"torsion housing"- the axis in which a trailing arm rotates around . . . Not using a torsion bar, just refer to this part of the chassis as the torsion housing because that is what is was called . . .
 

grantdcol

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You pointed out that CV joint angles are limited Plus they get weaker as the angle increases. In a IRS, wouldn't it be possible to use a double cardan joint (constant velocity) or a Cornay joint? Both are capable of up to 90 degree angles. The MacPherson TT used Cornay joints in the front for an AWD system:

http://www.drivetechnologies.com/page6.html

-Colin
 

FABRICATOR

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CV’s do loose strength with more angle but so does every other joint. You will get more travel using a narrow trans than a wide one. That’s why Corvette and other existing rears won’t work with long travel. A double Cardon will go more angle than a simple U-joint, but it won’t go anywhere near 90 degrees or even as much as a common non-plunging (Rzeppa) joint. The Cornay seems to be a bit of an illusion.
 

mosebilt

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LOOK! rear a-arms w/26" wheel travel,25 degree cv angle,2" ground clearance full compression w/35" tires,5 degree camber change through full stroke of suspension,outside tire stays vertical in corners and sway bar gives it the x-tra bite.works bitchen! pricey though.
 

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mosebilt

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we are going to be putting that set up in a "truck"-using a redline LS-1 w/auto mounted mid-engine to a Winters quick change rear end.keeping all the weight in the center of the vehicle (low polar moment) makes the car steer/corner well-but sacrificing straight line stability-the opposite applies to spreading the eight out in the car.the Winters is only 1.5" wider(.750 per side) than a Mendeola-can still use long axles and get wheel travel.the car runs 32" long axles w/Kartek mid board-micro-stubs.with the quick change rear end the gearing can be changed in 20 minutes and the availability of different gears makes "tuning" the gear ratio easier-almost limitless.rear end costs about $3000.00
 

ELITE10CAR

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I feel there are some misconceptions here about a arms. Many people seem to believe that a arms are not as strong as trailing arms, or that they do not work as good. We have never had an a-arm crack, break or fail in the three years we have raced our car, yet we have seen numerous trailing arms literally come off (two cars in our class at laughlin). Some believe that they do not work as good, but at laughlin we passed 17 cars on day two, in 44 miles, that can attest that our a arms do work. We finished fourth dispite the time lost passing those vehicles(just over a minute down). Many of our fellow racers have taken notice that a arms might not be such a bad idea after all. The facts are that trailing arms do work very well, but there is always something better. I feel the rear a arm design is like all other items in history, if it defies the social norm, it will take a while to become accepted. Others have used this design with success, yet it still has not been accpeted.
 

zjohnson

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Just one question for you A-arm rear suspension guys: Is there a succesful A-arm class one car? From my point of view, a trailing arm is more simple, and if built right, as strong as a well built set of A-arms But to me, I think that an A-Arm rear is just too many moving parts, and also to many parts to replace when you prep. I also dig the fact that a trailing arm does just that, moves back for most of its up travel if designed correct. I am just not sold on rear A-Arms, the scrub and the complexity is what bothers me. I am sure that enough time and money can result in a competitive car, but I like A-Arms for the front. Also, if you consider the angle of the torsion housing on trailing arm cars, your CV angle is determined by your transmission output flange location, and not the typical negative camber needed on a an A-arm car. (allowing for a greater magnitude of down travel, which is the most important travel number for a rear independent car.
Question for Mosebuilt: What is the scrub in the rear of your car, size CV, and power running through the trans? Just nice to know what people are trying. Also, not to pick, but 5 degree of camber change seems like a lot . . . how wide is the car?
 

ELITE10CAR

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A rear a-arm setup is in fact more complex than a trailing arm. There are more moving parts but that doesn't mean that there are more parts to break. If built right (as we have done) they are just as reliable as anything else out there. Just as stated before, I have seen and heard of numerous trailing arms break...probably because there are far more of them out there to break. If a car is well prepped and checked for cracks, breaks, etc, neither of them will break. The fact is that we are the only Class 10 or 1 running competitively with an a-arm rear....again...we have never broken or even bent our rear a-arms. There are just as many moving parts on our rear suspension as our front and everyone elses front. And for the record, you can get more down travel with an a-arm rear than with a trailing arms rear. This is do to the fact the axle can be perfectly perpendicular to your transmission and that is the only direction of travel. The front to rear angle on the axle never changes as it does with a trailing arm, therefore you will get more down travel. The CV never has to deal with a compound angle. You can also run plungeless CV's on a rear a-arm setup without $10,000 plunging axles. These are just my experiences as I have personally raced thousands of miles in our A-arm rear class 10 car. I have tons of in car videos (showing us pass many class 10 winners/champions) and as soon as I can get someone to make a few clips I will post them.
 

mosebilt

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5 degree's camber change through the entire stroke(-3 full droop,0 mid stroke,-4 full compression) isnt a lot when you consider irs is usually 3-4 degrees.we are running 934 cv's,as far as scrub is concerned i designed the arms to have aprox. 1.5" per side-to keep a more consistent plunge on the axle,so consistent that we might use non-plunging cv's next time.you dont notice the scrub in the back since your not steering and it might actually give you more bite.a-arms in the back need to be mounted level with the ground otherwise you loose a lot of traction,the raised torsion housing on irs cars works well for that suspension(i do it in all my cars) but the a-arms dont seem to like it-you get a lot of wheel-spin.we are putting anywhere from 400-850 to the ground through this stuff.car is 92" wide. your not picking.
 

geoff

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Fabricator -- what is the superior wheel movement that can be had with trailing arms? I would think that a camber cuve would be a good thing?

In my opinion there seems to only be benefits to be had once people open their minds to IRS especially in desert racing of all off-road motorsports. I feel it takes the same amount of money to make a really good 4 link rear as a good a arm rear.

thanks for your opinions tho guys its a really interesting thread
 
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elcaprerunner

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Any overall contending independant rear race car I've ever seen has a rearend kick. On some cars it's not so bad, on others it's really bad. I think that is a big reason you don't see too many IRS A-arm Trophy trucks. The two best I've seen were Ivan's and Skilton's (Kia). Letner's is fast but has a nice kick in the big holes, Dondel's had a really bad kick when it was first built. I think rearend kick is a big turn-off, having the front end go up in the air is much better than having the rear go up in the air.
 
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