A-arm tech

Xtreme Cartz · 03-01-2009, 04:25 PM

I've seen a lot of nice custom built A-arm front ends on here and was wondering a few things.
Are there rules to go by for proper arm and shock angles?
Do you only need to use heim joints at the upper and lower spindle to arm attachment points; and then rubber bushing/bolt at the arm to frame points?
How much longer do you make the lower arm compared to the upper?
What determines the distance between the upper and lower arms?
What's a good size tube for A-arms in golf cart use? How do you match heim joints and fit them to the ends tubing? Thanks!

dirtysouth · 03-01-2009, 04:41 PM

Xtreme,
Do you have any components to start with (shocks, spindles, etc.).
What kind of cart will you be lifting? There are several ways to make it.

groundpounder · 03-01-2009, 05:30 PM

send (todwil) a PM i bet he will help you out on this. he builds some nice a arms and has gave me some good info in the past.

Michigan Mike · 03-02-2009, 10:13 PM

There are no "rules" to building a proper front suspension. There are many factors involved such as :arm length, arm angles, caster angle, camber angle, king pin inclination and so on. There are however ranges that for those values that are considered "normal" or good to stay within. I cant tell you that you should make your upper arms X inches and your lowers Y inches, those lengths are dependent on so many other things.
To help answer a few of your questions:
The lower arms don't necessarily have to be longer than the uppers. However the advantage to having longer lower arms is that the tires gain negative camber when the suspension is compressed. This helps with traction in cornering, especially under speed. The angle at which the arms are to each other affects the cart's roll center or the amount of body roll.
The best shock angle is the one that closest follows the suspensions path of travel and uses the shocks entire effective stroke without over extending it or bottoming it out. Because of this I would reconmend building the suspension first to determine the travel of the shock you need and not building a suspension around a shock you already have.
As a rule of thumb it's better to have more distance between the arms. At the spindle end of the arms, this is determined by the spindle height, which is usually limited by the diameter of the wheel. So I'd say as far as your wheels will allow you to.
You can use heims or bushings at the frame pivot points, both have their ups and downs:
Bushings (I'd reconmend derlin) are simple, will last longer and are quieter. With bushings you must build the geometry correctly because it's "built in" and can't be adjusted.
Heims can be noisy and they don't last forever, but they offer alot of adjustability. You can even change your caster angle by moving either the front or rear piont in or out which causes the point at the spindle to move forward or back.
Tubing size? I'm currently building a custom suspension using 1 1/4" - .095 wall tubing. This is the same size Todwil tells me he used. The easiest way to attach heims is to use premade bungs that slide into the end of the tube and get welded around the perimeter. They are drilled and tapped to accept the threads on the heim's shank. To match the heim size, once you've determined the tube diameter you're pretty much limed to a few sizes. For 1 1/4" there are bungs available for 1/2", 5/8" & 3/4"....I'm using 5/8". What bungs are available also depends on the wall thickness of the tube.
I'm currently hung up on weather to use derlin bushings or heims at the frame...I think I'm back to heims, because I like the adjustability and hopefully my engine will be loud enough overcome the noise

I know that doesn't give you exact answers, but I hope it helps. I'll try to answer any other specifics I can.

Mike

Flintrock · 03-02-2009, 11:07 PM

Wow, MM, that's a pretty good "primer"! Makes me wants go out and build one!!!!

Xtreme Cartz · 03-03-2009, 05:50 PM

Mike thats great info!

dock98 · 03-03-2009, 05:54 PM

a wealth of knowledge.very useful.

C-BO · 03-03-2009, 07:42 PM

F ya mike! so basically what your saying! is if i take all them words and parts that you are talking about, mix them all together , add a few welds,
i will come up with some bad a$$ stuff? haha

haha

Michigan Mike · 03-04-2009, 01:20 PM

Sure, exactly C-Bo, simple as that

03-01-2009, 04:25 PM	#1
Xtreme Cartz The Fabricator Join Date: Dec 2006 Posts: 2,016	A-arm tech I've seen a lot of nice custom built A-arm front ends on here and was wondering a few things. Are there rules to go by for proper arm and shock angles? Do you only need to use heim joints at the upper and lower spindle to arm attachment points; and then rubber bushing/bolt at the arm to frame points? How much longer do you make the lower arm compared to the upper? What determines the distance between the upper and lower arms? What's a good size tube for A-arms in golf cart use? How do you match heim joints and fit them to the ends tubing? Thanks!

03-01-2009, 04:41 PM	#2
dirtysouth Gone Wild Join Date: Feb 2009 Location: P-COLA Posts: 1,176	Re: A-arm tech Xtreme, Do you have any components to start with (shocks, spindles, etc.). What kind of cart will you be lifting? There are several ways to make it.

03-01-2009, 05:30 PM	#3
groundpounder Gone Wild Join Date: Sep 2007 Location: maine Posts: 3,340	Re: A-arm tech send (todwil) a PM i bet he will help you out on this. he builds some nice a arms and has gave me some good info in the past.

03-02-2009, 10:13 PM	#4
Michigan Mike Not Yet Wild Join Date: Apr 2008 Location: Rochester Hills, MI Posts: 61	Re: A-arm tech There are no "rules" to building a proper front suspension. There are many factors involved such as :arm length, arm angles, caster angle, camber angle, king pin inclination and so on. There are however ranges that for those values that are considered "normal" or good to stay within. I cant tell you that you should make your upper arms X inches and your lowers Y inches, those lengths are dependent on so many other things. To help answer a few of your questions: The lower arms don't necessarily have to be longer than the uppers. However the advantage to having longer lower arms is that the tires gain negative camber when the suspension is compressed. This helps with traction in cornering, especially under speed. The angle at which the arms are to each other affects the cart's roll center or the amount of body roll. The best shock angle is the one that closest follows the suspensions path of travel and uses the shocks entire effective stroke without over extending it or bottoming it out. Because of this I would reconmend building the suspension first to determine the travel of the shock you need and not building a suspension around a shock you already have. As a rule of thumb it's better to have more distance between the arms. At the spindle end of the arms, this is determined by the spindle height, which is usually limited by the diameter of the wheel. So I'd say as far as your wheels will allow you to. You can use heims or bushings at the frame pivot points, both have their ups and downs: Bushings (I'd reconmend derlin) are simple, will last longer and are quieter. With bushings you must build the geometry correctly because it's "built in" and can't be adjusted. Heims can be noisy and they don't last forever, but they offer alot of adjustability. You can even change your caster angle by moving either the front or rear piont in or out which causes the point at the spindle to move forward or back. Tubing size? I'm currently building a custom suspension using 1 1/4" - .095 wall tubing. This is the same size Todwil tells me he used. The easiest way to attach heims is to use premade bungs that slide into the end of the tube and get welded around the perimeter. They are drilled and tapped to accept the threads on the heim's shank. To match the heim size, once you've determined the tube diameter you're pretty much limed to a few sizes. For 1 1/4" there are bungs available for 1/2", 5/8" & 3/4"....I'm using 5/8". What bungs are available also depends on the wall thickness of the tube. I'm currently hung up on weather to use derlin bushings or heims at the frame...I think I'm back to heims, because I like the adjustability and hopefully my engine will be loud enough overcome the noise I know that doesn't give you exact answers, but I hope it helps. I'll try to answer any other specifics I can. Mike

03-02-2009, 11:07 PM	#5
Flintrock Raised by coyotes Join Date: Nov 2008 Location: Central Texas Posts: 5,652	Re: A-arm tech Wow, MM, that's a pretty good "primer"! Makes me wants go out and build one!!!!

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03-03-2009, 05:50 PM	#6
Xtreme Cartz The Fabricator Join Date: Dec 2006 Posts: 2,016	Re: A-arm tech Mike thats great info!

03-03-2009, 05:54 PM	#7
dock98 doin it in the desert Join Date: Dec 2008 Location: Sonora Desert,Az Posts: 5,603	Re: A-arm tech a wealth of knowledge.very useful.

03-03-2009, 07:42 PM	#8
C-BO Gone Wild Join Date: May 2008 Location: imlay city, michigan Posts: 363	Re: A-arm tech F ya mike! so basically what your saying! is if i take all them words and parts that you are talking about, mix them all together , add a few welds, i will come up with some bad a$$ stuff? haha haha

03-04-2009, 01:20 PM	#9
Michigan Mike Not Yet Wild Join Date: Apr 2008 Location: Rochester Hills, MI Posts: 61	Re: A-arm tech Sure, exactly C-Bo, simple as that

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