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PostPosted: September 30, 2020, 10:47 am 
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Joined: April 1, 2010, 10:26 am
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Starting to think about winter projects, adding ARB's is on the top of the list. The rear is easy, the front is a little more complex. So has anyone added from bars particularly to a Kinetic front suspension setup. The Caterham technique is very neat but I am looking for other options.

Graham

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PostPosted: September 30, 2020, 11:40 am 
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A front sway bar is on my list of things to do as well. I am planning on adding it under the chassis aft of the control arms. The mounts will be in the in-board front/back frame parts. I'm still figuring out the running gear and if I can make or have to buy a custom bar.

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roadster_swaybar location plan.png


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PostPosted: September 30, 2020, 12:27 pm 
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hfmaxi, I would be concerned about the small angle of the bar you drew. From a gut feel, I think any wheel force would mostly be transferred to bending the end of the roll bar (beyond the chassis mounts) rather than making the twist necessary to transfer to the opposite side and then bending the opposite end. Anti roll (sway) bar function would be virtual nil IMO. Maybe you have chosen that for some reason and done the homework. Calculating the spring force is fairly straight forward when the ends of the bar are at 90 degrees from the twisting part. Are there any online calculators for that type design.

At some angle it works obviously looking at the Caterham design.

I could be totally wrong.

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PostPosted: September 30, 2020, 1:41 pm 
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hfmaxi, I agree with rx7locost, but a center bearing would stop the bar just bending. Drawing it is easy how would you attach it to the upper/lower control arms?

Graham


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PostPosted: September 30, 2020, 2:00 pm 
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I've only poked around the internet looking at some of the universal bars from addco and certainly the Caterham setup. I did find this: https://balancemotorsport.co.uk/suspension/anti-roll-bars#cal and if you put in the numbers your rate/in drops significantly with any angle. My current choices are based mostly on packaging and ease of fabrication. I am also ok about being wrong.

For attachment I was thinking some method on the 1/8" plate on the lower control arms. Could be easy like hole with a stud and bushing or maybe something fancier with rod end bearings.

Edit April 2021:

Here's a few picts of what I ended up with. Current bar is 4130 3/4" .058" wall but might go thicker in the future.

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front sway link.jpg

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front sway radiator.jpg


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Last edited by hfmaxi on May 4, 2021, 7:41 pm, edited 1 time in total.

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PostPosted: September 30, 2020, 2:01 pm 
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Joined: January 1, 2012, 12:44 pm
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Location: Boise, Idaho
Here's the front bar on my Locost and the attachment to the upper A-arm.


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PostPosted: September 30, 2020, 2:36 pm 
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Nice work seven13bt. So that is a straight bar with welded on ends? That would make the bending easier. Great work.

Graham


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PostPosted: September 30, 2020, 2:54 pm 
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Yes, it's a solid 3/4" bar. The finished bar has a gusset reinforcing the bend in the plate steel arm.


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PostPosted: October 1, 2020, 2:52 am 
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Related question: How do you figure out what size bar to use? I know it would depend on the shape of the bar as well, but never did figure out how to come up with some kind of starting point.


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PostPosted: October 1, 2020, 8:58 am 
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The size of bar to start with is a good question. I am going to the 7 event at NJMP in a couple of weeks. I will measure every bar I can find and see if there is any consistency. I will start there, but I am guessing 1/2" is a good starting point.

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PostPosted: October 1, 2020, 9:28 am 
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There are equations to figure out the resulting torsion, but at the end of the day it's a subjective thing anyway so you're just going to have to try several sizes to see what effect you want. Also, be aware that anti-roll bar stiffness is very dependent upon diameter, to the fourth power, actually. For example, going from a 7/16" diameter bar to 1/2" increases stiffness by 70%!

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PostPosted: October 1, 2020, 10:43 am 
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FastG wrote:
The size of bar to start with is a good question. I am going to the 7 event at NJMP in a couple of weeks. I will measure every bar I can find and see if there is any consistency. I will start there, but I am guessing 1/2" is a good starting point.

Graham


That's not a bad idea to see what people are using, but make sure you can tell if they're solid bar or hollow tube.

There are a number of discussions about anti-roll bars on this site. Try a search here. Also, there are a number of suspension design books, and even online calculators like this one here you can use too.

Cheers,

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PostPosted: October 1, 2020, 12:55 pm 
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Unless there are a lot of different stiffness bars available, it would be best to incorporate some adjustability into your sway bar install.
At least on one end of the car so you can adjust the feel.

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PostPosted: October 1, 2020, 2:14 pm 
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Most steels have very close to the same spring rate.

FWIW, blade style sway bars are but one way to make quick adjustments if you can fit them.

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“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE

And don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766


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PostPosted: October 1, 2020, 8:06 pm 
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When i was modifying my Legends car for autocross (no ARB) i found that using stiff springs (250-275 spring) made the car stop and turn really well, but it would bounce all over on rough surfaces.....i was fast at some places and awful at others. I dropped down to 160lb springs (i forgot the exact wheel rate) and added the missing 90 lbs with the ARBs. also added antidive. Then i had "soft" springs with good roll and dive resistance. The car was much faster and a lot easier to drive. The wheel rate ended up being about 1/2 of the sprung corner weight.
I made a simple "U" ARBs from normalized 4130 or 4140, cold bent, in 1/2, 9/16, 5/8 and 3/4 sizes I originally had multiple mounting holes on the outboard end to adjust rate but they didnt make much difference I mixed/matched the bars with a few different front spring rates too. The 160 spring with the 5/8 bar worked great. The rear is a 3 link, straight axle with and adjustable panhard bar - i used that to balance the car after making front end changes.

The ideal ARB size is a function of the rest of the suspension along with driver preference

BTW with the 3/4 bar, it would lift the inside front wheel off the ground coming out of tight turns....def not the fastest way around!


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