Custom Sway Bar Sizing

[gtpvette]

Need some help from the brain trust here regarding sway bar sizing. First some back ground,, I’m swapping a GM 3.6L V6 into my FRS (325-350(E85) HP). With that the original bar won’t fit as there is no room behind the cross member and steering rack. The current plan is a speedway splined bar mounted in front of the cross member and the arms up through some Racer-X LCA’s. The new control arms should provide the needed room for the sway bar arms. Not sure it’s going to work,,, but that’s the plan.


As for the car itself, not too far from stock, RCE Yellow springs, 17x9 6UL’s all the way around with 245/40/17’s. Also front end weight with the new motor won’t be far off from stock, new motor is 345lbs dressed, just a higher center of gravity,,, which is something to consider when picking a bar I would think. Car is primarily a commuter but I do like to drive it fairly hard. In a few years (after retirement) it’ll be a track rat.


Looking for neutral to a slight push, no desire to drift for me,, plus I should have enough HP to get the back end to step out when wanted.


OK,, as for sizing of a bar. One thing to keep in mind is I’m interested in the rate in pounds as my sway bar arms will certainly be a different length than stock and I'll select the bar based on arm length and rate in Lbs. I'm basing my numbers on the chart below. If you see an issue in doing that, I'd like to hear about it.

Andrew from RCE has said the stock front bar is 140lbs with a OEM 18MM solid bar. Using the chart below, going up to a 20MM yields a 52% increase (212 lb) and a 22MM bar is 123% increase (313lb). Based on what I see, most suppliers are offering these sizes (20,22) plus maybe a 25MM hollow (which RCE says is like a 22MM solid,, just lighter) . Hard to tell what the rate on hollow bars without knowing tubing thickness. Don’t see anything other than these sizes.

So my initial thought is a 20MM (212lb) target and skip updating the rear bar. Although,,, with the higher COG in the front maybe the 22MM bar (313lb) might be a better choice and change the rear bar if required. Something in-between should be doable as well. 265lb a sweet spot with no rear bar?

Thoughts????

Also,, lots of good info here....

http://www.ft86club.com/forums/showt...highlight=sway

[wparsons]

I don't think the raised CG is enough to justify going THAT much stiffer than you were already looking at. A 20mm is probably plenty, although if you get an adjustable one you could aim for that at the middle range so you can go up or down a little bit.

[x808drifter]

Originally Posted by wparsons

I don't think the raised CG is enough to justify going THAT much stiffer than you were already looking at. A 20mm is probably plenty, although if you get an adjustable one you could aim for that at the middle range so you can go up or down a little bit.

Thinking the same.

If possible see if you can do something adjustable.
I can't imagine anything more than a 15-20% increase would be needed to keep the car neutral/slight push.

[gtpvette]

Originally Posted by x808drifter

Thinking the same.

If possible see if you can do something adjustable.
I can't imagine anything more than a 15-20% increase would be needed to keep the car neutral/slight push.

Originally Posted by wparsons

I don't think the raised CG is enough to justify going THAT much stiffer than you were already looking at. A 20mm is probably plenty, although if you get an adjustable one you could aim for that at the middle range so you can go up or down a little bit.

Thanks. You're probably right,,, I'll try to stick to around 200Lbs (20MM) to start with. I've been looking at the Speedway rate charts. The problem is the shortest arm they show is 8" which by my guess will be way long for this application. I don't think it'll end up being more than 5"-6". So the question becomes,,, what are the rates for these bars with a 5"-6" arm?? I've reached out to Speedway to see if they have these numbers but haven't heard anything back.


I found one sway bar rate calculator but it doesn't follow the speedway chart when I plug in their values. There's another calculator that's referenced a bit,, but can't find a working version. If you know of another,, please post it up.


http://www.auto-ware.com/calcs/swaybar.htm



So I plotted the numbers from the chart for the first two bars, (3/4" (19mm) and 13/16 (20MM) ) and then guessed a bit as to what the rates would be from 7.5" down to 5" looking at the differences between the numbers every 1/2" and the shape of the curve in the graph. I assumes the graph shape should remain the same. Based on my very unscientific research I'm thinking the 13/16" bar with a 5" arm might be a good place to start at 212lbs.


Anyone with real math skills have any thoughts on the guesstimate numbers??

[strat61caster]

Originally Posted by gtpvette

Anyone with real math skills have any thoughts on the guesstimate numbers??

Edit: misinterpreted your question, you're trying to figure out what to order so this is moderately irrelevant and just background info for swaybar options on this platform.

Stock Sway ~141 lbs/in
http://www.ft86club.com/forums/showthread.php?t=26661

Different aftermarket options:
http://www.ft86club.com/forums/showthread.php?t=49659

1" hollow bars ~500-600 lbs/in depending on adjustment
~20mm solid bars ~200-300 lbs/in (very roughly speaking based on percentages in the link above)