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What sway bar size


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#1 Gareth. J.

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Posted 15 September 2011 - 11:57 PM

Hey guys, looking for opinions on sway bar combo's for a 240 track car, ride harshness is no issue. I currently have 23mm  front with 340 lb springs and 18mm rear with 220lb. I'll be upgrading to 280lbs in rears soon and will strengthen the front sway bar mount points. Run 16x8's with 225 semi's.

I'm looking go bigger as I feel its still got too much roll. Im considering 1 1/8" front and 7/8" rear (29+23mm) commonly used on imsa gtu cars and the 46bre Datsun. It's also listed in the Datsun hot rod and race book as a suggested sizing. 

What do you think? Is there anyone in Australia with these sizes?

Thanks, Gareth.

#2 luvemfast

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Posted 16 September 2011 - 09:03 AM

If they recommend them from BRE and Datsun book, its a good place to start.
I guess its more of whats available in Australia.

Can you just stop though? Its costing me a fortune trying to keep up with you  :P
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#3 peter mc

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Posted 16 September 2011 - 09:32 AM

it may be to big for the wheel size i may be wrong i have a 25 mm front you can try i will check if i have a large rear one as well

#4 DAZDA

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Posted 16 September 2011 - 09:43 AM

Gareth,

There are other ways to reduce the ‘roll rate’, for example reduce the distance between the Roll Axis and the CoG of the Sprung Mass
    • Lift the front and/or rear Roll Centres
    • Lower the Centre of Gravity of the Spring Mass
As opposed to increasing the roll resistance by
    • Increasing the spring rate front and/or rear (which you are actually doing)
    • Increasing the Anti-Roll Bar rate front and/or rear (which you are proposing)
NOTE:  Changing the front to rear roll resistance ratio changes the sprung mass 'weight transfer' distribution front-to-rear, which may be something to consider...

Another thing to consider is that the diameter is multiplied to the power of 4 when calculating the torsional stiffness of an ARB.  Fred Puhn’s book, How to Make Your Car Handle has a formula to calculate this.  So small changes in the ARB diameter can have big affects.

Also, one change at a time makes it easier to understand and ‘feel’ what affect it has had on the car’s behaviour.

For what it’s worth, I’m running 24mm on the front and 18mm on the rear...

#5 dat2kman

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Posted 16 September 2011 - 10:56 AM

Your current front to rear spring rates are too far apart, for now, leave the sways alone, but fit the stiffer rear springs, and go out and do laps and laps.

While testing, try the idea of slackening off the rear drop links to the rear sway, this will reduce the tendency of overseers at rear, due to the higher rear spring rate, even playing around with using either or rubber or urethane sway bar link rubbers, front to rear can alter things.

I used to practice a single constant radius corner in a large industrial carpark, and measure the time as well as car speed from one point to the next, on the radius, to see what playing around with sway bars, rubbers, no sway bars loose rubbers etc would do.

This is all detailed in the Fred Puhn book, as above mentioned.

#6 Scando

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Posted 16 September 2011 - 11:03 AM

It will be a very stiff setup for running on semi-slicks, keeping in mind that the bre cars ran on slicks. Your front is already much stiffer than I would recommend but it obviously works well going by the times you're doing. What does the balance of the car feel like now? Does it tend towards understeer or oversteer? On entry or exit? Unless the car tends towards understeer as it is now I'd be worried that the stiff rear springs and bar might give you some serious oversteer issues.

As dazda said, do one thing at a time and test it. Do a session with just the new springs in then try a bigger bar if you think it needs it, that's my 2 cents worth  :)

#7 Gareth. J.

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Posted 16 September 2011 - 10:20 PM

Well I'm no idea about some of the technical stuff mentioned  :o I have front offset bump steer spacers, rear delrin bushes, it as low as legally possible. The car is very neutral at the moment, no understeer, not twitchy at all. does that help? Lol.

I was looking at some pics and saw the car had heaps of roll, both inside wheels were completely unloaded. I was thinking stiffer bars would reduce roll and give more grip from the inner wheels.

How do you calculate the spring rates are too far apart?



#8 Whittie

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Posted 17 September 2011 - 03:58 AM

I'm not expert, but from what the guys doing my suspension, now as I type actually, say, this is what I will be running and is what they put in every 'street' track zed:

300Ib front
250Ib rear
22mm front bar
20mm rear bar

They seriously stressed the 50Ib difference front to rear was kept constant. I.e with a heavy motor move to 350/300 to account for more weight but still with a 50Ib split. They also hammered me about going heavier and adjustable sway bars and said it was unnecessary on a zed.

These cars like a bit of give, I've heard that a LOT of times and it certainly seems to be working well for me, I was running 250Ib front and a too soft rear in a car that was too low without roll center adjusters in the front, but still nice and soft all round. I'll see how the new suspension goes tho!

My understanding of suspension in general is that the car should be lowered so that the arms are just above parallel with the ground, forget street legality - The real issue is that you do NOT want them pointing upwards from the pivot to the wheel! This will cause the track of the car to change under spring compression, which will shorten the 'lever arm' of the front suspension and load it up harder, compressing it more, shortening the track more, etc, until the rear wheel completely unloads and you spin the car. There is absolutely no coming back from that.

The other thing is that to make use of really stiff suspension you need real sticky tires. R-comps are good, but they're not slicks and I would think that the route you're talking and with the spring rates you have will over power the tyre, not provide enough grip and you will either have issues with the car 'snapping' when it goes or it driving like a drifter, there will be no control past the limit of adhesion.

Just my, probably totally incorrectly informed, 2 cents.

#9 Scando

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Posted 17 September 2011 - 08:13 AM

The car is very neutral at the moment, no understeer, not twitchy at all. does that help? Lol.


If that's the case then I'd definitely stick with the rear bar you have and just try the springs.  I'd be worried it will get very tail happy with a big rear bar.  And it won't cost you anything  :)

What rear shocks are you running?  Are they going to be able to properly control the stiffer springs?

#10 Gareth. J.

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Posted 17 September 2011 - 01:50 PM

I have 4way adjustable kyb's in front and koni reds in the back, they seem upto the task. The red are a pia to adjust.

What is the reason for the spring rates being so close, I'd always heard zed's liked hard front and very soft rear for ideal setup.

#11 PeterAllen

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Posted 18 October 2015 - 10:21 AM

I'm just prep-ing and painting the front anti-roll bar (ARB) prior to fitting - 9 years after I removed it! The bar appears to be an OEM standard at 18mm dia. 

 

Is this okay for old fart touring or is a larger dia bar a necessary upgrade for even this activity? The sizes mentioned above seem quite extraordinary considering multiplying factor dia increases have.


Edited by PeterAllen, 18 October 2015 - 10:22 AM.


#12 Gareth. J.

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Posted 22 October 2015 - 08:05 PM

You could try the stock setup and see how you like them. From memory my car with the standard front bar had a large amount of body roll even on the street.

 

I upgraded to 24mm front a while ago now.



#13 Cozza

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Posted 23 October 2015 - 09:22 AM

Hi Peter
I have King springs KDFL08 and Tokico Illuminas on mine the springs have been tested to be 185 lb's/inch at ride height.
Using your 24mm Whiteline sway bar set to stiff, my car sits quite flat in the bends but still is reasonably soft over bumps. I think this is a reasonable "compromise" set up.
For a more track oriented car, I would prefer a much stiffer spring which would probably require a slightly smaller bar. This plus gaining some additional camber is what I intend on doing for my next mods.

I assume your car might behave a little different to mine due to the V8 and the fibreglass but probably not a huge amount.

Cheers
Mick

Edited by Cozza, 23 October 2015 - 09:22 AM.


#14 PeterAllen

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Posted 23 October 2015 - 12:53 PM

Mick, I have 250 lb/in springs allround so the 18mm ARB might be okay for starters.

 

Just got it back from the air/con shop this morning (cost near twice his estimate) and the plumbing make it near impossible to access the fuses and relays. I'll have to re-position them, YET AGAIN... Arrrrrrr. Also, the engine now idles but will not rev, AGAIN... Arrrrrr.

 

I know this is a big call but I'm starting to think women are easier to cope with than cars!






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