23mm Torsion Bars

[skeggyrik 3]

I'm soon to aquire a set of 23mm torsion bars for my beam rebuild. I killed a standard bar gettign it out and have used this as an excuse warrant spending more money

 

From my research, it seems common that this upgrade to 23mm bars is accompanied by a 25mm ARB upgrade. Has anyone run 23mm bars with the standard anti roll bar? if so what are your experiences of this.

 

What rate does a 23mm bar effectively give in lb terms? I know they are described as tarmac spec bars.... I ask as I've got a set of 275lb front springs that came with my gaz coilovers which I've seen some of you run with the above set up, but have reported them to be very stiff. Before I'd plumped to go to 23mm bars I ordered a set of 200lb front springs to go "better" with with a standard rear beam tahn the 275's. My question now is if I use the 200lb springs with the rear 23mm bars am I in danger of having a stiffer rear than the front and all the dangers that go with this set up. Anyone running 200lb springs with 23's at the rear? if so how is it?

 

I'm generally after feedback from pepole who have already gone through this process of upgrading and matching everything else to suit and what it felt like after.

[Sandy 189]

It depends more than anything on what the sprung axle weights are (the weight of the car on each axle, that the suspension supports). The spring rates are relative to the axle load, so to compare you need to compare like for like axle loads. You also need to consider track width and ride height, if it's different front or back, because the roll centre axis varies and is relative to the effect of spring rates too.

Edited January 24, 2007 by sandy309

[Rippthrough 98]

If it helps, 23's are a touch over twice as stiff as 19mm bars.

[peter 20]

I have been thinking a similar thing to you i curently have a 309 rear beam but with 300lb springs at the front and obviously this is not quite right but i would like to upgrade the arb and torsion bars but what thickness and im asuming 309 bars would need to be thicker again as they are longer so they are of a lesser poundage?

 

sorry if im hijaking the post

[pug_ham 241 3 Cars]

The difference in torsion bar length & thickness makes less of a difference to the poundage than you might think.

I'm sure Veloce200 posted a link & the formula to work out the rates last year.

309 bars are harder to come by though.

Graham.

[petert 554]

The difference in torsion bar length & thickness makes less of a difference to the poundage than you might think.

 

J=d^4/64

 

that 4th power really makes the numbers move!

 

So a double in spring rate is like going from 200lbs to 400lbs! So yes, the jump from 19mm to 23mm is huge and makes it very uncomfortable on the road.

[boombang 2]

Peter, sound thick here but can you break that equation down please?

 

d=diameter?

 

64=length?

 

When measuring the length, how much do you measure? The splined sections are fixed when located so I take it they are outside of the "twisting" section, and therefore not included in length?

[smckeown 1]

I'm soon to aquire a set of 23mm torsion bars for my beam rebuild. I killed a standard bar gettign it out and have used this as an excuse warrant spending more money

 

From my research, it seems common that this upgrade to 23mm bars is accompanied by a 25mm ARB upgrade. Has anyone run 23mm bars with the standard anti roll bar? if so what are your experiences of this.

 

What rate does a 23mm bar effectively give in lb terms? I know they are described as tarmac spec bars.... I ask as I've got a set of 275lb front springs that came with my gaz coilovers which I've seen some of you run with the above set up, but have reported them to be very stiff. Before I'd plumped to go to 23mm bars I ordered a set of 200lb front springs to go "better" with with a standard rear beam tahn the 275's. My question now is if I use the 200lb springs with the rear 23mm bars am I in danger of having a stiffer rear than the front and all the dangers that go with this set up. Anyone running 200lb springs with 23's at the rear? if so how is it?

 

I'm generally after feedback from pepole who have already gone through this process of upgrading and matching everything else to suit and what it felt like after.

 

what's the application ? road, occasional track, dedicated track ?

[petert 554]

Peter, sound thick here but can you break that equation down please?

 

d=diameter?

 

64=length?

 

When measuring the length, how much do you measure? The splined sections are fixed when located so I take it they are outside of the "twisting" section, and therefore not included in length?

 

d=diameter, 64 is a constant. Assuming the lengths are the same, length doesn't come into it. The answer J, is called the Second Moment of Area, units mm^4.

Edited January 25, 2007 by petert

[boombang 2]

Reason I asked regards length, it to work out the effective spring rate of standard (19.5mm?) and 21.5mm 309 torsion bars.

[tom_m 0]

effective spring rate calculator: http://www.stockcarproducts.com/pstech6.htm

[boombang 2]

Cheers Tom, any idea now what the arm length and effective bar length are for a 309 t-bar?

[tom_m 0]

nope

 

i just tried a search, i'm sure the figures are out there somewhere, but i haven't found them yet.

[Sandy 189]

Cheers Tom, any idea now what the arm length and effective bar length are for a 309 t-bar?

I use 10" arm and 39" bar for the 309 on that calculator. These aren't the exact values, but ones i've calibrated to the actual wheel rates of 20 and 22mm bars as i've tested them on the car; so they give pretty accurate results.

[boombang 2]

I use 10" arm and 39" bar for the 309 on that calculator. These aren't the exact values, but ones i've calibrated to the actual wheel rates of 20 and 22mm bars as i've tested them on the car; so they give pretty accurate results.

 

Excellent, I'll try that - I take it bar diameter is also in inches?

 

For 21.5mm (0.846 inch) 309 bars, using the above arm and bar lengths you get:

 

148lb/in

 

Makes 19.5 standard 309 bars 110lb/in

Also 22mm 309 bars 162lb/in

 

Sound about right? to me sounds a little low but then I've never looked into t-bar spring rates before.

[tom_m 0]

sounds about right to me, theres not a whole lot of weight back there to need supporting

 

sandy: how much do you knock off for 205 bars, is it 3 inches?

Edited January 25, 2007 by tom_m

[Rippthrough 98]

105lb/ft for the stock 19mm 205 bars then.

And 225lb/ft for 23mm bars.

 

Or just over double

[Sandy 189]

I haven't checked the 205 rates to compare. My old Rallye has 20mm bars and it's going back in my workshop next week, so i'll test it.

[pug_ham 241 3 Cars]

205 torsion & antiroll bars lengths;

Torsion bar; 991mm long.

ARB; 1095mm.

 

309 torsion & antiroll bar lengths;

Torsion bar; 1028mm.

ARB; 1130mm.

 

Should help if needed for any calculations.

 

Graham.

[boombang 2]

Is that the entire length of the bar, or the length of the active section of the bar?

 

I am assuming for calculation of rate, you use the measurements from inside of the held splined regions of the bars?

[pug_ham 241 3 Cars]

Entire length.

 

Graham.

[Sandy 189]

The numbers i've given are from testing the actual spring rate, at the wheel and making up bar and arms lengths to make that calculator work for the 309, it's not the literal, physical dimensions.

[pug_ham 241 3 Cars]

OK, there have been links posted before (on this topic & previous ones) that ask for the bar length to calculate the spring rating of the torsion bars diameter.

 

Graham.

[veloce200 3]

using the Gaz rear dampers with Selatex bumpstops I get a wheel rate of over 220lb - a lot cheaper than torsion bars to!

[petert 554]

An interesting topic. I just had some new 350lbs front springs made to go with my 23mm torsion bars.