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5 GT Turbo Torsion bar thickness
- Thread starter Brigsy
- Start date
DaveL485
Staff member
im going to get some measurements soon and see whats what 
Woznaldo
Active Member
Ok, I've been doing a bit more research on these Torsion Bars. My Access to a wide spread of parts is extremely limited, but I do want to some context.
Spring rates, i.e. the spring/torsion bar you fit is less important than the Ride Rate, i.e. the spring rate at the wheel. Now while your spring rate my be close to linear, it's likely that your ride rate isn't and this is because the ride rate changes as the geometry changes, assuming we want camber gain in roll and good things like that.
We also want the rear of the car to have a slightly higher Ride Frequency than the front of the car. This lets the front 'catch up' with the rear when you hit a bump and prevent the car from excessive front/rear oscillations. Now the suggested ride frequency for a sedan/saloon race car with minimal aero is somewhere between 1.5-2.0 Hz. The ride frequency takes into account the corner unsprung mass (the corner weight for that wheel).
To make things a little simpler, let's assume the motion ratio (the conversion from spring rate to ride rate) is one. Lets also assume the car (our GTT) weighs 750kg and has a front/rear weight distribution of 60/40 (heavier at the front). Let's also aim for a ride frequency of 2.0 Hz.
Therefore: Front corner weights are 225 kg per side, rear are 150 per side.
Front ride rate = 4*(pi^2)*((ride frequency)^2)*(corner mass)*(motion ratio^2) = 4*(3.14^2)*(2.0^2)*(225)*(1^2) = 35495 N/m = 3.61 kg/mm = 202 lb/in (not a lot!)
Rear ride rate = 4*(pi^2)*((ride frequency)^2)*(corner mass)*(motion ratio^2) = 4*(3.14^2)*(2.1^2)*(150)*(1^2) = 26090 N/m = 2.65 kg/mm = 148 lb/in (even less!)
So why are these ride rates so small? Well mainly because the car is light and it's front biased. When you factor in more realistic motion ratios you'd have use a higher front spring rate to achieve the same ride rate. You also need to consider that the GTT doesn't have a very stiff chassis, so that would mean you'd need to up the spring rate to compensate.
For reference: GTT rear ride rate is 2.84 kg/mm or 160 lb/in (using the same vehicle parameters as above), if using Kangoo torsion bars 5.76 kg/mm or 323 lb/in or ride frequency of 3.1 Hz!
Spring rates, i.e. the spring/torsion bar you fit is less important than the Ride Rate, i.e. the spring rate at the wheel. Now while your spring rate my be close to linear, it's likely that your ride rate isn't and this is because the ride rate changes as the geometry changes, assuming we want camber gain in roll and good things like that.
We also want the rear of the car to have a slightly higher Ride Frequency than the front of the car. This lets the front 'catch up' with the rear when you hit a bump and prevent the car from excessive front/rear oscillations. Now the suggested ride frequency for a sedan/saloon race car with minimal aero is somewhere between 1.5-2.0 Hz. The ride frequency takes into account the corner unsprung mass (the corner weight for that wheel).
To make things a little simpler, let's assume the motion ratio (the conversion from spring rate to ride rate) is one. Lets also assume the car (our GTT) weighs 750kg and has a front/rear weight distribution of 60/40 (heavier at the front). Let's also aim for a ride frequency of 2.0 Hz.
Therefore: Front corner weights are 225 kg per side, rear are 150 per side.
Front ride rate = 4*(pi^2)*((ride frequency)^2)*(corner mass)*(motion ratio^2) = 4*(3.14^2)*(2.0^2)*(225)*(1^2) = 35495 N/m = 3.61 kg/mm = 202 lb/in (not a lot!)
Rear ride rate = 4*(pi^2)*((ride frequency)^2)*(corner mass)*(motion ratio^2) = 4*(3.14^2)*(2.1^2)*(150)*(1^2) = 26090 N/m = 2.65 kg/mm = 148 lb/in (even less!)
So why are these ride rates so small? Well mainly because the car is light and it's front biased. When you factor in more realistic motion ratios you'd have use a higher front spring rate to achieve the same ride rate. You also need to consider that the GTT doesn't have a very stiff chassis, so that would mean you'd need to up the spring rate to compensate.
For reference: GTT rear ride rate is 2.84 kg/mm or 160 lb/in (using the same vehicle parameters as above), if using Kangoo torsion bars 5.76 kg/mm or 323 lb/in or ride frequency of 3.1 Hz!
Woznaldo
Active Member
I’m going to work out front motion ratios so everything in the rear makes more sense. Front what I’ve read/seen on Gp A Clio1, a very high end damper in the rear is where good gains are made. As my finances don’t really allow me to explore that option, I’ll try to get the ride rates where they make sense.
I was intending to hit the track in August (local Hillclimb), but world events may trip me up.
mom not really sue on how to work out the effective spring rate of the Anti-Roll torsion bars in a four bar beam? If anyone on here has an idea, please speak up.
I was intending to hit the track in August (local Hillclimb), but world events may trip me up.
mom not really sue on how to work out the effective spring rate of the Anti-Roll torsion bars in a four bar beam? If anyone on here has an idea, please speak up.
What about extra arb fitted to the beam same as 11t grp a? i believe only Ragnotti used it as he liked it lively at the back
Woznaldo
Active Member
I guess the biggest issue with the existing anti-roll torsion bars, is they’re not adjustable and it’s not a quick job to replace!
Using a traditional U-Bar where you can quickly change the lever arm length allows the setup to be tweaked.
There is of course, as mentioned, the fact that Jean liked it loose!!!! I would consider reducing/removing the std anti-roll just so you could increase the range of adjustment with the U-Bar setup.
Using a traditional U-Bar where you can quickly change the lever arm length allows the setup to be tweaked.
There is of course, as mentioned, the fact that Jean liked it loose!!!! I would consider reducing/removing the std anti-roll just so you could increase the range of adjustment with the U-Bar setup.
Woznaldo
Active Member
I've done a bit more work on the front geometry to determine motion ratios and camber change. My measurements weren't mm accurate, but close. Some interesting results so far. The MR at the front is also close to 1:1 it's something like 1:1.1 or similar. This was done for the phase2 setup. What I found most interesting was the camber change. The camber gets more negative for a fair after the lower wishbone passes parallel! The theory with a MacPherson Strut arrangement is you gain 'negative' camber up until a point and then it starts to go back to positive. I was expecting it to be somewhere just after the wishbone gets horizontal, but its actually a fair bit after.
I have measured the all the front suspension hardpoints (pivots and balls) and put them into 3D space using CAD (Catia V5R20) and measured the length of the damper/strut and compared it to wheel movement through the range of travel. i.e. when the strut has moved 10mm the wheel has moved 11mm etc.
I still need to refine the model, but I'll be able to modify later and add rollcentre correction (lowering the lower outer ball joint) and see what differences this makes to camber change etc, or compare Ph1 to Ph2. It will probably be easiest to display the info in a table format for the most people to digest.
We've probably drifted a fair way from Torsion bar thickness, so I might start a new thread once I've got some more results.
Getting back on track with the rear. The beam design is the limiting factor and yet Renaultsport have been able to achieve some great things. The rear beam differences between Clio1/GTT and 172/182/197/200 are down to how the sides are linked and that makes a difference in roll only. More to follow.
I have measured the all the front suspension hardpoints (pivots and balls) and put them into 3D space using CAD (Catia V5R20) and measured the length of the damper/strut and compared it to wheel movement through the range of travel. i.e. when the strut has moved 10mm the wheel has moved 11mm etc.
I still need to refine the model, but I'll be able to modify later and add rollcentre correction (lowering the lower outer ball joint) and see what differences this makes to camber change etc, or compare Ph1 to Ph2. It will probably be easiest to display the info in a table format for the most people to digest.
We've probably drifted a fair way from Torsion bar thickness, so I might start a new thread once I've got some more results.
Getting back on track with the rear. The beam design is the limiting factor and yet Renaultsport have been able to achieve some great things. The rear beam differences between Clio1/GTT and 172/182/197/200 are down to how the sides are linked and that makes a difference in roll only. More to follow.
Woznaldo
Active Member
I was thinking of using Kangoo torsion bars, but they’re too long by about 50mm. 
Express/Extra bars are hard to find (especially for me in Aus).
Who would be interested in a set of custom torsion bars? If so, how much would be willing to pay and what size OD. I’m thinking we could have 23, 24, 25 and 26mm OD bars. (Or around that).
I have a very reputable Renault specialist that uses a local (UK) engineering firm to make other Renault parts that can manufacture the bars.
Maybe I’ll do some conversions so we can determine spring rates rather than OD as this will be more useful to most.
What front springs are people using at the moment? This will also help determine workable rear rates. I currently run 250lb/in but I know others have run 300lb springs on track cars.
What rates do the racers run? >300lb??
This is not a suggested group buy, as I’m still waiting for responses on cost etc and I’m not in a position to manage from Aus.
Let me know what you think?
Express/Extra bars are hard to find (especially for me in Aus).Who would be interested in a set of custom torsion bars? If so, how much would be willing to pay and what size OD. I’m thinking we could have 23, 24, 25 and 26mm OD bars. (Or around that).
I have a very reputable Renault specialist that uses a local (UK) engineering firm to make other Renault parts that can manufacture the bars.
Maybe I’ll do some conversions so we can determine spring rates rather than OD as this will be more useful to most.
What front springs are people using at the moment? This will also help determine workable rear rates. I currently run 250lb/in but I know others have run 300lb springs on track cars.
What rates do the racers run? >300lb??
This is not a suggested group buy, as I’m still waiting for responses on cost etc and I’m not in a position to manage from Aus.
Let me know what you think?
Brigsy
Media Mogul. Instagram legend.
I used to run stock avo springs which were around 200lb from memory and 24mm torsion bars at the rear (stock van). The fronts were far too soft and as i did not have much knowledge just wound up the rebound to full, and you could feel the shocker bottoming out and spring going coilbound on fast corners on track. I reckon the rear could do with being stiffer to get it to rotate a bit.
I currently have 350lb in on the avo’s and they seem great on road use with damping set soft, its not bone shaker hard any more. Took it around a few b roads the other day, and it seems to corner quite flat.
I have a set of leda coilovers to fit that also have 350s in. Will eventually try them with -2.5deg negative camber, as much castor as i can get, ten mins of toe out overall. If i feel it needs to be a little bit harder will try 400lb.
Woznaldo
Active Member
Thanks Brigsy, I’m running Ledas and 250s which are a bit too soft. I might try some 350s eventually. I’ll work out some torsion bar spring rates and try to compare with the std front/rear setup. I was running -3.0 deg camber and similar toe out. Initial turn in was pretty good, but improved when I cranked up the rear dampers.
Woznaldo
Active Member
I may have some torsion bars available. Turns out a Clio1 racer ordered them and they were made, but never paid for. I'm currently confirming price and sizes (diameters) and will then let everyone know. The racer had them make a complete set of four (4) bars. Two (2) Ride Bars and two (2) Anti-Roll Bars. There are 10 sets!!! I'm not sure if they are the same size for all Ride and all Anti-Roll, but I'm going to nab a thick set if possible i.e. >25mm Ride and =>26.5mm Anti-Roll (maybe).
Standby for more info.
Standby for more info.
Woznaldo
Active Member
Ok. I’ve got some prices for torsion bars. Despite me eluding to different thicknesses, they are all the same. Torsion bars are 24.5mm and ARBs are 26.5mm. Price looks like GBP375 for a set of four (2+2) plus shipping. There are 9 sets and I’m taking one, so eight remaining.
I’m happy to be the test case to make sure the fit and finish are up to par, but will post a picture when I have one.
I’m happy to be the test case to make sure the fit and finish are up to par, but will post a picture when I have one.
