Question:>Need help with rear suspension - tire pressure etc?

[Anders-DK]

Hi Guys

My friend Rasmus "The Black Bulldog" and the rest of the "team"  are back from SCC 2009, and what a blast it was - Holey Moley



We need to pull these wheels up now or getting the 60ft down a bit (one-tenth is maybe out of range, but maybe ½-tenth is possible?)
We are going to Das Drag Day and can try to make some modification before the next race, but what shall we change?

Please feel free to share your ideas or thoughts

When he launch regardless trackbite or not, the start is very bounching and wheel spin

Car spec:
ET11.668 - 186.85km/t - 1.65 60ft (without trackbite)
ET11.83 - 180km/t - 1.62 60ft (with trackbite)
850kg with driver
2600ccm Type4 engine 250hp
MH 215/65-15 DOT slicks
IRS Transmission with 100mm Stub axles
30mm Torsion bars
Adjustable Spring Plates and JayCee Spring plate caps (Urethane IRS-Arm Bushings)
AOV shock absorber
Tire pressure 14-18 psi (depending on track)
Launch rpms ( approximate 4500rpm without trackbite / approximate 6000rpm with trackbite )

I will make some videos and post them here, maybe it's more easy to see how the car handle.

Thanks

[Fastbrit]

Personally, I would change the torsion bars to 28mm as I think the 30s are too stiff and not allowing the suspension to work properly. It's hitting the tyres too hard too soon, hence the wheel spin – you need more weight transfer to load the tyres progressively. Oh, and run slicks...

But that's just my opinion!

[Griebel]

Hi guy's..we had a nice trip to SCC this year,for sure 

When you get a "sideways" look at Rasmus' car going down the track,-this "springs" to your mind :
http://www.superballs.com/   
The rear suspension don't "travel" at all,and the car bounces quickly up'n'down on the tyres..

See y'all soon 

[Roman]

I had the same tires, shocks and torsion bars and approx the same weight. Most of the time I had 60 foot times between 1.50 and 1.55.
What clutch do you use? What front shocks do you use?
Have you trired to raise the front some? It can do magic for the 60-foot times.

[Anders-DK]

I had the same tires, shocks and torsion bars and approx the same weight. Most of the time I had 60 foot times between 1.50 and 1.55.
What clutch do you use? What front shocks do you use?
Have you trired to raise the front some? It can do magic for the 60-foot times.

Thanks guys for you answer

Yes Roman we know what you used on your car earlier on, that's why he bought the AOV shocks with 16 settings from UK, it was you own advice 
Rasmus bought the 30mm torsion because of the extra weight on the type4 engine, he used 23mm before. We have talked the whole weekend, if it would be better to step down to the 28mm torsion or less air pressure in the tires, maybe 11-12 psi.

Clutch is 228mm HD from Ahnendorp
Front shocks 90/10

To raise the front should be an easy task, worth trying

[Roman]

I have no idea if the clutch is to agressive or not.
What shock settings are you using? I used between 14 and MAX (16) on the AVO's, but if you have prolems with the traction you should loosen them up some.
I think I used down to 12 psi in the tires, but when I lowered it more it didn't get an even footprint. I also made really long burnout.

The raised front is something to test on any race day. It takes some runs before you find what is suitable. What worked for me with my driving style might not work for you.

I always stand on the 2-step rpm limiter and lift the left foot as fast as I can without really sidestepping and speedshift.
The shift RPM can be a factor as well, as at least I shift well before the 60-footer.

[Anders-DK]

I have no idea if the clutch is to agressive or not.
What shock settings are you using? I used between 14 and MAX (16) on the AVO's, but if you have prolems with the traction you should loosen them up some.
I think I used down to 12 psi in the tires, but when I lowered it more it didn't get an even footprint. I also made really long burnout.

The raised front is something to test on any race day. It takes some runs before you find what is suitable. What worked for me with my driving style might not work for you.

I always stand on the 2-step rpm limiter and lift the left foot as fast as I can without really sidestepping and speedshift.
The shift RPM can be a factor as well, as at least I shift well before the 60-footer.

The shocks are set to step1
was this the setup when you got the ET 11.29 with you old engine?
could it be that the IRS setup dont need the 30mm torsion but 28mm torsion would be better?
we will try to raise the front at Das Drag Day and maybe Rasmus will try to make a longer burnout 
But the first run at SCC saturday, he pulled a long burnout and he broke the drive shaft 

there's only one way to find out these things - Das Day will be a test weekend

[Anders-DK]

[SteveW]

Would raising the front be beneficial because it's becoming slightly more level? With it being so nose down is the weight transfer just being used to pull the front end up instead of all of the weight transfer going straight to the back wheels?

[Fastbrit]

TORSION BARS! Look at the rear of the car as it leaves the line. Absolutely no squat at the rear at all. Therefore tyres being hit hard, no weight transfer...

[Martin]

Have to agree with Keith, maybe the rear end is a little sezed that can happen with urithain bushes. they can be too tight.

I think i'd start by taking out the springs then re-assemble the rear end with out them and making sure it all moves nice and free. Once you have proved they are moving free then look towards springs.

as for air preshure the tires will tell you what to run. look at the contact patch, if the tire is not wearing to the outer edge then drop the presure. but by the picture they do look a little hard.

just my thoughts. hope it helps


Martin

[Anders-DK]

From first run saturday, ½ hour later the car was ready again in the lineup 

[Roman]

The shocks are set to step1
was this the setup when you got the ET 11.29 with you old engine?
could it be that the IRS setup dont need the 30mm torsion but 28mm torsion would be better?
we will try to raise the front at Das Drag Day and maybe Rasmus will try to make a longer burnout 
But the first run at SCC saturday, he pulled a long burnout and he broke the drive shaft 

there's only one way to find out these things - Das Day will be a test weekend

The setup was pretty much the same on both engines.
The diffence was 28 mm bars and 2-3 clicks from max on the old engine and 30 mm bars and the hardest setting on the big one.

What do you mean with step1? The hardest or the loosest?  If it is the loosest you have some serious problems with rear end movement.

Just as the other guys says: Remove the shocks and it should move easily. I could swing the rear end 2-3 inches just by pressing a couple of times with one foot on the engine case.
I can also lift my front end from the ground just by "bouncing" it  up and down a couple of times and I am not a big guy and the car is close to stock weight.
Roughly: The softer the spring is the more it will squat. The shock setting tells how fast it will go there, unless you are way out of range:
http://upload.wikimedia.org/wikipedia/en/thumb/e/e8/Damping.svg/512px-Damping.svg.png

Raising the front end will transfer mass to the rear faster. This is described in Gene Bergs blue book as "Adjusting the wedge".

[Anders-DK]

The shocks are set to step1
was this the setup when you got the ET 11.29 with you old engine?
could it be that the IRS setup dont need the 30mm torsion but 28mm torsion would be better?
we will try to raise the front at Das Drag Day and maybe Rasmus will try to make a longer burnout 
But the first run at SCC saturday, he pulled a long burnout and he broke the drive shaft 

there's only one way to find out these things - Das Day will be a test weekend

The setup was pretty much the same on both engines.
The diffence was 28 mm bars and 2-3 clicks from max on the old engine and 30 mm bars and the hardest setting on the big one.

What do you mean with step1? The hardest or the loosest?  If it is the loosest you have some serious problems with rear end movement.

Just as the other guys says: Remove the shocks and it should move easily. I could swing the rear end 2-3 inches just by pressing a couple of times with one foot on the engine case.
I can also lift my front end from the ground just by "bouncing" it  up and down a couple of times and I am not a big guy and the car is close to stock weight.
Roughly: The softer the spring is the more it will squat. The shock setting tells how fast it will go there, unless you are way out of range:
http://upload.wikimedia.org/wikipedia/en/thumb/e/e8/Damping.svg/512px-Damping.svg.png

Raising the front end will transfer mass to the rear faster. This is described in Gene Bergs blue book as "Adjusting the wedge".

Hi Roman

And thanks to you and the other guys with input, we really appriciate it.

When I said step1 it was at the loosest and when we try to push the rear down with one foot, it's hard as a rock, so this would be the problem, we need more weight pushed in the back and get the squat back again but not as much as before.
On friday we will dismount everthing, and then try from the beginning without the torsion and shocks, and if all movement is good, then we will use the 28mm torsion, we talked about taking the old 23mm torsion with us to Das Dray Day, there was no problem with travel when the 23mm was mounted, so I don't think anything is sezed. He just have to much squat back then.

[Roman]

BTW, have you preloaded your torsion bars?
I just slipped mine over the stock stop.

[Anders-DK]

BTW, have you preloaded your torsion bars?
I just slipped mine over the stock stop.

They are slipped in like yours, so no preload

[Anders-DK]

Hi guys

Thanks for all your answer and input.

We have found the problem 

The problem was not the 30mm torsion, but when Rasmus bought the 30mm torsions he also bought the JayCee spring plate retainers and adjustable spring plates.
And when mounted without any rubber the sprint plates was to tight to the pan, so the whole spring plate was sezed.

We have now used urethane inside and shims under spring plate retainers, so now there is good movement.

Thanks again guys, we are looking forward to see the result at Bittburg Motorpark

without the shocks:
<a href="http://www.youtube.com/v/IWLewF9WNx8" target="_blank">http://www.youtube.com/v/IWLewF9WNx8</a>

With the AOV shock at the loosest:
<a href="http://www.youtube.com/v/k21YL3B_Pkc" target="_blank">http://www.youtube.com/v/k21YL3B_Pkc</a>

[Martin]

Glade you got it sorted!


Martin

[BeetleBug]

Excellent thread! Glad to see you found the problem. I had the pleasure to look at your car from up close everytime you launched and I noticed that you did not have any weight transfer and/or very stiff rear suspension. Mix this with too much air in the slicks and your 60ft will be bad.

It will be interesting to see what the result will be on your next race.

Good luck,

Best rgs
BB

[Roman]

That is more like it! I think the 30 mm bars will be just fine. I would start with the shock setting in the middle and go from there. You will probaly end up with a setting around 14 to 16 on the shocks.

BTW, bring an extra pair of shorts to the pit area. If it hooks up real good you'll need them!

[PPRMicke]

That is more like it! I think the 30 mm bars will be just fine. I would start with the shock setting in the middle and go from there. You will probaly end up with a setting around 14 to 16 on the shocks.

BTW, bring an extra pair of shorts to the pit area. If it hooks up real good you'll need them!

Hi Anders

often flexes the chassis as much as you think it is wrong on shocks
 
I would try with 10-12 psi tire pressure 
I'm using AVO dampers  Shock setting Rear 60/40 forward 80/20 it works very well 
 setting 10 Rear forward 5  on the shocks