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Author Subject: Effects of my rear beam overhaul a bit crazy?!
devere

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Post #1
Right, ive just stripped down and rebuilt my rear beam. This has meant all new bearings and good trailing arm shafts etc.

With this beam, i am running Bilstein shock absorbers, a hybrid anti roll bar, and 23.5mm Peugeotsport torsion bars.

I have the car pretty low on the back now, and with this setup, its very very stiff.

Since its all been done, the car feels incredibly lively at the back end. It hasnt actually stepped out on me, but it feels like it wants to when going round corners at speed. Yet at the same time, the tyres seem planted.

Its hard to describe really! Tyres planted, yet the body feels like its going side to side.

Is this just an effect of it being very sharp on the turn in, or have i just created a crazy handling car..?

I also run no anti roll bar on the front. Although i have always run it like this.

Just as a sidenote, this is a rally car, so its not a daily driven road car, its just for tarmac competition.

Any help or advice would be most appreciated!!
Posted 12th Jul 2010 at 02:04
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phillipm

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Post #2
What model are the bilsteins, and has the geometery been checked since the beam went back on? (They don't always go on pointing straight!)

Beam mounts?

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Posted 12th Jul 2010 at 02:13
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Rich E Forum Admin

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Post #3
What condition are the mounts in, and are they solid or standard?

Sounds like the standard passive rear steer though.

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Posted 12th Jul 2010 at 02:10
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devere

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Post #4
I cant remember off the top of my head what model the shocks are now. They are proper cometition ones though, and bloody stiff! lol. The car isnt here at the moment, so cant check unfortunately.

It has solid mounts on the beam aswell tho.

The passive rear steer is something that would be noticeable whatever the beam as done then?

Like i said, it feels like the car moves, yet the tyres still feel planted. It does turn in bloody well. Just wary of the back overtaking the front!
Posted 12th Jul 2010 at 02:39
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Welly Forum Admin

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Post #5
If it's that stiff is it not cocking up on one wheel and getting tyre movement?

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Posted 12th Jul 2010 at 02:47
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devere

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Post #6
It always used to cock a wheel when taking some very sharp corners. But i dont know if it does now that its much lower and stiffer again.

I havent used it in competition like this yet, but i have given it s few runs with the proper competition tyres on and everything as it would be.

Im not sure if its how it should feel, and its just that its a lot different compared to before hand.

As for the geometry, i havent had the tracking guages on it yet, but i will do. If they are off, is there actually anything that can be done to move them?
Posted 12th Jul 2010 at 02:52
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hovis16

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Post #7
you sure its not the natural movement of the car??? they do tend to sway abit the stick like shit depending on your setup you have. if not is both sides of the arb bolted up?

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Posted 12th Jul 2010 at 02:53
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devere

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Post #8
hovis16 wrote:
you sure its not the natural movement of the car??? they do tend to sway abit the stick like shit depending on your setup you have. if not is both sides of the arb bolted up?


It may well be the natural sway of the car. This is what im trying to determine. Obvisouly now its much stiffer, it would be more noticeable as there isnt the same give in the suspension to cushion the movement.

Like i said, it doesnt step out from when ive been on the road, although i havent been at full chat round corners. Just feels like the weight shifts to the outside.

Just been a strange feeling as it hasnt felt quite like that before.

If its supposed to be like that when they are stiffer, then its fine, but i dont want to head to belgium again this weekend, and find its just crazy! lol.
Posted 12th Jul 2010 at 02:59
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phillipm

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Post #9
How low is it? Not whacking the bumpstops is it?
Death of a lot of tarmac rally Pugs comes from that!

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Posted 12th Jul 2010 at 03:05
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Denis

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Post #10
There is no any inherent problem with such setup. I’ve been driving for a few days with 25mm bars (upgrade from 21mm) and Bilsteins - no strange behaviour. Yes, it is much stiffer and you can feel the whole car moving over bumps but on smooth roads – completely planted.
I run my car only about 40mm lower than standard.

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Posted 12th Jul 2010 at 03:09
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devere

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Post #11
russian guy wrote:
There is no any inherent problem with such setup. I’ve been driving for a few days with 25mm bars (upgrade from 21mm) and Bilsteins - no strange behaviour. Yes, it is much stiffer and you can feel the whole car moving over bumps but on smooth roads – completely planted.
I run my car only about 40mm lower than standard.


Yeh i havent felt any problems going straight. Obvisouly i can feel the bumps more, but then i dont mind about that.

Its just the weight transfer of the car when going round corners. Its taken me by suprise thats all, as its such a different feel to it from before.

As for the bump stops, no its not hitting those.
I cant remember my original measurements from before i took the beam apart, but its low enough that the rear tyres are ever so slightly tucked in the arch.
Posted 12th Jul 2010 at 03:21
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Denis

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Post #12
What kind of spring rate do you have on the front? You need to look at the whole car to see if it is balanced.

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Posted 12th Jul 2010 at 03:30
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devere

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Post #13
russian guy wrote:
What kind of spring rate do you have on the front? You need to look at the whole car to see if it is balanced.


Thats something i thought about. But i cant remember for the life of me what they are. Bit of a bad move really, as i should know. Im not sure i even have it written down.

No way of finding out i guess either..
Posted 12th Jul 2010 at 03:34
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Denis

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Post #14
Normally it is written on the springs.

By making the back stiffer, while keeping front the same, more weight is transferred during cornering to the outside back wheel – this might be the feeling that you are describing.

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Posted 12th Jul 2010 at 03:42
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devere

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Post #15
Ill have a check then. The front is also very stiff, so in effect, i dont see that the stiffness of the rear is way over the top compared to the front. Its a struggle to push it down! lol.

Its a good setup, but i think the new effects will just take some getting used to. Need to get it all ready for use next weekend and find out i guess!
Posted 12th Jul 2010 at 03:50
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Denis

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Post #16
Indeed – drive it more and see!

If you are passing Cambridge at some point – I can certainly take you out in my car for comparison.

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Posted 12th Jul 2010 at 04:02
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devere

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Post #17
russian guy wrote:
Indeed – drive it more and see!

If you are passing Cambridge at some point – I can certainly take you out in my car for comparison.


Cheers, ill bare that in mind. My car is in Stowmarket at the moment. So the same applies, if you ever head that way down the A14, let me know and we can compare notes!
Posted 12th Jul 2010 at 04:14
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welshpug!

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Post #18
sounds rather low to me, especially as a rally car.

compare the ride heights at the jacking point front to back and ideally the front needs to be slightly lower, I would think that with the described rear ride height you'd be at about 50mm lowered, not ideal!

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Posted 12th Jul 2010 at 15:54
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devere

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Post #19
welshpug! wrote:
sounds rather low to me, especially as a rally car.

compare the ride heights at the jacking point front to back and ideally the front needs to be slightly lower, I would think that with the described rear ride height you'd be at about 50mm lowered, not ideal!


Yeh, having put on a beam we built from scratch. And the other one being so shagged the original measurements probably werent much to go by, i cant say for sure how much its dropped by.

Is raising it up likely to change the feel of it in the corners? Bare in mind ive only taken it round longish smooth tarmac roads so far. Im not thinking of the bumpy road scenario at the moment. Just how the car feels as it goes round the corner...

For all i know it might continue to stick to the road like shit to a blanket, but its a case of being in the right place to try it! haha.
Posted 13th Jul 2010 at 03:08
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welshpug!

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Post #20
indeed, a difficult one until its all road legal and working properly, trackday would be ideal.

Also difficult to specify what to set the rear at with such stiff torsion bars, 23.5mm is pretty much double the spring rate of 20mm bars, IIRC you'll be around the 250 lb mark there!!

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Posted 13th Jul 2010 at 03:48
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alastairh

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Post #21
Tried connecting the front arb back up?

Al

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Posted 13th Jul 2010 at 04:24
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Denis

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Post #22
I usually measure the height to the top of wheel arches or jacking points. Changes in height front / back (not so much overall height) make massive difference to the behaviour and feel of the car. You can fine tune the handling by adjusting the height: raise the back = more weight forward = sharper turn in and tendency to oversteer, lower the back = more weight back = understeer.
From experience I prefer to set it level when measured at the wheel arches (this is about 20mm higher at the back when measuring at jacking points).

My calculator tells me that 23.5mm bars are equivalent to about 230lb wheel rate.

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Posted 13th Jul 2010 at 04:31
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welshpug!

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Post #23
good point alistair, it'd need fairly hefty front spring rate for it to work balanced without a front arb and a rear spring rate that high.

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Posted 13th Jul 2010 at 04:39
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lotek

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Post #24
bit of a thread hijack but would
21mm torsion bars and 325lb front springs lead to understeer?
i think i know the awnser. just want it confirmed.
Posted 13th Jul 2010 at 05:34
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welshpug!

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Post #25
not excessively so, especially with a fair sized rear ARB.

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Posted 13th Jul 2010 at 14:38
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