CDTI strut brace

[mahomes]

Hello all, just bought a astra cdti and coming to the 3000k first service. Great car and couldnt be happier!

I find the car seats dont hold you in place enough and the car does experience a bit of body roll.. does anyone think the same? Was thinking of getting a front strut brace to stiffen up the front a bit, what do you reckon and any experiences or where to get one in Aus?


Thanks!

[MatsHolden]

A strut brace won't really help with body roll on it's own. You need to look more at sway bars... Strut brace will stiffen up the chassis by a small margin, you probably wouldn't notice.

[digifish]

A strut brace won't really help with body roll on it's own. You need to look more at sway bars... Strut brace will stiffen up the chassis by a small margin, you probably wouldn't notice.

Agreed, the Astra has a very stiff chassis already.

Interesting you think it has a lot of body-roll, what were you driving before?

digifish

[mahomes]

a Satria GTI! We decided to upgrade to the astra thanks to the addition of a new family member and the diesel was a good compromise between a sports and family car within our budget :)

I may be incorrectly assuming its body roll - what happens is I get thrown around in the seat quite a bit going hard into and out of corners...

Wouldn't a strut brace help stiffen up the front, reducing the car leaning into corners too much?

Has anyone then done any suspension mods to combat this sort of thing? With sway bars, thought they intruded on boot space or am I wrong?

[digifish]

a Satria GTI! We decided to upgrade to the astra thanks to the addition of a new family member and the diesel was a good compromise between a sports and family car within our budget :)

I may be incorrectly assuming its body roll - what happens is I get thrown around in the seat quite a bit going hard into and out of corners...

Wouldn't a strut brace help stiffen up the front, reducing the car leaning into corners too much?


I'd say the problem is probably more a lack of lateral support in the front seats, the dynamics of the CDTi in sharp changes of direction are well controlled in my opinion. I can't say there's a lot of diving and rolling under hard cornering either. However I have never been in a Satria GTI so I can't comment on how the two would differ.

http://www.granatellimotorsports.com/images/artlr/GM-STB-0507-Sbsmall.jpg

...you realise the blue thing is a strut-brace? It's job is to make the front end more ridgid and so make the steering
more accurate/precise under hard cornering loads. As noted body roll is controlled by sway-bars and spring stiffness

digifish

[btm]

rear sway bar would be the way to go, they dont take up any room in the car

[mahomes]

thanks.. then with the rear swaybar two questions:
1. How else does the rear swaybar change the dynamics of the car.
2. Know of anyone in Aus that does them for the 2006 astra cdti?

Thanks!

[btm]

www.whiteline.com.au

[btm]

this is the actual part https://www.whiteline.com.au/store/default.asp?part=BHR75

[mahomes]

had a look at whiteline..

the part you mentioned is for an "Astra TS Mk4 99-04 inc SRi Turbo".. will check with them compatability with the Astra H 06 models.. thanks for all your help.

[btm]

their website says its the same part number for both the TS and AH... may want to double check that though

[cbrmale]

The CDTi has stiffened suspension compared to standard Astras, but there are probably two problems with this model. One is the seats: the leather seats of the SRi have more side bolstering and certainly hold the driver in place well. The second is the engine weight, compared to a petrol-engined Astras there is (I think) more than 70kg of extra weight hanging forward of the front axle, which must affect the handling. Indeed, road tests state this to be the case.

Another issue with the Astra is that it is a short and upright sort of car, and sitting higher you sense any body roll a lot more than lower-slung cars, although I would never say that an Astra rolls that much! My SRi 2.2 has just done 4,000km, and what I did was take it along my favourite winding roads, pushing it harder and harder until I got a sense of how it behaved close to the limit. I chuck it around quite happily now, but remember I am tied down by the better seats.

A stiffer rear anti-roll bar will make a car understeer more, everything else being equal. A stiffer front anti-roll bar will reduce understeer and potentially increase oversteer. However, the CDTi has ESP, which should control understeer / oversteer transitions. However, tuning suspensions needs a more scientific approach than bunging on this or that.

If I had a diesel, I would probably think about better front seats and probably SRi-like 17" or 18" wheels with low-profile tyres (less tyre sidewall flex) rather than playing around with a suspension that is already very well set-up out of the box.

[EL BURITO]

AH sway bar dose exist thou cos I was a member on here that they used his car to design it.

[bornwild]

The Astra, especially the CDTi, has probably the stiffest chassis of any little hatch...ever, maybe the Focus has a stiffer one.

The problem lies elsewhere. To experience body-roll in an Astra you'd have to be driving a Touring Car Series with it.

[bornwild]

Guys, a strut-brace is more cosmetic....it don't really help.....at all....lawl :D

[shoey85]

i would be more incclined to change the springs, shocks and wheels b4 even thinking strut brace or sway bars, maybe even coil overs. as for the body role i must say that the cdti has alot less than the vectra c, imho i think the cdti handles well but could however be better.

[JR]

a strut brace is NOT going to reduce body roll. it does definately reduce the body flex upfront - hence ur steering n turn response is sharp.

u want to reduce body roll - get stiffer suspension n get swaybars.
definately get a rear swaybar.
a front swaybar won't do much for a FWD car. according to the experts that is - not me.

i've had both rear swaybar & front strut brace fitted - n trust me, it makes a huge difference.
even my mates have noticed. then again, its up to u.

.

[digifish]

Ok I did some experimenting on the way home from work last night...

It's not body roll, the Astra stays very flat (for a road car) when you chuck it about.

It's the lack of seat support. The seats are fairly hard and will relatively small bolsters. This causes you to roll about on-top of the seat

It's the relatively high seating position, this magnifies what body roll there is.

As a first step I'd suggest making sure the seat is as low as you can use and you tilt the back as far back as you can comfortably go. Perhaps experiment by getting someone to wedge towels and foam in and around the bolsters and see what you think.

digifish

[Alix]

Ok I did some experimenting on the way home from work last night...

It's not body roll, the Astra stays very flat (for a road car) when you chuck it about.

I admire your commitment to helping others digifish. Very commendable! :D

I too have noticed the lack of bolster support in my CDTi when taking corners whilst, er, um, simultaneously attempting to conserve forward momentum. I find the seats are quite comfortable to sit on (not "in") on long trips, but they're not sports seats by any stretch of the imagination.

[digifish]

I admire your commitment to helping others digifish. Very commendable! :D

I too have noticed the lack of bolster support in my CDTi when taking corners whilst, er, um, simultaneously attempting to conserve forward momentum. I find the seats are quite comfortable to sit on (not "in") on long trips, but they're not sports seats by any stretch of the imagination.

Well, as I was on my way home from work anyway :)

I agree they are particularly suited to long trips, thraputic even

digifish

[blueraven]

The problem lies elsewhere. To experience body-roll in an Astra you'd have to be driving a Touring Car Series with it.

thats funny, when i had one as a loan car i must have been driving in a touring car series on the way to work each day, because there was about as much roll as my astra when it was stock.

Get a rear sway bar, you will be amazed. best mod for the money as far as handling goes.

[digifish]

thats funny, when i had one as a loan car i must have been driving in a touring car series on the way to work each day, because there was about as much roll as my astra when it was stock.

Were you in the CDTi or SRi?

digifish

[bornwild]

thats funny, when i had one as a loan car i must have been driving in a touring car series on the way to work each day, because there was about as much roll as my astra when it was stock.

Get a rear sway bar, you will be amazed. best mod for the money as far as handling goes.

A lot of people mistake simple things such as not enough grip, bad seats and understeer as body roll.

[bornwild]

I say get some better seats and bigger rims if you're serious about your driving.

[blueraven]

A lot of people mistake simple things such as not enough grip, bad seats and understeer as body roll.

Yes, alot of people do. But the astra G seats are no more supportive than the H's (probably less) and i know understeer all too well. It has body roll, not as much as something like a corolla or mazda 3, but it has some nonetheless.


I say get some better seats and bigger rims if you're serious about your driving.


Or spend ~$200 on a tried and tested method of removing body roll by fitting a rear swaybar. Do a search and you will see just how impressed all of us are with them on our astra G's. If you do one handling mod, this is it.

[bornwild]

The anti-roll bar will most definitely help....But I still reckon the largest problem for his driving(and most noticeable) is that the wheels are small and his seats unsupportive. Even if he got the anti-roll bar he would still come back to this forum and complain about 'body-roll'. Get me?

Also, if purchasing an anti-roll bar, make sure you get the right one. You don't wanna completely screw up your cars handling. The anti-roll bar transmits bumps from one side to the other, in other words, it magnifies them.

[MatsHolden]

i would be more incclined to change the springs, shocks and wheels b4 even thinking strut brace or sway bars, maybe even coil overs. as for the body role i must say that the cdti has alot less than the vectra c, imho i think the cdti handles well but could however be better.

You'd be surprised as how Astra's and Corsa's respond to sway bars, even with stock suspension.

[mahomes]

I'm beginning to be inclined towards the seats as the main problem as well! though I agree, some sort of suspension mods would probably help but with the seats the way they are..

I'm only coming on to 3k on the clock now (and most of that is the Mrs) so will keep driving for the next few k and then should understand the car a bit better!

Not gonna purchase anything yet! Saving up for a green box first :)

Edit: Forgot to add.. played around a bit with tyre pressure.. looks like from holden they came 36 front and 36 back, dropped the back to 32 and kept the front at 36.. seems to have helped a little

[cbrmale]

More tyre pressure front to rear helping seems to point as the extra forward weight bias of the turbo-diesel engine being part of your problem. What you are doing is building in some oversteer, which makes the weight-driven understeer seem less. Remember if you fit a stiffer rear anti-roll bar, this will reverse the equation, reducing oversteer and increasing understeer. If this works with a petrol-engined G-model Astra, it doesn't mean it is going to work with yours.

I've only test-driven a standard Astra, but I remember the seats were not well bolstered compared to the car I had at the time, and much less bolstered than the leather seats in my SRi. I can build very high levels of g-force in mine, and toss it into momentary oversteer in the tight stuff if I want, and never feel uncomfortable about its handing.

For you I still recommend better seats and bigger wheels with wider low-profile tyres.

[digifish]

Edit: Forgot to add.. played around a bit with tyre pressure.. looks like from holden they came 36 front and 36 back, dropped the back to 32 and kept the front at 36.. seems to have helped a little

If you are chucking it around I'd be more like 38-40 front, 34-38 back.

digifish

[mahomes]

Will give 38 front and 34 back a try.. maximum permitted tyre pressure (as shown on the tyre) is 40 so 38 sounds good!

By the way, this was my first post on this forum.. great forum and very helpful.. thanks :angel:

[bornwild]

For you I still recommend better seats and bigger wheels with wider low-profile tyres.

This man speaketh the truth. If you drive safely(fast but with brains) you won't reach the point where you need the ARbar.

[GreyRex]

This man speaketh the truth. If you drive safely(fast but with brains) you won't reach the point where you need the ARbar.

I'd have to disagree just a little. The Barina SRi that I had didn't come with one. I put one on. It's not necessarily about reaching the point where you need one, it's the general security of knowing it's there. A definate must in my opinion. The dollars you spend for the improvement you get is worth it in my opinion... and others as well

[bornwild]

Does anyone know whether fitting a car with an aftermarket ARbar is legal? ARbar's can be very dangerous if not set up properly!

[JR]

Does anyone know whether fitting a car with an aftermarket ARbar is legal? ARbar's can be very dangerous if not set up properly!

gosh...u really got something against swaybars huh?

anywayz.....
u can put wider lower profile tyres, but how does that reduce body roll? the car will have a bigger footprint, but the dynamics of ur suspension does not change.

better bolstered seats will help reduce the "feeling" of body roll, but ur car will still have the same body roll

lower springs will help reduce the body roll - yup.

i can go through and explain the technical aspects of how a swaybar works - but i won't. many here have already said how much better their car improved.

.

[bornwild]

gosh...u really got something against swaybars huh?

I just think it's useless and quite frankly a bit dangerous if you're not going to do track days. It also worsens the ride softness as all the shock from one end is also transferred to the other...if not set up properly.

[cbrmale]

gosh...u really got something against swaybars huh?

anywayz.....
u can put wider lower profile tyres, but how does that reduce body roll? the car will have a bigger footprint, but the dynamics of ur suspension does not change.

better bolstered seats will help reduce the "feeling" of body roll, but ur car will still have the same body roll

lower springs will help reduce the body roll - yup.

i can go through and explain the technical aspects of how a swaybar works - but i won't. many here have already said how much better their car improved.

.

The CDTi comes with lowered 'sports suspension' as does my SRi. The sports suspension on my SRi is stiff to the point of being uncomfortable and keeps the car amazingly flat and enables me to generate surprising levels of grip, especially on fast sweeping bends. Both cars also have ESP, which means you can't get it into understeer or oversteer unless you are really, really silly.

The diesel CDTi doesn't handle as well as the SRi, because it has 16" wheels and narrow high-profile tyres, and the engine is heavier, giving it too much forward weight bias.

For both cars the stock stiff suspension does not need extra roll-stiffening, indeed it might get close to being undriveable at slower speeds around town. But the diesel certainly needs bigger wheels and better tyres to make use of the suspension's potential. And as others have pointed out, the standard Astra seats (which are fitted to the diesel but not the SRi), don't hold the driver in place, allowing him or her to flop around the cabin resorting to hold the steering wheel for support.

[digifish]

The diesel CDTi doesn't handle as well as the SRi, because it has 16" wheels and narrow high-profile tyres, and the engine is heavier, giving it too much forward weight bias.

Hang on, let's get some real here...the 205/55 R16 tires are not 'narrow' or 'high profile', particularly on a car this size.

http://intelligence.goauto.com.au/mellor/mellor.nsf/story2/CD0BB3F77C5B6E60CA25718C001569FA/$file/aaa.jpg

digifish

[J]

Does anyone know whether fitting a car with an aftermarket ARbar is legal? ARbar's can be very dangerous if not set up properly!


I just think it's useless and quite frankly a bit dangerous if you're not going to do track days. It also worsens the ride softness as all the shock from one end is also transferred to the other...if not set up properly.

As Mizled_SRi and JR had already said, I am not sure why you are so against swaybars/anti-roll bars...

Dangerous if it's not for track days? I had not merely upgraded, but added a rear swaybar on my old Magna, which is a heavier car to start off with, and just as nose-heavy, if not more, than a diesel Astra (thanks to the big 2.6 cast iron four!). I only do spirited street driving. The result? It stays way flatter through corners, because that is what swaybars/anti-roll bars are designed to do: to counter lateral weight transfer (correct me if I am wrong about this), thus reducing body roll, and raising the cornering grip threshold of the vehicle. They are even named anti-roll bars for that reason! Less sideways lean at the same cornering speed and steering angle, means you probably won't need the extra seat bolstering! Ride could suffer a bit, but should be nowhere near as much as lowering the car beyond the optimum ride height. The reduced suspension travel works great if we only travel on smooth roads, but reality is quite different...

Wider and lower profile tyres can help, but as it is already on 55 series tyres, there isn't a drastic amount of sidewall flex to start off with.

Not set up properly? Then find a mechanic or suspension specialist who knows what they are doing :)

Legality issues? I included it as part of my insurance policy with the NRMA. No questions asked. No premium raised :)

At the end of the day, we all have our limited (?) and/or biased (?) opinions. Throw the question to the experts at Whiteline (www.suspensionparts.info) and see what they say. All I know is: I followed their advice, and discovered what my old car was truly capable of :) Imagine a new Astra!! :D

[bornwild]

Mate, you need to get the bigger picture here. It's easy to go into something and just say "yeap needs an ARbar".

I'm telling you from a Mechanical Engineer's point of view, that the anti-roll bar will probably cause you as much headaches as it will help you out.

As for this,

Less sideways lean at the same cornering speed and steering angle, means you probably won't need the extra seat bolstering!
Only if your arse is welded to the chassis you won't need extra seat bolstering :). He'll be flying around in his car no matter how flat the car goes through a corner if he don't have proper seats.

[bornwild]

Hello all, just bought a astra cdti and coming to the 3000k first service. Great car and couldnt be happier!

I find the car seats dont hold you in place enough and the car does experience a bit of body roll.. does anyone think the same? Was thinking of getting a front strut brace to stiffen up the front a bit, what do you reckon and any experiences or where to get one in Aus?


Thanks!

Couple of questions for you mahomes:
-What kind of driving do you do?...City traffic? Freeway?
-Track days?
-What's the average speed?
-Through how many sets of front tires do you go annually?

[mahomes]

bornwild.. driving is a mixture of highway and suburbs.
No track days
I usually stick to the speed limit but enjoy the occasional hard driving around corners etc.. (which is when I get thrown about).
How many tyres do I go through annually? Well, in the Proton we had the car for 5 years and only changed the tyres once.

The car is new and so I dont want to buy new seats or spend large dollars yet on new shocks, tyres etc. I tend to replace parts with better ones when they're due for replacement (I dont change cars often!) Thats why I thought of the strut brace as being a relative cheap suspension mod which wouldnt affect things too much but thought it might help a little. I'm amazed at how much the tyre pressure change has helped. Am still looking for a strut brace though. Whiteline doesnt stock one and I know they're a bit harder to find for the diesels. Even if the strut brace doesnt help at least it will improve steering response and I'd still be happy!

[cbrmale]

J - a soft Magna is a bit different to an Astra with sports suspension! Suspension set-up 101, increase rear roll stiffness and the car will have more rear-end grip and therefore understeer more. Increase front roll stiffness and the car will have more front-end grip and therefore oversteer more. My previous car was quite fun: although it was a front-wheel-drive it didn't have much rear roll-stiffness and I used to toss it into oversteer to generate extra front-end grip. A front-wheel-drive with natural oversteer.

Astras have struts at the front, which mean lots of positive camber for the outside front wheel when cornering. Astras have what is known as a torque-tube (or twist-beam) rear suspension, which is a lot different to the strut rear end of a Magna. The torque-tube between the trailing arms has a lot of roll-stiffness, and this is augmented by a small anti-roll bar. I honestly don't know the impact of a heaver rear anti-roll bar on a Astra, and I don't think we can extrapolate a different make and model to find out.

The only thing I can say for certain is that my SRi has sports suspension like a CDTi but with a lighter petrol engine, and it has wider low-profile tyres along with leather seats . My SRi package has very sure-footed handling, and if there is one fault it possibly has too much steering response! It can actually be a bit tricky cornering on rough roads, although you get used to always having both hands on the wheel and being milimetre-precise. This seems quite different to Mahomes, who wants to improve the steering response on his car amongst other things.

[JR]

Mate, you need to get the bigger picture here. It's easy to go into something and just say "yeap needs an ARbar".

I'm telling you from a Mechanical Engineer's point of view, that the anti-roll bar will probably cause you as much headaches as it will help you out.

As for this,

Only if your arse is welded to the chassis you won't need extra seat bolstering :). He'll be flying around in his car no matter how flat the car goes through a corner if he don't have proper seats.

i give up :boohoo:

.