Astra-H VXR axle into Astra-G - My best chassis mod yet!

Hello all,

Thought I’d share the best chassis mod I’ve ever done to my car with you all. I’ve just fitted an Astra-H VXR rear axle to my Astra-G 2.2 Sri track car.

Why

More torsional rigidity (565 vs 260 NM/d), this vastly reduces understeer, same effect as fitting an extra RARB.

Less rear camber approx. ½ degree, = again less understeer

Less rear toe-in, approx. 6”, = improved turn in.

Bigger rear bush….. Improved ride comfort.

No real weight penalty vs fitting an extra RARB.


How

Really simple job, took me 2hrs going slowly, it’s probably easier than fitting an RARB! Firstly you’ll need to obtain an axle (beam) I got mine from eb&y for £50 & painted with hamerite.

To be certain it’s from a VXR it must have ident M9K (see photo), other Astra-H axles are not as stiff. I have all the engineering data if somebody wants a less stiff version and need numbers. See position of ident below, it's stamped and difficult to read.
upload_2016-4-12_18-42-48.png

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Obtain data points on each side to measure current axle alignment, I used masking tape and measured from the back of the wheel emblem.

upload_2016-4-12_18-39-7.png


Jack up car, put axle stands under sills. Remove rear wheels. remove shocks and springs.

Undo bolts for handbrake cable / brake pipes & ABS sensor harness brackets.

Undo the 4 nuts that hold the complete hub (Inc. Brakes) to the axle, place on suitable stand (bucket in my case)
upload_2016-4-12_18-47-26.png


Undo the 3 bolts each side of the underbody that attaches the axle to the car and remove the axle.
upload_2016-4-12_18-58-11.png


Fitting is the reverse, just make sure that your axle is in the same alignment as before otherwise your car will crab slightly. This can be a bit fiddly but you can adjust it without jacking and leaving the handbrake off.

upload_2016-4-12_18-54-55.png


The shock absorber mounting point is 15mm lower on the later axle so there will be less droop due to shock absorber lengths. The Bilstein B8’s I have fitted drive fine, but after speaking to Bilstein I’ve learned that the B6 version is internally valved as per the B8, but is 20mm longer so I’ll be fitting these soon.
upload_2016-4-12_18-52-42.png


The ride height is identical as the spring seat position is the same.

Results

Understeer massively reduced, back end comes into play much more. Be ready with the opposite lock when braking and lifting in the wet. I had a track day in the wet at Rockingham (probably the worst circuit for wet grip) and the oversteer was great to play with and not at all scary. I didn’t come close to spinning – the car was communicating brilliantly, it’s probably on a similar level to the 205 GTi I had many moons ago. In the dry it destroys the bends, much higher corner speed than before and still a little playful on the limit. Given I have no engine mods, I can’t believe some of the other cars that had to let me pass - Civic type R, BMW 130, Focus ST, Nissan 350Z all shamed by my humble Astra!

I still drive it daily and it’s much more comfortable over ruts & pot holes.

Cons

High speed stability is a reduced a little; it’s a bit more fidgety at motorway speeds.

Watch out for over-steer. I’ve changed the tyre pressures 34 front / 30 rear and now it’s much better for the road.

It's not adjustable - e.g. Whiteline sell an adjustable RARB.

Hope someone finds this useful.
 

evocarlos

Stupid Bollocks
Staff
had one laying about in the garden for some time never got round to fitting it :) october last year is the date on the pic
but then the mk4 setup with the whiteline camber shims and rarb make a big difference to the stock mk4 setup
have know about the difference for a while after chatting with jon at cs and Maverick at billing :)
WP_20151009_23_14_40_Pro (1).jpg
 

dewismotorsport

Senior Member
Car shouldn't feel fidgety at motorway speeds, I'd get the rear toe checked to see that the beam is straight and wasn't involved in a rear whack, I've driven both performance mk4 astra's and vxr's and neither ever felt fidgety at speed.

The original tolerances on the the astra beams aren't the greatest and often up to 2mm out toeing in from one side to another.

I'd get it checked on a laser aligner and adjust it suit.
 
@dewis, Beam is straight - hunter system shows...
LH toe-in 0°04', camber -1°07'
RH toe-in 0°08. camber -1°05
Thrust angle -0°02'
Driving back to back with standard axle it feels slightly more fidgety, in isolation it's fine and a trade off I'm happy with for now.
I expect the fidgety dynamics are more due to higher torsion rate of the beam when driving across uneven roads at speed especially when you factor in that a stripped out Astra-G 2.2 is much lighter (guess ~400Kg) than the Astra-H VXR.
I'll experiment with shims later to add some negative toe. Planning to make some full contact shims in aluminum so any advice greatly received.
 
patricks, specifically for rear axle?....get the lowest spec petrol Astra-H axle you can find. E.g. a 1.6 petrol version is still a bit stiffer than the your Astra-G version but the bush size is bigger therefore you'll enjoy a more compliant ride.
 

patricks

Regular Member
Project L850 thanks and no not specifically rear axle..anything really...i have driven a H it does transmit significantly less NVH (noise vibration harness) through the cabin than a G and i guess im chasing some of that refinement....however most automotive journalists here find the H not to be as sharp and as responsive handling as the G what are ur thoughts on that? Over here astra H not available in 1.6 guise tho 1.8 is and will that do? Your account is very interesting all the other cars that dont keep up with u are fitted with multilink independant rear ends.........
 

dewismotorsport

Senior Member
Well the beam sounds straight then as they are within the tolerances.

Might be down to it having increased torsion rate, are you sure it's double though? Seems a lot higher. The bushes on the astra g seem to break down badly, when I replaced mine for spherical bearings the old ones were really badly degraded and cracked so no doubt doing not a lot.

For track my rear beam is going to be set at -2 degrees camber and 3mm toe in, the reason for the extra toe in is so that I scrub the rear tyres slightly to help put heat in the rear tyres for races in the early laps.

Patricks, the overtaking and out performing the cars he listed is no doubt down to driver commitment. So track drivers have better cars but just not as good drivers or just don't push them to the limit. In a standard engine 2.2 coupe I have videos of me beating lotus exige s's and porsche boxsters, not because my car was better but I was just a lot more committed.
 

patricks

Regular Member
Well the beam sounds straight then as they are within the tolerances.

Patricks, the overtaking and out performing the cars he listed is no doubt down to driver commitment. So track drivers have better cars but just not as good drivers or just don't push them to the limit. In a standard engine 2.2 coupe I have videos of me beating lotus exige s's and porsche boxsters, not because my car was better but I was just a lot more committed.

Yep u must both sure be comitted then :). Here in Australia quite a while back i can recall the local touring car drivers actually preferring a live rear axle to independent ones because they said they offered better grip??? Multilinks etc exist more to improve ride on uneven surfaces not found on a race track so it doesnt really surprise me that a relatively unsophisticated design can keep up with and even beat the big boys toys. Congrats on your doing so!!!! How embarrassing for the guys driving the lotus lol. BTW had a 2001 porsche boxter as my wedding car - what a pile of crap it was - a toyota camry beat me at the lights with it lol
 
I'm somewhat commited, when your car cost just £490 you can afford to be so.;)

Dewis - Yep. 260NM/d vs 565NM/d. Tolerances are +/- 25NM/d (BTW your Coupe has the same rear axle as the GSi, this is 320NM/d...obviously without the extra RARB)
Interestingly the stiffest beam on the Astra-H platform is the twin top 1.9 d/ 2.0t version, @590NM/d. Couldn't find one at a breakers though.
Sounds like your rear end will be super stable with that set up. how are you measuring the 3mm toe-in? I'll start by splitting the difference between OEM settings and yours as I also daily drive my car so need to compromise with tyre wear. Was planning to polybush, would the bearings be too extreme for the road?

Particks - Astra-H 1.8 version rear axle is 370NM/d - this probably would make for a really nice road upgrade.. You could also fit the front wishbones from an Astra-H, but you'd loose some 'sharpness'....you can't have your cake and eat it with a passive chassis.
 

dewismotorsport

Senior Member
Wow that's a hell of a difference then. Tbh I may not need the rear arb as I plan to add 700lb rear springs (currently 400lb) as there too soft at the minute and I end up maxing out the damper settings to get it how I want.

I should imagine the spherical bearings will be a bit harsher on the road but not un liveable.

I used the laser supertracker at work to work out the rear toe and camber and I have eibach camber shims to fine tune it to what I want.
 
Sorry for confusion but is that 3mm across the rim, if so what size rims or is it the shim difference - so I can equate it to degree measurment.
Where are you sourcing your rear springs? I'm looking for some linear but all I can find are progressive which don't work too well with the shock.
 

patricks

Regular Member
Project L850 thanks again the rear beam swap is on my to do list - so i can expect improved ride and less understeer but with more oversteer at limit?? Is that a fair call?. I have stock set up and brand new shocks front and rear anything else i should be aware of? And sorry to be anal but my name is Patrick not "Patricks" it was an accidental typo when i joined the form lol hoping Matt will fix it for me please
 
Yep, fair call Patrick!
I expect that you'll still be on the safe understeer bias of nuetral, but if you often drive down hill corners in the wet and need to emergency brake I'd think twice about changing it....guess not in Oz!
 

dewismotorsport

Senior Member
This is the system I use
ai693.photobucket.com_albums_vv292_dewismotorsport_282B6FF0_68457b89f2a7ab1b465ca9216685bc82df.jpg
ai693.photobucket.com_albums_vv292_dewismotorsport_2799A1B1_971893a9a2676c6ef377e4265eca773287.jpg

Above figures are before adjustment, so it sits on 3 points of the rim (wheel size 18") and when reading the rear you have to remember the measurements are mirrored so on that scale above it reads +2.5mm toe out but because that's come from the opposite wheel it's actually -2.5mm if that makes sense. So my aim is to have both wheels at 3mm toe in (so not 1.5mm each wheel)
 
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Cool, looks like you were running toe-in 0°19' and are aiming for toe-in 0°23' that's not too crazy and just inside max values to OEM settings.
700 Ib springs on the rear is extreme though, that's 122N/mm in new money.
For reference OEM sport chassis springs are progressive 14 - 34 N/mm. So yours will be 4X max values.
Where are you sourcing the springs from? I need some linear rate that seat in the normal position.
 

patricks

Regular Member
Yep, fair call Patrick!
I expect that you'll still be on the safe understeer bias of nuetral, but if you often drive down hill corners in the wet and need to emergency brake I'd think twice about changing it....guess not in Oz!

Brilliant that's exactly what im after (y) .....suppose if i dont like it or find it too snappy at the back then i can put the old beam back in. I drive briskly but brake progressively well before grip is lost. I actually wrote off my first astra g 1.8 in the wet because the front end lost traction when changing lanes on the motorway - so a safer understeer is good news for me!
 

dewismotorsport

Senior Member
Should of said that the springs are on coilovers at the rear not on beam.

I'll be buying them through gaz as that's who make my coilovers. 700lb is high but not extreme, I know guys running over 1000lb springs :eek:
 
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