Project L850
Member
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.
Obtain data points on each side to measure current axle alignment, I used masking tape and measured from the back of the wheel emblem.
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)
Undo the 3 bolts each side of the underbody that attaches the axle to the car and remove the axle.
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.
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.
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.
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.
Obtain data points on each side to measure current axle alignment, I used masking tape and measured from the back of the wheel emblem.
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)
Undo the 3 bolts each side of the underbody that attaches the axle to the car and remove the axle.
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.
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.
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.