XB4 +2 rear suspension holders
 

I've picked up the two +2 rear lower suspension holders today from MB Models.
363311 and 363321. They are shown below compared to the regular kit rear ones.

http://courgette.jml.net/~neal/RC/IMAG1252_t.jpg

I've modified (Dremel) the kit RR holder to allow it to be mounted directly to the chassis, as i'd already removed the plastic rear section of the chassis for the ralls racing under-gearbox weight. I ran the car with the dropped gearbox and modified kit hangers on my slippy and it was excellent. Really helped lock in the rear of the car.

I've now got the new optional +2 hangers and they raise the mount points higher/closer to the outdrive by 2mm. really hoping this helps to lock in the rear end more on the slippy stuff with the dripped gearbox. Testing Sunday, will feedback. Anyone else done this yet?

I'd done the same as you in the past, but ordered the +2 hangers yesterday morning. Hoping they'll help rear traction at Worksop next weekend.
Fingers crossed

I got my hangers yesterday, going to run them at worksop and storm valley

Hmm, loose as a goose today with them on... Certainly didn't do the magic that I thought best part of £40 would ;-)
Ran with the dropped gearbox, centre insert, lower inner show tower, outside hub hole. I went to 4 deg caster and 1 deg anti squat, as well as moving to lower outer ralls racing tower hole, which helped a little. far looser than it was previously however? this is meant to be the xb4 low traction mod?

What effect on roll centre does this mod have? If moving the top ball down raises the roll centre, does moving the bottom pin up lower it?
With moving the gearbox down, and the wishbone pivot location up, do you need to move the top link up a bit also?

Does it actually move the wishbone pivot up above standard or does it just keep in in the stock position when the gearbox is lowered? And moving the pin up raises the roll Centre

I'm a bit confused, as when the gearbox is lowered (the instructions tell you to remove the 2mm plastic plate when the +2 hangers are used) and the +2 hangers are used, is there any difference apart from lowering the camber link? Or is that the idea?

Raising the pins 2mm will raise the roll-centre quite a lot, so will make the rear loose through the corners.

For maximum rear traction you'd want to lower the diff and lower the pins (sounds like that's how you had it before?). Lowering the diff will give more rear traction on the power due to the extra angle on the driveshafts (it works a bit like anti-squat).

the confusing bit is in the instructions for the kit, it states 'THE +2 HANGERS MUST BE USED WITH THE CHASSIS PLATE REMOVED', thus the rear wishbones mounted at the same height as with the kit hangers. this would mean the gearbox was lower, but wouldn't you want the gearbox raised for low grip?

hmm, the car was good when I ran it with the rear chassis plate off, and the hacked kit hangers.

I'm just therefore now confused as to why xray have released these parts which are meant to be for low traction, and they do the exact opposite of what's intended?

These +2 hangers are standard on the 2wd car, and optional upgrades for the xb4 in low traction.

I thought anti-squat was for forward drive, and reduced side bite. Therefore if the rear is loose, reducing anti-squat helps get more side bite, and helps lock the rear rotation. Please correct me if I'm wrong. When I've wanted more rear end grip I've always reduced the anti-squat and its helped (i'm taking on 2wd cars).

you are correct, as far as i'm aware. also a good point, raising the hinge pins +2 is what you'd do for high grip. confused. hopefully dale can explain with his f1 knowledge?!!

Less anti squat gives more side traction in corners and more rear traction for slick or bumpy surfaces, increasing anti squat gives less side traction in corners and more rear lift in jumps

Heres a reply from RC Disco

"when you cut/remove the rear part under the rear gearbox mate. If you then use the +2mm hangers - it re-positions the rear wishbones in the same place as they were before (ie with the 'insert' in place under the gearbox). It does however move the rear top link in relationship to the wishbones (moved them 2mm close together) - which gives you a bit more rear grip / less steering"

It doesn't! The back end was loose as a goose.
Has anyone else tried them? I'm interested to hear the feedback when someone else tries.

The way I see it is that you lower the roll Centre when you remove the rear plate, that should give more grip, you then move the roll Centre back up with the +2 hangers putting the roll Centre back where it was reducing it again , the distance between the pivot points is irrelevant

lowering gear box = give more grip (low traction)
if you use +2mm hangers with lower gear box (arms come back on sandard height, but you have more rear grip through the lowering gear box it's the reason xray say's for low grip)
if you want even more grip: you use standard hangers with the lower gear box (lowering inner hinge pin give more grip)

No that's wrong, the distance between will effect the roll Centre it's just the +2 blocks are moving it the wrong way

I'm wondering if these new +2 hangers only work with the new wishbones in low grip? may also be needed to make the hangers effective?

I'd expect them to each do something on their own, not requiring the other. I'll get the new wishbones when in stock, but the xray xb4 2014 spec sheet webpage still offers conflicting information as to which, arms forward or back, is suited to low traction.

I thought the only difference on the wishbones was wheelbase and the fact you can mount the shocks front and rear?

apparently the rear hubs are different (offset) and the rear geometry is different to the original xb4, so the rolls centres / characteristics don't bear too much resemblance to the original.