19 replies to this topic

[Bazcad]

Hey guys, Standard diff width on LX is 1440mm. I’m wanting to put 18x10” plus the widest tyres on the rear that I can fit without mini tub so my question is do you think it’s worth ordering a diff slightly shorter or just adjust the back space accordingly ??
Anything else you’ve come across regarding clearance issues other than shock and inner guard/boot clearance ?

Cheers Bazcad

[myss427]

Narrow the diff, will help with track.

[Heath]

Brake vs. shock can be a consideration as well, depending on rear brake selection. Commodore rear discs with banksia park brake is the main one people talk about - at least having to unbolt the caliper to remove the shock - not the end of the world.

 

And if you modify the lower shock mounts to make the shocks directly upright, the next thing that can touch is the inside of the wheel rim touching the upper seat for the rear spring (on the car's body, not on the diff). You can make this a bit better by taking a pie cut out of the side of the spring seat and beating it a bit flatter (so it doesn't draft out towards the bottom) and that will buy you another >5mm easily from memory.

 

Otherwise, you seem to have addressed the two main areas.

 

"Is it worth shortening the diff?"

If the car is unflared, absolutely.

If the car is flared, still yes. I shortened my diff (flared car) a modest amount and the extra dish you can run is just so fuc king goooooooood.

Edited by Heath, 20 April 2021 - 04:30 PM.

[Ando]

A lot of aftermarket wheels were made to suit the standard diff width for unflared or flared Torana's so why limit your options by shortening the diff.

Unless, your shortening the diff for a particular application, then go the custom made wheels to suit.

In my white flared SS, I had the 9" diff made to the standard Torana width. The rear wheels are 15x12 with 345 35 15 tyres.

That's about the limit you can go without tubbing. 

[Bazcad]

Jesus Christ Ando, that’s like God mode.
Any photos would be cool 👍🏼

Edited by Bazcad, 20 April 2021 - 07:09 PM.

[Bazcad]

Narrow the diff, will help with track.

[Bazcad]

Hey mate, any chance of some photos ? If that’s yours in the avatar picture - Wow 🤩 I’m going to do my 4 door in orange 👍🏼

Brake vs. shock can be a consideration as well, depending on rear brake selection. Commodore rear discs with banksia park brake is the main one people talk about - at least having to unbolt the caliper to remove the shock - not the end of the world.

And if you modify the lower shock mounts to make the shocks directly upright, the next thing that can touch is the inside of the wheel rim touching the upper seat for the rear spring (on the car's body, not on the diff). You can make this a bit better by taking a pie cut out of the side of the spring seat and beating it a bit flatter (so it doesn't draft out towards the bottom) and that will buy you another >5mm easily from memory.

Otherwise, you seem to have addressed the two main areas.

"Is it worth shortening the diff?"
If the car is unflared, absolutely.
If the car is flared, still yes. I shortened my diff (flared car) a modest amount and the extra dish you can run is just so fuc king goooooooood.

[Bazcad]

Gday Heath, thanks for the reply. What size wheels and tyres are you running and what amount of dish and back space do you have. I’m hoping to dummy mine up this week to get dimensions and looking at a Rodshop 9” with Wilwood discs.
Any photos ??

Edited by Bazcad, 20 April 2021 - 07:18 PM.

[dattoman]

I'd go with Karls advice

 

Give rims and tyres to diff guy...tell him to "conceal it"

 

[Bazcad]

Heh heh heh DOH

[Toranamat69]

Be careful with the legality of the offset of your rims if shortening the diff. With flares you might not get your wheels certified. When my 9 inch diff was certified, Max offset was 50:50 on a Ford 9" diff unless running full floating bearings.

M@

[Shtstr]

The width of the tyre is governed by the area they fit not the length of the diff. The offset of the rims are the only thing affected by the diff length.
Most cars run upto a 315 tyre without mini tubs and with a bit of effort 345 can be had.

[Bazcad]

I think the max is 25mm either side of centre to be engineered.
If it’s a deeper dish they need to go on the day after sign off.

[DanWA]

I think the max is 25mm either side of centre to be engineered.
If it’s a deeper dish they need to go on the day after sign off.

This is becoming an increasing problem leading towards stricter rules

 

You do something like that after sign off, sign off is essentially void

[Ando]

Jesus Christ Ando, that’s like God mode.
Any photos would be cool 👍🏼

 

 IMG_3541.JPG   267.63K   17 downloads

[Heath]

If you want off-the-shelf wheels (rather than custom, like mine) then what Ando has done is spot on. 

 

Gday Heath, thanks for the reply. What size wheels and tyres are you running and what amount of dish and back space do you have. I’m hoping to dummy mine up this week to get dimensions and looking at a Rodshop 9” with Wilwood discs.
Any photos ??

 

17x12" and they're a -36 offset. My tyres aren't huge because of my aesthetic preferences, but if I raise it to Ando's height I can fit 345's like him.

That size equates to a backspace of about 5". Ando's are probably more like 0 offset?

 

How much dish depends on the thickness of the centre, but fair to say a 12" wide wheel with -36 offset has a lot. Photos? N/A mate, gotta keep something up my sleeve lol.

Edited by Heath, 21 April 2021 - 12:56 PM.

[Redslur]

If you want to get real technical, then the maximum width a tyre can be is 30% bigger than the factory option. So an A9X has a 200mm tyre so that allows a 255 wide tyre as a maximum. That then determines the rim width. You then work out your maximum track increase of 25mm. So realistically any car with bigger is really not legal according to the NCOP. But engineers seem to sign off on anything nowadays.

Edited by Redslur, 22 April 2021 - 12:10 PM.

[Bigfella237]

Seeing as we've raised the NCOP... something else you need to consider is that, while you're allow to increase the track by 25mm, you aren't allowed to reduce your track measurement at all.

 

That means, if you shorten the diff to suit a particular set of wheels, you may not be legal with a smaller set of wheels, and certainly not legal with stock rims.

 

The upshot is if you get defected for the rear track measurement, you may find yourself needing to swap the entire diff out to get the canary cleared!

[claysummers]

Very true. Hang on to your original rear axle. Just put an LC diff under my FB ute with 235 60 on deep dish 14x7 steelies. Track is 10mm less than factory and it has to go over the pits for engine upgrade. Fingers crossed here. Worse case I will get the offsets modified and fit 225 tyres.

If it is dish you want then get your rims made to zero offset if that is maximum allowable. Then build diff accordingly. If you’re not that fussed about the dish then stock width rear is a safe bet, and build wheels to suit. Simples??


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[Bazcad]

Thanks for replies.
I’ve ordered standard width 3.5:1
Still making inquiries about rims and what markings if any as engineer won’t sign off without.