Jump to content


Tubbed LC backspace and offset calculation

Started by _ls1lj_ , Jan 14 2011 04:24 AM

  • Please log in to reply
18 replies to this topic

#1 _ls1lj_

_ls1lj_
  • Guests

Posted 14 January 2011 - 04:24 AM

Took a few quick measurements of the LC today and here is what i came up with:

Can someone confirm that i have used the correct terminology/measurement of the following:
Rim width - distance betweenthe inner lips of the rim, not including the rim lip.
Offset - distance from the mounting face to the centre of the rim (+ for wider,- forcloser to the car)
Backspace - distance from the mounting face to the outside of the back lipof the rim


Front
16 inch VR Mag, 7 inch wide running 225/50/16
No offset stamped on rim
Backspace was measured to be 139mm or roughly 5.5in
Offset = 139mm - half rim width = 37mm or 1.5in?????

Rear
My 9inch diff is faily short and has competion studs installed to suit welds so i couldn't fit up any rims to trial fit. In the end i knocked out the metal cups from some calais alloy rims so they would fit.

Calais 16 x 6in wide
Offset P43
Backspace 132

However i needed 22mm of wheel spacers to get clearance between the back of the rim and the tub so
Required backspace is 132-22=110 minimum

Then to find out how wide i could go i added 35mm of spacers to the previous 22mm but i still had 70mm of clearance to the inside of the guard. so a 10 inch rim will fit but i will run a 9 for clearance.

What offset do Weld rims have? was thinking of getting drag lites

I don't have a panhard bar yet but intend to fit one so that the diff can be centred and reduce diff movement

Does this all sound ok ?

Is there anyone in Darwin that has some welds that they can lend me for a trial fitment.

Cheers
Ben

Edited by ls1lj, 14 January 2011 - 04:28 AM.

#2 rexy

rexy

    Lotsa Posts!

  • Members
  • PipPipPipPipPipPip
  • 3,715 posts
  • Name:Rexy
  • Location:Melbourne
  • Car:Kia grand carnival!!!
  • Joined: 03-November 09

Posted 15 January 2011 - 03:20 PM

Is your LJ tubbed to the rail edge? Mine is and 15 x 8 draglites are beautifully centered in the wheel tub. If you can measure the width off your diff from brake bolt up face side to side that will help compare offsets. I will try to measure the width of mine and post it up for comparison as well as the backspace of the welds and convos that fit ok on it.

#3 rexy

rexy

    Lotsa Posts!

  • Members
  • PipPipPipPipPipPip
  • 3,715 posts
  • Name:Rexy
  • Location:Melbourne
  • Car:Kia grand carnival!!!
  • Joined: 03-November 09

Posted 15 January 2011 - 03:53 PM

The nine inch measures 1238 mm from BUF to BUF. On this the 15x8 draglites with 4.5 inch backspace are central. It currently has 15 x 8.5 convo pros on it with 5 inch backspace running 275/50/15 MT ET streets that fit without rubbing They are pretty close though and did require minor massaging of the lower rear edge of the standard wheel opening to fit. I dont have stretched wheel openings.

#4 _ls1lj_

_ls1lj_
  • Guests

Posted 15 January 2011 - 08:51 PM

Thanks alot Rexy

Was looking through some old photo�s and the car has had 28.0/9.0/15 MT slicks fitted before just to push around the workshop. No idea of the backspace or rim width though. The MT�s only just fitted by a bee�s dick with that combo, but the top of the rim was about level with the guard. So a 26in diameter combo should be ok at that ride height.



The car is tubbed to the horizontal part of the rail maybe just a bit further (ie it does not go all the way back to the horizontal part of the chassis rail).



Quickly ran a tape across the diff and I got 1190mm BUF to BUF so about an inch shorter each side than yours.



So if yours tubs are similar and fit a 4.0 or a 4.5in backspace then I should be able to fit a 3.0 or 3.5 inch backspace.



This is a good sign as it will have nice dish and i was worried that the backspace was going to be shorter than 3.5 = expensive custom rims.



Do any of the welds or convos have any offset?



I will upload some photo�s shortly.



Cheers

Ben


#5 _ls1lj_

_ls1lj_
  • Guests

Posted 15 January 2011 - 09:18 PM

Few Photo's

Posted Image

Posted Image

Posted Image

Posted Image

Posted Image
Posted Image

Posted Image

Edited by ls1lj, 15 January 2011 - 09:20 PM.

#6 _bunkerjest_

_bunkerjest_
  • Guests

Posted 16 January 2011 - 12:03 PM

no real input from me apart from saying that green car is NIIIICCCEEEE

#7 rexy

rexy

    Lotsa Posts!

  • Members
  • PipPipPipPipPipPip
  • 3,715 posts
  • Name:Rexy
  • Location:Melbourne
  • Car:Kia grand carnival!!!
  • Joined: 03-November 09

Posted 16 January 2011 - 04:41 PM

Your tubs look pretty close to mine in the LJ. I imagine you will have the same problem I do which is the outer front and especially back edge of the arch get in the way of a big tyre. I ended up gently massaging the back edge of mine to get things to fit.

#8 rexy

rexy

    Lotsa Posts!

  • Members
  • PipPipPipPipPipPip
  • 3,715 posts
  • Name:Rexy
  • Location:Melbourne
  • Car:Kia grand carnival!!!
  • Joined: 03-November 09

Posted 19 January 2011 - 03:50 PM

Pics.
The main car pic has the same 15x8.5 rim with 5 inch backspace but with 235/60/15 ET streets on it . All the others are with the 275/50/15s.

Attached Files


#9 rexy

rexy

    Lotsa Posts!

  • Members
  • PipPipPipPipPipPip
  • 3,715 posts
  • Name:Rexy
  • Location:Melbourne
  • Car:Kia grand carnival!!!
  • Joined: 03-November 09

Posted 19 January 2011 - 04:33 PM

A few more.

Attached Files


#10 _ls1lj_

_ls1lj_
  • Guests

Posted 19 January 2011 - 10:32 PM

That looks pretty tough :spoton: and thanks for the pics.
Is that a UFO hovering in your driveway in the first picture of the last post LOL!

I was hoping to get a 9inch weld draglite rim on the back but the only 9 you can get is special order from the states and only comes in 4.75 backspace so will have to settle for a 8inch rim on the back, 7inch on the front. I still want to get some to trail to be sure, but no luck as yet on finding any.

I also haven't measured both sides to make sure the diff is centred so might have a go at that tomorrow.

I think i will start looking for some tyre options for 275/50/15 on the back and 225/50/15 on the front
Going to have a play around with ratios to see if i can get the rolling diameter a bit closer and also see what i can fit with a set of 17s later on when the bank balance recovers a bit.

#11 rexy

rexy

    Lotsa Posts!

  • Members
  • PipPipPipPipPipPip
  • 3,715 posts
  • Name:Rexy
  • Location:Melbourne
  • Car:Kia grand carnival!!!
  • Joined: 03-November 09

Posted 20 January 2011 - 11:18 AM

The martians are landing everywhere... even my yard.
It goes pretty good with its LS1/ T350/ 3800rpm converter.
That 9 inch rim with the 4.75 backspace might be ok if you end up going to a slightly wider ventilated rear disc setup from your current commodore solids. You're right though to want to trial fit stuff first if you can - its always suprising how things actually fit c/w how they measure.

#12 _ls1lj_

_ls1lj_
  • Guests

Posted 20 January 2011 - 12:11 PM

The martians are landing everywhere... even my yard.
It goes pretty good with its LS1/ T350/ 3800rpm converter.
That 9 inch rim with the 4.75 backspace might be ok if you end up going to a slightly wider ventilated rear disc setup from your current commodore solids. You're right though to want to trial fit stuff first if you can - its always suprising how things actually fit c/w how they measure.


My DBA 020 slotted VN Clubbsport rear vented dics turned up yesterday and i have a set of R32 rear callipers to refurbish and go on. However my BUF to BUF will still be the same so should be no effect on backspace?

Do you have a build thred? *madly searches members projects*

That combo will be a weapon, I have apporval to do the same, but the 350 chev came with the car so will get it registed with that first then change to ls2/3 later on.

#13 rexy

rexy

    Lotsa Posts!

  • Members
  • PipPipPipPipPipPip
  • 3,715 posts
  • Name:Rexy
  • Location:Melbourne
  • Car:Kia grand carnival!!!
  • Joined: 03-November 09

Posted 21 January 2011 - 06:25 PM

And for no good reason a few more. I took these today hoping to show the closeness of tyre to rear of arch and the reshaping involved but dont think I succeded. Engine shot s merely for pose value. All have the 275/50/15s in them.

Attached Files


#14 _ls1lj_

_ls1lj_
  • Guests

Posted 23 January 2011 - 04:16 PM

Thanks for the info and pics so far, but have a few more Q for you....
Did you have to modify the rear part of the arch below the line in the body ie in the blackout section as this would be ok for me.
If you used Mcdonald bros adustable upper and lower arms to bring the diff forward slightly, do you think you could get enough clearance then without mods?

I measured the BUF back to the chassis rail and i got 120mm so the maximum backspace i could probably run is 4 inches if you take into account the ballon of the tyre.

Also do you think that the new flame tread pattern would be better and how do your M/T's perform when attacking corners agressively? Are they ok or fairly useless, unless you are a straight line junkie?

Your LS1 looks pretty neat with the hidden wiring. Do you run all of the standard LS1 accesories without modification inclding A/C? Also what sump and did it need mods?




#15 rexy

rexy

    Lotsa Posts!

  • Members
  • PipPipPipPipPipPip
  • 3,715 posts
  • Name:Rexy
  • Location:Melbourne
  • Car:Kia grand carnival!!!
  • Joined: 03-November 09

Posted 24 January 2011 - 06:41 PM

The rear arch mods are the result of gentle hammer reshaping and if its paint without bog it should move OK. The vast majority of the shift is in the black painted area on your car so would be an easy paint touch up. Your other choices are to cut the rear of the arch away which I couldnt bring myself to do or to go the whole hog and stretch the guard opening - lots of repainting needed then!

I doubt the adjustable arms would be a practical solution. I suspect you would need to come too far forward to be practical and by that point would have run into the front of the wheel arch anyway.

I will try to measure the BUF to inner tub when I get a chance and let you know what it is.

While I am predominantly a straight line man I have had the ET streets on a few cars and its fair to say they are much better than the midrange rubber of the same size they replaced. I am not sure how they compare to high end track style stuff. On the LJ they replaced 245/50/15 revenger GTs and are light years better in dry grip, wet grip and lateral grip. The 235/60/15 are on the LX and are overall much better than the rags they replaced for sure - only marginally less straight line grip too.

I run the engine without PS or AC pumps.

The sump is a commodore one which was cut into a million pieces and reassembled to fit.
I like the minimal engine look . Might look at a shiny inlet manifold at some stage.
R





#16 rexy

rexy

    Lotsa Posts!

  • Members
  • PipPipPipPipPipPip
  • 3,715 posts
  • Name:Rexy
  • Location:Melbourne
  • Car:Kia grand carnival!!!
  • Joined: 03-November 09

Posted 30 January 2011 - 03:42 PM

Measured the BUF back to the closest part of the tub and got 155mm. Hence the 5 inch backspace + balloon of tyre bag with a 275 fits ok.
Found anyone able to lend you a few trial rims and tyres yet?
I would happily lend you mine if you were local.
R

#17 _ls1lj_

_ls1lj_
  • Guests

Posted 05 February 2011 - 09:36 PM

Na never managed to find a set that would be representative/useful.

Decided on Weld centrline rims and ordered from vpw today:
15x7 with 5.5inch backspace for the front
15x8 with 3.5inch backspace for the back

M/T Sportsman S/R (Flame pattern) Tyres
26x8x15 front
26x10x15 rear - i think i can fit 26x12x15 but don't want to find out the hard way that they dont fit.

However i thought the rims were available in commodore stud pattern, but are not so will have to get my conversion hubs for the front drilled to HQ/Chev when i fit my new brakes.

#18 _Crosso123_

_Crosso123_
  • Guests

Posted 06 October 2020 - 08:44 PM


The nine inch measures 1238 mm from BUF to BUF. On this the 15x8 draglites with 4.5 inch backspace are central. It currently has 15 x 8.5 convo pros on it with 5 inch backspace running 275/50/15 MT ET streets that fit without rubbing They are pretty close though and did require minor massaging of the lower rear edge of the standard wheel opening to fit. I dont have stretched wheel openings.



Old post but trying to work out mine pretty sure my 9inch is 1238

Looking at running 15/8 3.5 bs will I have to shorten the diff and how will the track be affected trying to keep it working the 25mm

Na never managed to find a set that would be representative/useful.

Decided on Weld centrline rims and ordered from vpw today:
15x7 with 5.5inch backspace for the front
15x8 with 3.5inch backspace for the back

M/T Sportsman S/R (Flame pattern) Tyres
26x8x15 front
26x10x15 rear - i think i can fit 26x12x15 but don't want to find out the hard way that they dont fit.

However i thought the rims were available in commodore stud pattern, but are not so will have to get my conversion hubs for the front drilled to HQ/Chev when i fit my new brakes.



Did u have to short ur diff ? From the 1238

#19 rexy

rexy

    Lotsa Posts!

  • Members
  • PipPipPipPipPipPip
  • 3,715 posts
  • Name:Rexy
  • Location:Melbourne
  • Car:Kia grand carnival!!!
  • Joined: 03-November 09

Posted 07 October 2020 - 10:15 AM

Wth the different backspace the wheel won’t be centred in the wheel well. You might be ok with a small tyre but what’s the point? Why not use a backspace that lets you run the biggest wheel and tyre you can/want?


Back to Brakes, Wheels and Tyres


1 user(s) are reading this topic

0 members, 1 guests, 0 anonymous users

  1. GMH-Torana
  2. → Holden Tech
  3. → Brakes, Wheels and Tyres
  4. Privacy Policy
  5. The Rules! ·