calculating rims and tyres

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henpecked
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Brumby Rims , offsets and tyre sizes

Post by henpecked » Fri May 02, 2014 5:30 pm

On many forums I've been on there has been questions re legal/viable tyres/rims size combinations etc
particularly caliper clearances, extending past guards, hitting inside fenders or struts etc.

Many people have got bogged down on the question of rim offsets and what that means to fitting various alternative tyre/rims on their cars ( a number of nissan sites spring to mind here)

Linked below is the best site I have found to show what the outcome re clearances / speedo inaccuracies etc - is likely to be for your chosen combinations.

I believe that there may no longer be a legal restriction on the rim diameter increase that you can fit over OEM size ( this used to be +1") and that it is only now illegal to increase your rolling circumfrence ( ie change the speedo reading) - but I don't know for sure if this is true , or what the allowable increase is now eg +5% ??


EDIT #4
niterida wrote:Quoted from National Code Of Practice (which most states now follow) :

The overall diameter of any tyre fitted to a passenger car or passenger car derivative must not be more than 15mm larger or 26mm smaller than that of any tyre designated by the vehicle manufacturer for that model.

and :

The wheel track of passenger cars (or derivatives) must not be increased by more than 25mm
beyond the maximum specified by the vehicle manufacturer for the particular model. This
means that the rim offset must not be changed by more than 12.5mm.


There is no mention of the rim diameter, so you are correct it is limited by the rolling diameter and aspect ratio of allowable tyres.

this example is replacing 175/75/13 with 185/70/13s on identical rims and offsets. Which would seem to be "legal" in terms of circumference.

www.willtheyfit.com

The largest tyres I've read about on here on an unlifted L are 215 65 r14s . in this thread Biggest tyres on a Stock l series Which should have given a 21mm "body lift" according to the calculator, and is a 42.4mm diameter increase over the stock, which is 27.4 mm over the "national standards" allowed amount quoted above .

215 65 r14s


EDIT The largest/widest lyres LEGAL (ish) I have fitted to an un-lifted and non-cut guard arches Brumby ( MY ) is 195/65/14s which resulted in no appreciable change to the speedo reading, a 8.2mm "body lift" and a 16.4mm diameter increase over the stock, which is 1.5mm over the "national standards" allowed amount quoted above . - but its viability re hitting body work or extending past the guards MAY depend upon the 14" rim offsets being the same as the standard rims offset .
This set of alloys had a +50 offset, compared to the standard brumby +42

195/65/14

I have seen 195/60/15 on Peugeot alloys ( +20 offset ) fitted to a standard brumby. Just fractionally inside the wheel arches, but the tyres definitely would hit the arches on big bumps, but as they were fractionally below 24" in diameter (24.21") they did not hit anything turning lock to lock

195/60/15



RIM OFFSET
Below is a very clear post from another forum regarding how to measure your offset if you have located a custom set , or the sticker/imprint is no longer visible


how-to-find-out-the-offset/

Here are allegedly correct figures for the standard rim sizes and offsets for the MY and L series and for the Peugeots with 140.0 PCD

EDIT #1

SUBARU LEONE, BRUMBY 77-85 4 X 140 E 42
SUBARU L series 86- 4 X 140 E 55

PEUGEOT 504, 505, 604 75- 4 X 140 E 20
PEUGEOT 504 - ESTATE 70 > 80 4 X 140 E 25
PEUGEOT 504 - SALOON 70 > 80 4 X 140 E 35
PEUGEOT 504 75 > 4 X 140 E 20
PEUGEOT 504 - ESTATE 70 > 80 4 X 140 E 25
PEUGEOT 504 - SALOON 70 > 80 4 X 140 E 35
PEUGEOT 504 75 > 4 X 140 E 20
PEUGEOT 505 75 > 4 X 140 E 25
PEUGEOT 505 - GL / GR / SR / FAMILY 80 > 4 X 140 E 35
PEUGEOT 505 - TI / STI / GTI 80 > 4 X 140 E 20
PEUGEOT 506 75 > 4 X 140 E 20
PEUGEOT 604 78 > 4 X 140 E 25


EDIT #2

Below is a useful image.

High offsets (such as +50 for example) make the wheel fit inward toward the suspension. This helps the wheel clear the outside fender, but since the wheel goes in more, it could pose problems clearing brakes or contacting the suspension.
Low offsets (such as +25 or anything in the negative for example) make the wheel fit outward toward the fender. This helps the wheel clear a big brake kit, but it could pose problems with your wheels and tires rubbing against your fenders.

note that different offsets between sets of rims DO NOT automatically mean the rims will sit further in out out from the body/guards . The width of the rims ( image on left below is a shallow dish, middle image is a deeper dish) combined with the offset will determine where the outside edge of the rims will sit, and also if that particular set of rims actually alter the track or width of your wheel base, which can also cause problems with legality and safety.

Image

Image

if people have pictures of the stickers/imprints of any rims they have used on a subbie ( particuarly on MYs and L's ) that would be great to see posted up on this thread.

thanks

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niterida
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Post by niterida » Fri May 02, 2014 7:06 pm

henpecked wrote: I believe that there may no longer be a legal restriction on the rim diameter increase that you can fit over OEM size ( this used to be +1") and that it is only now illegal to increase your rolling circumfrence ( ie change the speedo reading) - but I don't know for sure if this is true , or what the allowable increase is now eg +5% ??
Quoted from National Code Of Practice (which most states now follow) :

The overall diameter of any tyre fitted to a passenger car or passenger car derivative must not be more than 15mm larger or 26mm smaller than that of any tyre designated by the vehicle manufacturer for that model.

and :

The wheel track of passenger cars (or derivatives) must not be increased by more than 25mm
beyond the maximum specified by the vehicle manufacturer for the particular model. This
means that the rim offset must not be changed by more than 12.5mm.


There is no mention of the rim diameter, so you are correct it is limited by the rolling diameter and aspect ratio of allowable tyres.
[SIGPIC][/SIGPIC]

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wagonist
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Post by wagonist » Mon May 05, 2014 11:24 am

But, I'm sure you could get it engineered if you wanted to. Don't go ridiculous with the offset however.
Get the speedo adjusted (EJ gearbox in L needs EJ sized wheels to read correctly, well at least mine did)
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Gazza01
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Post by Gazza01 » Sun Jan 18, 2015 12:37 pm

Very Interesting Reading. Thanks.

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Cliff R
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Post by Cliff R » Sun Oct 18, 2015 8:46 pm

If the Brumby, had an offset of 42mm up to 1985 what was the offset from 85 to the last of the Brumbies.

Did they fit the 55mm offset L series rims to Brumbies instead after 85 ?

SUBARU LEONE, BRUMBY 77-85 4 X 140 E 42
SUBARU L series 86- 4 X 140 E 55

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dfoyl
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Post by dfoyl » Tue Oct 20, 2015 7:54 pm

As far as I have seen all Brumby's had the same offset (+42 on 5" wheels) from 1982 to end of production. The 2WD MY's had a smaller 4.5" rim with +55 according to my 1983/4 FSM.
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