Mismatched front tyres - BP Outback

[boon]

The old man\'s BP auto Outback failed its WoF on one front tyre yesterday.

The guy at the garage noticed it had a mint condition full-size spare with the same profile tyre so he chucked that on. Obviously the rolling diameter is going to be a little different to the other tyre - is this going to lunch anything (thinking diffs) or is it only really important front-rear?

[Kiwi_Fozze]

Yes. All tyres should be within 5%, or you put extra wear on the difs.

Doesnt matter if front / back or side / side

[subieboy]

Yes

Basically Subaru states that ALL 4 needs to be of the same tread depth/pattern and manufacturer. Subaru goes further to state that all 4 should be replaced at the same time

Most major tyre companies, NZTA, MTA, and car manufacturers specify that if 2 tyres have to be replaced, and they happen to be the front pair, then the new pair should be rotated tot he rear as the car will be more stable under driving/braking/etc. Only a select few state otherwise - i.e. Holden Captiva is only car that specifically states the new tyres must go to the front due tot he cars drivetrain (i.e. they state it will break if you do it the other way)

Most manufacturers specify as above as well, some minor differences too

So if you must leave it on, move it to the passenger rear location, alternatively splash out and buy at least another 1 to match the full size spare, or get ready for a new gearbox

Also while on topic of tyres:

 

Regarding the use of “temporary puncture repairs in a can” “tyre pando” (the cheap sit from Repco/Suprcheap/et al)

As I understand it they are only to be used as an emergency get me home fix and that it renders the tyre unrepairable. Given that the nail or object needs to be removed for these to work this could also lead to water/moisture ingress into the injury channel which would start to compromise the belts etc.

[lachlan]

that quote is going to open a can of worms .

how does it render a tire un repairable ?

also i dont think you should remove what ever is stuck in the tire

[Roo]

 kwi_fozze said:

Yes. All tyres should be within 5%, or you put extra wear on the difs.

Doesnt matter if front / back or side / side

5% means I can run 215/40 on my 9\'s and 205/40\'s on my 8\'s and only be 3.9% difference? Making it okay?

[Kiwi_Fozze]

 Roo']

[quote name='kwi_fozze said:

Yes. All tyres should be within 5%, or you put extra wear on the difs.

Doesnt matter if front / back or side / side

/quote]

5% means I can run 215/40 on my 9\'s and 205/40\'s on my 8\'s and only be 3.9% difference? Making it okay?

I wouldn\'t

[subieboy]

 lachlan said:

that quote is going to open a can of worms .

how does it render a tire un repairable ?

also i dont think you should remove what ever is stuck in the tire

The repair goo forms a layer that is not-removable on the inside of the tyre, you cannot remove it hence the tyre cannot be patched (you need a clean clear surface to use the cement and patch on...

Also, the goo is harmful to aquatic life and hence has to be disposed of as a dangerous chemical - most tyre shops do not have the facilities/training to do so (no Bridgestone/TTSL/Beaurepairs store does). I know this for a fact...

[subieboy]

 jost']

[quote name='lachlan said:

that quote is going to open a can of worms .

how does it render a tire un repairable ?

also i dont think you should remove what ever is stuck in the tire

/quote]

The residue from the temporary sealant is pretty much impossible to repair and it stops the vulcanising solution from sticking to the tyre, so even if the damage is repairable you will pretty much never be able to get it to adhere correctly or safely.

Whats even worse is the goo gets into the actual damage/hole, it then gets to the belts etc and prevents the cement from forming a barrier to moisture...

[Roo]

 kwi_fozze said:

I wouldn\'t

You just said 5% a couple posts ago?

[subieboy]

 Roo']

[quote name='kwi_fozze said:

I wouldn\'t

/quote]

You just said 5% a couple posts ago?

I believe he is referring to the same tyre size i.e. 215/45r17 with worn tread within 5% of the other tyre also a 215/45r17...

[DRFVDR]

 Roo']

[quote name='kwi_fozze said:

Yes. All tyres should be within 5%, or you put extra wear on the difs.

Doesnt matter if front / back or side / side

/quote]

5% means I can run 215/40 on my 9\'s and 205/40\'s on my 8\'s and only be 3.9% difference? Making it okay?

I wouldnt either but hey its your diffs

215x40% = 86 215-86 = 129

205x40% = 82 205-82= 123

the 205\'s are 95% of the size of the 215\'s which really are just on the limit of the 5%

which means that the viscous centre will be working overtime trying to compensate=viscous fluid overheating=overtime it cooking and becoming fully locked=drivetrain issues

[m23]

just think about the word differential. understand hat it does. drive on

[Roo]

 We are borg said:

becoming fully locked=remove front shafts and problem solved

Cheers guys, sorry about the thread hijack there

[Joker]

 m23 said:

just think about the word differential. understand hat it does. drive on

refering back to OP I would not stress too much

if you\'re really worried get a piece of string out run it around the diameter

sure its not \'ideal\' BUT I have ever only replaced 2x front tires at any one time, never all 4, sometimes 1 tire for a wof

[m23]

 JoKer']

[quote name='m23 said:

just think about the word differential. understand hat it does. drive on

/quote]

refering back to OP I would not stress too much

if you\'re really worried get a piece of string out run it around the diameter

sure its not \'ideal\' BUT I have ever only replaced 2x front tires at any one time, never all 4, sometimes 1 tire for a wof

I am not "stressing" as you put it. just trying to get people to think. but I give up.

to the OP, I would not worry at all, that is one of the reasons that a diff is fitted to take up different rotational speeds

[Joker]

turning left will save you gas (you give way/idle less)

put that tire on you\'re drivers side and wear it out faster

[DRFVDR]

 m23 said:

just think about the word differential. understand hat it does. drive on

understand how a viscous coupling works and you would not post such an inane comment

[m23]

 We are borg']

[quote name='m23 said:

just think about the word differential. understand hat it does. drive on

/quote]

understand how a viscous coupling works and you would not post such an inane comment

how many outbacks have a viscous front diff?

[Marky]

Before it gets retarded

Realistically: probably fine

Better bet: at least have same on each axle

Ideal: have matching all around

Difference between different brands is probably comparable to if one tyre was run at higher/lower pressure for a while and wore a tiny bit more or less than the other 3

[subieboy]

Have popcorn at ready

[DRFVDR]

 m23']

[quote name='m23 said:

just think about the word differential. understand hat it does. drive on

/quote]

understand how a viscous coupling works and you would not post such an inane comment

how many outbacks have a viscous front diff?

not talking front diff, talking centre as they are all connected.

[m23]

 We are borg']

[quote name='m23 said:

just think about the word differential. understand hat it does. drive on

/quote]

understand how a viscous coupling works and you would not post such an inane comment

how many outbacks have a viscous front diff?

not talking front diff, talking centre as they are all connected.

you tell me then

[DRFVDR]

 Marky said:

Before it gets retarded

Realistically: probably fine

Better bet: at least have same on each axle

Ideal: have matching all around

Difference between different brands is probably comparable to if one tyre was run at higher/lower pressure for a while and wore a tiny bit more or less than the other 3

Too late

m23 Google it,then you will know

[m23]

 We are borg']

[quote name='Marky said:

b]Before it gets retarded[/b]

Realistically: probably fine

Better bet: at least have same on each axle

Ideal: have matching all around

Difference between different brands is probably comparable to if one tyre was run at higher/lower pressure for a while and wore a tiny bit more or less than the other 3

Too late

m23 Google it,then you will know

i have been playing with different types of diffs on 4wd cars for 40 years. I just wondered what the current batch of dreamers know

[DRFVDR]

Oh if you have been playing with diffs for that long then you maybe you should school us dreamers

Obviously we don\'t know diddley about anything to do with viscous diffs and such :