A/T with H/T as spare?

DriftaJosh

DriftaJosh

Forum Member
Joined
Dec 15, 2015
Messages
9
Location
Newcastle NSW
Car Year
2003
Car Model
Forester
Transmission
5 Speed Manual
Hi all,

I'm looking at buying a set of A/T tyres for my MY03 Forester (Tossing up between Geolandar G012 and Deueler D697). Both are availabe in a 215/65r16 but the current spare I have in the back is the standard 215/60r16, a Geolandar H/T tyre.

Am I correct in understanding that I wouldn't be able to run that spare because of the tyre size difference if I I went up to the 65 profile from the standard 60?
This also means that if the spare is replaced with a 65, that it will need to be deflated to fit in the spare wheel well?

Thanks guys
 
Yeah, Josh, right on both counts.

Running different diameter tyres on any AWD Subie will wreck some very expensive bits ...

They almost always need to be transported on a flat bed truck too.

These are the price we pay for having such a wonderful drive train. Not a big deal. Mine have had to go on a flat bed only once in 23 years.
 
Hey Ratbag,

Thanks for the prompt reply. I figured as much with the tyre size, my Foz is my first foray into the realm of AWD cars and just wanted to be sure before making a catastrophic mistake.

Any opinion on the Geolandar vs. Dueler? I'm leaning towards the former, but my old man (a landrover guy) is trying to convince me to go with the Dueler's.
 
Gidday Josh

The Dueler 697 appears to be very good. Ateday is running them, and so are some from WA.

Not available in 215/60 16 last time I looked, so you need to find somewhere else for your spare - rear bumper holder, roof rack, back seat ... :iconwink: :rotfl:.

Check that larger tyres are OK with your insurer. Get it in writing ...

Read the legals and insurance forum here about all this stuff.

https://offroadsubarus.com/forumdisplay.php?f=57
 
Hey mate, welcome to the site.
Myself, I ran 215/65r16 Bridgestone Dueler 697 AT on the factory steel wheels, with a set of 215/65r16 Kumho road tyres on WRX wheels. I'd use one of the other as my spare.
The D697 are an excellent tyre and the forester size is of commercial construction - it's an incredibly tough tyre and capable of anything you'll give it.
It definitely has more of an AT design than the Yokohama geolander at-s, and is better in mud because of it. The Dueler has far superior sidewall protection too.
They're quiet enough and grip/ wear well enough to be liveable as an only tyre too, as opposed to running two sets like I did.

Hope this helps
 
Ratbag said:
Running different diameter tyres on any AWD Subie will wreck some very expensive bits ...
Click to expand...

I've never got where this has come from with AWD's? 65 series to 60 isn't a huge difference in axle speed to begin with, Isn't that the reason they have diffs? Even the LSD in the rear would have to be driven at a super high speed for the differences in tire size to cause it to start to lock.

Not being an donkey, but do you have any links to where this has caused an issue, would love to have a read of what went wrong. I don't want to make the mistake if my thoughts are wrong. Was thinking of doing the exact same thing with tires and small spare.
 
Last edited:
Gidday OC

The Owners Manual ...

It appears that a difference in diameter of 6-8 mm is OK.

Without looking it up, the difference in diameter between 215/60 16 and 215/65 16 is over 20 mm. That will cause a significant difference in wheel speeds. AFAIK Subaru does not publish any figures on this, and the OM would almost certainly err on the side of caution.
 
It appears that a difference in diameter of 6-8 mm is OK.
Click to expand...
Does this mean we can assume a 8mm diameter difference between rear left and rear right tyres at 110km/h is ok for the rear lsd?

If so, this still isn't very much, if your tyres are below 50% tred wear, you can not run a new spare of the same type of tyre ... you'd actually be better of running 225/60r16 tyres with a 215/60r16 spare, as this keeps them closer in diameter over the life of the tyres.

Any way, calculations for 65vs60's
A new 215/60r16 has a circumference of about 2085mm. Therefore at 110Km/h is doing 879.3 rpm.
If you bring the diameter down by 8mm, which is what Subaru say is ok, you now have a circumference of 2061mm. Therefore at 110Km/h is doing 889.5 rpm.
So Subaru think it is ok to have a difference of 10.2rpm through their LSD.

A new 215/65r16 has a circumference of about 2154mm. Therefore at 110Km/h it is doing 851.1rpm.
So if you are running three 215/65r16’s and one 215/60r16, you will have a difference of 28.2rpm at either the front or rear diff. If the spare is on the front, or if you don’t have a rear lsd, then this figure doesn’t matter and the centre lsd will have a difference in diff speed of half of this, only 14.1rpm. This is still over Subaru's safe figures. To drop the difference in diff speeds to Subaru’s 10.2, you would have to drop your driving speed to 110/14.1X10.2 = 79.6 Km/h.

In conclusion
Driving at 80Km/h with a 215/60r16 spare on the front and three 215/65r16's will have the same wear on the centre lsd, as 4mm of tread wear between rear left and right tyres at 110km/h would have on the rear lsd.
 
I can attest to incorrect tyre diameters killing things.
My first SF5 GT Forester had 2 new tyres on one side of the vehicle and 2 nearly worn out ones on the other.
The rear diff let go due to the hard facing being worn off the planetary gears from constantly rotating and the gears eventually failing.

I've also had a dead centre diff in me last 2 Subaru's,
Both of which had a history of new tyres being replaced only 2 at a time by previous owners.
Basically ends up overheating the viscous coupling, the silicone goop inside cooks and no longer operates correctly, so you end up with a "locked" diff once the gearbox gets to operating temperature

If you have a mis-matched spare, put it on the front, where the majority of cars have an open diff anyway and drive only as far as the next servo or tyre repairer to get the good one fixed
 
^ good advice, Rob.

I have seen and photographed a dead centre. It's not pretty. In fact, pretty f'ugly ...

I have also seen one that was killed in a matter of days/weeks from doing burnouts/doughnuts.

Same as I don't use LR for launching on bitumen, and only when I must on dirt. It will wreck the transmission/drive train, sooner or later. Probably sooner ...
 
Wow! Thanks for all the information guys!
So after reading through everything posted in this thread, I bit the bullet and ordered my tyres today.
5x Duelers in a 215/65r16

Also picked up a 12v air compressor to mount in the engine bay (heat shielding?) to reinflate the spare when need arises.
 
If the tires are not the same size, another option is to have the same loaded radius by over-inflating or deflating a tire.
 
I'm pretty new to all this as my last Subaru was in the 70's, a Leone Wagon, had lotsa other 4WD's.

I have five identical tyres, i.e. full size spare, so if I rotate all five tyres every 5000Km I should have tyres that are within 10% tolerance shouldnt I?

Les
 
I usually measure tread depth when rotating and then decide which go on the front. I rotate with 6 wheels.
 
It has been my observation over some 20+ years that Subies always wear the front P/S tyre most (on RH drive cars in LH drive countries), even when the wheels are perfectly aligned. I expect that this effect would show on the front P/S tyre on a LH drive car also - the other side of the car however ... :iconwink:.

I have a theory about this ;).

One tends to go faster into RH bends than one does into LH bends.
On a RH bend, if one misses, one goes off the road.
On a LH bend, if one misses, one goes head-on into the oncoming traffic.

The instinctive self-preservation effect realises this difference, making one more circumspect on LH corners.

(the opposite is true for LH drive cars/ RH drive countries ... )

Over the life of tyres, one negotiates many, many corners, and this effect accumulates over that lifetime. This is reflected in increased wear on the front P/S tyre - specially if one tends to drive 'vigorously', as I do ...

It was almost immediately noticeable when I got my AWD Impreza ...
No other car I have ever owned had such a well balanced and aligned drive train and steering that this effect was noticeable.

The further proof of the above paragraph is the well known effect on handling (etc) that even the slightest misalignment causes with Subies. Both Roo2 and RonnyRoo handled like canal barges until the very minor misalignments were adjusted. Roo2 was within specification on all 4 wheels when I got it, but each of the wheels was pointing in a slightly different direction ...

By way of comparison, I drove my '68 Landcruiser for about 18 months with the front wheels some 1 1/8th inches out of alignment, and this had no noticeable impact on tyre wear, or handling!
 
A guy I new who owned a Bridgstone Tyre centre said the cause is from round abouts putting pressure on the R/H front passenger tyre in Australia.

He said it was great for the tyre industry when a public servant decided they where needed on roads

And I guess the cruiser went thru round abouts much slower than suby's
 
I've heard that many times too, Taroona. Always managed to get them to understand what I was saying. Sometimes grudgingly :lol:.

Roundabouts are a special case, I agree. Funny how it never seemed to have any particular effect on any of my other cars ...

As for my LC, sometimes it went around, sometimes over! Recirculating ball (or worm and nut/ball) steering is not renowned for accuracy, specially when combined with leaf springs on a front solid axle ... :rotfl:.
 
You must log in or register to reply here.
Back
Top