Another Spare Tyre Question

Submitted: Wednesday, Jan 06, 2016 at 10:44
ThreadID: 131285 Views:2270 Replies:5 FollowUps:14
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Hi All,

Calling on the collective knowledge of this great group...

My 2014 BT50 came with 265/65-17 Dunlop AT22 Grandtreks and a factory towbar.

I intend to run out those tyres on easy trips, but for outback treks I will probably get 70 profile BFG All Terrains. My first spare, carried in the canopy, will also be one of those.

The issue is the second spare, which is the current OEM spare - a 65 profile Grandtrek. It is under the vehicle immediately forward of the towbar. There is insufficient room between the towbar and the diff housing to accommodate a 70 profile tyre, so I cannot upgrade it without going to the expense of getting a replacement towbar - an expense I'd prefer to avoid if possible.

My question is

If I had to use the Grandtrek second spare, it would have a different rolling diameter to the 70 profile BFGs. Bearing in mind the mechanical fruit in the BT50/Ranger - stability control, traction control, etc - and given that the need to use the second spare might occur some hundreds of km from a repair shop, what are the implications of the different rolling diameters over that considerable distance?

There is no LSD on the BT, just open diffs and traction control, etc and a locker on the rear which I presume I should not use. Unlikely to need it out there anyway.

Would appreciate your comments and advice.

Cheers
FrankP

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Reply By: Les - PK Ranger - Wednesday, Jan 06, 2016 at 11:28

Wednesday, Jan 06, 2016 at 11:28
Having the Ranger, my OEMs were AT22's as well, they are a pretty good AT tyre, strong.
They work great on rocky stuff and are excellent on sand, beaches or deserts.
The only place they will let you down a bit with the finer tread is mud / clay / wet slick tracks if caught on them.

From your description, and without rear locker operating, you should be fine to run slightly different rolling dias, as long as there's no chance for mechanical binding, it might just look a bit odd, perhaps handle slightly different / pull to one side if they are on the front ??

If I read right, you are going from 265/65/17 to 265/70/17 ??
If so, this is just 3.3% difference, not too much to worry about in your situ as described.
I used this little site here to compare sizes . . . Tyre size calculator / comparison

Seriously though, outback trips if not in wet season, you wold be fine on the AT22s, that's what I'd do, rotate all through use each service, they can wear out evenly then you can replace the lot.
AnswerID: 594530

Follow Up By: Member-George (WA) - Wednesday, Jan 06, 2016 at 13:33

Wednesday, Jan 06, 2016 at 13:33
I agree with Les, I have Grand Treks 265 65 R17 AT22 on 2 Toyota 4WD's, they are a great tyre and have never let me down, soft sand, gravel and rock. Why change unless you are heading for the Victorian High country during winter. Cheers
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Follow Up By: Frank P (NSW) - Wednesday, Jan 06, 2016 at 15:35

Wednesday, Jan 06, 2016 at 15:35
Thanks Les and George,

Yes, Les, 265/65's to 265/70's. You've eased my mind somewhat re the mild unequal rolling diameter.

I haven't had as much luck with Grand Treks (on my previous tug, a 120 Prado) as you guys have apparently had, and hence my preference to change. But I will run these out rather than throw away tyres with useable life in them.

Perhaps I am being harsh on the Grand Treks. My tyre management practices have changed as I have learned. Perhaps that has had as much to do with better tyre performance as the change of brand. But I still like the BFGs as an all-round performer for what we do, so when it comes time to change, that's probably the way I'll go.

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FrankP

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Follow Up By: Les - PK Ranger - Thursday, Jan 07, 2016 at 07:58

Thursday, Jan 07, 2016 at 07:58
Cool decision mate, even though I have mixed and matched tyres once (got 2 couple of Maxxis ATs on the front at 10k to try), and ended up buying 2 new AT22's at one point, I wouldn't be paying what they're asking in general for them again.
There are too many slightly more aggressive AT's out there that are less $, and should go the distance for me.
I have 4 new Federal Couragia ATs on the bus now, and 2 x 3/4 depth tread AT22's for spares.
Once they go I will think about the move to 7" or 8" wide 16" rims, then either fit 245/70 or 245/75 (+ 4.3% or + 5.5% rolling dia respectively), that size would suit me nicely I feel.
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Reply By: Jackolux - Wednesday, Jan 06, 2016 at 12:22

Wednesday, Jan 06, 2016 at 12:22
I know TC and Stability Control can do strange things with different dia tyres , you could always just turn it all off , l presume you can do that with the BT50 , l know l can with my Dmax .

When I'm up the bush , l turn it all of anyway and just use my e-Lockers if l need them .

AnswerID: 594532

Follow Up By: Frank P (NSW) - Wednesday, Jan 06, 2016 at 16:03

Wednesday, Jan 06, 2016 at 16:03
Thanks Jackolux, yes, it's the affect on TC and SC that I'm concerned about.

I can turn off SC at any time. The way I read the manual, it implies that when SC is turned off, so is TC, but it doesn't specifically say that. I suspect it is so as the two functions are logically interlinked.

If the locker is activated, SC, and again I presume TC as well, is turned off.

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Follow Up By: Les - PK Ranger - Wednesday, Jan 06, 2016 at 17:30

Wednesday, Jan 06, 2016 at 17:30
..
Frank, suggest checking with a dealer re TC and SC etc . . . you don't want to take any chances on our mechs with binding type issues.

Seems to be another good reason to just run all the AT22s you have down, they'll be perfectly fine for your intended use 99% of the time (watch the greasy tracks !) and by rotating you can get them all worn evenly and then change towbar setup (if needed) and get 5 or 6 rims setup with tyres all the same.

Always a good idea to rotate all wheels / tyres at service, they'll all wear out evenly and spare(s) not get old and brittle, give you an extra 40k or so overall before needing new rubber, plus easier to keep all same brand etc when change is desired.
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Follow Up By: Frank P (NSW) - Wednesday, Jan 06, 2016 at 18:33

Wednesday, Jan 06, 2016 at 18:33
Rotation is made difficult, Les. BTs come with 4 alloys on the axles, one so-called "temporary" steel spare (same tyre size). Rotation means two dismounts and two re-mounts.

I have just bought a fifth alloy - will swap the main spare onto that and carry the second spare on the steelie. That will make regular rotation easier.

If found getting decent tech info from my dealer and Mazda Australia akin to trying to nail a jellyfish to a wall. Phrases such as "Mazda does not support ..." or "Mazda does not recommend..." but never anything like "You could try this .." or "Some owners have done ..."

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Follow Up By: Les - PK Ranger - Wednesday, Jan 06, 2016 at 18:36

Wednesday, Jan 06, 2016 at 18:36
Yeeah, I noticed that when reading some brochures a couple of months back, thought the tight arses !!
Should be mandatory to supply 5 wheels the same, ridiculous of them to be so tightfisted.
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Follow Up By: nickb - Thursday, Jan 07, 2016 at 04:02

Thursday, Jan 07, 2016 at 04:02
Not sure about your system but the TC in my Pajero is always on, regardless whether the SC is on or off. Putting it into low range automatically turns off SC but not TC. I would imagine yours would be similar.
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Reply By: Member - M&N's - Wednesday, Jan 06, 2016 at 20:50

Wednesday, Jan 06, 2016 at 20:50
Ello frank just a question that's right out there from my personal experience that i won't go into I assume you have a xtr or gt be cause of 17" rims have you checked your towbar is a xtr and is rated for 3500 kg braked towing and the rhs main bar is at a slight angle if it is correct than you should be able to hang your chosen tyre size underneath and still have allowance for diff movement just a thought mickb
AnswerID: 594558

Follow Up By: Frank P (NSW) - Wednesday, Jan 06, 2016 at 22:22

Wednesday, Jan 06, 2016 at 22:22
Hi Mick,

Yes, mine is a GTR dual cab. My towbar is rated at 3500kg, 350kg on the ball. It is straight across. I cannot put any larger tyre in there without fouling the diff. Stupid design.

Ford make a curved one that I'm looking into, but $$$. It will allow larger tyre diameters.

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FrankP

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Reply By: The Bantam - Thursday, Jan 07, 2016 at 01:50

Thursday, Jan 07, 2016 at 01:50
In the 4wd market, I believe there is an over emphasis on getting bigger tyres.

Truth to tell, most mere mortals will get to most places they want to go on near factory size tyres. ....... its not like modern cars come with narrow, dunlop road track majors on split rims.

The small increase in tyre size you are considering will give next to bugger all extra clearance, next to bugger all larger foot print and next to no real advantage.

You are better off sticking with your factory tyre size and making good tyre choices and using good tyre managment practices.

cheers
AnswerID: 594567

Follow Up By: Member - Blue M - Thursday, Jan 07, 2016 at 05:04

Thursday, Jan 07, 2016 at 05:04
Bantam,
I would have to agree with you on this one.

Cheers
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FollowupID: 863016

Follow Up By: Les - PK Ranger - Thursday, Jan 07, 2016 at 07:51

Thursday, Jan 07, 2016 at 07:51
Yes, larger rubber is often just fitted to look better (and it does look 'meaner' in most cases), but can cause issues if not done right with offset / track etc.
I feel people use will dictate if their need for more clearance for more challenging track work is required, nothing like cruising over larger obstacles where you used to touch before.
Having stockies / no lift on for a while does help you become a better driver, pick lines better etc.

I loved the extra 47mm clearance the 265/75/16s gave (+9.7% rolling dia), but now back on stock 235/75/15s it's a whole lot better vehicle to drive.
Once I wear out these 6 tyres evenly through rotation, I'll be looking at 8" rims in 16", and fitting either 245/70 with just + 4.3% difference rolling, or 245/75 at + 5.5%, that will do me nicely long term.
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FollowupID: 863018

Follow Up By: The Bantam - Thursday, Jan 07, 2016 at 11:30

Thursday, Jan 07, 2016 at 11:30
Remember folks ..... if you increase your tyre size by 50mm, even in theory you only get an extra 25mm of clearance ...... in practice once you account for the tyre being flat on the bottom and airing down ya gona get about 15mm of advantage ....... thats not a big deal.

Going for a wider tyre or one with a more advantageous profile or tyre type is a different story all together.

cheers
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FollowupID: 863038

Follow Up By: Les - PK Ranger - Thursday, Jan 07, 2016 at 11:36

Thursday, Jan 07, 2016 at 11:36
Mate, you lose the air down height on either tyre sizes, so you do get a small increased lift advantage with any larger rolling dia :)

I would stick to 70 or 75 profile, much better for traction when deflated and stronger in side walls from what I've seen, most have to be LT grade in the higher side walls.
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FollowupID: 863039

Follow Up By: The Bantam - Thursday, Jan 07, 2016 at 12:21

Thursday, Jan 07, 2016 at 12:21
Like so many things these days .... these 65 profile tyres are all to do with producing fuel economy and carbon figures ...... who in their right mind would have a low profile tyre as a first choice for off road.

Dropping rim size and increasing tyre profile will get a better result off road even at the same diameter.

cheers
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FollowupID: 863046

Reply By: Tim F3 - Thursday, Jan 07, 2016 at 06:53

Thursday, Jan 07, 2016 at 06:53
If you let most the air out of the larger tyre would it then fit under the vehicle,just pump it up when you need it..
AnswerID: 594572

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