Tyres - how much bigger?

Submitted: Wednesday, Apr 22, 2009 at 17:02

ThreadID: 68105 Views:3989 Replies:6 FollowUps:16

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beelzebug

We're off to the cape in early July in the wife's Navara. It came standard with HT tyres in 255.70.R16's, so these will have to go.

I want to go AT's in a slightly bigger size, as replacements will be more available if needed while up that way.

I'm leaning toward Bridgestone 694 LT's in 265.70.R16.
Is there anything to be gained to going up one size to 265.75's?

Looking forward to good advice as always.

cheers
Gary

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Reply By: Geoff (Newcastle, NSW) - Wednesday, Apr 22, 2009 at 17:32

Wednesday, Apr 22, 2009 at 17:32

A little more clearance under the diffs for starters.

You should also get a little more footprint out of them when deflated a bit for offroad work.

Geoff

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Follow Up By: Member - Mfewster(SA) - Wednesday, Apr 22, 2009 at 18:59

Wednesday, Apr 22, 2009 at 18:59

More footprint when deflated? Now I'm not sure about this and welcome the views/experience of others. The general theory that I have heard developed is that wider does not give better footprint deflated as the "bagging" that gives the extra footprint takes place longitudinally and narrower tyres "bag" longitudinally better than wider tyres.

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Follow Up By: Geoff (Newcastle, NSW) - Wednesday, Apr 22, 2009 at 19:05

Wednesday, Apr 22, 2009 at 19:05

Hi,

I had a bit of a play with my Troopy, a tape measure and a couple of tyres. A 7.50 x 16 and a 285-75 x 16

The 7.50 x 16's bagged about 8mm longer but are narrower than the 285-75 x 16's.

Therefore length x width gives area and in my test similar length times greater width equals more surface area.

Geoff

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Follow Up By: Member - Mark G Gulmarrad - Wednesday, Apr 22, 2009 at 19:07

Wednesday, Apr 22, 2009 at 19:07

is ti happy hour at the Lambton hotel is it Geoff????

alls good mate.....hahhahahahaha. :-))))

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Follow Up By: Geoff (Newcastle, NSW) - Wednesday, Apr 22, 2009 at 19:13

Wednesday, Apr 22, 2009 at 19:13

No but it's beer o'clock whilst watching the news!

How was Evans Head ya cheeky young bugger?

And do you have written permission to use my photo in your profile??

Geoff

Geoff,
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Grey hair is hereditary, you get it from children. Baldness is caused by watching the Wallabies.

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Follow Up By: Member - Mark G Gulmarrad - Wednesday, Apr 22, 2009 at 19:15

Wednesday, Apr 22, 2009 at 19:15

all he needs ( in the pic) is a fishing rod.....lol!!

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Follow Up By: Member - Mfewster(SA) - Wednesday, Apr 22, 2009 at 19:22

Wednesday, Apr 22, 2009 at 19:22

Hi Geoff.
Now this is interesting. What is the width of the narrower tyre? If I understand the markings you gave, you gave the aspect ratio and the diameter.

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Follow Up By: Geoff (Newcastle, NSW) - Wednesday, Apr 22, 2009 at 19:32

Wednesday, Apr 22, 2009 at 19:32

I actually mixed my metrics and imperials just like any good tyre thread!

The 7.50 x 16 is the standard 7.5" wide rag tyre fitted on split rims to Troopy's ex factory. (About 190 mm wide in metric parlance) They are I think equivalent to something like a 235-65 or 70 x 16.

The 285-75 x 16 is as stated, 285 mm wide and on a set of 100 Series factory alloy rims.

And I made the length measurements in millimetres!

Have I confused you yet?

Geoff

Geoff,
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Grey hair is hereditary, you get it from children. Baldness is caused by watching the Wallabies.

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Follow Up By: Member - Mfewster(SA) - Wednesday, Apr 22, 2009 at 20:03

Wednesday, Apr 22, 2009 at 20:03

I'm a little confused, but trying to stay with you. How much did you deflate the tyre? I would have thought that a deflated trye would give considerably more than 8mm increase in track length.

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Follow Up By: Geoff (Newcastle, NSW) - Wednesday, Apr 22, 2009 at 20:15

Wednesday, Apr 22, 2009 at 20:15

Hi,
I can see were you are confused, both tyres deflated to 16psi.

There was 8mm difference in their length when deflated.

The 285-75 x 16 was say 300 mm in length when deflated to 16 psi, the 7.50 x 16 was say 308 mm in length when deflated to 16 psi. (Those numbers aren't correct as I can't find my notes but I think you'll get my drift)

That's how I arrived at the notion the wider tyre had the greater footprint even though its footprint was 8mm shorter than the narrower tyre.

Geoff

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Follow Up By: Member - Mfewster(SA) - Wednesday, Apr 22, 2009 at 20:19

Wednesday, Apr 22, 2009 at 20:19

OK Geoff, now I follow. That looks convincing.

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Follow Up By: Malleerv - Wednesday, Apr 22, 2009 at 21:07

Wednesday, Apr 22, 2009 at 21:07

Taller tyres give better/longer footprint and more so when run at low pressure.

Also, most of the time a wider tyre is also taller in spec than a narrow tyre in the same profile range thus giving a wider and longer footprint.

Matt