BF Goodies KM2 -35x12.5R15/17/18

G'Day NP.com.au,

Hopefully someone out there can please pass on some practical experienced tyre/rim advice for another concept I'm currently toying with on my current build.

http://www.bfgoodrich.com.au/product...d-terrain-km2/

Have always 'personally preferred' and driven on BF MT's myself, did trial many others and always came back for what I felt the perfect balance of lugs/noise/performance on&off and overall longevity especially with the old KM1's.

With this new build, and having been out of the game for quite some years have just found on the link above a new '35x12.50R18'

In the old days the KM1's I believe only had R15 & rarer R16 option at a much higher price.

Fraser Island 1995, I foolishly swerved at 60-70kmph past Waddy Point Nth bound with KM1's R15's @ 20psi, scariest/luckiest most stupid thing I've nearly ever done as a young bloke yet kept her upright somehow?

Moving on from my stupidity, I am now theorising about these new found R18's and need some help please.

Query 1:
Physics (in sand)
If the rim size is say R18 and the OD tyre size '35" example' is the same size would say 20psi create a longer track/footprint than say would an R15 rim could?
(Absolutely I believe the sideways stability is greater but does the footprint length extend by any chance? )

Query 2:
Practicality (High Country home rocks/rutts)
Living here South in Mexico-Vic, majority off road work for this project will be rocky steel rim-smashing country.
(Would R18s with 35" OD's be destroyed faster than steel R15s ?)

I'm hoping if 'Query1' is scientifically tangible, then 'Query2' could see tyres kept at higher psi's in the High Country and hopefully cancelling/levelling out the rim smashing potential!

Many thanks MB !

Well the 15s will have a much bigger sidewall which would allow the tyres to bag out more. I reckon you'd have a bigger footprint with the 15s.
18" rims would definitely be more susceptible to damage because there is less rubber and air between them and the road.

The 18s will be hideously expensive to buy and almost impossible to replace in the outback anywhere. I have binned the 17s too and run 16x8 rims on my GUIV tuning 305/70r16 KM2s. I can buy a replacement tyre anywhere in Australia at reasonable coin.

If, for instance you went to do a Simpson Crossing and wrecked an R18 tyre at Mt Dare you might wait a week for a replacement. If your in a convoy you will be alone with the only 18 spare. Bugger of a size!!

Regards to your logic above. I would expect that the higher the side wall the longer the bag and footprint on deflation so the larger the rim the worse it will be. 15 wins.

Yep agree with Daz and Chris. .
The more rubber in the side wall the more the tyre bags..
So a 35" r15 will have a much longer footprint than the 35" r18..
Maybe not at 20 psi, but down at 15 you'd really notice the difference..

Thanks Gents truly appreciated!

We all know, against our Mrs best wishes that deflation in the sand creates length and stuff all/unnoticeable width :-)

Maybe it's my insomniac brain tonight but I'm still wanting to disprove to myself that 'in sand' central lineal axle weight/load on a rim maybe could bellow a lesser profile further-longer instead of wider?

Remember the old blokes you'd see driving everywhere up/down dunes on split rim pizza cutters about max 6" wide with 4" of rubber around running flat ?

There's something there I reckon? , smart old buggers :-) !

Alright, good call gents, thank you again :-)

Protractors, pencils & calculators have proven it also I hope !


R15" max R16 " on 35s is by far the best allrounder for a 35" OD tyre versus it's volume/pressure for lineal footprint.

The greater the rim size touches earth before bag reaches anywhere near a descent length!

Cheers MB

Quote:

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Originally Posted by MudRunnerTD

The 18s will be hideously expensive to buy and almost impossible to replace in the outback anywhere. I have binned the 17s too and run 16x8 rims on my GUIV tuning 305/70r16 KM2s. I can buy a replacement tyre anywhere in Australia at reasonable coin.

If, for instance you went to do a Simpson Crossing and wrecked an R18 tyre at Mt Dare you might wait a week for a replacement. If your in a convoy you will be alone with the only 18 spare. Bugger of a size!!

Regards to your logic above. I would expect that the higher the side wall the longer the bag and footprint on deflation so the larger the rim the worse it will be. 15 wins.

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What rim offset are you using?.
Do these 305/70 scrub anywhere?.
been looking at these same exact tyres,
humm what diff ratios are you running?, as I would need to remain std for towing.

Quote:

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Originally Posted by Robo

What rim offset are you using?.
Do these 305/70 scrub anywhere?.
been looking at these same exact tyres,
humm what diff ratios are you running?, as I would need to remain std for towing.

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I went for a 16 X 8 in a Neg6 offset and they ar perfect. The tyre is inside the guard and no scrubbing at all.

I still have 3.9 ratios and the TD turns them easy but real keen to find some 4.3s actually.