Tyre footprints
Submitted: Sunday, Jun 03, 2007 at 12:55
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Willem
I haven't taken my MFR Super Traction tyres into sandy conditions yet and with a short desert trip coming up soon I thought that doing measurents might give me some idea of where I might be at.
Measurements are only approximate.
Unfortunately I don't have comparisons with my now buggered Cooper STT's which performed very
well in sandy conditions. Maybe someone else has those measurements to share.
Front wheel Nissan GQ
MRF Super Traction 12 ply rating 750x16 tubed
Tread width 180mm
Sidewall bulge @ 40psi 40mm
Tread
footprint @ 40psi 285mm
Soft sand
footprint 285x 220mm
Sidewall bulge @ 35psi 45mm
Tread
footprint @ 35psi 290mm
Soft sand
footprint 290x225mm
Sidewall bulge @ 30psi 50mm
Tread
footprint @ 30psi 295mm
Soft sand
footprint 295x230mm
Sidewall bulge @ 25psi 55mm
Tread
footprint @ 25psi 300mm
Soft sand
footprint 300x235mm
Sidewall bulge @ 20psi 60mm
Tread
footprint @ 20psi 310mm
Soft sand
footprint 310x240mm
Sidewall bulge @ 15psi 70mm
Tread
footprint @ 15psi 320mm
Soft sand
footprint 320x250mm
Sidewall bulge @ 10psi 80mm
Tread
footprint @ 10psi 330mm
Soft sand
footprint 330x260mm
Cheers
Reply By: warfer69 - Sunday, Jun 03, 2007 at 13:13
Sunday, Jun 03, 2007 at 13:13
Your certainly a dedicated 4x4 man Willem,I would think not many would try and work all the above out ! But would not think twice about getting to their destination a.s.a.p getting bogged on the day and spending all day getting out and seeing it as an inconvenience...
Instead of doing what you have done,understanding fully what your tyres are about,driving without any issues and then spending all day sitting on their ass's/relaxing with a rod !
Cheers
warfers waffle
AnswerID:
244344
Reply By: Member - Doug T (W.A) - Sunday, Jun 03, 2007 at 13:21
Sunday, Jun 03, 2007 at 13:21
Willem
I think you better invest in one of these OFF roaders, RIGHT OFF
No tyres to worry about, won't get bogged
AnswerID:
244351
Reply By: age - Sunday, Jun 03, 2007 at 15:34
Sunday, Jun 03, 2007 at 15:34
Willem
Thanks for the figures. It is good to get some real dimensions regarding reducing tyre pressures. My quick in head calculations put it at 20psi, the load bearing and surface area has increased by 15.5% and at 15psi, by 21.6%. Means similar reduction in load per tyre per
footprint at a given point or over a given area. If you applied this over your 4 tyres, it is almost like gaining the equivalent to an extra tyre
footprint on the ground - makes the difference in real soft sand. All leads to better floatation in sand with reduced pressures
Cheers
A
AnswerID:
244383
Follow Up By: Muddy doe (SA) - Sunday, Jun 03, 2007 at 17:24
Sunday, Jun 03, 2007 at 17:24
Are you an accountant age?
A "quick in head calculation" and you worked out the % change to 0.1%!
LOL
FollowupID:
505353
Reply By: Member - Phil G (SA) - Sunday, Jun 03, 2007 at 19:22
Sunday, Jun 03, 2007 at 19:22
OK I'll bite...................
I used two pieces of 9mm ply in front of and behind the tyre to measure
footprint length. I didn't measure width because my sidewall doesn't touch the ground :-) But the tread is 220mm across - don't know how you got your 750's to be so wide???
Goodyear Silent Armour 10ply 265/75R16 Load Index 123 (same diameter as your 750R16)
43psi 260mm
35psi 280mm
25psi 300mm
20psi 320mm
15psi 360mm
10psi 390mm
7psi 430mm
5psi 460mm
My conclusion is that you won't be pulling the trailer over the dunes unless you go to 5 psi :-))
Cheers
Phil
AnswerID:
244456
Follow Up By: Member - Phil G (SA) - Sunday, Jun 03, 2007 at 19:28
Sunday, Jun 03, 2007 at 19:28
"don't know how you got your 750's to be so wide???"
Whoops missed the 180mm bit :-))
FollowupID:
505418
Follow Up By: Willem - Monday, Jun 04, 2007 at 05:56
Monday, Jun 04, 2007 at 05:56
Thanks for biting Phil :-)
With the sidewall I took into account that the tread would sink into the sand and the sidewall would stabilise against the side of the cut made by the tread.
Yes, it is going to be interesting to say the least. The Coopers at 15psi handled
well in the sand. Maybe that was a tad low and 18 would probably have been OK as
well.
An old desert traveller(name unknown) told me once in
Birdsville that when he ran his tyres in sand, he ran them at 14psi on the Troopy and at 10psi on the trailer and that this was good enough for the Simpson. He was running radials on splits. Now I am not quite sure whether he did any offtrack stuff. Beadell Tours run
MRF Supermilers on their Landy out in the desert and offtrack and it works
well for them but they don't tow a trailer.
I will start the experiment on
Little Red and see where it gets me....LOL
10psi on a
MRF 14ply rating M77, on the trailer, doesnt even look bulged.
Cheers
FollowupID:
505555
Follow Up By: Member - Phil G (SA) - Monday, Jun 04, 2007 at 11:15
Monday, Jun 04, 2007 at 11:15
Willem,
You and your fuel trailer remind me of the Leyland Brothers in 1966. They wrote a book "Where Dead Men Lie" which described their across australia adventure. They had 2 LandRovers, one towing an oversized trailer. Their technique described in the book, was to send the lightweight SWB vehicle with fat tyres over the dune with a long rope and pull the second vehicle and trailer by driving the first vehicle down the dune. They reckon it worked. But after they broke a couple of diffs near
Andado, I'm a bit surprised no other damage was reported until they got towards
Birdsville. There are rumours around that they may have utilised the newly built French Line but they deny this.
Theres an interesting bit of discussion on the French Line Site by the workers who were out there.
FollowupID:
505603
Follow Up By: Willem - Monday, Jun 04, 2007 at 16:28
Monday, Jun 04, 2007 at 16:28
Well Phil, Its like this....lol
I would havee loved to buy a ute. But the only ute in which I could fit comfortably sort of, is a new Nissan(or slightly second hand). Both beyond my financial reach.So I ended up with the GQ.
I have seen too many vehicles break from being overloaded. So, against my better thoughts, I went out and bought a trailer. The trailer weighs in at 800kg all up when leaving base. After first fuel changeover it gets lighter all the time.
Last year I dragged the trailer to the Geo Centre of the Simpson, out and beyond the
Cleland Hills, along the AB, DCarnegie,
Eagle Hwy and then 200km Offtrack to the Calvert Ranges. I broke a Ubolt later in the year on a track at
Warraweena. The trailer performed
well.
So now I am looking at doing some stuff in the Simpson again. If the easy stuff proves too difficult with the trailer then I will do the offtrack stuff another time.
I am very careful when travelling offtrack and look where I out the wheels so that the ride may be a lot smoother.
Cheers
FollowupID:
505664
Reply By: Robin Miller - Monday, Jun 04, 2007 at 13:36
Monday, Jun 04, 2007 at 13:36
Not sure I'd be happy with those figures Willem.
For actual road contact area , I use method of giving tyre surface a light spray with black paint , rotate wheel and lower on A3 sheet of paper , and work out later.
My Cooper ST 255/85/16 give a doubling of contact area between 35 and 15 psi
and the doubling point of all sets I have is in range 12-15psi so might be worth re-
check.
When in trouble - like yesterday! - I go for doubling pressure point soonest .
Robin Miller
AnswerID:
244641
Follow Up By: Willem - Monday, Jun 04, 2007 at 16:34
Monday, Jun 04, 2007 at 16:34
Hi Robin
Yes,
well!!!
I have a sandy driveway and did my measuring via the sand and a brush and a jack. As I said..."approximate" It will do. I see my tyre measuremnets aren't too far short of those of PhilG's
According to a 4x4 Monthly report, some time ago. A skinny tyre gave a longer
footprint than a wide tyre.
As said in replies above. I will see how things go.
Cheers
FollowupID:
505667
Reply By: Member - Davoe (Nullagine) - Tuesday, Jun 05, 2007 at 16:47
Tuesday, Jun 05, 2007 at 16:47
cant help you much Willem. I was running mine at 40 psi and dropped to 28 PSI for a more comfortable ride with little/no dsiscernable bulging. My only foray into sand was at Mt elvire and they didnt do
well at all . I didnt howevr have too many problems at the Gypsom dunes at th Saltlake I think you played in with the EG4WD mob at 40 psi
AnswerID:
244939