Large, Black, Bouncy Doughnut Thingies

Re blacktop use, I went for the two sets of tyres for
the car. I got the dealer to give me the original steel rims + a sixth as my
mags are after market.



I have bridgestone AT all around for van/car
travelling, but as I am on the blacktop most of the time with work, I went full
on road radials (Bridgestone H/T’s) for the mag wheel set.

I’ll review the A/T’s as my exposure to
the conditions grows, but with the H/T the difference on the L/C100 is more
than a little noticable, especially in the wet. So much so that I will always
have two sets even after retirement kicks in, as the cornering and braking are
a marked improvement. The relative small area of tyre is the only bit between
you and the road and besides the $ investment in equipment, it’s my life
and I want to spend it BT’ing for many years.



It does not take too long with a 3 tonne trolley jack,
but maybe when I get old and retired I’ll have to chase up a friend with
a hoist.



----------------------

Gary Harding

TriSys Engineering/III

G'day Larry, I always use a tyre with the highest load rating and speed rating possible in the size required. If you take a "L" speed index tyre (which is legal on F250's) it can maintain a speed of 120 kph indefinitely with a caveat of it not being overloaded and at the right pressure for the given load. If you take the speed rating of the tyres on mine now (standard) they have a speed rating of "R" which is 170 kph sustained ..... not that you would be doing this but the point is .... It is a physically tougher (higher priced as well) tyre to be able to stay at 170 k's all day long. It can take the heat generated by the higher speed. The higher speed rating also gives a greater margin for error .... slightly under inflated (generating heat) slightly overloaded (generating heat) because it can take the heat of the higher sustained speed. This works out well by, say, pulling up after 3 hrs at 100k and a tyre is very hot for whatever reason .... an "L" rated tyre might have destroyed itself by now but an "R" rated might just be under its heat limit and still ok. If the Cooper tyres and the BFG are the same i.e. size and both an A/T type I'd go for the "Q" rated tyre every time ... As Gary has said ... The tyres have to compromise their abilities e.g. puncture resistance V grip in the mud for one. I have been on the lookout for a new set of steels for my F250 (at a reasonable price) for a few reasons. I'm compromising by using a "All Terrain" tyre in the highest load and speed index in a 265/75/16 for the dirt. Back in town/ high speed bitumen travel BT on, I'll be using my alloys with the same size tyre in a road pattern. This gives me an advantage of using a beadbreaker and safety seals on the side of the road (dirt travel) without destroying the alloy bead edges. Have a good chat with the manufacturers they really know their stuff . The mind boggles with so much tyre tech. I buy as tough a tyre as I can afford at the time. As a side note I did some tyre temp/pressure tests on the way to Cania. The BFG 235/85-16 A/T's on the BT at 2900kg were inflated to 41 psi cold before leaving, ater 3 hrs of travel ( Ban Ban Springs) at 90-100 kph the tyres were at around 44.5 psi and running a sidewall temp of between 42-44 degs C. Not bad at all ... Regards Anthony Explore this Great Land ... Do it Easy ... Tow a Bushtracker

Hi, Just reading your earlier message re tyres. On my old 80 series cruiser towing a 19' BT for around 20K kms, I averaged around 60,000 kms on per set on BFG AT's. I now have a 100 series with BFG AT fitted new at delivery. Having towed the BT for around 6000 kms here in Tas with the new cruiser it looks as though I will only achieve arouind 50,000 kms on this set. Do I understand from your comments that you have achieved 100,000 kms per set of BFG AT's? I look forward to your comments. Regards, Peter S I

Peter I am on my third set of BFG AT's and achieved 100,000 kms from each of the first two sets. I changed them from vehicle to vehicle on the two 80 series that I have had. I have run them only on Speedy Desert Rat Sunraysia negative offset type rims. When I got them initially I was advised to run them at 35 psi and have religiously followed that pressure. They have been everywhere including Fraser Island, across the Simpson, the South Australia tracks and across the Alps five times. Over that time I haven't even had a puncture. After getting 40k from Dunlop (originals) and 45k from Bridgestone, I changed to BFG. Admittedly all these k's were done NOT towing the BT (until 20 months ago) but at the moment it's a personal thing but like mortein, when you're on a good thing, stick to it. Regards Jeff

Thanks Anthony, I am comfortable with the ratings and their implications as you have explained. What you, and others, have said highlights the compromise that I will have to make if I run 1 set of tyres on the vehicle that will suit my requirements. The BFGs and Coopers are the same size (I'm looking at 285/75/16s) and have about the same weight carrying capability however the BFGs are Q rated and the Coopers N. The Coopers are far better in slippery conditions. For towing, the BFGs win (Q vs N) but will Coopers do the job? Offroad the Coopers win but could I get by with the BFGs? Then there is the 'toughness' factor as well. I will pay what I have to to get the tyre that suits my requirements......there will be no compromise on cost - but I don't like to compromise on capability either....... And those are good temps/pressures you got for the Cania trip .......and support the good explanation you gave on a previous thread regarding weight/pressure/temperatures and the '4 psi rule'. regards Larry

Jeff, Thanks your comments- greatly appreciate them. I too will stick with BFG AT's and I also run them at 35 psi. maybe my 200/250k's per week on our Tasmanian gravel roads is not helping the performance of my tyres! Catch you soon. Peter

Larry, As you know you have more to worry about with tyre "checking" and inspection, while you travel, rather than the brand ... in the same type and size. If the Coopers provide a better grip in the conditions you are likely to be travelling across (in the main) I'd go for them. The "N" rated tyre is plenty for a modern 4x4 towing a BT. I believe most specify a "L" or "M" as a minimum. They are probably cheaper too .... Regards Anthony Explore this Great Land ... Do it Easy ... Tow a Bushtracker

((I always use a tyre with the highest load rating and speed rating possible in the size required. If you take a "L" speed index tyre (which is legal on F250's) it can maintain a speed of 120 kph indefinitely with a caveat of it not being overloaded and at the right pressure for the given load. If you take the speed rating of the tyres on mine now (standard) they have a speed rating of "R" which is 170 kph sustained ..... not that you would be doing this but the point is .... It is a physically tougher (higher priced as well) tyre to be able to stay at 170 k's all day long. It can take the heat generated by the higher speed. The higher speed rating also gives a greater margin for error .... slightly under inflated (generating heat) slightly overloaded (generating heat) because it can take the heat of the higher sustained speed. This works out well by, say, pulling up after 3 hrs at 100k and a tyre is very hot for whatever reason .... an "L" rated tyre might have destroyed itself by now but an "R" rated might just be under its heat limit and still ok.)) Sorry guys but I have to buy into this one, load capacity & high speed ratings dont go together, sure they can be made at a price, but for a given load the higher speed rated tyre will allways be lighter contruction & less resistance to fractures & punctures. The cause of most heat is side wall flex & the heavier & thicker the side wall (e.g. lower speed rated but stronger walls) the more heat generated. To lift the speed rating they either make the walls lighter or thinner & increase the pressure to make them stand up again, or increase the amount of air ( not pressure) in the tyre e.g.larger size. The best example of this like them or not was the originall Grandtreck on cruisers "H" rating really were an unsuitable tyre for the use, the mk2's are a "T" rated much tougher tyre but down rated speed wise, because of the heavier wall, same weight rating. On the side, Aust. specs permit the fitting of "N" speed rated tyres on all 4X4's in the country as long as the weight is right. Where does that leave the X5's & Mercs. ?? Will but out & go back on the side Regards DD

The more everyone goes into this the more we mortals are getting confused. I have been told by tyre dealers that I cannot fit BFG to my F250 as they don't meet the rating required. The Goodyears that came with the truck are performing well and have 63,000km so far, so I suppose I would be best to stay with them when the time comes to change. The Ford book says to run rear at 70psi and front at 45psi when loaded. I have noticed some F250 with BFG's fitted so some dealers don't bother about the legality of the tyres when they fit them. Brian

G'day DD, The following first paragraph I wrote is incorrect in that it has given the impression that a higher speed rating by itself means a tougher tyre against puncture, not so. It means they can dissipate the heat generated by the higher speed. In the second paragraph .... I still maintain that a higher speed rating has a greater capacity to dissipate heat so if kept within its spec (load index, pressure) it's greater capacity to get rid of heat gives a better margin of error for anything that generates excessive heat e.g. underinflation. If you take the speed rating of the tyres on mine now (standard) they have a speed rating of "R" which is 170 kph sustained ..... not that you would be doing this but the point is .... It is a physically tougher (higher priced as well) tyre to be able to stay at 170 k's all day long. It can take the heat generated by the higher speed. The higher speed rating also gives a greater margin for error .... slightly under inflated (generating heat) slightly overloaded (generating heat) because it can take the heat of the higher sustained speed. This works out well by, say, pulling up after 3 hrs at 100k and a tyre is very hot for whatever reason .... an "L" rated tyre might have destroyed itself by now but an "R" rated might just be under its heat limit and still ok.)) You are absolutely correct if looking at speed rating alone the higher the rating the lighter the tyre. As I said though ... I buy the highest load index and speed rating as possible as a combination. They might not go together technically but it works for me. Highest load index (as possible in the size required) is the prime factor then I look at speed rating. If I get a choice of tyre one at L/I 121 ... S/R "N" or L/I 121 or S/R Q I'll take the "Q" every time ........ because it can carry the same weight at a higher speed .... is this a mistake ??? As an example take the 265/75-16 tyre on the F250 it can carry 1550kg at 170kph all day long as this "is" the spec of the tyre. It might be in laymans terms but it sure can carry some weight at "some" speed. BFG, Michelin, et al dont even have a tyre to meet this spec in this country at this time. I am certainly not a tyre expert and before fitting a tyre consult the manufacturers engineers/techs as towing 7000kg in combination at 100 k sustained is hard on a tyre. If you can shed some more light on selection criteria (to make it easier to buy tyres ) I welcome your comments as I'm always learning ...... Regards Anthony Explore this Great Land ... Do it Easy ... Tow a Bushtracker

Anthony, We are all learning, I would not have come in on your second explanation, however my understanding is that a higher speed rated tyre does not dissipate heat all that much better, but it generates a lot less, normally done by lightening the construction, thinner walls & different cords, the same strengh tyre but all working against you if you need off road toughness, which was my point. Out of interest I lost it when I changed computers but I had a chart from Toyota comparing tyre patterns on a dyno "AT's" use almost 10% more fuel & power than a road tread - don't even mention mud tyres the worst was 18% down Back on the fence. Regards DD P.S. I tow with a cruiser all up weight 6400kgs last set of Grandtrecks came off with 98000k's 40 with the van on. Most people have trouble with that, yes we cruise at 100 where poss. but I wont talk fuel cons. its a petrol !!! Cheers

DD: "Sorry guys but I have to buy into this one, load capacity & high speed ratings dont go together, sure they can be made at a price, but for a given load the higher speed rated tyre will allways be lighter contruction & less resistance to fractures & punctures" Anthony: "You are absolutely correct if looking at speed rating alone the higher the rating the lighter the tyre." That's what I would have thought as well, but in the tyres I have talked about above: the BFG AT and Cooper ST 285/75/R16, Load 3300lbs (ish) for both.....the BFG is rated Q and is 3 ply while the Cooper is N rated and 2 ply......... so the BFG has the higher speed rating and it also has higher toughness and resistance to puncture. They are about the same price. This doesn't fit the theory.............hmmmmmmmmm...

Re high speed rated tyres.

The major design criteria of a high speed rated tyre is that it must resist the centrifugal force that attempts to tear the tread off. This force is proportional to the tyre's mass, times the square of the rotational velocity, divided by its radius.

High speed tyres have light, strong, wall and tread construction. They are also more likely to have a shallow profile. There is no meaningful correlation between their construction and their weight carrying ability, and no point in using a tyre rated at a higher speed than that at which you propose to use it.
Collyn Rivers

Hello everbody, Been following the discussion. Suggest a visit to toyo.com.au, a reasonable discussion of tyre technology and ratings should dispense with some of the uncertainties in this forum. I do not know what the specs are for F series tyres but I know there are a number of Toyos with ratings of 120Q - load range E - 10 ply. Coopers also have tyres in this class but are usually more expensive. Would someone please post the F series requirements. Thanks John

G'day John, The F250 rear axle has a max load of 2817kg and obviously needs a tyre to meet or exceed this to be legal. That means a load index of 121 or above ..... 121 is 1450kg, 122 is 1500kg 123 is 1550kg. The original tyre is a 265/75-16 mounted on a 16 x 7 inch rim and is a Goodyear Wrangler RT/S (road tread pattern) Load index 123 and speed rated "R". I believe Ford picked the 123 load index to be safe (way over 2817kg at 3100kg for 2 x 123 index) after their experience with the firestone tyre debacle which nearly sent firestone broke in a class action. Regards Anthony Explore this Great Land ... Do it Easy ... Tow a Bushtracker