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% Tread as a function of tire size.

Discussion in 'Commercial Snow Removal' started by muddy_blacklab, Dec 16, 2002.

  1. muddy_blacklab

    muddy_blacklab Junior Member
    Messages: 10

    I have been studying various tire sizes for my truck and have a somewhat unique application requiring maximum traction for extreme hills (30-45% grade with turns). I have read every thread about tire size in this forum, but there is still a question I am trying to get answered. My goal is to optimize the tire traction on hills (without chains…I use traction devices when I have to).

    I want the most lbs/sq in (skinny tire) to cut through the packed snow, but was wondering if the percent tread (space to lug ratio) changes as function of tire size. I am planning to purchase Cooper Discover M+S. Are the lugs constant size and simply spaced out more, or are the lugs proportional to the tire size as you go to larger sizes?

    If the lugs are simply spaced out more it would mean a 235/85 16 would have the same lbs / sq in as a 245/75 or 265/75, and in addition, the wider tire would have bigger spaces between the lugs (something I would like for my specific application). I therefore would optimize for the wider and larger diameter tire.

    If the second case is true, where the lug size is proportional to the tire (the % tread doesn’t vary with tire size) it would mean I should stick with the 235/85 16 for the most lb/sq in.

    Any insight would be appreciated.
     
  2. Alan

    Alan PlowSite.com Addict
    Messages: 1,393

    First, stay away from the Discoverer M + S! We ran a set last year and they are terrible tires. Not too bad if you're moving, but starting traction was very poor. At best they were only marginally better than the normal Discoverer, which I think is billed as an all season. In addition they didn't lst real well either.

    I think the tread pattern is proportional to tire size, with some limits. I know that when you make radical changes in width they sometimes add a row of tread blocks as the tire gets a certain amount wider.

    Not trying to be nasty here, but I think you may be over estimating your grades. 30% is hard to walk up, roughly the equivalent of a 4/12 roof pitch. We've got one steep one here that we thought was much worse than it is. Finally checked it with and inclinometer and correlated that with GPS. It turned out to be around 10%. It takes a REAL hill to make 45%.
     
  3. wyldman

    wyldman Member
    Messages: 3,265

    Alan - I'd be interested to hear more about your experience with the Cooper Discoverer M&S.How quickly did yours wear out ? I have seen pretty good wear so far,but they don't have a lot of miles on them yet.We have tried sets on several of our trucks and the drivers raved about them.The reason they liked them so much IS the fact they have so much starting traction.No need to get a run before dropping the blade.We have converted pretty much all of our trucks over now,and bought 8 more yesterday.I have found them to be awesome tires,especially on our heavier vehicles.Put a set on one of our Dodge Cummins yesterday,and have a hard time breaking the tires loose on solid ice !! And the truck makes some serious torque and HP.On the lighter trucks,they will slip a little on the ice but nowhere near a regular truck tire.I wonder if they changed something with the tires?

    muddy_blacklab - as far as the tread pattern question,it depends on the manufacturer.With the Cooper M&S,I find the tread blocks are more closely spaced on the skinnier tires.I too had been trying to decide between tall and skinny or a wide tire.I have tried both with the coopers,on the same truck,and both seem to work just fine,but do have their differences.The two sizes are 235/85R16E and 265/75R16E.Both are very close in OD,but the 265 is much wider.The tread blocks are also more spaced out.The 235's do a little better on sheer ice,or on ice covered in deep snow.The 265's push better when the pavement or packed snow isn't as slick,as you have more rubber on the road.On steep hills,the 265's feel much more planted,and I don't feel like I'm gonna slide back down.I also have found the 235's track much better on snowy,rutted roads,or when crossing a large windrow.The 265's tend to float up on this stuff and the truck gets a little loose.This is more predominant at higher speeds.If i had to pick,I'd go with the 265's for all round use.I would also highly recommend the Discoverer M&S based on my experiences,but would like to hear more from Alan as to why he was unhappy with them.
     
  4. Mick

    Mick PlowSite.com Veteran
    from Maine
    Messages: 5,546

    I've been pretty interested in this thread.

    Last year when I bought the one ton, I put on a full set of Cooper Discoverer M&S LT225/75/16 Load Range E and studded all six - DRW. This is a beefed up flat bed and carries a two yard sander. 6.5 turbo diesel. The truck was bought for sanding but I have used it during the summer to drive to work with no load.

    With the summer tires, it's great.

    The Coopers get a mixed review. I have no problem breaking traction even with the duals. However, I give the credit to the incredible power of the TD. I don't get the stopping action I think I should on iced over steep slopes. But I've attributed this somewhat to momentum of a loaded Vbox. At low speeds, the traction on the level or uphill is great. Sanded a road with a couple of fairly steep places this morning in 2wd. Then I slipped when I went to back up my own driveway and went to 4wd. What really puzzles me is how it acts at highway speeds on snowy roads. It always seems as if I'm about to lose control of the truck. Not sure if this is from very responsize steering or perhaps from the studs (I have experience driving with studded tires). On dry or rain-slick surface it's fine. I just can't figure it out.

    I use unstudded Trail Busters on the 1500 for plowing. Great tires.
     
  5. Alan

    Alan PlowSite.com Addict
    Messages: 1,393

    I think the wear can be at least partially attributed to a driver with a bit of a heavy foot when roads are dry. In hinidsight I was probably out of place mentioning that, although they were claimed to outlast the Weathermasters we ran in the past and didn't.

    As for traction, they would consistently break loose when starting from a standstill on slightly snow covered surfaces. For example, at the back end of a run, where you're on previously plowed pavement with a haze of snow and probably a little salt induced slush they would break loose. The drill got to be back up, stop, shift, spin them up once and then get off the throttle and let them hook up and you could go fine. Both of us who drove that truck regularly had the same problem. This is on a K2500, 350 auto with 3.73 gears. Heavy rig, vee plow up front and vee box in the back, usually not loaded heavily when plowing though. Tires were inflated to maximum pressure for load carrying ability, which could also be a factor, but has also been the case with everything else we ran for rubber.

    I will admit to being prejudiced about tire designs. The M & S has a narrow center rib. Particularly at high inflation pressures, that rib takes a bunch of the load, and being solid it acts like a skate blade. That is all my opinion, but I really try to avoid any tire with a solid rib, either in the center or on the shoulders.
     
  6. muddy_blacklab

    muddy_blacklab Junior Member
    Messages: 10

    Thanks Alan. Despite their aggressive (but worn) design, my current tires have two ribs about 1.5" wide located 2" from each sidewall. It took me a few seasons to realize these were acting like skis (vs. your single “skate”). I didn't notice the center rib on the Cooper Discover M+S when I looked at the tires but I see it now that you point it out. My tires have a cross sectional area of about 3” of these ribs. As you say the Discover M+S rib is narrow, and in the center. I am not saying this eliminates this tire choice for me, but it is another consideration.

    What PSI are you running? Does this tire pressure visibly change the flatness of tread and push the center of the tire out (e.g. the rib)?


    Wyldman- Thank you for such a detailed description on the variation of performance with the two sizes. Can you describe the 235’s on hills? Is it the opposite of the above? How much weight are you typically carrying and what tire pressure are you running?

    Mick – You sanded a road so can I assume your truck was empty when you slipped backing up the driveway? What pressure do you use to carry that load with duals?

    I think I will hold off my purchase for a week or two. Thanks for all your help.
     
  7. Mick

    Mick PlowSite.com Veteran
    from Maine
    Messages: 5,546



    No, it still had about a yard left in it. I was getting ready to sand my own driveway. As for pressure - whatever the recommended pressure is on the sidewall. I have my tires mounted for me at the beginning of the season. I do very little of my own maintenance work beyond checking fluid levels. I know some people believe in adjusting tire pressure, but I don't. If you need to adjust from the recommended pressure, then I'd think you have the wrong size or weight range tire.

    ps: I'm kind of confused with your question - being able to carry the load is a function of the tire itself not the air pressure in the tire. I think these tires are rated at 2650# each so the rear end should be able to safely carry 10,600# at the recommended inflation.
     
    Last edited: Dec 17, 2002
  8. Alan

    Alan PlowSite.com Addict
    Messages: 1,393

    These were either 245/75 or 235/85, can't remember just which although I think 245s. Either would have been Load Range E, 3040 lbs or thereabouts and have a maximum inflation of 80 psi. I think the tire takes on a more "round" cross section when inflated fully. That would tend to increase the weight carried on the center of the tread (I assume). I thinkt hat would make the center rib more of a factor than it would be at lower pressures. I would like to run softer, but when the vee box is loaded it's pushing the load capacity of the tires at full pressure.

    I'll check the tires we've got on that truck this year. It's another Discoverer variant and seems to work well so far. The tread blocks are a little bigger than I really like but they have quite a lot of void area and seem to clean well. Only used them for one storm so far, and that was without the vee box so the truck was light on the rear. They did seem to generate plenty of traction pushing 10" or so of wet snow on top of soft ground.
     
  9. plowking35

    plowking35 2000 Club Member
    from SE CT
    Messages: 2,923

    I previously ran the Cooper Discoverer CTD, they were a great tire, but Cooper has since stopped making them. I replaced them with Discoverer S/T. The S/T is avery good tire, but not quite as good as the CTD for traction. I also ran A/P on the front and they were not very good at all IMO. Only about 20K and traction was adequate at best.
    As for roof angles, a 30 degreeangle equates to about a 6/12 pitch. I believe a 4/12 is a 22.5 degree angle. 12/12 is 45 degree and 10/12 is 40 degree. 9/12 is 37.5, 8/12 is 35 degree, 7/12 is 32.5 degree
    Dino
     
    Last edited: Dec 17, 2002
  10. Alan

    Alan PlowSite.com Addict
    Messages: 1,393

    The Discoverer S/T is what we've got now, just confirmed that with my son.

    Dino, the original thing about slopes was in percentages not degrees. You got the degrees vs pitch right on the money. Percentage is ft of rise in 100 ft of run. Expressed as a function of X/12,, 12 is approximately 1/8 of 100 so 4 being roughly 1/8 of 30 I ball parked it at 4/12. In actuality it's on the order of 3.6/12, not all that steep, but still a bear to push up.
     
  11. plowking35

    plowking35 2000 Club Member
    from SE CT
    Messages: 2,923

    Ahhhhh Alan I see that % vs degree thing now. I have been framing a house, and the speed square was dancing all over the place as we have mulitiple roof pitches, and I was all excited about quoting numbers. I am humbled by your mathematics my friend.
    Dino
     
  12. muddy_blacklab

    muddy_blacklab Junior Member
    Messages: 10

    I emailed Cooper Tire with my original question on this thread and received the following response:

    "As a tread pattern is applied across a range of sizes the pattern is
    proportionalized for each size meaning that the lugs will get bigger both in
    width and circumferentially as the width and diameter of the tire increase.

    It sounds in your case you may prefer to use a 'skinny' tire but note that
    the tire size must also be capable of the load requirement of the vehicle"

    My original motivation for asking the question was to maximize the lbs/sq in, but in seeing the comments on this thread it has reminded me of my original concern with the cooper Discover M+S and that is that the groves are potentially too small and will fill up with hard packed snow at the slow speed of my specific application. I can barely fit a pencil in the horizontal groves when I looked at the tire. At 55 MPH the tire I suspect will be self cleaning, but again, I am plowing downhill VERY steep, and trying to control my decent, and going about walking speed. The groves may in fact fill with snow.

    The comment from Alan struck me and is possibly consistent with this theory:

    Why would the spinning of the tire improve traction? Maybe it is throwing the snow by centrifugal force, allowing a good bite. I don’t think it is because the tire is heating up.
    Should the thickness of horizontal groves be a consideration in tire selection that is optimized for low speed traction on hard packed snow?
     
  13. 90plow

    90plow Senior Member
    Messages: 738

    Wyld man

    Got one quick off topic question for wylde man... am I reading your profile wrong or do you really run a 12ft western plow on a dodge ram 2500?
    Eric
     
  14. wyldman

    wyldman Member
    Messages: 3,265

    The skinnier 235's seemed to slide a lot more on hills than the larger 265's when it's very icy.It's kinda hard to explain.The 235's have better starting and stopping traction,but when the whole truck starts to slide on ice,you don't have a lot of control.The 265's will still slide,but it's much easier to regain traction and the whole truck doesn't slide away.

    Lower pressures help alot,but I have to run them at the max 80 psi,as I'm usually very heavily loaded with the blade,salter etc.
     
  15. Alan

    Alan PlowSite.com Addict
    Messages: 1,393

    I think it actually is because the tire heats slightly. I'm talking about losing traction on the very thin coating of snow left right behind the plow. Barely enough to cover the pavement, might even be a very thin ice layer that occurs almost instantly when you peel the snow cover off. The tires might spin for maybe a second or less, but with the weight of the truck and load on them they would make heat very quickly. Then a brief pause as they "spin down" and you could feel them "catch" just before they stopped winding down. You could feel the slight jolt as they caught. Applying throttle after that would result in no spin, just instant movement.

    Interesting note here. I think my 245/75R16s are rated at 3040 lbs each at 80 psi. Yesterday I took on my normal spreader load of one buckte from the suppliers JD 244 loader. With the vee plow on the front the truck grossed 10,220, with 5,980 on the rear axle, 100 lbs under the max for the tires.
     
  16. muddy_blacklab

    muddy_blacklab Junior Member
    Messages: 10

    Enclosed is a photo of my current tire, Uniroyal Laredo AWT w/25,000+ miles (this is the first time I have posted a photo…so I hope it is enclosed). Notice the lack of horizontal groves. This tire slides on the hard packed snow left after plowing. The center has no horizontal groves. The nice thing, however, is the truck tracks fairly well to steering when locked up or pumping, going downhill. I attribute that to the 4 deep groves that run around the circumference of the tire. The Cooper Discover M+S has both lots of horizontal blocks and 2 big groves that run around the circumference. I would call the blocks small on the Discover M+S (about 1” by 1”). Does anyone have experience in both the large tread block (like commercial tread tires) and the small tread block tires like the Discover M+S?

    mvc-038s.jpg
     
  17. Got Grass?

    Got Grass? Senior Member
    Messages: 641

    If you take a look at trailer tires, including semi's thay only have vertical groves & no horizontal ones as there is no need for breaking power, only a need to keep it from sliding sideways & possible jack-knifing.
    Rain tires are designed the same way with verticial groves but also have horizontal ones to push the water from under the tire.

    Normal tires have some combination of both.

    Hoizontal grooves will provide the best traction for accerlating, breaking & to prevent getting stuck as you will see on heavy equipent such as skids & tractors. But thay also wear out much faster at higher speeds, just like how thay tear up the turf.

    Unfortunaly for us driving on wet pavement, turning on ice & power to push thoes large piles, & wear under dry conditions. We demand the best of all worlds. It's all a matter of finding a tire with a combination for your specific truck & your personal demands. Unfortunatly there is no ideal tire that works for everyone. So it's a matter of personal choice.