Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

Somebody with 39.5" TSL's

Discussion in 'The Garage' started by wayne, Oct 13, 2002.

  1. wayne

    wayne 3/4 ton status

    Joined:
    Feb 1, 2001
    Posts:
    6,178
    Likes Received:
    0
    Location:
    Carlisle, Pa
    Somebody with 39.5\" TSL\'s

    I need an actual height measurement of both 39.5x15x15 and 39.5x15x16.5. Thanks.
     
  2. zakk

    zakk 1/2 ton status

    Joined:
    Sep 21, 2001
    Posts:
    4,762
    Likes Received:
    0
    Location:
    San Jose CA
    Re: Somebody with 39.5\" TSL\'s

    approx. 38-38.5" depending on tread depth.
     
  3. 72THING

    72THING 1/2 ton status

    Joined:
    Nov 26, 2001
    Posts:
    501
    Likes Received:
    0
    Location:
    Ranburne, AL
    Re: Somebody with 39.5\" TSL\'s

    Mine are on 15" wheels and measure about 38.5" at 18 psi. They have about 85% tread depth. Hope this helps.

    Will
     
  4. MudbogAD

    MudbogAD 1/2 ton status

    Joined:
    Jun 29, 2001
    Posts:
    672
    Likes Received:
    0
    Location:
    Las Vegas Nevada, US
    Re: Somebody with 39.5\" TSL\'s

    Mine are right around 39.3" at 28 PSI and they're pretty much brand new. 39.5/15/15
     
  5. CK5

    CK5 In my underwear Administrator Premium Member GMOTM Winner Author

    Joined:
    May 19, 1999
    Posts:
    21,627
    Likes Received:
    704
    Location:
    CO
    Re: Somebody with 39.5\" TSL\'s

    There is no size differance between the 15" and the 16.5" TSL, just the size of the wheel hole.
     
  6. fulltopblazer

    fulltopblazer 1/2 ton status

    Joined:
    Aug 1, 2001
    Posts:
    484
    Likes Received:
    0
    Location:
    Altus,Oklahoma 73521
    Re: Somebody with 39.5\" TSL\'s

    my 39.5 boggers measure 38" aired up and they are nearly new
     
  7. zakk

    zakk 1/2 ton status

    Joined:
    Sep 21, 2001
    Posts:
    4,762
    Likes Received:
    0
    Location:
    San Jose CA
    Re: Somebody with 39.5\" TSL\'s

    DAMN!!! 28PSI!?!?!?/forums/images/graemlins/eek.gif

    I am running 17PSI and i am still wearing the center out /forums/images/graemlins/eek.gif
     
  8. jimmy88

    jimmy88 1/2 ton status

    Joined:
    Feb 17, 2002
    Posts:
    351
    Likes Received:
    0
    Location:
    Detroit, MI area
    Re: Somebody with 39.5\" TSL\'s

    You prol already been there interco tire just click on the tire style you want and a chart with all the dimensions will be under the tire's picture.
     
  9. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

    Joined:
    Jul 23, 2000
    Posts:
    36,188
    Likes Received:
    1,396
    Location:
    E-town baby!
    Re: Somebody with 39.5\" TSL\'s

    Those aren't real world numbers though...even Interco lies about true height.

    Rene
     
  10. jimmy88

    jimmy88 1/2 ton status

    Joined:
    Feb 17, 2002
    Posts:
    351
    Likes Received:
    0
    Location:
    Detroit, MI area
    Re: Somebody with 39.5\" TSL\'s

    Ahh, theres the rub; what do you mean by true height? Measuring a loaded tire from the ground to the top of the tire really means nothing. The only numbers that mean anything are loaded radius and unloaded radius or diameter. The loaded radius times 2 is what the speedo sees as the tire diameter. The unloaded radius or diameter is what you use for fender clearance. And forget about what the tire sidewall says, thats just for bragging rights.

    Air pressure and the amount of weight on the tire will affect the loaded radius. You can see that when you air down and watch the rim drop closer to the ground as the tire bulges out. You are effectively making the tire shorter or equal to a tire smaller in diameter. From what I've seen most tire spec charts do not give any number for this, they only give the unloaded radius or diameter.

    Soooo, to compare apples to apples you must state the loaded radius at a given tire pressure and the amount of weight on the tire. Also have to account for tire wear and rim width differences. The chart specs are for the specific conditions given in the chart and shouldn't be too far off. If they are then the tire company QC sucks!
     
  11. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

    Joined:
    Jul 23, 2000
    Posts:
    36,188
    Likes Received:
    1,396
    Location:
    E-town baby!
    Re: Somebody with 39.5\" TSL\'s

    What the speedo sees is the circumference of the tire. It does not change with air pressure or weight. The circumference will give you the theoretical diameter as well. Think tracked vehicles...

    Loaded radius is more critical when considering ground clearance. Unloaded radius is only useful for figuring out where the spare will fit/forums/images/graemlins/smile.gif

    So let's ask if anyone has measured the overall circumference of a 39.5" TSL along the center of the tread...

    Rene
     
  12. wayne

    wayne 3/4 ton status

    Joined:
    Feb 1, 2001
    Posts:
    6,178
    Likes Received:
    0
    Location:
    Carlisle, Pa
    Re: Somebody with 39.5\" TSL\'s

    You are correct in that they lie on the size. My 35"SSR's that they claim to be over 35" are no where close. /forums/images/graemlins/angryfire.gif Now my 36's actually measure 35 7/8" at 18psi on a 10" wide rim.
     
  13. jimmy88

    jimmy88 1/2 ton status

    Joined:
    Feb 17, 2002
    Posts:
    351
    Likes Received:
    0
    Location:
    Detroit, MI area
    Re: Somebody with 39.5\" TSL\'s

    </font><blockquote><font class="small">In reply to:</font><hr />
    What the speedo sees is the circumference of the tire.

    [/ QUOTE ]

    Yes, thats right, but its the loaded circumference. Now think about the aired down example. The effective radius is decreased by reducing the air pressure or increasing load. That in turn changes the effective circumference. As the tire rotates it squishes down acting like a smaller tire at every point around its circumference.

    The only analogy I can think of is a circular race track. The outside wall is the tire's unloaded circumference. Now apply a load to the wall and push it down to the inside wall. As you go around the track this loaded or pushed down section stays against the inside wall. So the inside wall is the loaded circumference and is smaller than the unloaded circumference. This is what the speedo sees.

    Hope that didn't just confuse the crap out of ya.

    Ok thought of another example. One last shot at this. You agree its all about the distance the tire rolls for each revolution of the axle shaft? Good, now put a crappy tire and rim on your truck. Fill the tire to the max pressure on the sidewall. Draw a line on the sidewall from the rim to the ground and mark the ground too. Roll the tire forward one revolution, until the line is pointing at the ground again and mark the ground. This is the distance traveled per revolution. Now roll back to the first mark and let all the air out of the tire. Roll the flat tire forward one revolution, until the line is pointing at the ground again and mark the ground. The second distance traveled is shorter. This is an extreme example, but this is what happens to a lesser degree when you load the tire or reduce the air pressure.
     
  14. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

    Joined:
    Jul 23, 2000
    Posts:
    36,188
    Likes Received:
    1,396
    Location:
    E-town baby!
    Re: Somebody with 39.5\" TSL\'s

    The logic doesn't support your argument. For the tire to go a lesser distance the circumference would have to change. The circumference cannot change until you got it flat where the tread would fold over itself effectively lessening the circumference.

    If a tire has a circumference of 113" it will travel 113" every revolution regardless of air pressure as long as the air pressure didn't get so low as to cause the tread to fold over itself (like a really weak car radial with no air)

    Imagine a tank track that could go from normal to completely round like a tire. If the circumference of the track was 25 feet it would travel that 25 feet whether it was round or not...

    Rene
     
  15. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

    Joined:
    Jul 23, 2000
    Posts:
    36,188
    Likes Received:
    1,396
    Location:
    E-town baby!
    Re: Somebody with 39.5\" TSL\'s

    I just wanted to add some real world numbers to the discussion.

    My tires are very worn 36" TSL's. Overall loaded diameter is 34". Loaded radius is 16.5". Circumference is 109". Gear ratio is 4.56:1 and i have a 4 speed tranny without overdrive.

    My job is a 45 minute drive down the freeway so I have lots of opportunity to check my speedo and I have checked it here as well as in many different states on road trips.

    I typically cruise home from work at 63 mph which is where the TSL's are dead smooth and the motor isn't over revving. I have a decent quality 8000 RPM tach.

    So if my speedo is seeing loaded radius my rpm's at 63 mph would be 2925 RPM

    If my speedo is seeing diameter my rpm's at 63 mph would be
    2839 RPM

    If my speedo is seeing tire circumference my rpm's at 63 mph would be 2781 RPM.

    Care to guess what my actual RPM is??





















    My tach reads just under 2800 RPM at 63 mph.

    Even allowing for a bit of tach error (although it's in it's most accurate part of the range) it is not off by 150 RPM.

    Rene
     
  16. jimmy88

    jimmy88 1/2 ton status

    Joined:
    Feb 17, 2002
    Posts:
    351
    Likes Received:
    0
    Location:
    Detroit, MI area
    Re: Somebody with 39.5\" TSL\'s

    1. The tires real or measured circumference does not change. BUT the loaded tire is not round. The contact patch is flat and gets longer with less air or more weight. This is how the "effective" circumference can be smaller.

    2. On the tank track analogy, speed would most likely be measured from the rpm of the drive sprocket and the length of the track would not matter, just the diameter of the sprocket. Changing the drive sprocket diameter would change the speed of the tank for the same rpm. Same as changing the loaded raduis changes the tires effective diameter and the speed of the truck.

    3. As for the real world numbers, it brings up a good point. How to take into account the tires tendency to grow at higher rpm, like dragster tires do.

    Tell you what, I still got the # for BFG. I'll give the guy a call tommorrow and see what he says, I think we can agree that they should know this stuff.
     
  17. wayne

    wayne 3/4 ton status

    Joined:
    Feb 1, 2001
    Posts:
    6,178
    Likes Received:
    0
    Location:
    Carlisle, Pa
    Re: Somebody with 39.5\" TSL\'s

    All this, and I was only looking for some real world hight numbers. /forums/images/graemlins/tongue.gif
     
  18. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

    Joined:
    Jul 23, 2000
    Posts:
    36,188
    Likes Received:
    1,396
    Location:
    E-town baby!
    Re: Somebody with 39.5\" TSL\'s

    Well when I was a kid I used to help out in the pit's for a local racer that raced hobby stock and hit to pass. They ran welded diffs and staggered tire sizes. Every tire was marked with it's circumference, not it's static height or loaded hieght or radius.

    By all means call your contact at BFG...I'd be very interested in what his take is on this.

    I agree loaded radius is important...for calculating ground clearance.

    I doubt an off-road tire is capable of 'growing' enough to make a difference like a wrinkle wall slick would.

    Rene
     
  19. jimmy88

    jimmy88 1/2 ton status

    Joined:
    Feb 17, 2002
    Posts:
    351
    Likes Received:
    0
    Location:
    Detroit, MI area
    Re: Somebody with 39.5\" TSL\'s

    Wow, this is getting too much like work.

    Using your numbers

    109" circumference = 34.7" diameter

    2800 RPM with 4.56:1 final drive = 614.0351 Wheel RPM

    63 MPH using 614.0351 WRPM = 9.0288 feet per revolution = 34.4874" dia (this is still smaller than the 34.7" dia)
    or 17.2437" raduis

    17.2437" radius - 16.5" static loaded radius = .7437" "growth"

    Notice the tire diameter has not grown larger than the unloaded diameter, rather the contact patch is shrinking. Is it unreasonable then to think the tire can, for lack of a better description, rise up on its contact patch 3/4" at 63 MPH?

    That will be the key issue, if BFG says that for anything above, say 25 MPH, you might as well use the unloaded radius for calculations due to the effects of centrifugal force, then this whole debate is irrelevant.

    I'll try to get a hold of BFG tonight, it will be intresting to see what they say.
     
  20. jimmy88

    jimmy88 1/2 ton status

    Joined:
    Feb 17, 2002
    Posts:
    351
    Likes Received:
    0
    Location:
    Detroit, MI area
    Re: Somebody with 39.5\" TSL\'s

    I am kinda bummed I didn't get to talk to the BFG guy that I had talked to about DW, but he left a message on the answering machine. (I talked to a couple other reps, stumped the first one, second one confirmed my thoughts but didn't know the extent of the effect and said she'd have the senior guy call me back) Anyway in his message he used the flat tire example too, but said that for a properly inflated tire, loaded radius has some minor effect, but not a great one. This matches up with your real world numbers. They said they use the unlaoded diameter to calculate revolutions per mile.

    Well, seems I was splitting hairs. Looks like for speed calculations use the unloaded diameter or circumference if you like and, like Rene talked about, for ground clearance while crawling use loaded radius at your aired down pressure.

    I went out and played with the air pressure to get some hard numbers and when I air down my 35's to 15 psi I loose 3/4" of much needed clearance (16-1/16" radius to 15-5/16" radius).

    One of interesting things the BFG guy said was that tires grow a little bit once they are mounted and inflated because the polyester casing stretches and there is a maximum to that after just a couple of days, but it doesn't cause a great change.

    One other thing, when there is talk about the charts not matching the tires "true" height, are we talking about loaded height or unloaded height?

    The charts for my Xterrains list them at 34.7"
    The loaded diameter = 33.37"
    The unloaded diameter = 34.6" (with 10" wide rims and a couple thousand miles on them)


    Using the loaded diameter (measuring the tire on the truck from the ground to the top of the tire) made a 1-1/4" difference.
     

Share This Page