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Old 07-12-2013, 06:49 AM   #11
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Here is a copy of the email I received yesterday from Maxxis, per my dealer request. (including original spelling)

Bobby,
The spped rating on for the Maxxis M8008 ST Radial is "Q", which is 99 MPH. However, according to the Tire and Rim Association the inflation pressures and load specifications in general for all ST Radial trailer tires, regardless of the manufacturer, are designed and rated at 65 MPH. If the speed is higher than 65 MPH, the pressure and load need to be adjusted according to the following guidelines:
From 66 to 75 MPH – the tire inflation pressure needs to increase 10 PSI (not to exceed the maximum PSI the tire is rated for) but requires no load adjustment.
From 76 to 85 MPH – the tire inflation pressure needs to increase 10 PSI (not to exceed the maximum PSI the tire is rated for) and load should be reduced by 10%.
We hope this information is helpful. Thanks for your email and interest in Maxxis Tires.
Best Regards,
The Maxxis Support Team

I am no curious as to why a manufacturer would state their tire is rated for a certain speed, then also say that an outside organization (which Maxxis is probably a member of) dictates the speed. You would think the manufacturer would be the one dictating what their product can or cannot do.
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Old 07-12-2013, 09:47 AM   #12
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Quote:
Originally Posted by wmtire View Post
Here is a copy of the email I received yesterday from Maxxis, per my dealer request. (including original spelling)

Bobby,
The spped rating on for the Maxxis M8008 ST Radial is "Q", which is 99 MPH. However, according to the Tire and Rim Association the inflation pressures and load specifications in general for all ST Radial trailer tires, regardless of the manufacturer, are designed and rated at 65 MPH. If the speed is higher than 65 MPH, the pressure and load need to be adjusted according to the following guidelines:
From 66 to 75 MPH the tire inflation pressure needs to increase 10 PSI (not to exceed the maximum PSI the tire is rated for) but requires no load adjustment.
From 76 to 85 MPH the tire inflation pressure needs to increase 10 PSI (not to exceed the maximum PSI the tire is rated for) and load should be reduced by 10%.
We hope this information is helpful. Thanks for your email and interest in Maxxis Tires.
Best Regards,
The Maxxis Support Team

I am no curious as to why a manufacturer would state their tire is rated for a certain speed, then also say that an outside organization (which Maxxis is probably a member of) dictates the speed. You would think the manufacturer would be the one dictating what their product can or cannot do.
With the caveat that the response is a little hard to understand, you would thin speed rating would be calculated at load, I am reading their response to effectively say the following:

For every 10mph over 65, adjust psi up 10 OR deduct load by 10%. Assuming that most of us run max psi regardless in our trailer tires, I am reading this to say that at 76 MPH you have 20% load carrying capacity. Of course this only applies to Maxxis tires.

IMHO this certainly adds to the argument that you should step up one load range when selecting new tires.

For me it works out as follows:
Maxxis M8008 radial in OEM tire size (225/75-15 LRD) is rated at:
2540 @ 65 MPH.
2286 @ 66-75 MPH
2032 @ 76-85 MPH
1778 @ 86-95 MPH
1524 @ 96-99 MPH (max rated speed)

Now I am curious if Greenball who posts a 75 MPH speed rating is rated for full load at that speed. And the same for Taskmaster who does not list speed rating on website but is reported through dealers to be N speed rating or 87 MPH.

If either of those report they are rated for full load at speed rating, they would be IMHO a superior product simply from the rating standpoint.

Going back to the M8008 tire, to get 2500 load capacity at 75 MPH I would need their E rated tire which is rated at 2830 @ 65 MPH.
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Old 07-12-2013, 09:54 AM   #13
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Originally Posted by wmtire View Post
Bobby,
The spped rating on for the Maxxis M8008 ST Radial is "Q", which is 99 MPH. However, according to the Tire and Rim Association the inflation pressures and load specifications in general for all ST Radial trailer tires, regardless of the manufacturer, are designed and rated at 65 MPH. If the speed is higher than 65 MPH, the pressure and load need to be adjusted according to the following guidelines:
From 66 to 75 MPH – the tire inflation pressure needs to increase 10 PSI (not to exceed the maximum PSI the tire is rated for) but requires no load adjustment.
From 76 to 85 MPH – the tire inflation pressure needs to increase 10 PSI (not to exceed the maximum PSI the tire is rated for) and load should be reduced by 10%.
We hope this information is helpful. Thanks for your email and interest in Maxxis Tires.
Best Regards,
The Maxxis Support Team
...
So if the max pressure on the side of the tire is 65psi, you are limited to 65mph.
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Old 07-12-2013, 10:06 AM   #14
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[QUOTE=OldCoot;419873][QUOTE=wmtire;419781]Bobby,
The spped rating on for the Maxxis M8008 ST Radial is "Q", which is 99 MPH. However, according to the Tire and Rim Association the inflation pressures and load specifications in general for all ST Radial trailer tires, regardless of the manufacturer, are designed and rated at 65 MPH. If the speed is higher than 65 MPH, the pressure and load need to be adjusted according to the following guidelines:
From 66 to 75 MPH the tire inflation pressure needs to increase 10 PSI (not to exceed the maximum PSI the tire is rated for) but requires no load adjustment.
From 76 to 85 MPH the tire inflation pressure needs to increase 10 PSI (not to exceed the maximum PSI the tire is rated for) and load should be reduced by 10%.
We hope this information is helpful. Thanks for your email and interest in Maxxis Tires.
Best Regards,
The Maxxis Support Team
...
Quote:

So if the max pressure on the side of the tire is 65psi, you are limited to 65mph.
Did you mean to say limited to 65psi? Their response clearly states you can run them over 65 MPH, but NOT 65 psi. However over 65 mph you lose load carrying capacity.
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Old 07-12-2013, 10:13 AM   #15
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[QUOTE=jeeplj8;419884][QUOTE=OldCoot;419873]
Quote:
Originally Posted by wmtire View Post
Bobby,
The spped rating on for the Maxxis M8008 ST Radial is "Q", which is 99 MPH. However, according to the Tire and Rim Association the inflation pressures and load specifications in general for all ST Radial trailer tires, regardless of the manufacturer, are designed and rated at 65 MPH. If the speed is higher than 65 MPH, the pressure and load need to be adjusted according to the following guidelines:
From 66 to 75 MPH the tire inflation pressure needs to increase 10 PSI (not to exceed the maximum PSI the tire is rated for) but requires no load adjustment.
From 76 to 85 MPH the tire inflation pressure needs to increase 10 PSI (not to exceed the maximum PSI the tire is rated for) and load should be reduced by 10%.
We hope this information is helpful. Thanks for your email and interest in Maxxis Tires.
Best Regards,
The Maxxis Support Team
...

Did you mean to say limited to 65psi? Their response clearly states you can run them over 65 MPH, but NOT 65 psi. However over 65 mph you lose load carrying capacity.
No, it clearly states: (not to exceed the maximum PSI the tire is rated for) so if you cannot exceed 65 psi, you cannot increase the pressure to go 75mph. Kinda weird IMO. Really doesn't make any difference to me, I limit mine to 65 psi and 65 mph.
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Old 07-12-2013, 10:17 AM   #16
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Coot, take a look at the chart Bobby posted earlier that lists load capacity at PSI. If you put that chart together with the formula in their response, the numbers get worse. you would be at 2270 capacity at 65psi at 75 mph.
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Old 07-12-2013, 10:25 AM   #17
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Coot, take a look at the chart Bobby posted earlier that lists load capacity at PSI. If you put that chart together with the formula in their response, the numbers get worse. you would be at 2270 capacity at 65psi at 75 mph.
Not arguing, but to me, if the max pressure is 65psi, you cannot run 75 psi period regardless of what the load would be. To me it is all ridiculous.
Outa' here.
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Old 07-12-2013, 10:44 AM   #18
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Ok, I'm not a smart man (I'm not even an attractive man). So, I'm going to try and talk myself through this. Especially since I am running Maxxis tires. (This is all a moot point- I almost exclusively run at 61mph. But, I do like the idea that I can exceed that if I need- like the night that we had a screaming baby for 55 minutes and had reservations that we had to plow through to get to.


-- My weights and tires:

Per axle, I'm carrying 5,800 and 5820 pounds. While it's not perfect, the simplest math is adding the 2 axles together and then dividing by 4 tires:
(5800+5820) / 4 = 2,905 for a ballpark of what each tire is carrying. (I know it's not exact as my camper is likely heavier on the driver's side than passenger side. But, let's ignore that for now.)

I'm running ST235/80R16 tires which have a maximum load 3,420 pounds. Per the chart, my actual PSI needed would be 65psi for 3,000 pounds.


--- 66-75mph:

That means, at 75psi, I can drive 66-75mph and still carry the 3,000 pounds. (Which, I actually am one of the simpletons and go with 80psi because that's the wheel and tire max and it's less thinking that way.)


--- 76-85mph:

Now, here's where I start to get confused. (I personally wouldn't knowingly exceed 75, so this is largely an educational discussion.) From 76-85mph, I need to increase another 10psi and I *lose* 10% of the capacity. The problem here is that I can't- my maximum sidewall and wheel capacity is 80 psi. (i.e. I can't go to 85 psi like I feel I'm reading).

But, looking at it another way - at 80psi, the load carrying capacity is 3,420 pounds. Taking away 10% of that is 3,078 pounds. Would I be OK at 76-85mph because my load is 2,905 and that's less than 3,078? Or am I not OK because I didn't increase the psi by 20 pounds?
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Old 07-12-2013, 10:54 AM   #19
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Not arguing, but to me, if the max pressure is 65psi, you cannot run 75 psi period regardless of what the load would be.
I think you two may be making different points. I agree with OldCoot - you cannot exceed the maximum PSI on either the tire or the wheel.

I think what jeep is saying is that to go faster than 65mph, you need to have a load that requires less than the maximum psi. (See my previous post - for my tires, I need 15psi less than the maximum to carry the approximate load on each wheel.)

While I prefer not to drive over 65mph, theoretically, according to the formula published by Maxxis, I can drive up to 75mph because I air my tires to the maximum specified on the sidewall and wheel itself (80psi vs. 65psi).

What gets confusing is once you want to exceed 75mph- you not only need extra PSI (again, not to exceed the maximum of the tire nor wheel) and you lose 10% load capacity at that PSI rating. Or something...

Again, I'm with OldCoot- I almost exclusively drive 61mph on the highway so it's largely a moot point. But, an interesting discussion none the less as long as people don't let their feathers get ruffled.
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