Speed ratings of tires

paul102a3 · August 16, 2009, 03:08:58 AM

This may be a dumb question but I have noticed a lot of you nice folks talking about how fast your buses go. I have seen comments like I hit 85MPH coming down so & so hill, etc.

I recently replaced the tires on my bus and I as I was comparing specs across brands, I noted that all tires in my size 12R22.5 had a max speed rating of 75MPH. My DDEC is set for 75MPH max speed (actual max speed by GPS is 74) so on flat roads I cannot exceed the speed rating rating of the tire.

I realize there is a significant safety factor built into these ratings and they will not fail at 76MPH but my question is how far can you push these tires. I have trucks passing me like I am standing still and I am at my max of 74MPH.

Just wondering.

Paul

John316 · August 16, 2009, 05:02:40 AM

I can't answer how fast you can "safely" go. However, I can say that we had our governor removed (it was at 75), because we wanted the extra speed for passing on two lanes, or whatever. Also, there is nothing more frustrating then trying to pass another vehicle, and not having the extra mile an hour to do it.

We have cruise, but before it was fixed, that was the cruise. Foot to the floor, and not over 75.

God bless,

John

paul102a3 · August 16, 2009, 05:52:05 AM

John,

Its funny that you say needing the extra mile an hour. Earlier this year we followed Kawadiver over to watch the shuttle not launch. Bill's speedo does not work and he did not have his GPS with him.

At one point I had to call him and ask him to slow down as he was about one to two MPH faster than me and driving off into the distance. My DDEC was at the limiter which on that particular day was about 74.5 MPH according to my GPS.

I keep thinking I should raise the limiter but that is far down the list of things needed to get bus dialed in.

Paul

John316 · August 16, 2009, 05:56:46 AM

I know. And try passing a truck that isn't being real good. You try to pass him, and he speeds up just a little, and you can't. You slow back down, and he does too

.

End result was remove the governor.

God bless,

John

Dreamscape · August 16, 2009, 06:01:52 AM

The faster you go, the longer it takes to stop!

I prefer staying under 70, if I am following someone that is going slower I either pass if I can or just sit back and enjoy the ride! I'm in no hurry anyway.

JMW,

Paul

Sean · August 16, 2009, 08:43:41 AM

Quote from: paul102a3 on August 16, 2009, 03:08:58 AM
... I noted that all tires in my size 12R22.5 had a max speed rating of 75MPH. ...

I realize there is a significant safety factor built into these ratings and they will not fail at 76MPH but my question is how far can you push these tires.

Paul,

The maximum speed rating for most tires is related to the load (and vice-versa). In the same way that the load ratings can be exceeded at lower speeds, the speed ratings can be exceed at lower loads. There is a complex formula to determine this, and most tire manufacturers publish tables. The ability to do this varies from tire to tire, so it is always important to check with the manufacturer first. For example, some 315/80R22.5 tires are strictly limited to 55 or 65 mph because the belts are so heavy that the tire can self-destruct above the RPMs associated with those speeds.

Not sure, though, why anyone driving a 20+ ton bus would want to go faster than 75mph, ever.

Quote
I have trucks passing me like I am standing still and I am at my max of 74MPH.

I would not rely on the judgment of a trucker who is exceeding the speed limit regarding tire safety.

-Sean
http://OurOdyssey.BlogSpot.com

John316 · August 16, 2009, 09:24:40 AM

Sean,

I wondered where you were. Great to hear from you. How's it going?

God bless,

John

Sean · August 16, 2009, 02:15:23 PM

Quote from: John316 on August 16, 2009, 09:24:40 AM
I wondered where you were.

I've been right here all along. There just have not been any threads in a while where I felt I had anything to contribute.

-Sean
http://OurOdyssey.BlogSpot.com

jackhartjr · August 16, 2009, 02:34:15 PM

Quote

Sean, that never stopped anyone else!

jackhartjr · August 16, 2009, 02:34:51 PM

Quote from: jackhartjr on August 16, 2009, 02:34:15 PM
Quote[quote

Sean, that never stopped anyone else!

paul102a3 · August 16, 2009, 03:26:00 PM

I too have no real desire to go fast and 65 is just fine with me under normal conditions.

The main reason for my question was to determine how safe or unsafe (based purely on the tire) it might be to hit 80 - 85 descending a hill. I suspect many of us don't think about the speed ratings when we are on the road in our buses as our primary frame of reference is our cars which have much higher speed ratings.

Any thoughts?

Paul

luvrbus · August 16, 2009, 07:58:35 PM

Paul, all 12r 22.5 are not 75 mph tires they come in different speed rating like any other tire.
There is a letter on the side that gives you the speed rating.
I have M rated tires which are a 81 mph tire

good luck

HB of CJ · August 17, 2009, 09:35:57 PM

Not trying to hijack the post, but does anyone know how high of speed rating can Bus Conversion tires have? An example would be does any tire manufacture make a 90 or 110 or even a 120 mph rated bus or heavy truck tire?

Hee, hee, hee, let us see.....3.08 gears, 11RX24.5 tires and a .75 to 1.00 top overdrive gear, plus the governor set at 2400 rpm would equal......hummm. Also wondering how much such a tire would cost? A bunch? HB of CJ