| Author |
Message |
Peter (Sdibaja) (66.123.252.180)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 28, 2002 - 8:32 pm: | |
I had a blowout in the desert (Tonopah, Az and 102 degrees HOT) at 10 pm on Friday night (left rear inner on a 4905). I spent 5 hours at a Rip Griffin truck stop, they many phone calls, and no 12R22.5 was available, new or used.
I had to mount my spare.
Several truckers, and the solo mechanic, thought a metric 16 ply load range H would be fine, but no one could X reference them for height over the phone.
There seem to be many metrics out there at 0 dark thirty, it could be real handy.
Any ideas?
Peter |
RJ Long (Rjlong) (24.127.74.29)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 28, 2002 - 8:42 pm: | |
IIRC, 315/80R22.5 is almost the same size.
Check the various tire sites to confirm. (Michelin, Goodyear, etc.)
Aren't you glad you had a spare!
RJ
PD4106-2784
Fresno CA |
Scott P. (152.163.204.191)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 28, 2002 - 9:17 pm: | |
When you can't find the cross reference, you can do the math to convert the tire sizes:
In RJ's example, a 315/80R22.5:
Width equals first number (315) divided by 25.4, which equals a 12.4 inch tire in this example.
Diameter equals the first number (315) multiplied by the second number (80) multiplied by 12.7, then add the third number (22.5). Diameter equals 42.3 inches.
Gets you darn close to actual sizes, although every manufacturer's tire is a little bit different by the time it gets out of the mold.
Scott P. |
Johnny (63.159.188.84)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 28, 2002 - 10:56 pm: | |
I can't speak for a 12, but an 11R22.5 & a 295/75R22.5 are within 1/4" in height--side-by-side on 2 identical (except for color) Freightliner trucks. Both were Michelins, IIRC.
Also FWIW, I've seen several coaches with 315/80R22.5 tires, so.......
Why everyone can't just use the same sizing system, I'll never know. |
RJ Long (Rjlong) (24.127.74.29)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 28, 2002 - 11:26 pm: | |
Johnny -
The automotive industry has long since gone to metric sizing for tires, and the HD trucking folk are now beginning to come around also.
Now, if the US would join the rest of the world using the metric system, things would be much simpler. . . And I've heard all the arguments for and against doing that, so don't flame me about it, ok? It's just my opinion, as I work with both systems daily, and I've formed my opinion after doing so. . .
RJ
PD4106-2784
Fresno CA |
Peter (Sdibaja) (66.123.252.227)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 28, 2002 - 11:35 pm: | |
I have been checking a few web sites, seems the 11R22.5 is H rated (16 ply) and carries about 500 lb. less than the 12R22.5 which is also H rated (16 ply).
The rim width is the difference, 9" on the 12, 7.5" on the 11... my head swims
Peter |
Peter Broadribb (Madbrit) (170.215.38.227)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 28, 2002 - 11:40 pm: | |
RJ,
No flame intended......
It depends upon how one looks at things. If I was to suggest that all things old including period cottages, antiques, old cars and buses, etc were thrown away and only new things were allowed because of one reason or another, there would be an outcry from nearly the whole world. I felt that the "English" systems of feet and inches and lbs and ounces was part of the England's quaint history and loved it. I was very upset at the demise of the Englsih pound shillings and pence system, just so "we" could be inline with the "French" metric system. It was supposed to make things easier for commerce, but we still have francs, gildas, marks, etc and so any simple computer system could have made the conversion in a second.
Many I know back in Limey-land, still gauge distant in feet and weight in lbs, and they are the ones who have to convert it to "bloody metric" to be politically correct........ LOL.
Glad to be living in America where the old values still exist, for the moment.
Peter. |
Johnny (63.159.188.84)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 28, 2002 - 11:45 pm: | |
It isn't just HD's--many trailers still use the old sizes. My car trailer had Goodyear 7.75x14C's when I bought it. It now has Tow master G78-14D's (which work out to a 215/75D14 in a Load Range D) on it.
OTOH, my J-20 called for 8.75R16.5D's, & my friend's RevCon motorhome has 9.50R16.5E's in front & 12R16.5F's in back. Off-road tires STILL use the old-style sizes (like the 30x9.5R15's on my wife's Jeep).
I'll stick to feet & inches. |
Peter (Sdibaja) (209.242.148.130)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 30, 2002 - 9:18 am: | |
It looks like with 9" rims I need to stay with 12R22.5 tires or the 315/80R22.5 H.
The 11R22.5 and smaller metrics are only good to 8.25” rims.
So, I may switch rims, anyone been using the 11R22.5 or smaller metrics?
The 275/80R22.5 H is rated at 6940 single and 6395 dual, that figures out fine on a 4905 with GAWR Front = 12,500 # and GAWR Rear = 20,000 #.
The 315/80R22.5 H is rated at 8270 single and 7610 dual… seems like overkill, but I run fast (70-75) and hot (100 degrees plus) and blowouts are no fun at all.
Of course, the 11R22.5 and 275/80R22.5 H are Much cheaper (and available on the road) than the 12R22.5 and 315/80R22.5 H.
Peter |
Dallas Farnworth (216.98.68.82)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 30, 2002 - 10:19 am: | |
Peter,
You might want to check with the mfg. of your tires....
Bridgestone/Firestone only speed rates certain tires. I'm not sure about the others. If you have a blow out at speed with a tire that's not speed rated, it can end up being your fault.
I didn't know this til I went to a couple of sites looking for tires for my 4103.
Dallas |
Jim Wilke (152.163.204.194)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 30, 2002 - 11:17 pm: | |
Peter, I have had 12R22.5 tires on my 8.25" rims for 3 years now. About 15000 miles. No problems. The tire guy said that 12R was as BIG as I should go on 8.25", not the other way as you are saying.
How do you know yours are 9" anyway?
Jim Bob |
Peter (Sdibaja) (64.165.10.152)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, July 31, 2002 - 9:53 am: | |
Jim Bob:
I did not know if I have 9" rims: I assumed from the various tire web sites that since 9" is the suggested width for a 12R, that 9" rims would be standard issue by GM.
I was wrong, they are 8.25" rims, it is stamped on the rims, and I checked it with my tape. They are probably not the originals but they have been on there in service for at least 12 years.
I spent some time inspecting the fleet of trucks and busses in the city yard, about 50 of them, of various makes and ages. Only the fire trucks have 12Rs, all the rest have 11Rs.
I also talked with the fleet manager; he says the 11R would be fine, it is rated for the load, and even the really heavy loaded busses and trucks have no failure problems.
He thinks the fire department has too much money or they would run 11Rs also.
I think I will seek out an 11R of the same height as my others for a new spare. When I replace the existing tires I think I will go with the 11R (or metric equal).
Peter |
Stephen Fessenden (Sffess) (208.230.117.47)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, August 02, 2002 - 8:37 pm: | |
There are some Metric tires that do not have an equivalent. Some Ford Mustang tires. That may not apply to bus tires. But if you think the numbers always mean exactly what they say, try putting a 1.75 X 26 bicycle tire on a schwinn rim designed for 1 3/4 X 26 tires. The tire dealer should be the expert here, not the board. |
RJ Long (Rjlong) (24.127.74.29)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, August 02, 2002 - 9:04 pm: | |
Good point, Steve, about the tire dealer being the expert.
That is, of course, if you can find one that's been in the business long enough to know what he's talking about and is truthful about it. . .
Busnut Daris B. of S CA has a nifty MPH calculator on his website that can help you when determining tire sizes and their effect on speed. His homepage is: http://home1.gte.net/res07rfl/
Click the "MPH Calculator" link on the left to get to it.
RJ
PD4106-2784
Fresno CA |
DaveD (216.18.113.69)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, August 07, 2002 - 9:28 am: | |
According to the MCI Parts manual, rims are 22.5" x 8.25". Tires are 12R22.5.
DaveD |
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