What Is Q78?? - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 08-21-2000, 06:02 PM
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What Is Q78??

I often see this when tires are being referenced. Is it a size or a style??

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Kevin
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post #2 of (permalink) Old 08-21-2000, 06:36 PM
 
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Re: What Is Q78??

It is a size....I think. My friend has them on his yj, They are swampers that are about 36inches by 11 inches wide bias plies. Hope this helps out.

Ben

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post #3 of (permalink) Old 08-21-2000, 11:56 PM
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Re: What Is Q78??

Just purchased a set of Q78x15 TSLs. Yep, the Q78 is a size, I think - What size??? Haven't got a clue. People at the tire shop - not noted for their debth of knowledge, maintained their rep on this one too. They didn't know either.
Basically it is a size between a 35 and a 36, and at least the TSLs are more true to size than a lot of the other tires, but wait, I don't know what the Q78 means, so it may not be true to size after all. [img]/wwwthreads_images/icons/tongue.gif[/img]. It is also more narrow than a 12.5 and wider than a 10. And best of all when a fellow wheeler looks over and says, "Is that those 34x9.5s I've heard so much about?" After a proper pause, you just kinda look down your nose a little, get an 'I'm sorry you're such a dumb $hit' look on your face, and say, "Q78s!!!" Huh?? [img]/wwwthreads_images/icons/laugh.gif[/img]
Seriously, if anyone knows what Q78 means, I would like to know. Then I can have a second shot when the guy says, "Huh??? What's a Q78?" [img]/wwwthreads_images/icons/laugh.gif[/img]


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post #4 of (permalink) Old 08-22-2000, 08:01 AM
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Re: What Is Q78??

Q78 is a size, it goes back aways, to the late 60's at least, when my '78 Scout II came with H78's on it, and my dads '68 Roadrunner had a letter size tire . I have seen a tire chart listing the letter sizes, but I'll be damned if I can remember where I saw it. Basically each letter stands for a size, and there are quite a few of them. Why the "Q" designation has remained I don't know, but I'll see what I can come up with. I have a few "old" manuals at home for various vehicles, so I'll see what I can dig up. If not, I'll ask my dad, he used to run an automotive shop in the 60's.

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post #5 of (permalink) Old 08-22-2000, 09:20 AM
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Re: What Is Q78??

Good old JP mag had it a while back.
This load-based system was introduced worldwide in 1968. The designation takes into account the load carrying capability and aspect ratio in the alpha character with aspect ratio and wheel diameter also included.

Example: Q78-16

"Q" designates the load and size relationship. Letters for passenger cars range from A to N. Above N indicates truck and severe use duty. If this were a radial, an R would precede the Q.
"78" indicates the series, better described as the size relationship between the sidewall height (section height) and the sidewall-to-sidewall width (section width). A 78-series tire has a sidewall height whose measurement is 78 percent of that of the section width.
"16" indicates wheel diameter.



JAY 75 CJ-5
post #6 of (permalink) Old 08-22-2000, 10:35 AM
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Re: What Is Q78??

<font color=purple>EJMAMMO basically spelled it out. Many of us remember the 1970's when hot rod cars had "50's" or "60's" on them. The 50 or 60 didn't designate the width (as many assumed) but rather the aspect ratio. The L, M, or N designated the width. So, you'd see cars with L60's on the front & N50's on the back.

BTW, the designated size (according to both Interco & Gateway - producers of the Buckshot Mudder) a Q78 is a 35.5X11 - mine measure 35.0" across the center mounted on 15X7's. Buckshots also come in one size larger - the R85, which is considered a 37X13. An old size that is suddenly all the rage again, BTW. At one time, the largest Swampers available were designated as 37X13 - a size designed to compete directly with R85 Buckshots IMO. That size has since been renamed 38X12.50 (sometime in the early 80's). That was a marketing move in an attempt to make sure the 36" & 37" TSL didn't cannabalize each other's sales & it took place prior to the release of the 38.5" TSL, so that was another reason for the move.</font color=purple>

TEX

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post #7 of (permalink) Old 08-22-2000, 10:51 AM
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Re: What Is Q78??

thanks for the info.

i wasnt around until the late 70's so most of this is new to me. LOL

Kevin
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post #8 of (permalink) Old 08-22-2000, 10:56 AM
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Re: What Is Q78??

<font color=purple>I'll consider my nose officially "rubbed in it". [img]/wwwthreads_images/icons/laugh.gif[/img]</font color=purple>

TEX

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