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Author Topic: '78 cb750f tire sizes - utter confusion  (Read 1725 times)

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Offline dboblet

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'78 cb750f tire sizes - utter confusion
« on: May 08, 2008, 03:48:23 PM »
OK, here we go again.  I've looked a little through the forums but here's my setup and question.  My tires are original equilpment.  (as in yikes!!) and though they still have some tread, there are some pretty interesting canyons that didn't used to be there back in '78.  The word POP comes to mind if I think about riding on 'em.  So, time for new.
Front 3.25H19  Rear 4.00H18
I believe that translates to
Front 100/90-19 and rear 110/90-18
two things. 1st what the #*&%*##@ do those numbers mean?  Well, the 18 and 19 are obvious.  But seems that the size tire doesn't exactly follow a smooth progression since the width varries as well as the height (?) 
All I really want to know is how large a tire I can put on the rims... hopeing for a larger rear, but not sold on it yet.
she's got the original rims (comstar wheels).
Once again, thanks in advance. (have I worn out my welcome yet?)
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matt365

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Re: '78 cb750f tire sizes - utter confusion
« Reply #1 on: May 08, 2008, 04:26:57 PM »
100/90/19

120/90/18

The first # is the width, the second is the % of the side compared to the width.

I've got an F, and those are the tire sizes I'm running.
The rear will deform the tire if you go any bigger than the 120 on the 2.15 comstar rim.
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Offline cafe750

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Re: '78 cb750f tire sizes - utter confusion
« Reply #2 on: May 08, 2008, 04:53:01 PM »
I'll bring the keg, if everyone else brings their own chair... ;)
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Offline dboblet

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Re: '78 cb750f tire sizes - utter confusion
« Reply #3 on: May 09, 2008, 09:06:58 AM »
hey, why are tires in the conversion chart given in two 'ranges' as in the chart excerpt below:
110/90   MP85   4.00/4.75
120/90   MR90   4.50/4.75

What I want is a 4.25.... but 4.00 is stock.  This chart implies the 110/90 REAR tire will be ??? somewhere ??? between 4.00 and 4.75 (yes ??)  Since 110mm converts (by math only) to 4.33" I would be inclined to think this the ideal tire.... yet there is a very distinct overlap.  Does this mean the 110 size is approximate and falls somewhere between.

I see a lot of questions on this subject... maybe time for a faq on tires? or does one exist already and I just didn't find it yet?
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Offline Gordon

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Re: '78 cb750f tire sizes - utter confusion
« Reply #4 on: May 09, 2008, 09:20:06 AM »
Quote from: dboblet on May 09, 2008, 09:06:58 AM

I see a lot of questions on this subject... maybe time for a faq on tires? or does one exist already and I just didn't find it yet?

We keep it hidden inside the FAQ section. ;)

http://forums.sohc4.net/index.php?topic=368.0
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Offline goon 1492

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Re: '78 cb750f tire sizes - utter confusion
« Reply #5 on: May 09, 2008, 09:26:08 AM »
Quote from: cafe750 on May 08, 2008, 04:53:01 PM
I'll bring the keg, if everyone else brings their own chair... ;)


 :P :P :P :P who's the first for a keg stand? ;D ;D ;D
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Offline scondon

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Re: '78 cb750f tire sizes - utter confusion
« Reply #6 on: May 09, 2008, 09:27:33 AM »
 When I find a tire I like I go to the manufacturers site. I always find tire specs like tire height, tire width, width of rim that is recommended and a minimum/maximum rim width that the tire can be used on(according to the manufacturer. Sizes are often given in inches and metric so you can easily compare a 4.00 to a 110/90.

   Visit the manufacturers website, it's a hoot ;) :)
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