Topic: tube sizes on 1975 CB750F Super Sport

[mboon85]

Hi! New owner of a CB750F SS. Also, this is my first bike purchase and i'm starting with very little knowledge about bikes. I'm being assisted, or rather guided, by a friend rather versed in the subject, though he hasn't worked on 70s hondas before.

The wheels, i believe, are stock. We need tubes. The cb750 manual on the manual link has this information promised on page 132 - but, just my luck, its missing page 132 in lieu of two 131s.

the front tire is a 100/90-19, and the rear tire is a 4.00-18. I'm not sure what tube i need, and other places have told me just to go to a honda dealership and ask for OEM tubes, but there isnt one in driving distance as i dont have a car. any help?

oh, here's a pic of it in my buddy's home garage.

[ekpent]

Get an 18" that will handle up to a  4.50 and you will be fine. There are different types of tubes though that are hyped out there as far as quality and brands. Kind of like an oil thread or tire thread so I will just mosey on along 
PS-That blue is a sweet color ----- Another Guy here has one that is just slightly souped up a tad       Anybody know his name   

[mboon85]

tks. the blue is super sweet, but up close its kind of beat up. ill have to post more posts about that later as its not a huge issue right now, but basically the "door" to the gas tank area is in pretty poor shape. lock and all.

so tr4? pv78? whats that mean. also, 18" for both wheels despite front being 19"?

[ekpent]

Front wheel tubes will be designated for 19"" wheels, there is a difference from a rear 18".
   Most any good tire website will steer you around to the options available then you can place an order or take that info to a brick and motor operation. Here is a starter thread though with the search function     http://forums.sohc4.net/index.php?topic=108971.0

[mboon85]

Right - I've been poking around tire websites for a few days now and im still unclear though on precisely what im looking for and what the measurements and designations translate to. for instance: if you google "tr-4 vs pv78" you dont get a clear answer. i do not know the difference and don't know which i need. i've been part of auto forums before and certainly understand the search function, but im not even sure what i'm suppose to be looking for.

can someone just point me to something that will work?

[mboon85]

guessed on the conversion! hope it works out. if not i can return it:P

[Bodi]

Tire sizes are pretty simple, the 4.00 is inches and the 100 is mm: roughly identical. For new tires, look at a sizing chart with the rim sizes you have, I don't know them offhand but you can find the stock sizes in the manual or measure the width. The "acceptable" sizes will be pretty narrow compared to modern bikes, but mounting an overwide tire, even if it clears the various obstructions, causes the profile to be distorted: it won't put more useful rubber on the road than a size designed for the rim width - you end up with tread where the bike is incapable of leaning far enough to use it
Tubes are sized for a range of sizes, since they are rubber they will expand to fill the space available and you just want one that's not too small so it's overexpanded and stressed or too big so there are wrinkles inside the tire. Tubes are not as available as in the past, new bikes are usually tubeless so demand is low. Getting a name brand tube generally gets you a better (maybe metal!) valvestem and more consistent rubber thickness which is better balanced. Cheapo tubes have flimsy rubber stems and are not so consistent on thickness... but work OK in my experience.
A flat at speed is a serious issue on a bike, so I don't scrimp on the rubber.

[mboon85]

these are the two i purchased: i believe the front one is dead on, not 100% about the second. i've also attached pix of the receipt for the tires. maybe this will help determine my accuracy. thanks.

[ekpent]

Think you will be fine. Happy mounting and check the inside of the rim for excess rusting. I use a brass wire wheel on a drill to clean them up if needed. Some guys spray a little primer in there to keep the rust at bay.