What Tires are compatible?

[lnuhring]

I am new to vintage CB's and I have a question regarding tire compatibility.

I have a 1979 Honda CB750k

The manual lists the tire sizes as the following:

Front Tire--3.50H19
Rear Tire--4.25H18

I would like to mount a pair of Shinko 270 tires.

The closest sizes that the Shinko 270 tire come in are as follows:

Front Tire--4.00x19
Rear Tire--4.50x18

I assume that these Shinko Tire sizes are compatible, as they are very close to the stock sizes, but I wanted to learn more about your thoughts on compatibility before ordering!


Thank you in advance!

 

[amc49]

The very early ones came more likely with 3.25 X 19 and 4.25 X 18, the wheels were 2.15 wide. The wheels got slightly wider later to 2.50 to then go to those sizes you mention.

With the 4 on the front you may rub OEM fender. The early forks were much narrower between the legs than later ones which widened along with the tire sizes and wheels.

You are going for a certain look there and yours to do with it what you will but be advised that a lot of people complain about how those type tires handle on grooved pavement, the bike is all over the place hunting. The tire tread grooving is too narrow to act like straight lines and then the grooves lock in road surface grooving to be very snaky as far as the handling goes. A guy a little while back was complaining about that exact tire you mention doing it. That particular tread design is from the 1930s and 700 lb. motorcycles that never leaned over hardly at all. Rain grooved pavement did not exist back then either.

Add to that the fact that many early DOHC show handling issues anyway on tires when they get only some wear on them, the front ends begin to wobble at speed. The F is the worst and I had one and the trouble, tires only half worn will act up. Some of it is tied to bike weight and road crown issues, you unconsciously lean back straight on crowned road and then the tires do not wear on front dead center, they wear to one side based on the road crown effect. Then bike gets to handling bad because tire is worn funny. It has nothing to do with bike wheel alignment. Several magazine testers pointed out the issue when the bikes first came out, they were running 24 hour marathons with them and kept having to change tires way too early. That may be why Honda widened the wheels.

 

[lnuhring]

Great advice. I will be sure to measure the distance between the front forks on the bike. I believe that they are wider rather than narrower. I have also heard about the issues with this particular tire and I must say that I do not intend on using it as a daily commuter to work (where I would be riding at highway speeds). The front fender shouldn't be an issue, as I plan to remove it entirely and perhaps find something aftermarket if at all possible.

I also recently found out that there are US spec and Euro spec hondas from that era (and I suppose modern ones as well). I am not entirely sure which spec I have (although I assume that it is a US spec). I understand that the rear wheel is different in diameter between the US spec and Euro spec. I will take measurements in the next few days!

Thank you for the response! It is helpful.

 

[amc49]

The forks opened up wider in '81. The wheels at that time got wider too.

US spec carbs have original idle limiter caps on mixture screws to not be able to turn them more than one turn. There is also an accelerator pump assembly built into the fuel bowl on the #2 carb, Euro bikes do not have it. Euro bikes have speedo in KPH instead of MPH.