Topic: Replacing Rear Tire on 750K4, but PO switched to 17 inch

[djwillard18]

I need to replace the rear tire on my 74 CB750 and want to get the best size and profile for the non-stock 17 inch rim.  It currently has Kenda Challenger 130/90-17, but from my research on the forum the stock size tire was 4.00 h18 or 110/90-18.  130 is too wide.  I think his mechanic just put one on that he had in the shop.

Should I look for 110/90-17 tires? Others on the forum have recommended 120/90, but it is not want Honda installed.

I am not a mechanic.  This is my first bike that I've been working on, but I ride it as much as possible and hope to take a overnight trip to meet my brother a 300 miles each way in a few weeks and would like to get the new tire on before then.

Thanks for your help.

[Bankerdanny]

110/90 would be an acceptable replacement for the stock 18, it would be a little small for a 17" wheel (110 is the width of the tire in mm's and 90% is the aspect, the % ratio of the sidewall to the width, so a 110/90 tire has a sidewall height of 99mm).

The old inch style tires installed in the 70's were basically 100% aspect, so the 4.00x18 was 4" tall and 4" wide.

The 130/90 is a common size for the 17" rear because you need extra width @ a 90% aspect so the sidewall is higher to make up for the smaller diameter rim. You want the total height of the tire/wheel combo to be about the same as stock so that the rolling diameter is as close to stock as possible.

If you look at the website for manufactures that sell tires in both the stock inch size as well as the metric sizes (the Avon Roadrider for example) they will tell you the diameter of the tire. The Roadrider 130/90-17 has a rolling diameter of 26.4in while the 4.00x18 is also 26.4. So the 130/90 is a good replacement size and should fit between the swingarm. My '76 750F had a 5.00" wide tire fitted to it that cleared just fine. I've not run across 110/90 in a 17" size, but it would be smaller and I wouldn't recommend it anyway.

How wide is your rim?

[754]

I am thinking, the 17 inch, May be easier to get tires form plus you .ca  go wider if desired.

[djwillard18]

Where would I find the rim width?  I inspected the rim and cannot find the width.


Should I look for an 18 inch rim or is it okay to run 17?

[PeWe]

Replace wheel with correct size?

[djwillard18]

Replace wheel with correct size?

Yes.  Should I do that for safety/performance issues?  It was switched to 17 prior to my ownership.

[Bankerdanny]

The 750 automatic and the 77-78 750K used 17" rear wheels standard, so it isn't a big deal and not a safety issue.

The rim size is generally engraved on the rim right at the valve stem hole. The writing is faint and can be hard to read if the rim is dirty. Most likely it is a 2.15, which is a little narrow for a 130/90, but will work.

[djwillard18]

The rim size is generally engraved on the rim right at the valve stem hole. The writing is faint and can be hard to read if the rim is dirty. Most likely it is a 2.15, which is a little narrow for a 130/90, but will work.

With your hint I was able to locate the size: 2.50x17

[Bankerdanny]

A 130/90 will fit that size rim with no problem

[djwillard18]

Thank you all for your time and information.

[754]

18 in are skinnier, the 17 in width makes more sense.