Topic: 17 inch or 18 inch Rear Rim and Tire?

[CB_Jeff]

All,
This question relates to a future build that will include parts from several different Hondas, specifically:
 - K3 frame and oil tank,
 - F1 Rear swing arm, hub and disk brake assembly,
 - GL1000 front end (spoked wheel, dual disk assembly, forks and triples),
 - K8 Engine and Carbs
... and other smaller bits from here and there.
I need to build the F-1 hub and lace it up to a shouldered allow rim (similar to the GL1000 front wheel that I have) that I have yet to procure and my question is as follows, is there a clear benefit to either the 17 or 18" rear wheel?  I like the looks of the 130 90 17 on my K7, but recall there not being much in terms of tire selection for the 17" wheel / tire.  I will also need to track down an alloy rim.
Other than the two pro's listed above, I cannot think of a compelling reason to go one way or another, but would be interested in input from others.
Thanks!
-Jeff

[Don R]

  An aluminum rear rim from a 750A looks right, it's 17" and works fine. It already has the cb750 hub on it. Depending on the tire, the OD may be close to the 18". I have an A wheel with a 130 x 17", it looks wide.

[la ca fe]

I am doing the same thing: f1 rear end to a k2 frame.
I did this once before years ago, swapped out an f1 swing into a k1 frame. It never really handled very well afterwards? I wonder what I did wrong.
I am using the factory, aluminum, 17" hondamatic/Goldwing rear rim. I have an extra set if you need?
I am using an Avon 4.50 rear tire that I hope fits.

I have a set of Borani shouldered aluminum rims, but I want to go with the Honda rims instead, only for aesthetics. I want to keep it Honda and I like the look and want to drop the rear end down 1" so the bike is not as tall as the 18" rear end.

Good luck on your build.

[70CB750]

Do not plan to use F rear MC, they are like hen's teeth and rebuild kits are not existent.  Much easier to adapt a later Honda MC.

My $0.02 only of course.

[MCRider]

Going 17" from an 18" all else being equal drops the bike 1/2 inch,not 1". Still, its lower, just not all that. Maybe get a lower profile tire as well.

[Henkies]

Going 17" from an 18" all else being equal drops the bike 1/2 inch,not 1". Still, its lower, just not all that. Maybe get a lower profile tire as well.

K7/8 came with a higher tire, leveling the difference in rim diameter.  I'm thinking about the upgrade to alloy rims. Is there no benefit in using 17 inch?

Otherwise I don't understand why they switched to 17 for 77 onwards. I like low profile tire with larger rim, but a cheap Goldwing set as well. So not sure yet what to choose.

[MikeSimon]

Lowering or raising the rear without doing anything else will change the steering geometry. Lowering the rear will increase, raising it will shorten the trail. If you really go to the extreme in your riding habits you may recognize the effect on the steering.
The 18" rear was usually combined with a 19" front. Reducing the diameter of the front, made them reduce the rear too. All the DOHC 4s had a 18/17 combo, for one exception, which had an 18/18.

[Henkies]

The 18" rear was usually combined with a 19" front. Reducing the diameter of the front, made them reduce the rear too. All the DOHC 4s had a 18/17 combo, for one exception, which had an 18/18.

So they changed the rim sizes as part of the changed geometry? (steering geometry and wheel base changed in '77)

[754]

I think the 17 may have greater tire availability,  but many may be lower profile.
The 17 isvthe fattest you can go on back with matching rims, the ND 16 type usually ends in mismatched rims.
The Wing alloy rims , look fairly good, but most alloy rims available look nicer, like Excel, Akront shoulderless or Sun..   but that is only my opinion...

 Wheelbase and fork offset changed in 77.

[fireman1073]

17 inch aluminum from a 76 750A on my 75k for reference
Steve

[seanbarney41]

Here is my 750f with GL1000 special edition rims...rear is 17" laces right up to 750 hub using the stock gl spokes...
KIMG0058 by Sean Barney, on Flickr

[Don R]

 Nice bike Seanbarney. One of my favorites. I made dual rotor fenders for mine, the right took parts of two lefts but it looked original. Sold it to get a sandcast.

[Henkies]

Thanks for the pictures as well guys

[seanbarney41]

thanks Don, glad to hear ya like it, I'm lovin' the hell out of it.  A couple years ago I had an F1 set up almost as good as this one and ended up trading it for a van that I really needed and am still driving now. I tried to get some of the special parts left out of the deal, but the guy drove a hard bargain.  It's the unique parts that make these bikes so much fun for me.  Didn't take too long to collect the stuff to put this one together, so all is well.

[Grabcon]

The rims on this bike that I built several years ago had rims from a Cb750A. The 17 rear is fine and tire selection was much broader than for an 18. But from an esthetics point there is a bit more clearance between the tire and the fender. I cannot remember the exact tire size but I want to say it was like a 130/80/17. The 80 profile closed up the clearance gap a wee bit.

[Grabcon]

Here is a little better picture showing the clearance