Topic: Alloy rims... Yes? No? Maybe?

[Tews19]

I'm selling a brand new 18" aluminum rear.

[calj737]

Excel or Sun rims seem to be the most popular aluminum rims. They can be ordered from Buchanans directly with spokes, or thru Cognitomoto.com. I'd discourage you from 18-18 as this will effect the handling of the bike. 18-17 or 19-18/19-17. If you think in the future you may truly want a GSXR front end, or modern equivalent, those are often best suited to 17-17. So bear that in mind. There are builds where members use modern front ends with 18-17, but don't recall a lot who go 18-18.

For a 550 rear, you can fit a 130 comfortably and squeeze a 140 in sometimes, depending upon swing arm. Generally speaking, a 140 or better rear wants an offset sprocket to move the chain outboard to clear the leading edge of the tire from the chain.

[DavePhipps]

I  believe if you search through the HiPo section you will find that most racing applications use the 18,18 combo, but then you need to modify the triple or fork length to get the geometry correct. If you want a bike that handle like stock then go stock sizes.

[lucky]

The rear rim on the K3 has had a flat spot since I bought it.
Plus it looks ratty - the PO gnarfed it good with tire irons.

So, I've been thinking about replacing it w/ an aluminum rim (because alu is lighter).
I assume aluminum isn't as strong as steel - but my rim is at least 41 years old so maybe modern alloys are better?
I know guys here build wheels with alloy rims but I can't find any discussion of the pros/cons
Any advice?

The CB750A had high quality aluminum rims.
Each wheel will be 6lbs. lighter.

The older rims would be the ones I would prefer.

[calj737]

Each wheel will be 6lbs. lighter.

The weight difference between stock steel rims and aluminum is not 6#. Someone is smoking crack. And a cheap brand of it from the looks... The stock rims don't even weigh 6#. All the weight is in the hub, and that's not changing. 

[Vinhead1957]

Crack is wack

[Tews19]

I will put my rim on a scale... weight report coming

[MCRider]

I will put my rim on a scale... weight report coming

My guess: steel = 5lbs. Aluminum = 3.5

Let us know.

[calj737]

I believe where "he" goes off the rails is: an equally heavy alloy rim can be much larger and still weigh the equivalent of the stock rim.

[Terry in Australia]

I  believe if you search through the HiPo section you will find that most racing applications use the 18,18 combo, but then you need to modify the triple or fork length to get the geometry correct. If you want a bike that handle like stock then go stock sizes.

Yep, here's a pic of my gold K2 which was built by Ken Piper, an old race bike builder and mechanical engineering lecturer at the Australian Defence Force Academy. It's fitted with 18 inch wheels front and rear, and was (I sold it a couple of years ago) the best handling CB750 I've ever ridden. (and I've ridden a lot)

Back in the day, the accepted wisdom was that same size rims were the best option for racing, but that might have just been to "quicken" the steering, I really don't remember.

There are lots of really good 17 inch wheels out there, and because of their availability they're really cheap too, but there's a problem with using them. Our engines are really wide compared to modern engines (BMW's new 6 cylinder engine is narrower than a CB750 engine) and by lowering our bikes with 17 inch wheels (and modern forks) it reduces the ground clearance and lean angles significantly.

That's handy if you're building a minimalist custom "bar crawler", as you won't need a sidestand, you can just lean it on your alternator cover, but not so good if you wanna go around corners. Cheers, Terry.        

[Retro Rocket]

^^^^^  thats almost the perfect 750 Honda, you should have kept that one....

[calj737]

It's fitted with 18 inch wheels front and rear, and was... the best handling CB750 I've ever ridden.

Anything in particular to the suspension front and rear that you attribute that to? Certainly 18/18 wasn't the only change, but I'd be curious as to what other changes made that such a drastic improvement.

I agree with Retro, really stunning looker! I hope you replaced it with an "upgrade"!

[Old Moe Toe]

There are lots of really good 17 inch wheels out there, and because of their availability they're really cheap too, but there's a problem with using them. Our engines are really wide compared to modern engines (BMW's new 6 cylinder engine is narrower than a CB750 engine) and by lowering our bikes with 17 inch wheels (and modern forks) it reduces the ground clearance and lean angles significantly.

That's handy if you're building a minimalist custom "bar crawler", as you won't need a sidestand, you can just lean it on your alternator cover, but not so good if you wanna go around corners. Cheers, Terry.        End quote
 

I put a 17 inch wheel from a K7 onto the back of my K2 and really like it. I much prefer the 130 wide tire, also because of the differing wall section of the tire compared to the standard one the overall outside diameter was pretty well exactly the same. Only modification was cutting a section out of the chainguard so the tire did not rub.

[Terry in Australia]

^^^^^  thats almost the perfect 750 Honda, you should have kept that one....

Thanks Mick, I loved it, but even with the 836cc engine, it didn't have the "oomph" that my old K1 with Mike Reick's head, big cam and other mods has got, and I can always upgrade the suspension and brakes on mine.

Now that my cuz has bought a huge Bridgeport mill, I might have to give it a test fire and make myself a set of billet triples for the 41mm FZR1000 forks I've got here, like the ones that Ken built for the gold bike. Cheers, Terry.