Topic: Alloy rim width recommendations for CB750K1 front and rear

[DesertKyorugi]

I am looking to get a set of front and rear alloy rims as a trade. What is the widest size rim that would fit? 19" front and 18" rear.

I am thinking 2.15" X19" and 3.5" X18" or can it go wider for the rear?

Thanks

[maxheadflow]

While no one answered, I too am looking at those sizes for my CB750K8.  The stock rim in the fron seems to be a 2.15.  Rear is a 3.0 x 17.    IIRC most CB750 run a 2.15 front.   On the K8 I'd bet one could get a 2.50 to work on the front.

I'm currently running a 100/90-19 in the front and a 130/90-17 in the rear Avon AM26s but thinking about a 130/70-18 in the rear on a new rim when the rear wears out.  The K8s fit a 130 tire easy.

[754]

I may be wrong here , but I thought stock 750 front was 1.85.
 Always measures where the bead sits.
 A 2.5  will likely mean a change in front fenders. I know with a 110 on mine it's hitting the brace several places and I have bent it for more clearance.. changing to GL fork will give you much more room..

[maxheadflow]

I could be wrong on the front for sure..  I compared the outside width of a 2.15x19 Excell to the steel on my k8 and the steel rim is about 0.060 wider. With the rolling of the sheet-metal to form the steel rim, the inside width could be narrower than 2.15.

[seanbarney41]

Stock front is stamped 1.85×19

[maxheadflow]

Sounds like I would have bet wrong.  I do think a 2.15 will fit.. At least for me.. Good point on the rim stamping.

Now back to the OP. What do you guys think of his rim selection?

[754]

It probably will fit , but it means a whole new fender design with the  right size rubber.
 We put a GL fork on my kids 750 and a 3.5  x17 with 130 tire fits in the front.

[seanbarney41]

Imo, there is really no reason to fit bigger tires unless you are racing.  The very small gain in contact patch width really spoils the steering accuracy and flickability and makes the bike overall feel like a tub.

Oh yeah...but the looks

[754]

 That wont stop people . Sometimes its just a visual thing they seek..

[seanbarney41]

I know...but i gotta try.

[JerrodR]

I think the biggest is 3", I have both of the Aluminum Lester Mag's, 16/3, and 18/3. I have seen guys do a swing arm conversation, and put modern rim and tire combos on. Looks pretty good, don't know how much work it involves though.

[DesertKyorugi]

Ok, so 3.00 X18" is the widest and not 3.50 X18" for the rear on a K1?

[seanbarney41]

probably no one really knows...It will work a lot better if you go backwards from your tire size.  Pick a tire size and then pick your rim size based on tire manufacturers chart for what rim size that tire fits best.  I can tell you a 130/90/18 will fit with minimal mods 140/90/18?  maybe with mods to chainguard, brake stay and brake rod.  To make matters even more complicated, tire sizing varies from manufacturer to manufacturer as a function of designed profile and then the width of the rim you use will have an effect too.  So...enjoy buying and trying if you want to stuff the biggest in there.

[DesertKyorugi]

probably no one really knows...It will work a lot better if you go backwards from your tire size.  Pick a tire size and then pick your rim size based on tire manufacturers chart for what rim size that tire fits best.  I can tell you a 130/90/18 will fit with minimal mods 140/90/18?  maybe with mods to chainguard, brake stay and brake rod.  To make matters even more complicated, tire sizing varies from manufacturer to manufacturer as a function of designed profile and then the width of the rim you use will have an effect too.  So...enjoy buying and trying if you want to stuff the biggest in there.

Thanks. I would like to put the widest tire without mods or guesswork. 130/90-18 would be nice if it is a drop-in fit. If not, 120/90-18 is fine as weill be installing the tire myself so I would like to make sure it is not too wide.

[grcamna2]

Imo, there is really no reason to fit bigger tires unless you are racing.  The very small gain in contact patch width really spoils the steering accuracy and flickability and makes the bike overall feel like a tub.

Oh yeah...but the looks

Exactly.

[maxheadflow]

I looked at my front rim and didn't see a size stamped in it tho there are 2 stick-on wheel weights that could be covering it up.  It is marked a DID so I suspect it's stock.

Rear wheel is a 2.5x17 and is marked. 

FWIW the K7s and 8s had a 4.50 tire as stock on the rear and a 3.50 as stock on the front.  I don't have any problem going to a skinnier tire but typically find the profile makes more difference than the size.   For me is issue is tire selection. For instance 100/90-19 are plentiful, 3.50s are hard to find.    It would be nice to use wheels that can accept anything from a 90 to 100 in the front and 120 to 130 in the rear.   IMO it's nice to go on the wide side for the rims as the tire profile won't fall off as fast.

Right now I'm leaning towards a 3.00x18 rim in the rear. 

BTW as far as I can tell, you can only get 4.10x19 K81s which makes them a little wide than a 100.

So what do you guys run for tires?

[754]

You can run a 4 .0 wide on the back , and I have run a 15  on the 750 rear with a stock 18 inch rim.
 But I was seeking traction, and a teeny bit of comfort..not handling..
 The comfort part was from no rear suspension, bigger tire volume provides a little bit of cushion..

 It really depends what look you are going for..  and to many, handling is a consideration.

I think on my son's chopper we will go smaller tire , down to 200 ish the one for mockup is a bit big at 230?

[seanbarney41]

Maxheadflow, I run stock size 3.25x19 and 4.00x18 Avon Road Runners om my K.  On my F, which uses a 17" rear from a Goldwing, I have been using 130/80/17 Avom rr's.  I have used lots of different tires over the years...stock size Metzeler Lasertecs are very good and look vintage.  Pirelli Sport Demons are very good but closet size to stock is 120/90/18 and 90/90/19.  One popular tire I always will avoid is Shinko, as I got a bad set of those once.  Resulted in some scary slides.  They are probably a good cheap alternative if all you are gonna do is putt putt around on perfect warm days...quite a hard compound that lasts and lasts.

[maxheadflow]

Thanks for the info.  I've been leaning towards Avons and Bridgestones but like the idea of running the K81s.. I do like the idea of going a little fatter on the front since the bike is set up with dual disks. It's been a while since I've run any Metzlers or Pirellis.. Compared to my other bikes, even with fatter tires the response is fine.

[grcamna2]

Quality rubber of the recommended size for the rim will keep you alive 'in a pinch' 

[Don R]

 Forgive me for the hijack but I'm planning a 750 performance minded build with A aluminum rims, triple discs and an F0 swingarm. The frame will be either an F1 or a K2 with an f1 rear m/c. I'm guessing Avon Roadrider's, does 130/90/17 rear and 100/90/19 front sound right? 

[DesertKyorugi]

Thanks for the info.  I've been leaning towards Avons and Bridgestones but like the idea of running the K81s.. I do like the idea of going a little fatter on the front since the bike is set up with dual disks. It's been a while since I've run any Metzlers or Pirellis.. Compared to my other bikes, even with fatter tires the response is fine.

I never ran Avons but I like the Spitfires a lot

[seanbarney41]

Forgive me for the hijack but I'm planning a 750 performance minded build with A aluminum rims, triple discs and an F0 swingarm. The frame will be either an F1 or a K2 with an f1 rear m/c. I'm guessing Avon Roadrider's, does 130/90/17 rear and 100/90/19 front sound right?

don, see my post above, my f is nearly identical set up as it ha gl rims which are the same as A rims.  I found that a 130/90/17 is actually taller than a 4.0x18, thus the 130/80/17 rear.  Imo, anything but a 3.25x19 on the front just feels like a fat turd on these.  I am not joking.  Try it.