Topic: 17" or 18" rear rim? CB750F1

[cobra2411]

This winter I plan on getting new rims for my 76 SS. I originally was going to go with 18 x 2.50 but now I'm thinking of going with a 17 x 3.0 rim with a 130/90 x 17 tire. For the front I plan on going with a 19 x 2.15 rim and a 100/90 x 19 tire. Could I go with a 110/90 x 19 tire or will that be too tall? I plan on using Dunlop D404 tires.

My original thought was to use TT100 tires but I'm a heavy rider (280lb) so I want something that's not going to squiggle around when I'm vertical.

Thoughts?

[Retro Rocket]

If you go down to a 17 on the rear then you are lowering the rear end an inch also. If i were you i would leave the rear an 18 and just get it re laced with a wider rim..

Mick

[cobra2411]

If you go down to a 17 on the rear then you are lowering the rear end an inch also.

No it's actually taller because the tire size is different. A 110/90 x 18, which is the closest metric tire I can get is 25.5" tall. The 130/90 x 17 is 26 which should be the same as a 4.0 x 18 stock tire.

I just noticed the rims I want are available in 2.15, 2.75 and 3.50 widths...  130/90 recommends a 3.0 width. Should I go 2.75 or 3.5?

[cobra2411]

What about a 140/90 x 16 on the rear on a 3.5 rim?

Here's where I'm at now.

Option A:

2.15 x 19 front with 100/90 tire
2.50 x 18 rear with 110/90 tire

Option B:

2.15 x 19 front with 100/90 tire
3.50 x 16 rear with 140/90 tire

I'm looking for increased performance first. Good looks are a very close second.

[BeSeeingYou]

If you go with a wider than stock tire on the front check the clearance of the bracket that holds the brake hose.  It is mounted on the inside of the fender support and is a tight fit.  May require a slight mod.

[HawaiiMike]

I think a 16" rim = cruiser, not a performance bike.  Same with 17". I'd stick with an 18" unless you like cruiser-type bikes.

[srook]

Modern sportbikes have 17" rims.  During the late 70s and early 80s many race teams started to use 16" rims on the front and back of their racebikes to improve turn in.  I don't  buy the 16" = cruiser argument.  They were used in racing and can be a period correct performance upgrade not just a fat rear tire for a chopper.

On the TT100/K81, your weight will not cause the tire to go squirley.  2 up riding adds more unladen weight to the bike than you are adding and the TT100/K81 is fine for that.  The only drawback on them is the rears seems to last only about 5,000 miles.
Scott

[MCRider]

Didn't it come with a 17 rear to begin with? The Ks did. Anyway, depending on a bunch of different things, I'd go wider in the rear staying stock diameter. Don't forget what happens to your stands. Don't go overboard on widths and yuk on the 16".

I think dropping the front to an 18" quickens the steering and lightend the load. JMHO Messes up the look under the fender tho.

[Retro Rocket]

Didn't it come with a 17 rear to begin with? The Ks did. Anyway, depending on a bunch of different things, I'd go wider in the rear staying stock diameter. Don't forget what happens to your stands. Don't go overboard on widths and yuk on the 16".

I think dropping the front to an 18" quickens the steering and lightend the load. JMHO Messes up the look under the fender tho.

K's had 18 inch rears.....

Srook, 16's were experimented with on the front not the back on performance bikes from the 80's, The GPX Kawasaki and VF 750 had a 16 inch front but still had an 18 inch rear wheel, there are good reasons for this. 18's work well on the front of our bikes.

Mick

[MCRider]

Didn't it come with a 17 rear to begin with? The Ks did. Anyway, depending on a bunch of different things, I'd go wider in the rear staying stock diameter. Don't forget what happens to your stands. Don't go overboard on widths and yuk on the 16".

I think dropping the front to an 18" quickens the steering and lightend the load. JMHO Messes up the look under the fender tho.

K's had 18 inch rears.....

Srook, 16's were experimented with on the front not the back on performance bikes from the 80's, The GPX Kawasaki and VF 750 had a 16 inch front but still had an 18 inch rear wheel, there are good reasons for this. 18's work well on the front of our bikes.

Mick

The late Ks had 17 rears I think. I thought the Fs had 17s already as well, but maybe not the F1 as the OP has.

[Skunk Stripe]

No, the 17 did not start till 77 for the spokes. I am "almost" 99% positive the 76f still had an 18.

[cobra2411]

Mine has an 18" rear. I'm 100% positive as I was given a brand new tires for the comstar rims that came with the bike. The Comstars are from a 77K and the rear is a 17 which makes it useless for me...

Anyway I'm going a little nuts here. Too many choices and not enough money. I just want to make sure that since I'm buying new rims and spokes I get ones that will look right on the bike and that I can get decent tires for. I'm not looking for max grip / sparks flying off the pegs at every turn kinda tires. I mostly ride on slower roads 30-40mph with lots of turns so the tires should have good performance.

The other area of concern is higher speed straight line performance (ie highway). Right now the bike squirms around a bit as if it's hunting for every little imperfection in the road. The bike is still a work in progress but seems pretty tight. The rear shocks were blown and I just put on a set of good but cruddy looking ones off a K7 and it seemed to help but it still wants to squirm around. I know the rear rim is bent; it looks like it hit a pot hole with low pressure. The tire doesn't show any sign of deflection but if you look at the rim as it's spinning you can see it deflect maybe 1/8". I also haven't checked the fork alignment or tracking of the bike. Both are on my list of winter / bad weather projects.

Anyway I want a tire that has good traction in the turns, although I'm not pushing to the limits. Somewhere between cruiser and sportbike. I also want a tire that's going to track well going straight. I like the vintage look of the bike and want to keep that but I have a natural desire to upgrade and modify everything I own. Heck I even messed around with the stickers on my lawn mower to make it more "mine" if you know what I mean.

I'm starting to lean away from the idea of a 16" rear rim. I was going to do the cafe look but didn't like the way the bars felt so now I'm going with a European look. So I guess I'm going to stay around the stock size unless there's a good performance reason not to.

Options so far are looking like:

K81's in 4.10-18 front and 4.25/85-18 rear

K70's in the stock size 3.25-19 front, 4.00-18 rear.

Conti K112 in stock size

Dunlop D404 in 100/90-19 front, 110/90 - 18 rear.

The first three are very vintage looking. The D404's I'm told have good grip. All except the K81's use the stock size rims, although I'm going to be getting new ones and will go wider. 2.15 front and 2.50/2.75 rear. The stock heights are 25.5" front and 26" rear. The D404's are a little taller front and a little shorter in the rear which should improve high speed handling correct?  The F1 has a little more trail then the K's from the factory so I don't know if it's a good thing to give it more with the tires or if it's not enough of a change to really notice.

As a side note my buddy's 81 CB750 "Bike-O-Lounger" has Comstars with a 16" rear... We swapped bikes yesterday and that thing is as close to an easy chair on wheels as I've ever seen... It didn't take long before I wanted my F1 back though...

Thanks for the replies guys... I'm driving myself nuts thinking about all the possibilities.

[MCRider]

You're heading right on tires. I would just say unless you really know what you want and why, I'd stick with stock sizes.

The squiminess is most likely steering head bearings. If the bike has 10K or more and they've never been changed that raises the likelihood quitre a bit.

Put it on the centerstand, have someone weight the back so the front goes up in the air, or jack it up. Turn the handlebars thru left to right "lock to lock". When you reach the dead ahead position be alert to what you are feeling in the bearings. If it feels like it has a "detent" in the bearing, like it wants to stay pointing straight ahead, then they need to be replaced. Not just serviced, replaced. Stock stuff is OK but will wear again. If you've been here long enough you've read many of us talking about upgrading to tapered roller bearings. Once installed they are lifetime service and not too expensive. about $50 i think for a set.

If you have the "detent"  in your steering and I'll bet money you do, it will make it hunt. When you lean gently one way or the other, the detent will try to draw steering back to dead center and you have to keep correcting. Same thing happens on a road with a crown as you have to steer against the crown to go straight, while the bearing is fighting you.

[cobra2411]

Head bearings have been replaced with taper bearings. I had serious handling issued with the old ones that looked like they'd never been serviced (32k miles). I'm due to go back and adjust them as I've got a little over 100 miles since I installed them. Maybe they're a little loose? It doesn't feel like it though. I do have a little side to side play with the swingarm though. If you have it on the center stand and put a little muscle into it you can see it move maybe 1/8". I plan on sending it to Mark (aka HondaMan) this winter for a rebuild.

[MCRider]

Head bearings have been replaced with taper bearings. I had serious handling issued with the old ones that looked like they'd never been serviced (32k miles). I'm due to go back and adjust them as I've got a little over 100 miles since I installed them. Maybe they're a little loose? It doesn't feel like it though. I do have a little side to side play with the swingarm though. If you have it on the center stand and put a little muscle into it you can see it move maybe 1/8". I plan on sending it to Mark (aka HondaMan) this winter for a rebuild.

Darn. Well, you're on the right track there too.