Topic: I am so sorry, but I have another wide tire question...

[q2418130103p]

I have just started my '74 CB550 project.  I have not yet decided on a set of tires for it, so this thread might be a waste, but I wanted to do my homework so I wasnt caught unprepared.

I understand that the normal tire setup is something like 110/90/18 in the back, 100/90/19 front.  I also understand that the widest tire that is generally considered mountable in the rear is a 120, but there may be some issues.

What would it take to put a 130-150 on the rear safely?

[Stev-o]

a wider rim.....

[cobra2411]

I've been going though this with my cb750 and if you search there's a ton of threads about it. Probably too many because I just ended up turning my brain into tapioca...

Anyway one big issue is the rim width. If you go too wide for the rim with it pinches the tire and it wears too fast and handling can be an issue.

[MCRider]

I have just started my '74 CB550 project.  I have not yet decided on a set of tires for it, so this thread might be a waste, but I wanted to do my homework so I wasnt caught unprepared.

I understand that the normal tire setup is something like 110/90/18 in the back, 100/90/19 front.  I also understand that the widest tire that is generally considered mountable in the rear is a 120, but there may be some issues.

What would it take to put a 130-150 on the rear safely?

You have a 2.15" rim now. (Maybe less). It would take at least a 2.5" rim to carry a 130/80 safely, according to tables i have from 2 sources, both agree.

A 2.75 for the 140, and a 3.0 for the 150. You'll have swingarm and/or brake arm clearance problems probably at the 130 level.

[q2418130103p]

Thanks for the quick replies guys.

I understand it requires a wider rim, but it cant be that easy can it?

I have read a lot of the CB750 projects, but I am always a little hesitant to accept the info because I am not sure what the difference will be between the CB550 and the CB750 as well as the difference between years, since I understand the late 70's models had a wider swing arm.

At what point will the wider rim no longer fit the swing arm correctly, at what point will the tire rub the chain, at what point will there front sprocket need an offset?

-EDIT- I must have written my post too slowly, MCRider ninja edited some comments on clearance issues, thanks.  What is the correct width rim for the 120 (looks like 2.5" according to some other threads)?

[MCRider]

The minimum rim width for a 120/80 is a 2.15 on one chart, a 2.5 on the other.

As to clearance issues on the 500/550, I don't know. But if its like the 750, the brake stay arm hits on the right side with a 150, the chainguard hits on the left, I think wiith a 130. If you reconcile these issues, next comes the chain on the left and the swingarm on the right.

At no point do the wider rims hit anything, its the tires.

[q2418130103p]

Assuming there was no chain guard, and the brake arm was modified to give more clearance, what is required to move the chain out?  A front and rear chain offset sprocket right?

Also, is there any clearance issue from the tire to the swing arm with the older, apparently more narrow, swing arms on the early CB550?

[TwoTired]

The stock 74 Cb550 rims are 1.85 width.

I don't know why you want wider tires on the bike except for looks.  If you just looking at it, rather than riding it, put whatever size on you think looks good and admire it in your garage and driveway.

With the stock size tires you can lean over far enough in turns without loosing traction to scrape metal things on the bike, so bigger meats aren't much benefit.  Further, oversize tires weigh more, making the bike slower to accelerate, and the extra un-sprung weight makes the whole suspension work worse so cornering capability will also be worse.

Cheers,

[q2418130103p]

Thanks for the info.

I was only thinking about it for the looks, not for performance or handling.  But I would still like to ride it and not fly off a cliff.

[dhall57]

My K6 has a 130/90/16 on the rear from the PO. Alot of riders did this to  there 750's back in the 70's. Im not really sure why though. Sooner on later Im planning to go back to the factory 18' rim, but it will be a little while because I just put a new rear tire on this weekend.

[q2418130103p]

I am guessing thats a Harley 16" wheel right?



If the suspension is a concern with larger tires, I assume its possible to compensate for the extra unsprung weight of larger tires with different damping rates for the rear shocks?

[Stev-o]

My K6 has a 130/90/16 on the rear from the PO. Alot of riders did this to  there 750's back in the 70's. Im not really sure why though.

That was part of the chopper craze. Drop the rear and extend the front...

[MCRider]

Assuming there was no chain guard, and the brake arm was modified to give more clearance, what is required to move the chain out?  A front and rear chain offset sprocket right?

Also, is there any clearance issue from the tire to the swing arm with the older, apparently more narrow, swing arms on the early CB550?

IMO moving the chain out is not a feasible issue. Anything is possible if you desire it enough i guess.

As mentioned, I have no specific knowledge on the 500/550 as to actual clearance limits/problems.

[cobra2411]

With the stock size tires you can lean over far enough in turns without loosing traction to scrape metal things on the bike, so bigger meats aren't much benefit.

That's what convinced my to stay with stock sizes on my 750. I can scrape the pegs with a 110/90-18 rear...

Listen @ 0:53

[Stev-o]

You COULD put a 330 tire on a 750, click here:

http://forums.sohc4.net/index.php?topic=63553.0

[MCRider]

Wider tires mounted on proper rims may actually increase cornering clearance. As you roll into the turn the extra width raises the hardware. For those hot shots who "need" the extra clearance, upgrading suspension parts will more than offset and control the increase in unsprung weight.  And these bikes need better shocks and springs from the git go. For performance riding, the unsprung weight increase is acceptable relative to the increase in cornering clearance. Its a trade-off.  IMO

[dhall57]

I am guessing thats a Harley 16" wheel right?



If the suspension is a concern with larger tires, I assume its possible to compensate for the extra unsprung weight of larger tires with different damping rates for the rear shocks?

Other than harley size rim, the shocks, and 18/48 sprockets on my K6 are still stock. I do like the look of the wider tire from the rear though and no harder than I ride this doesn't effect the ride or handling of the bike what so ever. Once again this size was on the bike when I bought it and thats the only reason I have it. I like the all stocker look myself.

[q2418130103p]

IMO moving the chain out is not a feasible issue. Anything is possible if you desire it enough i guess.

As mentioned, I have no specific knowledge on the 500/550 as to actual clearance limits/problems.

Why do you consider moving the chain out not [reasonably] feasible?  I haven't really examined the bike thoroughly to understand the geometry yet.

[MCRider]

IMO moving the chain out is not a feasible issue. Anything is possible if you desire it enough i guess.

As mentioned, I have no specific knowledge on the 500/550 as to actual clearance limits/problems.

Why do you consider moving the chain out not [reasonably] feasible?  I haven't really examined the bike thoroughly to understand the geometry yet.

I added "anything is possible"    Its just not something I would do. I can't imagine any reason for it. Personal.

[q2418130103p]

Gotcha