What tire to fit custom rim?

I am trying to figure out the best wheel/tire combination for a CB550
that I am suping up into a cafe racer..

The goal is to have wider tires, to improve handling and traction. I
plan to build rims using the original CB550 hubs, and aluminum,
shouldered and dimpled rims to make new spoked wheels.

Stock, the bike runs these wheels/tires:
Front: rim=19 x 1.85, tire=3.25 H 19
Rear: rim=18 x 2.15, tire=3.75 H 18

The custom wheels I'd like to build:
Front: 19 x 2.15
Rear: 17 x 2.50

Only questions are:
What is the ideal tire size to run on these wider rims? Also, do
manufacturers list (or is there some way to deduce) the outside
diameter of the tire once installed on a rim? I want to try to make
the outside diameter of the new wheel/tire setup the same as the stock
wheel/tire setup if possible, to keep the steering angle the same.

Any ideas?

 

You are opening such a bucket of worms for yourself. And they are
expen$ive worms.
Each experiment will cost you $75 to $100, and that is the price of
knowledge if you are going to try to out-think the engineers.

Don't ask how I know that. Sigh. The tire manufacturers' websites list
ideal tire sizes and installed diameters.

You might want to visit www.mawonline.com to find a list of all the
tire manufacturers and links to their websites. I have found that link
to be a quicker way to find links than googling for them and finding a
bazillion retail or discount places that are selling tires.

You can order a free paper catalog from www.denniskirk.com and it has a
chart of comparative rim widths in it. Study the ink off the pages,
it's a lot cheaper than buying tires that don't work out.

I studied the DK catalog for hours, looking for appropriate sized
rubber for various machines, but it seems that the sport has evolved so
fast it has obsoleted reasonably priced race compound tires that will
fit the narrower old rims.

If you don't want to buy expen$ive Avon tires that wear out fast,
you'll be stuck with crappy Bridgestone BT-45V's or Cheng Shins or
Maxxis or some Taiwanese crapolla.

I don't think Dunlop even makes a generic replacement tire that will
fit the rims you specify. Bias ply is such old tech. Radial tire
technology has been the Real Deal since the mid-1980's, and radials
need really wide rims, a lot wider than you're talking about.

I couldn't buy anything decent for my 1986 GSXR-750, since it has
narrow 18 inch rims, and I didn't want to convert to 17-inch rims
because the next obvious
modification would be a later model fork...

You'd be better off buying a later model machinefrom the late 80's or
early 90's for $2K than spending your time trying to update an old
CB550. I understand what it's like to be trying to update an old crock
on a shoestring budget, but, if you can get something newer that has
the 17 inch cast aluminum rims you really need, you can be riding the
motorcycle and having fun with other sportriders instead of fiddling
around in the garage.

All you would need to do is mount the original equipment tires or a
manufacturer's recommended *set* of their tires.

Some racers I know laced up a set of aluminum rims for a Suzuki 750 and
wound up using them on a CB550. The front was a 2.50 X 19 and the rear
was a 3.00 X 18.

Those were big feet for a little motorcycle. The larger tires made the
machine sit taller all the way around, raising the center of gravity
and there was more weight transfer on braking and the larger contact
patches actually made the machine wiggly, driving those racers crazy
trying to undertstand what was happening.

Besides issues of installed diameter, even if you do get the correct
width tire on the optimum rim width, you can still wind up with profile
problems. Before I mounted a sharp profile Bridgestone BT-020 on the
front of my FZR-1000, I never dreamed that a
17-inch front tire could feel just like a 19-inch tire, or that the
front end would shake and shimmy at such low speed over rough
rain-grooved pavement.

The rounder profile Metzeler tires I'd been using didn't act like that
at all.

 

Just get rims off a CB550 SS. They are mags, made for a wider tire.

 

I doubt that you'll really get this but it might look cool
to some and wear will probably be better. The real improvement
will be in modern rubber compounds.

Would give 102 mm wide and 677 mm wheel diameter on ideal
rim wich is 2.15. The narrower rim will give a minute increase in
diameter and decrease in width.

I have no data on this one but with some reasonable assumptions
I would say wheel diameter is 675 mm and 2.15 ideal rim. Width
around 117.

Front would take 3.25 (of cource),
- 4.10 at 117 mm wide and 679 mm diameter, ideal rim is
2.50
- 100/90 at 111 wide and 675 mm diameter, ideal rim is 2.50

Rear would take
- 4.50 at 141 mm wide and 682 mm diameter, ideal rim is
2.75
- 130/90 at 142 mm wide and 682 mm diameter but ideal rim
is 3.00 (2.50 is right at the just allowable = not good)
- 120/90 at 131 mm wide and 664 mm diameter,ideal rim is
2.75

These are the ones I can find that fit your criteria.

Not really, all measurements are highly "nominal", like a 3.50-
16 is 7 mm wider than a 3.50-17. The data I used was from
Metzeler but other makes will be close.

Be extra careful to ensure you have enough clearance
everywhere even at full suspension movement.

Good luck!