When I built my Cafe's conversion on my Savage, I did what everyone else does and looked at what RYCA and other folks were doing.  As a result I used a 2.15 x 18 front rim with a 100/90-18 tire, and a 2.50 x 18 rear rim with a 130/70-18 tire.  This looked fine to me - however next to a Sport Bike my tires look very narrow.  I have also noticed that my tires have a very "round" look across the tread pattern - while the Sport bikes appear more oval which results in more tread on the road.

I have a friend that has been around motorcycles most of his life, and he road races a Ducati, and regularly works on vintage Norton's, Ducati's, Triumphs and BSA bikes.  He rode my bike just after I got it running, and his first comment was the bike had too wide of tires and would handle better with a narrower tire.......

I needed to take my rear tire off, and since the Pirelli Sport Demon had a big flat spot worn down the center of the tread......I decided I might as well get a new tire.  I decided to order a new Battlax BT45 in the 130/70-18 size as it has a dual tread compound with a harder center to help prevent wearing out the center tread too soon.  The first thing I noticed when mounting it....was how far apart the beads were, and it was a bit of a challenge mounting it on my 2.50 inch rim.  I went for a ride that afternoon....and I noticed that I am just kind of teetering around on the center of the tire.....it would be impossible to lean over far enough to reach the edge of the tire and I am leaving huge "Chicken Strips" on the sides of the tire where I will never be able to lean over far enough to rub on the pavement.

So this morning I did a little research, and Bridgestone recommends that the 130/70-18 tire be mounted on a 3.50-18 rim....which is an inch wider than my 2.50 rim!

So....I am most likely going to take my friends advice and install a 90/90-18 on the front and a 110/80-18 on the rear.  Going to the narrower tires is supposed to make it handle "better".....and maybe that will help with how my bike currently steers.  MMRanch rode my bike and said at the first corner when he went to turn.....it felt like he was "Trying to bend a board".....the bike does turn really stiff.....you need a lot of pressure on the handlebars to initiate a turn.  The narrower tires will probably also make the tread profile a bit flatter - as the current tires are rounded excessively by the narrow rims pulling the beads in an inch more than they are supposed to be.  You can see in the attached photo how round the tread pattern is, and how far the tread rolls over on side of the tire...most likely a result of the tires being on too narrow of rims.

So.....I have no experience in this area - but it appears that I (and many others) may be using too wide of tires on the Cafe' conversions. Any experienced input is welcome.

Dave      

Notice the tread profile difference in the photo below.  The rear tire tread is rolled over onto the sidewall as a result of the too wide of tire for the rim - while the front tire is the proper size for the rim.  The "Chicken Strips" on the front tire went to within 1/4" of the tread edge on the front - and on the rear there was near a full 1" of tread that was rolled over onto the sidewall and not useable.

Kris01 wrote on 07/21/14 at 12:51:42:


I don't know if it is good info or not.....at this point I am torn between putting a 3.50 inch rear rim and running the 130 rear tire...or putting narrower tires on.

At this point I am most likely to put a set of narrower tires on......as that is what my "road racing" friend recommends, and mounting tires is cheaper and easier than lacing on a new rear rim.

Dave

No more "clown shoes" on your bike? Oh, the horror...  

You'll see a dramatic, immediately noticed improvement in handling, lean angle, launch feel and braking.

The stock rim set should be wearing 90/90-19 front and 130/90-15 rear tires. If you could still find 120/80-15 rears, even better. The factory goes for "the look" when choosing what tires to run, handling is irrelevant. Most customizers do the same thing.

You'll seriously love the narrower 18 inchers.

Serowbot wrote on 07/21/14 at 22:41:29:

Yeeeah, I know what gallo your tongue got pico of.  

Good on you, Dave. Cafe bikes look best on skinny tyres. Don't worry about the chicken strip thing. No one who matters cares how big they are. I can't lose the 1/2" strips on my Pantah and Enfield GT, and run out of ground clearance before I run out of tyre unless I really hang off the bike. If you fit the right size tyre, it will probably steer sweeter and be less effort to ride faster.

Yeah, the last thunder beach I seen the tire carving thing....was just for bike shows....
They put them on the bikes right before they put the bikes on display...

Last night I spent about 3 hours changing tires on my bike.  The local places wanted $ 30 - $ 35 a wheel for changing tires if I brought in only the wheel.  I suppose that I spent about 2 hours of time wrestling the tires on/off the rim.....the other hour went to taking wheels on and off the bike, getting a drink, adjusting the radio, etc.  I guess $ 30 an hour savings for my time is worth it.  I finished about 10:15 - so it was too late to take a ride last night.

Knowing that I might be changing tires more than once, I mounted some T-Nuts in the back of a piece of plywood, cut a couple of oak boards, and used some long bolts to make a way to pull the beads off the rims.



The tires are definitely smaller.  The rear one is not that noticeably smaller and looks fine.  A wider tire would look more "manly" - but this evenings ride will tell which handles and ride better.



The front tire is only slightly narrower - but is definitely shorter in height.  I don't like the way the front fender fits anymore.  If this tire works out better I will have to go with a shorter radius fender - lowering the fender would only get it close in the middle and the ends would still be high.



So...the test ride tonight will let me know if this is the right thing.  I will take it easy for a while to get the tires scrubbed in.  If the bike doesn't handle any better.....then I can go back to the 100/90-18 front tire on the existing 2.15x18 rim.  For the back rim if I go to the 130/70-18 tire I will change the 2.50x18 rim to a 3.50x18 rim....which is what that size tire is supposed to be mounted on.  These smaller tires don't do much for the looks of the bike - the rear pulley and other parts of this bike are kind of beefy looking, and the bigger tires help to compliment that look.  It is not a dainty little RD350 or similar petite looking bike in some respects.

Dave

As an update to this thread.......

I have been making a lot of changes in the bike.  One of which is to get rid of the RM400 forks - the small offset from the yokes to the steering stem made the bike have too much trail, and the steering was very stiff.  It was hard to tell any difference in the tires widths....as the bike was determined it wanted to continue in a straight line.  I have made a spacer that lowers the front fender so the gap between the fender and smaller tires is where it should be.

I currently have 2 sets of rims with tires mounted, and this summer I will be able to make some evaluations on what tire to use.  I have stopped using the 100/90-18 front tire....it just seems to be too tall, and there are limited tire choices in that size.  Several companies are making better performance tires that will fit the Cafe conversion (Pirelli Sport Demon, Battlax BT45, Avon Road Rider).

I have one set of rims with a 90/90-18 front and a 110/80-18 rear tire.  They are plenty of tire for the bike....although after seeing all the wide tires on motorcycles the rear does look a bit narrow.

I have another set of rims with a 100/80-18 tire on the front, and a 130/70-18 tire on a 3.50-18 rear rim.  The wide rim and wider tire definitely looks beefier.

I will be using both these rims/tires this summer and figure out if there is much difference in the way they perform.  My new GPS speedometer has a 0-60mph and a 1/4 mile timer....so I can see how much difference in acceleration the larger tires causes.