Wheel Sizing - Pro's and Con's

Hi Everyone,

I bought a 1979 XS650 a month a go and it runs nice, though I'm sorting out a clutch issue so I have not really gotten it on the road much. The one thing I can note is that it rides...well....a bit od.

The bike has the same 19" Mag wheel on the back as it does on the front. Yup, 19" Front and 19" Rear.

So I'm wondering if anyone has any experience with the effects of different wheel sizes for both front and rear. My general thought for the bike is café, but my first thought is to correct the wheels if this is where my "od" ride is coming from.


Thanks
Charles

First completely as you can , define "odd" .
Curiously enough this not only is an acceptable but actually useful modification .
Lead on I'll be here or find me by PM

~kop

Its hard to define "odd", but I'll give it a try. First off, I have probably 20 motorcycles in my life, most of them sport bikes, 1 GS (hated it), 1 Bandit, and some random others. I have only rode the bike 3 or 4 times as i'm still sorting out a clutch cable issue and this is the first time I have had a bike older than 1985. (the GS was an 85).

So that said, the bike seems a bit high due the large rear wheel. No "OMG ..whaaat" there. The bike also seems to be very eager to dive into a corner. More so that I would have expected for a non-sport bike with fairly skinny wheels. That's probably the biggest thing that seems odd is how it seems to want to dive and how I don't really trust it yet. (less than 60 minutes on bike so far)

Curious, why would this be considered useful? Il not sure if the odd is bad or good. Just not what I expected.

badduc,
I would say a 19" rear wheel on an XS has at least 3 advantages:
-If using the same tyre on a 19" vs 18", say a 4.00, the rpm would drop almost 4%. As the XS needs really small rear sprockets, this is a good thing.
-Increased ground clearance, since the rear axle now is 1/2" higher
-Quicker steering, as the rake/trail is decreased when the rear of the bike is higher. The same effect can be achieved with longer shocks, 10 mm longer C-C shocks with 18" wheel would raise the rear the same amount as 19" wheel with stock shocks.
The above all relates to 19" vs 18". The 16" wheels will be slightly lower, even with fatter section tyres, and basically slow down steering, decrease ground clearance, and give increased rpm for any speed, when the same final gearing is used. (As you can see, I'm no fan of 16" wheels on classic bikes....)

That about covers it . Tire selection , there are a bunch of dirt track tires with useful compounds and tread patterns all in 19" .

~kop

Looking at your pic, it appears that the front forks have been raised about 1", and the rear tire is almost touching the floor while on the centerstand, obviously longer rear shocks.

If I guess at 1" lower front and 2" longer rear, that works out to at least a 3° change in stance, and at least a 3° reduction in rake angle. Makes for snappier steering, especially during brake dive.

If steering and swingarm bushings are not in peak shape, I'd be concerned about high speed stability...

You might check the steering stem torque as well. Loose stem bearings cause heavy handling, as you describe, generally accompanied with deceleration wobble from about 45mph down, trailing throttle, no brake, let it have the bars and see what it does. Of course, you should make sure your tires are properly inflated before doing this.

No handling expert am I....

I'm with JD on those front tubes, I think I'd bring them back to flush in the clamps.
What size rear tire is on there? Might as well give the front size too. The front wheel in the back is done fairly often but it's a narrow rim, 1.85x19. The recommended tire size for that rim is a 100-90-19. Start spooning wide tires on narrow rims and the tire cross section goes from from round towards a spade shape, it's not hard to visualize the bike wanting to fall to the side of the Vee. You also begin to loose stability as the tire is forced to an unnaturally narrow and tall shape that the rubber is not molded to fit. I have never been able to persuade myself that the front rim in back is a performance upgrade, sorry.

Hey Badduc---Is the rear sprocket held on with 4 bolts or 6 bolts ??? Also how many teeth on the sprocket ??? tim

That rear sprocket looks like one of the ones from Rebel Gears that Omar's supplied with his disc rear conversion kits. If I'm right, that's a stock front mag, mounted on the rear. Not really a problem handling-wise. Fairly limiting to your rear tire selection choices, however.

I run a 100/90-19 on the back of my bike with little to complain about. However, I'm still interested to swap out to a wider 18" rim as funds permit, along with a 120- or 130-section tire. More for the looks and wheel strength than anything else; the bike handles great! If your bike feels odd, consider checking/upgrading the swingarm and steering bearings first.

Sorry for the late reply, did see the posts stacking up. Awesome feed back guys as I had of not thought of several of the items mentioned. I think the "odd" is resolved as just "different" than the other bikes I have owned. Hopefully when I get the new shift lever in, (on its way from 650Central) I'll get it on the road next week and put some miles on it.

1st thing I checked after getting the bike was to make sure the swing arm bushings were in good shape. Steering column is solid and the tires are inflated properly. Overall the bike was really well taken care of. I'm still shocked I have not found the original owner (who I think was from the Mercer Island area of Seattle) on this site.

@ArticXS - Your description of the quicker steering may be dead on.

@TimBeck - Rear sprocket is 6 bolts.

@Osteoderm - Your right on the stock front mag mounted on the rear. Tire size is the same front and rear. I'm pretty sure the tire is a 100/90-19 on both, but I'm at work and would have to check.

Thanks again every one!

If you count a little bit of the east side of the state and Portlandia you get a fair sized if not excessive group of XS650 enthusiasts that have some sort of web presence .
TwinLine in Seattle and Joe Wiseguy in Arlington (?) as well as a few of us underground single lift "shops" get quite a bit of XS650 traffic . Portland is a whole 'nuther (nutter ?) deal with a very active mod/resto/cafe/brat/bob/chop/thingy culture that is surprisingly easy to separate from the hipsters and posers . I have two real , one bike at a time builders in the neighborhood that were a bit tentative when approaching me . One because he wanted to maintain his interwebz anonymity and the other that thought I would jam his sawzall up his ass on first introduction .

Charles you know where and how to find me as do a few others . I'm surprised also because like you I belong to at least three widely known xs pages and contribute to another 3 or four blogs . I have never seen this bike before and to me that's odd .

Should you wish to go full on tracker ,spokes ,discs ,front and back save for the Barnes hubs and drive then Gary or I can lead you to the late common front hub and either the Suz or Kwack route for the rear . The wheelmaster isn't cheap but he is local and a bit less than Buchanan's work with I feel better parts .

In the mean time just ride it . We all have experience on 1.85 rim widths and are still alive . I did get a bit silly on the red bike with 2.15 x 19" front and the 2.50 x 18" rear shod with 7" plus wide dirt rubber , but only because that and the tires that go on them are absolutely the largest that will fit . So you think your bike handles "differently? heh . I've done this before and can guarantee mine is a pig on turn in unless you start sliding things around then it comes into it's own .
Enjoy , I'd like to see an extended ride report ;-)

~kop

Hi kopcicle. Thanks for the input. Once I get it on the road, please expect that ill reach to you to pick you're brain. I'm not sure where I want to take the bike yet in regards to style, but I do want to make it mine.

I like building stuff, have built a couple cars in the past (well, more like 20 years ago) and have restored a couple wrecked bikes; but building a bike in this regards is a new journey.