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Katana How-To's & FAQ's A forum filled with write-ups, FAQ's, and visual aids for
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Old 12-06-2009, 11:18 PM   #1
Kat King
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Default Fittment of a Wider Tire on Kat By Kreylyn

Depending on the year (Pre or post) and if it's Pre... the CC (600 swinger is smaller than 750) you have a couple of options.

First, let me address the aspect of fitment at the axle.

Pre or post... your only looking at a small difference in diam. inside to inside between the 2 arms. By my measurments about 1/4".

See pictures below... left is stock pre 600.. right is stock post Kat (bothy 600 and 750 are same on post).

Pre 750 uses 3.5 rim... post uses 4.5 rim. The Katana rims have a slightly smaller central width on the hubs as well. So, using a Katana rim it's not that hard to swap out between pre or post... the difference is easily made up with flex... The wheels were designed to be used with 17mm axles, and you have a width of about 5" at the center hub.

Lets move on to other wheels... like say, off a RF600 4.5" (curved spoke like the pre styled wheels) or the 1992 GSXR 600 5.5" (straight spoked like the Post). Both of these wheels were designed to be used with 20mm axles... and both have the same hub diam. of 5.5"

The difference is 1/2" that has to be made up. This will offset your wheel by half that much... but 1/4" that isn't really that much of an issue to be honest. You could still flex out the end of the swinger to compensate. Several people have already posted about getting bikes where someone forgot to put the sprocket side spacer back on before torquing down the axle, and permenantly flexing the swinger in by 1/4+".

See picture here.. GSXR axle, all spacers correctly in and spaced for the chain side... the difference is shown here...

It's not so much the axle point that you have to worry about. Pick the right wheel.. you can easily fit 3.5-5.5" rims in. The problem comes in when you look at the tire clearance.

So.... lets look at that.

The following are pictures of a GSXR 600 5.5 Straight spoke wheel with a Post Kat swingarm, a 190/50/17 tire is mounted on the rim. The sprocket carrier is the same for a Kat, the RF6, or the GSXR 6 for these model wheels. No difference there. Only differences then are going to be the size of the wheel hub, and the tire total width.

The difference in tire width between a 180/55 conti road attack mounted on a 5.5" (185mm wide) vs the 190/50 race tire (192mm wide) is 7mm total. Not that much of a difference. (anything over 180 a 5.5" rim will pull in, decreasing it's size... for example, a 200/50 tire is only 197mm wide on a 5.5 rim, but due to this the profile is way messed up.)

Sprocket side... appropriate clearance, with the wheel in correct alignment.

Other side though... shows the problem.. with the wider hub, pushing things to the other side offsetting the wheel, if it's lined up right you get this...

I could actually probably use a couple more mm clearance just to get the wheel perfectly lined up... getting it close pushed the tire against the swingarm at that point.

Now, I can flex the back end of the swinger to fit in the spacer. The point of contact for the wheel isn't going to flex that much though. That point is still going to rub.

This isn't even taking into consideration that stock brake arms are significantly closer to the tire than the swinger. Brake arms can be modified, or even custom made pretty easily if that was the only issue.... but, moving back to the tire clearance...

This picture shows I marked off where the widest point of the tire is by wiping off a clean spot from the grease on the swinger.

Now, lets move the wheel out and measure the clearance I have here for a stock arm...

So we have a total of 200mm clearance. That point is way to close to the cross support to get much more clearance at that point by flex. Your stuck with that if your keeping a stock swinger.

Maximum width I would suggest for that would be 180 TOTAL width for any tire... You need about 10mm clearance on both sides! Most tire sizes are going to be slightly larger in actual tire width than it's "size" that is listed when PROPERLY mounted on the right rim size. As I mentioned... My Conti sport attacks area bout 185mm wide on a 5.5" rim. Not enough clearance for the stock arm... not enough safely anyways in my opinion. And this is if you work out centering the new rim perfectly... which this one isn't as it sits.

So... what are the options that can be made to work?

Pre swingers can fit a 3.5 - 4.5 wheel. If you use a non kat wheel, they will be 1/2 wider... so your looking at a harder fit, but it will still work. Max tire size I would recomend for the tire to clear the swinger would be about 160, with a modified brake torque arm.

Post swingers can fit 4.5-5.5" rims, with a max size tire of 170 with a modified brake arm.

To properly fit a 5.5" wheel or larger with a 180 or larger tire... your going to need to make more clearance at the widest point of the tire for the swinger. The Cut/Weld option that I do offers exactly that as you can see in this pick of a post swinger modded to fit a 2002 5.5 GSXR wheel with a 200/50 tire mounted (these are even wider at the hub than the early 90s GSXR wheels).

That kick out right at the support brace gives you the room needed for the larger tires.

So... to cap that all up...

The biggest issue with a 180+ tire on the Kat... is clearance for the tire vs the swingarm. You can fit 170- on a post.. or 160- on a pre with the appropriate tires mounted to the right size rims... A 170 should be on a 5.5".. a 160 should be on a 4.5"... 150 should be on 3.5". Fit the right tire to the right rim size.

And before anyone posts... "I have a larger tire on mine without... " remember oversized tires on too small rims pull the tire in. A 180/55 tire mounted on a 4.5" rim is going to give you about a 170 - 175mm or less even total tire width... so your not really gaining anything but crappy performance and handling for your bike.

93 750 Kat

Modified Swingarm, 5.5 GSXR Rear with 180/55 and 520 Chain, 750 to 600 Tail conversion, more to come. Long Term Project build thread http://katriders.com/vb/showthread.php?t=96736

"I've done this a thousand times before. What could possibly go wron.... Ooops!"

Last edited by Kreylyn; 11-28-2015 at 10:11 PM..
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