GS500 Rear Wheel onto an XR250L

In continuing my attempt to make my 1992 Honda XR250L dual-sport more street-oriented, I wanted to get some decent street tires on the rear of the bike. A good way to get street/supermoto tires on a spoke dirt rim would be to re-laced the 18″ rim to a wider 17″ rim, but that would probably have cost hundreds of dollars. I opted to swap on the rear wheel and brakes from a 2000 GS500 (another reason I went this route is because I had a cast wheel up front as well, and I wanted them to match somewhat).

The 3.5″ rim allows the use of a 130 or 140 series tires, and the swap is relatively straightforward. The axles are the same diameter, and you’ll only need standard parts. The down side is that the rear wheel will be shifted 5-10mm to the right of center in order to get the chain lined up properly, and the brakes setup is suboptimal. What you’ll need:

• GS500 wheel, cush drive, bearings, sprocket, brake disc
• GS500 caliper, arm, and pads
• Some 16mm washers

Prep

The XR drive sprocket wants the rear sprocket on the GS wheel to be closer to the inside in order to stay as centered as possible. Flipping the sprocket around on the wheel buys you a few millimeters (it will offset inward instead of outward). The bolts that hold the sprocket on are weird. They are free bolts facing outwards that are kept from spinning by their shape inside the cush drive. If you pull them outwards, they will not spin as you remove the bolts the final centimeter. If they fall too far inwards, they will be allowed to spin freely. If you want, you can pull the sprocket and cush drive apart to see what’s going on in there.

• Rear sprocket bolts – (5) 14mm, dunno torque. Anyone?

Grab yourself a few 16mm washers and have them handy. The GS hub is narrower than the XR hub, so we’ll be using them as spacers on the axle, immediately inside the swingarm legs.

There is a bracket for the chain slider on the left hand side of the swingarm. The GS sprocket bolts will whack it if the wheel is towards the front of the bike (in terms of chain adjustment), so we need to get it out of the way. Cutting wheel to the rescue…It is only necessary to chop out a small piece.

Swap

Make a note of where the various washers are on the XR. You’ll want them to stay in the same place. The GS500 comes with a 39 tooth rear sprocket stock, and this [i]should[/i] work with the stock XR chain, depending on wear. Your mileage may vary.  Pull out the XR axle and set it aside with all the bits in order.

• XR axle – 5/16″ left, 17mm right, 69 ft-lb

All you need now is to swap in the GS wheel and brake arm and add the spacers. When you have everything together, check the chain run for straightness. It’s better to have a straight chain run than a centered wheel. For me, it worked well with one washer on the left, two on the right (contrary to the photos). Make sure the chain adjusters are matched on both sides.

Checking the chain run

Axle spacing, brake side

Axle spacing, chain side

Brakes

Before torquing the axle, attach the GS caliper to the arm (above the swingarm) and swap the brake lines from the XR caliper to the GS caliper (they should match right up). Replace the banjo bolt washers.

• GS caliper bolts – (2) 12mm, 28 ft-lb
• Banjo bolt – 12mm, 23 Nm

I’m not terribly familiar with the GS500, but my understanding is that the arm attached to the rear caliper is floating (ie, it moves freely back and forth around the disc). A torque arm is used to prevent this movement during braking. On the XR, the arm that the caliper is attached to is fixed. In other words, it takes a great deal of force to rotate the caliper in any direction.

Fabricated torque arm on an XR

Instead of using the GS torque arm (which would involve drilling or welding the XR swingarm), I just rotated the caliper forward until it butted against the bracket on the swingarm. With a strong piece of rubber stuffed firmly between the two surfaces to prevent excessive wear, I’m confident it will work fine. Note: This is untested. Since we’re talking about brakes here, that means it’s probably unsafe. I plan to keep a close eye on it. Never follow directions you find on the internet.

GS caliper on XR swingarm

Torque the axle, and bleed the rear brakes. In order to properly bleed the rear caliper, you will need to remove it from the brake arm and hang it above the rear master cylinder. This is usually necessary for most bikes anyway to get good feel, but something to know.

Thaaat’s pretty much it.

1992 XR250l with 2000 GS500 rear wheel

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