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SRX Spoked Wheels

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A number of people have shown interest in converting their SRX's to spoked wheels and more specifically what hubs to use, as such I thought I would share the detail of my conversion.
I thought long and hard about what I wanted to achieve with my conversion and came up with the following.
  • I didn't want it to look like a special, it should look stock. My feeling was that if the only people to notice the changes were fellow SRX owners then I would have achieved this goal.
  • It should have apposed piston calipers. I don't like sliding calipers, they may give extra spoke clearance but they seize up, need more maintenance, and in my experience often give a poor brake feel.
  • It should retain the look of an SRX.


NOTE: There are many ways of fitting spoked wheels this is just a description of how I did my conversion and the rational (at the time) for my choices.

Front Hub

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Using the above criteria I spent some time looking for suitable hubs. An obvious starting point is trail bikes, and whilst the majority of these spoked wheels, most seemed to use sliding calipers, as such they were ruled out. My assumption is that sliding calipers are used on trail bikes because the discs used are relatively small in diameter, and as such the caliper needs to be mounted closer to the hub. The closer the caliper is to the hub the less clearance there is for spokes, so the caliper needs to be thin on the spoked side, sliding calipers are therefore ideal where space is limited.
I have no doubt there are exceptions to this rule but it seemed to be a common theme with trail bikes.
So what bikes have spoked wheels and big discs ..................... SuperMoto's. Once I had realised this was the way to go the obvious choice for donor hubs was the TDR250, the fact that this used the same 320mm disc and caliper fitted to the later 3SX,3VN Monoshock models also helped in the decision. These wheels also ticked a number of other boxes including using standard Yamaha speedo drive, caliper and disc's.
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Front Suspension

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The TDR250 uses a 320mm disc, since the originals are 267mm I was going to have to find a way of mounting the caliper in the right position. The later SRX600 twinshock models (3HU/3GV) models also use a single 320mm disc so the plans was to try and source a fork leg or pair of forks from one of those models.
Since the TDR250 front hub uses the same size spindle (15mm) as my existing SRX forks I decided to trial fit the wheel into my existing. It was clear from this fitting that if I wanted to retain the Yamaha speedometer drive then this would result in the disc running very close to the fork leg, meaning there would be no way of sensibly mounting the caliper (Custom brackets were not a consideration as I wanted a stock look). Machining back the hub to move the disc back was an option but I felt the caliper would then run to close to the spokes.

At this point I was given a box of bits with the remains of an SRX400 Monoshock I had sold on, the guy I had sold it too had an accident and rather than repair it had decided to break the bike, what he couldn't sell he gave to me. In this box of parts was a set of fork yokes, on first inspection, apart from having larger clamps to accommodate 38mm forks, they look identical. On closer inspection I found they were 10mm wider, just enough to give the extra clearance I needed. The one issue was that the lock stops were completely different, rather than modify the frame I ground the originals off and had new ones welded into place. In hindsight it would have been easier to modify the frame.

The Monoshock SRX (3VN/3SX) uses 38mm forks so my existing forks (36mm) were going to be a problem, I also had the issue of how to fit the caliper. Early TZR250 forks looked like a close fit but sadly they are 39mm and I didnt want to bore the yokes to fit them. I bought a set of TDR forks (also 38mm) but decided they were too long. The ideal forks were SRX Monoshock (3VN/3SX) items but as I had found when repairing my 400 Monoshock they were very hard to find. Eventually I settled on a fork leg from a later 3HU/3GV SRX model (320mm disc) and had spacers made to allow me to fit the 36mm forks into the 38mm yokes. After this fitting the calipers was relative straight forward and only needed small spacers to line up. Result.
The new top Monoshock yoke looks identical to the twinshock items and the twinshock clocks bolt straight on. After some searching I found some SRX400 Monoshock (38mm) handlebars these look identical to the Twinshock items, so I had a front end which looked pretty close to stock.

In hindsight there are a number of other options that may have worked just as well. Early FZR400's use 38mm forks, the bottom yoke is pretty much identical to the SRX Monoshock item, the top yoke is however quite different it has a central ignition switch mount which would make it tricky to match to the stock SRX clocks. Early 600 diversions also use 38mm forks, and as a bonus have handle clamps, I have a set of these and at some point will be attempting a handlebar conversion, the main issues is how to mount and make the clocks look good.
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Rear Hub

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The Rear TDR hub uses a sprocket carrier design which is quite common to a number of Yamaha's, and as luck would have it there was an SRX 400 Monoshock carrier in my box of spares this has the same sprocket bolt pattern as the SRX twinshock making sprocket fitment much easier. There seem to be a number of carriers which look the same but have different offsets its possible to cut down and old sprocket and use that as a spacer if need be. I have subsequently also discovered an FZR250 carrier also has the same offset as the SRX Monoshock item.

The rear brake diameter proved to be a little more complicated. The TDR 250 rear disc is 210mm and shared with a number if different bikes, the twinshock disc is 245mm and thus puts the caliper to high for use with the 210mm disc. I toyed with getting a disc made, but ended up using a Brembo caliper and mount from an SZR660, this needed a bracket/guide to be welded to the swinging arm but other than that was quite an easy modification.

One area a lot of work was needed was the spindle size, the TDR uses a 15mm rear spindle and the SRX Twinshock a 17mm spindle. I had the option of finding a suitable length 15mm spindle or sticking with the 17mm spindle (which would increase rigidity) and replace all of the bearings and spacers. I decided to stick with the 17mm spindle, bearings are available (albeit slightly narrower) the main issue was with the bearing spacer between the bearings, this was a larger diameter than the original and fouled the casting flash within the hub. Once the flashing was ground out and new spacers made up it all bolted together.

Chain alignment brake alignment are obvious critical so if you do decide to do this, use your original wheels for reference and makes the spacers to suit. Once its all in place the wheel rim can be laced to ensure it is central, this is one advantage spokes have over cast wheels, its possible to alter the wheel alignment independently of the hub positioning. My ordering for calculating the spacers dimensions was.
  1. Brake aligment. Determined by the caliper mount to wheel bearing spacer.
  2. Chain alignment. Determined by the sprocket carrier inner spacer.
  3. Total wheel width. Determined by the sprocket carrier outer spacer.
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Summary

HubsYamaha TDR 250
Front ForksYamaha SRX 600 (3HU/3GV)
Yokes (Triple Clamps)Yamaha SRX Monoshock (3VN/3SX)
HandlebarsYamaha SRX Monoshock (3VN/3SX)
Front Brake caliperYamaha FZR1000 four pot
Rear Brake caliperYamaha SZR660
Rear Brake caliper carrierYamaha SZR660
Sprocket CarrierYamaha SRX Monoshock (3VN/3SX)