At the beginning of the year I wrote an article which explored the details and function of quick change axles, which can be found here: BIKE TECH – QUICK CHANGE WHEELS AND WHERE TO FIND THEM.
I was able to spend a bit of time up close with the 2017 Endurance World Championship winner Yamaha GMT94 and I wanted to continue to uncover the details of quick change wheel systems but also look at some other details the bikes are equipped with to deal with endurance racing.
In the previous article I covered how a quick release axle and rotating front fender mounts are required for a quick change wheel system. Here we can see how GMT94 have approached the design:
– Quick change axle:
For the quick change axle there is a typical threaded insert in the fork on the left hand side, retained by the axle pinch joint in the fork drop-out, which replaces the need for a nut.
On the right hand side there is a bushing in which the axle slides through. At this point I have not yet figured out how (or if) the RH fork is retained to the axle. Typically the axle pinch joint on the RH side would join the axle to the fork to ensure good front end stiffness without adding any side load to the fork leg, but this would not work for quick release axle.
Also present are the usual pull cups to allow for easy tool centering and aid in pulling the axle out.
– Rotational fender mount:
To move the calipers outwards and allow the wheel to be removed GMT94’s Yamaha R1 has rotational front fender mounts, as seen on all other quick change systems. They have utilised additional structures to support the fender, like Honda Endurance Racing’s CBR, which then mount to both the inner fork tubes and below the fork drop-outs.
The mounts are also spring loaded which allows the calipers to automatically spring out of the way once the wheel has moved forward enough for the calipers to clear the discs. When the axle is threaded it ensures the drop-outs are aligned and doesn’t allow the caliper to drag on the brake discs.
I also noticed these small tabs with what looks like a rubber pad on the inside. I believe these are to protect the rim when the mechanic pushes the calipers in during a fast pit-stop to align them with the disc. It may also position the caliper in approximately the correct position for quicker alignment.
For a quick change system at the rear, as covered in the previous article, only basic modifications to the rear axle are required. Here I’ve also looked at GMT94’s quick release sprocket system.
– Quick change axle:
The axle has been flipped around to be inserted from the right hand side, and the nut has been replaced by a threaded “axle” which is used to mount the sprocket; more on this next. Pull cups on the rear, just like on the front.
I like the convenient handles on the axle position adjusters for easy adjustment.
The caliper bracket must be bolted to the swing-arm from the inside to allow it to stay in place even when the axle is removed.
– Quick release sprocket:
I’ve called this a quick release sprocket for lack of a better name, but it’s actually a system that allows the sprocket to be fixed to the swing-arm, while the wheel can be easily removed.
The sprocket carrier is bolted to the swing-arm using the outer hub / “axle” and nut in the above right picture, and it stays with the swing-arm during rear wheel changes. This means that the mechanics don’t have to deal with the chain during wheel swaps for faster pit-stops.
For the sprocket to engage the wheel there is a quick release joint between the two. On the wheel there is a ‘flower’ shaped tool as the male-side in the joint.
On the sprocket carrier there is a half-formed female version of this tool (yellow and red coloured part in the left photo) that engages with the one on the wheel. The half cup allows the wheel to be easily removed and inserted to the sprocket carrier.
The axle slot on the left-hand side has most likely be increased in size to allow for this double axle setup, where the rear axle threads into the sprocket hub.
This means that during rear wheel changes it is only the wheel and tire that are changed, while the sprocket and rear caliper remain attached to the swing-arm.
– Quick release everything:
The great theme along the entire bike is quick release joints.
Dry-break front and rear brake lines.
All the coolant, vent and oil lines are quick release.
As the picture above shows GMT94 does mount a lot of bike protection parts; here some GBRacing engine case covers.
During an extended endurance race the chances of a crash become relatively high and so it’s vital to ensure that the bike can continue in any unfortunate event and get back to the pits for repair.
Crash bobbins and swing-arm protection. They also have the usual frame and swing-arm covers in carbon fibre. Additionally they’ve also fitted a lower chain guard to improve chain protection and also life.
Additional protection comes in the form of structure for the front bodywork and special guards for the forks as steering stops.
– Other details:
One-way bleeder valves for easier and faster bleeding of the brake system. Also notice the remote brake lever adjuster which extends to the left handle bar. This is to adjust lever position on the fly as pads wear out and the stiffness of the brake system changes during long stints.
And finally, on the oil fill there is what looks to be a sensor either for oil level or temperature.
This is all I could unearth from arguably one of the most performing and successful endurance bikes in the world, and I’m sure there is still much to learn from it.