A Stored Bike with Spongy Brakes, an Old Tyre and a Tight Chain
A friend asks you to look over a 2016 middleweight he has just bought privately. It has 24,000 km and stood under a cover outdoors for eight months. The front brake lever comes back almost to the grip before it bites, and the fluid in the reservoir is dark brown. The rear tyre has 1.8 mm of tread at the centre, is visibly squared off, and its sidewall is stamped DOT 2214; the front is stamped DOT 2021 and has 2.5 mm. With the bike on its side stand, the chain has about 45 mm of slack at its loosest point and about 20 mm at its tightest, measured over several spots. Cold tyre pressures are 1.9 bar front and 2.2 bar rear; the swingarm sticker says 2.3 and 2.8. The battery turns the engine over slowly, but it starts.
1. The brake lever comes back to the grip. Diagnose it and say what happens before the bike is ridden.
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A lever that comes back to the grip on a machine that has stood for eight months points to the hydraulic side, not the pads. Brake fluid is hygroscopic: it absorbs moisture from the air, and dark brown fluid is old fluid. Water in the system lowers the boiling point dramatically, and it also allows air or vapour into the circuit, which is compressible - hence a long, spongy lever.
The danger is that it feels usable at walking pace and fails when it is hot. A few hard braking zones, or a long descent, heat the caliper, the water turns to vapour, and the lever goes straight to the bar with no brake at all.
Before riding: do not test-ride it. Replace the fluid with the grade specified on the reservoir cap, bleed the system properly, check the hoses for cracks and bulges, check pad thickness and disc condition, check for fluid weeping at the caliper and master cylinder, and check that the lever has a firm bite with the prescribed free play. If you cannot do the bleed yourself, this is a workshop job - brakes are the one system where 'it works a bit' is not a category.
2. Give your verdict on the two tyres, using both tread and the DOT stamps.
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The rear goes in the bin, and not because of tread depth. At 1.8 mm it is still above the legal minimum for a motorcycle, which is around 1 mm at the tread wear indicators (cars need 1.6 mm). But DOT 2214 means it was made in week 22 of 2014: the rubber is well over a decade old, and the rear is the tyre on a bike that has stood outdoors under a cover. Aged rubber hardens, loses wet grip and can crack even with tread showing. Add the squared-off centre section, which makes the bike drop into turns and then resist leaning, and the tyre is simply not fit to ride on.
The front, DOT 2021 with 2.5 mm, is a different case: age is acceptable and the depth is lawful, but check for sidewall cracking, flat spots and glazing from standing, and check the DOT date yourself rather than trusting the seller.
The rule of thumb: on a motorcycle, tread depth is the minimum legal test, not the standard. A ten-year-old tyre with legal tread is still a false economy.
3. Assess the chain and the tyre pressures, and link both to how the bike will ride and how much fuel it will use.
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Chain. 45 mm at the loosest and 20 mm at the tightest is not a slack figure, it is a diagnosis: a 25 mm variation around the sprocket means tight and worn links and probably hooked sprocket teeth. Adjusting it like a normal chain is a trap - set to the book figure at the loose point and the tight spot will be far too tight, loading the output shaft bearing and restricting suspension travel. Replace chain and sprockets as a set, then set slack at the tightest point within the manufacturer's range and keep it lubricated.
Pressures. 1.9 and 2.2 against a specification of 2.3 and 2.8 means the front is 0.4 bar down and the rear 0.6 bar down - a lot. Underinflation makes the carcass flex, which heats the tyre, wears the shoulders, slows steering and increases rolling resistance and fuel use. Set them cold to 2.3 and 2.8, recheck when cold, and check weekly.
Economy follows directly: correct pressures, a correctly tensioned and lubricated chain, clean air filter and smooth throttle use are worth more real fuel than any additive. A worn, over-tight chain and soft tyres are both a handling fault and a fuel bill.