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Tyre Pressures

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In the Owners Handbook (English version) for the CZ 250/350 models 471/472 dated 1976 the tyre pressures are given in kp/cm3 front 1.3 and rear 1.5 rising to 2 with a passenger. These are Kilopascal units not exactly common in the UK.

The tyre sizes are front 300x18 and rear 325x18 for the 250 and 325x18 and 350x18 on the 350. Maybe surprising to find the same pressures are recommended?

This equates to 18/19 psi front (1.3 bar) and 22 psi (1.52) rear or 30psi (2.07 BAR) with pillion. Clearly the most accurate pressure measurement in common UK use is psi or pounds per square inch. Many bikes and cars run with this level of pressure. NEVER exceed the maximum pressure shown on the side of the tyre and do not ride at that pressure. Check pressures when your tyres are cold not after a fast run when a hot tyre will give a higher reading.

I tend to run my tyres a couple of psi harder. Remember if you run at a lower pressure than recommended you can be fined £100 (Fixed Penalty) and get 3 points on you licence per tyre. Challenge it and a court can fine you in excess of £2,000 plus points. You could also have insurance problems if you have to make a claim as low pressure can totally invalidate your insurance cover. The common defence is that kids let it down – your fault for not checking before use. You may escape if it has punctured during your journey but would need photo evidence and repair/renewal evidence.
Tyres on a motorcycle are so critical especially the front as that does all the steering and most of the braking so look after it and check for damage at least weekly or before each ride.

If the specified tyre size is no longer available it is probably safer to fit a larger tyre if there is space and it will not foul bodywork e.g. the mudguard – rather than a smaller tyre. I couldn’t get a Mitas in 300x16 and wanted to use a matched pair so opted for a 325x16 rather than a 275x16 that was available. Tyres are not expensive given their safety value. It is recommended that you change your tyres every 5 years even if they have plenty of tread left. You might as well change the inner tubes at the same time. Always check the inside of the rim for rust as chrome flakes or rough areas can lead to punctures. I clean off rust, treat it and then overpaint with a thick coat of Hammerite or similar. Make sure the rubber strip protecting the inner tube from the spoke ends is also in good condition and there is no indication that a spoke is starting to poke through. If there is a long spoke - then grind off the excess metal.

Modern tyres are well made and you may not need to balance the wheels. If you feel vibration through the handlebars then you may need to balance the front wheel. Normally you won’t notice a small imbalance on the rear. To find the heavy spot raise wheel off ground let it settle and put a chalk mark on the tyre at the lowest point. Spin again to check low point. Add weight in small increments opposite the heavy point. Keep spinning the wheel and letting it settle. You know the wheel is in balance when the chalk mark stops at random points round the circumference. Weights can be stuck on, clipped to the outer end of a spoke or my favourite is lead “wire” close to the adjusting nipple.

By Pete Edwards - July 2016

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