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I am thinking of buying a Swift. The tyres they appear to use are size 185-60-15. This appears to be not a common size, whereas 195-60-15 seems to be more common, and therefore probably cheaper? Would it cause any problems to fit the slightly wider tyre to a Swift?

The wider tyre will produce a slightly slower indicated speedometer reading, if keeping to the same sidewall height, as the circumference of the tyre will be different from the original tyres. You should also take into consideration that if you need to fit the original spare tyre at some stage, the ABS system will detect the speed difference and other complications will arise. I cannot see any advantages for you to change the tyre size. I recommend you stick to the original size. The 185/60/15 tyre size is a common one and GT radial, Continental, Bridgestone, Firestone and Goodyear make tyres in this size (and many other brands).

Hi Donovan,
Was just reading this thread, and a question comes into mind regarding what you said about the speedo reading.

i have a 7th Gen Corolla. The label on the door says to use either 175/60/14 ..or ...185/60/14.
However when i bought the car many years ago (used import from japan) , all 4 tires were at 195/60/14..and basically ever since i've been replacing them with 195/60/14.
It looks better on the car and it feels more stable than my mom's car (old startlet on 155).

Now when you say "slightly slower speedometer reading" , do you mean that speedo reading is Slower than actual speed ...OR ...speedo reading is slower than before changin to wider tires (as per OP's question) ...since for the latter, that means actual speed will still be slower than speedo reading BUT it'll be closer , ...i'm asking this due to the "higher-than-actual-speed" speedo calibration on all cars.

In this case the tyre size wont make a huge difference but the speedo will read 2% slower than actual speed. Speedo will show 100km/h when actually travelling 102km/h. It is possible the reading might be closer to true speed but you will have less tolerance to work with this. Different tyre sizes will have different effects on the speedo reading, you are better off sticking to the recommended tyre size.

Thank you !

Thanks for your comments and I have one further query: In your reply you said "if you need to fit the original spare tyre at some stage, the ABS system will detect the speed difference and other complications will arise". The second hand Swift I looked at had a space-saver 'biscuit' as spare tyre and I'm wondering if this is standard? If so, would this not be a safey issue as a space-saver would be smaller than most standard tyres, surely?

Space-saver wheels are for emergency use only and are not designed to be used over long distances. If you get a flat tyre and replace a wheel with a space-saver wheel, you should only use it to get directly home or to a place where the flat tyre can be repaired or replaced.