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It's being some time since I posted something out when I am still busy with project. The project is progressing still okay, maybe it's time to post something out.
Drivers normally put new tyres in front, and I don't really research more on this kind of thing, until when a customer told me that he wants to put the new tyres at the back, and told me that putting the new tyres at the back is safer than putting them in front (after watching a video). Perhaps it's time for me to research more about it.
Let's have a look on those videos (I have concluded the points below)
To conclude the above why putting new tyres at the rear
A. Michelin experiment showed that putting new tyre at the front will cause oversterring / spinning when you are driving too fast while turning
B. Kumho mentions that understeering and oversteering may occur and normal handling to steer (most of the time) will not happen. If you put new tyre at the rear, when understeering happens, you can steer back to the track (when front tyre does not meet maximium grip). If the front tyre is new tyre and meeting the maximium grip, it won't be easy to turn back to the track.
Likewise, in the cause of oversteering, rear tyre have a tendency to push to the front. If you put new tyres at the rear, you will have better trip at the rear. Hence, the rear (new) tyre will not lose grip easily when braking
Furthermore, most of the cars are FWD, manufacturer setup the car to make understeering easily
To conclude putting new tyre in front
A. The technicians (in Taiwan) said that driver can have better control of the car
My opinions on the video and research
1. Michelin experiment is not persuasive enough as both experiment were not in the same driving condition (speed and control). Because the driver is asked to keep accelerating in the second round of testing, when new tyre is put in front.
If I assume the same condition, putting new tyre at the rear may cause the car to crash as well as the front tyre does not have enough grip .
2. Kumho research is easier to understand and more persuasive.
3. It's understatement that putting new tyre in front will have better control, as most of us (drivers like you) normally put new tyres in front.
Conclusion
We are in Hong Kong after all. Driver may speed up until 60km/hr (not in high way), or up to 100 - 120 km/hr (highway). Some may be in a hurry, and speed up to 180 - 200 km/hr
Change all tyres to new one
So you won't have to think much about the old ones. And the main point I want to bring out is, it's better to have your car tyres swap from front to rear, and rear to front after driving sometime, (as your front tyre will rear off faster than your rear). In this case, tyres can be used longer, and you can have all your 4 tyres changed to a new one at the same time
If you still want to change 2 tyres because the other 2 just changed not long ago
Putting new tyre at the rear may suit you if you are driving at normal speed like below 70km/h (not at high way)
Since you are not driving fast like me, the probability of understeering occurs is low. On the flip side, probability of oversteering is higher than understeering due to lighter weight at the rear.
Putting new tyre in front may suit you if you are driving fast.
Driving fast require better grip and control. Though the occur of oversteering is uncommon (in HK). And of course it still have a chance to occur
As a result, it's still better to change all your tires to new one if you are driving fast.
As the adages goes, if you want to do better things, you will require better equipment. Just like Initial D - Project D, they change all new tyres in every race. :)))))))))))
A friend came recently to change tyres, and shared his experience at a Kowloon tyre retail store.
The technician (probably have no inventory for the size) suggested to change all 4 tyres with the same size. (225 40 R18). The rear tyre should change a longer width but the technician did not realize that, and change all 4 tyres to be the same.
A shorter width rear tyre caused a little gap between the rim and the tyre sidewall as followed
Before changing tyre (pic 1)
The side of the rim protruded. Without the tyre sidewall covering, the rim is prone to rock and stone "attack" on the road. My friend said that he needs to pump in air again every few days. That implies, the air is leaking out in between the gap.
Before changing (pic 2)
Zoom in to have a better look.
If you feel something is wrong with your tyre, do feel free to contact me, whatsapp the picture, and discuss about it :D
(Grabbing a little limelight here) The technicians sells 4 tyres (size 225/40 R18) Dunlop for $1500/piece. And I sold less than $1,000/piece. Perhaps that's the price difference between Kowloon area and New Territories area. Just like having a meal in Kowloon is more expensive than in New Territories.
After changing the appropriate size,
換呔後 (圖一)
The look is surely different from before. The size fits the rim.
English version
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After further studying (to avoid the same mistake I made in the previous post), to ascertain the reasons why we have tire wear in the middle or both side.
These two situations are related to the tyre pressure
1. tire wear in the middle
It indicates you have pumped in too much air in the tyre, resulting in the middle tread surface area sticking the ground more than both side.
2. tire wear on both side
It implies under-inflation. Tire tread on both side sticks on the ground more but not the middle tread.
Due to the stronger tyre sidewall, the middle tread will cave in under the situation of under inflation (when there is weight). The inner and outer side of the tyre's surface area touch the ground more than middle, hence, wearing both side easily. The same goes for over inflation.
Check your tire for the above situation will help your tyres to run for longer time.
If you have already followed the car manufacturers recommended tyre pressure, and still discover both side tire wear, try pumping in a little more air. Car manufacturers do not manufacture tyre afterall. Tyres characteristic may have changed over time with it's improvement and ingredient.
To be more professional, it's important to check what type of gas is pumped into the tyre.
Actually our store pump normal gas into the tyre (For your information) , the same as gases used in the petrol station.
For some tyre store / car maintenance company, they pump in Nitrogen
The difference is that Nitrogen is not easily affected by the temperature, but normal gas's kinetic energy increases when temperature increases. When tyre temperature increases, air pressure in the tyre increases as well if you are using normal gas.
The best way of ensuring the standard of air pressure, is to check how much tyre pressure increases after you started your car and drive for some time. If you are supposed to have 32psi for your tyre, and you have already pumped in 32psi at the beginning, the tyre pressure increases to 35 psi after driving, then you may want to release some of the gas in the tyre to 29 / 30psi.
(Revising the post and found out that I had written wrongly about the tyre pressure. It must be the heat!! [ Finding excuses for myself >< ]) The label on the car indicates the tyre pressure in cold temperature. If the label states 32psi, then it's recommended to pump in 32psi under normal temperature (which I assume is room temperature and pressure) There is actually a complex matrix to tell drivers how much tyre pressure should be pumped in under different temperature. E.g. pumping in 32psi during summer, and a little more psi during winter. To avoid complication, simply pump in the recommended tyre pressure on the label when the tyre is not hot would be good enough for most of the drivers. (If you don't have the time to wait for the tyre to cool down, just pump in 32 psi, or a little more would be fine) In sum, 32 psi (in this example) is the minimum tyre pressure you should pump in. Car manufacturer did not mention the best tyre pressure when the car tyre has "warmed up", and did not state whether to use Nitrogen as standard, or normal air as standard. Perhaps it's too complicated to involve in tyre?
(a little buffer should be fine for your driving)
Actually we don't really have to check so serious that we have to follow the rules as long as it does not affect our driving. However, if you pump in too much air, not only if you feel your car is "jumping" kind of feel, your tyre tread may worn off easily at two side (which I will talk about in the next part)
