It's been awhile since I blog about cars, since I sold my last #jdm I have totally lost interest in them. But, out of special request by 
Case study one. This is my car, I got a nice set of wheel, drove it for a year and decided to swap them over with another friend, for a small fee he top me up. He like how the wheel looks, and I am finding my ultimate comfort donuts. So, here's one, flash back to where the story begun.
I got this humble little car back in 2012 for a very cheap price(well it's even cheaper now at the age of 10 years old). It came with a 13inches wheels, and I thought the wheel looks really small and hideos. So I made up my mind to flush it and make it looks more like a beast!
Come on man, it's a plastic steelie with plastic hub cover, what do you expect. It looks extremely ugly, the whole car looks like and old fat seal.
After some struggle with what looks good on the car, finally decided to go for with the maximum size allowed in such a small car, 15 inches. Off we took the wheels, throw the steelies away, and getting ready to receive some ultimate good looking wheels.
And there we go! Looks so much better with such big alloy wheels on a small car, especially it came with a TRD spoiler(I know it does not belongs to a Proton, I like to call it Tornado Racing Development).
After I got my big wheels, I felt so much happier with it. The car felt way more steady. Oh yes, I finally got to know the spoiler belongs to a Toyota, so I quickly got rid of it. But now with my big wheels, I'm proud to say my car is as tall as an MPV.
It goes over all terrain, just as capable as an SUV for your record. Not that I'm making this up, take a look at the photo. See to believe it.
Parking amongst the peer, my girl looks like the tallest, as if a very long legged tall girl wearing a mini skirt, almost can see what is underneath.
After awhile, came to realized, the car wasn't as stable as I felt originally. And the fuel consumption of the car started to look more like pouring out rather than burning off. The so called "stability" are all happening in my mind. I'm not saying big tires are useless, I'm just saying with our average driving style, there are not much difference.
This is not my car, but then I started to realize, the gap between the tire and the wheel well remain almost the same. As if the tire has not increase size at all? But I remember I upgraded from 13 inches all the way up to 15 inches in diameter. Wasn't that directly increased the tire diameter by 2 inches? Now I started to wonder, why?!
I take a look at my car again, yes indeed. The gap remain unchanged, that simply means the tire wall thickness must have been reduced, to accommodate the change of the increased alloy wheel size. Imagine if the rubber remain as thick as it was when it's still a hideous stock tires, the rubber will be stuck on the fenders and the car will not be able to move anymore.
I've been chaging more wheels, finding the holy grail of comfort, control, stability, and everything in one piece. No matter how big the alloy wheel(we call it RIM here) I changed to, the tire has to reduce size otherwise it will not fit into the wheel arch. Which now, it leave me one thing. If the tire sidewall become shorter, which means all the road feedback will be directly transferred to the alloy wheel, and ultimately the suspension system is taking more impact. We call the foot work as ABSORBER, which referred to damper in a proper word to use, are supposed to dampening all the harsh road feedback are now working double time harder.
And, the tire is mounted on the alloy wheels, and the alloy wheels is hosting on the brake hub. And the brake up is connected with a bearing so it can spin, so the bearing is taking the first hit. And, a broken bearing can be a bearing hub killer because the broken bearing component inside the hub will be keep on griding into the steel housing without you knowing it. Until one day, the grind mark become too deep and finally the bearing could not move anymore due the grind mark too deep, the friction created were too strong to move further, then the wheel jammed, and the whole bearing shattered. There goes not only your bearing, but the entire knuckly for the front part of the suspention, or otherwise...
Break the whole bearing spindle, and the wheel fly away. Yes, this is also my car.
Back to the topic, sometimes, we need to see what car are we driving and what sort of road condition we're working with. With such a small car, the wheel well is only this big, there's no way we can fit anything bigger than the well can fit. That being said, if we increase the size of the alloy wheel(RIM) but did not increase the size of the tire, which means we're reducing the flexibility of the rubber sidewall provided by the rubber tire. Many speed demanding freak or cornering freak like low tire side wall because of the road feedback, which ultimately will create a lot of damage to the car suspension system without knowing it.
Photo was taken by my friend 
Here's what important to know on the tire specs. 195 is the width of the tire. 55 is th percentage of the tire wall measured from the width, and 15 meaning it's a 15 inches inner diameter tire that fits on a 15 inches wheel(rim).
Source from bmwofstratham
Let's talk about how much tire height that effectively save us from the stones and pebels on a gravel road. I'm gonna list down the typical Malaysia tire sizes below for small family sedan.
175/70R13
185/60R14
195/55R15
Now let's get on with the aspect ratio calculation.
175mm x 70% = 122.5mm
185mm x 60% = 111mm
195mm x 55% = 107.25mm
Feel free to hit the tire size calculator here
And, I know a SAGA has a big turning radius. If we use a 195/55R15 wheels on the Proton Saga, when negotiating a full turn, the wheel will scrub into the wheel well. So, usually the tire shop will put us on a 195/50R15 wheels to save us from complaining. And the calculation goes like:
195mm x 50% = 97.5mm
So, now I hope you have a better idea of, the tirewall is the most important aspect in terms of absorbing impact from the road condition. You can have the best suspention system in your car, but the bearing sits below the springs and the damper(car guy call it unsprung weight), so it has to take the toll before other component. The only thing that can save you from heavy repair bill, is the tire itself. Choose wisely on your next tire change. It's not how big the wheels can go, is how tall the tire side wall.