Tyre pressure: Why it is important to get it right

Hello JM,

You totally lost the plot on tyre pressure the other day. The customer wanted to know why most people inflate their car tyres to 35 psi when it should be 32/33.

I am a Mkamba and I should know something about tyres. Front tyres go for 32 because they carry less load and that is where all steering and handling feel is. The softer the better. Rear tyres carry more, so get the 33psi. Kenyans inflate to 35 because they know that their tyres will lose some pressure sooner or later.

Now this is where you misled us. You can’t tell your faithful to do as you say not as you do! Most of these people are novices who worship your every deed and word and will try to inflate to 40 just like you said you do. The consequences? Poor and bouncy handling, and worst of all, tyre wear at the middle while the sides remain new. Then in the next three months the same people will bore us, tyre experts, with the same question — why are my tyres wearing down at the middle while the sides are okay?

Donald Mutinda

Hi Mutinda,

I like how you say “front tyres carry less load” and yet that is where the engine is; and by your admission, where the steering and handling feel is. I will add that most of the braking effort is at the front as well.

Front tyres carry more load than rear tyres for most cars. Load is not always payload or baggage, or even weight; it means tasks or duties.

Front tyres carry a lot more responsibility and therefore undergo more strain than rear ones (doubly so for FWD platforms.)

Softer tyres heat up faster, so when you say the softer the better, it means you are encouraging the under-inflation of tyres. This increases wear — from rapid heating, increased sidewall flex and misshapen contact patches such that the outer fringes of the tread pattern wear out faster than the centre.

I have not met any of these Kenyans who inflate their tyres to 35psi.

Most people I know stick to 32 and below. I do between 35 and 40 because as I had said earlier, I have my own reasons for running custom tyre pressures; reasons which the layman need not know. I conduct all types of experiments with my car so take this as a ‘Don’t-try-this-at-home’ public service announcement. If you are as much of a tyre expert as you allege, you’d know why.

The followers are free to inflate their tyres to 40 if they want, but only if they have similar (and admittedly narrow) -sized tyres to mine (195-section, 65 profile). The harsher ride and “bouncy” handling are not as exaggerated as you are trying to make them sound.

I know the downsides of pumping my tyres up to 40 and they are not as dramatic as you try to paint them. Tyre wear in the middle? I have had my current tyres for almost two years now and they still look as good as new, despite the variations and disparity of load and environment that I have subjected them to (this includes two Great Run events).

So, it stays a case of “Do as I say, not as I do”. If you have 265s and try pumping them to 40 psi just because Baraza pumps his 195s to 40 psi, then perhaps you deserve every single ounce of discomfort that the subsequent tyre explosion will give you.

NB: (1) Softer running gear — tyres and suspension — are actually worse for steering feel, response and vehicle handling, by the way. That is why race cars have very stiff set-ups.

(2) As sternly as I can muster sternness in prose — tribe is not a substitute for knowledge nor is it a qualifier of arcana; more so when said knowledge is deeply steeped in engineering.

Not all Kambas are tyre experts, and not all tyre experts are Kambas.

For a ‘statement’ car, go German

Hi JM,

I am shopping for a new car and I’m torn between an Audi A6 2.0 and a VW Passat, both 2012 models. Which one would you recommend and why? Thank you.

Brian

Hi Brian,

Get the A6. When you go German, more often than not, it is to make a statement, so this is where all the clichéd platitudes come out. Go hard or go home. When you are walking on thin ice, you might as well tap dance.

Seriously, the A6 is one class up on the Passat whose natural rival is the A4, so that makes it superior in terms of space, spec, performance, practicality, style and whatnot.

The Passat is better to drive and maintain, but this is German flash we are dabbling in here, it has to be done properly. The sealing of the deal is the fact that Audis sport the best interiors in the world, this side of a Bentley. The A6 is no exception.

Currently, not all Subarus come with AWD

Hi Baraza,

Would you kindly shed light on Subaru AWD? How does it really work? Does it mean that the car powers all four wheels all the time? Does it (AWD) make the car consume more fuel than another of same capacity, but without AWD?

I have also gathered information that AWD cars experience under steer. How critical is this or does it seriously compromise safety? Do all Subarus come with AWD?

Patrick

Hi Patrick,

Yes, AWD means that all four wheels are powered constantly. On paper, an AWD car will consume more fuel than a similar 2WD version, but this rarely reflects in the real world, because in the real world, there are a myriad other factors that have a much bigger impact on fuel economy, chief among them being driving style.

(My family still does not understand how I drive a wagon longer than a 14-seater — with AWD and a turbo and a big exhaust — in record time from Nairobi to Western, and still burn through slightly less than half a tank of fuel or thereabouts. Driving style is everything.)

There is a tendency for AWD cars to experience understeer, but this can squarely be blamed on two brands: Subaru and latter-day Lamborghini. Subarus understeer are nose heavy, because their engines tend to be ahead of the front axle.

That explains their rather odd proportions at the front and why they have such long front overhangs, especially the Legacy. Besides, they use mechanical diffs that are reactionary rather than electronic diffs, which are proactive like its rivals do.

However, some modern Subarus have ditched mechanical diffs in favour of electronic units.

Lamborghinis understeer because they are bought by rich people with more money than talent; so to prevent costly and embarrassing lawsuits from grieving widows, their chassis are designed to understeer deliberately to keep the owners/drivers from killing themselves.

High horsepower cars are tricky to drive, especially in turns. For the terminally unskilled, understeer is your friend because it is easier to bring an understeering car to heel compared to one which is oversteering. Oversteer calls for a very advanced skill set to corral effectively.

Not all Subarus come with AWD. At one point they did, then they didn't, then they did again, now they don't. There exist cars like the Trezia, which may or may not be a real Subaru (taxi operators may recognise this vehicle as a rebadged Toyota Ractis), which is FWD unless otherwise specced.

Will I be in business if I start exporting European cars spare parts to Kenya?

Dear JM,

I want to start exporting second hand spare parts for European vehicles like BMW, Mercedes, Audi, Scania (both trucks and buses), Volvo and tractors like Holland and Fergusson. What market share do you think I can get out of these?

I intend to supply them in bulk to dealers, who after placing their orders, I ship them to Kenya. My focus is on vehicles that can’t get spare parts and a good percentage of Kenyans do not want to be seen driving a Japanese car.

Vince Giovanni Ong’udi

Hello Giovanni,

You will have to pay me; and pay me very well for this kind of information and research. It is an undertaking currently being conducted by a team of researchers commissioned by the Motoring Press Agency, which I helm, so how much are you willing to float towards the sale of this information from mine to yours?

Help me decide which sports car to buy

Hello JM,

Over the years, I have developed great liking for sports cars. Now I want to buy one and I am spoilt for choice.

The BMW X1 never used to be a common car, but nowadays I can count a few on our roads.

Initially, I had settled for the VW GTI, but when a BMW X1 or the 320i MSport pass by, I stop, get confused and think again. All these cars; X1, GTI and 320i have me confused.

I know The GTI is faster than the two BMW’s, but please help me decide on one of these three cars in terms of performance, power, reliability and fuel consumption.

Luis

Hi Luis,

The irony is you say you like sports cars and want to buy one then express interest in something that is patently not a sports car.

If you want a sports car (of sorts) then the GTI is it. The 320 isn’t (despite the M Sport tag), the X1 isn’t (despite its very cursory resemblance to the GTI); these are just ordinary work-a-day BMWs designed to make you feel good about yourself on your daily commute to the grindstone from which they cough up just enough shekels to convince you that owning a modern BMW is a good idea (this is the subject of a long discussion that I will avoid for now).

The GTI is definitely quickest in this lot, and the best handling (the 320 is not to be sneezed at, though. It has been the handling benchmark for almost 30 years now. The rest are only just catching up).

Power? 240 donkey thrusts for the GTI Mk.6. The early X1 has no M version (nor does the current one), but it has cubic inches on its side. The first gen car sports a pair of 3.0 litre six-cylinders, one of which is ‘turbo’d’ up to 300 zebra strengths. This is parried aside by the Golf’s kerb weight, which maxes out at 1500kg, while the X1 can get as lardy as 1765kg. That, and its taller profile, makes it difficult to outrun or outmanoeuvre the Golf.

The 320i shuffles between 155-170 llamaforce in E90 shape, a model where the diesel version is ironically more powerful — up to 185 — and has 1840 in its potty pushing rhymes like weight. That one is automatically out of the running. The newer F30 does 181hp versus 1745 key-lows. It, too, is forced to step aside. Nothing sporting here.

Reliability is a bit of a hard sell. There are anecdotes aplenty about Volkswagens and Check Engine Lights. These are not all unfounded. To that mythology, add a turbocharger and transmission fasteners in the DSG made out of wet newspapers and the little hatch is forced to concede to early retirement in this race.

The BMWs don’t fare much better. Modern BMWs are starting to generate a fair amount of dislike from fans and detractors alike; what with gasketry, Vanos, suspension, spontaneous disassembly, cooling, timing and goodness knows what else proving to be problem areas at one point or the other depending on which engine you have saddled yourself with.

Fuel consumption will be largely dependent on the degree of circumspection exercisable by your biological running gear, but be warned: Germans are very economical in normal use, especially the new ones but open the taps and they will chug alarmingly; engine capacity be damned.

Opinion: Of the lot, I’d pick the GTI. I may have opted for the 320 if it was an E46 model or earlier, but not any of these newfangled suitcases that are becoming increasingly difficult to tell apart.