After-market modification can make car unpredictable

Hello Bwana JM,

Thank you for humorously doling out wisdom on cars and English simultaneously. I would like to know: 1) How much weight can the Toyota Noah (2010-2013 model) comfortably withstand.2) Is there a way it can be modified to enable it to carry heavy loads (say 700kgs)?

I am a businessman in the supply industry who wishes to trade My Toyota Corolla DX, which packs like a pickup once I fold the rear seat, for a Noah.

Kindly advise.

Kihiko Kuria Joseph

Hello Joseph,

1) Toyota rates its van as having a load capacity of just about half a tonne (they say 400kg but one can get away with 100kg here or there)

2) You could carry a 700kg load in a Noah simply by installing heavy duty suspension, i.e springs and shocks of more substantial heft compared to the standard issue materials.

Whether or not you actually want this capability remains to be seen, because this sort of aftermarket engineering might not be exactly advisable. A car is built for its various systems to work in harmony; making one system withstand extra stress without beefing up the rest will lead to unpredictability.

Are the engine and transmission properly set up for extra loads? Will the brakes still work reassuringly? Is the frame capable of withstanding that kind of load or will it deform in short order?

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Hello Baraza,

I recently visited Thailand and noted that most of their motor vehicles, including vans, cars, tuk tuks, lorries, name it, are powered by gas, not petroleum (fuel).

1. Kindly explain how this mechanism works and is different from our Kenyan, fuel-powered vehicles in terms of cost, safety, speed and reliability.

2) Their vehicles are also relatively new models. The few I used were actually 2010-2012 models (Toyota Camry, Yaris, Innova, Prius, etc.) compared to our mostly 8-year-old cars; does that mean anything in terms of the future of car imports in Kenya and are we likely to use gas?

Arafathi

Hello Arafathi,

Ahem...! Gas is also fuel, just like petroleum (and its various derivatives).

1. The mechanism works more or less the same: fuel goes into the engine from the fuel tank via the fuel lines. Air goes into the engine from the atmosphere via the intake.

The two meet up somewhere and are mixed in their appropriate ratios before being set alight and exploding within the cylinders to create the force that pushes the cylinders down, thus creating torque.

I am not exactly clear regarding the similarities or differences of running these vehicles in Thailand in comparison to Kenya, but I know cost might be an issue since sourcing LPG locally might be a bit more involving than simply driving to a fuelling station, as is the case with petroleum (and its various derivatives).

Performance might vary slightly: in some cases, gas-powered cars might deliver a bit more power compared to their petrol equivalents, in others they might not.

Safety is not much of an issue since the storage tanks for gas are reinforced to prevent leakages. Reliability also seems not to be an issue and might, in fact, be superior in gas-powered cars since gas is gas and is unlikely to wash away oil from the cylinder walls as sometimes happens with petrol-powered cars on cold starts.

2. The only implication to Kenya’s future imports is that Thailand is ahead of us on the curve. As for the use of gas, I really can’t say; that will mostly be decided through government policy and the results of any feasibility studies oil companies might conduct in future (or might have already conducted).

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Hello Baraza,

How much should age play a factor when choosing between cars, especially when it comes to maintenance? For example, which one would be cheaper to maintain between a Mazda Axela 2008-2009 and a 2004-2005 BMW 320i?

Andy

Hello Andy,

Age is an important factor to consider when selecting a car to buy. It is as simple as this: who visits a hospital more often than the other, is it a healthy young person or is it the geriatric with one foot in the grave?

The same thing applies with regard to cars: an older car will require a lot more maintenance compared to a new one.

That said, 2005 and 2008 are not so far apart as to warrant a dramatic difference in the mechanical well-being of a car. This will boil down more to the vehicle’s construction and history rather than exact age.

It is in light of that that we easily conclude the 2008 Axela will be cheaper to maintain. For one, it’s a middle-of-the-road car from a middle-of-the-road Japanese brand. It is, therefore, intentionally built to be cheap to own and cheap to operate.

This is in comparison to an established German premium brand: these have never been cheap on any scale, not to buy and not to run.

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Hallo Mr Baraza,

Yours is a column I greatly admire because of the information you give on autos, coupled with your wit and sense of humour.

Talking driving, I have on several occasions heard people mention “defensive driving”. Could you briefly explain what it is.

As an automobile enthusiast, it has come to my attention that most people refer to dampers as shock absorbers. What are shock absorbers?

I would also like to know what jackknifing is as applied to articulated vehicles.

Also, in relation to suspension, what is the difference between a positive and a negative roll radius. How applicable is it to my 505 Peugeot station wagon or a friend’s Mazda Demio?

When would I consider my wagon to have had:

 1) Self-aligning torque.

2) Pneumatic trail.

3) Slip angle.

In respect to its tyres.

Finally, a friend of mine with a 4WD experienced a propeller shaft wind-up during one of his manoeuvres. What could be the cause and what would you advise to prevent a recurrence of the same, apart from using the third differential?

Lorento

Hello Lorento,

1. Defensive Driving: this is best summarised as driving in accordance with the tenets of Jeremy Bentham and John Stuart Mill, stalwart proponents of the theory of utilitarianism. Utilitarianism is the theory of doing the greatest good to the greatest number of people, so it follows that defensive driving is the kind of driving that benefits everybody. Google says it is driving to save lives, time and money despite the prevailing environmental conditions and actions of others.

It is essentially an advanced form of driving that reduces the likelihood of accidents by following certain stipulations such as the two-second rule (at any given speed, the safe distance to follow the vehicle ahead is such that you pass the same object the vehicle in front passes exactly two seconds after it does) and assured distance ahead, which, in summary, is what we call the braking zone or run-off.

2. Shocks vs. dampers: A damper is a shock absorber (depending on use, but this is an automotive column, so that is the use we will go with) and Google says a shock absorber is actually is a shock “damper”.

3. Jackknifing: This is the tendency of a trailer or bogie to skid or push the tractor to such a point that it spins around and faces backwards. The manoeuvre is similar to that of a penknife (or jackknife) as the blade is folded away. According to Google, one of the ways of preventing this eventuality could be by using antilock brakes (ABS) or EBD electronic brake distribution (EBD).

4. Roll Radius: I’ve never heard of positive or negative roll radius and neither has Google. However, Google apparently knows of scrub radii, terms I might have heard before but paid little attention to.

There is what we call the kingpin axis, which is the line between the upper and lower ball joints of the wheel hub (where the wheel is mounted). There is the contact patch, which is essentially the “footprint” of the tyre.

Now, zero scrub radius means that the kingpin axis meets the centre line of the tyre (as viewed from the front of the car) dead on the contact patch. Positive scrub radius is when the kingpin axis meets the tyre centre line below the contact patch, i.e somewhere inside the ground.

Negative scrub radius is when the kingpin axis meets the tyre centre line above the contact patch, which implies somewhere within the tyre itself.

The implications of zero, positive and negative scrub radii may be a bit too complicated to delve into right now and would require diagrams to explain fully.

There is also the rolling radius of a tyre, which is simply the distance covered by a tyre per complete revolution. It is also the circumference of that tyre. There are no positive or negative rolling radii: it is a scalar quantity (magnitude only), not a vector quantity (magnitude and direction) so positive and negative do not apply.

5. Self-aligning torque: Google claims this is the torque a tyre creates as it rolls along, which tends to steer it. I think this is what causes torque-steer in certain front-drive cars, though Google says nothing about this.

I thought tyres receive torque, not cause it. What Google also doesn’t say but I assume might be the explanation comes down to Newton’s Third Law of Motion: action-reaction of which both are equal in magnitude but opposite in direction. So maybe the driven tyre actually does cause “reverse” torque. I think I might have lost 95 per cent of my readers by this point.

6. Pneumatic trail: the remaining 5 per cent will also leave the room as they discover there is no end to the technical jargon, but we have already dived right into it we might as well see it through.

Pneumatic trail is... actually I can’t explain pneumatic trail without seeming senseless. I don’t know if Google is of any help. We are deep into advanced physics here.

7. Slip angle: This is a fairly simple one. The slip angle is the angle between the direction of movement of a tyre and the direction the tyres are actually pointing. That means for a car driving straight, the slip angle is zero (assuming toe is also zero on all tyres).

For a car with alignment issues (or variations in toe), or a car sliding (oversteer, understeer), there is a calculable amount of slip angle in a given axle. Google might provide diagrams to better explain this phenomenon if you haven’t understood it yet.

8. Propeller shaft wind up: this is the spring-like effect caused by twisting a propeller shaft rather than rotating it. It typically arises when one or more wheels catch air or when the transmission is overloaded: i.e the torque from the engine is excessive and the load, too, is excessive, so the only point of yield is the prop-shaft itself.

It is not a common occurrence but it does occur, more so if an SUV is driven in low range, first gear and it encounters an obstacle that is nearly insurmountable. Scylla and Charybdis, if you may.

Prevention is as simple as avoiding such a situation: if one or more tyres are unable to rotate for some reason under engine power, it’s best to resort to towing rather than revving in gear. You may have noticed the term “Google” appears several times in this response.

Could we try and use it next time before posing a question because I feel like this week we have really gone off the rails in jargon and technicalities.

Let’s keep things simple and interesting; my readership is a lot wider than post-graduate physics students and automotive engineers who are better placed to understand what this whole section has been about. To my less scientifically inclined readers, I apologise.

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