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Some of this week's Letters to AutoSpeed!

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Bad OHS Example!

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Building a Human-Powered Vehicle, Part 6. Whoever is doing the TIG welding has got no welding protection like gloves and long sleeve shirt. Not setting a good example for OHS!

Tony Goodlich

More re HPV Part Six

I’ve enjoyed the technical side of the articles on building an HPV, but I have a few comments on the most recent one. In Building a Human-Powered Vehicle, Part 6, the following statement is made...

“If the chain alignment is not correct, the pull of the chain will cause the rear suspension to extend or compress with each power stroke.

"The conventional wisdom appears to be that to avoid this, the chain’s tension path should be through the rear suspension’s pivot point. In other words, the chain pulls along the same path as a line joining the axle to the suspension pivot point. This is then claimed to place no resulting vertical force (up or down) on the wheel.

But this is wrong."

However it's not.... The vertical force is not placed on the wheel. It is placed between the cog and its pivot. The bearing opposes this force and nothing moves. I don't have a diagram, but it may be easier to show what is wrong with what was proposed may be easier.

What was proposed is that the chain force should run parallel to the suspension arm. However, the chain force and the reaction force are thus separated by the cog radius. The resulting force vector is zero - ie the suspension isn't pushed in any direction, however the torque force required to counter the chain force and arm reaction force is not zero. When summing the forces on an object, one always ends up with a resultant vector from a reference point and a torque which has no reference point. I'd have to review, but I don't think you've mentioned the torque (twisting) component in earlier articles either. This torque force acts on both the wheel AND the suspension dependant upon the wheel radius. I could draw a diagram and use some force equations and justify myself if you'd like.

A complication with the system is that it is a critically balanced one. So long as the chain passes through the pivot point, there is no net torque on the rear suspension – however, as soon as it shifts up a fraction, there is. This force tries to droop the suspension which most likely will make the chain move further away and generate more and more drooping force.

Russell Hocken
New Zealand

Perhaps we didn't make it clear enough in the article: we tried the chain line through the pivot point and it compressed the suspension with each torque application to the pedals. A very light suspension spring was fitted so that suspension movement would be obvious and torque was applied to the pedals with the rear tyre in contact with the ground. To give the least suspension movement, the chain axis most definitely was not positioned through the suspension pivot point.

Answer This...

Great magazine - keep it up. You have answered so many questions that have bugged the sh#$ out of me for ages!

Mark Leerberg

Super-Lean, Economical Ford

Regarding your article Electronic Ways to Improve Your Fuel Economy... I have a 330,000km stock five-speed EA Ford Falcon which has an aftermarket EMS-8860 specifically installed to improve fuel economy. With the wide-band Lambda auto tune feature, it allows you to do very accurate tunes quickly (especially around the cruise, light load areas). On the stock ECC4 computer on the same route I used to do around the 13.5 – 14 litres per 100km with granny driving style. Tuned to around 15.8:1 air-fuel ratio at cruise and light load and with ignition advance at around the 40 to 45 degrees, the economy on the same route goes down to about 8.5 - 9 litres per 100km (still with granny driving). I've also tried the same mod with an auto and found it didn’t respond any where near as well as the manual. I think with a fresh engine with higher compression, extractors and a few other tricks it’d be achievable to get low 8 litres per 100km.

Tony Goodlich

Combined Forces

I am fascinated by the two different avenues pursued to cut fuel usage - the direct injection turbo diesel route and hybrid technology.

It would seem that combining both would be even better, given that diesels are very efficient at part throttle on the flat, where the hybrid batteries may not be needed, or being charged. Have you heard of anybody working along these lines?

Robert Lawrence
New Zealand

See Torque Overload: the GM Allison Hybrid Bus for a diesel hybrid bus. It’d be great to see such a combination in commuter cars – but we’re yet to see any examples.

Can’t Find the Technology

Just looking at an article from December 1999 – Giant Muffler Comparison - Testing Procedures... To your knowledge, is the company ‘Exhaust Technology’ still in existence? A can’t seem to find their products on the web. I was very impressed by your test and the results that you obtained. Excellent job!

Curt Swan

Exhaust Technology’s contact details are +61 8 8272 7500,

$15k Fun

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I've been reading all your previous articles for a while now and I gotta say that I’m impressed by your guys' honesty and that you say what needs to be said. Ass-kissing outa the way... At the moment I’m after a new car and would value your opinion and experience greatly. Basically, I’m after a car that is RWD, turbo (would consider non-turbo), decent handling and less than AUD$15000. Do you have much experience with cars that fit my criteria? I was looking into S13s, MR2s, R32s and had thought about a NA Supra. Do you have any experience with these cars and do you have any preferences or other options?


Depending what you’re after, all of the cars you mentioned are great value in that price category. Don’t forget the Soarer and, if you want something with four doors, Ford V8/XR6 and Holden V8/supercharged V6.


I was just thinking maybe it would be worth looking into combustion chamber 'grooving' to promote greater engine efficiency. See His ideas are patented but he likes everyone to experiment with them and report their results. So far the news is good. A worthy tech article maybe?


Interesting idea – do any readers have anything to offer on the subject?

Memcal Hunt

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My son is chasing a memcal for a Holden Commodore VS Series 2 manual. He has converted the car to manual from auto and needs a manual memcal. Is it possible to exchange (or reprogram) an auto memcal for a manual unit?

Ian Peady

We suggest contacting a workshop that uses Kalmaker programming software for Delco ECUs. Try Adelaide’s Awesome Automotive - +61 8 8277 3927

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