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Tyre Pressures

"Tyre pressures should always be at the maximum end of the manufacturer’s recommendations however, I do not recommend some of the extremely high pressures that people chasing fuel economy sometimes run. (I’ve seen suggestion of pressures of 50 psi – the ride will be terrible, the handling suspect, and I wonder if the insurance company would even cover you if you had a1n accident.)"

I will assume you are referring here to the car manufacturer's recommendations and not the tyre manufacturer's maximum recommended pressure as printed on the sidewall.

http://www.hetnieuwerijden.nl/docs/Influence%20of%20tyre%20pressure%20.pdf
This study sponsored by the Dutch government evaluated the impact of tyre pressures on handling and comfort as part of energy-reducing measures in the traffic and transport sector. They reached the following conclusion: "The best possible option is still the recommended tyre pressure, specified by vehicle and tyre manufacturers. It provides the best combination of aspects like handling performance, comfort, wear, noise, etc. [...] Nevertheless an increase of 0.2 bar (advised tyre pressure plus 10% in all tyres) is not significantly changing the handling behaviour of the vehicles and is therefore seen as acceptable." I personally run my tyres at the maximum sidewall pressure, but I believe everyone should be running 10% over the car manufacturer's recommended pressure as a bare minimum.

Martin
Canada

Reducing Fuel Flow

have you heard of the "electronic diverter" by george wiseman of eagle research? this is a device that modifies the signal from the ecu to the fuel injectors, it allows one to reduce the amount of fuel injected into the cylindrers . i have the schematic diagram , let me know if you are interested, i can forward them to you . this sounds like a great idea if it works.

M. Benhabiles
United States

Reducing the amount of fuel that goes to the cylinders is very easy. The hard part is doing it when a car is in closed loop operation...

Batteries

First of all - Great publication. Ive been reading for many year and love all the stuff you guys do.

Now, why i am emailing you: Truck batteries. In this months article titles junkyard dawg where you went to the truck wrecker you mentioned the batteries. I worked for a certain large mobile battery service for a while and truck batteries new are readily available and not as expensive as some people would think.

The batteries we are looking at are mostly part of the n50 and n70 family (see the exide range). Your typical family car battery starts at about $149 and these start at about $179. They are quite good for the heavy duty/car audio thing and you can always run them in paralel like any other battery. Alot of the small trucks just use regular albeit premium batteries which you could fit into most regular road cars. They are also common place in 4wd's. Large truck and boat batteries are also worth investigating and are up to about 70cm long. They are quite expensive though.

So just a headsup truck batteries are a common deal i fitted a few to regular road cars one in particular was a honda prelude 4th gen with an n50 battery. He had a big car audio install in it and was using one previously and it all worked well. Fit right in aswell. This certain battery supplier/emergency service will let you fit a larger battery. Last i knew they would give you options over the phone and this certain prelude job was sent through to the pda with that battery listed. So id say if your in the market for a new battery to do a little research first. They arent all that expensive and you dont have to settle for a second hand job.

IF your looking for a second hand battery all of them are dated and to help you out - heres how :) The supplier probably doesnt want the world to know this but who cares?

Its an alfa-numerical code. 1 Letter, 2 numbers so as an example lets use G05. The G is the month the battery was produced: G being the seventh letter of the alphabet its a july battery because july is the seventh month. The 05 simply represents 2005. It is burnt into the batterys casing usually on one of the sides and usually on the top lip. Sometimes they are on the top. All batteries i know of have a date stamped into them. This code is specific for exide batteries but alot of batteries are just rebadged exide anyway.

You dont want to buy a battery that is over 2 years old. Its quite common for them to die in the 2-3 year bracket especially on trucks. The oldest lasting battery ive seen was on a hilux and the battery was 14 years old - The hilux was completely optionless though and id say the battery was a freak so dont go expecting 14 year old batteries from the wreckers to work. If there is a fair bit of black sludge under the batterys caps then stay away. Generally the less black sludge the better the battery.

George Pieratos
Australia

Tyre Grip

In your article "Tyres, Grip and All That ..."
[1] , you make an interesting point that friction of a tire is independent of the contact area (depending solely on the friction formula). However, I believe that to be an oversimplification. I'll just quote two paragraphs of an article I read on the matter:

"Classical friction theory must be modified for tires because of their structural flexibility and the stretch of the tread rubber. Instead of depending solely on the coefficient of friction at the tire-road interface (which is determined by the nature of the road surface and the tread rubber compound), maximum stopping ability also depends on the resistance of the tread to tearing under the forces that occur during braking." [2]

"Further, the size of the contact area is very important in car tires because the traction is dynamic rather than static; that is, it changes as the tire rolls along. The maximum coefficient of friction can occur anywhere in the contact area, so that the greater the area, the greater the likelihood of maximum traction. Thus, under identical load and on the same dry surface, the wider tire has a greater contact area and develops higher traction, resulting in greater stopping ability." [2]

[1] Tyres, Grip and All That...

[2] http://www.physics.sc.edu/~rjones/phys101/tirefriction.html

Chris Katko
United States

Need for Noisy Hybrids?

You may have read "Electric cars 'silent killers' (Mark Hinchlifffe, August 23, 2008, http://www.news.com.au/couriermail/story/0,23739,24224490-953,00.html) and wondered how this nonsense came to be. I started following this effort since April 2007 in a blind [persons] advocacy mailing list because I wanted to find 'the dead bodies.' But my interest increased after a bill was introduced to the USA Congress, HR 5734, April 2008. That bill, "Pedestrian Safety Enhancement Act of 2008", mandates noise levels from hybrid electrics. We call it the "Bell the Hybrid Act," as it would ban all hybrids and electric cars that didn't make enough noise.

HR 5734 tasks the USA National Highway Traffic Safety Administration (NHTSA) with implementation so they announced a hearing on June 23 to discuss the issue. I tried to get a "hybrid electric owner's presentation" on the agenda but "we already have our speakers." Still they invited me to attend and ask questions, I did (http://www.regulations.gove- search NHTSA-2008-0108-0023 for transcript,) and submit follow up materials for the record, I have (http://www.regulations.gov- search NHTSA-2008-0108-0020.) There were 29 submissions including one from Lotus Engineering.

Early in August, Lotus Engineering sent out press releases for a sound generator that makes engine noises come from a Prius hybrid electric. After a couple of weeks, reporters took the press release and contacted local blind advocates, government traffic safety officials and Toyota spokesmen about this noise maker. As expected, the blind who initiated the effort were enthusiastic; the government officials were 'aware of the issue' and; the Toyota spokesmen tried not of offend anyone Dozens of such stories appeared in the USA, Europe and Pacific papers and every time there was reader feedback, it has been filled with justifiable condemnation.
 
Now why would Lotus who makes no hybrid offer a modification to the Prius? Toyota has been busy working on cost savings in their hybrid electrics and made progress. But if Lotus can throw a little sand in the works or better yet, get a patent covered design that is legislated by the USA Congress, they can vampire their competition. It really is a clever business trick, legislate that your competition to use your patented device and thwart their cost savings effort. But let's go back to pedestrian safety and the blind.

Dr. Christopher Hogan, a Prius owner and professional data analyst, examined the NHTSA traffic accident data looking for 'the dead bodies.' He used all of the USA fatal accidents from 2002-2006, five years of Prius operation, and found: (1) Prius has the same rate of pedestrian accidents as ordinary cars; (2) no blind has been killed by a Prius, yet, and; (3) of 4,700 pedestrian deaths per year, only 5 were blind, killed mostly by pickup trucks and SUVs. In short, there is no pile of dead bodies with Prius tire tracks on them.

The NHTSA released "Backover and Non-Crash Events Special Crash Investigations" by Augustus Chidester, April 13, 2008 (www.regulations.gov- search NHTSA-2008-0108-0020.2) that details 50 backover accidents that killed 25 kids, mostly pre-schoolers who were crushed by rear bumpers and engine exhaust pipes. In two of the four accidents, the driver, a mom and a neighbor, didn't stop until they saw the body of the child in front of the vehicle. You could weld a noise maker to the exhaust pipe, take off the muffler, and the kids would still have died because noise is not the answer ... driver awareness is.

So what we have is legislated noise makers designed by the blind (to a man with just a hammer, all problems look like nails.) A Lotus business decision to harm their competition. Finally, something Julian has railed about in the past, intellectual sloth of a newspaper reporter. Hopefully this nonsense won't go as far in other countries as it has in the USA.

Robert J. Wilson
United States

Workshop Construction and Drills

Great series on construction of your shed/workshop [starts at Building a Home Workshop, Part 1]. I was really interested by your DIY drill - can you provide more detail on that? I've destroyed plenty of cordless drills (mostly the gearbox or battery life) in various projects and would love to revamp them...

Chris
Canberra

A drill with a defective gearbox is a hard fix, but if the batteries are worn out, just wire an external battery to the original battery terminals, using a long cable. I used two 12V sealed lead acid (SLA) batteries in series.

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