Johan is a particularly impressive man, with great knowledge. I value his expertise anywhere. Still, extremely slippery ice and snow is relatively less important in the southern hemisphere, although again, south america has much higher mountains than the rest of us enjoy.
One other component that Johan can expand on, is that i see some European trucks are running very high tyre pressures, I've read of pressures of 10 bar!, at least that is what I have read, as I have not had the pleasure of visiting there. Maybe Johan will invite me one day.....
another thing, drive tyre pressures are vital for semi and b double stability. I believe that drive tyre traction is paramount for minimizing the classic semi problem of jack knifes. Records show that an empty or lightly loaded semi is 2.5 times more likely to jack knife, which is in Johan's picture. With a lightly loaded semi or B double, the drive tyres will have 200 to 300% excessive tyre pressures. My customers, mostly B doubles, regularly run at 30 psi, 2 bar, in the drive tyres on the highway, with great experiences, with maybe 6 tonne on 8 tyres. I regularly run 25 psi on my single axle prime mover on highways. I have Michelin tyre charts showing the optimum pressures at these loads.
To further provide understanding, a toyota landcruiser typically weighs 2.8 to 3 tonnes on the road. Their recommended pressure on much smaller tyres is only 35 psi, or around 2.4 bar. That is 750 kg on small four wheel drive tyres, compared to 750 kilos on much bigger and stronger tyres....
So, yes, ice is terrible for traction. yes, Johan is quite right, many truck drivers do not load the drive tyres sufficiently. I see every day empty tip trucks (dump?) pulling a proper trailer with an excavator or similar. Our rules state that the truck (tractor yankee language) should weigh more than the trailer, but no one enforces it cause everyone breaks the rule. Improper loading along with poorly balanced brakes, combined with exceedingly high tyre pressures is a guarantee for problems.
In less slippery terrain, like loose gravel, and dirt roads, or sand, my customers would laugh at the idea that B doubles are dangerous. They push the button on the dash, drop the drive tyre pressures down to 30 (two bar) and go into and out of places a standard semi can't go, with conventional pressures. I go lower, as do a few of my customers. I regularly go down to 16 psi (1.1 bar), and it is amazing where we go. With a full load, you don't turn very sharp, but, the traction is awesome.
Hope that helps.
Chet
________________________________
From: Technical, operational and economic aspects of road freight transportation <[log in to unmask]> on behalf of Granlund, Johan <[log in to unmask]>
Sent: Monday, 3 July 2017 6:20 PM
To: [log in to unmask]
Subject: SV: Reports of B-double and other HCV safety performance
Dear Ale and all,
In the Nordic countries, we have noticed that tractor-trailer combinations are more accidentally affected than rigid truck + drawbar trailer combinations.
This is particularly noticeable on low friction road conditions.
The problem can be illustrated by the “Gamleby bridge crash”, which involved a B-double (= link) on thin ice, see attached picture.
Data from f.x. Australia presented at HVTT14 (Hassall et al) support our findings also on less slippery road surface conditions than icy roads.
Central Europe is staring blind to accessibility (=short tractor units instead of long tractors) and overrides safety.
Safest vehicle combination is always one where the pulling unit is very heavy, i.e. a conventional truck with load in front of the trailer/trailers.
If it has to be a tractor + semi-trailer combination, it is essential that the length limiting regulation allows tractors with a long wheelbase.
The long wheelbase allows the steering front wheels to determine over the friction in the fifth-wheel joint.
On low road friction surfaces, such as wet slick asphalt or ice slippery roads, this is of outermost importance.
Read our paper "TRAFFIC SAFETY RISKS WITH EU TRACTOR-SEMITRAILER RIGS ON SLIPPERY ROADS" presented at HVTT14: http://road-transport-technology.org//Proceedings/HVTT%2014//Granlund%20-%20Traffic%20safety%20risks%20with%20EU%20tractor-semitrailer%20rigs%20on%20slippery%20roads.pdf
TRAFFIC SAFETY RISKS WITH EU TRACTOR-SEMITRAILER RIGS ON ...<http://road-transport-technology.org//Proceedings/HVTT%2014//Granlund%20-%20Traffic%20safety%20risks%20with%20EU%20tractor-semitrailer%20rigs%20on%20slippery%20roads.pdf>
road-transport-technology.org
Granlund & Thomson at International HVTT14 Symposia: Traffic Safety Risks with EU Tractor-Semitrailer Rigs on Slippery Roads 2 1. Background
Furthermore, the European Union lacks a proper regulation on the distribution of load within the vehicle combination, aiming to prevent absurd vehicle combinations being used in traffic.
Norway is a country with extremely mountainous road network, with harsh winter climate.
Similar to Sweden and Finland, Norway has a sparse population in relation to road network size, resulting in limited resources for managing road slipperiness.
Being a non-EU member state, Norway has a national regulation with the above aim.
EU should seek to adopt this regulation.
It is proven efficient for safety on icy roads, and is relevant also for safety on better road conditions.
Here is a non-official translation to English from Norwegian of the efficient "1,5 factor paragraph":
“-A motor vehicle with maximum total weight exceeding 3500 kg and designed for speeds above 30 km/h is not allowed to pull trailers with current axle load / axle group load which together is heavier than 1.5 times the pulling vehicles current gross vehicle weight.”
Reference: Norwegian Regulation on use of vehicles (Norwegian title: Forskrift om bruk av kjøretøy, 1990), Chapter 5, §4-2.4.a https://lovdata.no/dokument/SF/forskrift/1990-01-25-92#KAPITTEL_5
Forskrift om bruk av kjøretøy - Lovdata<https://lovdata.no/dokument/SF/forskrift/1990-01-25-92#KAPITTEL_5>
lovdata.no
§ 1-2. Definisjoner. Definisjonene i vegtrafikkloven og i forskrift 25. januar 1990 nr. 91 om krav til kjøretøy, forskrift 4. oktober 1994 nr. 918 om tekniske krav ...
Best Regards
Johan Granlund (WSP Sweden AB) and Per Thomson (Thomson Konsult AB, Sweden)
-----Ursprungligt meddelande-----
Från: Technical, operational and economic aspects of road freight transportation [mailto:[log in to unmask]] För Alejandra Efron
Skickat: den 1 juli 2017 03:02
Till: [log in to unmask]
Ämne: Reports of B-double and other HCV safety performance
Hi all,
almost ready to launch in Argentina as a whole, I need your help asap to counterattack those who still state B-doubles are unsafe because of their length.
I need a few reports like the one from Australian NTI, where it shows exactly the opposite, and actually states that the B-doubles continue to be the best performer from a loss and safety perspective (page 20 of the last report)
It can be any HCV and the bigger the better actually. and the more visual the better as well.
Thanks
Ale
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