When RV’ers are considering a bosgarren gurpila trailer they often ask if it will feel more stable on the road than a travel trailer or a motorhome. Fifth wheels are very stable on a highway and are rarely affected by cross winds or passing trucks. But when you look at a fifth wheel’s design, it would be easy to wonder how they could be stable at all.

Kalitate handiko JSK casting bosgarren gurpila 37C

Bosgarren gurpil baten grabitate-zentroa oso altua da, haize gurutzatuak harrapatzeko alboko hormaren eremua izugarria da, unitate gehienek hosto-malgukien esekidurak dituzte, eta gutxi batzuek, berriz, xurgagailuak dituzte. Bosgarren gurpilaren engantxa ez da konplikatua. Lurraren gainetik lau oin gutxi gorabehera dagoen pibote-puntu sinple batez osatuta dago, oinarrizko ardatz bizidun kamioi esekidura baten gainean eserita.

Biratze-kutxek 90 graduko bira-erradio ikusgarria ahalbidetzen dute, baina autobideko abiaduran egonkortasun pixka bat galtzen da.

Compared with travel trailers, which can have a very low centre of gravity and a pivot point much closer to the ground (with weight distribution and sway controls), there is no contest between the two. When we do slalom and lane change tests, it’s obvious travel trailers handle much better. For example, a good handling travel trailer and tow vehicle can run through a 100-foot slalom close to 80 km/h. With a fifth wheel, the tires start leaving the road at 60 km/h. So, if I find myself in a situation where I need to manoeuver quickly to avoid an accident, I will take a properly set up travel trailer any time.

But fifth wheels do have their merits. Going straight down the highway on a windy day, it’s hard to match the driving ease of a fifth wheel in tow. This is due to one key advantage. Of all the measurements we conduct when assessing a tow vehicle for a trailer, a key element we have to consider is the amount of rear overhang. We look at the overhang as a percentage of the wheelbase. For instance, if the vehicle has a 100-inch wheelbase with 40 inches of rear overhang, the overhang is 40 percent of the wheel base (which would not be ideal). The best vehicles are around 30 percent.

But, with a fifth wheel, the overhang is 0 percent of the wheelbase. From a driving perspective, this trumps most other factors I previously mentioned about fifth wheels. Even when making an emergency manoeuver, it’s easy to drive up to the point where the fifth wheel’s centre of gravity becomes the issue. In the slalom, I have had the wheels of a fifth wheel come a couple of feet off the ground and it felt completely stable in the cab. The only thing that made me realize that the wheels were off the ground was a quick glance in the side-view mirror.

Historically, a factor that contributes greatly to the stability of a fifth wheel is the pin or hitch weight was always a higher percentage of the total trailer weight – usually 20 percent. On a travel trailer, it’s normally 10 to 15 percent. This allowed the fifth wheel to have a longer distance from the pivot point to the axles, which makes any trailer more stable. For example a transport trailer with tandem wheels almost at the back of the trailer carries close to 50 percent of its weight on the tractor.

Birako kaxa birakariek, funtsean, bosgarren gurpilen erabiltzaileei bidaia-trailer baten biratzeko ezaugarri berberak eskaintzen dizkiete. Baina zorrotzegi biratzen baduzu, bosgarren gurpila kamioiaren kabinara sartuko da, eta bi ibilgailuetan kalteak eragingo ditu.

Pull Rite irristagailu automatikoa.

Today, many fifth wheels are geared to tow with a half-ton, which means the loaded for travel pin weight needs to be less than 1,500 to 1,700 pounds. On many of these fifth wheels, the pin weight is 12 to 14 percent rather than 20 percent. The first time we had one of these lighter pin weight fifth wheels, I was quite concerned about what effect it might have on stability. On the lot we had two 10,000 pound fifths of the same brand and size – the only difference between the two models were the interior layouts. One unit had 1,100 pounds of pin weight and the other had 1,780 pounds.

Kamioi berean haize gogorrarekin bizkarrean bizkarrean atoian eraman eta manipulazio-ibilbide beretik pasatzean, ezin nuen manipulazioan desberdintasunik hauteman. Teorian, egon beharko luke. Uste dut grabitate-zentroak ezartzen dituen manipulazio-mugak pin-pisuaren diferentzia baino askoz lehenago sartzen direla jokoan.

Bosgarren gurpilak merkatuan sartu zirenean, kamioi guztiek zortzi oineko kaxak zituzten, atzeko ardatza kabinaren atzealdetik 54 hazbetera zegoenarekin. Horri esker, zortzi metroko zabalerako bosgarren gurpilak kamioiari 90 graduko bira eman zion maniobrak egiteko. Gaur egun, kamioi gehienek bost oineko, sei hazbeteko edo sei oineko eta sei hazbeteko kaxa dute, ardatza kabinaren atzetik 30 eta 40 hazbeteko tartea izanik. Horrela, zorrotzegi biratuz gero, bosgarren gurpila kamioiaren kabinara sartuko da, eta bi ibilgailuetan kalteak eragingo ditu.

Arazo horri aurreneko irtenbidea irristatze-gantxoak sartzea izan zen, zeinak eskuz irristatu egiten baititu pinaren posizioa atzeko ardatzaren atzean, abiadura baxuetan maniobra estuagoak egiteko. Hauek eraginkorrak izan ziren eta oraindik askotan erabiltzen dira. Abantaila da kaxa laburra irristakorra duen kaxa luzea baino ikaragarri maniobragarriagoa dela. 35 oineko bosgarren gurpileko atoia aparka dezaket kanpaleku estu batean kutxa labur batekin askoz errazagoa den 28 oineko bosgarren gurpilarekin kaxa luze batekin baino.

Duela 15 bat urte Pull Rite-k aitzindaria izan zuen irristagailu automatikoan eta Demcok orain ere egiten du. Engantxa hauek autobideko abiaduran bosgarren gurpil konbentzional baten moduan maneiatzen dute, baina automatikoki atzerantz irristatu egiten dira maniobrak errazteko. Alde txarra da $ 800 eta $ 1.500 garestiagoak direla antzeko kalitateko atoi finko edo eskuzko irristakorra baino. Ondoren, behin bakarrik ahaztu behar duzu eskuzko graduatzailea mugitzea eta kostu gehigarria aurreztuko duzu.

A few years ago a swivelling pin box was introduced on the market, which features a fixed hitch situated over the axle. The pin box doesn’t pivot in the hitch, but rather is locked into the truck portion. A 20-inch bearing is built into the pin box located behind the axle where the trailer turns. While it allows an impressive 90-degree turn with the truck, some stability on the highway is lost. Though the pin weight of the fifth wheel is still placed directly over the axle the side to side pivot point is 20” behind the axle or to put it another way your truck now has a rear overhang equal to 15% of the wheelbase. Ultimately you wind up with the disadvantages of a fifth wheel and disadvantages of a travel trailers without the benefit of weight distribution or sway control.

When the swivelling pin box was introduced on the market, I asked the developer what kind of testing was done to determine how much stability is lost. The developer said there wasn’t any loss. I said there had to be and the conversation went downhill from there. It never concerned me a great deal as the product was rarely seen. But now I am seeing some manufacturers offering it as an option and doubt they understand how handling is affected with a swivelling pin box.

Duela gutxi, bira-kutxa bat probatu dugu 20 hazbeteko iraultzeak benetan zenbat diferentzia egiten duen ikusteko. Pin-kutxa moldatu genuen, atoi-kamioi konbinazio berean atoi-kamioiaren konbinazio berean atoi-kamioi lerragarri baten eta biraketaren kaxa baten artean aldatzeko.

Gure proba egunean, haize leunak eta errepide leunak izan zituena, zaila izan zen jakitea engandea ardatzaren gainean biratzen ari zen ala 20 zentimetro atzetik. Hala ere, haize gurutzatuak gora egiten zuenean edo kamioi bat gure ondotik pasatzen zenean, atoiak kamioia bultzatzen zuela sentitzen zen. Espero nuena baino gutxiago izan zen, baina hor zegoen zalantzarik gabe.

Ihes-maniobra batean, hala nola, bat-bateko errei-aldaketa batean, guztiz egonkor geunden ehuneko 0-ko gainaldearekin. Hala eta guztiz ere, trailerra ehuneko 15eko gainazaletasuna baino askoz gehiago bihurtu zen.

Ehuneko 0-an, atoia berehala zuzendu zen errei-aldaketa azkar baten ondoren, baina ehuneko 15eko gainditzearekin batera, beste swing pare bat egon ziren alde batetik bestera. Nire kezka da engantxa-diseinu honek, pin pisu arinekin konbinatuta, egoera ezegonkorra ekar dezakeela.

Ezaugarri polit batzuk daude pibotaren kutxarekin. Graduatzaile automatikoa baino sinpleagoa da eta konektatzeko errazagoa da. Kontuan izan segurtasuna eta egonkortasuna trukatzen ari zarela funtzio horiek lortzeko.