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tomavis (17 posts)
Oct-04-01, 08:50 PM (EST) "Question" Just what do the small wheels in front of and behind the big drive wheels of a steam loco do?It seems to me if they are for holding the weight of the boiler the loco would lose traction.So what are their purpose?Thanks in advanced Alert Edit | Reply | Reply With Quote | Top
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Subject Author Message Date ID RE: Question rocketmorton Oct-04-01 1 RE: Question Kuchinator Oct-05-01 2 RE: Question lnghairedwizard Oct-05-01 3 RE: Question Xacto Oct-05-01 4 RE: Question plainsman Oct-05-01 5

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rocketmorton (8 posts)
Oct-04-01, 11:21 PM (EST) 1. "RE: Question" My understanding is that the front wheels are attached somehow to the boiler and help guide the engine around curves.The rear wheels help support the firebox.This is why you almost always see a pilot truck on steam engines, though not always a trailing truck if the firebox is light enouigh(?)For switching engines, you don't need the pilot trucks, since they move at slow speeds through mostly straight track in yard areas and such.Correct me if I'm wrong... Remove | Alert Edit | Reply | Reply With Quote | Top
Kuchinator (197 posts)
Oct-05-01, 02:40 AM (EST) 2. "RE: Question" makes sense, if it just had the huge drive wheels that are so close together in the center, seems like it would wobble alot on turns.
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lnghairedwizard (21 posts)
Oct-05-01, 07:09 AM (EST) 3. "RE: Question" rocketmorton is on the right track (pardon the pun...lol)the front trucks are not so much for spreading the weight as they are for guiding the boiler/engine into curves
passenger engines will usually have 4 pilot wheels (2 axles)because of their "need for speed" , freight usually 2 and 0 for swithchers....the rear wheels were added to support the weight of ever-increasing boilers sizes..... I've even heard of small steam "turbo" cylinders on tender trucks (wheelsets) to give added torgue/ starting tractive effort for starting heavy trains...Also the Driver diameter is based on speed/ torque requirements...large diameter drivers for passengers engines to achieve maximum MPH and small drivers on switchers for starting heavy loadslnghairedwizard Remove | Alert Edit | Reply | Reply With Quote | Top
Xacto (508 posts)
Oct-05-01, 09:20 AM (EST) 4. "RE: Question" "the rear wheels were added to support the weight of ever-increasing boilers sizes"To add to that comment, the firebox was the part of the boiler supported by the trailing wheels. Early locos used fireboxes that fit between the drivers, so no trailing wheels were needed, the last rear set of drivers could be right under the cab as they are an most 4-4-0's. As boilers got longer, the fireboxes needed to get larger and soon they couldn't fit between the rear drivers. Putting some of the weight over unpowered trailing wheels does reduce the potential tractive weight, but the increase in steam production due to the larger firebox was more important. Some locos used boosters on the trailing truck to add low speed tractive effort.Cliff Remove | Alert Edit | Reply | Reply With Quote | Top
plainsman (216 posts)
Oct-05-01, 10:58 AM (EST) 5. "RE: Question" LAST EDITED ON Oct-05-01 AT 10:58 AM (EST)The Selkirk was a good example of this. It added about 10-12,000 pounds of STE (MTE) with the booster action.
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