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 Post subject: Drive Wheel on 6816, should it be hanging over the rail ?
PostPosted: Wed Jul 11, 2018 5:36 pm 

Joined: Fri Mar 18, 2005 1:27 pm
Posts: 410
Location: Milford,Mass
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Hi All

I have a question in the shot of the fireless cooker at Steamtown in Vermont that I took in Oct 1980. The rear drive wheel should it be hanging over the rail that much? Just wondering why is it because the tires are overworn?


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 Post subject: Re: Drive Wheel on 6816, should it be hanging over the rail
PostPosted: Wed Jul 11, 2018 8:15 pm 

Joined: Sun Aug 22, 2004 1:51 pm
Posts: 8891
Location: Somewhere north of Prescott, AZ on the Santa Fe "Peavine"
Wider tires were common on many switchers that had to contend with tight curves and/or rough track. It gave a wider "margin of error" and theoretically reduced derailments, although the wider tires could themselves induce problems on places like street trackage.


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 Post subject: Re: Drive Wheel on 6816, should it be hanging over the rail
PostPosted: Wed Jul 11, 2018 8:41 pm 

Joined: Fri Aug 20, 2010 8:25 pm
Posts: 280
It's a little hard to tell from those photo's, but it appears that the center driver of that switcher is a "Blind Driver". These were relatively wide drivers without a flange (no flange at all just a flat tire surface).

These blind drivers along with wide tires on the other drivers were common with long wheel base loco's. They allow the loco to go through tighter curves without binding caused by the flanges.

I had not seen one applied to a switcher before, but it makes sense. The flanges on the front & rear driver tires "steer" the loco and the blind center driver just "pushes" the loco.

If this loco was built for a power plant or factory that had "tight" curves a blind center driver and wide tires could have been specified by the customer as an "option". Like power steering on a 1970's Chevelle.....

Cheers, Kevin


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 Post subject: Re: Drive Wheel on 6816, should it be hanging over the rail
PostPosted: Thu Jul 12, 2018 2:00 am 

Joined: Wed Sep 25, 2013 12:36 am
Posts: 257
Location: Anchorage, Alaska
Probably not applicable to this locomotive, but another reason for using a wide tire applied to a number of Moguls built in 1906 for construction of the Panama Canal and obtained by the Alaska Railroad in 1915. They were converted from 5 foot gauge to standard gauge in Panama. The drivers had wide tires to make the gauge conversion. I understand that they had some problems derailing at grade crossings during the winter when the drivers were lifted off the rail by ice on the outside of the rails that wasn't cleared by standard width wheels.


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 Post subject: Re: Drive Wheel on 6816, should it be hanging over the rail
PostPosted: Thu Jul 12, 2018 5:34 am 

Joined: Thu Apr 14, 2005 9:34 pm
Posts: 2150
Location: Copenhagen, Denmark
If the rail is light, it will make the tires look wider too.

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Danmarks Tekniske Universitet
Institut for Systemer, Produktion, og Ledelse


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 Post subject: Re: Drive Wheel on 6816, should it be hanging over the rail
PostPosted: Thu Jul 12, 2018 9:08 am 

Joined: Tue Sep 14, 2004 7:52 am
Posts: 1450
Location: Strasburg, PA
Alexander D. Mitchell IV wrote:
Wider tires were common on many switchers that had to contend with tight curves and/or rough track. It gave a wider "margin of error" and theoretically reduced derailments.

The standard width for tires is 5-1/2". By coincedence, we currently have a wheel set on the shop from a logging locomotive whose tires measure 6-1/4" wide.

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