# Def'n of truck's "frame rails"? **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [May 5, 2019, 1:16am UTC](https://community.cartalk.com/t/defn-of-trucks-frame-rails/139791 "2019-05-05T01:16:00Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [May 5, 2019, 1:16am UTC](https://community.cartalk.com/t/defn-of-trucks-frame-rails/139791/1 "2019-05-05T01:16:00Z")
Which parts are the “frame rails” in the photo on the link below? Only the two beams which run in parallel, the length of the truck? Or does the term “frame rail” include the beams that run at 90 degrees, i.e. the cross members too? > **[1961 - 1979 Ford Truck Chassis - Fat Man Fabrication](http://www.fatmanfab.com/product/1961-1979-ford-truck-chassis)** > > Get the improvement you crave with the precision of perfect and proven geometry in our Ford truck chassis.  Fat Man manufacturers a complete 1961–1979 Ford truck chassis with multiple options toRead More The reason I’m asking is b/c the repair manual says the truck’s aux fuel tank is located “between the frame rails” when it is actually located not in the middle, but on the side of the truck. It is between two cross members though. Or maybe they mean that while it is on one side of the truck, it is still technically between the long-axis frame rails? ---
**Author:** ![db4690](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/db4690/32/2583_2.png) [@db4690](https://community.cartalk.com/u/db4690)\ **Post date:** [May 5, 2019, 2:00am UTC](https://community.cartalk.com/t/defn-of-trucks-frame-rails/139791/2 "2019-05-05T02:00:37Z")
I’m of the opinion that the frame rails run lengthwise . . . whereas the cross members run horizontally Not only that, but that’s how our fleet’s documents, forms, literature, etc. refer to the components And that’s how I’ve seen it labelled in countless textbooks, service manuals, etc. you thinking of buying the kit and fabricating a truck . . . ?! ---
**Author:** ![Purebred](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/purebred/32/46796_2.png) [@Purebred](https://community.cartalk.com/u/Purebred)\ **Post date:** [May 5, 2019, 2:39am UTC](https://community.cartalk.com/t/defn-of-trucks-frame-rails/139791/3 "2019-05-05T02:39:11Z")
I would consider anywhere inboard of the frame rails to be considered the same as between the frame rails as opposed to outboard of the the frames rails. So my question is your auxiliary tank inboard or outboard of the rails? ---
**Author:** ![common-sense-answer](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/common-sense-answer/32/716_2.png) [@common-sense-answer](https://community.cartalk.com/u/common-sense-answer)\ **Post date:** [May 5, 2019, 11:31am UTC](https://community.cartalk.com/t/defn-of-trucks-frame-rails/139791/4 "2019-05-05T11:31:10Z")
I’ve always considered that any frame parts (even unibody, critical reinforced “frame” components where engines, suspension, etcetera, attach) are **frame members,** which is the broad family name for these parts. I consider **frame rails** to be front-to-rear frame members on cars which have separate frames (think parallel railroad rails). The cross-wise members I call **cross members** act as the _ties_ between the frame rails. I’d say a tank mounted anywhere within frame members on a vehicle with a separate frame would necessarily be mounted **between frame rails**. _ **CSA** _ 🌴🕶🌴 ---
**Author:** ![Cavell](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/cavell/32/43396_2.png) [@Cavell](https://community.cartalk.com/u/Cavell)\ **Post date:** [May 5, 2019, 1:49pm UTC](https://community.cartalk.com/t/defn-of-trucks-frame-rails/139791/5 "2019-05-05T13:49:20Z")
aux fuel tank is different than the main fuel tank