X-Frame

X or no X?

Recommended Posts

X OR NOT AN X - That is the question!

 

The examples (and there are others) I put together show what is considered a Transverse X brace chassis design. The earliest "automotive" use I have come across thus far is on the 1922 Hotchkiss AM. It, like the others, claim that it is truly an X design. Some people will dispute that even if the manufacturer state it is. Delage, as with authors, have made claim they have been using an X brace for years like shown, starting 1926.

 

Please stake your arguments here, pro or con, and why...and if you know any earlier use... Thanks

 

 

trans x.png

Share this post


Link to post
Share on other sites

The effectiveness of the X is limited by its ability to remain rigid.  As the main frame twists the two legs are subjected to opposite forces and naturally resists it.  The limitation is the method of manufacture.  A perfect X would have to have one of the legs welded in place.  The examples you show are fabricated with a front and rear half.  How these are joined will directly affect the results since the joint will be directly subjected to a twisting motion.  In other words one will be twisting up and the other down.  With that picture in the mind, you can see how the confidence in the design and manufacturing capability improved.  The 1922 Hotchkiss design employs a long joint so that it has better leverage and resulting short legs, which naturally can resist large displacements or flexing.  Each subsequent design has a shorter joint and longer legs as the design and manufacturing matured. 

 

After many years of driving Model T Fords, Dad realized the importance of a X member (now that the roads are better) so he installed on on his 1915 when he put it back together in 1965.  It's in the center of the wheelbase and is just wedged in.  Being above the drive shaft allows it be within the height of the main frame rails.  Several years later he made one for his 24.  However, this car now had a Warford gear box which previously was in the 15 when he drove that in the Thirties and Forties.  With the gear box sitting in the prime location for the X, he tried an off center torque tube design.  The results were disappointing.  The tube was not rigid enough and was twisting with the leverage arms.  So he made another X.  That happened in the Eighties and for that one I don't have an image in my head of what it looks like, so when I get a chance I'll have to take a peek.  And that is why I'm aware of the X member design.

Share this post


Link to post
Share on other sites
2 hours ago, emjay said:

The effectiveness of the X is limited by its ability to remain rigid.  As the main frame twists the two legs are subjected to opposite forces and naturally resists it.  The limitation is the method of manufacture.  A perfect X would have to have one of the legs welded in place.  The examples you show are fabricated with a front and rear half.  How these are joined will directly affect the results since the joint will be directly subjected to a twisting motion.  In other words one will be twisting up and the other down.  With that picture in the mind, you can see how the confidence in the design and manufacturing capability improved.  The 1922 Hotchkiss design employs a long joint so that it has better leverage and resulting short legs, which naturally can resist large displacements or flexing.  Each subsequent design has a shorter joint and longer legs as the design and manufacturing matured. 

 

I see you noticed the center section where halves meet kept getting smaller.  Most are riveted together and some welded.  Of course, this was not consistent and of course there were more traditional equal length legs from a central axis design being used on vehicles at the same time. (see Alvis X chassis used between 1928-1931 attached for inconsistency).

 

Strength also came from the fact that early on, engines were bolted to the frame at four points which kept it from twisting but when rubber mounting was introduced and of course, floating power, the frames became weak and the use of X bracing became fairly universal.

 

Is there a formula for the most effective X leg length or angle in mind?

 

alvis fwd FWD%20manual%20Fig%2000.jpg

Edited by X-Frame (see edit history)

Share this post


Link to post
Share on other sites

 

The 1924-1927 Delage GL was an early example of the more traditional X design used on an automobile long before the Cord L-29. 

 

 

delage gl.png

delage gl 2.png

Edited by X-Frame (see edit history)

Share this post


Link to post
Share on other sites

 

Even here in America... an example of the more traditional X being used in this 1924 Goodyear chassis:

 

 

 

1924 goodyear bus4.jpg

Edited by X-Frame (see edit history)
  • Like 1

Share this post


Link to post
Share on other sites

X, very odd chassis. Both front and rear end suspensions are very interesting. Also the exhaust, from a single pipe into a twin pipe back into a single. Perhaps they used this design to act as a muffler. The X brace is sure stronger than a single crossmember but if old Henry didn't like it, it wasn't going to be used no matter how good it was. He fought hydraulic brakes until 1939 and was still opposed to them until his death. Gas tank location looks like an OSHA nightmare!

Share this post


Link to post
Share on other sites
6 minutes ago, 46 woodie said:

X, very odd chassis. Both front and rear end suspensions are very interesting. Also the exhaust, from a single pipe into a twin pipe back into a single. Perhaps they used this design to act as a muffler. The X brace is sure stronger than a single crossmember but if old Henry didn't like it, it wasn't going to be used no matter how good it was. He fought hydraulic brakes until 1939 and was still opposed to them until his death. Gas tank location looks like an OSHA nightmare!

 

Ahhh... but of course Ford did use the X starting in 1933 and on convertible models only from 1949-1964 (Fords - Mercury and Lincoln had different time brackets of use)  I put together a visual identification example for them a couple years back for the 1935-1948 models.  The 1933-1934 was slightly different than the 1935:

 

 

1935-1948 Ford.jpg

Share this post


Link to post
Share on other sites
32 minutes ago, 46 woodie said:

X, very odd chassis. Both front and rear end suspensions are very interesting. Also the exhaust, from a single pipe into a twin pipe back into a single. Perhaps they used this design to act as a muffler.

 

Those double pipes are the mufflers with cylinder baffles in them.  Being small diameter they used two :)

Share this post


Link to post
Share on other sites

" Is there a formula for the most effective X leg length or angle in mind? "

 

An X member breaks the frame into three sections, before, after, and in between.  Typically frame rails are channels which are fairly rigid in one direction only.  Of course, everything can flex, but these earlier concerns for a rigid chassis assuming rigid is fine.  Therefore when the axles at the ends of the frame imputed a twist in to the frame, the sides and end members were consider rigid and the joints flexed.  (Manufacturers bragged about their flexibility and Ford advocated three point of support to allow twisting.)  So in theory inserting a "rigidizer" like an X member would create a rigid frame.  But of course each of the three sections can in fact flex.  Since the triangle formed by the legs and one side of the frame is flat by definition, one may tend to elongate the X so that the before and after sections are shorter and on a long wheelbase vehicle it can be important.  However, that makes the legs longer and become less effective.  There are so many variables and factors, that there can't be a simple formula to define the optimal design.  I tried to paint a picture of how everything interacts.  A full analysis is required to establish the design or each frame member.   Your new examples basically moved the joint to the axis of the frame which will be subjected to the same up and down twist (as a transverse joint) and became quite robust and had the drive shaft through it.

 

It may be an interesting project for an engineering student to model and evaluate the various designs on today's computer programs.  I would not be surprised if the old seat of the pants designing was fairly efficient.   On the other hand adding an X member to a vehicle that didn't have one, anything would be better than it was.  If you are considering one, I'd say start with 45° legs with a 90° intersections.  If the remaining frame is rather long, another X member can be inserted.

Share this post


Link to post
Share on other sites

emjay, the X is still being used today on at least (and may be the last) one production car today.  The London Taxi TX4.  I also know that the X is used by many custom high performance chassis makers, some reproduction boutique cars, and is in a form on a few NASCAR chassis so its importance and strength are still respected.

 

Edited by X-Frame (see edit history)

Share this post


Link to post
Share on other sites

Never doubted that.  Every new model reports some percent increase in stiffness.  The more the structure flex the less optimally the suspension performs.  However, most of that is done with the entire body structure.  My Jeep Comanche has both, a unit-body cab and an X member in the frame extension under the bed. 

Share this post


Link to post
Share on other sites

That is a strange looking chassis that you have listed as a 46 - 48 Ford.  I have had a few of that model and never seen anything like that. All the ones I have seen look like the 41 - 42 model that you show. Maybe it is a light truck or something.

I have a 47 Mercury chassis in my shed at the moment  ( same as the Ford except the front cross member is moved forward) and it is identical to the 42 model

Edited by DavidAU (see edit history)

Share this post


Link to post
Share on other sites
2 hours ago, DavidAU said:

That is a strange looking chassis that you have listed as a 46 - 48 Ford.  I have had a few of that model and never seen anything like that. All the ones I have seen look like the 41 - 42 model that you show. Maybe it is a light truck or something.

I have a 47 Mercury chassis in my shed at the moment  ( same as the Ford except the front cross member is moved forward) and it is identical to the 42 model

 

Maybe Australian imports were using older style frames as opposed as in the states?  Just like some Ford models in the 1950s lag a year behind in style in Oz.

 

Here are some of the later year examples from 1946-1948  The disassembled one on its side is from 1947.  The gray painted frame from 1946.  The one in the grass is 1948.

 

 

 

 

1946 ford 4832823_orig.jpg

1947_ford_car_on_side 2 door coupe.jpg

1948 2s-l1600.jpg

Share this post


Link to post
Share on other sites

You learn something new every day  however the 47 Mercury frame in my shed that looks like a 42 model came under the Mercury coupe I imported from Minnesota about ten years ago and is number matching so they must have been using up old frames or something..

Share this post


Link to post
Share on other sites

This style frame was used on all 34-36 Auburns. The body mounted over the frame and bolted into the sides and top for additional rigidity.

Frame 06 Nov.JPG

Share this post


Link to post
Share on other sites

In the 1960's, Studebaker Avantis, Lark convertibles and Wagonaires had an 'X' brace in the center of the frame.

 

Craig

Edited by 8E45E (see edit history)

Share this post


Link to post
Share on other sites

In the 50's, all Cadillacs had an X brace. From 1957 to 1964, the frame itself was an "X". The ones for the convertibles had just thicker elements forming the brace.

12 Caisse sur châssis.jpg

Edited by Roger Zimmermann (see edit history)

Share this post


Link to post
Share on other sites
5 hours ago, 8E45E said:

In the 1960's, Studebaker Avantis, Lark convertibles and Wagonaires had an 'X' brace in the center of the frame.

 

Craig

 

I had learned not too long ago that the Wagonaires used the Lark Convertible chassis.  Just like another oddity was the 1957-1959 Chrysler Imperial 4-door HT used the convertible X frame as well but did not need it.  Think there was another oddity as well but can't put my finger on it at the moment.

 

 

Share this post


Link to post
Share on other sites
5 hours ago, Curti said:

This style frame was used on all 34-36 Auburns. The body mounted over the frame and bolted into the sides and top for additional rigidity.

 

How about the 1931-1933 Auburn X... different?

 

 

Share this post


Link to post
Share on other sites
3 hours ago, Roger Zimmermann said:

In the 50's, all Cadillacs had an X brace. From 1957 to 1964, the frame itself was an "X". The ones for the convertibles had just thicker elements forming the brace.

 

Hey Roger... yes, the 1957-1964 Cadillac (and continued to 1970 on the Buick Riviera) was the Tubular Center-X chassis.  And true, there is usually a "fish plate" of about 1/4" thick stitch welded to the rails up to the kicks on convertible models.  Here is an example looking at one of the X legs with the convertible metal strip reinforcement...

 

 

1955 buick conv IMG_0232.jpg

Edited by X-Frame (see edit history)

Share this post


Link to post
Share on other sites
17 hours ago, X-Frame said:

 

How about the 1931-1933 Auburn X... different?

 

 

Yes, 31-33 as well.

Share this post


Link to post
Share on other sites

One thing for sure, looking at pictures of those chassis' and comparing them to my uni-body new car is like comparing the Brooklyn Bridge to a tin can. I know they clam the uni-body cars are safe with crumple zones etc, but quite a difference.

Share this post


Link to post
Share on other sites
24 minutes ago, 46 woodie said:

One thing for sure, looking at pictures of those chassis' and comparing them to my uni-body new car is like comparing the Brooklyn Bridge to a tin can. I know they clam the uni-body cars are safe with crumple zones etc, but quite a difference.

 

Yes, cars of today are supposed to be safer due to materials, design, and as you said, scientifically tested crumple zones.  And as you have also seen, cars of years past were heavier with thicker gauge steel but that created a problem.  They were so stiff (pre 1966 safety standards beginning) that people were injured more by the hard G-force impacts of non giving hard steel body and chassis designs because you were thrown harder upon impact than if the car crumpled and absorbed the impact. I am sure they were probably safer in slow speed crashes or non violent rollovers but more high speed impacts were an issue. 

 

Also, they knew that side impacts normally happen above the separate chassis side frame rails anyway - which was an issue and brought up during the whole 1957-1964 GM tubular center-x (no side rails) design frame debacle in which GM was sued for.  But at the time, GM was not held liable and was prior to the new 1966 laws.  This chassis design carried over until 1970 on Buick Riviera but they felt more confident since the body was built in unibody style attached to the separate frame so in essence had double protection but was very stiff.

 

 

Edited by X-Frame (see edit history)
  • Like 1

Share this post


Link to post
Share on other sites
10 hours ago, Roger Zimmermann said:

Yes, it's what I intended to explain. My English has some limitations...

 

Your English may have limitations but your talents don't!

 

 

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...