Chrome moly vs dom

[wayfast1]

Im gonna build a car should i use moly or dom so need some ideas wich way to go. Thanks

[zeroracing]

Are you familiar with welding chromoly?

If no, then don't touch it, improperly welded chromoly can fail easily and injur or kill. Personally I would only TIG chromoly, which many don't but that is the safer way to do it.

Also if your not using the strength of chromoly to go lighter then your only saving wallet weight.

[MasterSbilt_Racer]

If you can properly weld chrome moly, use if for the driver protection areas and DOM for the rest of the car. The stiffness of the two materials is the same. The yield point is what is different.

[F22 RAPTOR]

Chromoly, just say "NO".

I personally still prefer DOM, chromoly just seems to finicky. I've seen Chrome cars built by GRT and Masters crack and fail and they know what they're doing. Below is a Chrome Goat that broke in several places in a flip and it scares the crap out of me to even consider chromoly. If you look close both breaks were "Next" to the welds, first at the drivers left shoulder where the main hoop and top door bars meet. Then the main "X" split in two inside the main hoop. Sure the car stayed intact and the driver survived, but the cage isn't suppose to break, but bend. DOM for me every time. JMO

[merc123]

I personally still prefer DOM, chromoly just seems to finicky. I've seen Chrome cars built by GRT and Masters crack and fail and they know what they're doing. Below is a Chrome Goat that broke in several places in a flip and it scares the crap out of me to even consider chromoly. If you look close both breaks were "Next" to the welds, first at the drivers left shoulder where the main hoop and top door bars meet. Then the main "X" split in two inside the main hoop. Sure the car stayed intact and the driver survived, but the cage isn't suppose to break, but bend. DOM for me every time. JMO

Straight out of the GRT book:

"4130 material needs to be heat treated after welding....the weak point will be the area right where the heat concentration stopped while welding..."

This explains why it broke where it did. According to the book GRT builds 95% of their cars out of DOM and it is more forgiving in crash situations than chromemoly.

Also, my opinion, if you are asking what type of tubing to use maybe building a chassis isn't the thing you need to start with.

[F22 RAPTOR]

Straight out of the GRT book:

"4130 material needs to be heat treated after welding....the weak point will be the area right where the heat concentration stopped while welding..."

This explains why it broke where it did. According to the book GRT builds 95% of their cars out of DOM and it is more forgiving in crash situations than chromemoly.

Also, my opinion, if you are asking what type of tubing to use maybe building a chassis isn't the thing you need to start with.

Is that the old GRT book? I think that number has flip/flop'd now with most cars being chromoly these days and they offer Tig welding at an added cost. Seeing how this was a GRT car and I assume they heat treated the frame the way "they" recommend, it appears chromoly fails at the weld point anyway, regardless of prep. Me, I still like a 2x2 frame with DOM cage or at the very least 2"RND frame, but thats just me. These 1-3/4" cars aren't referred to as, "crash and trash" for nothing.

[zeroracing]

Great pictures of failures. A lot of learning can be done from them, thank you for posting.

[F22 RAPTOR]

Great pictures of failures. A lot of learning can be done from them, thank you for posting.

No problemo. I keep them just for that reason, to learn. I actually got them off Facebook, but nobody was even talking about the failure, just Ooo-ing and Ahh-ing the wrecked car... Go figure.

[jason29a]

All sprint cars and midgets are built out of moly, they don't break like that.... I have been in the fab business for almost 20 years and thats just a case of annealing the material. If it's welded right it won't break like that. It will bend to a point and break though. DOM is the way to go though IMO.

[dirty white boy]

chrome moly tube been used for years in NHRA an IHRA but there needed strengths are different than what strengths dirt racing needs,...think somebody needs to do some crash study analissies on dirt chassis like NASCAR an NHRA an such do....for safety sake...

[twisterf5]

I personally still prefer DOM, chromoly just seems to finicky. I've seen Chrome cars built by GRT and Masters crack and fail and they know what they're doing. Below is a Chrome Goat that broke in several places in a flip and it scares the crap out of me to even consider chromoly. If you look close both breaks were "Next" to the welds, first at the drivers left shoulder where the main hoop and top door bars meet. Then the main "X" split in two inside the main hoop. Sure the car stayed intact and the driver survived, but the cage isn't suppose to break, but bend. DOM for me every time. JMO

you asked to see pics of our new chassis. could not get them to load yesterday but you can go on my FB page they are there ( richard clew )
our new car is 100% moly as has been our owm cars in the past our last owm was 4 years old when it started cracking so we got rid of it. most people weld it wrong and think they can use the same wire they use on mild steel. we use a special moly wire that you do not have to heat bars before welding.it is around 15 dollars a pound /instead of the 3 bucks the other wire cost there was no expense spared on this chassis could of built 3 chassis for what this one cost.well we will see in march how it works out.

[twisterf5]

chrome moly tube been used for years in NHRA an IHRA but there needed strengths are different than what strengths dirt racing needs,...think somebody needs to do some crash study analissies on dirt chassis like NASCAR an NHRA an such do....for safety sake...

think that would cost to much/ i have welded several bars together with different wire and then put them i a press until they broke. that is as best as i can do with our budget LOL but feel 100% we will be OK with this chassis.

[dirty white boy]

think that would cost to much/ i have welded several bars together with different wire and then put them i a press until they broke. that is as best as i can do with our budget LOL but feel 100% we will be OK with this chassis.

seen the pics on FB,..its a nice chassis,..very professional looking!

[merc123]

Is that the old GRT book? I think that number has flip/flop'd now with most cars being chromoly these days and they offer Tig welding at an added cost. Seeing how this was a GRT car and I assume they heat treated the frame the way "they" recommend, it appears chromoly fails at the weld point anyway, regardless of prep. Me, I still like a 2x2 frame with DOM cage or at the very least 2"RND frame, but thats just me. These 1-3/4" cars aren't referred to as, "crash and trash" for nothing.

Maybe so, probably because that's what everyone wants now.

[MasterSbilt_Racer]

Is that the old GRT book? I think that number has flip/flop'd now with most cars being chromoly these days and they offer Tig welding at an added cost. Seeing how this was a GRT car and I assume they heat treated the frame the way "they" recommend, it appears chromoly fails at the weld point anyway, regardless of prep. Me, I still like a 2x2 frame with DOM cage or at the very least 2"RND frame, but thats just me. These 1-3/4" cars aren't referred to as, "crash and trash" for nothing.

It fails next to the weld because of the martensite that forms when the area cools from a molten metal to room temperature too quickly. The only way to avoid this process would be to heat in an oven and cool it slowly.

No matter what rod you use, this process still happens. It just may not be as big of a problem when an experienced welder uses a time-tested technique.

As I have said on here many times, why? Moly is NOT lighter. It is NOT stiffer. Only the yield and ultimate strengths are higher. (about a factor of 2). If your chassis has members that see stresses near the yield of mild steel, you need to go back to the drawing board.