Accident Where Integrity of CMC (cab mount chop) Questioned?

I did too. Just trying to inform the uninformed. I ride mtn bikes.

 

And by the way, "Hipsi" used the term " ultra high strength steel" in reference to what...Toyota truck frames? No offense buddy (really), but that is real funny!

 

Yeah man. I walk away from crazy threads all the time for the sake of my better sanity and to keep my blood pressure down.

 

Cab mounts and crossmembers. Yep. Toyota even touted this when the 3rd gen came out.

 

I wasn't concerned about liability, I was concerned about keeping my knees. I know everything we do in modifying our trucks can compromise the safety in some way in a bad accident(or evasive maneuvers or whatever), but I do think we should avoid advising people to do things that unnecessarily add more little compromises.

Well if you look at the thread that sparked this everyone was saying CMC, I don't think anyone else had suggested UCAs. People who know what they're doing use that as the first step to fixing rub, anytime I see it asked on the forums the most common response is CMC which I completely disagree with. I was also saying specifically with the stock OR wheels. OP on the other thread was asking if the aftermarket wheels he ordered would fix his rub on stock UCAs, I was saying forget the wheels and spend that money on some proper UCAs.

I've used it plenty on the trail and messed around with it in a spot I could get all different combos of bump and droop, it's very close to the mount but doesn't hit it anywhere. Haven't heard a thing going fast over whoops and such either. Maybe if I bottomed out going way too fast with the steering at exactly the right angle but it doesn't look like it would kiss. And yeah, I would consider a CMC if I went bigger in the future.

And yeah tiny bit of rub at full lock but that's easy, just don't turn the wheel all the way to full lock.

To your last point, sure if it's needed. On the flip side people should not be racing to suggest CMC when the suspension geometry is the core issue.

 

okay, fair enough and I stand corrected, Thanks! Who's laughing now?

So the mount grain structure (frame is too far removed) is compromised due to thermal cycles in applications of intermittent welding and cooling and possibly even "contact quenching." I would be interested to know (No, I'm not starting another thread) if there's enough carbon content to form martensite/bainite grain structures known for brittleness in said applications. I was wrong before yes, but I would question the likelihood given the requirements to bring on a brittle failure in steels. It would have to be red hot and cooled almost instantly to achieve this even the alloying were available.

 

Don't people "weld on" some versions of rock sliders directly to the frame? Not sure, just seen some mentioning of this casually reading.

 

Frame rail in middle is not as important as front, rear and crossmembers and cab mounts.

 

Whether or not you (or anyone else) believes that a CMC chop has no impact whatsoever on the structural rigidity, it IS to a degree about liability. That's why that argument comes up so frequently. As I said before, if you get in a wreck and there's significant damage to that area, and the adjuster determines that your modification was a proximate cause for the amount or degree of damage, then they would have a damn good argument for denying the claim. Then you're liable for the repairs. Sure, the risk may be minimal, but it's not zero. What then? Take them to court and prove your case that it's no big deal? Ha! Good luck running head first into that buzzsaw.

Then what happens if one of your passengers is injured and either you are underinsured for their expenses or you get denied altogether as in the scenario above? Personal injury attorney's wet dream, and you're stuck saying "do you want fries with that" on nights and weekends to pay off legal debt.

TW debates seem to be argued within the confines of TW logic with little to no regard for real-world implications. Severely overloaded truck with all of the overlanding crap that looks sweet on instagram? Substantially altered suspension geometry, height and center of gravity? Those can be potentially impactful changes that introduce more risk (and yes, liability) for accidents and incidents on the road. I'm not saying don't do them or attacking anyone personally, but just it's not a bad idea to take a step back and consider these things. It's not that hard to exceed the operational limits of these small, rudimentary trucks when we want them to function as sensible daily driver and Mountain Dew commercial stunt truck all at the same time.

 

The cab mounts on a 3G Tacoma are high strength steel, because they double as the wheel intrusion guard. The rear cab mounts and cross members are mild steel.



Ford does it a little differently, with a separate ‘wheel catcher/deflecter ahead of the actual frame cab mount to keep the wheel out of the passenger compartment in a small overlap crash. Below is a picture of the Ford solution to this safety requirement on my F150:




The gap between the frame and the wheel in a crash, is ideally minimal, which is why on a 3G Tacoma you gotta cut to fit 33”s. The engineers want to minimize the acceleration of the wheel moving backwards before the rest of the structure comes into play. I found an article on this subject a while back. I’ll see if I can find it and link it.

 

Worked at a Toyota approved body shop for a while. Same scenario, Tundra customer wanted to trade. Toyota denied because of CMC. They couldn't resell the truck with that being a liability. The truck belonged to quicksilver.

 

Could this be the case for any modification from stock? Sky is the limit!

 

Just because there is one particular design, say, a body mount, that doesn't mean that's the ONLY possible design, nor does that mean it's the strongest possible design. More than likely it is FAR from the strongest, or "best" design. It's likely just the cheapest and easier to reproduce that fit the basic strength requirements from the engineering team.

 

No, of course not. Simple things are fine. I'm talking about things that materially alter the handling and safety of the vehicle.

 

All this talk about being credentialed on this topic, and not one person claimed to be so because they slept at a Holiday Inn Express last night.

Disappointed

 

Some reading from the 1st link posted below:

“Small overlap frontal crashes primarily affect a vehicle's outer edges, which aren't well protected by the crush-zone structures. Crash forces go directly into the front wheel, suspension system and firewall. It is not uncommon for the wheel to be forced rearward into the footwell, contributing to even more intrusion in the occupant compartment and resulting in serious leg and foot injuries. To provide effective protection in small overlap crashes, the safety cage needs to resist crash forces that aren't tempered by crush-zone structures. Widening these front-end structures also helps”

https://www.iihs.org/iihs/ratings/ratings-info/frontal-crash-tests

The article below is full of mis-translated words (rocket instead of rocker etc) but maybe explains why Toyota puts the cab mount as close to the wheel as it does (screwing all the guys wanting 33”s). The smaller the gap between the cab mount and the wheel, the more likely the vehicle will be deflected away from the impact “glancing off”, which decreases the chance of serious injury. A large gap behind the wheel is not desirable. Not that a 1/2” taken off to CMC is likely a huge factor, but at least there is rationale to the Toyota design (if I am understanding what is written correctly).

https://www-esv.nhtsa.dot.gov/proceedings/24/files/24ESV-000244.PDF

^^^^^ Above a repost from this old thread:
https://www.tacomaworld.com/threads/cab-mount-chop-food-for-thought.577566/

 

I don't disagree at all, but the question was about what happens if you have an accident or injury insurance claim and you've modified a structural element of the vehicle. You may be 100% right, but you'll have a 0% chance of convincing an insurance adjuster who has made up his or her mind to the contrary.

 

Stocklocker,
LOVED your post with images, truly. So, I had to google-convert Mpa to PSI (I'm American dammit) to understand what Toyota meant by "440Mpa high strength steel" for the front mount and it shows the conversion to be roughly 64KSI which is anything but "high" strength steel IMHO. Your average "mild" steels will yield at 60KSI or more. How is this considered high strength and ultimately, how hardenable and alloy is it really? I'm confused!