whodat
New member
Wow,
You guys have hit on a lot of important topics in this thread! While most of what you guys posted is true and none of you really went out on a ledge you couldn’t get back from, it seems you are combining many questions and attempting to answer them all at one time. After reading through this thread here is what I perceive being asked:
1. If I add extra weight to the front of my vehicle will I need to upgrade the OEM suspension components?
2. If I add this weight in the form of a steel bumper will it make the occupants of the 4Runner safer?
3. How is the steel bumper different than the old bumper as it pertains to “crumple” zones?
Before we begin please take a look at this old guy named Newton and his three laws:
(BTW get a coffee and pastry or a Coke and nabs because this will take some time!)
1. First law: The velocity of a body remains constant unless the body is acted upon by an external force.
2. Second law: The acceleration a of a body is parallel and directly proportional to the net force F and inversely proportional to the mass m, i.e., F = ma.
3. Third law: The mutual forces of action and reaction between two bodies are equal, opposite and collinear.
Alright, got that? These won’t help answer the first question but will help answer the other two. OK, here we go:
1. If I add extra weight to the front of my vehicle will I need to upgrade the OEM suspension components?
Short answer – No. Whodat compared it to a fat kid sitting on the existing front bumper and that is as good as any. What you need to think about is what components will have an additional load by adding 60-80 more (New bumper – Old bumper) pounds to the front of the vehicle: Tires, torsion bar, Upper control arm and front suspension.
Tires – Remember your front tires are rated at a maximum load just like the rear tires and usually they are the same tire. You don’t think twice about putting 400 lbs on your hitch, two adults in the back and all kinds of gear in the cargo area so what are you worried about adding weight to the front? So tires should be no problem. Front suspension components though are a little different. You basically will be preloading them a little more with the new bumper. Will it handle different? Sure, a little but probably not any different than two 250 lb people in the front seats vs two 150 lb people in the front seat. I could calculate the weight delta at the CL of the front wheels of the bumper of adding 80 more lbs of bumper vs adding 200 lbs with the people but my gut tells me it would be close. Add it to the fact that a vehicle’s load changes from one trip to the next (500 lbs in the rear or 400 lbs in the backseat) and you see what I mean. Think of it this way: I add 80 lbs up front. To offset this weight I add “X” weight to the rear and the resultant will be a wash.
Personally I think you will have a little more shock wear over time. If it were me I would put some “C” rated tires on it which will give you more sidewall stiffness. I probably would add a heavier shock too but then again this is what I am going to do with my stock 4Runner anyway to help handling.
2. If I add this weight in the form of a steel bumper will it make the occupants of the 4Runner safer?
Answer = No. What it will do though is minimize front end sheet metal damage in a low speed impact. There are two ways people get hurt in a vehicle during an accident: A) Something that does not belong comes into the passenger compartment like a steering shaft, engine block, sheet metal, rock, etc. or B) Sudden acceleration or deceleration of the occupants. Item “A” is easy to explain. If you want to know more about item “B”, then Google Col. Jon Stapp. He was the “test dummy” that I learned about in Dynamics class 100 years ago or so. Suffice to say a human body can take a lot “G’s”. I will say that while the added bumper will increase rigidity of the structure it will also increase the sudden deceleration on the occupant, which in my mind will negate any gains. A quick word of vehicle safety from my sponsor:
The safest vehicles are modern race cars. If you really want to make a safe vehicle then add a complete roll cage, a HANS device, 5 point harness and helmets. This is what is required. Anything less you might as well keep it stock. Remember all the crash test data is at relatively slow speeds. Ever wonder why they don’t test at 70-75 mph? Because you usually don’t walk away from a crash at those speeds in any stock passenger vehicle.
The biggest problem though of adding that bumper is what you could do to a pedestrian. Vehicles are designed the way they are not because all engineers are thoughtful and safety conscious, but because there are rules and laws governing design. Pedestrian strikes are why front ends are designed the way they are. Of course slow speeds only as high speed strikes cannot be made safer. This brings us to:
3. How is the steel bumper different than the old bumper as it pertains to “crumple” zones?
My answer in a minute. Here are a few examples of crash scenarios. See if you can pick the one most likely to walk away.
• Bicycle hitting a Toyota Prius head on at 70 MPH.
• Prius hitting a Dodge 3500 Mega Cab 4X4 head on at 70 MPH.
• Dodge 3500 Mega Cab 4X4 hitting a Long Nose Kenworth head on at 70 MPH.
• Long Nose Kenworth hitting a Bridge Support head on at 70 MPH.
The answers are easy right? Referring back to Newton’s laws you can see that heavier is better until you get to the bridge support. Nobody wins when you hit one of those.
Never forget that the design of ANYTHING is all about compromise. Designing a vehicle like ours is no different. A consumer wants:
• Great looks
• High performance
• Safety
• Comfort
• Fuel Efficiency
• Reliability
• All at a low cost
Looking at the list above you can see how for example, fuel efficiency could be improved if we got rid of all the added weight of the airbags and safety hardware. Comfort could be improved if we added La-Z-boy recliners. That would make safety and fuel efficiency take a hit though. We could increase performance but reliability and efficiency would suffer. You get my point. It’s all about compromise. NOW to answer question 3:
It is probably easier and cheaper to make crumple zones. Full frames use a lot of steel and add weight, which decreases fuel economy. So, which one is safer? Go back up to the crash scenarios I listed above. Looks like mass is king there. In a low speed crash crumple zones are fine. They deform and protect the vehicle’s occupants. But at least in my mind mass wins at higher speeds. The vehicle engineers are constantly having to make compromises to meet the needs of consumers and to stay within the safety and fuel economy rules set forth by our government. I am a firm believer in safety but I understand compromise. Your steel bumper is no safer hitting a bridge support at 70 mph than anything else as your percentage of mass did not change much. Just remember, if something is designed to crumple, it will crumple even more at higher speeds.
While everything above is based on fact there are opinions in there too. Hope you enjoyed my answers. Good luck and I like the looks of them too!
Thank you, sir. Always like reading your lengthy, detailed, straight to the point posts! Do you ever get tired of being an engineer at work, then coming home and being an engineer on here
Thanks again for taking the time to post this. I'll post updates later when they come.
