If anyone wants another data point, I did some digging on this about a year ago and just found my old numbers. I didn't personally weigh any of these but rather used numbers I could find online so consider the source. The aftermarket numbers were easy to find from the manufacturers. The OEM numbers were harder to find and I would consider them less reliable. OEM 2017 Z71 wheel & tire (265/65/R18) combined weight: 65 lbs. 20x10 Fuel Krank & 325/60/R20 tire combined weight: 111 lbs. That's obviously only part of the story since the radius and mass distribution plays a huge role but, as you can see, just switching wheels and tires adds 46 lbs. per wheel.
What state are you in? Every state has different laws regarding tint. I’m not saying you should or should not follow those laws. Lots of people don’t but it would be a good idea to at least know what the limits are for your state. What are you going for? As dark as possible? Match the other windows? I believe 20% (the percentage is how much light is allowed through the tint - lower numbers are darker tint) will most closely match the smoked back windows that came from the factory. I chose 35% for my own truck. I wanted some tint to shield myself and the interior from the sun but not so dark that it was hard to see out at night. I move between states a lot so I honestly don’t know if it’s legal or not.
I appreciate the commentary, fellas. This is all good stuff. Going back to Grumpy’s comments earlier regarding Moment of Inertia, one question I conveyed rather poorly in the original post is this: Why don’t any of the countless online “gear ratio” calculators attempt to capture the requirement to compensate for the heavier/larger wheels and tires? Every calculator I have seen appears to be a fairly simple one that simply tries to give you a gear ratio that will return you to the OEM relationship between driveshaft RPM and wheel RPM. One reason for this might just be that the math is “too hard.” I reject that based on a (possibly erroneous) assumption that people willing to take the time to build something like that online are also going to give it their best effort. Another possibility is that, in the grand scheme of things, the heavier wheel/tire’s net effect on the rear diff isn’t a major contributor when compared to the other forces acting on it. Thoughts?
I mostly agree. Just saying "mechanical advantage" and "working torque" doesn't really say much. My point was choosing your new gear ratio will almost certainly account for those things as best you can. I completely agree that this entire situation begins with a huge sacrifice by departing from the design GM intended by lifting the truck. Without access to a wind tunnel, I can't account for all of those changes but arbitrarily going to lower gears beyond what the math, physics and geometry tell you likely won't help. It won't necessarily hurt but this isn't a case of "if 4.10 is good, 4.56 has to be better." My focus is on trying to restore stock performance. Obviously there are those out there that are looking for something else. Concur. I also don't know what that breaking point is. I hope to never find out. I only brought it up to say higher RPM than designed by any amount generally isn't a good thing. At some point, stuff will start to fail. That breaking point, as you alluded to, is likely well past the life of other critical components but there is still an unknown failure point out there somewhere. I completely agree. I think you would agree there are also a lot of people out there that will just do what the masses do because they aren't willing to take the time to analyze what's actually happening inside the truck. My intent of this thread was less to ask a question and more to start this exact conversation so others can benefit. I have learned immeasurable amounts from a lot of smart, experienced people who have taken their time to post things on forums like this one. I'm trying to do any small thing I can to return the favor.
I think we are both making the same points. I 100% agree that re-gearing is necessary for bigger tires. My main point was that "rolling mass" as it's commonly referred, likely isn't a huge factor and probably shouldn't drive people to a lower-than-necessary gear ratio to meet their other, more important needs. More specifically, my point in writing all of this is to say when someone says "I went with 4.56 gears because I really like the performance." I get frustrated. That statement is fine and certainly honest but it is also an opinion and falls woefully short of being useful feedback for two main reasons: 1. "Performance" can mean any number of things. What performance, exactly, are you getting from 4.56 gears that you like so much? 2. You an I probably don't like the same things. What can you tell me about the truck itself that would help make a decision?
I would submit, when it comes to gears, whether the mass is "carried" or "rolling" isn't relevant. Your differential gear (and transmission, driveshaft, etc.) doesn't know the difference. Weight in the bed of your truck or on your wheel/tire setup is the same to the differential gear. It is all just mass that is resisting changes in movement. Obviously if we start talking about suspension performance, frame stress, etc. it matters where the mass is but the gears won't know the difference. I agree that your desires (MPG vs. performance) should influence the decision but I get the feeling, and maybe I'm wrong here, that most people equate "performance" to a lower gear ratio. I would submit that isn't always the case and you'll find diminishing returns (and potentially higher risk of damage) as you go lower and lower in your gearing. The RPM at cruise speed is also constant regardless of mass. That's assuming you don't change gears, of course. That also assumes a level road and no wind. Once you start to consider hills (gravity) and drag (both from external factors and changes in speed), things get more complicated. I concur that a common benefit to re-gearing is so the truck isn't "hunting" for gears at highway speed. I guess one of my other points is that going "beyond" (lower gear ratio than stock equivalent) the stock setup isn't necessarily the best fix for that. A tune, for example, might be a better path if you're not happy with the shift points after you re-gear. Those shift points, of course, were chosen based on the stock setup that we don't have any more.
I was going to post this as a follow-up in the 4.10 gear thread about re-calibrating the speedometer but it seemed like a bridge too far in terms of a thread jack so I thought I'd start a new thread. I suspect I'm going to cover ground that has already been covered in a few threads so I apologize but hopefully this helps someone. Also, if you don't want to waste your time with my nerd-ery throughout, just go to the last two paragraphs. Re-gearing for different tire sizes is a topic that I have followed for some time with keen interest. For one, I have a lifted truck with 35-inch tires (more on that later) still on the stock gears and am eagerly awaiting the moment I have enough cash to re-gear it. I hope to do so in the next couple months. Second, this topic is interesting to me because it seems to be loaded with opinions about the correct gear to choose, which is surprising since gear ratios and their effects are a known quantity. Full disclosure: I have never worked in the auto industry and I am NOT a certified auto technician. I do have a BS in Aerospace Engineering (I am NOT a practicing engineer) and a fair amount of technical experience so I consider myself at least partially qualified to discuss technical topics in general terms. As always, there are definitely people that frequent these forums that know more than I do. If you fit that description, please chime in and correct my errors. Pointing out that I'm wrong won't hurt my feelings. I will feel bad, however, if someone spends a bunch of money or makes a poor decision based on my bad information. Everyone has different desires for their truck's performance so I always cringe when I see a new thread with the topic "What gear ratio should choose?" The only thing that makes me cringe more is when someone posts in that same thread "You should get 4.56. That's what I did and I love it. You'll be happy." That's great but it's also totally useless feedback in my opinion. Without any explanation for the reasoning behind the decision and likely with no knowledge on what will make someone else happy that's a pretty big leap. I find myself frustrated when someone's emotions drive their recommendation for a specific gear ratio based on how they feel when they drive their own truck. I don't know anyone on this forum personally. I respect all of you for our common love for our own trucks but I will always be skeptical when a relative stranger gives me a recommendation based on their "feelings." On to my specific example: my own 2017 Silverado 1500 LT Z71. I bought the truck from the dealer with a 6" lift, 20-inch wheels and 35-inch tires already installed. I love my truck. What I didn't do, largely due to a lack of experience and research was get new gears installed right away. I wish I had. I plan to do so soon so the natural question is "What gear ratio should I get?" I don't tow much. When I do, it isn't especially heavy. I bought a 1500 for that reason. I love the bigger, stronger trucks but at this point in my life I just don't need one. So if you're like me and have 35-inch tires and the GM stock 3.42 differential gear (6-speed transmission), the determination on the new gear ratio now depends on what I want to do with the truck. In my case, I want to get back to stock performance/drive-ability, or as close as possible. To figure out how to do that, there is no opinion needed. It's a question of geometry and its associated math. If you Google the phrase "gear ratio tire size" you will be inundated with calculators that will tell you what you need. I picked the first two that popped up. One said my current effective gear ratio is 3.17 and I need to be a 3.98 to get back to stock. The other said my numbers were slightly different but not by much. The difference is likely because one calculator used a simple "tire diameter" figure and the other used actual tire sizes. With that info alone, I will round to the next lower ratio (numerically higher) and go with 4.10 gears. The common response to this line of reasoning that I see is "But, dude, what about the rolling mass of the new, bigger tires?!?" Great point. First off, I'm a nerd so what we should probably be referring to is "angular momentum" which is what is probably meant when people say "rolling mass." Every wheel/tire out there is rolling mass but it's the angular momentum of that wheel and tire that we're concerned about. Specifically accelerating when we're talking gears. First, a few relevant formulas: L=I*ω "L" is Angular Momentum "I" is moment of inertia "ω" is angular speed, aka how fast the thing is spinning I=r^2*m "r" is radius "m" is mass The second formula just states the obvious - a bigger/heavier wheel has a bigger moment of inertia than a smaller one. What might be less obvious is the impact each variable has. Moment of inertia increases linearly with an increase in mass but exponentially with an increase in radius. To make it relevant, if my 35s and your 37s, including wheels, are the same total weight you have a much bigger angular momentum problem to deal with than I do. You can see from this point already that accounting for angular momentum is difficult because it's based on speed. Turning your new big, heavy wheel/tire combo gets harder as you go faster so it's very difficult to account for that stress on your drive train since it changes as you accelerate. I would submit the bigger discussion here is the need for better brakes but that's a different topic. I haven't been able to find a good calculator to account for angular momentum differences with wheel/tire combos and haven't been willing to really dig down to generate an answer. Part of that is because of the speed variability. Another part is because I had had a surprisingly difficult time finding the actual weight of OEM wheels and tires. Finally, I'm not sure the difference in angular momentum makes a huge impact on the overall stress on the drive train. While The additional weight/radius of the tires is relevant, I don't know how much it matters when those wheels are still sitting under a truck that weighs over 5,000 lbs. This point is a bit speculative on my part and my instinct could be way off how in how much angular momentum affects the overall drive train forces. Real engineers, feel free to chime in here if I'm way off base. With all of that in mind, my conclusion is that changing gear ratios for new wheels and tires is hugely important because it allows you to match your differential ratio back to your transmission. The "system of systems" inside the truck were designed for a specific reason and matching your gear ratio to your new tires will get you back in that "sweet spot" the GM engineers found when they designed the truck. Using the online calculators to determine your new gear ratio based purely on the new radius or your tires is likely enough to answer the mail. Based on those calculators, I need to go to 4.10 to get back to stock. The guys that jump up and down saying 4.56 is the answer because they "like it" are potentially introducing new engineering problems in their truck by forcing all of the rotating internals to spin at a higher speed than originally intended for long periods of time. I'm not saying there aren't reasons to go to 4.56 but I would argue that gearing too low can be as risky as gearing too high if your goal is to have a safe, drive-able truck that lasts a long time. Again, I hope this is helpful and I welcome any feedback anyone has to make this info more useful.
I have the same truck as you. Purchased in Feb 2017. Time will tell but I’m two years in and haven’t had any moisture issues related to the OEM fender liners. No rust at all. The first year and a half for the truck were in Memphis. I’m in Virginia Beach now.
A couple updates. I uploaded a better clip of the tail light LED bulbs in action: I also opted to swap out the "dot" style marker lights in the tow mirrors for some Boost Auto "strip" style lights. They went in this past weekend: I have a few more items on the list in the coming months but first I need to get a little cash together.
Armo325 replied to Bucketmouth's topic in Audio, Electronics, OnStar, MyLink, Intellilink & SiriusXMThanks! The carpet on the box didn't turn out great and is something to work on for the next one. I am still happy with the result and I love the sound. As was mentioned earlier in the thread, I ran the power down one side of the truck (the driver's side in my case) and the signal cables went to the passenger side. I went with a Kicker 12CX300.1 600 Watt Mono Class D Amplifier. The sub is a Rockford-Fosgate P3SD4-10 10 inch. I have done audio work in every vehicle I have ever owned and I have always had good experience with RF subwoofers. Good luck with your project and let me know if you need more info.
Armo325 replied to Bucketmouth's topic in Audio, Electronics, OnStar, MyLink, Intellilink & SiriusXMI built my own. It was the first time I ever built a box but I wanted a sub enclosure and storage on the other side. There exists under seat storage and boxes for one or two subs but nothing that combines the two. Choices for the double cab are particularly limited.
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