What did you do to your Ram today???

[HSKR R/T]

Yep, the contact patch does increase for a 275/60/20 vs a 275/55/20. Rolling resistance also plays a big factor like you mentioned.

A 275 width tire is always a 275 width tire. Contact patch doesn't change by increasing sidewall height.

 

[R.A.M]

Just got the phone call lift kit (BDS 4inch air ride) and Tires (Nitto Grapplers 35X12.5R20) are at the shop. 2 weeks out on install date. Got my wheels Brixton Forged ready and cross drilled rotors all ready to go.

Looking at that bds lift too. If you don't mind me asking how much plus the install? Just trying to gauge how much it might run me here in Canada.

 

[R.A.M]

I think it might be the width of the tires too. My thought has always been, wider tires = more contact patch which will = more rolling resistance. not sure if that's true, but I feel like it could be.

Also you said you don't have it aligned yet so your truck can be toed in or out causing some rolling resistance.

The 275/60 will give you overall more height than the 275/55 as it is %60 of the 275 vs %55. Contact patch will remain same for both.

also, I was once told, you can think of wider tires as "skiis" vs thinner as "pizza cutter". Might sound counter intuitive but in most conditions the "pizza cutter" will dig and bite more. Although I don't know how well that's been tested. I guess older guys with more wisdom and experience

 

[Idahoktm]

The 275/60 will give you overall more height than the 275/55 as it is %60 of the 275 vs %55. Contact patch will remain same for both.

also, I was once told, you can think of wider tires as "skiis" vs thinner as "pizza cutter". Might sound counter intuitive but in most conditions the "pizza cutter" will dig and bite more. Although I don't know how well that's been tested. I guess older guys with more wisdom and experience

Yep, you're right. Pizza cutters do better in virtually all situations except sand and deep, loamy dirt. Big, wide tires just look so much better.

 

[Jeepdinger]

The 275/60 will give you overall more height than the 275/55 as it is %60 of the 275 vs %55. Contact patch will remain same for both.

also, I was once told, you can think of wider tires as "skiis" vs thinner as "pizza cutter". Might sound counter intuitive but in most conditions the "pizza cutter" will dig and bite more. Although I don't know how well that's been tested. I guess older guys with more wisdom and experience

There are a couple simple principles to keep in mind when doing the tire, lift, rear axle gear versus mpg discussion.
1. mpg is related to engine rpm (fuel usage). higher engine rpms use more fuel which equals lower mpg. i suspect this is more related to number of times each injector fires rather than duration of each injection (WOT versus partial throttle).
2. aerodynamic drag is roughly related to front cross section area (total area). so anything that increases the area that needs to push through the air will increase drag and reduce mpg. wider tires, taller truck (larger diameter tires and/or lift) will all increase frontal area. also, as you lift the truck you expose more of the underside of the truck to airflow increasing drag. 'messy' airflow equals drag. drag = lower mpg. the above 'ski' versus 'pizza cutter' analogy is correct in terms of frontal area and how the tire 'cuts' through the air when driving down the road.
3. tire rolling resistance will affect mpg but this is more complicated than just contact patch discussions. more effort to roll tire does reduce mpg. interestingly, this is affected by tire pressure and tire design (how belts and sidewall are constructed). higher tire air pressure may reduce rolling resistance, and higher tire air pressure will reduce possibility of hydroplaning. so if you're driving in heavy rain areas, it may be useful to run higher tire pressure (less hydroplaning).
4. tire weight drives how much energy is needed to get them rotating and to maintain rotation. more mass to rotate equals more fuel needed (lower mpg).

These are presented in a simplistic way as i've listed them. But you can get the idea. Lifted trucks on larger tires really start to see mpg reduced due to combination of factors all increasing fuel usage. wider tires will theoretically increase fuel usage just due frontal area increasing but the effect is probably less than the increased height of the truck. I won't get into having tires 'poke' out from the truck. This messes up the aero which decreases mpg, but it looks cool and it's safe to say that most people prefer the look. I haven't seen anyone do a 'one step at a time' mod to their truck and try to calculate each step's impact on mpg.

 

[Whoa_Ram]

Hmmm... maybe width plays a small role, but my tires are a 1/2" wider and 1/4" taller and I'm getting 1.5 mpg better with the majority of my driving in town.

I can't imagine 33's not being off by 1+ mph. If I remember correctly, I gained about 1-2 mpg after I calibrated my speedo.

Nice. Your tires are also on the lighter side within them not being E rated. Have any good pictures?

 

[zj4x4]

That is the best looking cover that I have seen on a Ram Box.

Would you mind sharing the model number and where you purchased.

It is an American Roll Cover from Trucks USA: https://www.truckcoversusa.com/american-roll-cover/

The key selling point for me was the Rack system: https://www.truckcoversusa.com/american-rack-system/

I ordered it with the racks pre-installed on the rails but otherwise unassembled from a dealer local to me in Denver named Super Trucks USA and installed it myself. I found them and a couple others using the dealer locator on the manufacturer website and shopped around for the best price.

The installation documentation wasn't super clear but if you're decently handy you'll figure it out. I did call with a question and they immediately answered the phone (and my question), which was great! The quality at installation seemed good, though it will take some getting used to this style after using a tri-fold on 2 trucks in a row. I was pleased that I didn't need to use the key system unless I wanted to. With the locking tailgate and the fact that the slide is locked by default it only provides a mechanism to open the bed without opening the tailgate, which is rarely an issue for me but I can always grab that key when I have a bike rack or am towing.

I guess this ended up being a "first impressions" post.

 

[zj4x4]

Now I get the fun part of finding fun stuff to put on the racks.

 

[Ellisstrong]

That’s what’s confusing me a lot. I tend to trust Waze with its GPS because it matched the truck when it was stock, and it still matches. When I check all the tire calculators though, I should be about 2 miles an hour off at 70 miles an hour, and as far as I can tell, it’s dead on within less than 1 mile an hour.

Do you think I should try to do a correction anyway? I’m not sure how much sense that makes, but maybe it would make a difference?

The other thing was I was doing pen and paper method on the last two tanks it was still getting crappy mpgs. Doing a correction though might make me feel better when I scroll through the menu though, lol

Your waze is linked to the truck gps and is showing the same speed as the speedometer. I have the same issue and thought for sure the Speedo corrected itself. Don’t plug your phone in and run waze on your phone and the speed should show different than your speedometer.

 

[ferraiolo1]

Or download a free gps speed app. And run that


Sent from my iPhone using Tapatalk

 

[djevox]

Your waze is linked to the truck gps and is showing the same speed as the speedometer. I have the same issue and thought for sure the Speedo corrected itself. Don’t plug your phone in and run waze on your phone and the speed should show different than your speedometer.

Or download a free gps speed app. And run that


Sent from my iPhone using Tapatalk

You guys just blew my mind. I had no idea that was a possibility for the app to gather data from a vehicle. I’ll try that today, thanks

 

[Scap]

Got this on the way home last night....so gonna see if I can get it fixed at lunch before it grows.

 

[shrubs2000]

If you are upside down in this market, then you got raped on the initial purchase. I know more than a handful of people that traded in, or sold their trucks back and made money over what they initially financed, or leased. Had a local friend just sell back his 2020 bighorn lease to dealer ans got paid $2000 more than his buyout amount and that's after driving the truck for a year.

I had my RAM for 23 months and just over 25K miles. and ended up selling it for $6K more than I paid for it. While I liked the truck, I couldn't pass up that offer.

 

[c3k]

There are a couple simple principles to keep in mind when doing the tire, lift, rear axle gear versus mpg discussion.
1. mpg is related to engine rpm (fuel usage). higher engine rpms use more fuel which equals lower mpg. i suspect this is more related to number of times each injector fires rather than duration of each injection (WOT versus partial throttle).
2. aerodynamic drag is roughly related to front cross section area (total area). so anything that increases the area that needs to push through the air will increase drag and reduce mpg. wider tires, taller truck (larger diameter tires and/or lift) will all increase frontal area. also, as you lift the truck you expose more of the underside of the truck to airflow increasing drag. 'messy' airflow equals drag. drag = lower mpg. the above 'ski' versus 'pizza cutter' analogy is correct in terms of frontal area and how the tire 'cuts' through the air when driving down the road.
3. tire rolling resistance will affect mpg but this is more complicated than just contact patch discussions. more effort to roll tire does reduce mpg. interestingly, this is affected by tire pressure and tire design (how belts and sidewall are constructed). higher tire air pressure may reduce rolling resistance, and higher tire air pressure will reduce possibility of hydroplaning. so if you're driving in heavy rain areas, it may be useful to run higher tire pressure (less hydroplaning).
4. tire weight drives how much energy is needed to get them rotating and to maintain rotation. more mass to rotate equals more fuel needed (lower mpg).

These are presented in a simplistic way as i've listed them. But you can get the idea. Lifted trucks on larger tires really start to see mpg reduced due to combination of factors all increasing fuel usage. wider tires will theoretically increase fuel usage just due frontal area increasing but the effect is probably less than the increased height of the truck. I won't get into having tires 'poke' out from the truck. This messes up the aero which decreases mpg, but it looks cool and it's safe to say that most people prefer the look. I haven't seen anyone do a 'one step at a time' mod to their truck and try to calculate each step's impact on mpg.

Good stuff.

Tire Pressure and Hydroplaning. If all else is equal (tread depth, tread design, water depth, etc.) a higher pressure WILL prevent hydroplaning at a faster speed than a lower pressure tire.

The formula is Hydroplaning Speed = 10.35 x (square root of tire pressure)

So, 36 psi means 10.35 * 6 = 62.1 mph or below and you should safe from hydroplaning. (In a relative sense.)

Go up to 49 psi and you get 72.45 mph as the speed you can go up to and be relatively safe from hydroplaning. (Again, pumping action of the tread matters. A bald tire WILL hydroplane before a new tire.)

Take the extreme of someone running 32 psi vs someone else running 65 (assume an LT tire capable of 81psi on the sidewall). The lower pressure gives 58.5 mph, the higher gives 83.4 mph.

This is why it is recommended to slow to 50 mph in heavy rains. It protects the vast majority of cars, with tread depths within wear guidelines, from hydroplaning.

This also explains why 18 wheelers go through stuff without hydroplaning while cars going slower than the trucks, end up losing control. My understanding is that large trucks run tires inflated up to 200 psi.

All the above from memory and AIUI.

 

[Whoa_Ram]

Good stuff.

Tire Pressure and Hydroplaning. If all else is equal (tread depth, tread design, water depth, etc.) a higher pressure WILL prevent hydroplaning at a faster speed than a lower pressure tire.

The formula is Hydroplaning Speed = 10.35 x (square root of tire pressure)

So, 36 psi means 10.35 * 6 = 62.1 mph or below and you should safe from hydroplaning. (In a relative sense.)

Go up to 49 psi and you get 72.45 mph as the speed you can go up to and be relatively safe from hydroplaning. (Again, pumping action of the tread matters. A bald tire WILL hydroplane before a new tire.)

Take the extreme of someone running 32 psi vs someone else running 65 (assume an LT tire capable of 81psi on the sidewall). The lower pressure gives 58.5 mph, the higher gives 83.4 mph.

This is why it is recommended to slow to 50 mph in heavy rains. It protects the vast majority of cars, with tread depths within wear guidelines, from hydroplaning.

This also explains why 18 wheelers go through stuff without hydroplaning while cars going slower than the trucks, end up losing control. My understanding is that large trucks run tires inflated up to 200 psi.

All the above from memory and AIUI.

Holy smokes I learned something new today and it’s barely 6am. That’s pretty F’n badass and I thank you. I love learning new things.

 

[MannyN]

Good stuff.

Tire Pressure and Hydroplaning. If all else is equal (tread depth, tread design, water depth, etc.) a higher pressure WILL prevent hydroplaning at a faster speed than a lower pressure tire.

The formula is Hydroplaning Speed = 10.35 x (square root of tire pressure)

So, 36 psi means 10.35 * 6 = 62.1 mph or below and you should safe from hydroplaning. (In a relative sense.)

Go up to 49 psi and you get 72.45 mph as the speed you can go up to and be relatively safe from hydroplaning. (Again, pumping action of the tread matters. A bald tire WILL hydroplane before a new tire.)

Take the extreme of someone running 32 psi vs someone else running 65 (assume an LT tire capable of 81psi on the sidewall). The lower pressure gives 58.5 mph, the higher gives 83.4 mph.

This is why it is recommended to slow to 50 mph in heavy rains. It protects the vast majority of cars, with tread depths within wear guidelines, from hydroplaning.

This also explains why 18 wheelers go through stuff without hydroplaning while cars going slower than the trucks, end up losing control. My understanding is that large trucks run tires inflated up to 200 psi.

All the above from memory and AIUI.

And where is the weight of the vehicle, the width of the tire in that calculation?
295/75R22.5 LR “H” when run as a dual is rated at 6,005 lbs. at 120 psi. That's about the max for truck tires.

 

[c3k]

And where is the weight of the vehicle, the width of the tire in that calculation?
295/75R22.5 LR “H” when run as a dual is rated at 6,005 lbs. at 120 psi. That's about the max for truck tires.

None of that matters. What matters is the pressure per unit area. Water will resist being moved. Above a certain psi, the tire wins and pushes the water out of the way. Above a certain speed, the water will push the tire up and you'll hydroplane.

Remember how I prefaced my original: "Tire Pressure and Hydroplaning. If all else is equal (tread depth, tread design, water depth, etc.) a higher pressure WILL prevent hydroplaning at a faster speed than a lower pressure tire."

Let's say your truck weighs 10,000 lbs. (You've got a load of gravel.) And, that load is evenly distributed. Each tire carries 2,500 lbs.

If your tires are at 36 psi, then their contact patch will be sized: 2,500 lbs / (36 lbs/in^2) = 69.4 square inches of contact. Each inch has 36 psi. So, if your tire is a 295 width ( 25.4mm to 1 inch) then the contact patch will be ~ 11.6" wide (the 295mm) by ~6" long. A wide, short contact patch. But, each and every inch that pushes on water is only at 36 psi.

Now, you dump the gravel. Your truck weighs 6,000 lbs, evenly loaded. Same maths. 1,500 lbs per wheel at 36 psi = 41.6 in^2 contact patch. Given your tire width, that means the patch is the same ~11.6" wide by ~3.5" long. A VERY short patch. But, each and every inch that pushes on water is only at 36 psi.

Both cases, the water has a resistance based on speed. (Jump off a high bridge, water resists like concrete: you die. Jump off the edge of a dock, and it feels great.) In both cases above, the tire "cuts" into the water with 36 psi. Hydroplaning will result ~ 62 mph and above.

Wide tires only help by gaining "flotation" in soft surfaces (loam, sand, dirt). That, again, is dependent on psi. (Airing down in sand, etc., greater surface area, lower pressure against the soft surface.) Also, traction is greater in soft surfaces with wider contact patches than narrow ones.

If you're running narrow tires, the contact patch changes shape, from your wide/short to a narrow/long. There are benefits and tradeoffs to going with one shape over another (part of which is dependent on suspension geometry). But those all effect handling, wear, efficiency, etc., not hydroplaning.

But, overally, none of that matters with hydroplaning. The tread depth, pumping efficiency (related), water depth are variables. The PSI determines at what speed those factors cannot overcome water's physical characteristics.

 

[Jeepdinger]

None of that matters. What matters is the pressure per unit area. Water will resist being moved. Above a certain psi, the tire wins and pushes the water out of the way. Above a certain speed, the water will push the tire up and you'll hydroplane.

Remember how I prefaced my original: "Tire Pressure and Hydroplaning. If all else is equal (tread depth, tread design, water depth, etc.) a higher pressure WILL prevent hydroplaning at a faster speed than a lower pressure tire."

Let's say your truck weighs 10,000 lbs. (You've got a load of gravel.) And, that load is evenly distributed. Each tire carries 2,500 lbs.

If your tires are at 36 psi, then their contact patch will be sized: 2,500 lbs / (36 lbs/in^2) = 69.4 square inches of contact. Each inch has 36 psi. So, if your tire is a 295 width ( 25.4mm to 1 inch) then the contact patch will be ~ 11.6" wide (the 295mm) by ~6" long. A wide, short contact patch. But, each and every inch that pushes on water is only at 36 psi.

Now, you dump the gravel. Your truck weighs 6,000 lbs, evenly loaded. Same maths. 1,500 lbs per wheel at 36 psi = 41.6 in^2 contact patch. Given your tire width, that means the patch is the same ~11.6" wide by ~3.5" long. A VERY short patch. But, each and every inch that pushes on water is only at 36 psi.

Both cases, the water has a resistance based on speed. (Jump off a high bridge, water resists like concrete: you die. Jump off the edge of a dock, and it feels great.) In both cases above, the tire "cuts" into the water with 36 psi. Hydroplaning will result ~ 62 mph and above.

Wide tires only help by gaining "flotation" in soft surfaces (loam, sand, dirt). That, again, is dependent on psi. (Airing down in sand, etc., greater surface area, lower pressure against the soft surface.) Also, traction is greater in soft surfaces with wider contact patches than narrow ones.

If you're running narrow tires, the contact patch changes shape, from your wide/short to a narrow/long. There are benefits and tradeoffs to going with one shape over another (part of which is dependent on suspension geometry). But those all effect handling, wear, efficiency, etc., not hydroplaning.

But, overally, none of that matters with hydroplaning. The tread depth, pumping efficiency (related), water depth are variables. The PSI determines at what speed those factors cannot overcome water's physical characteristics.

Good stuff. Much more detail than I remember from my engineering classes, and I was lazy and didn't bring the math into it. To add a little to what you're saying. Force = pressure X area or Pressure = F/A. so if your tires air pressure is constant then as the truck weight increases the contact area increases proportionally to satisfy the pressure equation. Now you can think of hydroplaning as the water has to cause an opposite force strong enough to separate the tire from the road. For a given situation, the tire pressure and contact area are constant and you basically have the air pressure working against the water pressure on road. water pressure will increase with speed. Therefore, the higher you run the air pressure the more force the water has to create to 'lift' the tire off the ground. Effectively improving your truck's resistance to hydroplaning. Or increasing the speed at which hydroplaning will occur (higher speed equals higher water pressure acting on tire). Higher air pressure won't stop hydroplaning, but it will improve resistance to it. Newer tires with full tread depth are of course better than worn tires. No matter what, the tire should be working to remove water from between the tire and road. I think it's safe to say that a tire at 65psi will 'push' the water out of the way better than a tire at 35 psi because it is applying more force to the water. I do not advocate running bald tires just because of the air pressure comments here. Run good rain tires, and if you are really worried about hydroplaning bump up those pressures a bit. Most 'comfort' tires can run 40 psi without issue. Heavy truck tires (LT and whatnot) can go much higher with their sidewalls designed for high loads. Higher tire pressures also have the benefit of reduced rolling resistance (better mpg), but you may lose contact patch (cornering ability). But you shouldn't be worried about that unless you're in your sports car.

 

[Scap]

Got this on the way home last night....so gonna see if I can get it fixed at lunch before it grows.
View attachment 109775

Got it fixed at lunch. Hopefully the glare from the fracture lines doesn't bother me too much. Otherwise, I'll be covering it with a sharpie or a sticker of some kind.

Glare is to light as rattles are to sound.

 

[djevox]

@Ellisstrong @ferraiolo1 you guys were right, Waze is drawing metrics from the truck. My speedo differences between the truck in Waze match what the tire size difference calculator on tiresize.com says.