Forum Discussion
158 Replies
ShinerBock wrote:
This website will help you find the grade of that road. It is made for cycling, but you can select to follow the road. You will have to select start and the click the where you want to start on the road and then click again where you want to end. Then select show elevation and gradient to see those.
If this is the road then Cummins is right. It even gets steeper than 14% in some areas.
Mapometer
This was in 2016 after going to DRV and MORryde. I remember a lot of it being very steep! I was honestly thinking I may have to up shift when at 3,200rpm in second. But it held there. It was exciting to be honest!4x4ord wrote:
Cummins,
I think I know the place where you are talking of the 14% grade. Is it highway 12 south of Boulder UT? The highway drops down to Calf Creek campground and you reach the bottom of the hill at Escalante River. The highway is marked at 14% so some short stretches must be that steep but if you actually take an elevation reading at Escalante River and another reading 2.5 miles north east of that point the average %grade of the highway over that 2.5 mile stretch is only 5%. Maybe this helps explain how your truck can hold back 33k lbs on a 14% grade.
map
I am sure that was the road.
Good explanation. Like I said it was wound tight at times. But a 5% grade is nothing for my combo.
I never run auto.- This website will help you find the grade of that road. It is made for cycling, but you can select to follow the road. You will have to select start and the click the where you want to start on the road and then click again where you want to end. Then select show elevation and gradient to see those.
If this is the road then Cummins is right. It even gets steeper than 14% in some areas.
Mapometer - Cummins,
I think I know the place where you are talking of the 14% grade. Is it highway 12 south of Boulder UT? The highway drops down to Calf Creek campground and you reach the bottom of the hill at Escalante River. The highway is marked at 14% so some short stretches must be that steep but if you actually take an elevation reading at Escalante River and another reading 2.5 miles north east of that point the average %grade of the highway over that 2.5 mile stretch is only 5%. Maybe this helps explain how your truck can hold back 33k lbs on a 14% grade.
map Me Again wrote:
^^It does not, at least on our 2015 RAM's. FWIW that is a really stupid thing for them to do. The uninformed could get their brake REALLY hot and not know it.
I haven't played around with my Ford while towing on steep grades enough to know exactly how the Ford cruise control works but it certainly does apply the wheel brakes. I think it applies the brakes to slow the vehicle down and also causes the transmission to downshift. It is possible that the wheel brakes are then released to allow the engine to hold back on its own.
The automatic mode on the exhaust brake is what I use and it works excellent. You simply set the exhaust brake to automatic and the truck tries to maintain the speed the truck was going at the moment the brake pedal or accelerator was released. So say on a steep grade I have the exhaust brake set to auto as I come over the crest of the hill. If I let off on the accelerator at say 60 mph the EB will try to maintain 60 mph. If the truck starts accelerating down the hill the system will adjust the turbo vanes to produce more back pressure. If the truck continues to accelerate the system will apply the wheel brakes which will trigger the transmission to start downshifting at which point the wheel brakes automatically release and the EB adjusts to maintain the desired set point. If the EB can not maintain the set speed the wheel brakes will be applied again causing another downshift (so long as the downshift results in an engine rpm within the limits of the engine). If the transmission can not downshift further and the turbo vanes are maxed out the wheel brakes are applied momentarily to gently bring the truck back to its set point at which time the wheel brakes release until the truck gets going too fast again. If I know the hill is long and steep, I can touch the brake earlier which will cause the downshift to take place without the truck accelerating first. If I want to slow down a little more I simply brake to my desired speed and let go of the brake pedal .... now the new speed is set. If I want to speed up a bit I simply accelerate a bit and the speed i'm travelling at when I let off the accelerator becomes the new set point.
Edit: When the wheel brakes apply they come on very smoothly. If the dic is set to "towing" the amount of trailer brake power is displayed during the brake application. The other indicator is that if I watch in the mirror at night I can see the brake lamp glow reflect off the front of my trailer during the brake application.
Cummins: I can't help but think this is how the Ram system works while on cruise. If you're on that steep grade again it would be interesting set the EB to "on" without using "auto" or cruise and see if it still holds back.- I would probably not believe my story if I were reading this. There were some tighter curves on the road that I did brake for just to be safe as I always do on an unfamiliar road.
It was wound TIGHT for sure! I was over 3k a bit but not by much. My redline starts about 3,200rpm. If I remember correctly I had to have cruise set at least 5mph lower than the speed I felt was safe.
I am so glad I had plenty of downhill experience before this grade using cruise control or I most likely would have been heating up the brakes!
We were heading from Hanksville, UT Blondie's Famous Burgers to Bryce canyon. Maybe Hwy 12 it was a two lane road. Cummins12V98 wrote:
I have posted the picture of the sign several times in the past. Is says “14% NEXT 4 MI”. I’m having trouble posting pics. It was several miles and it was STEEP.
It was second for sure. I can’t lock first and can’t go 30-35 in first.
I believe you..... I'm just having a hard time time understanding it..... Here's my thought process:
If it takes 430 reverse HP to hold your unit from accelerating on a 14% grade, and if 40HP comes from drag and rolling resistance the driveline needs to account for the other 390. If 60 HP is lost through the driveline the engine would need to generate 330 reverse HP. Spinning the engine around at 3000 rpm, without an exhaust brake, might take about 75 HP. So, the exhaust brake would have to generate another 255 negative HP. If the engine is thought of as an air pump it would be pumping 6.7 x 3000 rpm = 20100 liters per minute of air = 710 cfm.
Pumping 710 cfm @ 100 psi above atmospheric pressure requires about 180 HP so I am left wondering where the additional negative 75 HP could be coming from. (and that would be with 100 psi back pressure which I believe is more than your exhaust brake would generate)Me Again wrote:
4x4ord wrote:
Me Again wrote:
4X4ord. 2 gear(2:1) in a Aisin and 4:10's out back is going to hold back a lot on the full exhaust brake setting. If the VGT exhaust brake makes 75HP of braking, then in 2 gear wouldn't that equal 600+ hp of braking at the rear wheels?
AT that weight, what speed would 600 hp hold.on that grade. You seem to be able to compute the numbers going up, so you should be able to computer them coming down. I know at 24,500 in 4th(1:1) and 3.42 out back, I had to step on the throttle once in a while on 6% grades to not slow down to much. Would that not be 225HP of braking at the rear wheels?
Torque is multiplied through gears not power.
So if torque is what gets a load moving would in not also be needed to slow down a load?
Sort of. It takes a force on the outer edge of the tires to hold the load back. The force on the outer circumference of the tire can be very easily approximated .... on a 6% grade the force is about 6% of the truck and trailer's weight. (actual value is 5.989) and on a 14% grade the force is about 14% of the weight of the truck/trailer. (actual value is 13.865%). (At steeper grades the error gets a little out of hand so on a 30% grade the actual calculation would be 28.73% and on a 100% grade the actual value would be 70.7%)
When the engine is holding back this force on the outer edge of the tire is producing torque on the rear axle. So the the radius of the tire is the length of the torque arm. So 6% of 24500 lbs is 1470 lbs of force. 1470 lbs x a 16 inch tire radius gives a torque of 23520 lb inches or 1960 lb ft on the rear axle. When this torque is moving backwards through the driveline gears it gets reduced. So the 3.42 axle reduces the torque to 573 lb ft of torque. The transmission could further reduce the torque. So in your case with the transmission in direct 573 lb ft would be required on the crankshaft to hold the truck from accelerating.
If you have 32" diameter tires your rear axle will be rotating 578 rpm at 55 mph. The reverse horsepower at the rear axle is 578 rpm x 1960 lbft of torque/5252 = 215 HP. Now the engine is going to be running 1977 rpm at 55 mph in 4th gear so the reverse HP at the crank is 573 lbft x 1977 rpm/5252 = 215 HP. (torque is multiplied through gears ... not power)
In actuality wind resistance and rolling resistance acting on the truck and trailer will reduce that value to something more like 115 HP. Then inefficiencies in the driveline might further reduce it to something like 100 reverse HP.- The new Powerstroke did a good job here. However, with the water cooled intercooler on the PSD, I don't think it would have the same outcome if the outside temps were in the 80's instead of in the 20's.
Intake temps play a huge roll in how much power a diesel engine can sustain and just a 10 degree difference in outside temps can increase/decrease EGT's by as much as 50 degrees causing the engine to pull fuel and power to keep them in check. One of the draw backs of a water cooled intercooler is that they get heat soaked under heavy load for long periods of time because the coolant that is keeping the intercooler cool is also getting hot. This is fine in cold weather, but not so much in hotter weather. - A way to understand gearing. Take a 25lb weight and hold in your hand.
Start with it close to your body = lower gear ratios.
Now extend your arm until it is straight out = higher gear ratios.
The 4,6, or 10 steps of extending your arm would be the shifts through the gears from 1st to the top gear. The amount of effort for you to hold the weight is like torque. The amount of effort to hold it over time is power.
