81 replies to this topic

[rando]

Unfortunately, its not same loads:

     For loaded F-150  "loaded with 1,500 pounds of rock salt"

     For loaded F-250  "When loaded at max payload"

Ford brochure lists 2018 F-250 max payload at 4250 lbs.

 

Indicates that the F-150 in a panic stop should not be affected by the load of a 1500# camper.

 

Would be interesting to see what the stoping distance of the F-250 would be with the same 1500# load.

 

Shorter stoping distance of the loaded F-150 due to rear tires having more contact? 

 

True on the loads, and disappointing that they didn't explicitly state the loads in the other tests.  But it backs up my point - an F150 with a 1500lb load (plus driver + passenger, which is ball park what an FWC weighs) still stops faster than even an unloaded F250.    Similarly a loaded F250 stops faster than an unloaded F350.   

 

None of this is really surprising as in each truck I am sure the brakes are sufficient to stop the wheels from turning, which is confirmed by the discussion of the ABS.  This would indicate that the stopping distance is determined by other factors than the brakes - tires, abs programming, electronic brakeforce distribution programming, and apparently weight. 

 

I doubt the shorter loaded distance on the F150 is actually significant, they don't quantify what the uncertainty is for these tests, but I would be surprised if it were repeatable to 0.1'.  But the fact that it doesn't change with load suggests that Ford has a good implementation of EBD in the F150. 

 

The variability between the different models also explains Vic's experience.  Some combinations of weights/tires/programming work better than others, and looking at the Tundra, it performs particularly poorly and doesn't have very good 'brake feel'.

[Stan@FourWheel]

I always wonder about this too.

 

Our 2012 Tacoma show truck with a full loaded Fleet Model and tons of gear (heavy) always felt like it would stop MUCH faster than our loaded Dodge Ram 3500 Diesel with a Grandby Model on it. The Tacoma was just so much lighter.

 

I wish I could have done a real test before Tom took the Tacoma.

 

But that said, all of my 1/2 ton trucks, the brakes always seemed like the weak point.    

 

1987 Ford F-150

1997 Ford F-150

2000 Ford F-150

2005 Tundra Access Cab

2004 Tundra Double Cab

On all of these trucks I have had, the brakes always seemed wimpy when I was fully loaded with a camper, food, gear, water, and family.

 

That said, these are older trucks.

 

The New Tundra trucks have much bigger brakes and it doesn't seem to be as big of a deal !

 

 

 

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Edited by Stan@FourWheel, 28 January 2019 - 07:15 PM.

[PaulT]

Part of the brake feel in the Toyota’s is likely due to the Japanese preference for “soft” pedal feel as compared to US and European consumers. I chose an Isuzu Impulse over a Honda Accord in 1983 partly for that reason. I was told later that the Impulse was largely an Opal (German/IItalian) product design rather than a Japanese design. The Isuzu brakes were great with a pedal that felt very firm. The Honda brake pedal felt like stepping on a balloon.

Similarly different feel between my father-in-law’s Dakota brake pedal & my 2010 Tundra although I believe the Tundra brakes stop faster with a load. It just never feels like stepping on a brick like the Dakota.

My $,02
Paul

[Andy Douglass]

Can we complicate the brake thing more and add in exhaust brakes? I wonder if a HD truck with an exhaust brake could stop quicker than a 1/2 ton. Anyway, my comments about brakes in my earlier post were not so much about stopping distance but brake fade, which to me is a bigger concern anyway since I keep several football fields between me and the vehicle in front of me. One of the key differences between 1/2 tons and HD trucks is heavier brakes, and its like that for a reason. Heavier brakes are better for hauling heavy loads. There's no question that people can successfully carry a slide in camper on a half ton, as long as consideration is paid to the weight. Hauling our camper in our 1/2 ton worked, but I had to worry about weight as well as make the suspension upgrades. To us, it is worth it to take a lot of worry out of the equation with the 3/4 ton. It took 2 hours for FWC to wire the new truck and that is all I need to do to it.

 

And as others have said, the maintenance schedule and longevity of diesel motors make them completely viable once you get past the big investment up front. I'm not sure why the one poster thinks DEF is expensive. I think it is about 10 bucks for 2.5 gallons at a quik stop, which is the most expensive I have seen it. I think that lasts approx. 1500 miles? Probably more, DEF is used up so slowly I haven't paid attention to how long it lasts. I remember hearing about people buying those Mercedes sprinter vans and being raked over the coals buying official Mercedes DEF to avoid warranty issues. Maybe thats where that came from?

[ntsqd]

If you're keeping several football fields between you and the vehicle in front of you, you're clearly not driving in KA!

 

Something that caught my eye about brakes a page or so back. There is no variable in the Brake Torque formula for the pad's surface area or the rotor's swept area. It is only interested in clamp force (line pressure times piston area) [F], the pad's Coefficient of Friction (at that specific time - they vary with temperature) [m], and the distance from the center of rotation to the Centroid of the pad [R]. T = Fm X R

 

You can change the pad to one with a different Cf, you can change the rotor's OD (which presumably changes the Centroid distance), or you can change the clamping force to change disc brake's torque. Of the three the pad is the easiest and the rotor OD seems to be the most effective means to increase braking torque.

 

Our '91 Suburban had ABS right up until it took away braking when I needed it badly and caused the truck to fly. Something it really wasn't designed or equipped to do. Once I did get it stopped I ripped the connector out of the ABS control unit and never plugged it back in.

Threshold braking is an art form and doing it well takes frequent practice. A good ABS system will do it better than you can. A bad one will cause flying trucks and other undesirable conditions. I've never noticed the rear only ABS on our '96 CTD, and the light isn't on so presumably it does work.

 

Pedal feel is highly subjective. The two best that I've ever owned was my '84 VW turbo-diesel Caddy (pick-up) and my '88 V6 4runner.

 

Exhaust brakes are more like the "drag brake" on a tandem bicycle than a normal Service Brake. In some places and by some mfg's they referred to as a "Speed Retarder" in that they are intended more for holding a speed when the vehicle would accelerate w/o it. Not to say that they can't or aren't used as part of the service brakes, just that they were designed with a different goal in mind. That was to create a speed retarding function in a diesel engine that worked the way that closing the throttle on gas engine works to maintain or slow a vehicle.

[JaSAn]

 . . . my comments about brakes in my earlier post were not so much about stopping distance but brake fade, which to me is a bigger concern anyway since I keep several football fields between me and the vehicle in front of me . . .

 

To my thinking panic stopping distance is the more important metric because you cannot compensate for it.  You can't keep a football field distance between you and a child darting out into the street from behind a parked car or a deer running across the freeway.  Brake fade can be compensated for by going slower, using engine braking, stoping more often to let your brakes cool.  But an unanticipated crisis in front of you cannot.

[klahanie]

Something that caught my eye about brakes a page or so back. There is no variable in the Brake Torque formula for the pad's surface area or the rotor's swept area. It is only interested in clamp force (line pressure times piston area) [F], the pad's Coefficient of Friction (at that specific time - they vary with temperature) [m], and the distance from the center of rotation to the Centroid of the pad [R]. T = Fm X R

 

You can change the pad to one with a different Cf, you can change the rotor's OD (which presumably changes the Centroid distance), or you can change the clamping force to change disc brake's torque. Of the three the pad is the easiest and the rotor OD seems to be the most effective means to increase braking torque.

 

I looked up the brake specs Ford gives for a 2019 F250 vs F150 HD. No surprise the F250 is bigger in most measurements listed but what stood out is the rear caliper dual piston and accompanying larger pads:

 

F250: Dual piston, 2.01 in Dia,/ Pad Area, 9.89 sq.in./ Gross lining area per axle, 39.6 in.

F150: Single piston 2.13 in Dia,/ Pad Area, 3.88 sq.in./ Gross lining area per axle, 15.5 in

 

Perhaps that's excess braking capacity in an empty and lightly loaded F250 but presumably the greater "F" available is useful when there is a heavy load on the rear tires. (what the truck is designed for). And the rear is then able to contribute more to stopping the vehicle. Don't know if the brake boosters make a difference in line pressure between the two vehicles (also, my diesel is hydro boost).

 

---

 

The F150 HD, can have a very respectable +3000 lb payload capacity, in the range of some F250s, but I see the rear brakes as being a bit different. Might just be the limit of the F150 series, IDK, whereas the F250 shares the brakes of the F350.

 

As for changing tires, I believe it because I've experienced it with a car. For 1/2 tons I've read of many folks changing to (heavier) E load rated tires. Wasn't clear to me what was used for the test but I wonder the affect adding rotational mass would have on stopping distance. I believe if the radius is bigger, more force is required to stop. Whether all that would fall within the OE brake capacity to stay at the edge of the ABS kicking in, IDK.

 

As for whats more important, panic stop or lessening brake fade. I'm voting for both ! It's surprising how little you may need to use the brakes when driving with just a modicum of attention on the highway. But city and off highway, esp in the mountains, it's a lot tougher, careful driving notwithstanding. I expect my brakes are going to get warm or even hot, and they still need to be there when I really need them.

[klahanie]

Re: the "modern diesels are high maintenance vehicles" comment. I think if a prospective buyer is going to look at maintenance, then consumables cost is as important as required frequency. Because the poster missed mentioning that angle, I looked it up ...

 

According to RockAuto, for my era truck 5.4L gas vs 6.4L diesel:

 

Oil filter: $3.39 vs $17.31

Oil capacity: 7qts vs 15qts

Fuel filter(s) $12.20 vs $45.79

DEF: Not required

 

These are all Motorcraft brand - after the diesel engine up charge, I'm not using anything else.

 

I didn't look up frequency for the gasser and besides,newer trucks might be different. But in my case, the diesel costs more to maintain. The only reason I bought it, is the only valid reason I could come up with - I simply wanted one.

 

... and, fwiw, I could use the same reasoning for the whole 1/2 ton, 3/4 ton question.

[Bill D]

F250: Dual piston, 2.01 in Dia,/ Pad Area, 9.89 sq.in./ Gross lining area per axle, 39.6 in.

F150: Single piston 2.13 in Dia,/ Pad Area, 3.88 sq.in./ Gross lining area per axle, 15.5 in

 

Thanks, good info.  That's a substantial difference.

[ntsqd]

Where the pad area makes a difference is in pad friction material volume, which translates into how long the pad will last in any given set of driving conditions. That is really the only place that I know of.

 

I wouldn't read too much into the rear caliper piston size and number. The ABS will dial rear braking back until it doesn't skid. Which means that the designers can put more rear brake on the truck than it should ever need, tempered by what the cost accountants will let them do, and the ABS will keep them from locking up.

 

In the old days 1200 psi was max effort, panic stop line pressure regardless of the booster size or type. Boosters, as originally designed, were intended to achieve that 1200 psi with a lower pedal effort. Not to raise the line pressure. With the advent of ABS some mfg's have stepped that up to 2000+ psi and they may be using the booster to do that.

 

EDIT: Not that it's something that anyone here would do, but some racers in limited classes would grind or machine the friction material off the lower part of the pad. That moves the Centroid up increasing Brake Torque by just a little bit. In classes like those every little advantage adds up.

Edited by ntsqd, 01 February 2019 - 02:30 AM.