RPM vs Speed vs Tire size

[SuperJoe]

Quite a few conversations have been about getting more speed from the deuce, changing the tire size, engine rpm, and safety. The normal speed for all stock trucks seems to be aprox 48 to 52 MPH. This is at a engine speed of 2300RPM. Some people will "push" the engine to 2600RPM for that max at 55-58 MPH. Some will change tire size to get same speed but less engine rpm, to save the engine. And there are those with the overdrive upgrade. All these options for more speed then get the other half riled about safety. With such a low speed relative to todays traffic, and also the weight and low tech of these old trucks i do see safety being an issue on both sides of the coin.

What do you fellas feel is the best in all situations? Engine life speed, road speed, tire size, and stock or modified parts to achieve your views.


Being mostly conversation, but still about modding the deuce this is where i thought the thread should be. If this should be in the conversation area could a mod please move it.

 

[Ford Mechanic]

I'm running the 395's and I am hitting 55mph or so at about 2000rpm. It's hard to watch the gps and the road so 2k is as fast as I go. At that speed the speedo shows about 42mph. I don't care to go any faster. I do pay close attention to stopping distances though, and take plenty of time getting to 55. If the folks don't like it behind me they can pass.

My fdc is by-passed, Pyro coming soon, WMO 80% for fuel, spring perch flip for more caster, and the 395's. Brakes have just been gone through and axle seals redone.

 

[SCSG-G4]

Engine life, since I have to depend on others to swap out engines and rebuild them.

 

[redrocket78]

I don't take mine over 2400 rpms. About 52 mph. Stock drive train. They engineered it this way and it works. Not changing it. I'll get there when I get there.

 

[jwaller]

I've got all the bells and whistles on my deuce. I run 65mph. I could run 75 if I wished but 65 keeps it off the redline and keeps speed with most traffic on the interstate.

 

[Amram]

I run at about 55 MPH at 2000 rpms. I did it to extend the life of the engine. Also the truck looks way cooler with those 395 MVT's on it. Oscar loves to boogie down the highway.

 

[patracy]

Depends on my mood honestly.

Sometimes I'll run it at governed high speed with the 395's. (Driving to the Rally on I-20) Other times I'll run 55.

I've got the means to replace anything as well. (And have )

 

[SuperJoe]

jwaller what size tire do you have?

patracy what is the governed speed?


i think i want to run the 16-20s on mine (since i have some) and im just looking for an rpm at about between 65 and 70 Mph. no reason for faster than that. its only about 10 minutes per hour difference in seat time.

 

[Amram]

2500 RPM is governed speed on most trucks. My IP starts backing off around 2500.

 

[patracy]

Mine pulls to 2700-2750.

 

[sandcobra164]

I'm on 11R20's and the speedo is only a little off. Mine loves 48 MPH indicated which is 53 or so ground speed. I like the idea of 395's, they equal 55 for 42 indicated? That sounds like the way to go and if you can post some evidence proving that, 395's are my next procurement project. I've also been top to bottom in my truck to include wheel cylinders, master cylinder, air pack and soft lines. On flat ground, it could easily pull a taller gear or taller tires.

 

[steve6x6x6]

I don't take mine over 2400 rpms. About 52 mph. Stock drive train. They engineered it this way and it works. Not changing it. I'll get there when I get there.

My A3 on the stock tire 14.50 x 20 to get 52 mph was 2,950 rpm.

 

[shannondeese]

I commute 100 miles everyday with my bobber with 395's. I cruise at 2300 RPM on the I-5 in So-Cal. Indicated speed is 50 MPH. Not sure what my actual speed is but it's fast enough for me.

 

[Rambling Wreck]

My A3, according to GPS, goes about 47mph at 2,700rpm (with stock 14.5 x 20). I really don't like to run it wide open like that, just to stay above the minimum interstate speed. Ideally I would like to run about 60ish mph at 2,100rpm.

OP, You are a brave man to open this can of worms.

 

[SuperJoe]

its an all can participate thread. anyone that has noted there speed can get in on this. there is no opinion or best, so far, and that was how it was intended. so we can share and compare ours to others. there is a formula to dictate the mathematical speed of things. i dont know what it is, but i wanted to compare it against actual real life situations, that have many more variables and across a wide range of locations and driving styles

 

[LowTech]

We run two on most of our travels, the She Beast is on mod'd Hemmts w/ 395s. Mine, the little Draggin' is still running stock 900x20s.
She has about a 300 RPM drop when we are going the same speed. When I'm running 24/25 hundred she's around 20/21. She has no trouble pulling away from me on the flats and down hills, . . . come to a long grade and I can run circles around her Her rig is weighing in heavier than mine as well. I've got an almost empty 105 hardtop and an empty truck bed, while she pulls a 105 w/ extra fuel.

I've heard that it's 15% added on when you go from 900x20 to 395s. 50 on the speedo would be 57.5. From the last 4000 miles of travel, I'd say that's about right.

 

[gimpyrobb]

I have found that 2500rpm is about 63mph with my 395s, thats about where I run it. The smartest choice(imho) would be 1100s with the overdrive kit. You get cheap 1100s and still have the speed. If you need to go crazy places, 1100 chains are easy. I would have gone that route, but 395s were cheaper then. They are very popular now and are $$$!

 

[LowTech]

Can you get a good / cheap / two piece / tubeless rim for them?
I'm debating the use of 1100x20 w/ myself right now.

 

[gimpyrobb]

Not to my knowledge. The stock rims have many advantages imho, I would use them. If singling out a truck, I would look for the off-set 135 rims.

 

[11Echo]

Same truck, different tires. Garmin verified at indicated 2600rpm.

900-20 55mph
1100-20 64mph
14.5-20 64mph
395-20 72mph

These are top speeds reached. I do not drive around at 72+ mph with the largest tires. I do spend a lot of it running 55-65.

My deuce trucks seem happiest running 43" tires. You start losing noticeable power with the 395's and larger anywhere but on the flats.

Even spotting my bobb'd deuce that has 395 Goodyear MVT's a head start, my M35 with 1100 NDC's will catch and push it up the second half of a long grade.

I ran 1400's on the bobb'd deuce and took them off. I wouldn't run 1600's on a deuce unless for ground clearance and hauling it to an off road park and likely using low range to get around.

YMMV

Useful tire size link. Army Military Tires