The Stovebolt Site Forums The Shop Area General Truck Talk 1950 3100 max speed??

What is the maximum constant speed I can drive my truck without damaging it. What should the RPM be at 60mph? I have a 235 engine in it with 3 on tree
Dan

60 is probably the limit, under 3000 RPM, less is better for long periods - remember when the truck was new the roads were narrow and poor with a lot of 45mph speed limits

Bill

Hi Dan
I am just up the road from you in Burlington. I have a '51 3100 and before I changed the rear end it seemed to settle in at about 29 mpg. After the change I don't think I would want to do more than about 46 mph.
I think 60 would be unobtainable in my rig.

Peter,

What rear end did you change to (from your 4.11:1)?

If you have the standard 16" tires and the original 4.11 rear-end, the RPM at 60mph would be about 3050.

calculator (at the bottom)
4.11 rear end
27.2 rolling diameter of tires
60 MPH
1.00 transmission high gear ratio

Agree with Tim. I just had my stock '50, 3600 out yesterday and for some reason I was
paying special attention to the tach. I say stock but I have changed out the 4.57 for the
later 4.10 gear and I've installed a small SunPro tach powered by a voltage booster cube.
The tire diameter is the same as the original 15" tires that it would have come equipped
with.
At 60mph I'm running right around 3000rpm. The motor feels happiest between 2700 and
2800 rpm and I think I could run cross-country at that engine speed all day long.
When you consider the slight difference in the gear ratios and the smaller tire size
between the 1/2 and 3/4 ton trucks, it would only seem logical that a stock 3100 would be
straining at 60 mph. Pete and I drove his stock '52 to KC and back a few years ago and it
ran fine at 55mph and got the mileage that you would expect from a stock truck of that
vintage, i.e. around 15mpg plus a little. My 3600 being somewhat heavier consistently
gets a little less than 15mpg.

DG

29 mpg - that seems miraculous

Something's not right....a 3:55 gearset in my 52 lets me go 65-75 all afternoon (with tall tires and a warmed up 235). 16 mpg was about my average at those speeds.

some folks don't think about the accuracy of their old odometer and speedo - or that a different rear ratio needs a different speedo drive gear I'm with Tim, miracles are unlikely even if measured in imperial gallons

Bill

I hear ya Bill. I took mine out on the Queen's highway with a limit of 110 kmh(68 mph)where trucks will push you along if doing less and held my own. GPS is a pretty handy way of determining gauge inaccuracy nowdays.

I have heard 55 mph is fine with the original setup. I think that is what Denny said.

I am happy with that. But when I get the moola I will change to 3.55.

But then again, I need to get old blue back together and running

Talking about max speed without discussing brakes might be a bit short-sighted IMHO.

1950 3100
54 chevy 235
235/75r/15
stock rear
216 manifold
carter 787s

max speed ever
62.7mph (phone app) down hill 6% grade, tail wind
up that same hill 45mph
runs good at 50 to 55, above 60, white nuckle

avg mpg 16mpg... fill at same station, same pump, same octane

Dan,
if you can look up your tire size here The Tire Rack you will find the rev/mile. If you multiply that figure by the rearend ratio (I believe stock should be 4.11) you will get the RPM at 60 mph. In my 1 Ton it works out to around 2700 RPM. I do run at 60 mph when required with no problem with my 216, however most of my higher speed driving is done at 50 mph.

Denny
what size/type tires are your running?

Lets just say that I wanted to "validate" the size of my tires. How do you measure the diameter. Parallel to the ground or perpendicular? I'm thinking parallel, but I'd like to here your thoughts. I know I can read the markings on the tire and look up the size on line. I want to be able to compare the two numbers to see how accurate they are.

Right now my 58 Suburban, '78 250 six, stock 3 on the tree and stock 3.90 rear, runs at 3,000rpm at 55mph according to the GPS. I have been told "you're running pretty short tires." They are cool looking white walls, but not that great for highway cruising. The speedometer in the truck also reads 5mph fast. So at 55mph on the GPS it reads 60mph. I'm thinking that if I get a little bit taller tires I can correct the reading and get a little better cruising revs.

On a related note, I'm running all stock original drum brakes. The truck stops straight and even. I think the previous owner did a brake rebuild before I got it. It actually drives quite nicely on the road.

Cooper SRM-II, Radial LT, 8.75R16.5LT. Took another ride
yesterday and paid a little more attention to the tach. 2500rpm
= 55mph, 2800rpm = 60mph. This taint scientific now, with
everything bouncing around at 60 I could be off by a bit and
remember this is a $29 tack a 62 year old speedo and not the
original tires and not the original rear gear. But it's close.
I usually read a few miles per per hour slow when I run thru
the speed minders, don't know how accurate they are either.

The best way to figure the tire diameter is where the rubber
meets the road. Draw a line on the tire in line with a spirit
level and mark this point on the garage floor, roll the truck
across the floor till the line makes a complete turn, mark the
floor and measure the distance (circomference).
Diameter = Circumference over Pi (3.1416).

dg

I think the miracle was only a typo.. Reads to me that Pete meant to say 29 "mph" with the old gears not mpg.

That is sad to hear, 29mph in high gear. We used to cruise 15-20mph faster than that on 2-lane country roads in my '48 1/2 ton panel with the 4.11 rear-end and a tired old 216.

Denny;

Hooah. Thanks. I'll give that a try.

you can run these at 60 all day long. I drove my 53 with a 216 for 28 years that way, still do, but its a different engine. (still a 216) Today though, I am in the midst of installing the 355 gears, then I will be completely confused.I agree you should make sure the brakes are good. You don't really need discs, although they do work better, my uncle had a 69 roadrunner, would do like 160 MPH, all it had was drum brakes. Not saying it was the right thing, but then again they hit a horse doing about 130 in it too....

reply to tclederman
I changed the rear end to 3:55 and it made a big difference.
But, there must be something else missing because there is no way I could go highway speeds.
Spring is almost here and I hope to have the truck on the road this year (for sure this time) and I will be able to give him a real run and see he'll do.
Also, yes that was a typo - meant to say 29 mph not mpg. Sorry if I confused.

Peter,

Have you done a "time trial" on a highway that has distance markings? If you do, go 30 mph for 10 marked-miles and measure the amount of time it takes. Calculate the miles per hour.

As red posted above, when you change rear-end ratio (and tire diameters), your odometer's MPH will be off.

I'll take it out when I finally get it on the road this summer. I used my Garmin briefly on a quick road test last year and was doing about 46 mph which I thought was about as fast as I wanted to go safety wise.
I used to be navigator for a rally team and am familiar with the speedo calibration run - although that was in the last century and we have now gone metric in Canada. Nothing is simple anymore!

I did 200mi straight in a day at about 60mph. No speedo back then but I hung with slower traffic on the interstate. Managed to pass some too. My truck ('51 3100) has a mostly rebuilt 216, 3OTT, 4.11 and 7.50x16 tires.

Having 3" more tire definitely helps keeps the revs down for that old 216

What is the outside diameter of the 7.50x16 tire? Thanks

I would say it is about 31" in diameter give or take 1/2"

A 31 inch diameter will have a 97.3 inch circumfrence if you need that.

Curt B.
What size "tall" tires do you run in the back? My truck has the stock rear axle and currently has old 28" tall tires. I'm shopping for radials and thinking I should get a little bit taller tire for easy cruising.
Thanks

Mine are 255/70/15's which are listed as 29.1" tall. I bought them before changing the rear gearing and in retrospect I could have gone a bit shorter and still had sufficient highway speed. Personally I find no shortcomings with the stock brakes in as new condition and have no intentions of a disc brake upgrade.