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math question

R

Ralph 1111

Member
I want to increase my tractor speed from 7 mph to 12 mph I have a
1942 Allis Chamers C ,with 24" wheels now
What size of wheel do I have to go to acheive this increase in mph? Does anyone know what size of wheel I have to? I do have the ability to fabricate and weld the centers for the wheel.
Thanks in advance for all help with this matter.
Mathemathically challenged.
I want to increase speed for tractor rides.
a1243.jpg

a1243.jpg
 
You need about 40% more circumference on the rear tires. If yours are now 36 in height C=PIXdia. 3.14159X36=113" 113X.4=45.25more inches needed. 113+45.25=158.25 158.25/pi=50-3/8 inches. so a tire of about 50 inches total would do it. The math is approximate, but rounded in places. I do not know what the real diameter of your tires is. JimN
 
Wheel size and tire size matter. For instance if your tire now are 9.5X24 and you switched them to say a 12.4X24 you would increase you speed a lot. How much I do not know but its not just wheel size but tire size that matters. Now yes you might be able to find a 28 inch rim that could be made to fit but again tire size will matter a lot also. And you also have another factor. How much will the engine pull in which gear. You might end up with a fast tractor that will only pull on flat ground or down hill
Hobby farm
 
Along with that you will have a very tall AND narrow tractor. Something called the center of gravity is kind of important. Better off finding an overdrive gear/gearbox IMO.
 
Not going to trudge through the snow to check now, but sounds about like a 28 inch wheel from a WD45 or D17 would be about right, and with gary's comment, he should put duals on to maintain stability.
 
I came up with the same numbers, but you posted first. So I'd say that some 28's, maybe like you might find on a Farmall C, could come pretty close. Of course, you might have to re-gear to turn 'em, but look at how your fuel economy would improve...since you'd always be going downhill.
 
I doubt very much that you have enough power to move up 40 percent in top speed, maybe a good hill would suffice.

Walt
 
Looks to me like someone needs to recheck their math. To go from 7 to 12 mph is a 70% increase. That would mean if the tires are now 36" dia. they would neeed to be about 62" in dia. to make that speed.
 
How can he increase speed by going with a wider tire? Thats like saying if I replace the 14.9x38's on my tractor with 18.4's I will gain speed. It doesn't work that way, a wider tire might have a very small height differnce but not enough to do what he wants to do.
 
Hi Blinwmi, You are correct that usually wider does not mean taller but in many cases it does. For instance in my Firestone farm tire data book it shows 13.6-38 OA diam. 61.5 in. and 20.8-38 at 72.4 in. as you look around you see a lot of different types of construction especially in the newer metric tires.
 
With some clubs they require a speed like that to participate, makes it a little safer on the roads against other traffic. Our anual show is kicked off the night before with a parade thru town with the police at every intersection to control traffic and to participate we must be able to travel 12 MPH (not sure but think the city required it to get permission for the parade so as to not disrupt the flow of traffic too bad)
 
Huh?????? 5MPH increase out of 12 is 41%. Can't find the link to the Firestone tire chart. You can just look there and figure out what size you need based on the needed increase to the size you've got. Your biggest challenge may be getting hubs. once you figure out what size you need, post this on the Allis forum for ideas on how to get there. There may have been a "high crop" option for veggies that may work. Good luck
 
I would go about this from a completely different direction. I would try to use a trailer with an automotive style rear end flipped over to be the correct direction and run it with the PTO. You would still need to figure out the appropriate ratio and tire size. Now you still have all the original gears and the original tractor, just engage the PTO for the higher speeds.
 
One other thing to remember, when you increase wheel diameter by a percentage you decrease effective braking by the same percentage.
 
First off, I don't think this is a good idea.

If you want to anyway... Here is my stab in the dark:

Factory top speed: 8.5mph
Factory rear tires: 9-24 (apx to 124" rolling circ)
Factory governed rpm: 1400

Raise the governed rpm by 20%, to 1680rpm
Change the rear wheels to 13.6-24 (apx 139" rolling circ)
New ground speed: 11.4mph

The tractor wasn't really built for this type of operation. Seriously consider what you want to accomplish before you spend $800 on rims and tires. $800 will be a good start on another tractor that could go that speed without heavy modifications. Good luck.
 
The tractor "looks level" now. If you put on
higher rears the nose will be downhill and the
oil will run to the front of the pan, and you
could starve the rear bearings.
(I don't really know this, and am just "pulling
your leg", but it's something to think about.)
 
RAW in IA has it right. His "top" speed is now 7 mph. He want to add 5 mph to this. 5 divided by 7=.714286 % increase. 7X.714286=5. 7+5=12, which is the speed he wants to go to.
If you only add 41% to his original speed, he'll only get a little less than 10mph out of it.
 
Anything inside the diff or those final drives that can be swapped from another model/version of an Allis for higher ground speed? If the finals are chain driven a speed increase is easy but......1st and reverse are going to be way too fast.
What sort of rpms does she run now? I hesitate to suggest the concept of "hot rodding" it for some more rpms but it could work. She would look stock and still have a reasonably slow 1st and reverse gears.
It wouldn't take much to add heavier valve springs,aluminum pistons to reduce reciprocating weight and balance the bottom end. She would run super smooth.
Being rated at 1500rpm, 23.3HP with 5.75 to 1 compression, 3.375 X 3.50 bore and stroke and weighing 3000lbs.
It wouldn't cost very much to get a set of four of these automotive sized pistons made. With today's 87 pump gas she could go 7 to 1 compression for for hill climbing power without knocking.
 
Most have aluminum pistons already and at least 7:1 ratio. The engine could easily handle 2000 rpms maybe need heavier valve springs. But pretty easy to make taller rear wheels. I made 38" for my WC in 6 hours and having never done it before. They run as true as a new wheel. Then you could put taller front rims on too like 19". I think that would be the route I'd go.
 
I agree with Dave2. Please don't ruin that pretty little tractor. If you have to run 12 mph, buy a tractor that will do it in stock form. If you are going to be in parades a lot, you need reliable brakes. A Ford 600-series with a Sherman over-under will do in the 30's if you want to go fast.
 
I went through the same exercise trying to get my C with woods mower to move faster in 2nd gear. I used the titan tire size chart to make my diameter assumptions. Most of the 9.5x24 titan tires are about 41" inches in diameter. (Yours might be less which would help things).

Here's the math... The basic formula here is speed/circumference=Revolutions per time unit
The only tricky part is keeping your units of measure the same.
Since we know that your speed is 7mph and your tire is approx. 41", we can calculate your wheel RPS (Revolitions per Second), 0.96 Rev/S. Knowing this, we can rearrange the formula to speed/revolutions=circumference. We now know you want 12mph and your tractor wheels are rotating at 0.96 Rev/S in that gear and throttle speed. So, doing the math you'll need a tire with a diameter of 70.3 inches to go 12mph. This would be a tall and wide 38" tire. Way too big for your tractor.
Here's some examples using the Titan Sizes
11.2x28 = 8.1 MPH
11.2x34 = 9.1 MPH
11.2x36 = 9.5 MPH
11.2x38 = 9.8 MPH
18.4x38 = 11.9 MPH

Derek
 
True the taller wheels would work but.......The center of gravity will be raised.
1st gear and reverse already plenty quick at 2-1/2 and 3.0mph are going to get faster. More difficult to control on and off trailers etc.
Brakes will be less effective.
Higher to step up onto and off the seat.
Hard to say what the valve train condition is. Most rebuilders never test valve spring pressure or measure lobe/lifter wear. A set of springs and fresh ground cam/lifters are very economical. And eliminate a lot of mysteries of why a fresh engine doesn't run smooth or make decent power.
I wonder if there was an option for electrics on those C's. Lights while on the road or putting around are handy.
 
Putting only taller rear tires on the back of the tractor will improve fuel efficiency. The tractor will always be running downhill.
 
Stand a 9.5X24 next to a 12.4X24 and there is in fact 1 or 2 inches difference in the 2 of them. So yes if does in fact make a difference. Lie going from a 195R-15 to a 235R-15 the 235 is wider but also a good bit taller. Sorry but I have BTDT and know that when you go wider you also go taller by a good bit. So your wrong on this
Hobby farm
 
Get another tractor that will run the speed you need with enough power to pull a trailor with your pretty little allis on it.
 
However you change effectively the "gearing", you may find tractor cannot pull top gear anymore. I did something like this with motorcycle and could not use 6th gear any longer. Only 5th would pull me along. Did this on 65 Chrysler and 2nd gear was over 110 mph. Third would hardly wind at all. Bigger tires equal more friction and rotational losses.
 
Thanks again to all for all the suggestion,also enjoyed the joshing . Seriously it open up some serious question i had not considered, I will leave as is.
Later Ralph
 
Used to hav an f12 Farmall with flathead ford v8 engine. Used torque tube rearend for trailer. Hooked up drive shaft to power takeoff . Run about eighteen mph at governed speed on engine. Much faster with baling wire on throttle rod. Bernie Steffen
 
you may have one tire that that is true for but it IS NOT always the case. In many cases it is exactly the opposite, if you go from a 15.5 to an 18.4 you actually lose height, same if you go from a 18.4 to any size over it. same if you go from a 14.9 to a 15.5. So like I said, what you suggested may not work, you do not always gain height by going to a wider tire. You may find one or two sizes that do but it won't gain this gentleman the speed he is looking for by going with the minimal increase you are suggesting.
 
Well in ALL the years I have worked with tires so far I have never found that to be true till the newer tires used on todays car. I have worked with tire now for around 35 years and other then the newer low profile tires on the newer cars I have never seen it. I do in fact have tractors with the 9.5 and the 12.4 tires on them and the 12.4 do in fact stand a good bit taller. I even ran into one tractor that had 36 inch tires on it and a 16.9X28 was in fact as big as the 11X36 was but only because of how wide it was
 
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