Bigger Tires and Lower Gears

Hypersprint

My 25x10x12 Power Grip tires have held up very well over the years but have worn down to a measured 23.75 inches and I am no longer the big kid on the block. Using the Speed Calculator I determined that my 2 speed EMP motor is turning about 4700 RPM on the High Speed setting with these tires and stock gears getting about 27mph and 3800 RPM on Low getting about 22mph. While I would like to go faster in High I am happy with my trail and mud performance in Low. Here is my problem, when I was in my 20s I had a Toyota pickup with 42" Super Swampers which was a great combination and it was rare that I was the one being pulled out of the mud, well now that I am in my 50s the 25" tires on my cart are just not big enough

Well, I bought one of the new axles from "Sunoco" that were originally made for Stealth Manufacturing (I have not installed it yet), these are suppose to be heavy duty with 14.76:1 gears and 2 inches wider than stock. Now using the same RPM numbers I got from the Speed Calculator to reach the same speeds that I do now I could run a 28" tire.

My big question is that even though the math works out would I in fact have similar performance with this gear and tire combo to what I have now

The Power Grip tires give a rough ride and are very loud on pavement which is about 80% of my drive time, so I am thinking my next tire choice would be something like the GBC Dirt Devils or the ITP Mud Lite XLs which are suppose to be smooth and quiet but still eat up mud but I'm just not sure how long they will last on pavement.

I also plan on converting the rear suspension to a crossover 4 link and hydraulic disc brakes on the rear (also from Sunoco) and going lithium which will save a lot of weight.

Thanks
Rob

BGW

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JohnnieB

With 23.75" tires and 12.44:1 gears, you have a final drive ratio of 12.57:1.
With 28" tires and 14.76:1 gears, you have a final drive ratio of 12.65:1

The proposed tire height and gears will give you slightly more torque and slightly less speed.

At 4700RPM, your current setup goes 26.7MPH and the new set will go 26.5MPH.
At 3800RPM, your current setup goes 21.6MPH and the new set will go 21.4MPH

The torque increase with the new setup will be about 1%.

Be aware that the height and width dimensions stamped on a tire's sidewall are very, very approximate. It may be an inch or more off in either direction.

Also, going to Lithium will drop the weight considerably, which will increase the top speed due to lowering the rolling resistance.

bokeasmowl

Check out the Kenda Bear Claw HTR tires. Nice big chunky tread for the mud and run smooth and quiet on pavement. The HTR stands for hard terrain radial. Radial construction with great off-road capabilities. I'm using the 25x10x12's on all corners so I can rotate them when I'll need to. I've had them for over a year with very little tread wear.

Hypersprint

Thank You JohnnieB

Ya, the 28x10-12 Dirt Devil is actually 27.8x9-12 at least when it is new.

Now the big question, what if I went with the Axle Inc (formerly Imaginative Manufacturing) 2 speed rear end that has a 10:1 low range and a 20:1 high range? Using a 28" tire I came up with the following numbers with the speed calculator.

Axle in low (10:1):

3800rpm = 15.8mph
4700rpm = 19.6mph

Axle in high (20:1):

3800rpm = 31.7mph
4700rpm = 39.2mph

With these numbers in mind I'm thinking:

- with the motor and axle in low I might be able to pull stumps out
- with the motor in high and the axle in low might be good for the mud and trails
- with the motor in low and the axle in high might be ok being in Florida with flat streets.
- with both in high I'm not sure if it would be usable, like in my Toyota with 42s 5th gear was unusable.

Thanks
Rob

Hypersprint

Those look nice Boke, I'll have to check them out

Hypersprint

The reason for looking at the numbers in post #4 with the Axle Inc rear end is for the possibility of upgrading to there 4x4 front, and I like the possible speeds in high range on the rear end, I could keep up with most of the guys in my neighborhood again.

Has anyone used the 4x4 system from Imaginative Manufacturing?

Should I just stay with the 14.76:1 rear end that I have available and just use the electric front hubs when I decide to go to 4x4? Can anyone report on how well these work for them?

Thanks
Rob

Hypersprint

Sorry, my labels are backwards

Should be

Axle in low (20:1):

3800rpm = 15.8mph
4700rpm = 19.6mph

Axle in high (10:1):

3800rpm = 31.7mph
4700rpm = 39.2mph

What are your thoughts on this axle and those gear ratios turning 28" tires?

Thanks
Rob

JohnnieB

With the 28" tires, I'm not entirely sure the cart would take off from a standstill when the hi speed (10:1) gears are selected.

Using your current setup (23.75" tires and 12.44:1 gears) as a baseline, The high speed gear setting (10:1) will cost you about 32% of the torque you now have.

On the other hand, the high-torque gear setting (20:1) will up your available torque by about 36%.

If you can shift the gears while moving, it might be usable, but if you can't, I suspect you'll be having some motor overheating issues when the 10:1 gears are used to accelerate from a standstill.

Hypersprint

My motor is switchable on the fly and the axle is suppose to as well. That's what I was thinking going from low on the axle and high on the motor (about 19mph) then on the fly switching both motor to low and axle to high (it'll be like the old days driving truck) accelerate to 30 then hit high on the motor and see if she has enough to continue accelerating without overheating.

Thanks for your help
Rob

JohnnieB

Attach a thermocouple to the motor case and keep and eye on the temperature. (Attached are a couple pictures of how I did it. They show the stock PDS motor I used to run, but I monitor me D&D motor the same way)

Max recommended temperature for a motor with Class-H insulation is 239°F, so stay below that.

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I hear you about shifting gears. Back in the late 60's I had the pleasure of occasionally driving a conventional cab Pete with a 425 Cat and it took while to get through all the gears. IIRC, it was a 5-speed manually shifted box connected to a 3-speed pneumatically shifted box (Road Ranger RO-16?) and two speed driver axles. It was set up for hauling oil field equipment off road as well as on-road, so you didn't use the low speed gears much, but you had them when you needed them and they sure were handy at times. I can't remember the sequence of moving the stick from hole to hole and flipping the 3-way pneumatic switch on the top of the stick, but driving on the highway you only used about 13 gears.

I could shift up through the gears and down through the gears okay, but when I had to drop speed by over 10 MPH or so quickly, I was lost. I'd either be under 1800RPM or over 2100RPM when I let the clutch out.

My wife at the time's stepfather owned a trucking company and would let me tag along on the weekends (I was in the Air Force) and drive his personal truck while he rode shotgun. It was fun, but I don't think I could have done it to make a living.

To this day, I play nice with the big rigs I'm sharing the road with and often get double blinks of the clearance lights.

Attached Images

	Thermocouple on motor.jpg (911.9 KB, 0 views)
	Thermocouple attached to DMM.jpg (913.8 KB, 0 views)