Speed of a MaxIV w/21" tires

[thebuggyman1]

I'm currently in the planning stages of a new project and exploring gear ratios.
Shhh super secret custom mystery shhhhh I'll start a thread later when I actually begin the project.
By changing out sprockets, I come up with a drive ratio similar to a MaxIV with 21" tires.
I know there are a few machines out there like this, and I was wondering how they do on the trails? Do they lag behind the pack, or have to run high rpm's to keep up?

This project is going to use a low hp motor for low noise, so I don't want to be running real high rpms all the time.

[msafi65]

I do a lot of gear changes on MAX II and buf trucks. My II has 34 tooth main sprockets with stock ratio on the drop chains. I haven't GPSed speed but top end is still faster than I drive. It will easily keep up with stock IVs. It pulls a trailer loaded at just above an idle with 16 hp Briggs. We have one buffalo truck with37 tooth mains and its top speed with 26 inch tires is 12 mph. It will climb over backward at just above idle. Very easy on the belt now when loaded heavy. Hope some of this helps.

[LarryW]

If the goal is low noise maybe bigger engine is better. Like automotive vs weed Wacker.

[thebuggyman1]

Doing the math on gear ratios and tire diameter, and assuming that clutching is the same and out of the equation. A MaxII with 21" tires (27 tooth sprocket) has a very similar ratio to a MaxIV with 26" tires (34 tooth sp.)....... 36 1/4" vs 36" of ground traveled per revolution of the t-20 output shaft. I'm looking at getting approx 30 1/2" of travel instead.
The math is easy, but the perception of speed/time is the hard part. I really want it to pull stumps, but if I can walk faster, what's the point?

[LarryW]

The point is elementary. Can you pull stumps while walking? . Do it!

[LarryW]

What about a 2 speed gearbox feeding the t-20?

[LarryW]

If I did it right. 1760 revs per mile and 2077.3 revs per mile. Should be 0.84737602 percent slower. So instead of 25mph you would do 21.18.

[thebuggyman1]

I get 1760 and 2112, 83%, so assuming normal speed of 25mph, I'd be at 21mph.....
So, yes, you are correct. I'm not confident the 25mph is accurate, but I'm sure it's close enough.
Even if we assumed 3mph less, that still puts the modified gear ratio at about the same speed as an Argo I think it will work perfect

[6X6]

Jim, for low noise I don't really think going to a smaller engine will be a big benefit, or any at all. You'll be using more throttle, even with taller gearing, simply because you will need to turn more RPMs. I would recommend a sub-muffler. (Run a glass-pack muffler inline, before the main muffler.) Also, since the engine makes a good bit of noise that isn't coming out the exhaust, fiberglass engine bay insulation would help as well. Of course you can't close off vents, but if they're baffled so it's not quite a straight shot for the noise to escape, that should help a bit also. A bilge blower for a boat would help if you have too much decrease in ventilation flow My .02

[thebuggyman1]

Jim, for low noise I don't really think going to a smaller engine will be a big benefit, or any at all. You'll be using more throttle, even with taller gearing, simply because you will need to turn more RPMs. I would recommend a sub-muffler. (Run a glass-pack muffler inline, before the main muffler.) Also, since the engine makes a good bit of noise that isn't coming out the exhaust, fiberglass engine bay insulation would help as well. Of course you can't close off vents, but if they're baffled so it's not quite a straight shot for the noise to escape, that should help a bit also. A bilge blower for a boat would help if you have too much decrease in ventilation flow My .02

I think I gave the wrong impression here. I have a MaxII I bought a couple weeks ago that I'm turning into a donor machine. The low horsepower engine is a 18 Briggs......I say low noise because the Kohler 40 hp in my other MaxII is quite loud. Some of that noise is exhaust and some is plain old motor noise, but it is hard to even have a conversation with it running. I'll be very happy to have stock motor noise in this machine....