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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. QUOTE]
Kind of hard to take pics while running down the road. Mabey I can talk the wife into doing it this weekend for you
You really don't even have to go through that trouble. You can prove it mathematically very easily if you know just a little information.Kind of hard to take pics while running down the road
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11Echo, want rims are those that you are using? It looks like you've used the same rims for all the diff tire sizes, is that true?
No. I looked high and low, and wasn't able to find anything short of custom-made, so modified the stock wheels.
Ron(11echo) is using Canadian (mlvw?) combat rims.
opcorn:,
I have 1100's and .69 OD.
I have a spreadsheet to calculate these things. I guess .xls extensions aren't allowed. No macros - just formulas. It includes a bunch of tires we've been discussing and several gearboxes including the Spicer. Email me or PM and I 'll send you a copy of the spreadsheet. I hope that's allowed -- I didn't actually check to see if I could offer a spreadsheet off-forum ;-{
You want to use the tire manufacturer's Rev's per Mile value, NOT the circumference based on OD -- especially with Michelin military tires. The revs per mile is often quite different because the loaded radius is much smaller than 1/2 OD. Then take engine rpm and divide out all the gearing (tranny & axles in high range) to get axle rpm. Multiply axle rpm times loaded circumference and divide into a mile (using whatever units you used for tire size -- e.g. a mile is 63,360 INCHES. Multiply times 60 (Revs per minute vs hour) and you have MPH.You really don't even have to go through that trouble. You can prove it mathematically very easily if you know just a little information.
For argument sake, assume the following:
Original Setup
Engine RPM = 2,500
Original Tire Diameter = 40"
Speed = 45 mph
Potential Setup
Engine RPM = 2,500
Proposed Tire Diameter = 46"
Speed = X
To solve for X all you need to do is determine the ratio between the original and proposed tire size diameters. In this example the ratio is 46/40 = 1.15. That means that your new top speed would be 15% greater than your original top speed. In this example that means 45mph * 1.15 = 51.75mph. This is the most simplified way that I can think of to estimate a speed based on tire size (it does not account for things such as wind resistance and rolling resistance that could restrict the RPM's from reaching the original level and it is assumed that these factors are negligible (for instance this method would not work well if you planned on installing tires that were 10' tall)).
So, if you know what the diameter of your existing tires are and what speed you can attain from them at a certain RPM, then you can figure out your new theoretical top speed based on the new tire diameter. A good source for tire diameter information is: Army Military Tires
