I've always heard that getting larger tires will cause you to lose speed. Is this true, or does your speedometer just show you're going slower, because of the larger tires?
The speed of your atv or any vehicle is measure by how many times the axle spins per a given amount of time. So, if you have 25 inch tires, one full rotation of the tire will take you 78.5 inches (pi x 25). With 27 inch tires, one rotation will take you 84.78 inches.

Well, with larger tires, it will take the axle longer to make a full revolution, but the atv will also be traveling a farther distance.

For example, I had a friend and his Foreman would do 48 mph with 25 inch tires. He got 27 inch tires and now the speedometer will only read about 44 mph.
Ok, 48 mph means in one hour you will travel 48 miles or 253,400 feet. One full turn of a 25 inch tire will take you 6.542 feet. 253,400/6.542 = 38,734. 38734 is the number of times the axel turns in one hour.
So anyway, does larger tires actually cause you to lose speed, or does it just throw the speedometer off by causing the axel to make less revolutions per distance traveled?

 

it can cause u to loose speed yes....if u go to large of tires you will not have enough power to pull those larger tires causing you to loose speed.....but going to larger tires if u have the extra power to pull them will get u a higher top end speed it will just take longer to get there...

 

I have an '04 Foreman with 25 inch tires. Would 26 inch cause me to lose much top or low end power & speed?

 

no my mom mother has an 04 foreman with 26 inch tires it hasnt lost much of any power nor speed. i have an 04 with 27inch it doest feel like u have lost much.

 

I dont know what alot of the guys here are running the bigger tires on, but I have 27" Blackwater XT's on my '98 forman 450 and if anything the bike can attain a higher top speed now becuse the tires cause a taller final drive ratio. You have to account for the speedo error caused by the bigger tires, there are lots of wheel size calculators on the net, but larger tires will cause the speedo to read slower.

There is some truth to the machine possibly being slower, due to the extra weight of the wheels. 1lb extra wheel weight will equal adding 8lbs of weight on the machine itself, you may notice that on a smaller machine like a rancher, but it will be less obvious on the larger machines.