Originally Posted by 123Cookie (Post 1175257)

your speed on your speedometer is based on rotation of tire - when you change the size of the tire - the speed on the speedometer changes - NOT the speed of the cart - you are not going any faster - just your speedometer is no longer accurate!

Originally Posted by burky (Post 1177020)

Cookie - FYI the speedometer on any vehicle knows nothing about the tire diameter. It either assumes the factory default circumference or allows you to enter a new one in a Setup screen. The speedometer is essentially measuring the RPM of the engine, then calculating the tire rotation in RPM by converting engine speed to tire RPM using the transmission/drive train gear ratios.

Thus if the speedometer is calibrated to think you are going 20 mph at an engine RPM of 4850 with a certain sized tire, and you put a bigger diameter tire on the vehicle, you will then be actually going faster over the ground at that 4850 RPM but the speedometer (not knowing you have changed the tire size) will not be changed but will still be reading "20 mph" at the 4850 RPM engine speed even though you are really traveling faster than that with the new bigger tires.

Originally Posted by OhioBuckeye (Post 1177078)

I worked in the auto industry for 38 yrs. & I'm no expert on drive trains but it makes sense to me that 8 in. tires will make the rear axle run faster & your engine will only pull the cart as fast as the engine will let you but 10 in. tires spin the rear axle slower so in turn the engine will spin the rear axle faster because the bigger tires will spin the axle less times. I asked this same question to my salesman when I bought my golf cart & he said bigger tires make no difference. So what's the difference, better ride? I disagree with the salesman. Bigger tires will make your cart run a little faster. The only con I can see is, don't complain if you get pulled over for going over 20 mph.

Originally Posted by Dr Winston O Boogie jr (Post 1177144)

The problem with your whole theory is that that the tires do not control the rate at which the axle spins. The engine and transmission determine how fast the axle spins. Putting on a larger tire means that a point on the outside of the tire will move further in the same amount of time that a point on the outside of a smaller tire will move if the axle spins at the same speed thereby traveling further in the same amount of time.



For example, if the outside diameter of a tire was 12" the the circumference would be approximately, 18.85" A tire with a 14" outside diameter would have a circumference of 22". The 12" tire would travel 18.85 inches every revolution and the 14" tire would travel 22". Assuming that the speed of the revolutions is the same, the larger tire would travel 18.85 inches sooner then the smaller tire. Or, the larger tire would travel 22" in the same time that the smaller tire travels 18.85 inches. Either of which is the definition of going faster.



The argument might be that putting on a larger tire may make the axle turn slower because of the weight. If that's the case, then we'd have to know exactly how much slower the axle turns and exactly how much further a point on the outside of the tire moves to determine whether the cart will go slower, faster or the same. But, in my experience and in the experience of most experts that I've spoken with, larger tires will give you a bit more speed. In other words the amount that the axle is slowed down, if at all, doesn't offset the additional distance the tire will travel.



Another point is that if you put larger tires on the back of the cart and not on the front and your speedometer is attached to the your front tires, no adjustment to the speedometer needs to be made. The speedometer is simply measuring how many revolutions the tire is making and multiplying that to how far each revolution make the cart travel.

Originally Posted by Dr Winston O Boogie jr (Post 1177144)

snipped by Alan

For example, if the outside diameter of a tire was 12" the the circumference would be approximately, 18.85" A tire with a 14" outside diameter would have a circumference of 22". The 12" tire would travel 18.85 inches every revolution and the 14" tire would travel 22". Assuming that the speed of the revolutions is the same, the larger tire would travel 18.85 inches sooner then the smaller tire. Or, the larger tire would travel 22" in the same time that the smaller tire travels 18.85 inches. Either of which is the definition of going faster.

snipped by Alan...

Originally Posted by ajbrown (Post 1177238)

You had me right up to the paragraph i left from your OP. If I have not made a silly error here are the details...

If the OD of a tire is 12 inches, the circumference is 37.7 inches.
If the OD of a tire is 14 inches , the circumference is 43.98

A more real world example is the stock tires on an 8 inch rim that came with my Club Car versus the bigger 205-65-10 tires on 10 inch rims.

Stock tires: 18 diameter has a circumference of 56.55
205-65-10: 20.5 inch diameter has a circumference of 64.4

I go about 8 inches further with the larger tires during one revolution.

Originally Posted by Dr Winston O Boogie jr (Post 1177844)

Maybe someone can help me with a problem. I have a Schwinn Speedometer on my cart and the battery died. I replaced the battery an a four digit number appeared on the bottom of the screen. I played around with it for a bit to get to where it shows the speed and distance traveled. It showed that I was going 51 mph.

I then realized that that four digit number is a code for the tire size. Can someone help me out with resetting the correct code?

I have a Club Car DS with standard 8" tires on the front.

Originally Posted by Dr Winston O Boogie jr (Post 1177844)

Maybe someone can help me with a problem. I have a Schwinn Speedometer on my cart and the battery died. I replaced the battery an a four digit number appeared on the bottom of the screen. I played around with it for a bit to get to where it shows the speed and distance traveled. It showed that I was going 51 mph.

I then realized that that four digit number is a code for the tire size. Can someone help me out with resetting the correct code?

I have a Club Car DS with standard 8" tires on the front.

Originally Posted by Bobs GolfCart Speedometer (Post 1177926)

The correct tire size (circumference) for standard 8 inch cart tires is 1440 cm. Here's a link to an owners manual for the Schwinn 12 function speedometer that's most commonly installed on carts here in The Villages.

K3PGP - Experimenters Corner - Schwinn 12 Function Bicycle Computer Manual

The first page explains how to setup the tire size again after changing the battery. You can skip the part about how to calculate the correct tire size, just use 1440.