Question on tires

[kojo]

I'm thinking about going to 24x8x12 tires all around, tires that came on cart are 23x10.5x12. I was thinking that it may speed it up (probably not much) going not only an inch bigger but also a little narrower. I just so happened to measure my tires and they look to be only 21.5 in. tall and 9.5in. wide. Their on 12x7 rims. My question is why aren't my readings matching what's on my tires and will a 24in. tire measure 24in. or 23in. Thanks for any advice guys.

[kojo]

I might go with 23x8x12, either a all-trail or slightly more aggressive type tire, but I don't know if a 23in. tall tire is gonna actually be 23in. or not. I like the taller tire look but, for NOW I'm stock except for freedom plug which I mainly keep in low speed for range purposes.

[JohnnieB]

Originally Posted by kojo

......... My question is why aren't my readings matching what's on my tires..............

The dimensions stamped in the sidewalls are "Nominal" dimensions.
The information you want is MTD and MTW (Mounted tire Diameter and Width), which may and often does, vary considerably from the nominal dimensions.

Carlisle is one of the few tire companies that lists mounted dimensions on their website and here are some examples of "Stock" height tires mounted on identical rims.

18 X 8.50 - 8 Links----------- MTD= 17.4" MTW= 8.6"
18 X 8.50 - 8 Multi Trac C/S - MTD= 17.6" MTW= 8.3"
18 X 8.50 - 8 Turf Master ---- MTD= 18.3" MTW= 8.1"

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Another thing to be aware of when choosing a tire is the inflation pressure.
Low pressure tires have more rolling resistance the high pressure tires and take more torque to turn, so the cart's max speed and max range will be lower.

[kojo]

Thanks JohnnieB. for the insight, I knew something wasn't right because a measuring tape doesn't lie, but sometimes my eyes do and I fall for it every time

[whizzo]

As mentioned the mounted dimensions differ from the nominal dimensions.

We also must understand thet our carts run a family of tyres that is different to all others.

They belong the the flotation and wide base tyre family.....related to tractor tyres.

Even the tyres from this family that are used on road going 4wds are generally smaller in mounted diamter than printed on the sides....31x10.5R15s and similar actually work out to being arround 1/2 an inch shorter than printed...even with agressive tread.

This is because the nominal size may be calculated on far chunkier tread on the same carcase.....so consider a tractor with lawn tyres, the tread will be fairly shallow compared to the same carcase moulded with lug treads used in a field tractor.

As for the width, the width of the moulded tread will often be less than the nominal width of the tyre...even on the standard test rim.
The section width ( the actual outer measurement) will vary depending on the width of the rim the tyre is fitted to.

Imperial sized normal tyres and metric sized tyres are not sized by outer tread diameter and will be more consistent tyre to tyre.

In my country we have a wheel and tyre association that publish a tyre standards manual.....it lists all the relivent dimensions of all the common tyres......I believe there is a similar association and manual in the US....any good tyre dealer should have a dog eared coppy right at his elbow....a look at one can be most informative.

cheers

[kojo]

Thanks Whizzo for the info.