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Why is 18 inch rear better for off-road?

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I never could figure that out.

More sidewall. Less chance of pinch flatting, and more flexion (not sure that's a word), for climbing obsticals.

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MX tracks don't have logs, tree roots and big rocks.

18" rear provides extra cusioning. Less flats.

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Not to mention that taller tires offer more stability (something to do with the gyroscopic effect of taller tires), something thats helps during slow-speed riding.

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i think having a 18 rather than a 19 is better because it would give you more torqe. think about it if you had 40 inch tires on you truck for ever one ravolution you would go 40times pie(3.1415) = about 120 inches if you had a 20 inch tire for ever revolution you would go 60 inches. since your at the same rmp it would give you more torqe. i tryed not to be technical.

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I think the flatting issue had more to do with it than anything. Also the larger sidewall offered a supple ride for small off-road obstacles like roots. More and more top off-road riders for CNCC and WORCs events are runing the 19" for less roll over on the side wall since the speeds are higher and they run either bib's or tire balls to eliminate flats. With more advanced suspension, higher speeds, and more riders with other riding expierence ie motocross, more people have stayed with the 19" rear. The diameter of each set up is almost identical due to the difference in side wall hight. You still see the 18" alot in enduro as there are place where it is an advantage.

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As stated above, the 18" and 19" tires have about the same diameter (within a few mm) due to different side wall height. The 18" tire has better resistance to pinch flats over the 19".

Another difference is that the 19" having shorter sidewalls is lighter. This gives it less rotational inertia for the engine to overcome which makes it spin up faster, and that's a good thing at the MX track. The increased rotational inertia of the 18" wheel acts similarly to a flywheel weight reducing the bikes tendency to stall in tight single track, which is a good thing in the woods.

Lots of good reasons to run one or the other, depending on where you ride.

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i think having a 18 rather than a 19 is better because it would give you more torqe. think about it if you had 40 inch tires on you truck for ever one ravolution you would go 40times pie(3.1415) = about 120 inches if you had a 20 inch tire for ever revolution you would go 60 inches. since your at the same rmp it would give you more torqe. i tryed not to be technical.

It is a driven force, not the driving force. You will loose torque.

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It is a driven force, not the driving force. You will loose torque.

what, :thumbsup: the tire is driving the bike. anyways it dont matter having a smaller tire will give you vary little but still more torqe.

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i think having a 18 rather than a 19 is better because it would give you more torqe. think about it if you had 40 inch tires on you truck for ever one ravolution you would go 40times pie(3.1415) = about 120 inches if you had a 20 inch tire for ever revolution you would go 60 inches. since your at the same rmp it would give you more torqe. i tryed not to be technical.

thats really irrelevent because the outside diameter of the 18" and the 19" is very very close.. as someone stated above, probably no more than a couple mm so yea.. but i do agree that a smaller outter diameter would increase torque..

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An 18" tire is more resistant to getting flats due to the added protection the extra 1/2" of sidewall offers. Another benefit is that 18" tires are easier to change than 19's. Last, there are more 18" off road tires available so it is more likely that you find something you like rather than learning to like what's available. :thumbsup:

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i dont know if anyone else has felt this before, but after riding my yzf and my old mans wr back to back, i can totally feel it, and i'm not a sensitive ryder. when coming up short on jumps and sharp bumps, i can feel the tire soking it up apossed to the suspension. one day i would like to convert to 18" and 20" up front.

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what, :ride: the tire is driving the bike. anyways it dont matter having a smaller tire will give you vary little but still more torqe.

The crank/flywheel is the driving force, what ever it has to drive takes power away......

Quite simple really. :thumbsup:

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one day i would like to convert to 18" and 20" up front.

I'm interested in the 90 size front tires. The 20" fronts wern't that popular, but I think they would be great for offroad. I don't like the idea of having to buy a front wheel (easier than changing rim and spokes) to change the front tire. Rear 18" wheels are easy to get hold of for real cheap if you have a YZ.

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The crank/flywheel is the driving force, what ever it has to drive takes power away......

Quite simple really. :thumbsup:

Agreed :ride::applause:

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The crank/flywheel is the driving force, what ever it has to drive takes power away......

Quite simple really. :thumbsup:

yeah your right but the 19 inch is still a bigger tire so i takes more power to turn it. :ride:

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No, the 19" tire is NOT a bigger tire. Read the thread again. The outside diameter is almost exactly the same.

As far as power goes, it takes more power to accelerate the 18" tire because the engine has to overcome the tire's higher rotational inertia.

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I agree with the above comments about more sidewall = less flats, but there's another reason too. Trials tires aren't made for 19" wheels. :thumbsup::ride::applause:

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