Why does a WR have a 18" rear?

I was reading up in dirt rider about the new WR 450 and they said yamaha kept some of the goodies like the rear 18" rear wheel and bla bla. I'm relatively new to motoing so why is that a goodie as they say? What is the advantage to having a smaller tire in the rear rather than the bigger rear that the YZ sister has giving more clearance (or does it)? And on another question I have, in that same article they claimed that they kept the wide-ratio five speed. However on Yamahas website they advertise a constant mesh 5 speed for the 07 WR. Who had the facts straight yamaha or dirt rider? What does wide-ratio mean compared to the yz-f trans, and what in the world is a constant mesh transmission?

Most if not all manual transmissions are of the constant mesh type. The transmission gears are always in mesh and rotating, and not rigidly connected to the shafts. A wide ratio tranny's gears are more widely spaced, so there is more rpm drop when you shift up, but it offers more speed range with the same number of gears... So the WR has a constant mesh wide-ratio 5 speed transmission.

18 inch rear wheels use taller tires which are more forgiving and offer more traction in rough terrain, where the WR was intended to be operated. The 18 inch wheel/tire assembly is also heavier than the 19.

As Dominator said , all transmissions are constant mesh otherwise we would all be grinding our gears on every shift. The WR's wide ratio gearing is designed to be good in applications from slow single track to wide open desert racing. The YZ is designed more for track use where the gearing would be more concentrated on keeping the shift points closer together for a motocross track. The 18 inch rim actually holds a tire with a greater outer circumference than the 19 inch tire. The 18 inch tire has a much wider sidewall to absorb the impacts of rocks, roots , logs etc. that are not usually found on a motocross track. That's why the 18 inch tire and rim assembly is a bit heavier than the 19. WR Dave.

The 18 inch wheel is virtually unchanged throughout the WR's history. I run a 18 from a 426 for my paddle tire at the dunes on my 05 WR450. Lets hope Yamaha doesnt change it for a long time. The 18 is much better for off road and paddle tires than a 19 motorcross wheel.

good thread...I've pondered the question of 18" vs. 19" many a time

On the other hand the 19" has a lower profile so it will roll less in the corners.

Steve

On the other hand the 19" has a lower profile so it will roll less in the corners.

Steve

and pinch flat more on rocks.

for offroad riding, the 18 is the way to go.

and pinch flat more on rocks.

for offroad riding, the 18 is the way to go.

Yeah there is that. I prefer the 18" off road myself.

Steve

As Dominator said , all transmissions are constant mesh otherwise we would all be grinding our gears on every shift. The WR's wide ratio gearing is designed to be good in applications from slow single track to wide open desert racing. The YZ is designed more for track use where the gearing would be more concentrated on keeping the shift points closer together for a motocross track. The 18 inch rim actually holds a tire with a greater outer circumference than the 19 inch tire. The 18 inch tire has a much wider sidewall to absorb the impacts of rocks, roots , logs etc. that are not usually found on a motocross track. That's why the 18 inch tire and rim assembly is a bit heavier than the 19. WR Dave.

Do you know the weight difference?

You guys are a great. Thanks for your help. Now the big step...who wants to trade me their wr for my yz :applause:

I don't know the exact weight difference , but I beleive it is in the 2-4 lbs range depending on the thickness of tube being used. Other guy's on this site might have a better idea.:applause: WR Dave

I don't know the exact weight difference , but I beleive it is in the 2-4 lbs range depending on the thickness of tube being used. Other guy's on this site might have a better idea.:excuseme: WR Dave

Thanks for getting back to me. :applause:

Do you know the weight difference?

This is also why you'll find 2 rimlocks on the WR 18", there was thread in here a while back where people were stating you did not need two rim locks... the heavier weight means more rotating mass therefor the need for the 2nd rimlock, plus if you get a flat out in the middle of no where it's a little easier to keep the tire on the rim..:applause:

the 18" rim with the tire weighs 23.5 lbs. and the 19" combination weighs 22 lbs. this dosn't sound like a lot but I was able to shave 12.5 lbs. off of my WR 1 lb. at a time, its basically a YZF with electric start and larger fuel capacity.

You guys are a great. Thanks for your help. Now the big step...who wants to trade me their wr for my yz :applause:

What year YZ? I might entertain that offer :excuseme:

its a 06 WR that weighs 236 lbs dry.

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