18 vs 19

If you plan to race motocross then go with the 19 and if you plan to do some trail/woods riding then go with the 18.

Well considering my advice doesn't "hold a whole hell a lot of water", I'll tell you my thoughts.

Unless you're a B or A class, or better, the 19" rear will only make your tire changes a bit more challenging.

If not, I doubt you would even notice the difference. Tire selection would probably of more importance.

Hopefully someone with more knowledge and a better perspective will offer a better idea on where to go with this decision?

You do have a sweet vintage ride, enjoy the hell out of it.

My 83 KX came with an 18 and old school hook shaped spokes
I bought a 19 and the holes were drilled slightly at the wrong angle.
When I tightened the spokes they bent lightly because one side of the spoke nipple hit the rim before the other.
I had to grind the inside of the rim to correct it so they pulled strait .A ton of work .

I bought a 84 wheel with strait pull spokes. I was able to lace a 19 to bit no problem. The spoke pattern on the straight pull spokes was perfect for the modern rim.

If you can get a rim that is drilled correctly I'd choose a 19. I think they look better. Other than that I'll bet you or anyone else couldn't tell what rim was under you if you didn't look first.


Be sure to order your rim to match the spoke pattern is moral of my story. I don't know why I never heard this from anyone else. I couldn't be the first person ever to want to lace a new rim to an old hub.

Lacing and truing a wheel was so much easier than I thought it would be.

The main reason would be weight, i have not put it on the scale and confirmed myself.. But If you have same od the 19 would have a lot less rubber.
I suspect it will vary between different tyre brands also, think Nino did compare some tires in a thread

Personally, I think there is only one reason to use 19's on "old" bikes. If you have a modern bike as well, it makes buying tyres easier.

There are some supposed improvments using 19's, less tyre flex, a slight reduction in weight. There is also more tyre choices, although I've never had an issue finding 18" tyres. I've run Dunlop MX52's, Michelin S12's and now Bridgstone battle cross (best tyres I've ever used!).

Eric Gebores claims he lost a 500cc world champoinship because he stayed using 18" rears tyres. I'm gonna say that's more than likely all in his head, but what do I know!

On a twinshock I feel that the extra flex in the tyre actually helps, it gives a little extra "cushion". I also don't think older bikes look right with 19" but thats just me!

Stevie

In the late 70's & early 80's, some open class mx'ers came with 5:00 x 17 rears. I guess the thinking was the big footprint helped with traction, but in reality the big sidewalls just created an undamped air spring. IE:The shorter the side wall ,like on the 19"ers, means less undamped (or uncontrolled) air spring action. I think the current use of 19 inch rims came about as suspension technogy became more advanced.

Personally, I doubt the average guy can tell the difference between the 18 or 19. Since you're building a Evo bike, I'd go with a 18 inch , but that's just me.

RB

My RM250 has an 18 inch on the rear. Feels a lot more plush, I ride on hardpack with rocks so it soaks up the harshness a little better. Harder to feel what the rear wheel is doing compared to a 19. Not all tire companies support 18 inch rims so if you have a favorite tire it may not be available.

19 on the 81

Unless you are running at national level speed and have a contract (you are being paid to race), then seriously, I wouldn't worry about the gearing. I have both 18 & 19 on vintage bikes and on my vintage 125's I only run 18s, but only because I use Cheng Shen tires, which are much small than a normal 18" tires (normal 18s tires rob you of HP on a vintage 125s). But on my 250 & open bikes, I would run a 19 (if I were shopping for one or the other). If you have the funds then go with the 19 and be done with it and if not, then stick with the 18. Either one will work, but is the average rider really going to notice the difference...probably not...we'll the 18 will be a bit more comfortable for sure...here's a photo of the 19 I put on my 83 CR480, 18 on my 83 CR250 & the Cheng Shen 18 on my 1980 YZ125. Mike

Only use a 18
Better ride, that is what the bike came with!

19 inch wheels look stupid

I remember Rick Johnson going to a 19" rear sometime in the late 80s and it was mainly for SX originally.

I love the old 18 wheels, used to hear that 19 rims had been fitted for extra tyre options. But plenty out there now for the 18's.

Am running Michelin MS3 for MX on an 18 rim which is exactly the same tyre I run on my modern bike although obviously that ones a 19 rim.


I'm with Stevie I think the 18 compliments the old suspension and works perfectly.

I also find that the old twinshock bikes are not so fussy tyre choice wise and seems to work with most tyres as long as they are new. Believe that's the simpler suspension that makes them work.