Why 19" rears?

[FastMarty]

Hey guys, as I have been riding road bikes for years, I haven't really paid attention to dirt bike advancements for ages. Last time I looked, 18" rears were on everything. So how come the change to 19"'s on motocrossers ? Thought the 18" would be much stronger?

 

[THUMPINOZ]

I think that maybe the main reason is less weight, The 19" tyre has a lower profile sidewall & would make the tyre much lighter (Less moving mass equals faster acceleration & better braking) & the larger the circumference of the tyre the more area for grip & also a larger wheel will go over small bumps much smoother, Their may be a better explanation from someone else?

The 19" is good for MX tracks but not good for enduro type riding around rocks or any sharp edges as the 19" tyres are easier to get a flat or put a flat spot on the rim, Lots of enduro riders on MX bikes swap the 19" rear wheel for an 18" for that same reason

 

[FastMarty]

Thanks Thumpinoz . sounds feasible. I guess it makes sense, but still would have thought that the would be a strength and flex issue? When did the manufacturers change over?

 

[SwapperMX]

Yeah ThumpinOz's description is pretty on the money. Well explained. The change over from 18-19 pretty much happened throughout the 80's. Honda was the last to switch the CR range from 18" to 19".

 

[FastMarty]

God what rock have I been under since the 80's hehehe