20 vs 21

[Mad Dog]

What are the pros and cons of a 20 vs a 21?
Is there a prmary purpose for a 20"?

[nmdesertrider]

ty davis was a big proponent of these, good thing is it eats up rough stuff. bad thing is there are only a couple dunlops available in this size

[AlisoBob]

The smaller the tire, the quicker the bike steers....

[britincali]

Would that not make these even more prone to headshake

[AlisoBob]

Not if its off the ground....

[redrocket190]

The smaller the tire, the quicker the bike steers....

...only if the overall size is smaller like 16.5" fronts on Supermoto bikes. I think the 20" concept here was to run a taller and fatter tire for more front-end grip. Mike Larocco was a fan in Supercross and the idea got some play from MXA. However there were never enough tire choices to make a go. Now you can get wider 21" tires - but not all brands and types.

[teemtrubble]

I run a 20 inch 756 Dunlop and a 18 inch 756 Dunlop for all of those reasons you all mentioned.

[AlisoBob]

Mike , I thought you told me you run the 20" for pipe clearance and quick steering?

Maybe not?

[redrocket190]

The Dunlop 756 in the 20" size is .5" smaller in overall diameter, but given there are so many cheaper avenues to quicken the steering I don't think that's what Dunlop was after. And you can guarantee they didn't consider pipe clearance on a CR500AF conversion.

from Pirelli's web site...

What's the difference between a 20" MX front tire and a 21" MX front tire?
The 20" front tire offers a larger footprint and so it helps to improve front wheel damping, braking and traction.

[Apollo]

One of the reasons for the twenty inch tire that Honda used was the fact that it had more tire wall and made the suspenision more plush to help out with the 2nd generation frame being stiff, even though it was tons better than the 1st gen frame. It was what MXA said any ways. I bought into it on my 01 CR250R, tried it and it was more plush and offered more traction at turn in. I did not use it for long, I like the 21 inch better. It is lighter and seemed to hold a line better than the 20. The 21 just felt better to me. I will sell my 20 inch combo if anybody wants it. It is complete accept for the rotor and it has maybe 2 or 3 hrs on it.

[teemtrubble]

from Pirelli's web site...

What's the difference between a 20" MX front tire and a 21" MX front tire?
The 20" front tire offers a larger footprint and so it helps to improve front wheel damping, braking and traction.

[90cr500guy]

Remeber Honda using 23 inchers on early '80's xr's

I have a 21 with a 3.50/3.00 21 tire
Thing looks like a monster

[redrocket190]

The 1979 Honda CR125R Elsinore came with a 23" front wheel. The concept was to have the front wheel roll better over bumps. The 21" was back by 1980. It didn't help that tire choices were extremely limited. Vintage racers go to a 21" wheel and then try and dial out the changes in rake and trail...

[teemtrubble]

79 XR500 had two built a cradle frame for one of them a few years later with a 21 inch front wheel CR250 plastics my friends said 4 stroke "what a joke" but, they're all riding 4 strokes now pssf "what a joke" hahahaha

Yeah I remember the 23 inch wheel...

[redrocket190]

I know of two projects; one to restore a C&J-framed XR500, the other to put a XR500 engine in a '79 CR250R frame. At the time, there simply wasn't the investment available to make engines light enough to be practical. A change in the rules altered the manufacturers' priorities and the rest is history.

[eyesky2002]

Here is a 18 and 20 I found during my travels on the Bay of e searhing for wheels for my conversion, but thought maybe another hoon might like a set http://cgi.ebay.com/ebaymotors/ws/eBayI ... 06472&rd=1