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Old 12-10-2012, 10:46 AM   #30
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kellymac530's Avatar
Joined: Feb 2010
Location: so. cal.
Oddometer: 1,052
Originally Posted by boatpuller View Post
OP here.

One of the Sportster models comes with a 21" spoked wheel stock. Not sure if it's a good adv tour wheel, but it's already there and I'll probably try it.

If I understand this thread so far, a 21" wheel is not ideal for the road, especially the twisties. It's probably okay for the highway and non-aggressive riding. The narrow contact patch may want to follow road grooves, or it may not, or it may depend. The 21" wheel/tire will have greater diameter, even though the tire appears to be lower profile than the 19 or 16 inch wheel's tires. The Sportster is too heavy to be lifting the front wheel easily (unless I so overload the weight behind the rear axle, like they did in the Cannon Ball Run Movie....). There is disagreement on the advantages of floating over loose material or slicing through loose material, with slightly more leaning toward slicing through.

I'm building this for long highway trips to off pavement destinations, like Prudhoe Bay and the Trans Canada Ride for example. So, I should consider the importance of safety on the pavement. Is there a braking reduction with the narrow contact patch of the 21" wheel's tire?

In case this little bit of history helps any, Most of my long rides this decade have been on big heavy touring bikes with fat front tires. They just glide down the highway effortlessly. Haven't taken these 900lb monsters on too many fire roads, but they did surprisingly well on the few bad gravel roads I had to take, and on the few patches of dirt my shortcuts demanded.
BP {the OP} Based on what you want to do with your steed I personally think I would go with the 19" front wheel. Harley did make a 19" cast wheel with like 10 spokes which is tubless, the best way to go for what you want to do imho, but they also made a 19" laced wheel with a aluminum hub and if I remember correctly even an aluminum outer rim ring. You may want to look at any narrow glide front end even like the Dyna std and the Dyna low rider and Dyna sport which may be the aluminum rim model.

If you were planning on doing more dirt/sand/off-road than you describe then I still am with Woody and Jimmy Lewis and his wife, 21" all the way.

Yes you are correct that the narrow contact patch and usually a more knobbie design on 21" tires makes the less steady on pavement. If you are NOT going to run knobbies I would never run a 21" given the option. If I am running a street biased tire I would go 19".

Your original questions on soft dirt and sand and the "floatation" concept has been debunked imho. Only a few dissenters and I will bet they are looking at it from a different angle and not to be disrespectful, but they are wrong.

Here is a pic of a true sand rail, note the differential in tire size front to rear. The front is remarkable narrow for a car. Most even use a blade or fin around the center to act as a rudder as I stated earlier.

JD, you commented on "only" 5-6% increrase in diameter, do you want a 5-6% decrease in pay? That is substantially more than you think it is. The issue is not ONLY diameter, but the amount of circumference that comes with diameter. As Hondos simple diagram shows {while exagerated} the circumference plays a role in that obstacle bridging.

For you pavement based riding with the occasional gravel or graded fire or service access road then the 19" is great. You CAN ride any trail with any size tire, but comfort level and ease is aided by tire size that is appropriate to intended uses.
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