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Old 12-02-2012, 09:06 PM   #16
JerryH
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The larger in diameter the front tire is the better, to a point, for all the reasons mentioned above. Back in the early '80s, Honda used a 23" front tire on their XL500 and 250. I've never ridden one, so I don't know how well it worked, but they did go back to 21". With mountain bikes, 26" has been standard forever. But now many of the high dollar mountain bikes have gone to 29" wheels, and have used them for some time. I have never ridden a 29er, but most who have switched to them claim they are better. Anytime you have something turning, centrifugal force comes into play, and the more the weight, the higher the centrifugal force. This doesn't matter nearly as much on street bikes, but on dirt bikes, you want wheels that can stop and start turning with relative ease. Those big monster "adventure bikes" are meant mostly for road use, and occasional dirt road use. They are not trail bikes or MX bikes. I tend to think of them more like a pack mule, capable of carrying a lot of stuff over rough terrain at slow speeds, but no match for a race horse. You should choose your bike for the type of riding you intend to do. I have a cruiser for road riding, and an XT225 for off road riding.

Many cruisers also have a 21" front wheel, but it is only for looks. It actually hurts the handling, making the front end floppy. Mine has a 19" front wheel.
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Old 12-02-2012, 10:53 PM   #17
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Very insightful additional information. Kind of messes up the consensus we were getting for the 21" front wheel, but good to have nonetheless.
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Old 12-03-2012, 09:00 AM   #18
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29" wheels on MTB's are actually used because they 'span over' dips and bumps that would possibly swallow a 26" wheel. There is little if any centrifugal advantage to using a slightly bigger diameter at the rotation speeds turned on these bikes. It's more about increasing your contact patch.

There is a downside to making spoked wheels bigger, they become weaker and are less able to hold their true when subjected to abuse.
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Old 12-03-2012, 04:04 PM   #19
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Originally Posted by boatpuller View Post
Very insightful additional information. Kind of messes up the consensus we were getting for the 21" front wheel, but good to have nonetheless.
I still think the 21" wheel is a product of Motocross and most pure offroad bikes are sold as Motocross bikes. (Trials bikes could be the one exception.) The push for high performance Dual Sport bikes causes them to be compared to MX bikes and made as close to a MX race bike that can still be made street legal. Back in the late 60's and early 70's the "Dual Sport" bikes were "Scramblers" and the light two stroke bikes were "Enduros". The scramblers were all 19" wheeled.
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Old 12-03-2012, 05:56 PM   #20
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Scramblers are gone for a reason Strong Bad. 19" wheels were NOT better in the desert. Not even close. It is what was used back in the day of those pics. Once DIRT bikes of all types went to 21" they never went back. NO ONE uses a 19" in the desert. If they were better they would use it. Johnny Campbell would be using one, Mouse McCoy....

19" wheels on your bigger ADV bikes are pure there as a comprimise and NOT because they are BETTER in the dirt.

The comments about picking the right tool for your job is exactly right. If you are gonna ride alot of hiway and some dirt gravel roads a 19 is BEST...for that. If you are gonna ride alot of dirt, sand, mud, and loose stuff and 21" is it.

there is NO floating effect on a 19" wheel. As I stated before, until you go to a really fat tire it is not effective. Look at all sand toys. they use a ribbed front not to float but to rudder basically.

21" suck on long hiway stuff. Not great wear, not that that is impossible but no one I know make a long lasting 21" knobby. very little contact patch because of its narrow width and generally knobbies minimize contact patches as well.

As for the 23" on the Hondas back when, they ran them on the CR125 in 1979 I think as well as the early 80s xl500s. I had one...It was that TOO A POINT thing. The 23" was a bit too far. Not neccesary and made the steering heavy. It never took off and tire were then and still tough to find and thus expensive.

In the early 2000s Mike Larocco tried running a 20" front tire for SX that was a bit wider thinking it would stick better and there are no big rocks in SX but it just did not work either. It did not carve the same in ruts.....

21" in dirt. 17" on tar, 19" if tar dominated but occasional dirt.
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Old 12-04-2012, 10:19 AM   #21
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Originally Posted by kellymac530 View Post
Scramblers are gone for a reason Strong Bad.
I highly doubt you were riding when Scramblers were at their height, let alone when light weight race bikes became available to purchase from the dealers. Scramblers and desert sleds went away simply due to the advancement of lightweight two strokes. Now lightweight high performance four strokes dominate. The key here is weight and ability to un-weight the front end of the bike and that is where the 21" shines. The OP here on this thread is taking about a bike (550 lb 1200cc Sportster) that weighs TWICE what a high performance bike does. A bike with a heavy front end that has a tendency to plow will benefit from a 19" wheel with a wide tire.
Quote:
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19" wheels were NOT better in the desert. Not even close. It is what was used back in the day of those pics.
IF you were racing back in the day of desert sleds and the big front end heavy Greeves show in my pics, you would know that indeed 19" wheels were far superior. There was a reason they were used, simply because they worked. I know, I speaking from personal experience, I was racing the dez in the 60's and I still race the dez today.
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Once DIRT bikes of all types went to 21" they never went back. NO ONE uses a 19" in the desert. If they were better they would use it. Johnny Campbell would be using one, Mouse McCoy....
Duh..... no one is racing bikes that benefit from running the 19" wheel any more, but that doesn't mean that when they did race them, they didn't benefit from them. And as you say, NO ONE (not even Mouse or JRC) are racing a 550lb Sporter either.
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Old 12-09-2012, 11:58 AM   #22
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I don't think anyone argues that the most capable heavyweight off road bike is the KTM 950/990. Service intervals, road manners, and reliability is why many if not most shy away from them and turn towards the GS/GSA. Off road ability is by superior on the KTM and the reasons are suspension and the 21" front wheel.

I did not start my riding lifestyle as early as you, but I did start in 1970 when 19" fronts were the norm. I had a 380 Greeves but mine did not have a leading link fork, it had Cerrianis and 21" front and far out handled the 19" bikes.

Sand and soft dirt is what the OP was asking about on a heavy bike. Sand is similar to water and a flat bottom boat planes above the water, floating, but it still needs a rudder to steer.

Floatation on sand does not make for good steering, there is NO control and if you are trying to use steering input while the tire is floating on sand and it happens to dig in it dives right or left and plows. Look at how many pics there are of GS/GSAs laying on their sides in other threads.

Your arguement is also flawed on the point of heavy bikes being somehow different that the 300# ish 650R that JC rides. My arguement for that would be if a 19" worked better anywhere except the street than Cyril Despress, Marco Coma, and Gaston Raiher would have ALL used on when racing in the sands of Africa on their 500# ish bikes....yet NONE did.

Just because someone is not as old as you or has a different opinion does not mean they know nothing.

OP put a 19" on your sporty ans enjoy the street riding and the occasional hard pack fire road. Follow old farts ideas and ride it in the sand and post pics of it regularly laying on its side....I love those.
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Old 12-09-2012, 12:24 PM   #23
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Here's a graphic that I made to better visualize the obstacle concept-

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Old 12-09-2012, 07:55 PM   #24
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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.
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Old 12-10-2012, 03:29 AM   #25
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here's another thread discussing it in real time...

hi guys,,just happened to cruise the new posts and found this well worn topic,,,

here's a thread that shares the experience of folks having ridden on 19/17 and then tried the 21''

http://www.advrider.com/forums/showt...=663107&page=2

check out what jimmy lewis one of several adv/dual-sport riding gurus,,i\first american to podium ona bmw in the paris/dakar rallye several years ago,,,test/development rider for BMWs HP-2 project and learn to ride maestro...has to say not to mention his wife Heather even commented on her experience in post #106

http://www.advrider.com/forums/showp...&postcount=106

i tend to create solutions that you will appreciate in real world riding....

so tell me/us what ya noticed whe riding your bike with different wheel diameters on different types of terrain....
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Old 12-10-2012, 04:43 AM   #26
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everyone must already know that there is only a 5-6% difference in mounted tire diameter between the common 19 and 21 DS type tires, hardly seems a big enough variance to make a difference traversing varied terrain, especially on a DS bike, as opposed to a dedicated offroad moto.

the section width of the same tires is a different story, with the variance being over 20%.

so it's unlikely the diameter that accounts for handling reports in mud, sand, etc., the argument comes down to running skinny versus not so skinny.

i like the 19 for running both paved and gravel, does well on both.
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Old 12-10-2012, 07:39 AM   #27
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and there ya have it...

Quote:
Originally Posted by jdrocks View Post
everyone must already know that there is only a 5-6% difference in mounted tire diameter between the common 19 and 21 DS type tires, hardly seems a big enough variance to make a difference traversing varied terrain, especially on a DS bike, as opposed to a dedicated offroad moto.

the section width of the same tires is a different story, with the variance being over 20%.

so it's unlikely the diameter that accounts for handling reports in mud, sand, etc., the argument comes down to running skinny versus not so skinny.

i like the 19 for running both paved and gravel, does well on both.
regarding my first hi-lighted statement....well as amatter of fact it does make a difference as evidenced by all the positive feedback from those that have actually ridden the various upgrades ...

and the second hi lited staement of yours:,,,,and that is why 90% of the dual sport market is supplied in this configuration,,why we call it our 50-50 set up,,not the ultimate on the pavement or in the dirt,,,hence,,the need to get set-ups that work for your specific needs/riding style /location/intent .

w
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woody's wheel works screwed with this post 12-10-2012 at 08:26 AM
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Old 12-10-2012, 08:57 AM   #28
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regarding my first hi-lighted statement....well as amatter of fact it does make a difference as evidenced by all the positive feedback from those that have actually ridden the various upgrades ...



w
woody, maybe i wasn't clear in my statement. do you think the favorable reports on 21" DS wheels is due to the only slightly larger inflated tire diameter or the much smaller cross section tire width, or both?
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Old 12-10-2012, 10:18 AM   #29
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IMHO,,,regarding why the 21'' works better in the dirt...

Quote:
Originally Posted by jdrocks View Post
woody, maybe i wasn't clear in my statement. do you think the favorable reports on 21" DS wheels is due to the only slightly larger inflated tire diameter or the much smaller cross section tire width, or both?
well for starters the 21 does not have a ''slightly larger'' inflated tire diameter...i just measured several variants of 21'' and 19'' tire diameters...FYI,,,the average 21'' measures 28'' OA as opposed to 26'' for the 19'' set-up...that alone accounts for the smoother ride in the dirt

the 21'' front wheel assy is generically circa one pound lighter than the 19''s.. and with proper choice of hubs/discs/rims have been able to make them 2-4+ lbs lighter...now that is significant because that all equates to less un-sprung weight...which of course makes it easier to loft the front end and makes the ride more supple.

i'll need to get a more definitive ie scientific answer regarding what the narrower rim does [truth is i have customers banging at my door who need my attention NOW] to be cont'd
excuse me for a few,,
woody
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Old 12-10-2012, 10:46 AM   #30
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Quote:
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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