19" Vs 21" Front wheel, Pro's and Con's
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Road Captain
Joined: Jul 2008
Posts: 738
Likes: 6
From: Brigham City, Utah
19" Vs 21" Front wheel, Pro's and Con's
I keep seeing a post here and there about upgrading to a 21" front wheel over a stock 19".
I have a 06 Street Bob that has been lowers 2 inches in the rear.I had read somewhere that excessive lowering of the rear of a Dyna and doing nothing (Lowering) to the can/will cause wobble and tracking issues or something along those lines.
So what would happen to the bike should one opt to switch over to a 21 inch front with a 2 inch lowered rear?
I guess it would really only be raising the front end 1 inch but is that going to through everything off and make it unstable?
Karsten
I have a 06 Street Bob that has been lowers 2 inches in the rear.I had read somewhere that excessive lowering of the rear of a Dyna and doing nothing (Lowering) to the can/will cause wobble and tracking issues or something along those lines.
So what would happen to the bike should one opt to switch over to a 21 inch front with a 2 inch lowered rear?
I guess it would really only be raising the front end 1 inch but is that going to through everything off and make it unstable?
Karsten
You are really talking about two separate things here. Lowering (only) the rear causes trail to increase. That's not necessarily a bad thing, as long as it doesn't exceed 6" or so. Running a larger OD tire up front will also increase trail. Again, not necessarily bad. However, doing both is probably going to result in too big a trail number. Going from a 19" wheel to a 21" wheel will not necessarily result in a 2" increase ... or as you noted, a 1" lift. It's the overall outer diameter that is the determining factor, and that is dependent on tire profile as much as rim size. It is possible to have a zero net OD increase or as much as 1.5 inches. To further confuse things, you can't just stick any tire on any rim of the correct diameter. The cross section also has to agree with the tire width. for example, the skinny MH90-21 and 90/90-21 typically get installed on a 21" x 2.15" or 2.25" rim. The larger (fatter) 21 inchers though typically use a 3.5" wide rim.
Your best bet is to figure in advance what you want to do, and then get the required rim width and tire OD figures from the tire mfg's website. Next, run the figures through the RB rake/trail calculator and see if you are in the ballpark. HTH and GL!
http://www.rbracing-rsr.com/rakeandtrail.html
NOTE: The calculator is based on a level framed bike. If yours is already lowered to the point where it is no longer level F-R, use a chalk line and plumb bob to determine your trail instead (or lower the front end).
Your best bet is to figure in advance what you want to do, and then get the required rim width and tire OD figures from the tire mfg's website. Next, run the figures through the RB rake/trail calculator and see if you are in the ballpark. HTH and GL!
http://www.rbracing-rsr.com/rakeandtrail.html
NOTE: The calculator is based on a level framed bike. If yours is already lowered to the point where it is no longer level F-R, use a chalk line and plumb bob to determine your trail instead (or lower the front end).
Elite HDF Member
Joined: Aug 2006
Posts: 3,863
Likes: 21
From: Kennewick, WA
You are really talking about two separate things here. Lowering (only) the rear causes trail to increase. That's not necessarily a bad thing, as long as it doesn't exceed 6" or so. Running a larger OD tire up front will also increase trail. Again, not necessarily bad. However, doing both is probably going to result in too big a trail number. Going from a 19" wheel to a 21" wheel will not necessarily result in a 2" increase ... or as you noted, a 1" lift. It's the overall outer diameter that is the determining factor, and that is dependent on tire profile as much as rim size. It is possible to have a zero net OD increase or as much as 1.5 inches. To further confuse things, you can't just stick any tire on any rim of the correct diameter. The cross section also has to agree with the tire width. for example, the skinny MH90-21 and 90/90-21 typically get installed on a 21" x 2.15" or 2.25" rim. The larger (fatter) 21 inchers though typically use a 3.5" wide rim.
Your best bet is to figure in advance what you want to do, and then get the required rim width and tire OD figures from the tire mfg's website. Next, run the figures through the RB rake/trail calculator and see if you are in the ballpark. HTH and GL!
http://www.rbracing-rsr.com/rakeandtrail.html
NOTE: The calculator is based on a level framed bike. If yours is already lowered to the point where it is no longer level F-R, use a chalk line and plumb bob to determine your trail instead (or lower the front end).
Your best bet is to figure in advance what you want to do, and then get the required rim width and tire OD figures from the tire mfg's website. Next, run the figures through the RB rake/trail calculator and see if you are in the ballpark. HTH and GL!
http://www.rbracing-rsr.com/rakeandtrail.html
NOTE: The calculator is based on a level framed bike. If yours is already lowered to the point where it is no longer level F-R, use a chalk line and plumb bob to determine your trail instead (or lower the front end).
Kind of makes me dizzy reading this.....I understand it but I have to think too hard about it and tonight my thinking has gone to 
!
Tourer
Joined: Dec 2008
Posts: 396
Likes: 0
From: Central Missouri
You are really talking about two separate things here. Lowering (only) the rear causes trail to increase. That's not necessarily a bad thing, as long as it doesn't exceed 6" or so. Running a larger OD tire up front will also increase trail. Again, not necessarily bad. However, doing both is probably going to result in too big a trail number. Going from a 19" wheel to a 21" wheel will not necessarily result in a 2" increase ... or as you noted, a 1" lift. It's the overall outer diameter that is the determining factor, and that is dependent on tire profile as much as rim size. It is possible to have a zero net OD increase or as much as 1.5 inches. To further confuse things, you can't just stick any tire on any rim of the correct diameter. The cross section also has to agree with the tire width. for example, the skinny MH90-21 and 90/90-21 typically get installed on a 21" x 2.15" or 2.25" rim. The larger (fatter) 21 inchers though typically use a 3.5" wide rim.
Your best bet is to figure in advance what you want to do, and then get the required rim width and tire OD figures from the tire mfg's website. Next, run the figures through the RB rake/trail calculator and see if you are in the ballpark. HTH and GL!
http://www.rbracing-rsr.com/rakeandtrail.html
NOTE: The calculator is based on a level framed bike. If yours is already lowered to the point where it is no longer level F-R, use a chalk line and plumb bob to determine your trail instead (or lower the front end).
Your best bet is to figure in advance what you want to do, and then get the required rim width and tire OD figures from the tire mfg's website. Next, run the figures through the RB rake/trail calculator and see if you are in the ballpark. HTH and GL!
http://www.rbracing-rsr.com/rakeandtrail.html
NOTE: The calculator is based on a level framed bike. If yours is already lowered to the point where it is no longer level F-R, use a chalk line and plumb bob to determine your trail instead (or lower the front end).
Wow! Look at the brain on this guy. Well done Mr. Lucky. I've actually wondered the same thing myself. I have 1in drop in rear and 2in drop in front with 21in front. I also though only in terms of lift/drop. So I though everything was pretty much evened out. Although I have to read your post a couple times because you are obviously 2,000,000 times smarter than I am, I think I now understand.
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