21 front wheel
#1
#4
I had no trouble balancing my 21" wheel and I really liked the look. Stepping up to that size will change trail numbers a little bit though because touring triple trees are raked. The increased wheel diameter changes the geometry in terms of trail. The result will be an increased tendency to straighten the front wheel. In other words, the bike will need a little more work to corner but keep straight easier.
I ran a 21" front wheel on my '03 FLT and went back to 18" with 25.3" tire diameter because I didn't like how the bike handled with the larger wheel. The 21" tire diameter was 27.39" (Dunlop D408 130/60B21). The result is a trail of roughly 6.7" as opposed to 6.2" for a stock touring model up to 2013.
#5
#6
Lowering the forks tubes does not appear to bring the trail back in. Even if shorter tubes did change the trail back, Street Glides (OP) already are lowered and I don't know if they could be lowered more without losing enough suspension travel to hit the front fender.
There are rake and trail calculators on the web that can be used to see the impact of any change to the front end. Here's a good one that covers the basics and it let's you enter rake in the trees:
http://www.rbracing-rsr.com/rakeandtrail.html
If you enter 26.75" as opposed to 27.75" stock tube length (which would not be enough to compensate for the straight up 1" rise of the wheel axle) it doesn't reduce the trail number.
Adding rake to the triple trees to adjust trail length.
Trail usually is between 4" and 6". Harley touring models are 6.2" up until 2013 and 6.8" 2014 up from what I've found in the specifications. I found that on my bike the 21" wheel made the bike noticeably more sluggish in the corners so I changed back to stock diameter. YMMV...
I hope this helps.
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ratpick (01-21-2018)
#7
Ah, got it. Yeah, not sure I remember my trig well enough to calculate shortening of hypotenuse necessary to lower 1", but would be something slightly more and wouldn't correct trail in any case. Interesting--so 21" on pre-2014 would put trail roughly equivalent to rushmore models. Wondering why they did that...
Thanks for info--much appreciated
Thanks for info--much appreciated
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#8
Ah, got it. Yeah, not sure I remember my trig well enough to calculate shortening of hypotenuse necessary to lower 1", but would be something slightly more and wouldn't correct trail in any case. Interesting--so 21" on pre-2014 would put trail roughly equivalent to rushmore models. Wondering why they did that...
Thanks for info--much appreciated
Thanks for info--much appreciated
Yes, I hear you. We all know it's 'just' trigonometry but how exactly did that work again?
#10