Geometry for little wheels
The gears are turning here. Are trail and HTA usually about the same for similar handling regardless of wheel size? More specifically, to more or less copy the handling of my nonsuspension 26 in tourer, could I just figue out the existing HTA and trail, then use those specs with an adjusted offset for a new 20 inch build, or do the smaller wheels normally require different steering axis or trail? I did try searching bent and folder sites, but "trail" keeps getting me talk about routes in most and BROL apparently won`t let me search without registering.
Handling characteristics are much more effected by weight distribution, wheel base, tire type and inflation pressure than moderate alterations in steering geometry. On all my 'bent builds using 20" wheels (with a variety of HT angles), I limit trail to 1" (25.4mm) or less. Much more and 'flop' becomes an annoying issue. Smaller diameter front wheels inherently 'feel' more sensitive, but tiller length, handle bar width and tire selection can usually be tweaked to offset any extremes.
Last edited by PaPa; 11-17-09 at 01:19 AM.
Thank you, PaPa! I don`t know how much comparrison can be made from `bents to upright DF, but I`m glad to have some kind of ideas.
1 inch max trail? Wow! What`s the range of tiller length in your builds? I was thinking about a 4 in stem, but with 20 X 1.75 tires it would be easy to adjust front center and stem length to give me from zero to maybe 8 inches without any toe issues, but it would be pretty heavilly loaded on the front wheel if I went with that long a stem. Then again, maybe a heavy front is a good thing. As far as the trail goes, I decided to try first with an adjustable offset fork- was thinking of a range that would give me from ~25 to 50mm trail, but now I`ll make sure it`ll let me get down close to zero trail on the close end.
For HTA, I found a thread on another forum where a Bike Friday NWT was supposely measured at 73* and I was able to get a rough measurement on a couple Dahons with a little angle finder- looks like about 73 also, so I`m going with that.
Any rate, thanks for chiming in. If you have any juicy tidbits to pass on concerning weight distribuiton or tiller length I`d be happy to hear them. I must admit I hadn`t thought much about the weight and hadn`t thought any about tiller.