Recumbent - Hey, front-drive 'bent owners...

I finished building a no-weld front-drive 'bent a couple days ago and there certainly is a big learning curve! It took a while to learn to push-off but once I got that down riding in a straight line was something else entirely. I haven't quite figured out tight turns yet, but I can already tell it's way more comfy than any other bike I've owned. My question is how should I, or should I, adjust the trail? I have a 26" rear wheel and a 24" front. The handling becomes dicey when picking up speed (coasting down a hill). It seems a little hard to control even on long flats, but I think that's just my inexperience. It's tough learning to trust my legs to do most of the steering. I've never tried a Cruzbike, but that's where I got the idea. I just don't know enough about steering geometry. I'd appreciate any advice on the subject!

Thanks in advance!

We will need pictures of your bike to be able to help you. Well others will be able to help you as I'm not knowledgeable about the physics of bike geometry.

If you want help analysing the geometry of your bike, the best photo angle is a side view about 20 ft away zoomed in to full frame.

On the surface, it appears you took a 26" wheeled bike and lowered the front axle by 1" which increases the steepness of the head angle and lowers the trail. That, combined with your lack of riding experience and the assymetrical forces inherent with a moving bottom bracket front wheel drive (MBB FWD) are likely exaggerating the pedal steer.

For any recumbent other than MBB, if the bike remains twitchy while coasting at speed then it's likely a problem with geometry. If not, then it's probably the rider. On any Cruzbike or clone, pedal steer will always be an issue. For many it will never be a factor, but for some, it can be an overriding problem.

:)ensen.

Instability while coasting down hill is a concern, but might as you suspect be due to rider inexperience. You might try some coasting on level ground or very slight downhills staying dead relaxed with only a very loose grip to see how that feels.

So, here's a picture of the bike. Would a 26" tire on front solve the issue by raising the front of the bike to it's original specs?http://i734.photobucket.com/albums/ww346/pablodiablo6276/HPIM1300.jpg

Why? Maybe it's just me, why would somebody want to even fool with a "thing" like that? No wonder people stare...

Where's your sense of adventure videoboy?

A bike designed for a specific wheel size usually handles best with used with that wheel size. Changing wheel diameter alone always changes handling. Going back to a 26" will increase the trail and give more centering force to the steering. Of course, you'd have to move your brake bosses.

If there's room try reversing the stem so that your hands are opposing the leverage in your legs.

As I said, if it won't coast without problems, it's probably the geometry. If you only get problems while pedalling, then it's probably you.

:)ensen.

You could also try this for a quick experiment... Change out the REAR wheel to a 24 inch Wheel to restore the original trail angle. You could always put it back easily if it didn't help.

I think I'll try a 24" wheel on the rear and see how that affects the handling. The bike the new front triangle/bottom bracket came from was sized for the 24" wheels. I don't know if it will accommodate the 26" wheel. As it is, at a stop my toes just touch the ground. I'll try this first then let everyone know how it works out. Thanks again for all the input everyone!

Nice job, I saw one like this at a recumbent rally 2 weeks ago. I've been thinking of making something similar after seeing it online, but ended up finding my EZ-1 at a price that couldn't be resisted.

Thanks! It didn't take long to build. I have (had) a few junk bikes lying around and after restoring an old road bike and riding that for a little while, I'd decided I'd had enough of the numb wrists/crotch and sore neck and built this one. It's been like learning to ride all over again but after having had it out for a few miles, I'll never go back! It's super-comfortable even though the MBB (movable bottom bracket) is a little weird at first. Inexpensive, too. A rear-view mirror is absolutely essential, though.

Where's your sense of adventure videoboy?

Heres my adventure..I mean my freaking nitemare never ending fwd trike project.
http://www.modelingdvds.com/images/toypics/rollingchassis.JPG


Just after this picture was taken the front wheel bearing supports broke through the weld. :mad:

A lot of stuff is test jigs to try to get the steering and suspension working.

DH

Videoboy-I humbly kneel before you and your superior skills! Did you mold that seat? That is some nice work!

If I read that photo correctly, the pedals are practically in between the two front wheels and your CoG is much closer to the rear axle than the front axles. If so, you will get a very large amount of understeer.

That of course is the compromise with tadpole trikes. Best handling comes with a perfectly even weight distribution of 1/3 on each wheel. That requires CoG to be at the geometric middle of the triangle created by the tire contact patches, which leads to the CoG being placed about 2/3 of the wheelbase ahead of the rear axle. This can lead to problems under hard braking as the height of the CoG can combine with it's forward positioning to create a tipping situation. In addition, having only 1/3 of the weight on the rear tire can create an issue with traction on sketch surfaces.

:)ensen.

Videoboy-I humbly kneel before you and your superior skills! Did you mold that seat? That is some nice work!

No skills as I'm redoing everything it seems, but will get it together someday. Carbon seat was bought from Power On Cycling shop, located here in Florida.

To answer purplepeople, the front tube that holds the crank is not inserted/assembled yet...goes into green piece. Coast testing. Excessive caster-corrected, excessive Kingpin angle due to bearings and ujoint width- corrected, Left wheel shudder and binding when turning right- not corrected and part broke during troubleshooting. (mismatched metals during welding) Didn't know 7000 series alum isn't weldable for stuctural parts.

Working on new pieces. Never ends. Two years now on and off. Lots of test and jigging pieces shown.

DH

Oh... I see. The front drive half-shafts tie into the short large-diameter tube there between them. Smart move for traction an a tadpole, but especially complex when you add in what appears to be independent suspension.

:)ensen.

Didn't know 7000 series alum isn't weldable for stuctural parts.Actually, some are - 7005 TIG welds quite easily and isn't as susceptible to post weld tensile loss as 6061, thus permitting the fabricator to forgo post heat treating. For that reason, many of the aluminum frames manufactured across the pond use 7005. However, sourcing 7005 stateside is a problem.

So, I threw a 24" wheel on the rear and took it for a test-ride and I think that may have straightened out the handling issue. I'm guessing that as long as the front/rear wheels are the same size, the trail is correct. While coasting down some fairly steep descents, the bike seemed to remain fairly stable. I think now I just need some serious saddle time to become more familiar with the quirks of the bike. I've discovered that, while coasting, the hands are more in control. Under power, the legs much more so. Does that sound accurate?