Vision R40 SWB stability

I had a Vision R40 recumbent given to. The previous owner switched the stock 16 inch front wheel for a 20 inch front wheel and never rode it. Well I rode it and yes I'm still learning the whole recumbent experiece, but it seems to be unstable when going at faster speeds. Almost like it doesn't want to turn, then it zooms to that direction, over compensating. I'm wondering if it has to do with this 20 inch wheel being put in the stock fork that was originally made to have a 16 incher. Would this slight increase in trail cause this? Or is this just the nature of the beast of a SWB bent?

MIke

Hi There!

I've got a Vision R45. But with a 16" front wheel. It sounds like the frame stability is being compromised at speed because the 20" wheel may be acting like a giroscope.

Personally, just for your own safty I would put a 16" wheel back on to it!!

Is the bent a USS (Under Seat Stearing) or OSS (Over Seat Stearing) and does it have front suspension?

USS should (in therory) be more stable at higher speeds. But USS is less stable at low speeds. And the opposite is also true. (That how I've been found it!)

Regards
jdkewfi

And the opposite is also true FOR OSS. (That how I've been found it!)

Regards
jdkewfi[/QUOTE]

Hi Mike

As a new 'builder' of a SWB 'bent I had some fun with trail on my newly completed prototype. The first pass left me with a 'trail reading' of 2+ inches (the angle of the headtube to the maintube was reversed during welding and only picked up once assembly started) which made the beast a horror - ridable but very 'unstable'. We sliced the headtube out and rewelded to the correct angle - trail down to 3/4 inch. She became a darling immediately - very stable and easy to control. Which leads me too your problem - a larger front wheel in the same or longer fork is going to raise the front of the bike and up your trail (unless rake is changed) which, if my experience is anything to go by is sure to mess up the 'stability'. Just my 'in-expert' 5 cents worth.

Go back to the 16 inch wheel and I'm sure all will be resolved.

__________________
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MTB: Schwinn MOAB 1 Only the frame left now!
'Bent: Homebuilt - SWB - 4130 - Prototype

Mike, I have a SWB 40 with a 20" front wheel and over seat stearing. It is an 03 so the wheel base is a bit longer than earlier models. I am assuming that when the 20" wheel was installed on your bike, that the correct fork was also installed. There could be other factors at play in its handling other than just the wheel diameter. What is the condition and adjustment of the headset? How many mile do you have on it? (I'd recommend taking it easy the first 100-200 miles)

When I was getting used to mine, I found that moving my hands as far outboard on the bars as possible helped reduce my twitches making the bike twitch and I had to learn to relax. If you choose to go back to the smaller wheel, make sure you use the correct fork. Vision had different forks for the different diameters. Good luck and don't give up on it, just take it easy until you get it sorted out. They are a wonderful bike.

Ken