Twitchy stearing on Seiran 24

GuyY

New Member
My Seiran 24 (Challenge) likes to straighten up repeatidly on gentle curves when light stearing pressure is applied. In a straight line it feels fine. On a moderate curve the stearing feels steady. But on a very gentle curve, e.g., coming out of a roundabout when your riding path switches curve direction, the stearing feels will suddenly "correct" the direction of travel into a straight line if your not firm with the pressure on the stearing. This effect is very disconcerting, especially when you're indicating with your hands and is particularly noticeable at light stearig pressure. There's a bit of slack in the stearing rod [in the joint component of the rod itself rather than the ball/socket joint parts] which is probably the culpret. Anyone else experienced this fault/characteristic? Anyone had exerience of 'tweeking' the stearing rod arrangement [and not ended up in a hedge!] on one of these things: what should I look for, touch, don't touch, etc.?
 

Fiona N

Veteran
Are you sure it's not just a problem in the steering/headset bearings. It sounds exactly like the problem you get on an upright when the bearing race gets a bit uneven and the balls like to fall into the hollows.

Of course, I'm not totally au fait with Seiran equipment but it might be worth checking the obvious before tinkering with the steering geometry.
 

arallsopp

Post of The Year 2009 winner
Location
Bromley, Kent
When you're stationery, can you move the bars without detecting a corresponding deflection in the wheel? Likewise, can you rock the bars clockwise/anticlockwise at all? (imagine they're the wings of an aircraft and the boom is the fuselage. Can you raise a wingtip?)

On my Furai (also a challenge) the front wheel has a tendency to throw crud at the steering bearings, which kills them pretty sharpish. The resulting play means that the front wheel will move independently of the steering (we're talking max 1 degree here) and that can be odd around cambers, quick S bends, stone chippings, etc).

When I replace them, I'll mount a bit of something to deflect the spray from doing it again.
 
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GuyY

New Member
I'm fairly happy that the bearings are OK (only had the bike since the end of March...so famous last words). In terms of crud thrown at the bearings, the Seiran came with mudguards which sit tight over the tires so they should be providing sufficient protection from crud. The only definite observation I've detected is a slight movement between the ball/socket fitting and the main stearing rod. The ball/sockets are tight (for now) but where the ball/socket inserts into the main shaft of the rod, I see 'slack movement' of about 1-2mm(could be 2-3mm). I think(?) I'm surprised by the apparant relationship between the degree of movement in the rod compared to the change in wheel angle. I'll do a more thorough investigation when I get home tonight (kids allowing) and keep you updated.
 
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GuyY

New Member
The play in the steering rod is about 2mm which is OK. But I think the engineering design used to connect the front fork to the handlebars (USS design) is an issue. If I plot the effort needed to turn the front wheel from 10 through to 2 (with 12 as straight ahead) I have two peaks of effort close to and either side of the 12 position. Leading up to these peaks the increase in effort is gradual before suddenly falling away to almost nothing next to the 12 position. This is when the stearing suddenly goes light and twitchy, as if something is loose. On the road, coming out of a roundabout the wheel could be tunred at an angle that sits it on the inner slope of one of these 'peaks'. So if I'm not concentrating the wheel 'drops' into this 'central zone' and the bike appears to suddenly run straight untill I re-correct it. When starting the turn I need enough curvature in my direction of travel to allow me to 'nudge' the stearing beyond these 'inner slopes'. I guess it's something I'll have to live with :-( ....otherwise the bike's really good fun !
 
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GuyY

New Member
All looks as it should. No slack anywhere other than the joint between stearing rod and the ball/socket end piece. When the bike is stationary the effect is more marked than when moving. The faster I go the less the effect is felt (or so it seems) due to forces induced by a spinning wheel (?), although the stearing is light when in a straight line. The tires are 47-507 which may amplify the effect compared to thinner tires perhaps? My instinct is to think that the geometry used in the stearing is creating this pattern of "effort" for the front fork. I'm not an engineer, either practical or academic, so I'm at a bit of a loss. I'll carry on checking everything I can on a regular basis and see if any physical changes match the effects.
 

arallsopp

Post of The Year 2009 winner
Location
Bromley, Kent
Any chance of a photo of the undersides? Got a cruddy camera phone here, so will take some snaps of how mine looks. I'm thinking along the same lines as Catrike here. Could be my pics don't match yours at all.
 

ACW

Well-Known Member
Location
kilmaurs
from what you describe as the effort required to move the stearing it sounds like the head bearings to me, you get dents in the bearing race and it takes a bit of force to move the stearing to the straight ahead position then the balls fall into the dents in the race and it goes light, but then requires more force to move the stearing out of this position, i would disconect the stearing link arm and try moving the forks on there own,
good luck
 

ACW

Well-Known Member
Location
kilmaurs
had another read at the posts and it definitely sounds like the head bearing, desire to run straight ahead is a classic example of this
 
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GuyY

New Member
I took the steering rod off as suggested and 'lo-and-behold' the variation in force needed to turn the front wheel is still there. In fact when moving the wheel by hand the variation in pressure is even more pronounced. If, as you guy's suggest, the bearings are indeed "shot" then I'm very disapointed with Challenge's build quality as I've only had the bike since 12th March riding approx. 650 miles on roads in that time. What next? Take it to a reputable local bike shop to get them to confirm (from a professional point of view) the nature of the problem and depending on their findings, chasing Challenge via London Recumbents? Other options?
 
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