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- Nov 4, 2007
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Hi, I had thought that with more offset on the fork yokes affect inversely the trail , so reduce stability ..........less offset on the yokes increase trail ?
marinatlas said:Hi, I had thought that with more offset on the fork yokes affect inversely the trail , so reduce stability ..........less offset on the yokes increase trail ?
Matchless said:Yves,
As you have done plenty of miles on your beautiful (& very shiny) Seeley, how well does the frame stand up to the vibes. Have you experienced any cracking? Also, what balance factor have you used & are the vibes tolerable on a long ride. Sorry if this has been covered in a previous post.
Martyn.
Fast Eddie said:Yves,
Nice looking forks sir!
Do you know if the internals are specially made, or are they 'off the shelf' items from another bike?
You must surely be running out of things to do to that Seeley??
acotrel said:The two extremes are stability or self-steering in corners. With a rake of 27 degrees does increasing the trail theoretically increase stability or decrease it ? What happens when the rake is 24.5 degrees as with a featherbed frame, and you increase the trail ? I can only tell you what happens with a Seeley MK3 when you have too much offset on the fork yokes. The rest simply tangles my brains. Perhaps there is no continuity of trend when you alter rake and trail ? Sometimes you might end up with lead instead of trail ?\
All I do is consider what the steering geometry is on certain benchmark bikes. e.g. a 70s TZ has neutral steering with 18 inch wheels and 26 degree rake, a manx slightly self-steers with 19 inch wheels and 24.5 degree rake but becomes too stable with 18 inch wheels. Our Australian replica manxes often have 18 inch wheels and 26 degree rake and handle like Suzukis. When I fixed the Seeley, I knew about the TZs and figured one degree difference in rake might be tolerable - ARSE BEATS CLASS every time !
If you can make sense out of the figures, you are better than I am. I don't believe there is a formula which fits the evidence. I've read a bit of Tony Foale's stuff, as well as a paper on motorcycle handling from the Society of Automotive Engineers. The conclusion from the latter was that they did not know what they were talking about. Tony Foale is quite a bit smarter than the SAE engineers..
The problem is that with this steering geometry stuff is there are plenty of ways to get it wrong and if you get it wrong the result can be dangerous. When you consider the wheelbase of a Seeley is about 54 inch and mine self-steers when you gas it, what fraction of a degree do you think the rake changes as the rear end squats about 3 inches ?
acotrel said:I suggest you should send a message to Kenny Cummins and ask his opinion about what the best offset would be for your purposes. I know some Seeleys feel very stiff as they come out of corners - tend to run wide. You should not have a problem unless you road-race the bike or get silly on a public road.
I raced for years and never twigged to this steering geometry bullshit.
Holmeslice said:acotrel said:I suggest you should send a message to Kenny Cummins and ask his opinion about what the best offset would be for your purposes. I know some Seeleys feel very stiff as they come out of corners - tend to run wide. You should not have a problem unless you road-race the bike or get silly on a public road.
I raced for years and never twigged to this steering geometry bullshit.
Hi Acotrel,
I appreciate your posts and intensity of having correct offset on your yokes, and your desire to instill this important factor into our psyches. However, I detect a running intensity in your writings that you're at the verge of death every time you go out on your bike!
I have ridden and raced a good many different bikes - Manxes, Seeleys, Commandos, SV650, KTM, Guzzi, Aermachis, etc - each with a considerably different rake and trail than the others, and I have never felt like I've been on the edge of death with the steering. Yes, each of the bikes mentioned have their idiosyncrasies, but after a lap or two you lean a bit about how the bike handles and (hopefully) ride into it. Yes, we all fall down sometimes. But in my time I've not felt like I was racing a bike that was going to kill me. I have been out on poorly setup bikes, but I bring them right back in and put them away!
As for Yves - He needs no consultation. His bike is superb, and makes me smile every time I see it. He is using the same yoke offset as all our NYC Norton bikes run at every different kind of track you can imagine. It is a beautiful bike and very well put together. And I expect Mr. Yves knows how to ride a solo quite well. :wink:
There have been various posts over time containing a lot of mis-information about offset and handling. Ken Canaga has a way of setting everyone straight in a subtle way (see above), and I will impart a bit. At the risk of over simplifying - the MORE offset you have (decreased trail) the quicker the steering will be on the bike, and turn-in will be easier. The less offset (increased trail) the slower the steering but increased stability in a straight line. Bike makers alter their offset to compliment their rake. For example, a Super Motard bike I raced once had the steepest rake I'd ever ridden, but also very little offset in the yokes. This by design, not accident.
Lots of fun here: http://gotagteam.com/KTM_Days/Story_Pag ... _RC8R.html
Respectfully,
-Kenny (my last name is) Cummings