Various Seeley Frames (Mks)

SteveA

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acotrel said:
I've just measured the offset of the Arces fork yoke s which were fitted to my rolling chassis when I bought it, and caused the bike to stand up under brakes and turn. The measurement is 65mm (2.6 "). I haven't checked the head angle on the frame yet, however it is an original Mk3 Seeley and should be 27 degrees. The difference in handling between the Arces fork yokes and the TZ350 yokes is extreme, you cannot miss it. I could not race the bike when it was fitted with the Arces yokes, it was simply impossibly dangerous
I understood that fairly small changes in offset make a considerable difference. (I was given 2.25" as the offset used as standard on Seeley, Rickman, Featherbeds and Commandos) I was considering trying around 2.0", but decided to build and ride first with something probably more 'neutral' since I going with longer shocks and plenty of scope for leg length adjustment. The bike is on 18" rims and last time I rode this actual one it was on 19" so plenty of change anyway...

I can see that 2.6" would likely be too much offset.....1.4" also seems extreme in the other direction and I guess what you really describe is a need to use power to steer it at all!.....so I am guessing that if you fitted 2.25" it would give you more neutral steering....might be more less 'fun', but less worrying?

Since I also now have slightly longer swinging arm I can see that I may want less offset in future....but we will see....just need an engine and gearbox in it to find out!...If I did change I don'tthink I would go less that the 1.75" DWS first mentioned...

BTW 2.6" is nearer to 66mm by my calcs and we seem to have gone over a range of different figures quoted in each post.....I noted my own error for which I apologised, I thought initially my yokes were 2.5" but rechecked my figures and corrected to 2.25".....a change from 2.25 to 1.75 is I understand significant and I guess I am surprised to see figures much outside of these in use on any period frame be it Norton Twin or 7R/G50 or Manx.
 
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Dances with Shrapnel said:
The 500 Norton with the Mk 2 frame has Ceriani forks and a very low profile. When I first got on the bike Herb Becker warned me about the turn in rate. Turn in is lightening fast and first impressions are alarming but you grow accustom to the set up. I am very happy with it but the bike literally drops into a turn.
I see I was not clear on tha above post and should have restated that the 500 Norton Seeley Mk2 has a 1.5" triple clamp offset. The 500 takes very little physical effort to initiatate a turn whereas the 750 Norton Seeley Mk2 with the 2.5" triple clamps does take a noticeably greater physical effort to initiate a turn yet still very light to the feel. I like the lightening feel of the 500.

All bikes I cited are with 18" wheels and I suppose the relatively lower smaller tire profiles (front and rear) that I have on the 500 have something to do with the lighter feel.
 
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'1.4" also seems extreme in the other direction and I guess what you really describe is a need to use power to steer it at all!'

Not true, if you ride it normally, the steering is lightning fast. I only noticed its self-steering when I started gassing it much earlier in corners. I think in general terms, the larger head angles and offsets, and fatter tyres give more stable steering.
My Seeley is fitted with 18 inch wheels and I will let you know the tyre sizes by updating this post after I've had a look.
Years ago I changed wheel size in my 500cc Triton from 19 inch to 18 inch. I instantly regretted doing that. The bike always tried to run wide, was heavy and tiring to ride fast. Several of our guys have done this to orignial manx Nortons in attempts to get decent tyres, it is not the way to go. The replica frames with the 26 degree head angles handle like a TR suzuki. To me it seems like idiocy to do that stuff, If I wanted to race a modern bike, I would do that and not turn a fifties manx into one.
Thanks for your comments on this subject, I'm beginning to get a much better understanding of where the original Seeley was as far as handling goes. The last time I raced was in an historic race at Winton a few years back. In one race I got the usual poor start but was up just behind the first few guys who were riding the fast 1100cc CB750s. On turn two they were all out on the ripple strip when my bike turned underneath them. I had the circuit open in front of me, the bike accelerating hard, when it popped a fuel line and stopped. There was methanol all over t e motor, however it did not catch fire. I was lucky, because I found my mate had pulled the fairing up to give hand clearance , and that se verely limited the steering lock. If I'd ended up in a situation, I probably would have crashed. I don't usually do historic racing, but I will try to have another go at those guys this year. I have never believed the Seeley has so much potential - it is extremely easy to ride it very fast.
 
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I have just looked at my Seeley - tyre sizes
front : 100/90 - 18 on a wm3 rim
rear: 120/100 - 18 on a wm4 rim

If anyone ever copies the exercise of using TZ350 fork yokes on a Seeley, I'd be interested in their observations on changes to the handling. To fit the yokes on my bike only the spindle had to be modified. The Ceriani fork staunchions fitted perfectly, and the centres are correct for the front wheel.
 
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Hi on my Seeley MK2 the offset of my trees will be 1,57 (40mm), both 18" wheels , as it's a long term project (pockets not deep enough!!) I do not have put it on the road yet ......but as they are Yamaha R6 yokes (trees), I could play with the stanchions protruding into them , as well with the shocks wich may be adjusted in height , so I will see............
 
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I would be interested if you report how your bike handles, on this forum. You might not often gas it early enough in corners on public roads to really notice it self-steering. When I use the effect, I always leave a bit of room so that if things go wrong, you have time to recover. It seems to be all about anticipation. The worst experience was when I had too much offset, and the bike stood up and turned the wrong way during a race. It was sheer arse that I looked for a soft place to crash it, and turned the wick up again to get there, and it came out of it's antics.
 
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I just got my wife to hold the bike and I've remeasured the specified points to calculate the trail.
the difference on the ground between the line down the forks, and the line vertically the or the axel is 134mm. The forward offset is 35mm. So I believe that is 99mm of trail. I apologise for my earlier figure. I think I said it was 72mm. The last time I tried to measure this I was on my own and struggling to do several things at once. The marks on the ground I ended up with this time were the same distance apart as the ones I made the first time, so I must have stuffed up a simple subtraction, or written the answer down erroneously. I think the errors in my current measurement would be less than 2mm in any one measurement and it is unlikely the errors would add.

Your figure of 115mm seems to support the current value I've just calculated for my own bike.

I've found the quick steering really good on a race circuit, however on a road and with isolastics the story might be different. The self-steering effect is great, it is just hat I have a problem really trusting it. I wouldn't like it happening on a bike with a hinge in the middle.
 
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I was interested in Dances reply. It gives a perspective from someone with race experience, used to picking up the differences in handling. The only reason that I used the TZ yokes is that I had them lying around, and I knew my bike had a head angle only one degree different to the TZ. I couldn't go very far wrong. And if I had made a set of yokes, what offset should I have given them ?

'Bullshit baffles brains' ?

Begs the question - how many guys are racing converted road bikes and simply riding around their handling problems ? The difference in my Seeley's handling was dramatic.
 
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acotrel said:
I just got my wife to hold the bike and I've remeasured the specified points to calculate the trail.
the difference on the ground between the line down the forks, and the line vertically the or the axel is 134mm. The forward offset is 35mm. So I believe that is 99mm of trail. I apologise for my earlier figure. I think I said it was 72mm. The last time I tried to measure this I was on my own and struggling to do several things at once. The marks on the ground I ended up with this time were the same distance apart as the ones I made the first time, so I must have stuffed up a simple subtraction, or written the answer down erroneously. I think the errors in my current measurement would be less than 2mm in any one measurement and it is unlikely the errors would add.

Your figure of 115mm seems to support the current value I've just calculated for my own bike.

I've found the quick steering really good on a race circuit, however on a road and with isolastics the story might be different. The self-steering effect is great, it is just hat I have a problem really trusting it. I wouldn't like it happening on a bike with a hinge in the middle.
I might be wrong but your method of calculating trail doesnt seem quite right, shouldnt it be the intersection of a line through the steering head stem (not the fork leg) and a vertical line from the axle?
From the top of my head your trail is more than 99mm due to the projected distance of the 35mm offset being less than 35mm (a trig function of the head angle). Also your method relies on the fork tubes being parallel to the stem which they may or may not be (the 850 commando isnt)
 
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The difference due to angularity when calculating the amount to subtract from the forward offset is minor. What It did was simply subtract the yoke offset from the distance I measured from the line down the staunchions to the vertical through the axle. You are quite correct that the angularity introduces an error, however when I am finding the points of contact of the lines on the ground I use 6mm steel rods. I believe the figures I have given have errors up to about one millimetre, and that the errors don't add much. Even measuring the Yamaha fork yokes is not easy. All I can suggest is that if you have a Seeley with 18 inch wheels, and can easily find a set of TZ yokes , try it.
 
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in the late 90's i built a seeley road bike - using an xtz 660 race tuned engine.



once built , the bike was an amasing ride - never have i ridden a bike that handled so well......

it weighed 101kg wet.
 
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the front forks were marchzocchi from a 70's ducati - married to wheels from a Suzuki 350 rebel

with alloy rims. I wanted to keep an early 70's look . The brakes were fantastic TLS on the front

that would 'scream' the AVON endurance racing tyres at 70mph - and could induce a 'stoppie'.
 
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There seems to be something dimensionally wrong with it. It all looks too small ?
 
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The first photo of the bike with the single cyclinder e ngine has a Mk3 frame the same as my own. I use fork yokes with much less offset. The Cooper bike, I suspect the frame is Mk2. A Mk4 is similar except where the swing arm pivot mounts.
 
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