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The rake of the fork looks on the large side so trail could be very low but other than that I can't see why anything else would make it twitchy unless you have a faulty headset or something as twitchy can mean different things?
Unless you are just not used to this sort of bike? Get someone else to ride it and see if they feel it is twitchy or normal.I still think it looks like it has very low trail which would give it a different feel to most bikes.
Looks similar to this. Have you measured the rake of the fork as it looks large.
Much as it might seem difficult to take technical advice from Igglepiggle. Kerley had it spot on from the start, and even supplied an image. The fork looks to have too much rake for the frame. A fork with less rake, will infact increase trail. going from the image above to this....
....not that I expect a second from Calvin and hobbs to carry much weight ;)(* obviously guesswork based on image only, and no measurements)
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PS: IMHO bars have nought to do with it. You should be able to ride your bike with 5" dildo bars if the geometry of your front end is correct.
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Nims23 could change is forks but end up with not solving the problem. I thought of the bars as this seemed the cheapest as a starting point. unless a pair of diferent forks could be borrowed of course. It is trial and error. Its just doing it with the minimum amount of fuss and expense. someone mentioned the wheels. I used deep rim wheels and the only draw back with those is when you get side draft or winds where you feel the bike pull over more. other than that they are great.
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Nims23 could change is forks but end up with not solving the problem. I thought of the bars as this seemed the cheapest as a starting point. unless a pair of diferent forks could be borrowed of course. It is trial and error. Its just doing it with the minimum amount of fuss and expense. someone mentioned the wheels. I used deep rim wheels and the only draw back with those is when you get side draft or winds where you feel the bike pull over more. other than that they are great.
I would measure the trail to check if it was between 50 and 70 mm (using plumb line and a long ruler). Then measure the head tube angle, so I could calculate my fork rake (easier than measuring).
From here I could decide wether or not to start actually usng money ;)
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I would measure the trail to check if it was between 50 and 70 mm (using plumb line and a long ruler). Then measure the head tube angle, so I could calculate my fork rake (easier than measuring).
From here I could decide weather or not to start atually usng money ;)
I understand what you mean mate.
nim23, I think smallfurry has the right idea and will save you money. Its got to be worth checking as a start off point.
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I understand what you mean mate.
nim23, I think smallfurry has the right idea and will save you money. Its got to be worth checking as a start off point.
I was also considering what a PITA it would be to test different forks. Best to have a starting point.
I'm really just echoing Kerleys observations really. Its possible that the fork is more vintage than the frame. In days of yonder road bikes had slacker head tube angles and longer rake forks, as the roads required more front sus.
It might be fine though. There's nothin in the pics that shows that there is definitly a mismatch.
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The forks are definitely the matching pair to the frame, same serial numbers on them etc...
What I did find interesting on the Dave Moulten site, it mentions...
"Other older established builders, still clinging to the little or no trail theory, shortened the fork rake but at the same time made the head angle steeper to maintain the trail status quo.
This made for some very squirrelly bikes being built in the 1970s, with 75 and 76 degree head angles and front wheels almost touching the down tube. Shorter chainstays to shorten the rear end of the bike were pretty much universally accepted."
This is what I reckon the problem may be with mine, being a 70s frame, the head tube looks fine but the rake seems quite a bit. As I say ill measure tonight.
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Right... My rough measurments...
Id say the headtube is 75-6 degrees, the rake is about 45cm maybe more, and the trail is about 6cm.
That sounds quite a bit to me.
If your head tube is 75 degrees (pretty steep), and your rake is 45mm (pretty standard), your trail would be 43mm. I would say (IMHO and all that) that this is too low (50 - 70 = modern norm).
If your head tube angle is 76 your trial is even smaller at 37mm.
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*
[I]"Other older established builders, still clinging to the little or no trail theory, shortened the fork rake but at the same time made the head angle steeper to maintain the trail status quo.*
This made for some very squirrelly bikes being built in the 1970s, with 75 and 76 degree head angles and front wheels almost touching the down tube. Shorter chainstays to shorten the rear end of the bike were pretty much universally accepted."
[/I]
This makes sence, as the headtube seems to have been made very steep. The fork rake has not been reduced enough to 'maintain the status quo' though. If the framemaker had reduced the fork rake further though (say 35mm), the trail would have returned to a more road friendly 50 something.
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I'm getting my trial/rake headache now. Hope that helped.
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Most 60s road frames were built with the standard 72x72 frame angles. I still have my Alan Shorter track/time trial frame built for me in 1963/4. its got steep angles and very very little fork offset. Very difficult to ride hands off but also very responsive. Is it possible to measure the angles. Take the angles from the top tube to the head ( steerer ) tube and the same to the seat tube.
Also you could look at the " http://www.classiclightweights.co.uk site for a visual site of the older designs. -
Just an update.
More precise angles:
72x72 frame680 diameter wheel inc. tyre, 45mm rake.
Makes my trail 63mm
I have however, bought some carbon forks with a lower rake. This will increase my trail by about 5mm, plus I get some sexy lightness on the front end ;-)
and???!!!.... dont leave us in suspense. has it worked??!!!
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Sorry to hi-jack this thread a bit, but I have a similar sort of problem. While I wouldnt say that my bike is twitchy, Im terrified off taking my hands of the bar. Can someone just confirm one way or the other, if I hold my bike off the ground and center the bars, should they be able to stay reasonably straight? Mine always turn (sharply I might add) to the left.
Is my headset too tight/loose? -
are your brake/gear cables moving the bars?
ideally there should be no deadspots and the bars should move freely from one side to the other
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The bars move freely and I doesnt seem like its the cables that are causing them to turn. It just seems like the bars are reluctant to stay centered if I unweight the front end in the slightest then they turn to the left, maybe its just me and Ive just got to get used to it/become more confident.
No-legs
Smallfurry
kerley
lot14
clockwork_killa
dancing james
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About
Twitchy steering..?
Posted by
Jokers! ;-)
Its the top picture people should be going by for the bike geometry.
The bottom picture was when I just put it together with a random saddle to see what it looked like.
The top picture, the saddle sits far back and a bit higher. Im just over 6ft so the frame isnt too big for me.
How is this facepalm? so far ive come to the conclusion that the bike being an older frame could probably do with a little more trail from the Dave Moutlon site, invaluable information I think!
I ride another road bike so im used to riding drops. Isn't it all about getting you bike to ride as nicely as you can? Its all fine tuning from here on... ;-)