Ti Bikes

General cycling advice ( NOT technical ! )
glpinxit1
Posts: 6
Joined: 25 Jun 2019, 7:45pm

Re: Ti Bikes

Post by glpinxit1 »

Are Lynskey no longer imported to the UK?
User avatar
531colin
Posts: 14028
Joined: 4 Dec 2009, 6:56pm
Location: North Yorkshire

Re: Ti Bikes

Post by 531colin »

biketips666 wrote: 16 Sep 2021, 12:27am Most titanium bikes don't seem to have titanium forks. Why is this?
I think there are lots of reasons.
Perhaps most importantly, carbon forks are "normal" now....they are just "what you have".
When titanium frames started to be manufactured, there were quite a lot of failures, often in the "weld-affected zone" . A frame failure won't usually kill you, but there were also some well-publicised failures of forks, which is pretty hazardous.
I was involved with some fairly early titanium forks, before tapered steerers ; or at least before I had come across tapered steerers. So the steerer was straight inch and eighth titanium. Now titanium is about one third less dense than steel, but its also less stiff to about the same degree.....it follows that a titanium steerer will be more flexible than a steel steerer the same size. The forks were wonderfully comfortable, but with cantliever brakes a flexible steerer causes fierce pulsing of the brakes on and off, so when you put the brakes on you got a kangaroo ride. I doubt we were the only people to find this. (The Tricross had a bad reputation for this, at about the same time.) The engineering solution to this is a tapered titanium steerer ; the only one I came across at the time was from Paragon machine works, and as I recall it was staggeringly expensive, I guess machined from solid. Just now I can't get their website up.
You might well run into similar problems with a disc brake putting all the braking torque on one fork blade.
User avatar
531colin
Posts: 14028
Joined: 4 Dec 2009, 6:56pm
Location: North Yorkshire

Re: Ti Bikes

Post by 531colin »

Audax67 wrote: 16 Sep 2021, 9:56am
biketips666 wrote: 16 Sep 2021, 12:27am Most titanium bikes don't seem to have titanium forks. Why is this?
Resonance: Ti forks are springy and liable to cause shimmy. A friend of mine had an early-2000s Passoni all-Ti bike and had fierce shimmy at certain speeds. Carbon is stiffer. I just visited the Passoni site: they're using carbon forks these days.
The clue is in the "at certain speeds".
Shimmy is generally recognised to be a flexing of the frame (at its resonant frequency) driven by something else occurring at the same frequency.....usually thats the wheel doing the "magic number" of revolutions per minute at a certain speed.
recent thread viewtopic.php?f=5&t=147525&p=1633265&hi ... y#p1633265
De Sisti
Posts: 1227
Joined: 17 Jun 2007, 6:03pm

Re: Ti Bikes

Post by De Sisti »

biketips666 wrote: 16 Sep 2021, 12:27am Most titanium bikes don't seem to have titanium forks. Why is this?
My titanium bike has titanium forks. No issues whatsoever. Been using them since 2006.
Image
User avatar
531colin
Posts: 14028
Joined: 4 Dec 2009, 6:56pm
Location: North Yorkshire

Re: Ti Bikes

Post by 531colin »

De Sisti wrote: 16 Sep 2021, 12:35pm ................
Image
Could probably have got away with a slacker seat tube angle?
Inch and eighth straight steerer will be OK with sidepull brakes, no kangaroo ride.
Fork blades round and same diameter all the way down? I could probably have a guess at who built it.
De Sisti
Posts: 1227
Joined: 17 Jun 2007, 6:03pm

Re: Ti Bikes

Post by De Sisti »

531colin wrote: 16 Sep 2021, 5:10pm
De Sisti wrote: 16 Sep 2021, 12:35pm ................
Image
Could probably have got away with a slacker seat tube angle?
Inch and eighth straight steerer will be OK with side-pull brakes, no kangaroo ride.
Fork blades round and same diameter all the way down? I could probably have a guess at who built it.
Why would it need a slacker seat tube angle (whatever that means). Bear in mind; I'm not one
of those people who is sensitive enough to detect if there's a £10 note under their mattress when they're in bed. :lol: Scrutinise all you want, the bike is comfortable enough for me*.

[edit: when I ordered the frame I specified the chainstay length, headtube length and that I wanted space for mudguards (to be fitted when this eventually gets a side-move to winter riding duties).

*Many 100 mile+ rides done on it. No issues with comfort or reliability.
Jamesh
Posts: 2330
Joined: 2 Jan 2017, 5:56pm

Re: Ti Bikes

Post by Jamesh »

De Sisti wrote: 16 Sep 2021, 12:35pm
biketips666 wrote: 16 Sep 2021, 12:27am Most titanium bikes don't seem to have titanium forks. Why is this?
My titanium bike has titanium forks. No issues whatsoever. Been using them since 2006.
Image
How do you rate those wheels?

Just brought a pair!

Cheers James
De Sisti
Posts: 1227
Joined: 17 Jun 2007, 6:03pm

Re: Ti Bikes

Post by De Sisti »

I bought the wheels 2nd hand for £100 in 2010 from a guy (with lots of money) who was using
them on his commuter bike :!: They've needed little attention since then. They are super-lightweight and accelerate up to speed very quickly. One of my best bargain buys.
User avatar
Hellhound
Posts: 426
Joined: 19 May 2021, 7:39am

Re: Ti Bikes

Post by Hellhound »

glpinxit1 wrote: 16 Sep 2021, 10:51am Are Lynskey no longer imported to the UK?
I bought my frame-set direct from Lynskey in 2019.At that time CRC were selling their frames but it looks like they no longer have any.
User avatar
Audax67
Posts: 5186
Joined: 25 Aug 2011, 9:02am
Location: Alsace, France
Contact:

Re: Ti Bikes

Post by Audax67 »

531colin wrote: 16 Sep 2021, 12:29pm
Audax67 wrote: 16 Sep 2021, 9:56am
biketips666 wrote: 16 Sep 2021, 12:27am Most titanium bikes don't seem to have titanium forks. Why is this?
Resonance: Ti forks are springy and liable to cause shimmy. A friend of mine had an early-2000s Passoni all-Ti bike and had fierce shimmy at certain speeds. Carbon is stiffer. I just visited the Passoni site: they're using carbon forks these days.
The clue is in the "at certain speeds".
Shimmy is generally recognised to be a flexing of the frame (at its resonant frequency) driven by something else occurring at the same frequency.....usually that's the wheel doing the "magic number" of revolutions per minute at a certain speed.
recent thread viewtopic.php?f=5&t=147525&p=1633265&hi ... y#p1633265
From what I've read it's the combination of frame & fork, with the fork in antiphase to the frame, but that could indeed simply be the frame flexing left and taking the pivot with it. I first had it on my own Ti/CF bike within 100 metres of starting the descent from Mt. Ventoux, on a -8% slope at 38 kph - not that steep and not that fast, and nothing that I hadn't done before with nothing untoward happening. However, I was nervous at the time and holding the bars rigidly, so maybe I was acting as part of the oscillating system - the more tightly I gripped the worse it got. I later found that a seatpost rack + bag lowered the resonance frequency, so that shimmy set in at 25 kph-ish. Putting a HB bag on completely damped it out, no matter what I had at the back.

Unfortunately I've got shorter in the last few years and the bike hasn't, so we rarely ride together these days. Shame.
Last edited by Audax67 on 17 Sep 2021, 2:30pm, edited 1 time in total.
Have we got time for another cuppa?
slowster
Posts: 2586
Joined: 7 Jul 2017, 10:37am

Re: Ti Bikes

Post by slowster »

De Sisti wrote: 16 Sep 2021, 6:09pm Why would it need a slacker seat tube angle (whatever that means). Bear in mind; I'm not one
of those people who is sensitive enough to detect if there's a £10 note under their mattress when they're in bed. :lol: Scrutinise all you want, the bike is comfortable enough for me*.
It looks like the saddle is as far back as the rails will go in the seat post, and the seat post itself looks like it has an unusally large amount of setback (it appears to be an older model Easton seatpost - current versions have no more than 20mm setback). That is presumably your preferred/ideal saddle position, but you probably would not be able to move the saddle back any further if you wanted or needed to do so later, something which can be prompted by age or a switch to a saddle with shorter rails, such as a Brooks. I think having the saddle as far back as the length of its rails permits also puts more stress on the saddle, and might result in premature failure (some manufacturers even put limit marks on the rails to stop the saddle being too far back or forward on the rails).

It is good practice for the designer of a custom frame to select a seat angle which will result in the seatpost clamping roughly on the middle of the saddle rails, so that the rider will have a range of both fore and aft movement from their current preferred position, and the gap between your rear tyre and seat tube shows that the designer could have reduced the seat angle by probably at least one degree.

Fitting a seatpost with an unusally large amount of setback and sliding the saddle as far back as it will go is something which might be necessary with an off the peg frame, some of which have quite steep seat angles, e.g. 73.5 or 74 degrees, but it should not be necessary with a good custom frame that has been designed for an individual rider.
De Sisti
Posts: 1227
Joined: 17 Jun 2007, 6:03pm

Re: Ti Bikes

Post by De Sisti »

slowster wrote: 17 Sep 2021, 11:15am you probably would not be able to move the saddle back any further if you wanted or needed to do so later, something which can be prompted by age
We're all different. Your diagnosis won't apply to everyone.
slowster
Posts: 2586
Joined: 7 Jul 2017, 10:37am

Re: Ti Bikes

Post by slowster »

De Sisti wrote: 17 Sep 2021, 11:39am
slowster wrote: 17 Sep 2021, 11:15am you probably would not be able to move the saddle back any further if you wanted or needed to do so later, something which can be prompted by age
We're all different. Your diagnosis won't apply to everyone.
Indeed. The problem is none of us knows with absolute certainty how we and our bodies will change with age, so it makes sense to have as much leeway as possible to be able to accommodate change if and when it becomes desirable or necessary.

It's similar with threadless headsets - it's best always to err on the side of caution and leave a good bit more of the steerer uncut than current handlebar height requires, to give the option to raise the handlebars later if needed.
Last edited by slowster on 17 Sep 2021, 4:18pm, edited 1 time in total.
De Sisti
Posts: 1227
Joined: 17 Jun 2007, 6:03pm

Re: Ti Bikes

Post by De Sisti »

I would have thought one would move a saddle forward with age (assuming less flexibility).
User avatar
Audax67
Posts: 5186
Joined: 25 Aug 2011, 9:02am
Location: Alsace, France
Contact:

Re: Ti Bikes

Post by Audax67 »

De Sisti wrote: 17 Sep 2021, 12:45pm I would have thought one would move a saddle forward with age (assuming less flexibility).
I think the distance from the point you sit to the vertical through the pedals is critical for power development, not to mention ankle/knee/hip stresses so, assuming that that is OK, I'd prefer to bring the bars backwards (shorter stem) and maybe set them a bit higher to reduce neck stress. You increase windage, but you can't have everything.
Have we got time for another cuppa?
Post Reply