Cycling UK Forum

Colin, Out of interest how much does the 54" titanium touring frame weigh by itself ? (Spa website lists weight with fork, which you can assume is around 1.1kg ish, but would be interested to know the breakdown) What is the fork offset recommendation? ta! Im trying to think if I can get my perfect light weight audax bike by swapping my thorn audax frame for a spa touring frame with the only think other I think I'd need to change would be getting some cantilevers...

You would need to get the shop to weigh a frame, I don't have one here.
As on the shop website, fork needs to be 385mm axle to crown for a 71 degree head angle, which wants 54mm offset or close.
An audax Mk3 fork if it was the 55mm offset variety would do nicely (apart from restricted tyre size?), the stray 5mm length is worth about 1/4 degree.....thats going to be from one of the Thorn audax bikes that don't suit a carbon fork (45mm offset)
http://www.sjscycles.co.uk/700c-thorn-audax-mk3-r-steel-fork-blue-prod36924/

honesty wrote:Out of interest how much does the 54" titanium touring frame weigh by itself ?

Mine is 1,655g including seat clamp. Lighter than I was expecting, and lighter than the 55.5cm Kinesis Gran Fondo Ti Disc, which at 1,770g is a fair bit heavier than expected.

And 195g lighter than the 54cm Spa Roughstuff.

Thanks. That is interesting. I was working off the weight given on the spa website that gives 3kg for the 54" frame, estimating a steel touring fork weighing in at 1.1kg would give a frame weight of 1.9kg. I assume therefore that the 3kg weight also includes the weight of the headset which then makes the frame weight comparable to other titanium frames (for example the Sabbath Silk Route is quoted at 1.65kg for the same size).

How would a fork with offset of 45mm and axle to crown length of 390mm effect the trail?

54" frame? presumably you mean 54cm?

cheers

oops. yes!

honesty wrote:...........How would a fork with offset of 45mm and axle to crown length of 390mm effect the trail?

Spa tourer has a head angle of 71 deg with a 385mm fork, an extra 5mm is going to slacken the head angle a touch, maybe 1/4 degree, I'm not even sure stuff is made to that degree of accuracy.
45mm offset and 72 deg is considered by many to be the "sweet spot"....45 offset and 71 deg. is often used to get a shorter reach on small bikes, the steering is noticeably slower, but its something I quickly get used to, however I don't mind "slow" steering, i hate "twitchy".
From memory, Van Nich. go down to 70.5 deg with 45mm offset I think thats their Amazon.
In conclusion, if you don't mind slow steering, go for it. If you like lively steering, I don't think you will like it.

Just to update this slightly.

Due to the good weather, I took the old racer out for the commute. Its about 5kg lighter than the commuter. While overall there is no much difference in speed, there is a subtle difference. I think its a couple of things:

1. The bike is easier to manhandle
2. It accelerates faster, but more importantly I seem to use less energy so overall the journey is much easier (or I can ride another 3-4 miles and not feel knackered)

The above was echoed when I rode my mtb on the weekend, as its weight is on par with racer. It felt easier climbing with no loss of comfort and just felt slightly nicer. If I change my mind when I take the commuter I will report back. However it seems like the lighter weight, just makes everything just bit easier and nicer, however if I never rode one I would not really notice.

what you describe is not uncommon. Lightweight machines (if they are not built too stiff) are very often just 'nicer to ride' in a way that is difficult to describe.

I think that part of the improvement comes from the effect of the bike being (to all intents and purposes) part of the 'unsprung weight' in the system. Anytime that is reduced, the tail wags the dog a bit less and everything just gets that bit nicer as you go down the road. There's a lot more to it than that but I think it is a big effect.

cheers

There are a couple of other aspects to this, as well...

On hills, the extra weight may not seem very different, but it does take more energy to get up. For my commute to work, unless I deliberately pedal harder, it seems to cost me about 1 minute for every 100 metres climbing.

The other thing is that I tend to use the gears available to me. My bottom gear is higher (more gear inches) on my road bike than my other bikes, so I tend to go a bit faster (or pedal slower )

This is one of the reasons that I use a road bike as a commuter when the weather warrants it. If nothing else, it's always nice the first time I ride it to work in the spring

531colin wrote:

honesty wrote:...........How would a fork with offset of 45mm and axle to crown length of 390mm effect the trail?

Spa tourer has a head angle of 71 deg with a 385mm fork, an extra 5mm is going to slacken the head angle a touch, maybe 1/4 degree, I'm not even sure stuff is made to that degree of accuracy.
45mm offset and 72 deg is considered by many to be the "sweet spot"....45 offset and 71 deg. is often used to get a shorter reach on small bikes, the steering is noticeably slower, but its something I quickly get used to, however I don't mind "slow" steering, i hate "twitchy".
From memory, Van Nich. go down to 70.5 deg with 45mm offset I think thats their Amazon.
In conclusion, if you don't mind slow steering, go for it. If you like lively steering, I don't think you will like it.

Thorn has a 380mm axle to crown. Presumably the smaller offset means more chance of toe overlap.

How would an 853 fork eg http://www.sjscycles.co.uk/700c-thorn-mer853vc-steel-fork-stealth-black-prod30602/ compare with similar 631 fork in terms of ride?

Your link tells me the Thorn forks are 383mm axle to crown, and either 46 or 52mm offset. (against 385 and 57). The steering will be a tiny bit slower with the 52 offset.
My Reynolds information doesn't list 853 fork blades, the information for 631 is on a previous page. Thorn are always ready with the hyperbole, I wonder if you will get any actual information out of them about the fork blades.
I think they are staggeringly expensive at £239 for a pair of forks made in the Far East; Lee Cooper, who has built me a couple of pairs of forks, will build you a made to measure 631 FRAME and forks for £565, you can have 1" threaded steerer if you want, and if you specify 60mm offset and 70.5 deg head angle, you can have nice handling and a short top tube for a given front centre dimension. http://leecoopercycles.webs.com/framesandforks.htm

As to the ride, on the previous page I describe how on the road I wasn't sure I could find a real difference between a carbon disc fork with inch and eighth alloy steerer and 631 forks with inch steel steerer; I found a slight difference off-road under rather specific circumstances. I would be surprised if there was much difference at all between 631 and 853 in terms of ride.

Thanks for that Colin. Certainly something worth investigating.

531colin wrote:

I don't much care for what discs do to the forks, either.......a



Could you expand on this Colin? Are you referring to some sort of strain they put on them?

Being simplistic my take is that the fork is a long lever compared to the brake caliper, and moves brake forces into the less supported and thinner end of the fork. Long levers and all that stuff means unless severely beefed up, forks must flex more with discs (and flex unevenly as a twisting force is applied to one fork leg only?), and that should introduce shorter lifespans due to increased fatigue.

I think that in steel, you will almost certainly be buying 'a beefed up fork' if it has a disc mount on it vs what is otherwise possible. Those who have tried fitting a disc mount to a normal (I.e. flexible) fork have often come unstuck.

Some manufacturers have blurred the issue by simply making their non-disc fork the same as their disc fork but without the mount. You can often tell when they have done this by comparing the weights. The result is that all their forks are stiff and horrible rather than just the disc versions....

cheers