Help with frame related questions

[Bicycle Repair Man]

Now then folks

I owe you all a large apology for disapearing for most of the year !!! Earlier on in the year I was struck down by the lurgie which left me completely donald ducked for over two months. Then we had a rather extensive bulding project which over ran and caused some headaches. I suppose I just fell out of the habit of looking at the computer.
However all is well now, I feel fine, the building work is finished and I have even been getting out on my bike again (not very far and not very fast) after being inspired by helping at the Kirton control on LEL.
Any of you whose queries I have missed, if they are still of concern let me know and I will see what I can do.

Cheers

Dave Yates

[Biggsy]

Welcome back. 

Do you have any thoughts on Stumpy's crack?:      STOPPIT

https://yacf.co.uk/forum/index.php?topic=76166.0

[Bicycle Repair Man]

Welcome back. 

Do you have any thoughts on Stumpy's crack?:      STOPPIT

https://yacf.co.uk/forum/index.php?topic=76166.0

Sorry about delay, had a nasty little bug in the computer. Gone now, all is well !!!
The BB shell in question is a Long Shen cast shell. This is the first one of these that I have ever seen crack. This sort of failure is usually seen on pressed shells where micro cracks have formed during the forming process. Withou sight of the inside of the shell it is difficult to give an assesment.
As to fixing it, a new shell is the surest fix but that is expensive and then the frame needs respraying. The job is a nightmare as the shell has to be dissected and taken off a piece at a time then the tubes cleaned up and the new shell brazed in using a jig to ensure accurate alignment.
Yoave's suggestion of a tig weld along the crack is a good one and would be my preferred method if cost was an issue. A repair like that cannot be absolutely guaranteed but of all the similar sort of repairs I have done none have come back !!!
It comes down to how much you value the frame.

Cheers

Dave Yates

[yoav]

Hello Dave,

What do you think of this;

http://www.ebay.co.uk/itm/Fixed-Gear-Fixie-RoadToPista-track-dropout-adaptor-Road2Pista-adapter-/271304352459?clk_rvr_id=539674322164

Good idea or bloody dangerous?

Cheers

Yoav

[Bicycle Repair Man]

Hello Dave,

What do you think of this;

http://www.ebay.co.uk/itm/Fixed-Gear-Fixie-RoadToPista-track-dropout-adaptor-Road2Pista-adapter-/271304352459?clk_rvr_id=539674322164

Good idea or bloody dangerous?

Cheers

Yoav

Hi Yoav

I have to say my first instinct is "bloody dangerous"  There appears to be only one bolt holding the fixed dropout to the frame. Kick back hard on that and I suspect the single bolt will not be sufficient to hold it. In addition the device will raise the back end of the frame thus altering the head and seat angles.
Not the smartest idea I have seen !!!!!

Cheers

Dave Yates

[AndyMorris]

Hi Dave,

Over the past 8 or so years I've broken 6 frames, One was an old 501 Raleigh, One of a very nice M. Steel handbuilt, replace for no cost, two pompino's and two alloy fixies from Pearsons. All of them went around the BB

I'm a hefty chap (16 1/2 stone +-7 lbs) who does like stonking up hills and I'm now resigned to buying a new pomp every year or so.

I think you should be able to find some pics here

Any idea?

[Ian H]

A friend of mine had a similar problem, except that he broke random parts of successive Dawes frames, including cracking a headtube. The supplier (Thorn) got fed up with replacing under warranty and offered to build him a frame he couldn't break. They used oversize tandem tube. Apart from one rear dropdown, he hasn't had a problem (still breaks cranks regularly).

[Bicycle Repair Man]

Hi Dave,

Over the past 8 or so years I've broken 6 frames, One was an old 501 Raleigh, One of a very nice M. Steel handbuilt, replace for no cost, two pompino's and two alloy fixies from Pearsons. All of them went around the BB

I'm a hefty chap (16 1/2 stone +-7 lbs) who does like stonking up hills and I'm now resigned to buying a new pomp every year or so.
I think you should be able to find some pics here

Any idea?

Hi Andy

There is a pattern here !!!  Most "off the peg" frames are designed for Mr or Ms average. Alas you are not within that category. You have, as I see it, two choices. Either buy a custom frame from someone who knows what he is talking about or continue to break frames and replace. It is perfectly possible to build a frame to take your weight and riding style, just need to use a bit more metal in the right places. It really depends on your budget and cash flow as to which course you choose.

Cheers

Dave Yates

[Bicycle Repair Man]

A friend of mine had a similar problem, except that he broke random parts of successive Dawes frames, including cracking a headtube. The supplier (Thorn) got fed up with replacing under warranty and offered to build him a frame he couldn't break. They used oversize tandem tube. Apart from one rear dropdown, he hasn't had a problem (still breaks cranks regularly).

Ian

I have repaired more Dawes frames than I care to remember. A lot of them were cracked head tubes. Several others were cracked bottom head lugs. The head tube issue was, I believe, due to the use of inferior quality head tube ie mild steel not 531 or similar. The head lug issue was due to poor brazing ie not enough brass. Both are cost issues. Dawes frames were built down to a price not up to a standard. having said that there are hundreds of thousands of Dawes frames out there doing the job they were designed for with no problems which shows they got it right for their target market. In that situation if they have one failure in, say, a thousand frames that is acceptable in their commercial model. Alas it is always the odd dodgy one that gains attention.

Cheers

Dave Yates

[Ian H]

Ah yes, 'three main tubes'. It probably didn't help that he rides a 26" frame.

I've never broken anything worse than a spoke (except once, long ago, and that was with the aid of the rear wing of a minicab).

[AndyMorris]

Hi Andy

There is a pattern here !!!  Most "off the peg" frames are designed for Mr or Ms average. Alas you are not within that category. You have, as I see it, two choices. Either buy a custom frame from someone who knows what he is talking about or continue to break frames and replace. It is perfectly possible to build a frame to take your weight and riding style, just need to use a bit more metal in the right places. It really depends on your budget and cash flow as to which course you choose.

Cheers

Dave Yates

Seeing as I can get a pomp a year for 130 quid I'd have to be convinced that a custom frame would last forever, seeing that it would cost up to 10 times that, but something that works, has proper lugs, takes dual pivot brakes, 'guards and a rack and has old fashioned long horizontal road drop outs, spaced for fixed would be very tempting, the pomp is a bit agricultural.

[Ian H]

A friend of has a frame exactly like that: rack, guards, fixed, built to his spec by a certain Mr Yates. It's survived a lot of abuse over quite a few years.

[yoav]

...... a very nice M. Steel handbuilt ......

Hi Andy, I am seriously impressed by your ability to break frames, including one of Dave Yates' own, it would seem?

[Bicycle Repair Man]

including one of Dave Yates' own, it would seem?

Not necessarily !!!  Of the approx 12,500 ish frames built whilst I ran M. Steel's frame shop I only built about 3500 personally. The "standard" frames were built by a team of three whilst I built "specials", tandems, oddball TT frames, Pro team frames, etc. The BB shell was a pressed item and I refer you back to previous comments about frames being designed for "Mr average". If you design a frame to handle all possibilities then to almost all people it will be too heavy. A very large percentage of customers state they want a "light" frame. If I am designing a frame for a specific customer then I take all factors into consideration. If I am designing a "standard" frame to be sold off the peg  it is a balancing act of weight v durability to cover most of the mid range of possible riders and styles.

Cheers

Dave Yates

[Russell]

Hi Dave

Can you help with this issue?

Mrs R is a little chap and a while ago we bought her an Islabike Luath 26 as a second bike.  After changing the bars to a swept back type it fits well enough.  A bit short in the chain stays perhaps but reach and standover are OK.  The steering however is another matter.  It is too light and floppy and the bike tends to over steer into corners.  This may be because of the change in riding position - more upright - and with those shorter chainstays this has taken weight off the front wheel.

How feasible would it be to change the offset of the forks to provide more stability?  I believe the offset would need to be increased, ie greater bend.  What kind of change would be required (how long is a piece of string question I know!)?  The forks are polished cro-moly.

Thanks

R

[Biggsy]

While you're waiting for Dave.....

Fork offset would need to be REDUCED to make the steering more stable.  Every few mm makes a noticeable difference.

See http://www.phred.org/~josh/bike/trail.html

For a given steering angle, offsetting the hub forward reduces trail, while offestting the hub backward increases trail. This may seem counterintuitive, since very stable cruiser bikes usually have more fork rake than twitchy track bikes. But the other factor at work is the angle of the steerer -- cruiser bikes have very slack head tubes, so they have more trail despite their fork rake, not because of it.

[Bicycle Repair Man]

Hi Dave

Can you help with this issue?

Mrs R is a little chap and a while ago we bought her an Islabike Luath 26 as a second bike.  After changing the bars to a swept back type it fits well enough.  A bit short in the chain stays perhaps but reach and standover are OK.  The steering however is another matter.  It is too light and floppy and the bike tends to over steer into corners.  This may be because of the change in riding position - more upright - and with those shorter chainstays this has taken weight off the front wheel.

How feasible would it be to change the offset of the forks to provide more stability?  I believe the offset would need to be increased, ie greater bend.  What kind of change would be required (how long is a piece of string question I know!)?  The forks are polished cro-moly.

Thanks

R

Hi Russell

Without seeing and more importantly measuring the bike in question I cannot give a hard and fast script. However, in principle "wot Biggsy said" If you increase the offset you will reduce the trail thus making it even more twitchy. I once rode a Dawes Kingpin small wheel shopper bike that the owner had "modified" by increasing the offset so much that the result was negative trail. It could be ridden in a straight line with both hands on the bars but at the least provocation the front wheel would try and reverse itself. Absolutely lethal !!!
The point to consider is that if you reduce the offset then the front centres and thus toe/wheel clearance will be reduced. However as Biggsy points out even a few mm could make a noticeable difference in this situation. As the forks are steel then altering the offset is perfectly feasible.

Cheers

Dave Yates

Cheer

[Russell]

Thanks Dave and Biggsy.  I'll check the front centres clearance against her other bike to see how much is available.  In the absence of a bike workshop what techniques could be employed?  My friend has a metal workshop with large vices and presses which I could use.

R

[Biggsy]

How about just replacing the forks instead of modifying them?  Carbon fibre could be a nice upgrade.  Or is there no choice of road forks for the wheel size?

Switching from 45 to 43 mm fork offset was enough on my full-size racer to go from being barely possible to ride no-handed to safe to ride no-handed.  The difference with hands on the bars is subtle, but still a pleasant little improvement.  I'd guess Mrs R would want more difference than that, but you've got to be careful not to go too far.

(I don't know how these numbers translate to little bikes).

[Russell]

The bike is based around MTB 559 wheels so we would be looking slim road forks with mudguard eyes and canti studs.  Not a common fork I suspect.

I wait to be proved wrong.

[rafletcher]

While you're waiting for Dave.....

Fork offset would need to be REDUCED to make the steering more stable.  Every few mm makes a noticeable difference.

See http://www.phred.org/~josh/bike/trail.html

For a given steering angle, offsetting the hub forward reduces trail, while offestting the hub backward increases trail. This may seem counterintuitive, since very stable cruiser bikes usually have more fork rake than twitchy track bikes. But the other factor at work is the angle of the steerer -- cruiser bikes have very slack head tubes, so they have more trail despite their fork rake, not because of it.

I've been comparing frame geometries, and was surprised how close in trial a "race" oriented frame (73 head angle, 45 offset) was to a "sportive" one (71.3 head angle, 53 offset). The difference in trial with same sized tyres was just 2mm (larger for the sportive frame). A difference that could be eliminated by changing one tyre size (from 25mm to 23mm of the Sportive). Would the handling then be the "same" for both?  I used this calculator http://yojimg.net/bike/web_tools/trailcalc.php

[Biggsy]

There's more to handling than trail, but steering stability would be basically the same.

[yoav]

Not my problem but seen on another forum;
http://www.lfgss.com/thread120041.html#post4024652
and wondered what Dave would say about this?

[Bicycle Repair Man]

Hi Yoav

Looks pretty terminal to me. Not the smartest move threading an aluminium steerer, bound to break sooner or later not enough metal there. I am not familiar with Allan forks, probably possible to replace the column ie cut old one out, glue new one in. Personally I would not trust such a repair, far too critical an area.
Best bet, new forks

Cheers

Dave Yates

[yoav]

If it's an original Alan from the 70’s then it would be all aluminium including the forks with a threaded steerer. I suppose its a miracle it lasted this long.

I remember seeing one when they first came out; oddly futuristic and strangely attractive. I couldn't afford one.