Fitting a steerer extender . . .

[robgul]

I want to raise the bars on my Boardman Adv 8.9E bike to be more comfortable (it's sold as a gravel but I have it configured with different bars etc as a tourer)  It already has a shorter reach (80mm) stem with a rise.

The obvious is to fit a stem extender BUT the steerer tube is carbon and it seems there are differing views on whether it's a good idea for an extender on carbon steerers.

The very rough pic shows what I was thinking might work:



1 Use a "Problem Solver" immediately above the upper headset collar lockring to take up the preload (usual way with spacers, stem, top cap bolt etc in position)
2 Take out the spacers and fit a steerer extender butted onto the Problem Solver ring, torqued as spec.
3 Fit spacers, stem etc to the extender (fitting a non-load bearing bung merely to retain the top cap - or use the extender's long bolt into the bung in the steerer)

I guess the concern might be potential leverage on the steerer tube at and above the extender - there is a substantial 30mm or so deep bung that is, and will remain, in the very top of the steerer tube making it "solid"

Views, thoughts appreciated

[Paul H]

There isn't going to be a definitive answer.  The point of failure seems to usually be the top of the headtube, the leverage at that point is from where the weight is on the bars, it makes no difference how it's achieved.  With your shorter stem, you can raise the bars for the same leverage. I would assume the fork was designed for the longest common stem, say 130mm and 10mm rise plus 30mm of spacers, the equivalent leverage with an 80mm stem would be with around 100mm rise. You could work that out more precisely and be confident you were not doing anything beyond what was intended.  Then factor in the rider (And bike) weight and that a gravel fork will have been designed for some rough riding, that's likely to be a fair chunk of leeway, but there's no knowing how much.
How much higher do you need?  If a 45 degree stem was enough it would be a lot simpler. 

[robgul]

There isn't going to be a definitive answer.  The point of failure seems to usually be the top of the headtube, the leverage at that point is from where the weight is on the bars, it makes no difference how it's achieved.  With your shorter stem, you can raise the bars for the same leverage. I would assume the fork was designed for the longest common stem, say 130mm and 10mm rise plus 30mm of spacers, the equivalent leverage with an 80mm stem would be with around 100mm rise. You could work that out more precisely and be confident you were not doing anything beyond what was intended.  Then factor in the rider (And bike) weight and that a gravel fork will have been designed for some rough riding, that's likely to be a fair chunk of leeway, but there's no knowing how much.
How much higher do you need?  If a 45 degree stem was enough it would be a lot simpler.

You've pretty much covered all the issues I could think of!   The steerer does look as if it's a pretty hefty gauge of carbon tube with thick walls.

The 45 degree stem option would be simpler BUT unless it's a very short stem (which doesn't give much more height) the length of the stem will push the bars further away from me - that then becomes a problem because as a result of some drastic surgery around my middle I can't bend too far forward . . .  which brings me full circle to the higher bar desire!

[Paul H]

The 45 degree stem option would be simpler BUT unless it's a very short stem (which doesn't give much more height) the length of the stem will push the bars further away from me -

For hours of fun:
https://www.myvelofit.com/stem-calculator/

It looks like a 100mm stem with a 40 degree rise would give the same reach and 30mm more height than 80/25. 

[grams]

What's the purpose of the problem solver? The extended tube should clamp to the steerer and keep the headset preloaded.

[robgul]

What's the purpose of the problem solver? The extended tube should clamp to the steerer and keep the headset preloaded.

a) keeping the "tension" as low as possible on the steerer tube, and b) I use Problem Solvers on a couple of bikes to be able to turn the bars for easy transport in the car . . . the preload holds, I just have to loosen and re-torque the stem bolts (carrying a small 6nm fixed torque key)

[Adam]

You could also fit bars with a riser.

https://www.merlincycles.com/controltech-one-riser-gravel-handlebars-295321.html

[Dickyelsdon]

One big issue with steerer extenders (in addition to them often not being made very well, tolerance wise) is the bolting arrangement often tends to pinch the steerer tighter at the bottom of the clamp than an even spread of load. This is because the top of the clamping area has the extension attached to it, and so wont flex in as much when clamping like a stem would. Uneven clamping force, especially when concentrating force at the bottom of the clamp, is VERY bad for carbon.  Id be very wary for that fact.

Look at this image, the top bolt has no chance of providing a balanced clamping force on the steerer.


PaulH suggestion is one to look at tho. Due to the bikes head angle raising the bars with a steerer extender also brings them towards you, so you need to consider the head angle when you consider where you want your bars.

[robgul]

One big issue with steerer extenders (in addition to them often not being made very well, tolerance wise) is the bolting arrangement often tends to pinch the steerer tighter at the bottom of the clamp than an even spread of load. This is because the top of the clamping area has the extension attached to it, and so wont flex in as much when clamping like a stem would. Uneven clamping force, especially when concentrating force at the bottom of the clamp, is VERY bad for carbon.  Id be very wary for that fact.

Look at this image, the top bolt has no chance of providing a balanced clamping force on the steerer.


PaulH suggestion is one to look at tho. Due to the bikes head angle raising the bars with a steerer extender also brings them towards you, so you need to consider the head angle when you consider where you want your bars.

Absolutely - I've discarded the steerer extender as the bolting and carbon seems risky.   I'm going to eperiment with a short. very steep stem . . . it just happens I have a customer's bike in for service that has just the stem, I'm going to borrow it for my machine and see how it feels for a few miles tomorrow.

[iddu]

If you're playing a lot with the angles, consider one of

https://www.contec-parts.com/en/produkte/bike-parts/stems-headsets/stems/03167384-contec-stem-cobra/ or
https://www.amazon.co.uk/XLC-Comp-ST-T15-A-Head-Vorbau/dp/B00449OAXG?th=1

unless you've got (access to) a big box of tat spares collected over the years.

[robgul]

Aaargh! I can't bring myself to fit such an ugly hinged stem. 

The few miles with the borrowed stem seemed to work.

[Frank9755]

I would buy a new fork rather than mess around with workarounds.  I've done this twice before, and bought one from Carbonda last year.

Good quality carbon forks aren't so expensive any more and you can get them with mounts for luggage. Rim brake variants might be harder to find but they do exist

[De Sisti]

I would buy a new fork rather than mess around with workarounds.  I've done this twice before, and bought one from Carbonda last year.

Good quality carbon forks aren't so expensive any more and you can get them with mounts for luggage. Rim brake variants might be harder to find but they do exist

Blimey, I wish I would have thought of that, even buying one that could take tyres wider than 25mm.