THE FORKS ON MY NEWEST bike were, I’ve always thought, rather flexile. It was something I only ever noticed when out of the saddle, sprinting on the flat or big-ringing it uphill, and as it turns out I’ve spent the last couple of seasons bad-mouthing an innocent BMC SLR01 Team Machine.
Unfairly the butt of my opprobrium for nearly two years, BMC’s pretty ‘Total Compliance Concept’ fork wasn’t spongy at all: the problem was higher up
For twenty or so races I’d ignored the issue, but this season I considered junking the frame and beginning again – until a sense of extravagance and disproportionation kicked in, and I began looking into replacing the fork with something stiffer. But good forks, ‘better’ than those already on what was a top-of-the-range frame like this ain’t cheap, and the slight bother of researching trail, rake, offset and what-not put me off that avenue too.
I’d already tried various front wheels in case I was barking at the wrong component, but the problem was manifest whatever wheel was underneath me.
Could it, I wondered, be the stem? It’s on the long side at 120mm as I’d gone for a super-small frame for racing, and it would’ve been little bother to whip it off and try another, I imagined. As it happened my stem was a beautiful-looking but ill-conceived Crank Brothers Cobalt 2 item. It doesn’t have a face-plate, so removal necessitated unwinding bar tape and detaching a brake/shifter before wiggling the damn stem along and off one side of the handlebar – it’s no wonder the £55 retail price of a Cobalt 2 stem is now just a fiver at some online stores. I wouldn’t even pay that for it now, just because it put me through that palaver.
Anyway, some faffing later and a £25 Giant Contact stem installed, was this still going to be the fork in hell?
No it wasn’t, and here’s why.
Despite doing everything ‘by the book’ when installing the new stem, I now couldn’t even get the fork steerer to stabilize inside the head tube – applying front brake was giving me a front-to-back rocking that I knew indicated an insecure stem attachment, and I hadn’t even yet pedalled anywhere to check the fork.
What I discovered, and is really the whole point of this post, is that whether or not you like to have spacers above your stem (perhaps to future-proof yourself against losing your flexibility if you have spacers there, or for a neater look if you don’t), the steerer tube itself absolutely must be submerged about 3mm below the top of the tallest spacer or, if there are no spacers above the stem, below the top of the stem that fits over it.
Without this precise amount of space the headset bearing can’t be properly ‘tied down’, because those 3 or 4 mm mean that tightening the headset top cap bolt with your Allen key pulls the steerer tube up into the head tube, while pushing down on the stem at the same time. Whereas if the top of the steerer tube is level or within 1 or 2 millimetres of the stem or top spacer, there is no way to create the necessary pressure and the top of the steerer would simply butt up against the underside of the top cap, giving that rocking effect when the front brake is held and the bike pushed. Conversely too much space, that is a steerer tube that’s been cut down by so much that there’s 5mm or more between it and the top of the stem and your stem will be insecure – as mine must’ve been these last two seasons. A very stupid person might think ‘fork in hell’, I’ve got a terribly-made bicycle. Which they haven’t.