: Staus Quo

By: g | 2 Comments » |

I was in the shower and the thought crashed out of the sky on me — “did we allow for sag in the head angle?” (we all have moments like these in the shower, don’t we?). Over to Skype to call up Mr. X and a conversation something like this ensued (rather abridged):

Me: “Did we adjust for sag at the head angle?”

X: “No, we don’t really allow for that.”

Me: “Well, that means when we say 70 degrees, it’s not, it’s 70 less whatever it slackens by whatever when the shock allows for sag.”

X: “It’s not a problem, because everyone does it. To change that would mean that that the buyer has no benchmark ie. your 70 will be different from everyone else’s.”

Me:”OK, I can see that…”

And I did. But when I thought about it some more, accepting this status quo is even more wrong than when I first thought about it.

OK, so what am I talking about?

Back in the days when there was no rear suspension, when you claimed that your bike had a 71 degree head tube, that’s what it had because the rear end did not sag when you sat on the bike. Today though, with full suspension bikes, when you sit on the bike the rear end (on a well designed bike) will sag X amount to create what is called negative travel. Negative travel is critical for suspension as it allows the wheel to stay in contact with the ground by loading the rear wheel. A side effect of this is that the head angle slackens by an amount and our 71 degrees slackens off to maybe 69, maybe less. See the issue?

The argument that was proposed to me was that because no one allows for this and states the head angle for FS bikes in the ‘unloaded’ state, there is no point stating the factual angle as it will confuse people when they try different bikes — a true 71 will be different to a ‘claimed’ 71. That’s a fair enough argument and if every bike on the market was a full suspension frame, then it would not be an issue. It occurred to me though that hardtails still account for many bike sales, so therefore the angles stated for FS bikes can not be used to compare against handling characteristics of hardtails.

Right, I’m hearing you saying “so what?”.

Well, that’s a fair question but as I spoke about in my last piece, MTB Misinformation, discrepancies like this only add to confuse and make it difficult to make fair and baseline comparisons between bikes of various brands. Like trying to ‘factualise’ numerous claims made by marketing departments in regards to suspension designs, I think there needs to be a more open and clear way to compare the various design and performance characteristics. ‘Reach and Stack’ is one such attempt to sort out sizing between all manufacturers of mountain bikes, initiated by Turner and transition Bikes. ISIS previously and BB30 now are attempts to standardise bottom brackets and while for a period there was some harmony, it’s on for young and old again as ‘the boys’ are at it with their respective 10 speed systems — which are also tied to BB shell specifications. It’s become such a mess now that manufacturers themselves are in the dark with some electing to design and allow for one and forget about the other, as by allowing for one, you can’t easily allow for the other. To make matters worse, a particular 2×10 engineering spec goes so far as to make designing an effective FS bike for it increasingly difficult making life difficult for their key customers, the OEM companies!

Madness!

From where I sit, I’d like to be able to line three bikes up and look at the specs for each and get a solid feeling for how they are actually going to perform before I get on them. Right now, I can grab a hard tail and know it will perform in a particular manner just by looking at the numbers, making comparing hardtails easy. If I hop on a FS with similar geometry though, the way it will behave will be guess work until ride time. This makes the task of buying difficult as I either have to guess and hope for the best, spend a lot of time riding a lot of different bikes, which is very difficult, or buy something and hope there is not something closer to my liking. Personal experience tells me that looking at the current claims of figures for most bikes tells me very little about how the bike will feel or ride.

I might be alone in this, I might not be. Judging from some of the comments made by various people I work with, I think there is a feeling for a factual comparison system and less of the deeply seeded marketing hype one that surrounds the industry currently. I personally don’t feel accepting the accepting the status quo is a good enough reason to stay with something, especially if it is counter to what should be best practice, or to the detriment of the end buyer.

g

 

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So far, 2 people have said: about “Staus Quo”:

1. Don’t forget about the sag in the fork too… setting up suspension to suit personal preferences can change the feel of the same bike big time. Not to mention all the other little things you can change. I reckon once you find a few bikes that seem about right the only way to tell which is for you is to jump on and go for a ride.

Sean

2. Ya, true.

   That said, most forks don’t sag enough to compensate for the angle changes caused by the rear end dropping, especially as the sag is a near vertical drop so tends to affect the head angle far less (the rear sagging pivots the whole bike through the front axle).

   But yea, there are many ‘personal’ tweaks one can do to affect handling. These though should be independent of a correct baseline.

g

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