The difference 1 degree in Head Tube angle makes ?

Raffles

My Caad 8 has a headtube angle of 73 degrees, a specialized roubaix has a headtube angle of 72 degrees and both bikes have the same seattube angle of 73.5 degrees.

That 1 degree in difference in headtube angle, what difference does it make given that seattube angles are the same ?

lawrences

really?

Zoomer37

I'm no expert, but I think its makes a difference of about 1 degree

lawrences

Imagine cycling along with the front wheel in the air and the handlebars scraping the floor. It's only about 1/180th that bad.

slowsider

Try
http://www.calfeedesign.com/tech-papers ... -handling/

ddraver

The slacker (lower) head angle will give slower steering response (but by contrast will be more stable). A steeper head angle will be twitchier but will allow for faster steering.

For an extreme example, if you wanted to go in a straight line for ever, then a slacker angel would be better (for example, longer travel Downhill MTB's have slacker head angles for better steering at high speeds) but if you wanted to dive in and out of gaps at a crit then a steeper angle will be better ("classic" XC race bikes had super steep angles for better climbing, but that's changing now...)

However, in reality there are many other factors in frame geometry that will affect all of the above...

LegendLust

Raffles wrote:

My Caad 8 has a headtube angle of 73 degrees, a specialized roubaix has a headtube angle of 72 degrees and both bikes have the same seattube angle of 73.5 degrees.

That 1 degree in difference in headtube angle, what difference does it make given that seattube angles are the same ?

Buy this month's Cyclist magazine - there's a great article in there all about frame angles etc

crankycrank

You also have to take into consideration a number of other factors such as fork rake, wheelbase, BB height, tyres, stem length, bike weight, handlebar width, frame flex, etc., etc.

gozzy

The angles will affect top tube length, for the same seat tube angle a steeper head tube angle will create a slightly longer toptube, conversely a slacker angle will give a shorter tube, hence race bikes have a steeper angle for longer lower position, whereas a shallow angle will give a more upright comfortable position.

Raffles

Gozzy wrote:

The angles will affect top tube length, for the same seat tube angle a steeper head tube angle will create a slightly longer toptube, conversely a slacker angle will give a shorter tube, hence race bikes have a steeper angle for longer lower position, whereas a shallow angle will give a more upright comfortable position.

Its top tube length and the effect that 1 degree difference brings with it. the size 54 roubaix has a top tube length of 548mm which at a glance seems pretty long to me for the size of the bike. would the slacker 72 degree headtube angle make the bike feel more like it had top tube length more like 543mm territory ?

imposter2.0

Top tube length does not affect handling - only fit. You are over-thinking this by a long way..

Raffles

Imposter wrote:

Top tube length does not affect handling - only fit. You are over-thinking this by a long way..

Im not thinking of handling at all

548mm top tube seems very long for a size 54 roubaix, what im curious about is does the slacker 72 deg head tube make the size 54 roubaix fit like it had i.e a 543 mm approx top tube instead of a stretched out 548mm

imposter2.0

Raffles wrote:

Imposter wrote:

Top tube length does not affect handling - only fit. You are over-thinking this by a long way..

Im not thinking of handling at all

548mm top tube seems very long for a size 54 roubaix, what im curious about is does the slacker 72 deg head tube make the size 54 roubaix fit like it had i.e a 543 mm approx top tube instead of a stretched out 548mm

If you're not worried about handling, then why concern yourself with head angles?. 548mm TT is 5mm longer than a 543mm TT. That's all there is to it. The head angle makes no difference to that.

MountainMonster

Raffles, why do you ask so many over thought questions? Do simple ideas just baffle you?

Raffles

Gozzy wrote:

The angles will affect top tube length, for the same seat tube angle a steeper head tube angle will create a slightly longer toptube, conversely a slacker angle will give a shorter tube, hence race bikes have a steeper angle for longer lower position, whereas a shallow angle will give a more upright comfortable position.

do you understand me now Imposter ?

imposter2.0

Raffles wrote:

Gozzy wrote:

The angles will affect top tube length, for the same seat tube angle a steeper head tube angle will create a slightly longer toptube, conversely a slacker angle will give a shorter tube, hence race bikes have a steeper angle for longer lower position, whereas a shallow angle will give a more upright comfortable position.

do you understand me now Imposter ?

I understand that you seem confused, if that's what you mean. Minute changes in angles are only noticed by magazine bike testers, and most of them are lying about noticing the differences anyway. Test ride - that's the answer.

ddraver

Raffles, a bike designer would adjust reach by varying top tube length and adjust handling by altering head angle (all other things being equal - which they re not)

The OP asked about seat angle. Seat angel will vary where you sit over the BB and the fore/aft balance on the bike. This can be slightly adjusted by moving the saddle. Obviously seat angles are only part of the issue though...

neeb

The simple answer is that head tube angle is one of the two factors that determines trail, and trail will affect handling slightly. The other factor that determines trail is fork rake, or offset.

It's counter intuitive - slacker head tube angles need more rake to produce the same trail. For example, a 73 degree head tube angle and a 43mm rake produces a trail of 58mm, as does a 72.5 degree head tube angle and 46mm of rake. In practice, most bikes these days are fitted with either 43mm or 45mm rake forks, so slacker head tube angled bikes tend to have more trail. More trail usually makes a bike more stable at speed, but less reactive.

You can use this website to calculate trail for any combination of rake and head tube angle. Don't forget to enter 23mm (or whatever) for the tyre width.

http://yojimg.net/bike/web_tools/trailcalc.php

Trail is a bit of a personal thing - personally I like to keep trail between 55 and 60mm. Despite the added stability of extra trail, the one bike I had with a trail over 60mm was the one I was least confident descending on, perhaps because I tend to under-steer when I am nervous on a descent and the bigger trail accentuated that.

Head tube angle will also affect wheelbase (the distance between the front and rear wheels). Slacker angles increase the wheelbase (especially if paired with forks having more rake to produce the same trail), and a longer wheelbase will also make the bike less reactive.

Another thing to bear in mind with head tube angle is toe overlap - smaller sized bikes tend to have slacker headtube angles to minimise this.

neeb

P.S. in terms of fit, head tube angle will have a pretty minimal influence, as effective top tube length is usually measured to the top centre of the head tube. However, the effect it does have will be greater the more spacers you have. The reach of two bikes with the same seat tube angles but where one has a 72 degree headtube and the other has 73 should be effectively the same with a slammed stem, but with a few cm of spacers the 72 degree head tube bike will have a slightly shorter reach. I believe you are only talking a very few millimetres though, you could work it out with basic trigonometry.