Fork travel upgrade. Different handling. Explain.

ThePriory1978

I have upgraded my front fork and the bike now feels. Weird. Not exactly bad just different.
I cant decide weather i've screwed it up or if i'm just not used to it yet. Its a Kona Caldera hardtail. Used to run a billy-basic and heavy 100mm coil fork with a 31mm headset stack.
It now has a 120mm air fork donated from a Specialized, the steerer tube was a lot shorter so now only has a 10mm headset spacer.

Quick explanation-
The new fork is a lot lighter than the coil fork and the extra 20mm of travel has lifted the front end 20mm slackening the headtube angle. The handlebars are pretty-much in the same place however as the stems positioned 20mm lower due to the shorter steerer. So everythings much where it used to be i just have more travel.

The bike now feels racey, almost too fast.
The steerings ligher, faster and more responsive than before needing very little input? It now takes more concentration as what feels like the tiniest steering input makes me dart off in that direction. Is this normal? Why is this?

I though if you fitted a longer fork slackening the headangle the steering became less twitchy slowing down the steering which is why downhill bikes have such slack headtube angles, long forks and wide handlebars?
I seem to have had the opposite effect.

Thanks in advance for advice and input?

albo

On the whole a fork with more travel will make the steering feel more twitchy.

I always thought DH bikes had slack head angles because they are aimed downhill 99.9% of the time.

In order to make a fork more efficient you'd want it to be close to vertical.

e.g. If a downwards force were to be applied to a fork at 45% - as opposed to 90% - it wouldn't "work" as well.

What is the make/model of the fork?

ThePriory1978

Rock Shox Recon Solo Air

TuckerUK

Tip: Don't go by travel measurements, measure the crown to axle distance of each fork, and remember to take into account the sag you use on each fork.

albo

I don't think you can lower the specific fork.

You have various options..

Get to love it.
Sell/Trade it.
If you have any spacers under the stem, put them above the stem.
Get hold of a new stem which will give you a lower handlebar height.
Get hold of a new handlebar, with little to no rise.

These MAY help, they may not...

ThePriory1978

Thanks for the advice.

I think its something i will get used to. It dosent handle badly.

I was more hoping if someone could explain the technicalitys of headtube angles, what different angles do to change handling.
Manufacturers seem to spend lots of time tweaking a headtube angle/headtube lentgth of a frame by a degree hear-or-there from one year to the next to adjust handling, sometimes for a longer travel fork or sometimes just to tweak handling.
But why do they do this? For what reason and to what end if it worked before?

If i could understand headtube angles vs fork lengths = handling characteristics. It would be easier to know what to adjust to suit specific riding styles or requirements. I realise there is a Lot more to put into the equation than just angles however.

1mancity2

Have you set up your sag and rebound?

benpinnick

The reason it feels faster is probably as it is. Quite literally. Cheap forks are generally quite sloppy, so turning the bars is in effect twisting the forks and turning the wheel. Your new forks will be much stiffer (probably) and hence far more direct in their feel.

The 20 mm you lost will also probably not be a net 20mm when you take everything into account, so your new set up likely has a lower bar height than before, which will make it feel racier. Don't worry about it. 3 rides in you'll have forgotten what the old set up was like anyhoo.

The Northern Monkey

TuckerUK wrote:

Tip: Don't go by travel measurements, measure the crown to axle distance of each fork, and remember to take into account the sag you use on each fork.

+ potato

What is the difference in crown - axle length between the 2 forks?

ThePriory1978

benpinnick wrote:

Your new forks will be much stiffer (probably)

The new fork has power bulges. The fork equivalent of Hoff in a Speedo. So yeah i hope they are stiffer.

benpinnick wrote:

So your new set up likely has a lower bar height than before, which will make it feel racier.

True dat. Even though i measured everything and the bar should be in the same place. (longer fork but shorter headset stack) the bars are actually 10mm lower than previous. If i dont get used to it a higher rise handlebar should fix it.

The Northern Monkey wrote:

What is the difference in crown - axle length between the 2 forks?

Difference between top of crown to axle is 25mm longer than previous. Near as dammit.

nicklouse

25mm is one degree head tube angle which is not "near as dammit" it does make quite a change in handling by increasing the trail.

ThePriory1978

According to manufacturers geometry spec. My 18" frame as standard has a headtube angle of 68.5°
So with 25mm extra in crown - axle length.
My headtube angle is now 69.5°?

Thats still relatively normal. Right?

http://www.konaworld.com/09/09_caldera_en.cfm

RevellRider

Nope, other way around. The longer fork slackens the static head angle. Though depending on how much sag you run on your fork the head angle whilst riding may vary by more than that.

supersonic

It also slackens the seat angle - you are now sat further behind the bottom bracket. This alters weight distibution. The fornt end now feels 'lighter' than before.

Try moving the saddle a bit further forward on the rails, and maybe a slightly longer stem.