Help, I Have a Twitchy Front End!

furiousox

I've noticed the front end on my CR1 is a bit lively.
(If it was a car I would say it was oversteering)
A small movement of the bars seems to have a more drastic effect on the steering.
You have to always give it your full attention, especially descending.
Throw a crosswind into the mix and it's not much fun.
I had a Canyon before which was more precise and predictable in comparison.
I have a 110mm stem and 30mm (3x10) of spacers underneath the stem.
I'm just wondering if I put a 100mm stem on, pulled the saddle back 10mm and dropped the stem by 10mm what effect it would have.
Would it make the front end more stable?

clog

Shorter stem length tends to make the steering more twitchy rather than less. Also having a bit more weight on the front may make the steering more stable.

I would Stick a longer stem on and drop a couple of spacers and see how you get on.

I have a CR1 and don't find it especially lively but as with any bike set up is the key. (here's a pic of mine).

rollingscone

You could always try another fork but it'd probably require a fair bit of experimentation.

furiousox

Thanks clog.
Yeah wasn't sure if a shorter stem would be a help or a hindrance.
I don't think I can have a longer stem due to fit but I'll remove a spacer and see if that helps.
I think I'm sitting a little far forward as it is so I have a setback seatpost on the way to replace the inline one.
(Nice bike btw, here's mine)

ford2600

furiousox wrote: »

Thanks clog.
Yeah wasn't sure if a shorter stem would be a help or a hindrance.
I don't think I can have a longer stem due to fit but I'll remove a spacer and see if that helps.
I think I'm sitting a little far forward as it is so I have a setback seatpost on the way to replace the inline one.
(Nice bike btw, here's mine)

Saddle will probably bring you back 25mm. With a 10mm longer stem you'd still be back a bit with more leverage?

mirv

Somewhat controversially, I reckon shorter stems (without taking into account weight distribution) are less twitchy. You've got less leverage to steer with a short stem or a narrow bar. That's why MTB people who run tiny stems need ridiculously wide bars to make their setup more twitchy/reactive.

Think of when you climb uphill - you hold the bars in a narrow grip near the stem and you spin smoothly uphill in a relatively straight line. If you stand up and dance on the pedals you need a wider grip on the hoods or drops as you need more leverage to counteract your increased force on the pedals.

If you try to stand up and pedal with a narrow grip, you'll probably end up on the floor as you won't have enough leverage to steer away from the side you're putting your entire bodyweight upon.

That said, if you don't have enough weight on the front wheel your steering will be very light/twitchy regardless of your stem length (think of how light the steering is if you pop a wheelie) - this is a major cause of speed wobbles especially with taller cyclists as they sit relatively far back on the frame compared to shorter cyclists. It might be a case that you need to sit a little bit more forward when descending or to put some more weight on your hands. Do you use the drops or hoods when descending?

mirv

By the way, dropping a couple of spacers while increasing stem length and moving your saddle position all at the same time will mean you'll confuse the hell out of yourself figuring out your preferred position. One change at a time!

smacl

Read the thread title and thought I'd somehow jumped into after hours...

furiousox

It's to lull people in.....:D

furiousox

mirv wrote: »

...do you use the drops or hoods when descending?

Hoods usually, with my butt pushed right back on the saddle to compensate for the inline seatpost.

mirv

I find the drops less twitchy as well as more safe if you hit a bump while braking on a descent. Are you tucking? Or relatively upright and taking weight off the front wheel (i.e. sailing). Standard position is to squirm back a tiny bit on the saddle, hands on the drops, tuck your chest in and knees hugging the top tube gently once you're coasting.

Maybe alternate between the two and see how it feels. I'm betting that you'll feel more planted when you're on the drops/hooks of the bars. Also, you shouldn't have to push yourself much further back on the saddle when descending than when you're pedalling as normal, maybe an inch or so at the most unless or are descending very steep >15% grades.

(or are trying to be super aero dorky)

furiousox

Day off today so dropped the stem 10mm and went out for a spin.
Definitely an improvement in the handling, less twitchy and a bit more predictable.
107km door to door, nice day for it!

lennymc

I have a 130 mm stem at home you can borrow if you wanted to try that to see does it make a difference

mcgratheoin

mirv wrote: »

Somewhat controversially, I reckon shorter stems (without taking into account weight distribution) are less twitchy. You've got less leverage to steer with a short stem or a narrow bar. That's why MTB people who run tiny stems need ridiculously wide bars to make their setup more twitchy/reactive.

I think you're confusing slightly how leverage works on a bike. Essentially the force requirement of the lever calculation is almost negligible - nobody has a longer stem/handlebars because they are unable to turn the wheel with shorter ones. Therefore the main important component is the distance from the end of the lever (the handlebars) to the fulcrum (headset). The reason a shorter stem and narrower handlebars are twitchier is because the same movement of your hands creates a larger movement in the wheel due to the smaller lever. If you think about having your hands close to the stem - moving your right hand forward by 1cm will turn the wheel pretty agressively, whereas with your hands on the hoods, moving one hand forward by 1cm will turn the wheel significantly less.

The reason you can't climb out of the saddle while holding the bars very narrowly is because the deflection of the wheel caused by the instability of your body/hands is greater than when your hands are wide. You easily have the leverage/strength to turn the wheel, what is lacking is the body/motor control to stand out of the saddle and support your weight without the stable base of wide handlebars.

mirv

I think you're half understanding my point, and getting confused between leverage and strength in your second paragraph.

nobody has a longer stem/handlebars because they are unable to turn the wheel with shorter ones

This is because forces required for steering inputs are relatively tiny on road bikes, due to their relatively low inertia as well as the lack of need for aggressive turning. Think MTBs, motorcycles, articulated trucks, buses, anything big generally requires a larger handlebar or steering wheel.

If you think about having your hands close to the stem - moving your right hand forward by 1cm will turn the wheel pretty agressively, whereas with your hands on the hoods, moving one hand forward by 1cm will turn the wheel significantly less.

You are correct in that if you move your right hand forward by 1cm when it is close to the stem it would be quite an aggressive steering input compared to if you moved the same distance forward when it is on the hoods. However you're failing to acknowledge that it is far more difficult to move that 1cm when your hands are closer to the bars as the lever is shortened.

Think of removing a stiff screw or bolt with a tiny spanner - it can be quite tricky. If you had a larger spanner it would be easier to turn, despite the fact that moving the tiny spanner 1cm forwards would result in more rotation of the screw/bolt, relative to the larger spanner.

That's why you spin uphills with a narrow grip - more aero and less steering input leverage as it's assumed that you're spinning smoothly. Your bike has enough inertia and weight on the front wheel so that you can go in a straight line with a narrow grip, which dulls the bikes response to turning.

If it were only about the sensitivity of the input without regards to the lessened leverage due to a narrow grip, you would be correct and TDF riders would be wobbling and falling over on every mountain stage, but fortunately that's not the case.

The same reason is precisely why you need a wider grip when standing on the pedals - you need more leverage to counteract your entire bodyweight being transferred onto a single pedal.

mcgratheoin

mirv wrote: »

This is because forces required for steering inputs are relatively tiny on road bikes, due to their relatively low inertia as well as the lack of need for aggressive turning.

However you're failing to acknowledge that it is far more difficult to move that 1cm when your hands are closer to the bars as the lever is shortened.

Aren't you making two different points here? My point is the first one, that the level of difficulty needed to move 1cm might indeed be greater closer to the bars, but it's still pretty tiny. I'm not disputing your understanding of levers, what I'm failing to understand is how you can equate a longer lever with being twitchier? Are you actually talking about the bike having a finer level of control? Twitchy to me means that the front of the bike tends to move around quite a lot (as a result of small hand movements)- I can't quite see how you could get a bike twitchier with wider handlebars (or longer stem)

That's why you spin uphills with a narrow grip - more aero and less steering input leverage as it's assumed that you're spinning smoothly.

Personally, I spin uphill because at lower speed aero matters less to me and by putting my hands in a narrow grip i can get a more comfortable upright position. Surely if aero was important then everyone would climb in the drops? Not sure it has anything to do with leverage.

mirv

I'm saying that by gripping the bars narrowly (but really, I mean having a point of leverage closer to the steerer) you're making it more difficult to turn the steerer, which makes it less twitchy by both our definitions. It's just simply a lot harder to weave in a 'S' shape with a narrow grip than it is to with a wide one.

If you were asked to ride a test course - say like one of those motorcycle courses with cones on the ground, you would pick a wider grip on the handlebars to make turns around the cones, wouldn't you?



That's because if you had narrow bars like these, you'd probably go in a straight line and miss every turn as you wouldn't have enough strength to overcome the tiny amount of leverage those bars allow.

mcgratheoin

mirv wrote:

I'm saying that by gripping the bars narrowly you're making it more difficult to turn the steerer

Ok - but you can equally say that by gripping the bars narrowly you're making it more difficult to keep the steerer straight- which is the definition of twitchy in my book - the bike not going where you want it to go.

making it more difficult to turn the steerer which makes it less twitchy by both our definitions.

Now I understand what's going on. I'm pretty sure that we're agreeing on all the scientific points but we definitely have a different idea of twitchy - I think twitchiness is a function of control, not of responsiveness - a more difficult to control steerer is twitchier in my book than one I can easily make fine adjustments on (with a longer lever).

It's just simply a lot harder to weave in a 'S' shape with a narrow grip than it is to with a wide one.

I completely agree that it's harder to weave with a narrow grip, and I would say that this is because the bike is twitchier - i.e. it is harder to get the bike to do what you want it to do and there is a higher likelihood of losing control.

That's because if you had narrow bars like these, you'd probably go in a straight line and miss every turn as you wouldn't have enough strength to overcome the tiny amount of leverage those bars allow.

I don't agree with this - the reason I would miss every turn with this set of bars is that I don't have the fine motor control to make the millimetre scale (or smaller) adjustments compared to making the adjustments at the end of a lever. Think about cycling with no hands at all - you can easily cycle no hands around a roundabout merely by shifting body weight - so the strength required to turn a steerer is pretty inconsequential, however it becomes much more difficult to control.


As an aside - have I been misunderstanding what the cycling community means by twitchy? Can anyone else clarify this for me?


*edit* Real-life scenario - my understanding has always been that a twitchy bike is one that wobbles/throws you off at the slightest deflection - e.g. hitting a stone on a descent - this would be exacerbated by a shorter lever for all the reasons you've described about ease of turning the wheel

mirv

Ok - but you can equally say that by gripping the bars narrowly you're making it more difficult to keep the steerer straight- which is the definition of twitchy in my book - the bike not going where you want it to go.

Yes, but the combination of rider/bicycle momentum, friction in the steerer, and the gyroscopic inertia of the front wheel tends to keep it going in a straight line (on a flat smooth surface of course). That's why you can chuck a bicycle and have it coast off in a fairly straight line.

As an aside - have I been misunderstanding what the cycling community means by twitchy? Can anyone else clarify this for me?

I think it means different things to different people. In comparing different bar/stem setups on the same geometry bike I think it means responsiveness - a twitchier setup means it's easier to change direction or to turn.

In the case of how a bike handles - the interaction between its steering angle, trail and rake - it means how quickly the bike wants to dive into corners, as opposed to uprighting itself after releasing steering input. A less twitchy bike in this context means that you need to really countersteer the bars quite hard when cornering, and it will stand itself up very quickly if you release.

Suppless

Most pro riders run bikes with very long stems so it seems there may be something of an issue in regard to handling when the consumer buys the same frame and puts a stem 3cm shorter on. The longer stem certainly adds to stability.
Most people who are not racing on the ragged edge will enjoy cycling more on a bike with a little more trail than many top race bikes. Ultimately its the trail measurement along with the stiffness of the fork/front wheel, which most influences the handling. Dropping one spacer should make no major difference.
To Mr.Furious, it sounds like you need a bike fit, moving your saddle about is not the answer.

mirv

Trail measurement taken without context of the head tube angle is meaningless though. Imagine a chopper-style motorcycle with a very slack headtube, as long as it has humongous rake at the dropouts, it could have the same trail as a road bike. My guess is that it would steer very differently though.

I think the original poster's main problem was that 1) he was sitting very far back on the saddle and 2) using the hoods not the drops. The combination of those two meant that he wasn't putting much weight on the front end, so his weight balance meant that he was half way to popping a wheelie - hence his twitchy handling. Dropping a spacer does help with regards to weight balance in this case.

There's no point paying money for a bike fit if you don't understand the very basic mechanics of arse and hand position. Neither will a fit fix his descending technique.

Suppless

Mirv, the guy said he was going to get a setback seatpost. & secondly most people spend most of the time on the hoods. Your really not making a lot of sense. Even if you drop to the drops i doubt there is a substantial weight transfer to the front, if your bum stays in the same
place.
And lastly you said their is no point paying an expert to help you if you are unsure of things. What?

mirv

His first post clearly states that the problem is worse when descending or in crosswinds, and later he says he descends on the hoods. It really does seem like a weight balance and technique issue. Going on the hoods (and being upright) and shifting back on the saddle as well as getting a larger setback post only exacerbates the issue of not weighting the front wheel enough, especially if you are a taller rider.

Watch what happens when you unweight the front wheel at speed, and what happens when he puts weight on the bars again:

My point was that he should play around with it and get an idea of what works, and more importantly WHY it works BEFORE resorting to paying someone to tell him what to do. Teach a man how to fish... you get the idea.

mirv

Check out this bit at 8:32 in this video. It's hilariously plain to see what to do.

The bit about the lighter the rider the more the weaving is motorcycle specific, as you don't sit any further back if you're heavier or taller on a motorcycle unlike on a bicycle with a backwards angled seatpost.