- Understeer, anyone had it, causes/solutions?
Built up a new bike but i'm getting alot of understeer which i've never had on a bike before.
Before i start swapping everything over i thought i'd see if it was common ish and the usual causes. All the kit has come from another frame which was fine but obviously may work differently on the new one.
Causes i'm thinking are: me! forks, stem, frame?
taPosted 8 years ago
He's not talking about slack/slow handling. He's talking about understeer, which is entirely different.
Personally, yes I have had it and I don't like it. For me it was crappy tyres that did it, and I've found that one tyre that works well on a certain bike, might be no good on another…..
But it could be poor bike set up (Not enough weight on the front, frame too big) tyres pressures, suspension settings (Too harsh) or any number of other thingsPosted 8 years ago
I could never work out why, but this was the problem with my old Stumpjumper FSR. I suspect their wasn't enough weight over the back, which I don't quite understand as when descending on it, it always felt as if I was being pitched over the bars; the two things seem to contradict each other.
But on some highly un-scientific tests, if I made a concious decision to get my weight forward and 'push' the tyre into a corner, it seemed to bite better. Always difficult to tell if this is a genuine result, or whether it's actually an increase in determination to make the corner…?
PP – I think that too long a fork as well as creating the slow handling you mention, can also lead to understeer as described. The longer fork puts you further back and you end up with even less weight over the front wheel.Posted 8 years ago
I knackered my Judy fork the first year I went to Spain & borrowed a 130mm Marz fork. This greatly improved the feel of the bike going downhill, but on anything that was flat or even slightly up, the front end just did not want to go round corners & would just wander off in a straight line.geetee1972Member
Isn't understeer simply when the front wheel(s) have more grip than the back (with oversteer being the reverse)? In which case as long as you have at least one front and one back wheel, then you can get understeer?
On a bike it's felt by the front wheel pushing wide of the turn, i.e washing out, i.e. when the front wheel has reached the limit of traction and breaks grip, i.e. understeer.
As it's a new bike it may simply be down to you not having found your balance on the bike; your body may be used to sitting in one position and you need to shift your weight forward a little to weight the front wheel more in turns so that it has more grip. I've just built up a new bike and its a good 30mm longer in the wheelbase and a little longer in the top tube so I am finding that I have more opportunity to move my weight forward and weight the front wheel appropriately.Posted 8 years agosi-wilsonMember
You cannot get understeer on a two wheeler. I think you need to define a little more what is happening. People often use the term understeer but it is not correct.
I see your point, but if the op is having to put more into turning his bikes into corners or getting the feeling that the bike is not turning is that not understeer?Posted 8 years ago
I should have written that I managed to improve the situation slightly by moving the seat forward on the rails & getting a stem with slightly more reach, but more importantly a lot less angle, which put my weight over the bars more.
TJ – can you explain why a 2-wheeled vehicle cannot understeer?Posted 8 years ago
PP – I think that too long a fork as well as creating the slow handling you mention, can also lead to understeer as described.
Yeah, that occoured to me after I posted too, but I've not had the time to edit or comment since then. 🙂
You cannot get understeer on a two wheeler
Sorry TJ, you usually seem to know your stuff but on this occasion you're 100% wrong. 🙂
Definition of understeer
Understeer is a term for a handling condition in which during cornering the circular path of the vehicle's motion is of a greater radius than the circle indicated by the direction its wheels are pointed. The effect is opposite to that of oversteer. In simpler words understeer is the condition in which the vehicle does not follow the trajectory the driver is trying to impose while taking the corner because the effective slip angle at the front is larger than that at the rear, instead following a less curved trajectory
So, if you're front tyre starts to slide before the rear, that's understeer. I'd imagine you've had it happen. I imagine every MTBer in the world has at some point 'lost the front end' at some point. The problem being when this happens too readily, at too slow a speed. Then something is wrong and you have to do something about it, as our OP has found.Posted 8 years agoLionheartMember
I must be sooo slow the above 5-6 appeared whilst I did this:
Put more power down! but more seriously – My SS understeered half of yesterday morning, pumped up the front tyre after snow riding, bad back means I am less willing to weight the front wheel and very muddy – slippy conditions.
As a motorcycle instructor we used the term understeer. But I agreed we need more info…..
WikiPosted 8 years ago
'Several schemes have been devised to rate the handling of bikes, particularly motorcycles.
The roll index is the ratio between steering torque and roll or lean angle.
The acceleration index is the ratio between steering torque and lateral or centripetal acceleration.
The steering ratio is the ratio between the theoretical turning radius based on ideal tire behavior and the actual turning radius. Values less than one, where the front wheel side slip is greater than the rear wheel side slip, are described as under-steering; equal to one as neutral steering; and greater than one as over-steering. Values less than zero, in which the front wheel must be turned opposite the direction of the curve due to much greater rear wheel side slip than front wheel have been described as counter-steering. Riders tend to prefer neutral or slight over-steering. Car drivers tend to prefer under-steering.
Peter – a two wheeler when in the turn has no steering angle above a very slow speed – in order to decrease the radius of the turn you steer the opposite way to the way you are turning.
So – to turn left you actually steer to the right. The bike tips into the turn by gyroscopic precession and by the fact the contact patch is now to the right of the COG. The steering returns to the straight ahead position. The turn is maintained by camber thrust, if you want to tighten the turn to the left you steer to the right again.
Therefore if the bike is running wide it is a totally different mechanism to understeer as understeer is when a car is turning less sharply that the steering angle. As a bike has no steering angle when in a turn then it cannot understeer.
all this only applies at speed.Posted 8 years ago
Qwrety, I did my homework on understeer before I opened my gob. 🙂
More on bike understeer
Because the front and rear tires can have different slip angles due to weight distribution, tire properties, etc., bikes can experience understeer or oversteer. Of the two, understeer, in which the front wheel slides more than the rear wheel, is more dangerous
From here (A pretty good explanation of all types of bike handling IMO)Posted 8 years agobuzz-lightyearMember
"You cannot get understeer on a two wheeler"
Hmm. If you tip the bike into the corner at speed but don't press into the front wheel, it takes a wide arc, arguably understeer. If you press sharply into it, it carves a tighter arc. I over-did this yesterday after being too chilled and nearly overshooting a turn. I almost high-sided as the bike suddenly whipped into it. I need to get better at this!Posted 8 years ago
I am just being pedantic really but as what people call understeer on a bike is a completely different mechanism to understeer in a car and the cures are different then its not helpfull to use the same term for two very different phenomena.
If the front wheel is washing out you need one / some / all of :
More rebound damping
More weight on the front
A tyre with more grip
a steeper castor angle
More sag in the suspension
More body lean to the outside of the turn to increase the camber thrust by increasing the lean angle of the bike.
Motocycles and bicycles also react very differently because of the relative widths of the tyre, the % of weigh in the bike and rider and the height of the COG. Trying to ride a bicycle in the same way as a motorbike does not work.Posted 8 years ago
So – to turn left you actually steer to the right.
Yep, I understand that, I've done it myself and it's irrelevent. Why? Becasue that's just HOW you get a bike to turn, not what happens in the turn. However you choose the angle of the turn or maintain it is also irrelevant. If the front wheel slides more then the rear – BINGO! – Understeer! 🙂
And of course your theory (Which sounds like it based on solely motorcycles) you admit " only applies at speed". I also imagine we've had slow speed front end slides….. 🙂
You'll be trying to tell us bikes can't oversteer as well I imagine? 😉Posted 8 years ago
HTTP404 – Member
The gyroscopic turning affect employed by motorbikes/bicycle is how they turn at speed.
It doesn't mean a motorbike or bicycle cannot understeer.
Wrong – camber thrust is how the turning force is generated. Gyroscopic precession is one of the mechanisms for initiating the turn but it does not produce the turning force – it produces the lean ( along with the movement of the COG) and its the lean angle that produces the turning force.Posted 8 years ago
what people call understeer on a bike is a completely different mechanism to understeer in a car
Oh yes, granted. But the oucome is the same: Front slides wide = Understeer. 😀
That's like saying because you buy your milk at the shop it's real milk and because I get mine delivered, it's not.
End product is the same – Milk in the fridge! 😉
EDIT2Posted 8 years ago
Unless, of course, you count MrsPPs skimmed milk. Which obviously isn't real milk at all…… 8)
PeterPoddy – Member
"what people call understeer on a bike is a completely different mechanism to understeer in a car"
Oh yes, granted. But the oucome is the same: Front slides wide = Understeer.
My point simply is that if two different mechanisms cause a similar(but not the same) effect then to call the two different things the same word causes confusion – especially as the cure is different.Posted 8 years ago
it cannot understeer in the classic sense
You mean your sense I take it? 😉
I'm going to quote myself and underline a bit, just to make sure….
understeer is the condition in which the vehicle does not follow the trajectory the driver is trying to impose while taking the corner because the effective slip angle at the front is larger than that at the rear, instead following a less curved trajectory
🙂Posted 8 years ago
Weight over the front probably won't help. That only helps with certain bike geometries and in certain types of corner ie long fast smooth ones.
When you steer your bike pivots around an axis through the rear wheel. The further forward your weight is, the more it has to move from side to side in twisty stuff. So the harder your front tyre has to work.
In the twisty singletrack at Swinley forsest my Orange 5 is much much faster than my Kona Heihei because it has a slacker head angle and my weight is further back meaning the bike can turn easier. On the Heihei the only way to get any kind of speed through the singletrack was to hang my arse out over the back.
Getting traction from the tyres and steering the bike are different things….Posted 8 years agoswisstonyMember
Blimey, i didn't expect that many responses!
tO clear the matter up, understeer or at least what i mean as understeer is basically when i go round a corner and turn the bars/body/bike as much as i usually do to get round it's not enough and i'm running wide.
The tyre isn't washing out, running swampthings, i'm just running wide?
ps it's a hardtail, forks are correct lenght so won't affect desired headanglePosted 8 years ago
TJ – you pedantic knob you are not helping. Understeer in a car has certain causes and solutions, the phenomenon widely referred to as understeer on a bike has different causes and possibly slighly different conditions, and different solutions. We are talking about bikes, so how can there be confusion?
EDIT: Do not listen to TJ's advice about how to reduce bike understeer. He clearly does not know how to ride a bike. I'll bet he's much slower in singletrack than I am 🙂Posted 8 years agotronMember
How does the contact patch move in a turn on a two wheeled vehicle?
Caster increases camber with steering angle which should aid turn in, even if it isn't the mechanism that maintains the turn.
Weight over the front end also helps turn in.
When you think about it, the dynamics are entirely different to those of a 4 wheeled vehicle. A full on sports car will run a lot of Caster (say 7 degrees or more) to keep the contact patch relatively flat and maintain negative camber during a turn. It'll probably also run around 2 degrees static negative camber.
On the other hand, the twitchiest bikes are road bikes, which have far smaller caster angles than MTBs, a lot more weight over the front, and all bikes have zero static camber. So I would say get some weight forwards! I seem to remember this was part of Brant's design for the inbred.
Anyhow, I think it's very difficult to apply anything that's related to motorbikes to pushbikes. At speed on a motorbike will be talking > 30 mph. At speed on a bike is talking > 8mph? A motorbike also has far more opportunity to use the suspension for dynamic weight transfer into bends by loading the suspension up under braking, whereas a cyclist will generally be trying to brake as little as possible.Posted 8 years ago
Peter – I don't know if you have followed this debate in the motorcycle press – I have over the years. "understeer" is sometimes used as the term for pushing the front but many folk in the motorcycle world follow the line I do and to reduce confusion prefer to call it "pushing the front" as as you agree its a totally different mechanism in bikes to cars"
You can get this phenomenon in a two wheeler without a significant slip angle if you have mismatched tyre profiles for example.
anyway – its a purists semantic argument and a long way from the OP.
Op – apologies for hijacking your post.
If you are running wide then more front grip or more camber thrust is needed. More wieight on the front, lean the bike more, better gripping front tyre, more rebound damping to prevent unloading of the tyre, steeper steering head angle ( more sag???)Posted 8 years ago
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