My road bike with 700x23 tires is some what unstable. I want it to turn and cornor better. Should I get new tires? If so, which tires? Also, it is a 2012 trek 1.2 with stock tires.

It depends on the rim size as to what size tire it can take. Check the rim for something like 622x14 or something like that. Then look here https://sheldonbrown.com/tire-sizing.html. I have no problem with 700x23 and you'd probably get used to it, but I did just switch to 700x28 for a much smoother ride and I'd guess they'd give you the feel of more stability especially on rough roads, loose dirt, gravel, or debris. Buy some cheapies and use them for a while and then if you decide you like the size upgrade to some quality tires keeping the cheap ones for spares. Probably use the same tubes.

Your complaint is that it's unstable, and you want it to turn and corner better?

Either your description of the problem is off, or you're asking for the impossible. A bike that's stable and solid in a straight line will be sluggish around corners, and a bike that's nimble around corners will be twitchy on the straightaways. You can't have a bike that's both solid and nimble around corners simultaneously.

There'are plenty of different degrees of compromises though, so if you don't like the way yours is handling you can always measure some frame geometry specifics and then go shopping for another bike more to your liking.
Or you can try swapping out the fork first, forks to contribute a lot to how the bike will handle.

Tires are a so-so thing, and unless you're doing something really strange at the moment I don't think changing the tires will do that much to alleviate your problem. But it's always worth trying a couple of different tire pressures.
On a road bike, you shouldn't be able to run too low pressures, as that would most likely cause snakebite flats.
But you might be running too high pressure, which can make the wheels kinda bouncy.

Hi,

It had Bontrager carbon forks and 23mm Bontrager T1 tyres.

They should be run about 100 psi for average weight with the
rear somewhat higher than the front, due to weight distribution.

Going to 28mm drops pressures to about 70 psi and gives
more grip due to a bigger contact patch and a smoother
ride at the cost of some added tyre weight - which might
make the front feel a little more stable, not sure though.

rgds, sreten.

Will a bike that comes stock with 23mm tyres have enough clearance for 28s?

I assume "turn and corner better" refers to stable and fast cornering? It may feel unpredictably overly responsive now? You may be experiencing the benefits of a "racing bike" configuration: fairly steep head-angle, short trail, short-wheelbase/chainstays, with narrow, high-pressure tyres results twitchy front-end behavior. Over the past 30-year, there has been a trend with manufacturers and shops pushing more and more "racing bikes" because people get the impression that they'll be "faster" like pro-racers.

However, "faster" geometries come with a price, super-quick and nervous handling. Without decades of practice on "slower" bikes, very few people can hop on a racing bike and make it ride like the pros. At this point, other than buying a bike with more relaxed "touring" type geometry that was more common decades ago, (which still makes more sense for the majority of cyclists today), you can still make some changes to the bike to make it more stable.

As mentioned earlier, fit the largest fattest tyres you can into the frame and run it at low pressure. Measure the clearance on the sides and tops of the tyres to the frame/fork and see how much larger you can go. A 26-28mm tyre may be able to fit. Pick a tyre with a rounded cross-section profile, rather than one that is pointy at the tread. The change in tyres will make the bike more stable in a straight-line and turn-in to corners more predictably. It also won't dart around and change directions at random in the middle of corners when you hit bumps.

Also relax your arms and bend our elbows, while lightly gripping the bars with your weight balanced on the heel of your palm so that you don't slide off the front, rear or sides of the bars. This will help absorb road-shock and prevent it from flipping your bars around.

Have fun!

The tires probably aren't the cause of cornering instability. If your tire starts sliding instead of rolling in a high speed corner you're almost certainly going to fall down. Frame and wheel stiffness are more likely culprits. Based on your bike, I'd say it's probably the wheels. How heavy are you?

It depends upon the bike. My Specialized Allez Epic came with 21mm tyres and i use 26mm front and 28mm rear tyres. Sure it rubs the chainstays if the wheels aren't true to +/- 0.5mm, but it certainly handles the corners much better! Especially when I weighed 115kg. Down to 72kg now and have let out a lot of the tyre-pressure, and kept the same sizes.

How much deflection is there in the wheels? Perhaps 0.5mm max? A tyre deforms over 4-6mm depending upon size, pressure and rider-weight. Tyre-pressure makes a HUGE contribution to handling-feel and cornering-grip. A lot of people over-inflate their tyres and the result is a lot of bouncing around and nervous handling. Pressure should be based upon tyre-width and rider-weight to arrive at about a 15% sink-rate (tyre compression). Here's a guide to inflation pressure from Michelin. And some others:

Frank Berto - Tyre Inflation
Bicycle Quarterly - Tyre Drop

As has been said I'd look elsewhere...rider...before thinking that 23mm tires...pretty much the standard on most "road" bikes...are the cause.

+1 Cornering properly at speed is not necessarily intuitive, and some riders lean exactly the opposite direction from what they should on low speed turns.

Hi,

Well they'd never get round the corner leaning the other way.

rgds, sreten.

(People are nowhere near as thick as you like implying.)

I corner better on a shorter wheelbased bike. It usually means, also, I'm not going to be able to fit wider, taller, tires. But if you have the room, it will provide better contact with wider tires and be a little more stable on turns.

I know that my bike with 700x25c tires will feel like its slipping when the tires are low on pressure (below 80psi or so). I tend to keep my tires up around 110psi because I'm quite large.

What psi do you keep your tires at?

Hi,

Generally it will as 23mm / 25 mm is for racing and 25/28mm is for training.

rgds, sreten.

In fact plenty of riders when making turns at low speed lean to the outside and some also put out their inside foot in case they fall.

I am not here or anywhere else implying anything, merely stating my observations. Possibly what you are referring to is that I often go into detail about the process of diagnosis, or explaining the why of how one solves a problem rather than just the how. That is due to my "teach to fish" vs. "give a fish" philosophy. It's not a matter of assuming people are dense but rather helping those who need it to become more self-sufficient by being able to generalize to other situations they may meet in the future. I'm confident those who are already knowledgeable can readily skim over what I post, or add anything I have missed.

Hi,

I'd say they swing out on a path that counteracts the initial lean
and as they turn in the lean takes over. I've never seen anyone
lean the wrong way into a corner with their outside foot hanging
out, that is just plain utterly stupid, they will simply never get
round the corner, and there is no path to learning such a stupid
approach. Fact wise, I have no idea what you are talking about.

rgds, sreten.

Again, I'm not speaking of the bike lean, or about the setup of initially turning the wheel counter to the turn direction, but rather the upper body, and it's the inside foot that is put down. Perhaps I would be more accurate to say that they fight leaning inward wth the bike and instead keep their upper body more upright. In any case it's a small point, and typically done only by very casual riders.

Hi,

Your severely contradicting yourself, not good style at all.

rgds, sreten.

Tire changes won't have much impact on stability. Before changing the tires consider all factors, starting with what you see as instability, then possible causative factors including; tire pressure, headset, frame geometry, rider weight distribution, frame/fork alignment, and last but definitely not least rider experience and confidence.

Many people who complain if instability, simply aren't used to the nimble handling of sport or race bikes.

Not good style - that's ironic. I'm outta here.

Be careful here. The "generally" is misplaced. Insufficient clearance for 28mm tires is an oft posted complaint of many high-end bikes. 25mm is almost always OK, but 28mm is pretty iffy.

Sreten, I believe you may have misunderstood what CNY actually said.

This makes sense - people don't always like to lean with the bike, so if they're turning left they lean their upper body to their right, but because the whole bike is being leant over to the left, the overall effect is their upper body stays upright. The same people often prepare to put their inside foot (in my example the left) down in case they fall.

This isn't a particularly good way of doing it.

Either way, the initial comment might not've been clear, but there's no contradiction.

Hi,

It does sound like an awkward way of doing it. Putting your inside foot down
and sticking it out is probably the only way you would get round the corner,
as it will move your CofG enough to the inside to facilitate the (slow) turn.

Not leaning your upper body as much as you should into a corner is not the
same as leaning the wrong way, you'd never get round the corner if you did.

Leaning the wrong way can have two meanings : Not leaning properly or
leaning in the opposite direction to that needed, maybe the confusion.

I did stick my inside leg out sometimes on tight turns when I started
riding again but cannot recall doing it after the first month or so.

rgds, sreten.

My routes do have some awkward offset pedestrian barriers
so I do get to practise tight turns a little each time I ride.

Thanks for all the replys. I plan on going to a bike shop and out fitting it with the largest/widest possible wheels and tires. The large turning radius is probably the most apparent problem. I may also just need to get used to road/race biking.
-Thanks again

Well, that makes as much sense as the first post. I hope things work out for you.