Turn in not sharp - tyre pressure / tyre shape

boombang

Short question is at a certain tyre pressure (i.e. going low) can a tyre deforming make turn in a bit wooly?

Could it also be attributed to a wider, taller tyre impacting geometry, and if so would you expect a moving from a 34mm tyre with edge knobbles to a 38mm tyre with blockier tread?


Basically I stuck some WTB Nanos on my spare rims a few weeks ago, tubeless with sealant. Idea was to give me a big volume tyre and some extra capability on the CX bike for mucking about in woods. They measure up 38mm at 35-40 psi. Blocky tread and rounded profile, at 35psi front and 40psi rear the tread flattens off on contact patch.

I usually run the cheaper performance line X-Ones which measure 34mm or so on my rims. Run these around 45psi, at that pressure the tread also flattens off and they are fairly comfortable with minimal risk of pinch flat (run less on mud).

The WTBs are without a doubt faster over firmer surfaces and wondering if is simply a confidence thing.

tgotb

Yes, though I'd generally expect it to happen at lower pressures. If you corner beyond the limit, one of two things will happen:

1. The tyre will maintain its shape and slide sideways. This is what happens with a relatively hard tyre in mud; you can improve traction by lowering the pressure (increasing surface area).
2. The tyre will fold over. This is what happens with a relatively soft tyre on a grippy surface (esp tarmac). You can stop this happening by increasing the pressure.

In a muddy race, you'll generally go low, and accept a bit of sketchiness on the few grippy bits in return for more grip in the mud. Conversely, if it's dry you'll probably go for a higher pressure in order to be able to corner harder where there's grip, and accept a bit of sliding in the odd muddy bit. This is one reason you should ride at least some of the course at race pace during your warm-up, as you want to get a feel for how the tyres will behave while you still have a chance to adjust them. For instance I pre-rode yesterday's course at ~20psi, and could feel the tyres folding over on the corners because it was grippier than I'd expected; I ended up racing closer to 25psi.

I'm sure many people on here have had the experience of forgetting to pump their tyres up before riding home from a muddy training session, and nearly stacking it at the first road junction.

boombang

Experimented a bit and think the shape, tread pattern and width of the tyre must change handling subtly but significantly.

WTBs take a little more lean or bar turn to follow same path as the X-Ones, enough to feel unnatural but not enough that you can't ride around it on right surfaces.
When it's muddy or slippery the X-Ones have much more grip on the shoulders, so really is about riding the bike a bit differently on the WTBs and being sensible about tyre choice for the ride.

The WTBs have however turned out to be sublime on fine gravel and surprisingly effective on grass, just better off avoiding mud.