Do I really want a square tyre profile

I have been toying with the idea of new wheels for my 650b and 29er. The current vogue is for wide rim profiles, with the ever popular LB carbons being offered in very wide sizes.

Is there an optimum rim width:tyre width ratio?

It seems that putting a tyre on a rim that’s too wide will give me a very square tread profile. I can see how that will give me a bigger contact patch when my bike is upright. But what happens when im trying to lean the bike over to turn?It now seems that the tyre profile is comletely wrong for cornering banked.

Been using 35mm wide rims for over 5 years, works really well, I wouldn’t go for 50mm unless you’re fully rigid and using a 3” tyre.

What size tyre are you using? Anything you have found you can’t use?

I’ve been happy with mine!

You must be riding very specific trails sidewinder.

It’s complicated! The size of the tyre matters but what arguably matters more is the shape of the tyre. You’d think a carcass would be circular in cross-section but when the tread is moulded onto it it can take a more squared off shape. And more importantly the tread blocks themselves change the shape of the tyre. So the High Roller below is a squarer tyre:

Whilst the Trail King is a rounder tyre:

Put a High Roller on a very wide rim and it’ll roll much more slowly, corner nervously on harder ground and be difficult to tip into turns on loose ground (though it will bite well once it’s onto its edge). Put a Trail King on a narrow rim and it’ll be prone to squirming unless at very high pressures and will struggle to find any sort of bite when cornering.

What complicates things further is that the Trail King has a lot of carcass volume compared to the tread width so it won’t suit a super wide rim – for that you want a tyre which is relatively shallow of sidewall and fairly round in profile like a Minion DHF:

But go too wide and that’ll end up too square…

My Minion DHF 2.5 on my DH bike is sat really happily on a rim that is 28mm external width, so im guessin internally it’s about a 24.

Is there a resource to say what tyre works with what rim to make it all easier?

Or do i have to guess at inflated profiles from the shape in the shop?

I was running a Rubber Queen/Trail King on Blunt 35’s last summer (2.4″ front, 2.2″ rear).

Although they end up fairly ’round’ and the sidewall sticks out further than the tread when you look from above I never had problems with leaning over too far and running out of tread/grip. I wasn’t running super low pressures (approx 20-25 psi) though. It certainly wasn’t the ‘Mohican of tread’ that was referred to in the recent stw mag review of wide rims.

A few mm on your internal rim width makes very little difference to your tyre profile.

But if you think of it as widening the base of a triangle you can see how it makes your tyre much more stable. The contact point of your tyre (peak of the triangle) stays between the rim walls and is much less likely to deform or burp.

That’s how it makes sense in my head anyway.

kind of agree with chiefrgrooveguru there

I definately think the high roller has more drag going from a 30mm to 35mm rim
but
I find the highroller2 corners much better than a trailking on hard or soft ground, i can get it much further over, which is the opposite to what i expected
(this is front tyre with 35mm rim)

I was using a Racing Ralf 2.4, a Weirwolf 2.5 and Ardent 2.4 – on the rear, all work well with a 35mm rim, pressure typically 20 psi with tubes. Also a beaver 2″ for mud duties.

I think the squaring off of tyres is quite over inflated as an issue (see what I did there?) A tyre is around 60mm at its widest, whereas even a 35mm LB is still internally only 29mm. So if you add 7 or 8 mm to a tyre’s seat, thats still not making a previously round tyre square, its just changing its diameter, and hence the pitch of the circle when it contacts the ground. Also, when you compare say a stans rim to an LB, the height of the bead on the rim is very different, the wider rim pinches the tyre much higher than a stans, meaning its rounding off the tyre again, albeit not a total compensation. Im sure it does have an effect, but no so much that I notice when swapping from a wide rim to a narrow one. What you notice more is the increased stability of the tyre at lower pressures on the wider rim I think.

Forget what’s en vogue, most of these fashion whores aren’t pushing their tyres close to their limit of grip anyway.

wider rims is just the new purple