esoteric17

hey all,

Currently on a 2017 Allez with a pretty aggressive geo. Having trouble finding a new frame that fits my needs.

My question is, why do current bike manufacturers generally put larger tire clearances (>30c) only on their endurance geo bikes, as opposed to incorporating larger tire clearances on more aggressive geo bikes? Is it because bikes with aggressive geometries and large tire clearances won’t sell, or are there mechanical/ geometric reasons? I understand that aerodynamics, weight, and rolling resistance can come into play, but is that it? Would larger tire clearances lead to design issues? Ideally, I would love to run a larger tire for training rides and then swap wheel sets with narrower tires for races.

*example: why not put larger tire clearances on a tarmac or Emonda? Why only on the Roubaix and Domane?

I’m excited to hear BF’s thoughts on this.

canklecat

Different bikes for different types of riding. While the new conventional wisdom says bigger tires at lower pressure are "faster" or just as fast, that's generally true only over mixed terrain and longer rides -- including rural chipseal and busted up urban roads, rather than closed courses or velodromes.

But most people who race are riding local crits. Those are usually on pretty decent pavement -- closed courses (if they're lucky), big parking lots, business/industrial parks after hours, etc. 700x23 tires at maximum pressure are pretty fast on good smooth asphalt. And crits have a lot of tight turns and need quick handling, so the frame geometry and BB height are different than endurance bikes.

63rickert

It's because they wouldn't sell. The loyalty to skinny tires and belief in skinny=faster remains strong. Those who have been sold on wider tires are going straight to gravel bikes. If the big brands sell the marks one more time on a frame without clearance they still have a chance to sell a wide clearance frame to same customer next season. For what you want best choice is a custom. First time you do a crit corner on 700x30 (or wider) you won't ever look back.

Have Roubaix and Domane finally gone wide clearance? By what standard?

MoreLowGears

Bike manufactures actually are increasing tire clearance on race bikes, e.g., the Venge clears 32mm tires and the Tarmac and SystemSix clear 30mm tires. Many race bikes like the TCR, SuperSix, Dogma F10, and others clear 28mm when a few years ago they could barely do 25mm. I expect race tires to get wider as wider aerodynamic wheel become more widespread.

Expanded tire clearance does require some compromises though. Race bikes have very short wheelbases (distance between the wheels), which allows them to turn rapidly at high speeds. If you look at some of the race bikes mentioned above, you'll notice there's very little space between the tire, chainstays, and seat tube. Wider tires are larger in diameter, so at a certain point the wheelbase has to increase to make space for the larger tires. Wide tires that are close to the bottom bracket get in the way of the seat stays. My Kona Rove DL (a gravel bike) has kinked chainstays that bend around the tire to avoid it. This is undesirable on race bikes because it reduces chainring and heel clearance, and of course because it reduces StIfFnEsS. Finally, dual-pivot brake calipers have limitations for how wide of a tire they support.

edit: Compared to a medium Tarmac SL6, my 57cm Rove DL's wheelbase is 2.3" longer. Plenty of room for larger tires.

The latest Roubaix clears 33mm and the 2020 Domane Trek just announced can do 40mm 38mm (!) tires. This is according to the manufacturers, who tend to be conservative with those numbers.

esoteric17

I see. So yeah, there are some geometric limitations to larger tires. To keep the same handling characteristics while incorporating longer wheelbases, the head tube angle, (maybe seat tube angle too?) trail and offset numbers would have to change.

Now I’m wondering if changing wheelbase length changes the “responsiveness” of the bike to rider inputs. If you are to leave all of the geometry numbers the same minus wheelbase, the bike would still react to rider inputs in the same way, but just have a “larger” turning radius, correct? I’m guessing that a longer wheelbase with the same geometry numbers would make the bike feel less agile though. All just a matter of perception?

WhyFi

Yup, it's not just gravel/endurance. Aero bikes are going wider, too, (Madone and Venge officially clear 28mm and 32mm, respectively, though you might be able to squeeze in a little more), so I wouldn't be surprised to see 28mm+ on just about every category very soon.

WhyFi

Justin Williams is riding disc versions of the Tarmac and Allez Sprint with 30mm clearance. He's mentioned that they're his favorite bike to date - I mean, he's obviously sponsored, so take that with a grain of salt, but his race results seem pretty okay.

Trakhak

Pardon the car analogy (frowned on in these parts), but: if you've ever driven a short-wheelbase car, especially a sports car, versus a car with a conventional wheelbase, you should have a inkling of what a difference wheelbase makes.

When I shop for bikes, the only measurements I concern myself with are head tube length (short) and wheelbase (also short). If those numbers are acceptable, I know I'll like the bike. (I don't care about tire clearance; I'm happy with 25-mm tires.)

redlude97

they're called cyclocross bikes

Seattle Forrest

Cervelo nailed it with the C3/C5.