johngwheeler

I am looking at changing out my 700x32 Bontrager HD5 tyres for something wider that I can run at pressures below 60psi - I find the ride a bit jarring.

Before I do this, I'm curious about whether others are happy to run this size tyre and pressure off-road, or whether I'm just being over sensitive, or have unreasonable expectations about the comfort of a wider tyre.

Any thoughts?

John

mstateglfr 

I wouldnt use them for what i ride. But thats the important difference- gravel near me is different from cali is different from mississippi is different from vermont.
Areas of my state differ even. 32s may be great some places.

HTupolev

Depends on what "off road" means. Yesterday I hit some "gravel" on 23mm road clinchers and was mostly fine-ish, because the "gravel" was smooth hardpack that was fairly clean. If it's bumpy, you might want the long-travel suspension offered by wide tires. If it's loose, you might want the ability of a wide tire to provide a nice wide cushion that doesn't sink.

Marcus_Ti

Depends on how big the gravel is. How packed it is. And whether it is dry or wet.

Barrettscv 

How much do you weight?

chas58

I have a set of 32mm I use for relatively smooth hard pack maintained roads, and a set of 40mm for rougher softer trails.

off road you can run the
32s at 50-60psi
40s at 35-40psi.

that alone will make a difference in comfort.

Jiggle

I try to stick with 32a tires for gravel.

johngwheeler

I weigh 71 kg (158lb). On hard packed dirt, the 32s are fine. On loose gravel, sandl they lack traction and stability.

Would 40mm tyres be a lot slower on the road?

Barrettscv 

I've used the Vittoria Voyager Hyper in the 700x32, 700x37 and 700x40 sizes and find that the bigger tires are faster on gravel and badly damaged pavement, but requires more power to accelerate and hold higher speeds on smooth pavement. If your typical pace is 16mph on most surfaces, the bigger tire has reduced rolling resistance with reduced power required to maintain this pace. If your pace is above 19mph on pavement, the aerodynamic resistance of the fatter tire is a significant factor and the bigger tire requires more power than the smaller tire.

If the bike is used on gravel during most rides, the bigger tire has the advantage. However, if the bike needs to hold higher speeds on smooth pavement, the smaller tire is more aerodynamic and accelerates faster due to lighter weight.

As a lighter cyclist, and if your cycling is primarily pavement and smooth, well-maintained gravel, you would probably benefit from a moderate sized slick tire at moderately low air pressure. The tire will be faster across most surfaces while maintaining sufficient traction on typical surfaces. However, you will need to use restraint and skill on loose gravel, particularly while climbing and descending.

These two tests are a good read that verifies the assertion that bigger tires have lower rolling resistance up to a point. However, the tests do not factor in aerodynamics or inertia. Tires in the 35-38 range provide a ideal balance of low rolling resistance, moderate weight, moderate aerodynamic performance and sufficient traction.

https://www.bicyclerollingresistance....on-32-37-40-47

https://www.bicyclerollingresistance....0s-ii-23-25-28

CV-6 

I am riding Vittoria Cross XN Pro which are nominally 32, but measure more like 30. I weigh north of 200 and ride them at 60-65PSI. I find they perform adequately on gravel but actually have no real comparison as those are the only tires I have ridden on gravel. Well actually I now recall that is not true. I rode Vittoria Cross tubulars a couple of times (32 also, and measured 32) and ran into clearance issues. I would like to try bigger.

So I guess you can say I am happy to run that size. I wonder if your jarring ride has to do with the tire itself. I find the Vittorias to be a comfortable ride.

bch238

John, I recall you ride the levees in Broward, right? If not, this wont apply, but if so, I think a 35mm or wider tire is the way to go south of Lox, but north of Lox is a lot smoother and those 32's will likely be perfectly fine.

NoGears

My rides have not shown any difference in average speed between 28c slicks, 35c knobby with slick center, and 40c gravel tires. Only time my speeds suffered was when I tried 40c knobby tires (WTB Nano). The speed didn't drop but the effort was harder. I'm on 40c GravelKings now and I'm just as fast as I've been on any other tire which isn't saying too much because I'm slow no matter what...lol...but the comfort and stability increase going to 40c tires outweighs any small lose in speed IMO. Unless you're racing and seconds count. Then maybe I'd sacrifice some comfort. But I don't race.

I'll also add that after going with a 40c tire...I'd never run even 35c again unless it was 100% pavement riding and even then...not sure I'd drop down below a 40c tire. Just so much more comfortable.

johngwheeler

Must be a different John; I'm in Sydney, Australia :-) But thanks for the reply!

johngwheeler

Thanks for the advice. It certainly sounds like it's worth trying 40c tyres, which will be a modest investment for the experiment. Is there a minimum rim inside width for these tyres? I think my external width is about 25mm, so probably about 20mm inside.

HTupolev

If you add a pound to your rims, and you pedal at 200W, it'll take you in the rough neighborhood of 30 seconds longer to ascend Alpe d'Huez, or a quarter second longer to accelerate from 0 to 25mph.

Wider tires should have a bit larger aero profile as well, but we're looking at a fractional increase in a fairly small minority of total aero drag for bike+rider; unless you're width-matching tires to fancy aero road racing rims (where extremely tiny changes in width can cost a few watts, and where the presumption exists that you got the wheel specifically to avoid that loss), my opinion is that it's not something very worth worrying about.

I have a bike with 53mm tires, wide but otherwise built like road racing tires. Cruising the flats, I haven't been able to distinguish a performance difference between it and my Emonda ALR with 23mm Bontrager R3s.

If you use tiny rims with wide tires, the bulbous inflated shape of the tire can be flexy about the tire-rim interface, resulting in a squirmy ride. 40mm tires on 20mm internal-width rims should work fine, though.

Hiro11

I like wider tires for several reasons. First, they generally allow lower pressures. Secondly, controlling for all other factors wider tires have (apparently, I personally can't tell) lower rolling resistance. Thirdly, wider tires last longer in my experience.

12strings

This seems high if comfort and/or off-road grip is the goal.

I run 30mm cross tires on my bike at 40 psi for gravel and grass. (I weight 160lbs).

Actually I've run 60psi on my 25mm road tires without any problems other than slowing me down and feeling a bit too squishy.

grolby

I've ridden 32s for the gravel events I've done. It's mostly fine, but I find myself wanting more traction on high-speed descents. Otherwise, they're fine. This is on Vermont roads, which are on the smoother side, but still no joke if you venture onto the occasional Class IV road.

I wouldn't consider a 30 second difference up a climb small. Especially if attributable solely to one piece of equipment. The aerodynamics aren't a trivial concern if you care about performance.

canklecat

I've seen folks locally riding 32c or even narrower tires on our MUP's relatively well maintained gravel/chat trails. Personally I'm not comfortable with anything narrower than 38, but I'm not fast so there's no advantage to running narrower for me.

A couple of weeks ago I saw a fellow on a drop bar bike with fairly narrow wheels/tires dart up a steep railroad incline lined with rail ballast, those huge chunks of jagged rock. He zipped through that stuff faster and more steadily than I can on my hybrid or mountain bike with 700x42 tires.

I suspect it's as much skill and balance as the tires. They got it. I ain't got it.

kickstart

You must be a racer.

To someone like me with different priorities, 30 seconds in 9 miles on an average 8% grade has no meaning. That could be a drink of water, rubbernecking at some scenery, taking a picture, or some other inconsequential distraction. I rather have the extra comfort for that hour+, than the 30 seconds.

grolby

NoGears

I'd spend more than 30 seconds standing on the side of the road crying if I had to do a ride like that....lol

Marcus_Ti

I'd spend an extra 2 hours stopping at every bar on the way up for a stiff drink.

chas58

Yeah sure, you can go lower for gravel and grass of course.

The pressures I gave were more for road.

For road, generally anything below 80 psi under 30mm the resistance starts to go up under 80, but 60 still isn't bad. For me, that would be a pinch flat problem on a tubed tire (which most narrow tires are).

Anything from 30-45mm is going to start to show markedly increase in resistance below 45 psi. 30-45 change typically increases resistance by 20 watts a pair, which can be a 50% increase in resistance for a good set of tires.

But yeah, gravel, grass, sand changes things. Off road 50psi for a 25mm, and 35psi for a 40mm tires is fine. Going lower can work, but you increase the possibility of pinch flats, hitting the rim, and/or burping. Its all doable though with the right technique and circumstannces...

chas58

Than 32mm? not really. It depends

There are some factors to consider.
1) carcass construction is the biggest. With the same carcass & tread, they don't roll a lot slower. Most larger tires have stiffer carcasses (and often different tread) that can make them roll slower. companies like compass specialize in tires that don't have these disadvantages compared to a smaller tire.
2) bigger tires are heavier, and will accelerate slower every time you stop.

Yeah, I ride 32mm on hardpack, and 40-45mm on dirt and sand. It makes a difference.