Noonievut

My current gravel bike for summer riding is a chromoly steel beast of a bike that can take a beating. It's heavy, has long chain stays, a B17, and touring rims (Mavic A719). While it doesn't have disk brakes, and those may make it more beastly, the riding I do in the summer doesn't need them. I also have a gravel-capable bike that I use in the winter months, it has an aluminum frame and disk brakes...and clearance for 40mm tires. I use this on some summer gravel rides where there is single track mixed in, as it has shorter chain stays and overall geometry more suitable for tight turns, clearing logs, etc.

Both bikes work well, though both are heavy.

This got me thinking about whether a lighter frame/fork (maybe one designed for such riding) would be faster while retaining it's comfort over gravel/dirt, etc. There are various steels out there that are lighter than chromo, there is of course aluminum (though I find it harsh for such riding unless paired with the perfect tires at the right psi), and well there is carbon. I've never actually ridden a carbon bike...and while I've read that they're lighter and stiffer, how would it compare over gravel to my steel bike? Big difference, or little?

While my current bike is heavy, I do have a B17, triple chain ring and other parts that are not light, but the B17 is a must and the other parts I got for a great deal...so I don't feel like spending too much to save a pound or less. To be honest...I don't even care that much about weight, but when I ride my road bike (steel as well -columbus spirit- but with ultegra and lighter wheels...tips about 19 pounds versus probably 23-25 for the beast) it's so much zippier that I thought the ultimate bike for me, cause I love gravel riding, would be something as zippy but comfortable over gravel. Note - my gravel is not the flint hills of Kansas, it's more like dirt/gravel roads with a mix of compacted dirt, pea size gravel, and a fair share of small pot holes and other bumps to keep things interesting.

My thinking is that the most important factor for comfort is tires...larger the better and lower the psi more comfortable...that's what makes my aluminum bike feel great (MSO 40mm). But a small part of me wants to just up and buy another bike...

flargle

You've kind of contradicted yourself here. The determining factor in ride quality is the tire volume, not the frame material.

IMO a fully rigid 29er with some sort of trekking/H/butterfly handlebar and ~50mm tires (tubeless, PSI in the 20s) is the best choice for gravel riding. Compared with standard CX tires, you practically float over the chatter. And if you have a steep rutted descent, there is really no comparison. With the correct tire and tread, you give up absolutely nothing w.r.t. rolling resistance on pavement.

This advice goes against the current trend in "gravel bikes". But remember, "gravel bikes" are being sold by companies who have a financial stake in pushing the trendiest bikes. But seriously, find a decent hardtail 29er, add a rigid fork, et voila.

unterhausen

I like a road bike geometry for gravel, so a hardtail 29'er is likely to be a little short for that. Otherwise, I think that a 29'er would be a good choice, nothing stopping you from putting drops on one if the reach is long enough. I am running 38mm tires on my gravel bike right now, I think they are plenty big enough for most of the roads we have here, and the roads here feature large, sharp rocks. A lot of the gravel road bikes will clear a tire like that. I am riding an All City Macho Man Disc, and it has been working out fine for everything I throw at it, including jeep trails that might as well be rocky singletrack

NormanF

Entry level 29ers like the Marin Muirwoods 29er can be good poor man's gravel grinder bikes. As long your bike can take fat tires and disc brakes, don't get too hung up on whether its a particular type of bicycle. Any bike built to go off road in general, will make a good gravel grinder bike.

Noonievut

so if I get a light frame that accommodates larger tires, I will get that same zippy feeling as with my road bike, minus a bit of zip due to having say only 45psi. I like road style frames with drop bars...bit I have a mtb and agree it would be most plush on gravel, but to me it's overkill.

thx

flargle

With all due respect you have it backwards. You GAIN zip by running a high-quality tubeless semi-slick 1.8-2.0 tire (like the Stan's Crow) at 22-25 psi, on a fully rigid 29er. Until you've ridden this sort of setup on gravel, you won't appreciate how much speed you lose by bouncing around on those CX clinchers.

With a trekking or H bar, which gives you the option of a center-forward hand position, you can make your position as aerodynamic as you want by your choice of stem. Or just go with flat MTB bars with aero clip-ons. (Just make sure the stem puts you in the right position.)

The fellow who said mountain bikes are short is off-base, too. TT for Niner EMD size M is 60cm. This is why I would NOT recommend drop bars, unless you work out the numbers and down-size the frame for that specific setup.

Most people don't really grok this kind of setup until they've tried it for themselves. You can build up this kind of bike, even with steel frame and fork, pretty light. Go with full carbon rigid like the Niner bike, and you can get a superlight setup indeed (though for $$$).

Noonievut

The zip I refer too on my road bike was I believe due to it's lighter weight, stiffer crank and bottom bracket, stiffer wheels and 'maybe' the 25mm tires pumped to 100psi. I wonder if I ran wider tires and lower psi if the zip would be gone (couldn't fit wider tires in there).

With respect to mtb on gravel, the rides I'm doing where there is gravel are rides with quite a bit of paved roads (cause of where I live), plus I prefer drop bars. If I was riding mainly on gravel and dirt, I would certainly consider a 29er. I have a 26 FS for single track and while I have ridden it on gravel where it's around the single track, it of course handles awesome. I like your ideas of how to make the 29er more of a gravel ready bike though. Food for thought!

Kopsis

Not really. 4 - 6 lb just doesn't make that much difference outside of competition. Take that as a percentage of bike + rider + gear weight and you're looking at less than 3% for an average size rider. When you run the numbers it's about an 18 second difference over a 30 mile ride at 150W. If you were pulling weight out of the wheelset instead of the frame it would be more noticeable, but the effect over the course of a ride still isn't that great.

Noonievut

Sorry for my continued questions, I'm trying to learn

I have a 19 pound road bike with 25mm tires that I run at 100psi. It's colombus spirt steel frame with Ultegra group and mavic cxp33 wheels.

I have a 25 pound road bike with 32 tires that I run at 45 psi. It's chromoly steel frame with mainly Tiagra group and mavic A719 wheels.

On the same paved roads the 19 pound bike is much zippier, with quicker accelerations and higher average speeds. I've ridden both bikes so many times that quite often the conditions are very similar, and I know that I average approximately 2 km faster on the 19 pound bike...more if lots of climbing. I'm 140 pounds and would use the same gear/water on both bikes (so total weight is 6 pounds more on heavier bike). I'm about 8-10% faster on the 19 pound bike. Why?

If my 19 pound bike could accomodate the same 32mm tires, running at the same PSI (granted the tires would add a few grams), would I be faster (than running those same tires on the heavier bike?).

Once I better understand the above questions, I can re-think my original question. And to be honest, I'm not that much of a weight weenie (I have brooks on all my bikes, and virtually no carbon), I actually prefer comfort over stiff/light, but I'm curious as to whether I can get 5-10% faster if I had a lighter frame, and whether a different frame 'can' be as comfortable (because the tires take care of that, no?).

Thanks for your patience!!!

unterhausen

depends a lot on the tire. On my commuter, I went from some Serfas POS to a Continental Winter, same size, maybe more tread on the Continental, and the difference was night and day on the amount of effort it took to pedal the bike. I agree that on gravel that a bigger tire with less pressure will make for faster rides. I'm not really willing to go back to smaller tires, too scary. I am building a bike that will take 2"+ tires for gravel, it's a good size. I wish there were more frames that would take mountain bike tires, the changes would be small at this point.

BTW, my previous post had it backwards on tt length, that's what I get for posting when I'm recovering from surgery. However, the point being that whatever frame you get, make sure the frame can be made to fit your contact points with reasonable stem/seatpost combinations.

Kopsis

2 kph faster at what speed? Above about 30 kph, aerodynamic drag starts to dwarf all other losses. A better (more aero) riding position could easily account for the difference (and narrower tires and a possibly more aero frame may be helping too). Also note that depending on how closely your fit is matched (or not matched), you may actually be putting out more power at the same effort on the road bike just due to more favorable geometry.

Rolling resistance also makes a difference. And wide tires at low pressure definitely have more loss. Remember that every time a tire "flexes" it's converting kinetic energy to heat. Your legs have to replace that lost energy. Having squishy tires is not much different than having a flexy bottom bracket. Less of your energy is going into forward motion. So to get that comfy ride, you have to sacrifice some speed or increase your power output. If you want to test this, take your 32 front up to 50 psi and the rear to 70 psi (or the rated max pressure, whichever is less) and see if you get more "zip".

Here's another test. Four 20 oz water bottles weighs about 5 lb. Take the road bike out with two bottles in the cages and two in your jersey pockets. See if you notice a big difference from the extra weight. If it doesn't make you 5-10% slower, then I wouldn't expect dropping the same amount of weight from your gravel bike will make you 5-10% faster.

Noonievut

i think this is the nail on the head. I dont want to sacrifice comfort for speed, so I'll stick with my heavier but more comfortable bike.

flargle

FWIW

Rolling Resistance | Schwalbe North America
"Wider tires roll better than narrow ones. This assertion generally generates skepticism, nevertheless at the same tire pressure a narrow tire deflects more and so deforms more."
"Above all, a bicycle with narrow tires is much easier to accelerate because the rotating mass of the wheels is lower and the bicycle is much more agile. At constant speeds of around 20 km/h, the ride is better with wider tires. In practice, the energy saving is even greater than in theory as the elasticity of the tires absorbs road shocks, which would otherwise be transferred to the rider and so saves energy."

https://www.schwalbetires.com/wider_faster_page
"Higher pressure was only faster on the road. Off-road rolling resistance was lower, the wider the tire and the lower the pressure."

fietsbob

A old beach cruiser is what Opie rode in Mayberry RFD.

ride_anywhere

" The determining factor in ride quality is the tire volume, not the frame material.. . ."

Tire volume is only one factor contributing to ride quality. Frame material is another as is tube selection and geometry. Some folks can't feel the difference just like some can't appreciate the difference between "lite" beers and artisinal craft beer. But there is a very notable difference in frame materials. I have bikes of all common materials (steel, aluminum, carbon and titanium) and they absolutely do provide different ride quality. Frame weight matters too. But again, YMMV.

Kopsis

Perhaps, but how on earth is that a valid comparison. At equal pressure, at least one of the tires is running at seriously sub-optimal pressure. I understand Schwalbe wanting to spin a "wide is good" story, but that's really reaching.

Yes, and OP was questioning whether weight or rolling resistance (or something else) accounts for the observed speed difference on the road.