msu2001la

Anyone else experience this?

I had a huge tailwind on the second half of my ride today, and was hitting 35-40mp at times with some fast spinning (110-120rpm). I was running 33mm Donnely MXP tires at around 40psi (so pretty spongey) and wow... they were all over the place at those speeds. Downright terrifying. 40psi is good for off-road (these are tubed clinchers, so 35psi is about as low as I go with them) but maybe a little low for pavement I guess.

Even on a flat/straight road I felt like the rear was squirming back and forth with every pedal stroke any time I got north of 30mph. I was having fun spinning up and trying to hit top speeds, but a few times just stopped pedaling and coasted because I was worried I'd bite it.

These tires are great on gravel and hardpack dirt, and generally feel like they roll pretty fast on pavement (relative to other knobby tires), but today has me second guessing them for faster rides. I've been mostly riding Conti GP5000's lately so maybe I just am not used to the change and wasn't ready for it.

chas58

I'm probably riding 45-60psi in that size. Still, I'll do 30+mph at 25psi on those rims with the right tires.
Obviously your sidewall is gonna get spongy, which isn't a bad thing on gravel as you don't have the traction anyway.
That and of course the knobs are going to make the tires feel squirrely at those speeds, so two hits against ya.

I once made an ebike with Panaracer fire tires. Looked nice, but was pretty spongy at speed on the road (that and knobby tires pick up a lot of junk on the roads that leads to flats).

unterhausen

I ride 38mm tires on gravel and down around 20 psi feels good on gravel, but scary while cornering. 30-40 feels fine at whatever speed. Not sure I would ride a 32mm at 40psi, because it would bottom out for me.

Chi_Z

wide slicks are the way

Rides4Beer

Probably the large knobs. I haven't had any issues going fast on smaller knob gravel tires, or the Pathfinders I have now, which have a solid block in the middle for pavement.

msu2001la

Thinking about this in combo with another thread, I realize the carbon rims I'm using with these tires are only 19mm internal, which is probably why the tires are feeling so squirmy at speed.

This is on my old bike, which is rim brake. I typically use a wider alloy wheelset for CX tires (21mm internal) but one of the hubs has a problem on that wheelset. Not wanting to spend money to fix it, I decided to swap CX tires onto the carbon road wheels, and may have inadvertently discovered a reason why this isn't a great idea.

trailangel

No, rim width is not your problem. I'd rather ride a 19mm internal width on pavement with that size tire... will make the tire rounder.
Your tire pressure was way too low. 60 psi would have been right.

Bosco13

I was easily going 30+ mph on my gravel bike yesterday with no issues. 38 wide tire running at 42 psi.

Rides4Beer

I don't think it's pressure or internal wheel width. I've run 40mm tires on 19c rims at 36-38psi with no issues, and I'm 185lbs. I think it's the tire, specifically the knob height and spacing (which probably performs really well offroad). But as always, ymmv.

chas58

Good point. I don't like going below 55psi on my 19ID rims and 32mm tires, but I'll do 30psi on my 22ID rims. pinching the sidewalls together requires a bit of air pressure to keep the tire centered in the rim when there is a side loading.

Hondo Gravel

I run 38s at 70 psi both on pavement and gravel. A little rough on gravel sections but not too bad. If I was strictly on gravel I would lower the air pressure.

pbass

I hit 30 mph on the road on my WTB Ventures 47mm tubeless quite often - all the way back to my house is a long winding descent on the road. No issues, not squirrelly at all. They're more of a file tread with some slight knobbies on the sides, so that may be a factor.

shoota 

Agreed. 100% this is due to the tread pattern. (and 35 psi tubed is way too low).

Like others I've hit 40+ mph routinely on a variety of small knob tires over the years with never a hint of instability.

Chi_Z

damn that's hardcore, i am running 60psi on 32mm

Helldorado

Ain't physics a b*tch, eh?

plodderslusk

I ride Wtb Horizon 650b on gravel and tarmac, With 60 psi they are absolutely useless on singletrack but they are great on roads of every kind. No problems going fast downhill either.

ofajen

Yeah, too low of a pressure for road. 40 PSI on 32s on a road surface and I would be all over the place.

Best to either run a little higher for the whole ride or stop and add air when you get on the road surface. I typically run 32s at 50-55 front and 55-60 rear which is plenty for 200 lbs of bike and rider. A bit more than needed for a crushed stone trail, but my rides always have a road component.

Otto

JackR

All about the pressure. I spent a winter on 2.05" ice spiker pros. Pumped them all the way up to 50 psi for paved rides, the sound they make above 40km/hr is amazing. Sounds like the end of the world.

Koyote

No problems here, with tubeless tires up to 43mm wide at pressures as low as 30psi.

On one of my bikes, I am running 35mm slicks tubeless, and the pressure (if I haven't topped it up in a few days) is often <40psi. I hit 40mph on pretty much every ride, and they handle just fine.

chaadster

That’s the tire I’m running, too, 650b x 47c at 60psi for dirt roads and pavement. Runs along pretty damn good and feels great everywhere, and while I’ve not been over 31mph on them yet (I don’t think), I wouldn’t expect any problems...my 230lbs butt keeps things anchored to the road pretty good!

Helldorado

You hit 40 MPH on straight down-hill stretches, no doubt. But not on turns or in the flat sections. Hardly indicative of much of anything, I'm afraid.

Koyote

How do you know what happens on my rides?

chaadster

Noobtelligence...it’s a thing. 😆

Russ Roth

I run Clement xplor which are now the Donnelly xplor in a 35 and I run them about 60/65psi front/rear; never had an issue at any speed on those tires. Had a torturous ride into the wind at 11mph and turning around had no trouble keeping 40 with the wind shoving me along, was a lot of fun with no squirm. For gravel I drop it to 55/60 and find it to be fine on the cinder and packed gravel I run across.

Helldorado

I don't actually know what you do. But I do know what you don't do. And you don't A) ride 40 MPH on a flat surface (under your own power that is...), or B) corner anything other than a very wiiiide turn at 40 MPH (going down hill, of course).

Am I wrong?