DOS

Hi

I needed to replace a Hed Belgium + rim on the rear wheel of my caad10 after a run in with a pothole at speed created a pretty big ding. I bought a Hed Belgium R, which recently replaced the + in the Hed rim line up, discovering after purchase that the max recommended pressure for my Schwalbe pro 25mm tires, which blow up to 27mm when inflated, is between 70 and 75 psi. This is considerably lower than 100psi max of the Belgium + and just about every other hooked rim I have looked at. At 215lbs, I have been riding the Belgium + at about 90psi, which seemed a sweet spot for comfort and rolling on my tubeless set up. So dropping to 70ish psi seems really low, although pinch flats arent a worry, and considerably lower than what most calculators recommend. My rides are moderate group rides and I am not worried about corning hard during crits.

Welcome thoughts on Hed’s low max pressures, whether I should adhere to them, and
and implications for someone my size riding at sub 80psi pressures.

DOS

Hi

Cross post from road cycling, figuring wrenches nd wheel builders might have more to say.

I needed to replace a Hed Belgium + rim on the rear wheel of my caad10 after a run in with a pothole at speed created a pretty big ding. I bought a Hed Belgium R, which recently replaced the + in the Hed rim line up, discovering after purchase that the max recommended pressure for my Schwalbe pro 25mm tires, which blow up to 27mm when inflated, is between 70 and 75 psi. This is considerably lower than 100psi max of the Belgium + and just about every other hooked rim I have looked at. At 215lbs, I have been riding the Belgium + at about 90psi, which seemed a sweet spot for comfort and rolling on my tubeless set up. So dropping to 70ish psi seems really low, although pinch flats arent a worry, and considerably lower than what most calculators recommend. My rides are moderate group rides and I am not worried about corning hard during crits.

Welcome thoughts on Hed’s low max pressures, whether I should adhere to them,
and implications for someone my size riding at sub 80psi pressures.
__________________

FBinNY 

As a general rule, I prefer to put heavier riders on wider tires at lower pressures when possible. However, the formula for Hoop Stress, or the outward force that air pressure places on rims is very simple. It's Pressure X Width.

I find it hard to believe that your Hed rim max pressure for a 27mm tire is that low, since 25mm tires are generally used at 100psi or more. I'd read that guide 3 times to be sure I read it right, then either ignore it, or contact Hed for clarification.

For the record, what did Hed say was the max for 25mm tires? If it's greater than 75-80psi someone's math is off.

headasunder

Personally I would stick to the rim manufacturers max, especially for tubeless. Better to be safe than have the tyre blow off the rim at speed

DOS

According to what is printed on the rim, max is 80 psi for 23mm, 75 for 25mm, and 70 for 28mm (see pic). I found it hard to believe as well, which is why I didnt think to check before buying the rim.

DOS

Thats where I am going to start. Hopefully not too squishy.

DOS

Pictured is pressure chart from the Hed website. It is listed under the Hed Ardennes wheelset, which use basically the same rime as the Hed Belgium R.

FBinNY 

The numbers are consistent with each other, but all seem ridiculously low.

25mm @ 75psi is woefully inadequate for even a moderately heavy rider on metro NY roads.

DOS

I, perhaps foolishly, already built the wheel rather than returning the rim, so I am stuck with it. I did send Hed a message asking clarification so will report back of I hear from them. But I am completely befuddled by the numbers because there is literally no other rim I have encountered with so low max pressures. Its not even a hookless rim. Hell, I inflate my wife’s 23mm tires more than 80 psi and she weighs in a bit more than Jonas Vindegaard but not as much as Tadej Pogacar.

datlas 

Good question. My understanding is max pressure is primarily a TIRE spec more so than a rim spec, although of course both can contribute to a blowout failure. I suspect you are probably ok running your tires at 80-90PSI. But see what the others say.

ps if you are really concerned move to 28 or 30mm
tires which are probably fine at 75PSI.

Kontact

It sounds like the rim really has a max rider weight based on pressure. But it would have been better if they stated it that way instead of having the same PSI max from 180 to 240 lbs.

well biked

DOS, I have a couple of wheelsets I've built with HED rims, both for gravel bikes. I run the tires tubeless on these wheels, and the inner width of the rims is wider than I would have used just a few years ago for the tire width I use on these wheels (42-48mm tire width, 25mm inner width rims). Running tubeless, and wide tires, max pressure is a non issue, I'm usually trying to play around with how LOW I can run the pressure for gravel riding, not the other way around. My general impression of the rims is that they are excellent in every respect for my purposes.

But for your situation, with a true road rim, I'm pretty shocked at those stated max pressures published by HED for the various tire widths, just like you are. I've certainly not observed anything about a HED rim that would make me think it would be less capable of handling conventional tire pressures in running tubed tires in traditional road widths than any other quality, hooked-edge, modern rim.

Curious to hear what HED says in response to your message about this.

cb400bill

Merged duplicate threads.

Please do not cross post.

DOS

Well first ride on the new rim went well. 51 miles on some wet roads after an early morning storm. I don't know about other factors, but riding at 75psi was lovely from a comfort standpoint. Very plush. I didn't notice any sluggishness and my average watts, according to ridewithgps based on my heart rate monitor, was same as a similar ride a few weeks ago (whether that means anything, I have no idea) and my speed was almost a mile an hour faster (aided by a nice tailwind over the second half of the ride). I was a little nervous on some fast down hill turns, mostly due to wet conditions but pressure was also on my mind, so I took those easy. Ill give it a few more tides before I test the cornering ability of the wheels.

DOS

I had same thought and alluded to that in my note to Hed.

well biked

Just curious, did you ever get clarification from HED on this?

DOS

No, really annoyed that they haven't responded.Why have a “conatct us” form if you sre not going to respond? I may try calling this week

DOS

I talked to Hed customer service. Max rider weight is 240. They claim that the max pressure recmmendation for my previous HED Belgium + was the same 70-80 psi, which is not what I recall (always thought 100). I rode those closer to 90 routinely without issue. They said riding at higher pressure at higher psi did not risk blowing tire off rim but compresses rim more, reducing spoke tension thereby increasing frequency/likelihood of spoke failure. Interestingly, when I built the wheel, I retensioned spokes after inflating tire to about 110kgpf with tire at 90psi, so I think I am good there. I have to say, after a second 50 mile ride on tires inflated to 75psi, I am quite enjoying the plush ride. Sinai guesss I will stay there until I encounter some issue I can attribute to under inflated tires.

FBinNY 

It's interesting how a pervasive myth can ripple out and create weird conclusions in other areas.

First of all, the myth that low tension somehow causes spoke breakage is inconsistent with the principles of structural engineering. Of course, while it is true that excessively low tension is problematic, deflections under load are the same regardless of tension, so a moderately tensioned wheel will have the same mechanical properties as a higher tensioned wheel. It's also known that rim compression occurs when tires are inflated, but that's been factored into spoke tension guidelines for eons. FWIW - it would be interesting to know how the linear modulus of compression of these rims compares to that of light aluminum rims.

Instead of publishing an unreasonably low tire pressure spec, Hed might have provided build guidelines like reminding people to use either higher tension or thinner spokes to improve elongation, and improve the margin for rim compression. Or they might have published a maximum rider weight or other info, limiting the applications for which their rims were suited.

Blaming possible spoke tension loss due rim compression for a low max pressure limit puts the cart before the horse and makes no sense from a product design standpoint.

tFUnK

Maybe I'm just old school but that seems really low. At my weight the optimal pressure is 90psi with 25mm tires. But I guess if it works it works. I would send them a picture of every pinch flat I ever endure at those recommended pressures 😁