29" rims & tires for road riding

I create a new topic to not make more off-topic on the subject of power meters.

First of all some background on the combination of a rim and a 29" tire for road riding.
I had made a similar topic on the French forum a few years ago. The origin was related to numerous schwalbe tire blowouts with the KH 47mm rim.
Most unicycle rims are particularly wide compared to bike rims. Rather designed for extreme off-road use with a wide tire at low pressure.
For road use, these rims can show their limits since the need is to have a rim that holds a high pressure and with a narrower slick tire.

I quote Harrison’s post, there are a lot of interesting references.

For the rims, I rather looked at 25 mm gravel rims with hooks for the good holding at high pressures.

The rim I identified was the lowest and the lightest (and the cheapest). After that, between 35 and 38 mm high, it’s similar. The second one is in the “PRO” series, maybe it’s better. As far as the look is concerned, I prefer the PRO rim. :slightly_smiling_face:

I couldn’t find the new rim you were talking about in the store and I finally found the ad for the new gravel and MTB rims. I have the impression that they are very similar, both have an internal width of 24mm, hybrid hooks, asymmetrical profile, announced weight of 250g.

Yes they look perfect (I don’t see what makes them different, maybe it’s the same rim, with 2 names to sell it for gravel and MTB…), but it’s so light… they are 150g lighter than the gravel rims I mentioned. It almost scares me to ride on it.

For the tires, René Herse tires look very good, but they seem to be almost impossible to find in Europe.

I think I’ll go for a g one speed 28x2, I’ve already seen that it’s not the most rolling, but it’s better than a studded tire and it looks pretty durable.

To be continued (I don’t have time to write more).

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Well, several reseach shows that the best combo is the narrowest tire at the max pressure riding in a perfectly flat surface. When you swap “flat surface” with “tarmac with small imperfection” suddenly the best combo is a 35ID with a mid pressure able to save more watts when the tire gets a very small vibration than the watts lost in the rest of the ride (compared to a high pressure tire+rim). Than consider how much energy a unicycle rider will spend to solve the small vibration compared to a bicycle rider and imagine how much more watts a unicyclist should use with a high PSI combo.

IMHO the best combo is ralated to the width (2.2-2.4) and a medium PSI. That Rene Herse Hatcher 48 in the thoughtest version seems a great tire. Hope we’ll receive also data from a slightly lower pressure than the maximun rated, just to understand if it is true also for a unicyclist that a small amount of cushioning improves the rolling resistance

35ID ? You mean a rim with an internal width of 35 mm?

I have 2 carbon rims on my 2 29" : 33mm and 35mm. I find it a versatile size, but more off-road oriented than road.

It’s not in the title, but I’m talking about carbon rims.
For an hooked aluminum rim, 35mm maybe is a good option. But for a carbon rim, it’s too wide.

By the way, recently I mounted a schwalbe g one speed 29x2.35 tire on a hookless 33mm carbon rim. I thought like you that it could be a good combination, but it gave me several problems.

I first rode 2 weeks with an inner tube at 3 bars, without any particular problem. Except that I was not very comfortable in the turns. The tire seemed a bit wide, maybe it’s just the profile, but I like round profile tires.
And then I thought it was time to switch to tubeless (I especially wanted to ride on paths with this wheel). Everything was fine, the beads snapped, and in the process the tire buckled. There was about 3 bars. Now, he tire is good for the trash.

My rim is a hookless MTB carbon rim. And it is well mentioned that you should not exceed 2.75 bars / 40 psi. For me, this is not enough pressure for such a tire. What is sure is that you should not buy this rim for exclusive use on the road.

I’m going to switch to a hooked gravel 25mm rim, and I’m considering a tire between 2 and 2.2".

I’m not saying this is best for everyone. But I think for someone who wants an optimized set up for road riding, that’s the direction to go. Having only one wheel means that you have to use much higher pressures than on a bike (for similar feeling) and hookless MTB rims don’t offer enough guarantee of pressure resistance.

The AR25 and XC924 are interesting… brings up a very interesting point about rim and tire compatibility.

They have exactly the same dimensions and weight, but

  1. XC rim is for 2.1-2.4" tire, 40 psi max
  2. Gravel rim is for 28C-50C tire, 70 psi max

A narrow tire at high pressure exerts different forces compared to wide tire at a lower pressure. I spent some time drawing these diagrams and writing some equations… and I convinced myself that they are different.

But then, for us, we want a wide tire at higher pressures, which is extreme on both ends. So which design is better??

I emailed them, and hopefully they have a recommendation too.

One interesting note about 40psi max on their mtb rims is that when I bought mine, it said 70psi max… and now it says 40psi. I even have an email from them stating this!

With my 22mm internal width mtb rim, I have ridden my 2.35” Big One tire tubeless at 45 psi (31 bar) quite a bit (multiple hill climb races and training) Luckily I have not had any blowouts… funny it is narrower than my gravel rim.

All of their gravel rims only recommend up to 50mm wide. So even within their pressure recommendation, if we use a wider tire, that means more tire case tension and a risk of blowout…
I have tried these on my hookless 25mm internal gravel rim (WR38):
29x2.35 Big one at 45 psi
29x2.2 Rene Herse Antelope Hill at 48psi
700cx32 Continental GP5000 at 50psi
All with tubes. I could try higher but will need to add one more layer of rim tape.

I really don’t know what matters the most: rim width, hooks, strength/stiffness, bead strength?

Too narrow, the rim might split since the wide tire pulls outwards a lot. Even if it doesn’t break, it will be bent outwards. Thus, at some point it could be too narrow, and weight will have to go up to reinforce the rim.

Too wide, there is too much pressure compressing the rim causing it to shrink. So again, it would require more weight and reinforcement.

Hooks help, but for the same strength would be heavier.

Stronger and stiffer in general always helps, but again also causes increase in weight.

Stronger tighter bead helps, but of course adds weight. Each tire size and company might use something different.

So, my conclusion is all of these variable will affect tire retention. However, each one that helps come with a weight penalty.

When we aim for the lightest parts, we are hoping they still have the right combination of reinforcement and margin of error built in so that it works with our higher pressure and width.

The bike world optimizes for different tires/pressures and their usual equipment, which is different from us.

For example, Schwalne big one 29x2.35 has a max pressure rating of 50psi. That likely means on a somewhat narrow rim with hooks, it can handle a max pressure like 60psi (some margin above 50psi)

So with a wider rims, maybe 50 psi is now the limit.
Add on hookless, maybe 45 psi is the limit. Then add on the fact we are choosing some of the lightest rims which might be weaker, so we are down to 40psi…

If we want 50psi at 2.35”, we can add weight back with a hook, with thicker layers of carbon, with a tire that is heavier with a higher rating and stronger bead, a narrower and reinforced rim, etc.

But, in reality we have a limited number of choices, so I think we can just guess and check and find a pretty good combination. Hooks seem likely to be the least weight increase for how much it might help!

Starting there is probably the best bet for road riding

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I think this means that all their gravel rims can be used on all gravel bikes.
They don’t need to specify that you can mount a 2.3" mountain bike tire on a gravel rim. No one buys a MTB to mount gravel wheels, a slick tire and inflate 3 bars on the front and rear. :crazy_face:

You know more about bikes than I do, but in the bike industry there are standards for wheel clearance. It seems to me that most gravel bikes just don’t allow tires larger than 50mm.

The max pressures listed are partly related to the tire size.

In any case, it’s hard to see with the naked eye what makes these 2 rims different. :face_with_monocle:

LightBicycle responded to me with this:

Good news that it is okay to run 2.2’ tires with 50psi for the reinforced AR25 rim at 270+/-15g, which will cost extra USD12/pcs. Is that okay with you?

Yes, it is true gravel bike frames don’t allow larger tires than 50mm. However, that is also why the rim manufacturers would not need to design the rims to handle such large tires. (theoretically…)

This diagram shows the different forces for different tire sizes.

The blue arrows are air pressure. Pushes on the tire and also the rim.

The small red arrows is tire case tension. This is because of the blue arrows pushing on the tire.

The big red arrow is the force on the tire that keeps it in shape.

The big black arrow is the reaction force the rim has to provide to help keep the tire in shape.

With a narrower gravel tire at high pressure, the rim see more pressure. (bigger blue arrows). But, the big red and black arrows are smaller! The smaller tire has a smaller partial circle shape, so less force to keep it in it’s shape.

In summary, maller tire+higher volume VS larger tire+lower volume have different forces. If we use both larger tire AND higher volume, there will be more stress on the rim.

Here’s a picture of someone with a broken aluminum rim… it might be due to high pressure + large tire.

https://www.mtbr.com/threads/cracked-rim-opininon-needed.718410/

The fact they can reinforce the rims is really nice though!

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This bicycle tire stuff seems a bit like the wild west, or maybe fitting rims with tires is like going on a blind date? And made even worse by probably out of date standards and frequent design changes by manufacturers, and with drastic mismatch consequences if both the tire AND rim are at the limits of lightness.

I am really happy with my aluminum 590g hooked rim with 30mm ID matched to a 2.4 inch wire beaded MTB tire (with tube), but it is certainly NOT optimum for the road.

I suppose something like a carbon 26mm ID rim and a light and smooth tread 2.2 inch tubeless could be ideal (if both rim and tire are matched and can handle the needed pressure).

But I wonder about hooked vs hookless. Rim manufacturers say that manufacturing the hookless can be more precise (an exact BSD) than hooked (and if you want to match tire and rim you need precision). They also say that hooked rims are more likely to “burp”, and that they are weaker. BUT the “blow off” is still a worry for hookless, and the tire is the problem - it needs to also be precise in bead diameter and not too “stretchy”. Don’t ask me how you know in advance whether your high class rim is mating with an inappropriate tire partner (although apparently some rim manufacturers make recommendations).

It can be scary looking at rim + tire cross sections, and imagining the pressure and the forces and the tire expansion and creep, but I think it is important to remember that the tire is a “doughnut” (or toroidal) shape, and that the air pressure on the opposite side of the wheel (29 inches way) is to some extent balancing, so the net effect is just a uniform expansion of the tire cross section (rather than an outward force). Anyway, it still points to an accurately made reasonably stiff tire with a good bead strength as being the best partner for a high quality rim.

[and off topic a bit - looking around on the web for rims, it seems like there must be a “carbon revolution” - even if I search for aluminum rims, the main hits are carbon rims. And 32 hole (or even 28H) is certainly more popular than 36H].

Yes, it is a toroid. The other side of the tire is what helps keep the bead in tension, otherwise the tire would fly off with just 0.1 psi.
However, the same forces are still pushing the tire out. The diagram shows meridional stress. I did not add any of the circumferential forces in the diagram, but that actually makes the tension even higher.

I believe that hookless improvess dimensional accuracy and strength. Manufacturing the hook is more complicated and this example below from lightbicycle makes it clear that it is weaker with as hook if it hits the ground. (too low tire pressure hitting a bump)

Not sure about burping…? This article says hookless can burp more. But, it is because the tire is not up against the rim bed (and engaged with the hook). This can also happen with hookless though…

For unicycle road riding, I think we don’t need to worry about the rim hitting the ground. Given we have tire blowout problems, given an option, a hook seems like a good idea. Also, we are at higher pressures and probably don’t need to worry about burping.

This is great since it likely means they tested the tires and know they mate well! I doubt they recommend just based on the manufacturer’s claims of adhering to standards.
We just need the same data but with unicycle road riding pressures/tires/rims.

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I’m not enough familiar with the technical details. But I understand that the main risk would be that a too weak rim would crack with the use of a slightly too wide tire inflated at high pressure.
Beyond this aspect, there is probably no other reason why a 25mm gravel rim is limited to 50mm, while a 25mm MTB rim is limited to 2.4". The profile of these rims looks similar…

I already find it very exciting to be able to use a 400g rim with a light and rolling tire. Even if the 250g rims look interesting, I don’t feel ready to do the test. I feel you are more ready. :wink:

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