Roadgraveller

Hi,

I have 700c - i25 tubeless rims (inner width 25mm) which I know is quite wide for a road bike, it's on my Gravel bike which I use purely for road riding now. I currently have 35mm tubeless tires, however I want to move down to 32mm which is beyond what most manufactures state (I'm sure they like to be cautious). Has anybody ever had a tubeless tire blow off their rims? Would putting an inner tube in add any extra safety? or doesn't it matter?

Thanks for your thoughts and views.

trailangel

Well, 25mm inner width would be just right for MTB 40-60mm tires. 32mm on those would change the profile of the tire too much IMO. Besides, I like to have narrower rims and a bigger tire so if I go flat there is some rubber between the rim and asphalt. I think you are right at the edge of "WTF are you doing?"

Roadgraveller

I love the "WTF are you doing" quote. Brilliant.

This is what WTB say: https://www.wtb.com/pages/tire-rim-fit-chart lowest 35mm. and it's WTB 32 Expanse I'd like to use, but maybe it's too far off the scale to be safe like you say.

trailangel

I think you can do what you want.... just be aware.

tyrion

Not sure it's clear that higher rim/tire width ratios increase likelihood of blow off. Note the road race optimizers recommend the Rule of 105 - a rim wider than the tire for aerodynamics:

https://blog.silca.cc/part-5-tire-pr...d-aerodynamics

dsbrantjr

What do you hope to accomplish going to such narrow tires?

Bill Kapaun

My rule of the thumb for going narrow is have at least 2mm > than EXTERNAL rim width. Just to keep the rim off the curb if you get too close. Hopefully you have enough rubber in the way to not scratch a rim.

smashndash

Looks like nobody here (EDIT: besides @tyrion) got the memo yet. i25 has been in for road bikes for a while. Zipp, 3T, LB and Enve (and possibly others) make wheels with that dimension, suited to 28mm tires. You are totally fine using 32mm tires with a 25i rim. 3T is also releasing a 29i rim for 35mm tires.

That being said, tubeless blowoffs are a thing, regardless of rim width. The narrower you go, the more likely it is.

For the record, I used 25mm tires on 23i hooked rims for few miles (put it away since race season got cancelled) and did not get any blowoffs. The sidewalls took a beating though.

79pmooney

I've blown a tire off a rim. No, not a tubeless. Just a tired old clincher. Going between 20 and 25 mph. Not something I ever want to repeat, One of my top 5 crashes in 50 years of riding. Doing that going far faster downhill scares the **** out of me. (All my wheels will be rebuilt as tubular wheels as rims die. yes for "the ride" but mostly for peace of mind going fast.)

Ben

Roadgraveller

Brilliant thanks for the detailed reply. Wider rims are still relatively new, most folk are in narrow rims and moving to wider tyres so my questions isn't that common yet. Like you say many companies are moving to wider rims.

Roadgraveller

Hi, I was hoping for a little better rolling resistance with a more road focused tire (no nobbles) and weight saving on the tire.

I read that around 28mm on a road bike is a sweet spot so 32mm should be better than 35mm.

Roadgraveller

Man that sounds scary, I think it's probably most peoples #1 fear - fast downhill crash. It's the main reason behind the post. Sounds like you were very lucky to make it back on a bike.

FastJake

"Wide tires are slower." The number one myth in cycling! https://www.renehersecycles.com/12-m...es-are-slower/

I did a 60 mile ride on my most hardcore road racing bike yesterday, with narrow tires (32mm) inflated to a relatively high pressure (50/60psi). It felt miserable and punishing compared to the 52mm Compass Rat Trap Pass tires I've been typically using for the past few years. And I wasn't any faster. I have no idea how I used to ride 23s cranked up past 100psi. On gravel, sometimes! The roads around here are rough, chip-sealed, or both. Anything narrower than ~38mm is worse than anything wider.

Roadgraveller

Thanks for that, a very interesting article. Funny how they knew even back in the 1920 that wider was better.

Dave Mayer

I think we have to cut through a lot of nonsense regarding tire rolling resistance. Look at this:

https://www.bicyclerollingresistance...000-comparison

So the 32mm tire has a 1 W advantage in rolling resistance over a 23, when both are pumped to 100 psi. But when the 32mm tire pressure is reduced to 60psi, which is far more reasonable for a tire of its size, it has a relative handicap of 2 W. Fat tire weight penalty: 90 grams per tire, which in the world of elite-level cycling, is an unacceptable and insurmountable handicap. But all elite-level cycling is done on tubulars, past, present and forever, due to a number of advantages to tubular tires and tubular rims. Safety is a key consideration, as 79pmooney summarizes well. Warp-speed descents on clinchers spook me as well; I feel much more confident and safe on tubulars, due to their cornering characteristics, and ones ability to ride-out a flat.

Regardless: we are talking about single digit numbers of watts here. Put this in perspective, while riding, we're putting out between 100-400 watts. Aero and rotating weight are far more important.

I'm heading out on a ride... I do 50 mile rides on packed gravel on 22mm tubular tires glued to 300 gram rims. This setup is far far faster than the fat 28mm clinchers I have on another bike. Sure, the ride is a bit rougher, but if you go fast enough, every surface smooths out.

TobFromme

On my new bike, I opted to have the LBS convert to tubeless. Rode for a few blocks around town with no issues.

Get home and about to go on a ride and the front tire blows off the rim just sitting in the driveway. Back to the LBS, the owner finds a bit of rim tape where the tire seats. Removes that, pumps it up to 100 psi and it blows off again. We're thinking the tire is a bit out of spec in diameter. It literally fell onto the rim while being installed.

LBS put tubes in for now and two new tires on order. I'm not hoping for a repeat of that.

FastJake

Yes, unfortunately we are facing almost 100 years of non-sense. The link you posted is useless except for the weight measurements because the testing is done on steel drums. Does your bike ride on steel drums without you on board? Hysteresis losses are indeed higher for wider tires but they are offset by the reduced suspension losses. Narrow tires inflated to higher pressures feel faster due to the increased vibrations.

Read the link I posted. Here it is again: https://www.renehersecycles.com/12-m...es-are-slower/

The pros have moved on to wider tires than you're using, even on smooth pavement.

Roadgraveller

After smashndash post, I checked out 3T, Enve and Zipps websites and all indeed make 25mm inner width wheels (700c i25 wheels/ETRTO 622c 25) which are optimised for 28c and 30c tyres: https://www.3t.bike/en/products/whee...2-ltd-637.html 3T have hooked rims (as do on my Hollowgram Cannondale rims), 3T don't appear to have any restrictions on the manufacturer of the tyre. 3T say they are hooked for safety I assume to keep the tyre from coming off. Enve SES 4.5 AR 'tubeless only tyres' https://www.enve.com/en/products/ses-4-5-ar/ are hookless but do have quite a list of tyres which aren't compatible, I'm sure this will change over time. Also Zipp's Firecrest 303 is 25mm internal: https://www.sram.com/en/zipp/models/wh-303-ftld-a1

All specify PSI pressure around 50, it's crazy to me think only a while ago people were going 120+ PSI.

Cheers for all the advice, I feel far more confident using my new 32mm tubeless tyres.