Internal Rim Width
 

I'm considering a new Look 765 Optimum Endurance bike; an Ultegra bike; $4,900 closeout; 34% off. The model I'm looking at has carbon rims, Look R 38D, weighing around 1,600 grams with an internal rim width of 19.3 mm. I'm OK with the weight but am concerned about the internal rim width and bike maximum tire size. 19.3 mm and 34 mm tire.

Is this too future limiting? Many endurance bikes are now 38mm capable and 21 to 23 mm internal rim.

Your opinions?

Personally, I'd be fine with a 34mm limit. I can't imagine going wider than 30mm on a road bike

It's almost a requirement on hookless rims. My new bike's rear wheel has a 25mm internal width, and if running a Continental GP5000, the narrowest you're allowed to run is 30mm.

That's what I was thinking too. Most reviews I've seen indicate that things get slower (on average) over 30mm.

The good news is that the wheel is hooked.

You could increase the 30mm tire width with a slightly wider rim, like 21mm internal, and improve the aero profile of the tire/rim interface. You maybe could go as wide 23mm, but I have 24mm IW rims on which 30mm Pirelli P Zero Race RS measure out at 34mm, so that’s getting perilously close to the Look’s max capacity.

If the frame has a 34mm max, I don't see the issue with that rim's internal width.
The rim will obviously fit a road tire that is 28/30/32/34mm wide without issue.

I also don't know what concern there is about 'future limiting'. If you don't want to ride a tire that is wider than 34mm, then you are fine. Tires narrower than that will continue to be made.

Yeah 34mm is plenty on a road bike. I will never go over 32 I’m sure.

2010: 23s are perfect
2015: 25s are the right balance of weight and aero
2020: 28s blend rolling resistance and aero
2023: 30s are the ideal blend of aero, rolling resistance, and comfort
2025: 32s are the perfect...
There's a pattern here.

It's still just a general purpose wheelset IMO. Not a deep enough section to be useful for aero. And any tire over 25mm will just make it's little bit of aero, less aero.

Consider if you are wanting a aero wheelset. You might go up a tier or two on that bike if Look prices the same frameset with differing components.

Bet they aren’t available with that discount though

Naaaah, I'm pretty sure NOW we nailed it! :thumb:

What's your frame's max tire width?

19.4mm is fine even on modern road bikes. I don't personally see why one would go wider than 30-32c. Might as well get a gravel bike at that point.

I have 21mm internal width on both front and rear and a 30mm tire inflated measures 30mm. Same setup but with 19mm internal width would be just fine.

Wound up buying a Giant Defy and the Visions SC 45 SL carbon wheels to go with it. 23mm internal width.

Is there a reason why there’s an upper limit to the tire width a rim can accommodate? I remember as a kid putting 2.1” mtb tires on narrow rims, and I run 35mm GravelKings on some old 17.8mm road rims for light gravel riding.

My Bora C23 rims are 23mm wide, and 30mm GP5ks fill out to 33mm on them. Plenty cushy, even at my weight. Though if tire manufacturers are able to make lighter, lower rolling resistant casings, i wouldn’t be surprised to see Tadej sporting 32mm or higher in a few years (he’s already on 30s). Of course, by then it’ll be time for n+1, no?

Happy new year!

I think it comes down to optimizing aerodynamics (if that even matters to you). The rule of 105 that rim external width should be 105% of the tire width. But certainly there is no issue to putting 35 to 40 mm tires on an internal 23mm rim. But it is difficult to imagine a setup with a 40mm tire that still conforms to the rule of 105. That would be one hellashiss wheel !! Interesting that you are getting 33mm out 30mm tires on your rims. My rims are also 23 internal and my 30mm Conti's measure 31mm. My rims are hooked (Vision SC 45 SL). Are yours perhaps hookless? Just trying to figure out why the same tire on the same internal rim width would measure so differently. I HAVE chosen to run tubes (TPU) with a standard Conti clincher tire. Are you running tubeless?

If it really is just an aero issue, then why does it matter that the rim can only accommodate 34mm? All that would mean is that a 38mm tire is suboptimal, not dangerous.

The bike with the Boras runs GP5k S TRs tubeless, yes. And no, the Boras aren't hookless. I'll dig around for my calipers tomorrow, but at 73psi, I'm pretty certain they're 32+mm, bordering on 33mm.

Agreed, there is nothing dangerous about it. But beyond aero considerations, and I'm too slow to worry about that, the wider rims do open up the tires more for better contact and a better ride; as you are experiencing.

Did you see Dangerholms 50mm wide, 70mm deep rims?! Hellashiss fer rizzle!

https://cimg7.ibsrv.net/gimg/bikefor...6cd1d556f.jpeg

Much will depend on the make of the tires you use. My main steed has alloy wheels with a 17 mm inner width. No tubeless tires held air well enough until I got a set of Michelin Power Cups. I'm thinking that 34 mm should work on 19 mm, but you're pushing it. Can't you go 30 or 32?

Wow!!

Yes.

1600g for a sub 40mm depth carbon wheel is terrible. A good aluminum wheel is not that far off in terns if weight. Also 19mm internal width is firmly now in the out of date category. If the baseline spec tire on new bikes is now 28mm and that bike can fit up to a 34mm, yeah those stock wheels are trainers at best.

IMO find something 1400g or less and something at least with a 22mm+ internal and 30mm+ external. Heck even a last gen 21mm/28mm would be better than those stock wheels

Yes, in the end that was the conclusion I reached as well. Wound up buying a Giant Defy with Di2 that had the nasty Giant alloy brick wheels and tires. Then bought some Vision carbon wheels with 23mm internal width and mounted some 30mm Conti's. Reduced the bike's weight by 1 Kg right there; and rotating weight at that. As an added bonus, the Vision wheels are hooked vs the hookless Giant wheelsets.

Thanks for your point of view.

Currently 30-32 is the prime space for road applications due to aerodynamics. There is a toll that starts to be paid crossing that 32 threshold...says josh who has spent decades in the wind tunnel. That's not going to change in the near future. This is akin to back in the day when we adopted the "deeper rims are more aero" so deeper at all costs mentality. Fashion is pushing to ever wider tires but that fashion will also change at some point. I mean mtb on the road is something I don't want any part of. It's bad enough we are selling and riding 90's mtb's and just calling them "gravel" bikes.

I totally agree with you.