Doomrider74

Hi folks.

Following on my fom my new wheels threads, my bike mechanic buddy can get me a great deal on some Bontragers (RSL 51): However, they are 23mm internal, 30mm external width. Specialized say my SL6 can take up to 30mm tires, so it should be fine, but does anyone have any real world experience?

I understand Bontrager tested them with 25mm R3 tires and I believe they blow up to 29.5mm so, again, they should be OK, but I want to be sure.

Thanks for your help.

WhyFi

Why can't you measure your frame?

Typically, when a manufacturer says that their frame fits XX tires, it means that there's XX + 4mm on each side (generally considered the minimum debris/wheel deflection clearance), so if Specialized says that it'll fit 30mm, there should be at least 38mm between the stays/forks.

You could also look at your current wheels/tires and use hex keys as feeler gauges at the pinch points - if, for instance, you know that your rims are 24mm wide, you should be able to slide in a 6mm hex on either side, with a mm or so of wiggle room, you're at 38mm (~7mm+24mm+~7mm).

Like most manufacturers, Specialized/Roval are going wide with their wheels - I wouldn't be surprised if the 30mm figure is a little conservative and slightly larger could fit, while providing appropriate clearance.

Chandne

The area where the tire is widest is well about the rim. I bet you would be fine with tires that measure 32. The rims are of no concern.

nebula

I want to know this mechanic buddy

I have a set of Pro 51 on a 2019 SL6. Set up with 25mm GP5000 (which measure ~28mm on these wheels), they fit fine. The 25s look a bit narrow, but wider tires could be a close fit with the frame (and probably would be less aero for these wheels).

Doomrider74

Apparently, Bontrager do their aero testing of these rims with Bontrager R3 25mm tires, which work out at 29.5mm when mounted on the rims.

summithockeyc20

Just make sure you have clearance and there is no frame rub

nebula

Yeah, given the 31mm external width, 29.5mm tires is just about right for the rule of 105.

I just checked and with the GP5000s (25mm, measuring ~28), there is 6+ mm of clearance everywhere, except the chainstays where clearance is right about 5mm. So you are probably fine to run the 25mm R3.

Doomrider74

Thanks for that. I'll check when I get home, but always good to get other opinions.

Doomrider74

I had a look at my frame when I got home and I can fit a 8mm Allen key either side of the rim, so there's about 16mm spare width between the chain stays. I believe the DT Swiss R470db rims I have at the moment are 23mm external width, making a total spacing of 39mm between chainstays at the rim.

At the apex of the tire, there's a total width of approx. 36mm, which obviously increases as you go further towards the rear hub; that's with a more rounded profile than the Bontragers will produce.

Mathematically, they will fit.

Sy Reene

Is the 105 rule calculated where the tire meets the rim, or measured against the widest part of the rim? They're often not the same. One random example

nebula

Widest point; can't post the link but if you google "rule of 105" and click on the Silca blog link, Josh Poertner has posted some details.