Originally Posted by
63rickert
You don't want to be riding on sidewalls. At all. Don't do it.
You are doing beta testing. Wide rims changes everything and absolutely no one knows all the answers, or even all the questions. Until ISO speaks on the issue (which could be a while) the only authoritative guide is ETRTO. They say no more than 17mm internal width on the rim for a 25mm tire. 20mm rims don't work for them until the tire is 32mm. ETRTO is very conservative. If you and the rim and tire mfrs follows their guidance there will never ever be a problem. Riding outside their guidance you get what you get and you can tell us how it worked.
If cornering hard is what you do it makes little sense to use lower pressure in front. Downhill cornering all the weight goes to front. Cornering of any type involves deceleration and will transfer weight to front. Front/rear pressure differential is for getting maximum wear out of your tires.
I admit I sort of knew these were murky waters when I bought these wheels - and that’s what intrigued me the most. I won’t starve if I end up having to sell these wheels, thankfully, so if these wheels turn out to be unviable, I’m ok with that.
I assume you saw that updated chart from mavic about rim widths vs tire widths. 28c is approved for upto 25mm rims. The ratio of tire to rim is close enough for me that I’m not worried about inflation - especially since I don’t weigh very much.
What is confusing, though, is that it’s unclear what a 25 or 28c tire is supposed to measure to. GP4k, GP5k, Sworks Turbo and P zero tires all measure differently on the same rim despite having the same or similar nominal widths. For example, I would not run a 25c GP5000 on these rims because they are quite narrow. A 28c GP5000 is closer to a 25c P zero. Regardless, I am not worried about inflation issues for the time being.
I would certainly be riding on sidewall if I put a 25c P Zero on a 21mm rim - an approved ETRTO combination. I don’t believe that a 2mm increase in rim width is to blame for 3-5mm of sidewall use on either side of the rim. However, the jump from 17mm to 23mm is enough that I can feel the sidewall a lot earlier (or at least I think I can), which concerns me. This entire issue has not been even remotely addressed by the bike industry. I’ve never even seen tread width addressed as a measurement. The ETRTO probably has not standardized tread width - an obviously important element of tire construction. In the meantime, it may be wise to avoid tires with overly narrow treads like the P Zero. This is an utter failure on the part of the bike industry, in my opinion, because mountain bikes went through the exact same issues and yet the road tire industry refused to learn from them.
I run my front tire low for extra traction on rough descents. Not really for equal wear.
I’ll shut up for the meantime about this whole sidewall issue. I think I’ve blabbed enough about it and people get the point. Let this thread resume LB related queries.