Ivan
Eats Squid
Isn't it also about moving the support point for the sidewall
That's what I said.
Isn't it also about moving the support point for the sidewall
The circumference must have changed though, by 11mmI had to do a search for my original post in the American Classic Wide Lightening thread:
My OEM Spesh rims (DT 450SL) are 18.3 internal and the WL's 29.3mm so I was interested to see the effect on my Schwalbe RoRo front (2.25) and RaRa rear (2.25), both snakeskin versions and tubed (as I would initially also run on the AC's for direct comparison). Pressures would be the same also (23psi front, 27psi rear; 95kg smooth xc only rider).
Tyre size:
On the old rims, the 2.25 RoRo measured 54mm across the tread and 53mm at the widest point of the carcas. On the AC's this grew to 56mm across the tread and 58mm across the carcass.
On the old rims, the 2.25 RaRa measured 55mm across the tread and 55mm at the widest point of the carcas. On the AC's this grew to 56mm across the tread and 59mm across the carcass.
The final carcass dimensions for the RoRo on the AC's match the 2.35 version of the tyre (on 18.3mm internal rims), so AC's claim that the wide fitment takes a tyre up one size seems to hold, albeit in volume only as the 2.35 tread width is 60mm (and a bit more aggressive).
Tyre diameter was unchanged (static, no load) between OEM wheel and WideLightning.
I actually recorded the static (unloaded) tyre crown shape as well out of curiosity and there was negligible difference as a function of rim ID for both tyres. In any case the fundamental form is more construction driven and so any change in the static (unloaded) shape is irrelevant to what occurs at the grip (loaded) interface.
Going tubeless made no difference to dimensions, but made noticeable improvement to performance and ride.
Tyre volume is one thing, tyre footprint and carcass stability is another. Pick one (given ID is a constant).
No, as my measurements indicate, the base of support just widened. Tyres are really pretty flexible in the width department, not so in the overall tyre circumfrential department..The circumference must have changed though, by 11mm
And if the circumference has changed then the average diameter has too, they are inextricably linked. Its just it might not be very easy to measure
On the tyres I measured the 19mm ID gave a calculated circumference of 16.4cm. This gives a calculated diameter of 5.22cm. The 30mm ID rim has a calculated circumfrence of 17.5cm giving a calculated diameter of 5.57cm. An calculated average difference of 3.5mm. Where that would appear on the tyre I don't know, what I am sure of is that something there abouts is there somewhere.
Ivan gets it.
- No-one should ever (I'm mainly looking at you rim manufacturers!) discuss rim width in external measurements. The internal width is the only one that matters.
- Wider rims were never about making tyres wider (unless your talking plus sized wheels and tyres). It was always about:
- Increasing tyre volume which allows for increased contact patch due to lower acceptable pressures (at the same rider weight),and;
- Moving the sidewall outwards to support the cornering knobs, especially now that the tyre has less pressure.
Yep, tyre fundamental dimensions are fixed so circumference change is function of rim ID (variable), just don't over think the rest of it.So if you are using the same tyre on a wider rim then I can't see any way that the internal circumference can't have increased and as the pressure in the tyre (unweighted of course) will make the overall internal shape more or less round then with increased circumference comes increased diameter
So the diameter diameter had changed on your tyres?Yep, just don't over think the rest of it.
Tyre OD has not changed. Tyre construction dictates (or constrains) that (tyre size constant).So the diameter diameter had changed on your tyres?
Not quite sure what you mean
OK, I disagree with this but its irrelevant to the discussion anyway so no worries. Just wanted to make sure I wasnt missing anythingOD has not changed. Tyre construction dictates (or constrains) that (tyre size constant).
Effective circumference has changed because rim ID (ie variable) has changed as you are adding additional arc to the circumference through additional rim ID.
You are entitled to you opinion, but where is the evidence to support it?OK, I disagree with this but its irrelevant to the discussion anyway so no worries. Just wanted to make sure I wasnt missing anything
This!!!I think redbruce is taking Ians reference of 'circumference increase' to be that of the overall rolling circumference of the tyre. Whereas he is actually referring to the cross-sectional circumference cut through the rim/tyre combination.
It would be the rims I'd imagine. What brands/models were they both?I am running 28mm ID and constantly seem to flat spot my rims..... on my second rim now!
Running Maxxis High Roller 2 EXO TR, tyre pressure at 32psi, set up tubeless, shock sag set at 30% and doesn't bottom out on big hits. Had the same setup on narrower rims and never experienced this.
Yup, the rim is wider, it will hit more rocks and be more likely to slice the tyre than a narrower rim..I am running 28mm ID and constantly seem to flat spot my rims..... on my second rim now!
Running Maxxis High Roller 2 EXO TR, tyre pressure at 32psi, set up tubeless, shock sag set at 30% and doesn't bottom out on big hits. Had the same setup on narrower rims and never experienced this.
I'd agree too. From what I've now read on this I believ that;im no expert but 32psi seems hi for a tubeless setup........
+1 on what N.S.M said......
also,are you tough on gear/ride very rocky trails.