bluemonkey136

I recently purchased a Specialized Roll Elite which has the Nimbus Sport 650b 2.3" 60TBI tires on it. PSI says 25-50 but at 40 - 45 I still feel like if I am compressing the tires a bit much while sitting on it. I currently weigh 288 lbs is it okay to run at max tire pressure of 50 PSI at my weight? The tires I don't think are at risk of pinch but I feel like I'm forced to ride a bit less aggressive.

CliffordK

If the tires are rated to 50 PSI, there is no reason not to go all the way up to that pressure. The end point should still have little margin, and you may be able to go even +5 or +10 PSI (do at your own risk), but be aware that the pressure could go up if the tire gets very hot (sun, or heavy braking on long, steep hills).

2.3" tires sound awfully wide to get pinch flats, but I suppose it depends on what you're rolling over.

wphamilton

I'd probably run them at around 35, and you'd need about 40% more than someone at my weight so that sounds about right.

Big tires put a more stress on the rim, so I'm more concerned with how the wheel holds up at that pressure. If it's a solid wheel I'd figure that it's ok, although bigger guys tend to go through wheels at a faster rate in general so maybe prepare for replacing it after some good use.

fietsbob

What is marked on the tire casing for a pressure range?


I would not exceed 50 in that case.. keep them topped up before each ride.

Smaller volume tires function at higher pressure.



Just in Case, get an extra tire.. rear blow outs are usually not a control loss like fronts can be..
... So always put the newest tire on the front.

I bring a 3rd tire on my bike tours when carrying more weight, than that.




...

Carbonfiberboy 

50 lbs. would be the usual rim manufacturer's rating for that tire size, so that's nice. I'd say 5 lbs. over would be safe. I think the only thing you'd see from inflating past the usual limit is that your brake tracks won't be able to stand as much wear as they would at a lower pressure, but you probably wouldn't notice the difference. From my tandem experience, my guess is that 50 lbs. would actually be just right for your weight.

rumrunn6

can you elaborate? I don't understand

CliffordK

I'm not sure that is true, as PSI (Pounds per square inch) should be the same irrespective of the tire size. Perhaps there is pulling on the sidewall beyond the pressure from the air on the bead.

The 650b rims may not be designed for high pressure tires, but the 700c rims should be able to take at least 120 PSI tires, and the 50 PSI tires would apply much less stress on the sidewalls.

Carbonfiberboy 

Yes, it's PSI but as tire size goes up, so does the (area* PSI) number = force.

Carbonfiberboy 

Barring spokes pulling through the rim, a rim wears out when the brake tracks get so thin that the tire pooches the rim bead out and the tire will eventually pop off disastrously, usually when braking. This happens much much sooner if you ride in the rain a lot, particularly in hilly terrain. You'll usually have a warning: a pulsing of your brake lever during gentle braking. Upon inspection, you'll see that the brake track is very concave and that the bead above the brake track is leaning out at an alarming angle, usually just in one spot. You can usually get home as long as you go slow and don't use that brake again. Time to replace the rim.

wphamilton

There are more square inches on the bigger tire so more total forces on the rim at a given pressure.

OP has a 650b tire I believe.

bluemonkey136

Thanks for all the responses guys! I think I may try pumping them up to like 48psi or so to leave a little room for pressure increasing on a longer ride. I was just kinda concerned at max psi with my weight it might have been too much pressure for the tube or another part would maybe give. I feel confident about pumping them up more now. I will definitely go ahead and order and extra tube and tire for when the day comes though. Thanks again for all the advice.

bluemonkey136

48lbs worked out great and made for a much smoother ride thanks again for everyone's suggestions!