ScrawnyKayaker

My spousal critter has a new Orbea ebike (about 35 pounds? maybe 40), isn't carrying any gear and weighs 150 pounds. After the first commute, she complains that it rides roughly over bumps/cracks, tree route ridges in the asphalt, RR track and stray pebbles on the street. I didn't measure the pressure, but the shop probably inflated the 50 mm (x 700c) tires to 70 or 80 PSI, at a guess from the quite firm feel of them.

Seems like it is defeating the purpose of the wide tires to run them that hard. Speed is not an issue, since she only wants to go 12 to 15 MPH. She could go on multiple rides without draining the battery, so no need for trying to eke out the last bit of rolling resistance. Obviously, I don't want to get down to having the tires wobbling (did that commuting on my fat knobbies recently) or risking pinch flats. For an all-up weight of 190 pounds, what PSI would you start with for experimenting with a better (less jarring) ride on the road and good handling?

smashndash

That phrase concerns me. 🤨

https://axs-stage.sram.com/tirepressureguide

I assume you have a tire pressure gauge or a pump that includes one. You are right that 70psi is WAY too much in a 50mm tire. SRAM seems to suggest around 35psi. I’d say that’s pretty accurate. You could go lower, but under 25-30psi, you’d probably start risking pinch flats from minor impacts.

elcruxio

I think my 47mm rear tire has 58-60 psi and front tire of course less. But I weigh more than your spouse and bike combined.

HTupolev

Even if you were trying to optimize rolling resistance, over-pumping tires tends to be a bad idea: if you're getting rattled, that rattling is being stolen from your forward momentum. Smooth is fast.

Anyway, I have a similar bike+rider weight on my gravel bike with 52mm 26er road tires, so a somewhat comparable situation.
If I'm riding smooth roads, I pump to about 40r/35f. If she's complaining about compliance, go lower than that. I tend to use no more than 30r/25f on gravel rides, and when the bike is pumped like that, it's still reasonably composed on pavement.
If the tires are a fairly tough stiff urban/e-bike model, they can probably go lower than my tires before behaving weirdly (and may need to be pumped lower to achieve good compliance).

ted_major

You should be able to go significantly less. I have an all-up weight of probably 210, and with WTB Byway 650Bx47 tires, I run 25psi in the front and 30psi in the back.

c_m_shooter

30 psi or so should be fine.

63rickert

First check the width of tire. Last 700x50 tires owned measured 44. Current tires on the city bike are 42mm. Older bike, sit almost directly over rear axle. 40 psi rear and front doesn’t matter until below 20. My weight is 195, bike is 30 and that bike is always carrying something.

VegasTriker

Read the information printed on the side of the tire. Every tire I own has a pressure range embossed on the tire. You will be a little faster at the upper end of the range and perhaps a bit more comfortable at the lower end. As long as you keep the pressure within the limits you should not get pinch flats. It's much harder to pedal a bike that is seriously underinflated and you may eventually destroy the sidewalls running it too low.

ScrawnyKayaker

Adapted from "Congress-critter," which I think I first heard from Molly Ivins or Jim Hightower, so maybe it's a Texas thing?

I used to have a hand-held Presta gauge, but I haven't seen it in decades. Maybe it's still in one of my bike crap boxes. My Silca floor pump will have to do.

Right before I made the OP, I let the rear tire down noticeably and the front tire substantially, to what at a WAG seemed like they felt like something reasonable for her to test out. Popping the floor pump on it just now, the front is at 40 and the rear at 52, so they were definitely overinflated by the shop. But they are probably allowing for people who weigh 100 kilos walking in and asking to go on a test ride.

ScrawnyKayaker

As mounted, they measure 48 mm, so not TOO badly mis-sized.

veganbikes

You can lower the pressure. Figure out what the minimum and maximum pressure of the tire is and maybe get a nice gauge and play around for a bit. Also you might consider looking at the Kinekt seatpost, she will love it. They have a carbon version if weight is a factor. Will isolate you from the bumps.

FiftySix

The widest tires I have right now that see mostly pavement time and some "off road" time, are 700x42. The bike is 30 pounds and I am 185 pounds. When filling the tires up, the rear gets 55 psi and the front gets 50 psi. That will go down to around 45 psi rear and 40 psi front before I get around to pumping them back up.

For my 35 pound bike with 700x38 tires, I bump up the starting pressure to 60 psi rear and 55 psi front.

For my wife's cruiser bike with 26"x2.125" tires, the starting pressure is 45 psi rear and 40 psi front. I'll let that wander down a bit before pumping them up again, just like the other bikes.

ScrawnyKayaker

Wow. On my road bike, with 28 mm tires and all-up weight of 175 pounds, that calculator suggests 65 PSI front and 70 PSI rear. Thoughts? I'm waiting for some GP 5000s to arrive to put on it, so can't try that just yet.

smashndash

I think that’s pretty good. It takes a mentality shift though. You have to believe that a harsh ride means losing energy through vibration in your body. The pressure should go as low as necessary to get that “gliding” feeling. If you have a super plush bike or really smooth roads, you may not need as low of a pressure.

ClydeClydeson

40mm tires generally don't need to be pumped past 50 psi. You certainly can go higher than that, bet I bet that much higher will rattle your teeth out over rough surfaces.

ofajen

My old MTB has about the same tire width and same total weight and I typically run 35-38 in rear and 32-35 in front. If you ever use your brakes or pedal standing up, I would respectfully suggest not running the front tire pressure more than 10% below the rear pressure.

Otto