davei1980

Thought I would keep with the theme of ultra-controversial topics:

I just got my Nashbar tires in the mail - they're 700x28C (28x622).

What tire pressure should I be running?

Here are my vitals-

- I weight 173lbs and dropping
- My backpack (which I ALWAYS have) is 10-15 lbs (I need to carry my laptop with me and it's a boat anchor)
- Bike weighs 19lbs with my duck bill fender, lights, cyclocomputer and emergency kit, soaking wet
- I commute on paved roads and pathways, gravel encounters are rare

According to the Michelin table I found on the internet, I should be running max pressure which is 100 psi in these tires.

I have heard of people running lower pressure in the front because less weight is on the front.

wphamilton

Weight distribution on road bikes is 40-60 front/back, or 45-55 if you're more upright. Tire pressure can be set at the same percentages.

Even at 200-205 pounds I wouldn't run the 28's at 100 psi. 85-90 probably.

ThermionicScott 

+1, I'd be using 70/85psi at that weight.

davei1980

The sidewall says 80psi min.

You still maintain your position or would you up it to 80-85?

wphamilton

I'd trust him over the sidewall. TBH, my 28's right now have about 60 front 70 back - time for an air-up. I have no issues at that pressure (weighing about 20 pounds less than you).

Generally you want just enough air to avoid pinch flats and feeling squirrely on fast corners, and not so low that the tire has more drag. There is a variable depending on how you ride - if you jump off curbs or hop over potholes for instance you'd probably want higher pressure. But lower gives us a better ride and less rolling resistance in some conditions, which is kind of the point of 28's. Even below the sidewall rating, for me, is no problem.

davei1980

Thanks guys!! I am anxious to learn more about the science surrounding the relationship between psi and rolling resistance!!

wsgts

I have 28s on my primary commuter and typically have 100 in the front and 130 in the rear. I am at 260, plus have a rivbike under seat bag (guess would be another 10 pounds for that). My sidewall says max pressure 100psi but have had no issues at 130 in the rear. At your weight, 100 psi would probably feel very hard over any bumps you may encounter. So +1 for not necessarily trusting sidewalls.

Most people simply put the max pressure in without any consideration to what they are doing or how much weight will be hauling. That what most bikes shops do in my area as well.

ThermionicScott 

I'm standing pat! None of my front wheels are over the "minimum pressure" recommendation, if given. All that they are is a customer satisfaction dodge -- they don't want people to come back and complain if they get pinch flats or sidewall damage from running the tires too low. But the amount of pressure to achieve 15% drop has never led to any issues for me.

davei1980

This discussion of weight and pressure makes me wonder- what is the max weight of a bike? I have a coworker who’s easily holding down 300, he’s young and active and I think I can get him to ride if I could convince him the bike will hold him.

Is this possible? What does it take-
Smaller wheels? Greater spoke count?

Stormsedge

I run my 28s at 80-90...no issues. My weight about the same as yours given your backpack and gear.

rumrunn6

fwiw, went out on my road bike which has 25mm tires this weekend. pumped 90 up front & let the pump burp so it had less. the rear got 100 w a little less after removing the chuck. seemed good for me w me, gear & bike weighing approx 250lbs. I've ridden w the tires harder, but the roads right now are cr*p

chas58

I run my 28's at 70 front 90 rear
or on gravel (or tubeless) 50 front 65 rear.

Good topic for studying up on!

Google: bicycle quarterly tire pressure
and maybe read some of the tests here: https://www.bicyclerollingresistance...d-bike-reviews

What is interesting is that wider tires have less resistance (all other things being equal). That is balanced a bit by the fact they have extra weight. I was shocked to purchase some 60mm tires that have less rolling resistance than my 23/25mm race tires. Its kinda cool!

Cross racers run a course dropping pressure, until they hit the rim, and then put a little PSI back in.

If I do that with inner tubes, I get pinch flats. But I'll do that running tubeless.

chas58

More tire pressure?

I have a bike that has a 120kg (264lb) weight limit. But that is a light racing bike. Get a good solid steel frame bike and you can probably do anything. I do have a tandem that is a bit over built (compared to a single). It has a beefy fork and 36spoke wheels. It depends of course a bit on how you are riding it. Bigger tires (well, more than 25mm) are going to help as there is less of a chance of bottoming out and pinch flatting. That tire pressure chart I mentioned above goes up to 154lbs per wheel (covering your friend's needs).

If my brother and myself can ride a fully loaded tandem, I wouldn't worry too much if you have a decent bike in good shape.

davei1980

Nashbar has great deals sometimes on steel frames set up for 26" wheels - sounds like my next build! now I just have to convince him to ride to work with me!

mc510

I've actually never even considered running anything less than max pressure on theory that "more is better" (at reducing rolling resistance), so this is very interesting! Do you run lower pressure primarily for ride comfort?

ThermionicScott 

It turns out that the steel drum tests done in the 1980s that led to the "more pressure = less rolling resistance" mantra ignored a big source of energy loss -- vibrations in the rider's body. Quite a few watts can be lost by jiggling around on hard overinflated tires, so letting a little air out is not only more comfortable, but can get you to your destination feeling less spent.

davei1980

A MAZ ING


Go easy on the 1980s- remember - this is the same decade that taught us to eat lo-fat. Nevermind the fact that the sugars used to replace fats in foods turns to fat the instant it's processed by your liver......

ThermionicScott 

To quote our President at the time, "mistakes were made."

noglider 

There is a LOT of leeway with those sidewall pressure ratings. In fact, I don't even bother with them. I bet you could run 60 psi in the rear. See the chart here. Note that the weights are per wheel, not per bike.

davei1980

Exactly! The same decade which elected Reagan twice and Bush once!!! Unleashed a war on workers which we still haven’t recovered from

52telecaster

being a real stickler for tire pressure i generally inflate all of them to 100 psi and then forget for a month before i re-inflate.

works for me.

davei1980

I like it! It's like these debates over ideal tire/wheel sizes: they're all round, they all spin around a hub.....

Abe_Froman

I'm 190 and run 85 in the back, 75 front. I could probably drop it some, though streets aren't the best here and I do occasionally space out and go right into a pothole.

Don't worry about pressures listed on the sidewall, for all intents and purposes...they mean nothing.

Rolling resistance really is sort of a fascinating topic when you really dig into it. There are all sorts of variables involved, probably the most important of which is the specific tire you use, but generally, the gist of current research is saying that you really do not pay much of a penalty when using larger tires sizes.

This is especially important in the context of your 300lb friend. Get him bigger tires. Riding at 130psi to keep from getting pinch flats on skinny tires is no fun, especially if you've got 300 lbs jiggling around over every imperfection in the road. Some nice, flexible 40mm tires at 50psi will feel great, and be just as fast as your 28s, unless you guys are in the tour de france.

davei1980

Thanks! I am thinking a high quality, steel MTB frame set up for 26ers would be perfect - he can run wide tires/36h rims PLUS the standover is not high (kicking the leg over may be tough until he loses weight) and the riding position is upright (he carries all his weight in the front, leaving little pedaling room for his legs with his belly)


I am happy to build him a bike because he is still so young and active there's no reason for him to be unhealthy

Abe_Froman

A MTB might even be a bit to aggressive. A hybrid would probably be great, cheap, and comfy riding position.

Just make sure you don't use old cheap/knobby MTB tires. Especially with a big heavy load...those things will be SLOWWWWW on pavement. Nice, fat, slick, fast tires IMO. I used voyager hypers, but those are 700c only I believe. Compass is great from what I hear, but very expensive; probably not a great invenstment for someone that might not stick with it. Panaracer paselas get great reviews, are cheap(ish), and come in fairly wide 26" sizes.