MagnaRota

Ah that's the problem, I don't use Google!


I see that point too and went to a site where they did the experiment. It turns out to depend on many things; terrain, tire consistency, speed, weight, just about everything involved in riding a bike, whether you want more or less pressure for lower rolling resistance. One thing to remember is Newton's laws, and when you lose speed going up onto an obstruction you get some of that back when you come back down off it just like you do on a hill, and also when the tire is compressed by an obstruction that doesn't come for free, you are doing work with that compression and you lose some energy there. Which is better is probably complicated enough as to be incalculable.


Consider that this is a subsection intended for those quite a bit larger than a competitive cyclist, and we have to put a lot of pressure in road bike tires to get a reasonable contact patch and avoid flats anyway so we're not going to be running at much less than max no matter what.


https://velo.outsideonline.com/gear/...ce/?scope=anon

bbbean 

So use whichever search engine you prefer.


Note that the reason I encouraged you to dig a little is it isn't one site and one experiment. Over the past decade or more, a body of research and experience has confirmed the consensus that wider tires and lower pressure reduce rolling resistance and increase speed. You may also notice that the professional peloton has moved from the rock hard (120-160 psi) 19 and 20mm tires everyone used 30 years ago to the current use of 25-30mm (wider than that at some races) tires running at 60-80 psi.

xroadcharlie

I bought some new 26 x 1.9" Vee Rubber tires recently that have the recommended tire pressure expressed in a peculiar way. 65 psi for road, 40 psi for off road. In either case their minimum is still way less (25 psi front/ 31 rear) then I get from the Cycles Chinook online calculator which is based on the 15% drop principle. They don't need my E-mail like Silca. I inflate the front to the minimum of 40 psi and the rear to 50 psi, since there's more weight there, and go by feel. When they feel low with thumb pressure I re-inflate them.

I tried inflating them with a tiny hand pump but could barely get to 25 psi. Inflating them to the pressure I normally use made them roll much easier. Probably because these tires are 50mm wide. I'm pretty sure the pressure suggested by the calculator would be fairly accurate for road bike tires for a good balance between speed and comfort. It shows 61 psi front / 66 rear at 175 lbs total weight on a road bike with 28mm tires.

chaadster

You make a lot of misguided assumptions, but stating that Clydes/Athenas are not competitive cyclists is the worst, because it’s also insulting.

MagnaRota

OK I took your advice and did one better, I did the experiment! On a gravel trail I'm very experienced on, I dropped my tire pressure to 65 PSI (rated 50-75 PSI) instead of my usual 85 PSI, and gave it a go.

I will never do that again! Slightly lower average speeds and a lot of work.

It appears that for the Spandex-wearin' Bud Light-drinkin' spokesbois who are usually in races they aren't compressing the tire significantly at either very high or medium pressures, so they will get some benefit from the softer tire over the rough terrain, but for someone like me I will be pushing the tire down into the gravel even at high pressures, and seriously deforming the tire at lower pressures resulting in more resistance.

But thanks for the information, I'm glad I tried it and had a learning experience.

bbbean 

I'd love to see your data. What power meter did you use? How many times did you replicate to rule out various sources of error?

Now I really want to see your data! Interestingly, a number of people who have tested out have pointed out that riders tend to associate high frequency vibration with speed, and may feel slower operating with lower pressures, even though they are moving faster with less power. If your study contradicts that, there are a lot of people who want to know.


Oh.I made a mistake. Thanks for clarifying yourself. You just can't hide a good education. Have a great day.

MagnaRota

I used Open Tracks, which monitors speed. Normally I do this course with a 9.8 MPH average speed, and this time it was 9.5 MPH. Pushing as hard as I can, as always. I get in a little better condition with every ride and on all my other courses my speed increases slightly with every ride.

Look, in order to say I'm wrong, you'd have to come here and try that route yourself, on my bike, and if that's you in your avatar pic, with a couple of 45 pound plates strapped onto you as well. You appear to be a much more advanced rider than I am and I get that, which is better is going to depend on a multitude of conditions that are going to be different everywhere and for everyone and can't be exactly replicated.

But you did give me another good idea- what if I set up my phone as an accelerometer and attached it to the seat to measure vertical vibration with different pressures?

chaadster

Picking tire pressures at random is garbage, so it’s no wonder you had a rubbish ride.