Optimum Tyre Pressure
 

Hi there, I am new to the forum.

I have been cycling two months now and thouroughly enjoy it, fitness wise and time wise, get a great adreneline rush. I cycle 11 mile a day, and at 45 years old, i need the exercise to keep me in shape.

If someone could advise me on tyre pressure, I have a Univega Alpina HT510, which i use solely for on the road, My original tyres where 26 inch by 1.95, which i used 40 Psi, now i have changed the tyres to Scwalbe Marathon 26 inch by 1.5, they recommend between 45 to 100 Psi, that is quite a range, As i said, i cycle only on the road, about 5 mile to my work,

Would appreciate any suggestions as to the optimum tyre pressure.

Thanks

Your weight (that is You and the weight of your bike & equipment) is a prime determinant for setting correct tire pressure, as the tires are carrying it all. Since you are riding on the road you want to keep the tires pumped a bit former than if you ride on dirt or gravel.
You want the pressure to be 10% more in the rear tire than in front. The absolute pressure number is also determined by the width of the tires; more for narrow than for the wider ones, as the higher pressure compensates for the lesser volume of air.

If you weigh less than 200 lbs you might want to start with a pressure of 50 lbs rear and 45 lbs front; then raise the pressure in 5 lb increments if you're feeling too much drag while riding. I like to keep mine a bit soft in order to absorb the bumps in the road.

Because of the risk of pinch flats it probably wouldn't be a good idea to go any lower than the 45 lbs they recommend.

Thanks for that, my weight is 157 pounds, the bike has a lightweight frame.

You will really like the quick, easy, roll on those Supremes, at 85-90 pounds per square inch.......

Would that affect the comfort of the ride?. i.e would i have a bumpier ride?

Higher pressures can result in a bumpier ride, if your road surface is rough. If it helps, think of the max pressure as what you'd run if your roads were smooth as glass. When you rough up the surface, you let some air out to absorb the chatter.

The point of diminishing returns for softening the tire is the point at which your rim starts pinching the tube on bumps and causing flats, or where your tire starts to roll a bit on sharp turns, but generally, softer is comfier.

Cfd's advice looks sound.

I just always thought you put in the max.

There is a theory, which has supposedly been proved with some careful testing, ( sorry, no link ) that says the optimum, is enough pressure to result in a 15% deflection of the sidewall when loaded. If not racing, any more pressure results in a harsher ride, and possibly losses from bouncing, with little gain from reduced rolling resistance. I try to follow this now, and while it does seem a tiny bit slower, the ride is very nice on Supremes at 60/65 Front/Rear.

Of course, if racing, then seconds count.

You can see a discussion of the 15% tire drop inflation recommendation here.

That article only discusses tires up to 37 mm wide. I put together a spreadsheet that extrapolates the tire size up to 60 mm. The coefficients for 18 to 37 mm tires follow smooth curves so the extrapolation is probably reasonable, just be aware that it is not based on data for tires larger than 37 mm. I think the principle here is that less than maximum pressure in a tire will often result in a smoother ride with nearly no penalty in rolling resistance. On rough roads a lower pressure can reduce the rolling resistance in fact. But the pressures recommended in the article or my spreadsheet are not Gospel, they are good places to start and you might want to use higher or lower pressures once you have tried them.

The system here does not allow me to post the spreadsheet but I can post images of the charts the spreadsheet can generate.

KenAttachment 149625Attachment 149626Attachment 149627

Thanks for those charts, according to those, I should be running 43/53.

I run the maximum pressure in my tires as stated on the tire which depending on which bike and tire i have the pump on of the bikes I have now could be anywhere from 80 to 180 psi. But then I have never had a bike that had a tires with such a large pressure range of 45 to 100 psi.

Sure most of us do and have done since we were kids. On a smooth road the highest pressure gives the lowest rolling resistance. On a rough road however a lower pressure has been shown to be better in testing. And the ride is better with a lower pressure. Even on a smooth road the amount of reduction in rolling resistance above the point where you get 15% tire drop is supposedly small, although I have yet to see a chart that shows how small that is. As with everything concerning bicycles this topic is somewhat controversial and if you want to run at max pressure you are certainly in the majority. But perhaps the majority is wrong....

BTW, this site has a podcast interview with Jan Heine the author of the article linked above.

It is the second article on the page currently and it titled "It's Simple: Comfort = Speed". There are a number of other podcasts on that page and they are all worth a listen if they are as good as the Jan Heine interview, the only one I have listened to.

Ken

Look here for mtb tire pressure guide:

http://www.michelinbicycletire.com/m...essuremtb.view

Look here for road tire pressure guide:
http://www.michelinbicycletire.com/m...rpressure.view

It depends on the tire.

I've had best results with the following:

Hutch Spiders -- 45f, 48r, best all-around performance on- and off-road. 26x2.0
Intense Micro Knobby -- 60/60. 26x2.25
WTB NanoRaptor -- 60/60. 26x2.1.
Hutch UST Scorpions -- 50/50. 26x2.0

I'm running considerably less pressure this year, since becoming aware of the tire drop school of thought, and notice no slowdown and an increase in comfort. Previously, I had always tended towards Max Pressure all the time.

Tried out 60/65 and it seems smooth, i think a bit higher would give me a harsher ride, and at 7am, I like a bit of comfort.
Not fully understanding the charts, I am 70kg and my bike is about 15kg with all the equipment, so, what would that equate to?
From what i can see, I should be a bit lower.

With 40c tires (about the same), I find that my best pressure is at about 70-75 psi front and rear, but that's with my 200 lbs on a 30 lb bike.

45 lbs would be good for singletrack or off roading.

You have 1.5 inch tires which is 38 mm so you would want to use the 37 mm line since it is the closest to your tire width. You could interpolate between other lines but that would be more work than necessary since these are guidelines more than dictates. Your loaded bike weight is 85 kg, these pressure charts are per tire though. Ideally you would weigh your front and back wheel separately with you on the loaded bike to get the actual weights on the tires. Again this might be a little obsessive compulsive so you could just use the 40% front, 60% rear figures from the article for a typical racing bike since it seems to be in the middle of the extremes of the examples given in the article. That would mean that you have 34 kg on the front and 51 kg on the rear. According to the 37 mm line you would want to start with 33 psi in the front and 50 psi in the rear. Since Schwalbe wants 45 psi minimum you would probably want to run 45 front and 50 rear. If that seems too soft you can increase it some and if you end up thinking 60/65 is best there is no harm in that. The idea is not so much that these charts are the perfect pressures for all people, tires, and conditions as it is that you should try lower pressures than the max printed on the sidewalls, especially if you have tires wider than 25 mm or so. You can get very nearly the same performance with a better ride at lower pressures and wide tires do not need max rated pressures to carry most riders.

Ken

Thanks for that explanation, most appreciated