Bike Forums

Bike Forums (http://www.bikeforums.net/forum.php)
-   Clydesdales/Athenas (200+ lb / 91+ kg) (http://www.bikeforums.net/clydesdales-athenas-200-lb-91-kg/)
-   -   Air pressure for Clydes (http://www.bikeforums.net/clydesdales-athenas-200-lb-91-kg/666220-air-pressure-clydes.html)

CraigB 07-27-10 09:14 AM

Air pressure for Clydes
 
I'd like to get some feedback on road tire air pressure from fellow Clydes. Placing a heavier load on tires than other smaller cyclists, I always inflate to the full value printed on the sidewall, and maybe even 5% more. My thinking is that it helps me avoid pinch flats at bumps in the pavement. Lately though I've been hearing that isn't necessarily true, and that all high pressure does is transmit harsh pavement to the rider, and decreases traction in questionable conditions.

What are you all doing? What have you found works best for you?

10 Wheels 07-27-10 09:24 AM

Lower PSI and larger tires will give you a softer ride.

I toured with 700 x 35's and found the ride to be nice, but the tires also soaked up some of my energy.

Changed to 700 X 28's to get more speed but less comfort.

Your road conditions and personal preference all come into play.

chasm54 07-27-10 09:41 AM

Quote:

Originally Posted by 10 Wheels (Post 11183182)
Lower PSI and larger tires will give you a softer ride.

I toured with 700 x 35's and found the ride to be nice, but the tires also soaked up some of my energy.

Changed to 700 X 28's to get more speed but less comfort.

Your road conditions and personal preference all come into play.

+1. Whatever tyres you use, inflate to pretty close to the maximum pressure. That will be higher the smaller the tyre, and for a heavy rider it is really essential to run 23mm tyres at >100psi or pinch flats will result. But of course that's a harder ride. Bigger tyres, lower pressures, softer ride.

CraigB 07-27-10 10:32 AM

So it sounds like if I want a slightly softer ride, I need to get it with a little larger tire, still run at or slightly above recommended pressures. Makes sense.

Thanks!

cyclist2000 07-27-10 12:29 PM

I think that it really depends on size of tire, your weight and riding style. I have many bikes and all of my road bikes are filled to 90-100 psi before a ride. My bikes tire diameters vary from 23 to 32 mm, I don't normally get pinch flats except the time that I didn't fill my tires before riding. I weigh 235 lbs and don't ride down steps, curbs and slow down when I ride over uneven pavement joints. My tires are rated for higher pressures than 100 psi but I don't think I need pressures that high, especially since I am inflating the tires in an air conditioned house and riding in 90-100 degree temps.

jonathanb715 07-27-10 02:14 PM

Quote:

Originally Posted by chasm54 (Post 11183274)
+1. Whatever tyres you use, inflate to pretty close to the maximum pressure. That will be higher the smaller the tyre, and for a heavy rider it is really essential to run 23mm tyres at >100psi or pinch flats will result. But of course that's a harder ride. Bigger tyres, lower pressures, softer ride.

Not entirely true - I used to run Michelin Carbons - their max pressure for 23c size was 116psi. Now I'm using Vittoria Open Corsas - max PSI for the same size is 140! In the case of the Carbons I was able to run at 100 front/105 rear without pinch flats; the Open Corsas are far more supple and I run them at 110/115. So tire brand and construction do matter. I'm currently using a 25c size of the Open Corsas, and run them near the stated minimum of 100psi in the front, 105 in the back. These are tires intended for racing, but have a sweet supple ride that is hard to match. Unfortunately, they also wear out pretty fast.

My experience is that as heavier riders we do need to run somewhat higher pressure than others, but the optimum pressure depends on our weight and the tires we're running, and can best be found by trial and error - I start at 120 psi, adjust the front down about 5 psi (the front bears less of the load) and go out for a ride. If it seems buzzy and harsh, I'll pull about 5 psi out of each tire and keep experimenting until the ride is acceptable, but handling is still sharp. Too soft, and handling gets a little squishy - the bike won't take a good set leaning into a corner. If you start getting pinch flats, that's definitely too soft and you need to put some more air back in. I don't notice any real difference in rolling resistance when I play around with tire pressures within reason.

JB

chasm54 07-27-10 02:22 PM

Quote:

Originally Posted by jonathanb715 (Post 11185083)
My experience is that as heavier riders we do need to run somewhat higher pressure than others, but the optimum pressure depends on our weight and the tires we're running, and can best be found by trial and error - I start at 120 psi, adjust the front down about 5 psi (the front bears less of the load) and go out for a ride. If it seems buzzy and harsh, I'll pull about 5 psi out of each tire and keep experimenting until the ride is acceptable, but handling is still sharp. Too soft, and handling gets a little squishy - the bike won't take a good set leaning into a corner. If you start getting pinch flats, that's definitely too soft and you need to put some more air back in. I don't notice any real difference in rolling resistance when I play around with tire pressures within reason.

JB

Yeah, OK, but much depends on what you consider "within reason". Take the obsolescent 25mm Schwalbe Stelvios I still have on one of my road bikes. Minimum pressure 85 psi, maximum 115. Play around within those limits by all means, but the heavier you are the more I'd encourage you to err towards the top end.

dscheidt 07-27-10 02:52 PM

Quote:

Originally Posted by CraigB (Post 11183126)
I'd like to get some feedback on road tire air pressure from fellow Clydes. Placing a heavier load on tires than other smaller cyclists, I always inflate to the full value printed on the sidewall, and maybe even 5% more. My thinking is that it helps me avoid pinch flats at bumps in the pavement. Lately though I've been hearing that isn't necessarily true, and that all high pressure does is transmit harsh pavement to the rider, and decreases traction in questionable conditions.

What are you all doing? What have you found works best for you?

You almost certainly don't need to run your tires at the maximum inflation pressure. You neglect to provide useful information, like what size tire you ride, what type of tire you ride, and how much you weigh, but reduce your tire pressure to 80% of what the max is, and go for a ride. if you pinch flat, or the tire feels wobbly from underinflation, add more air. You probably won't, though. Ride and see what you think about the ride quality. Find the piece of road that you don't ride because it transmits so much vibration into your hands, and see if it's different.

CraigB 07-27-10 07:42 PM

Quote:

Originally Posted by dscheidt (Post 11185308)
You almost certainly don't need to run your tires at the maximum inflation pressure. You neglect to provide useful information, like what size tire you ride, what type of tire you ride, and how much you weigh, but reduce your tire pressure to 80% of what the max is, and go for a ride. if you pinch flat, or the tire feels wobbly from underinflation, add more air. You probably won't, though. Ride and see what you think about the ride quality. Find the piece of road that you don't ride because it transmits so much vibration into your hands, and see if it's different.

Weight is currently 231.5, and falling. I didn't mention specific tire size because I didn't ask for a specific PSI. That would obviously change with the tire size, but I had assumed, perhaps incorrectly, that rough percentages might be close to equal across different tire sizes, e.g., a suggested inflation of X% of the tire's stated maximum, whatever that might be. For the record, I'm riding 700x25Cs on the road bike.

XR2 07-27-10 08:05 PM

1 Attachment(s)
I was 296 yesterday AM. I used this article and chart to determine pressure for my 700 X 32 Marathons. I'm running 86F/90R. No flats,decent rolling and fairly comfortable.




Attachment 161896

Wogster 07-27-10 08:42 PM

Quote:

Originally Posted by CraigB (Post 11183126)
I'd like to get some feedback on road tire air pressure from fellow Clydes. Placing a heavier load on tires than other smaller cyclists, I always inflate to the full value printed on the sidewall, and maybe even 5% more. My thinking is that it helps me avoid pinch flats at bumps in the pavement. Lately though I've been hearing that isn't necessarily true, and that all high pressure does is transmit harsh pavement to the rider, and decreases traction in questionable conditions.

What are you all doing? What have you found works best for you?

I think we usually get it backwards, we think of tire size, rather then contact patch size, then pick a tire that provides the proper size at a reasonable pressure. Let me explain, Take a rider and bicycle who are 300lbs, with a 60/40 rear to front weight ratio. That back tire needs to support 180lbs, the tire will flatten out to balance the pressure inside, if the pressure is 100PSI that means the tire will need a contact patch of 1.8 square inches. This probably means that the optimum tire is fairly wide, 35mm or so. Put on a 23mm wide tire, your contact patch is still going to be 1.8 square inches, BUT tire depth between the rim and ground will be much less (more chance of pinch flats) and rolling resistance will be much higher. The solution is to make the contact patch smaller, by putting more pressure in the tire, however as you increase pressure, the ride gets harsher. The other solution is to lower the weight of the load, which isn't always easy.

funrover 07-27-10 08:59 PM

On my 700 X 23 I am running 120 psi

jonathanb715 07-27-10 09:01 PM

OP: rather than looking to find "the answer" on the internet, think about a process so that you can find the answer that works for you, with your tires. Even though Sheldon Brown actually gives pressure recommendations, he notes that most cyclists should experiment to find their optimal pressure: http://sheldonbrown.com/tires.html#pressure

JB

NoReg 07-28-10 12:33 AM

I`ve toured with well over 300 pounds plus bike, and on 700x35s and around 25 pounds in the tires. Reason for this was getitng floatation on a soft trail. I actually thought I had only lowered to say 50, but didn`t measure. My pump had a built in pressure gage, and it showed me what I had done when I re-inflated. I didn`t have any pinch flats. I was riding fast for about 40 miles, but was very careful when I came to stuff like bridges where there were little curbs, or potholes etc...

XR2 07-28-10 04:49 AM

Quote:

Originally Posted by Wogsterca (Post 11187209)
I think we usually get it backwards, we think of tire size, rather then contact patch size, then pick a tire that provides the proper size at a reasonable pressure. Let me explain, Take a rider and bicycle who are 300lbs, with a 60/40 rear to front weight ratio. That back tire needs to support 180lbs, the tire will flatten out to balance the pressure inside, if the pressure is 100PSI that means the tire will need a contact patch of 1.8 square inches. This probably means that the optimum tire is fairly wide, 35mm or so. Put on a 23mm wide tire, your contact patch is still going to be 1.8 square inches, BUT tire depth between the rim and ground will be much less (more chance of pinch flats) and rolling resistance will be much higher. The solution is to make the contact patch smaller, by putting more pressure in the tire, however as you increase pressure, the ride gets harsher. The other solution is to lower the weight of the load, which isn't always easy.

How do you determine that?

CraigB 07-28-10 07:14 AM

Quote:

Originally Posted by jonathanb715 (Post 11187306)
OP: rather than looking to find "the answer" on the internet, think about a process so that you can find the answer that works for you, with your tires. Even though Sheldon Brown actually gives pressure recommendations, he notes that most cyclists should experiment to find their optimal pressure: http://sheldonbrown.com/tires.html#pressure

JB

You're absolutely right about my need to experiment on my own. I was only hoping here to get a general sense of what other riders of similar weight have found to be effective for them, so I can use that information as a starting point in my own explorations.

Wogster 07-28-10 08:02 AM

Quote:

Originally Posted by XR2 (Post 11188170)
How do you determine that?

Easy, weight divided by pressure in PSI, if you have 180 lbs and 100PSI then divide 180 by 100 to get the area. The contact patch may not be square, it depends on the type of tire, the rim, tire diameter, tire tread shape, tire construction.

dscheidt 07-28-10 09:40 AM

Quote:

Originally Posted by Wogsterca (Post 11188746)
Easy, weight divided by pressure in PSI, if you have 180 lbs and 100PSI then divide 180 by 100 to get the area. The contact patch may not be square, it depends on the type of tire, the rim, tire diameter, tire tread shape, tire construction.

The contact patch pressure is only equal to tire pressure for a small range of pressures, which for a typical tire, are lower than most people run them at. Limits of carcass flexibility limit the range that it's true for; outside of that range, there will be a region of higher than predicted pressure at the front and rear of the patch, surrounding an area of lower than expected pressure. this effect is one of the reasons that tires at higher pressures are less efficient at transmitting power to the ground in poor traction situation.

cyclist2000 07-28-10 12:41 PM

Quote:

Originally Posted by dscheidt (Post 11189249)
The contact patch pressure is only equal to tire pressure for a small range of pressures, which for a typical tire, are lower than most people run them at. Limits of carcass flexibility limit the range that it's true for; outside of that range, there will be a region of higher than predicted pressure at the front and rear of the patch, surrounding an area of lower than expected pressure. this effect is one of the reasons that tires at higher pressures are less efficient at transmitting power to the ground in poor traction situation.

Strangely, that one went right over my head.

XR2 07-28-10 03:59 PM

Quote:

Originally Posted by Wogsterca (Post 11188746)
Easy, weight divided by pressure in PSI, if you have 180 lbs and 100PSI then divide 180 by 100 to get the area. The contact patch may not be square, it depends on the type of tire, the rim, tire diameter, tire tread shape, tire construction.

OK thanks. However how do you determine the contact patch you seek by tire size? Not doubting you I really want to understand what goes into picking a tire. In my case I picked 700 X 32 because thats all the frame will allow. The next build will give me greater freedom and I want to be satisfied with the result.
Thanks again.

Wogster 07-28-10 09:23 PM

Quote:

Originally Posted by dscheidt (Post 11189249)
The contact patch pressure is only equal to tire pressure for a small range of pressures, which for a typical tire, are lower than most people run them at. Limits of carcass flexibility limit the range that it's true for; outside of that range, there will be a region of higher than predicted pressure at the front and rear of the patch, surrounding an area of lower than expected pressure. this effect is one of the reasons that tires at higher pressures are less efficient at transmitting power to the ground in poor traction situation.

Let me try to explain my point, as I think you missed something. Take 2 tires, the same construction, one is 23mm wide, the other is 32mm wide, at the same pressure, with the same load, the contact patch will be the same size. However the narrower tire will also have much less height from rim to tread, as it spreads out to the larger contact patch size. It's this lack of height that causes pinch flats, so the pressure required may be much higher in order to prevent them. In fact the pressure needed to prevent pinch flatting may be so high as to exceed the design specifications of the tire. For example with our example load, if the tire is rated 140PSI, but needs 180PSI to prevent pinch flats, you have too narrow a tire for the load.

Your right too about higher pressures, given two tires that are a specific width, one at lower pressure and the other at higher pressure, the higher pressure tire, will have a smaller contact patch, reducing the amount of rubber on the road to produce traction.

Wogster 07-28-10 09:29 PM

Quote:

Originally Posted by XR2 (Post 11191641)
OK thanks. However how do you determine the contact patch you seek by tire size? Not doubting you I really want to understand what goes into picking a tire. In my case I picked 700 X 32 because thats all the frame will allow. The next build will give me greater freedom and I want to be satisfied with the result.
Thanks again.

I think a general rule is to pick a tire where the tire doesn't need to widen out significantly in order to support the load, then pump those tires to the maximum pressure go for a ride, then repeat at repeating lower pressures until you get the best balance of comfort and efficiency. At 296 pounds, which I think you stated a couple of messages back, 32mm should be a reasonable starting place.

XR2 07-29-10 08:23 AM

Hopefully when the next build is done the number will be smaller than 296. Well it was 312 on July 1 so we're headed there. Thanks again.

CraigB 07-29-10 08:26 AM

Congrats on moving in the right direction, XR2. Keep it up.

I'm down from 304.5 to Monday's weight of 231.5, with another 66.5 to go to my final goal.


All times are GMT -6. The time now is 04:06 AM.