Trye pressures (continued...)

Schoie81

There has been a few threads about tyre pressures just recently, and rather than just hijack one of those threads, I thought it'd be more polite to ask this in a new thread.

What are the pros and cons of high and low tyre pressures on a road bike? It seems there is certainly some amount of personal preference? I understand that low pressures can lead to pinch punctures, and it seems logical that lower pressures would provide more cushioning so a slightly more comfortable ride. So why go high? 120psi would reduce the chances of getting pinch flats, and I assume it reduces rolling resistance to some extent - is that the main reason for hard tyres? How does tyre pressure affect grip? Would lower pressures lead to more lateral movement of the tyre when cornering and therefore there's more stability with harder tyres? Does tyre pressure matter more in the wet?

Just curious as to what the pros and cons are....

kajjal

Roughly speaking the balance is trying to get the best for your riding style. Too high a pressure and you get hit with loads of vibration from the road and potentially less grip due to this. Too low and you go slower, have more punctures and less grip again as the tyres start to roll off the rims when pushed round corners etc.

Grip is affected by pressure but as long as you are roughly at the right pressure you will be fine. Don't forget to allow for your weight plus the weight of the bike etc. when setting tyre pressures. After that you can adjust to personal preference.

Cornering is more effected by the road conditions (wet, mud, leaves), compound the tyres are made from and your technique unless you have abnormal tyre pressures high or low.

captain_tiara

I think you've pretty much covered the differences!

Harder tires roll faster & deform less, & seem to puncture less. However the development of tubeless, wider rims etc basically means you're riding a different system with different characteristics.

Try a ride @ 80 psi & another @ 110psi. Changing surfaces will affect your choice - A roads or farmers tracks?

Quality of rubber is essential. Black Chilli for me please; Force, Attack, GP4000s, Grand prix, grace different wheels at different times of the year.

Runtothehills

You've covered most of them but harder tyres don't always roll faster, if they did all the pros would be on solid tyres with no air at all. Depending upon rider weight, the bumpiness of the road, wdth of the tyre and a few other variables the optimum pressure for rolling resistance will change but as high as you can go is not always best.

For example on a very smooth surface like an indoor track you'll want a higher pressure than on most road surfaces. If you go for too high a pressure on roads the bike jumps between small bumps rather than deforming to roll over them, wasting energy as it bounces. Equally too low and it deforms too much, wasting energy in flexing the tyre.

Barteos

Harder tyres roll faster on glass floors, velodromes and on forums but not on real roads.

You can lower you pressure as much as you want and you're more likely to kill your rims/tyres/tubes or crash on the first corner before you notice any loss of speed even on smooth roads.

The study carried out by Bicycle Quarterly Vol. 11, No. 3 (Spring 2013) demonstrates that on a smooth race track adjusting pressure in a range of of 60-120PSI makes practically no difference to how fast the bike rolls. That applies both to basic and high end tyres.

Also... http://www.training4cyclists.com/how-mu ... RKnPO.dpuf (see 4. Normal bike, reduced tyre pressure only 3 bars.)
Climbing Alpe D Huez with just 3 bars! resulted in even marginally faster time (normalised power). That's on a smooth road!

... or how about doing a TT at +28mph with half-flat tyre - 30-40PSI? http://teamdrag2zero.co.uk/2012/09/22/r ... -7-report/

Logically If lower pressure costs nothing even on smooth tarmac, it can only make you faster on any rougher surface.

Simply use the lowest possible pressure that still offers good and safe handling and no pinch flats/rim strikes. More than that offers no benefits or will slow you down.

16mm

So running road tubeless would get rid of the pinch flats, and the lower pressure would provide much more comfort than carbon everything. That's quite a good argument for tubeless. (and I don't intend to go tubeless anytime soon).

It would be interesting to see the comparisons when sprinting, rather then steady state TT and climbing.

ForumNewbie

When I put my road bike tyres up to 110 for the first time recently (usually have them at 100) the bike definitely felt faster. It didn't seem to grip the road as well when there was a cross wind, but it was faster.

Neil_aky

Kajjal wrote:

Roughly speaking the balance is trying to get the best for your riding style. Too high a pressure and you get hit with loads of vibration from the road and potentially less grip due to this. Too low and you go slower, have more punctures and less grip again as the tyres start to roll off the rims when pushed round corners etc.

Grip is affected by pressure but as long as you are roughly at the right pressure you will be fine. Don't forget to allow for your weight plus the weight of the bike etc. when setting tyre pressures. After that you can adjust to personal preference.

Cornering is more effected by the road conditions (wet, mud, leaves), compound the tyres are made from and your technique unless you have abnormal tyre pressures high or low.

Really unusual to see such a good answer regarding tyre pressures - the above is spot-on. Usually the answers make this sound like a black art. Follow the manufacturers advice for minimum pressure based on weight (to avoid pinch flats). then it's up to you up to the maximum pressure.

rolf_f

ForumNewbie wrote:

When I put my road bike tyres up to 110 for the first time recently (usually have them at 100) the bike definitely felt faster. It didn't seem to grip the road as well when there was a cross wind, but it was faster.

Felt or was? Which one? Where the weather conditions the same eg wind, temp. Air temp in particular (getting colder now) has a huge effect on speed.

I'd say the fact that you felt the higher pressure was faster is meaningless - any difference caused by going up 10 psi is probably only going to be noticeable on careful analysis of ride data. Without power data and very similar weather conditions, you can't be sure what any differences are caused by.

Hawmaw

I rode my Conti Ultra Race at 100psi and had more than my fair share of punctures. I recently swapped to Vredstein Fortenza Tricomps and upped the pressure to 120psi. There is no noticable difference in speed or rolling resistance however ride quality is significantly harsher. I'm going to knock it back to 110 for a while and see how that goes.

I recently went for a 20 mile run on my old Claude Butler single speed with 1 1/4 tyres. It was a slog , like cycling through treacle. When I got back I found that there was only 40psi in the tyres. It may seem obvious but I would suggest that a large drop in pressure will increase resistance and slow you down.

ForumNewbie

Rolf F wrote:

ForumNewbie wrote:

When I put my road bike tyres up to 110 for the first time recently (usually have them at 100) the bike definitely felt faster. It didn't seem to grip the road as well when there was a cross wind, but it was faster.

Felt or was? Which one? Where the weather conditions the same eg wind, temp. Air temp in particular (getting colder now) has a huge effect on speed.

I'd say the fact that you felt the higher pressure was faster is meaningless - any difference caused by going up 10 psi is probably only going to be noticeable on careful analysis of ride data. Without power data and very similar weather conditions, you can't be sure what any differences are caused by.

It not only felt faster, it was faster. It was on a 14 mile hilly circuit that I have done many times over the years, and that was my fastest time yet. It wasn't great conditions as fairly windy, but luckily it was dry as I wouldn't have felt safe on wet roads with the tyres so hard.

Barteos

ForumNewbie wrote:

Rolf F wrote:

ForumNewbie wrote:

When I put my road bike tyres up to 110 for the first time recently (usually have them at 100) the bike definitely felt faster. It didn't seem to grip the road as well when there was a cross wind, but it was faster.

Felt or was? Which one? Where the weather conditions the same eg wind, temp. Air temp in particular (getting colder now) has a huge effect on speed.

I'd say the fact that you felt the higher pressure was faster is meaningless - any difference caused by going up 10 psi is probably only going to be noticeable on careful analysis of ride data. Without power data and very similar weather conditions, you can't be sure what any differences are caused by.

It not only felt faster, it was faster. It was on a 14 mile hilly circuit that I have done many times over the years, and that was my fastest time yet. It wasn't great conditions as fairly windy, but luckily it was dry as I wouldn't have felt safe on wet roads with the tyres so hard.

The most likely explanation would be fitness gains or other changes in equipment.

Neil_aky

If the bike 'feels' faster, sometimes it has a positive effect on the rider and you ride faster.

I had the same when I changed from the supplied 23mm tyres to Michelin Lithion2 25mm tyres.

The bike felt better and my rides were faster - I still don't know if the bike really was behaving significantly different or if I just had more confidence and the placebo effect meant I rode faster.

In the end, the real reason doesn't matter, my rides are faster with these tyres...

kajjal

That's the main thing. If you enjoy riding your bike you will go faster.

Other ways to go faster are fitness, technique, a good fitting bike, a well tuned bike and not wearing a big loose top / jacket that acts as a massive wind brake.

neeb

I've no reason to question the findings that lower pressure tyres supposedly run just as fast, but like others, I simply don't like the feel of lower pressures, they definitely feel slower (except on really poor surfaces) and for me at least, produce slightly slower times (I'm talking, say, 23mm tyres at 80 oor 90 psi compared to 115 psi for me at 63kg on reasonably smooth tarmac). I'm quite prepared to accept that any actual speed differences could just be down to the fact that lower pressures (for me) make riding less enjoyable and thus decrease motivation, but the net effect is that I am certainly not any slower, and may be faster, with slightly higher pressures.

The science is clearly very complicated with lots of variables and interacting factors. For example, I wonder if the findings that Barteos quotes about pressure variation between 60 and 120 psi making no significant difference on a track allows for differences in riding styles imposed by terrain. How does accelerating hard up a hill out of the saddle (something you don't do on a track) affect tyre deformation? That's when I notice the "squishiness" of lower pressure tyres most, especially at the front.

ForumNewbie

If your car tyres are lower in pressure than they should be, your mpg will be lower than it should be, i.e. you are using more fuel than you should be using. Is the same not appropriate for cycling, in that if your tyre pressure is a lot lower than it should be, you would have to use more energy to do the same number of miles at the same speed - similar to using more fuel in your car?

neeb

ForumNewbie wrote:

If your car tyres are lower in pressure than they should be, your mpg will be lower than it should be, i.e. you are using more fuel than you should be using. Is the same not appropriate for cycling, in that if your tyre pressure is a lot lower than it should be, you would have to use more energy to do the same number of miles at the same speed - similar to using more fuel in your car?

Basically, yes. But the debate is about exactly how low bike tyre pressure has to go before it has a significant effect on speed for the same energy input. If you believe the low pressure brigade, just about any pressure high enough not to be a serious risk for pinch flats on a 23mm road bike tyre is not going to be significantly less efficient.

I think a lot depends on the road surface. It may be the case that the optimal pressure for many UK roads is significantly lower than for decent road surfaces you get on the continent (in Finland where I am they are sort of intermediate, but generally quite a bit better than U.K. roads).

In any case, for any given road surface, tyre type and rider weight there is presumably a single optimal pressure for efficiency, which balances losses from deformation (greater at lower pressures) with losses from poor tyre contact (greater at higher pressures).

neeb

neeb wrote:

In any case, for any given road surface, tyre type and rider weight there is presumably a single optimal pressure for efficiency, which balances losses from deformation (greater at lower pressures) with losses from poor tyre contact (greater at higher pressures).

Actually on second thoughts that's not necessarily true. It's possible that gains in efficiency from higher pressure could be exactly offset by losses and visa-versa over a range of different tyre pressures, although it seems unlikely.

Monty Dog

I'm a big fan of fatter tyres and lower pressures - spent years of frustrations with 20mm tyres giving a harsh ride, poor handling and lots of punctures like everyone else in the 80s/90s when we didn't know better. Over the years my preferred tyre size has increased, handling and comfort improved and punctures reduced. Riding a 32mm CX tyre at 3 bar on mixed road/trail conditions shows only a minor reduction in average speed on tarmac - 1-2kph. Likewise, I can easily wind my 29x2.5" tubeless MTB tyres up to 40kph on the road which is a good way of catching-out unwary road riders!