This entry is short and sweet but hopefully useful, with a look at the 'ideal' tyre pressure to use in your road bike tyres.
Traditional wisdom is that bike tyres should be very well inflated, perhaps to 8 bars (116 psi) as a reasonable guide.
The principle is that a well inflated tyre has less area in contact with the ground, and hence less friction - so you will go faster. There is usually a slightly less comfortable ride with a highly inflated tyre but that is a price we are happy to pay!
So the principle sounds good - but is it actually correct?
There is another argument that suggests that if a tyre is highly inflated to a pressure at or near the maximum tyre pressure, the tyre will in reality be 'bouncing' slightly along the road. Not great big bounces but enough to reduce the contact area with the road sufficient to actually reduce your efficiency at cycling. Lower pressures also help reduce skiddding, especially in the wet, and increase comfort levels.
If a tyre is too underinflated however, and I would tend to think anything lower than 6.2 bars (90 psi) is pretty low for road bike tyre perssures, there is a significantly increased chance of punctures - which will certainly slow you down a lot!
But I recommend you try the half-way point, somewhere in the range 6.5-7 bars (95-100 psi).
This will certainly feel notably softer than a higher tyre pressure, but my own experiences suggest that the lower pressure does not at all reduce my timings, and possibly even slightly increases them, so perhaps the 'bouncing along the road' suggestion is actually correct. An equally plausible explanation is that the more comfortable ride at lower pressures means I can keep going at 100% for that little bit further.
Whatever you think of the arguments for and against different tyre pressures, why not try it for yourself. No harm done and you might just find it makes you that bit better at longer distances. Some bikes are more sensitive to slight changes in tyre pressures than others.
One other consideration is riders weight - a heavier rider will need greater tyre pressure than a lighter rider. It is sometimes suggested that rider weight divided by 10 gives the correct tyre pressure in bars (1 bar = 14.5 psi), and this is a good starting point as long as you are not particularly light (it is unlikly you would use pressure less than 6 bars just because you only weigh 50kg) or heavy (keep in mind the maximum recommended pressure for the tyre).
Something else to try - different pressures in the front and rear tyres. I usually have 7.7 bars in my rear tyre and 7.3 bars in my front tyre. This seems to give the best results for comfort and performance for me, but every bike and every rider will be different.