Bicycle Mechanics - Can I replace my 700cc x 28 tyres with 700cc x 23 tyres?

As the titles say can i replace them. I have a specialized Sirrus Elite and the front tyres are worn and need changing. All the ones i have seen on ebay are 700cc x 23 whilst mine are 700cc x 28.
If i can change them wahts the advantages or disadvantages??

You didn't specify what rims your bicycle has. For a number of years this model was made with Alex S500 rims which has an inner width of 14mm (look for a label on the rim that says ETRTO 622-14 to confirm). According to Sheldon Brown 23mm tires will work on a 14mm rim http://sheldonbrown.com/tire-sizing.html#width.

If i can change them wahts the advantages or disadvantages??

The wider tires can be run at lower air pressures without affecting rolling resistance and without pinch flatting. That yields a smoother ride. The more casually you ride the more you'll benefit from wider tires.

The narrower tires need a little more air pressure but everybody runs them at higher air pressures anyway. That generally yields a little less rolling resistance. Narrower tires also have less frontal area so they're obviously more aero. The faster you ride the more benefit you'll get from running narrower tires.

A wider tire offers a little more float on semi-soft earth and gravel. A 700x28 will feel more stable off-road than a 700x23, but won't turn your bike into a mountain bike.

My problem is that I am going to Holland next sunday 29th, and need tyres sorted before then. I have no idea about the width of the rims due to the bike being at a friends place till friday.

I run 28mm Parcela TGs and am happy with the everall ride and don't notice any extra resistance. As far as pressure goes here's the answer. https://www.adventurecycling.org/resources/200903_PSIRX_Heine.pdf

My problem is that I am going to Holland next sunday 29th, and need tyres sorted before then. I have no idea about the width of the rims due to the bike being at a friends place till friday.

700x28 will fit 99% of the rims on road bikes made in the last 20 years, including whatever is on Specialized Sirrus Elite.

If you're a big guy I'd recommend 23mm for the front and 25mm for the rear.

Refer to a chart like this to get the pressures right for your weight - low pressure risks pinch flats, and high pressure lowers comfort and after some point adds rolling resistance.

http://www.bikequarterly.com/images/TireDrop.pdf

Ok my rims say
S500 DOUBLE
6061H-1H-P6 622X14

Is that any help??

I think you could use 19mm tyres on those if you wanted.

Ok my rims say
S500 DOUBLE
6061H-1H-P6 622X14

Is that any help??

You have the rims I suspected. 23mm tires (or tyres for you) will fit.

What are the roads in Holland like? And will you be riding light or packed down with touring stuff?

23mm tires are more of a racing and serious training tire. They really aren't the best option for riding with a bunch of gear on your bike or even a bunch on your back. And because they need to be pumped up to a serious pressure they tend to be a rather unforgiving ride.

Frankly I'd stick with the 28's. Especially if you're going to be packing a load. Or at most drop down to 25's. But even then your baggage should be minimal.

There's more suppliers than just Ebay. What about the shops in Britain that sell online? London is also a big place. Don't you have some sort of outdoor gear super store that sells bicycle stuff like tires at a good price?