Tyres on a hybrid...

[swiftylee]

Just picked up a hybrid bike with 700 x 28c 28 x 1 5/8 x 1 1/8th tyres

Can I put 700 x 23 race tyres on it....

 

[Kies]

Yes. I have done this to my hybrid

 

[AndyPeace]

You can but likely at a loss of performance. Tire sizes are best matched to appropriate rim widths. If the width of the rim is too wide, it will make the tire handle less effectively. This may be of use :
http://sheldonbrown.com/rim-sizing.html

 

[MikeW-71]

^^ as above. Depends how wide the rim is. 25mm would be a definate and aren't slower than 23mm.