Different sized tyres on same bike

[Rob500]

Hi

Despite owning my bike for a while now I've only just noticed that my 2 tyres are different sizes. Says 25=622 on front and 23=622 on back. Is that a totally random thing or a common thing for cyclists 'in the know' so to speak?

I've always bought spare inner tubes in the range 700 18-25. Is the 24-25 too much for the back tyre? Should I get a few of the 700 19-23 ones that I've seen? Would they be ok for the front as well?

 

[gaz]

Your tubes will be fine in either tyre.
Normally if you run 2 different size tyres, the bigger one will be back and the smaller on the front.

 

[HLaB]

Perfectly fine, I'm running 22mm front, 23mm rear on my kinesis at the moment and plenty of other times I've ran 23/25mm no problem. I usually run the bigger tyre on the back but occasionally some people prefer the other way round, the late Sheldon Brown debates the merits of both. The 18-25 tube is fine as it covers both, the 19-23 will be too small for the 25mm front, although, I'm not sure of the consequences it certainly wont hurt in the short term.

Edit: Sheldon's piece

Most bikes come with identical tires front and rear. This is all right for general use, but if you want to optimize your bike, you should consider using different tires front and rear. The front and rear tires have different loadings and different requirements.

• 
  Narrower Front, Wider Rear
  If lightness is the primary goal, tire width/weight is limited by the risk of pinch cut flats, a.k.a. "snake bites." Since there is more weight carried on the rear tire, you can get away with a slightly narrower tire in front than you can in back.
• 
  Wider Front, Narrower Rear
  A wider front tire makes sense in many applications, however, when handling and ride comfort are considered. A wider tire will generally provide better cornering traction than a narrower one, assuming appropriate inflation pressure. A wider tire also provides superior shock absorbency. I personally prefer a slightly wider tire in front, since I suffer from some wrist discomfort on occasion.

 

[Rob500]

Thanks Guys. That's a great help and eases my now increasing 'bicycle paranoid mind'