Rob123

I just bought a bike and the tyres are a little worn and have decided to change them.

When I looked at the size the front is 700x23 and the rear is 700x25.

Is this a bad thing, should the tyres always be the same size. What is the recommended set up?

It is a Boardman E4P road bike.

soyabean

No, as long as the tire is not too oversized for the rim width.

Rear tires take more wear than the front, and many folks often put a slightly wider tire.

It doesn't even have to be the same brand.

It just have to be a good tire you like.

Iride01 

It's unlikely you are going to put too wide a tire on that rim without first maxing out the size tire that will fit in the bike frame without rubbing the seat tube, or other parts of the frame.

23 to 25 mm isn't even enough difference to sneeze at. While many want their tires to be the same size, same brand and same model of tires, there is no issue doing your own thing if it pleases you.

You aren't planning to ride down hills at 60+ mph (≈ 96 kph) are you? If not, you'll be safe enough.

Rob123

I guessed it wasn't much of an issue. I just wondered why they would do this more than anything. I the was some kind of perceived benefit. I had intended to just change the tyres and have the same size, never thought about it until I realised they were actually different sizes.

Thanks for your replies.

Andrew R Stewart 

I don't think rider speed has much to do with whether the rear tire being about 8% wider than the front and rider safety. Just look at motorcycles, they often run wider rear tires and go a lot faster than 60mph.The vast part of safety in real life riding is controlled by the rider's decisions and skills and not their equipment.

I've run about a 3 or 4mm tire width difference on many of my bikes over the years (25/28 and 28/32) and only appreciated the slightly greater comfort and traction the wider rear tire offered.

Of course this flies in the face of what BMX racers did for decades (and still might...) with running the skinnier tire on the rear. Their thinking had been (again might still be) that the skinnier tire is faster to spin up to speed on and if they were to loose traction with one tire it is "better" for the rear to slide. Andy

base2 

Orthodoxy says to: "Put your best foot forward." It says this so that the rear is always the oldest most worn/fatigued/riskiest tire.

Other people who simply have switched tires frequently enough to have any perceptible wear sometimes put the more worn tire on the front to equalize wear on the set. Same as is done on cars. The reasons could include cosmetic (tan/black sidewall, or tread pattern, for example), availability of an exact match, a desire to have a summer/winter set, a desire not to brand switch one wheel at a time, etc...

This is a contentious topic here on BF. Most people in Camp 1 will spout Orthodoxy & ignore that nobody in Camp 2 is suggesting to put a worn-out tire on the front, (because that would be actual dangerous; Camp 2's position is only the "more worn of the two, as condition allows.") Camp 2 will try & lose to Camp 1 as they write 40 posts trying to articulate a deference to the individuals ability to think, to rationalize, & reach an appropriate conclusion based on the available evidence.

KerryIrons

Actually, rear tires are pretty much the only tire that wears, assuming that by "wear" you mean loss of rubber from the tread. Tire wear is caused by the scrubbing action of power being transferred from the tire to the road. Only when braking does this happen on the front tire. I once left a front tire on for over 6,000 miles and it had lost only a gram or two of weight. Two rear tires were worn down to the casing in that same number of miles and each had lost nearly 15% of their weight in tread wear (around 30 grams from each tire).

Iride01 

When I went from 23mm tires to 25mm tires, I didn't replace them both at the same time. I replaced the one that needed replacing. Back tires wear more than the front by quite a bit. While it is proper to put the best and newest tire on the front, I don't really ever worry about it unless there is some other pending reason for me to dismount the front tire.

70sSanO

You’ll never know why unless you ask the person who installed the tires.

”Theoretically” a narrower tire steers easier, although I have my doubts about a 23 vs 25.

A SWAG, as already stated, is that the rear wore out and the former owner decided to use a 25.

The ironic part of this is 23mm and 25mm tires are not the same size from mfg to mfg. you might even find the 23 is wider than the 25.

Many, if not most, people opt for the widest tire that will fit (within reason of how the bike is used), so going to 25’s front and back is fine. There will be those who say 28’s if they fit. I imagine few will recommend 23’s these days.

John

Bill Kapaun

My "grocery getter" has a 26x1.25" front and a 26x1.6" on the rear by choice.
I'll put up to six 12 packs of soda pop on the rear rack/baskets to go with my 200+ lbs.

JanMM

One of my bikes has 406-32 front and 559-40 rear tires. I’m ok with different sizes on a bike - all the bikes I ride have 20” front and 26” rear wheels. Keep in mind there may be a touch of what seems like OCD playing into matching tires or having QR levers on the same side, etc.

SoSmellyAir

Maybe the bike belonged to a Fremont Tesla worker.

Tesla Is Dangerously Messing Up With Tire Assembly - autoevolution

SoSmellyAir

I am intrigued. Is this a chopper? Photo?

urbanknight

My dad ran 25 in the rear and 23 in the front way back in the day. He had heard that it was a good idea since the rear tire took more of the weight, and he pointed out that the 25 deflected less for the same air pressure than the 23. I didn't see why that was so important, but it's obviously one reason people did it.

JanMM

No....not a chopper. I ride two different short wheelbase recumbents and also a recumbent tandem.

LeeG

Recommended set up is what works for your weight and riding conditions. As mentioned there’s enough size variation between manufacturers for the same printed size on the tire so as to be meaningless. I’d be more inclined to pick a light sticky supple tire on the front and heavier more durable tire on the rear. Rear flats are more common and recovering from a rear wheel slide is easier than a front wheel slide.