kathy_cocker

I wonder if anyone can help, I have 27 1 1/4 wheel rims. At the moment the back tyre is a 27 1 1/4 and the front tyre is a 27 x 1 1/8. I'd really like to invest in a pair of 27 x 1 tyres. Not only would they look sleeker , they would (I presume) give me a bit more speed . How would the handling of the bike, the comfort, and the speed be affected by these slimmer tyres?

Any advice on whether this is possible? Or would I need to buy new wheels AND tyres?

Cheers.

mjolniir

Speed is affected by the:
Size of the engine, (that=how fit you are)
rolling resistance of the tires (how smooth and how pumped up the tires are)
body position of the rider. (back = flatter then faster)

I have bought a lot of different tires for my bikes, I can say that the thinner the tires, the faster it feels. I still seem to get the same places in around the same time.


So, speed is one thing. All things being equal, thinner tires should be less rolling resistance. You'd also have to pump them up harder to get this. Comfort will go down. Handling is kind of a push, it will be different, but better or worse I can't say.

If in doubt, do what I do, buy them anyway and see how they feel.


by the way. tires should fit, provided they're both ISO 630mm. Have fun, you fast thing you.

kathy_cocker

Cheers! I will do just that!

Whooooosh (that's me on the new tyres!).

Bill Kapaun

I'd suggest buy just one to start and put it on the front. Reason being, is the smaller tire will transmit a lot more road vibration to the hands. It may be more than what you want to put up with.
If it is, transfer it to the rear and go slightly bigger on the front. IF NOT, go ahead and get the second.
Also, getting one will still give you an idea if you are faster.
Keep in mind, that going smaller on the rear will also gear you down a bit and make pedaling easier. It's only about 2%, but that's about 1/3 of a tooth equivalent on your top cog.
That may make you THINK you are going faster. A speedometer will tell the story there.
OTOH, if your cadence is a bit slow, it may help put you in a slightly more efficient range.
Let us know how it works out for you!

cny-bikeman

I would not feel too secure on turns with that big a disparity between tire and rim width. I would bet that the time in your dealing with this question online, plus purchasing and then mounting the tires would result in much higher speed if put into riding instead!

Bill Kapaun

I hardly consider 7MM difference a "big" disparity! 27" rims tend to be pretty skinny anyway.

cny-bikeman

Well, a true 27x1 1/4 rim is not very skinny, and 7mm is 20% smaller than the tire width for which the rim is designed. Not only turns but impact protection will be compromised - as you indicated in reference to a smaller diameter with the 25mm tires. The 25mm tires have less height by design and when put on a wide rim they will sit even lower. I would recommend against going below 1 1/8 width, especially as many manufacturers push the lower limit of a given tire width so that their tires appear lighter than others of the "same" width. Check Sheldon's page on tire/rim width.

Bill Kapaun

I'm quite familiar with Sheldon's tire size chart and see absolutely no problem.
People routinely use 26x1.25" & 26x1.5" street tires on rims that came with 1.95-2.125" tires with no problem. That's a bigger % change than 1-1/4" to 1"!

Retro Grouch 

I don't think so.

1. If everything else is equal, a wider tire will have less rolling resistance because it has to deform less at the contact patch on the bottom.

2. Everything else is never equal. In this case, you generally have to use more air pressure in a skinnier tire to keep from pinch flatting. The greater air pressure will result in the tire deforming less at the bottom and make the rolling resistance equal to the wider tire.

3. Pumnping up tires ultra hard makes them feel faster but doesn't necessarily make them faster. They feel faster because they because they bounce around more over bumps. Unfortunately, that bouncing uses energy that you have to provide that lifts you up vertically rather than horizontally down the road.

meb

As Bill pointed out, it's in the compatibility range acceptable per Sheldon's tire chart, but I'd be uncomfortable going thinner to 7/8 inch tires.
I've got a bike that had the rims and tire combination the OP enquired about.
Handled fine, I did have a few pinch flats but I'm 230.

I've been converting that bike into a reliable commuting tank, with reliability gained at the expense of perfromance. Accordingly, I've replaced the wheelset with 48 spoke tandem wheels, and have gone to 27 x 1 3/8 tires. But I suspect the OP is much lighter than I, so 1 inch tires are less of a concern.

Bob Dopolina 

Interesting information about rolling resistance and contact patch:

Continental did some testing a few years ago to address these very issues. They tested ties from 18c-28c. They used the same tires (thread count, compounds etc) at the same pressure under the same lab conditions and discovered that 23c was the fastest size. It is actually a mixed calculation regarding the area of the contact patch and the amount of energy lost when a tire encounters an obstacle (the bending around small things like gravel or imperfections in the road).

The average size of a contact patch is about the size of a dime (this obviously varies with tire pressure and rider weight, but, like I said, it is an average). It is a long, thin oliptical area a few cm in length. They also concluded that tread patterns made absolutely no difference to traction. There was no displacement of water under any conditions.

Some useful information for you all.

kathy_cocker

Now I'm really confused. So, if I wanted 27 x 1" tyres, what rim size would I need? I mean the tyres must be designed for a certain size rim. I must admit I presumed that 27 x 1 1/4 rims were pretty standard and didn't realise that 27" rims went any smaller. I suppose that in terms on width (if you look at the tyres in terms of mm), I would be going from approximately 32mm to 25mm, which is only a 7mm difference. Considering that my current tyres (looking at the wheel front on) seem to come over the rim slightly, surely thinner tyres would just be flatter against the rim?

At the moment my back tyre is the thicker one (1 1/4) and my front one is the thinner (1 1/8). Would it be worth swapping these round to get better speed? To tell the truth the tyres are pretty damn old anyway, so I will need to replace them soon-ish. Just need to know what my best option is.

meb

I doubt you'd perceive any speed gain/loss in swapping those tires.
Since you have more weight on the rear, you probably get a better ride with the wider tire in the rear.
A wider tire up front would give a little more protection against slipping on loose gravel or more protection against pinch flats against a chuck hole or curb.

If you look at Sheldon's chart at the bottom of the page, you have a 12-16mm window of tire widths acceptable for a given rim, so there is no mismatch problem with the 1 inch.
Since your a female, I assume you likely are below 180 lbs, so pinch flats on 1 inch tires are not going to be a huge concern.
Sounds like for your straightline speed over comfort objective the 1 inch is the way to go.

My option to go wider was dictated by my desire for reliability when commuting to work-the heavier tandem wheel increase reliability but adversly impact performance. I've also gone to stronger steel drop bars replacing the lightweight French Atac aluminum bars that snapped when I hit a bump on the bike trail.



https://www.sheldonbrown.com/tire_sizing.html

cny-bikeman

"Now I'm really confused" That's a good sign - only narrow-minded people suffer no confusion. It's a necessary transition between being uninformed and being truly knowledgable.

OK, here's my perspective. As you can see from the above three comments you don't get something for nothing when it comes to tires (or anything else). A narrower tire will be lighter and easier to get past the brakes to mount and dismount the wheel, will very likely take a higher pressure and will tend to perform better on turns (when matched with an appropriate rim). Those are the only solid advantages. You can't count on rolling resistance to be lower or for them to be faster on all but smooth roads, as noted above. The disadvantages are more tendency toward flats, more difficulty in mounting and preventing tube pinches, and a harsher ride.

"Considering that my current tyres (looking at the wheel front on) seem to come over the rim slightly, surely thinner tyres would just be flatter against the rim?"

Actually, NO. As you can tell from Sheldon's chart, how well a 27x1 works depends on interior rim width. I would agree with his assesment, even though conservative. 27x1 1/4 can be up to 20mm in width (inside) and I would absolutely not put a 27x1 rim on one of those. A narrow tire will spread out on a wider rim, and by design it already will have less height than a wider section tire, so you will have very little distance between your rim edge and the road surface. In that scenario you not only are assured of more pinch flats but also possible impact damage to your rim.

There is no way for you to accurately measure the effect of the 27x1, you just have to try it. Given you preference for better speed/performance I would suggest an upgrade to a wheel/rim with an interior rim width of 15-16 mm. that way you're in the center for both 1 1/8 and 1 inch tires. I've found problems with the super narrow rims. If your current rims measure more than 17mm inside I would recommend against using 27x1 at all. Get a pair of 27 x 1 1/8 tires that will take 100lbs instead. I found some very good kevlar tires of that size at Performance on sale for $9.99.