mrtrinh

So I know the benefits of having wider tires on a wider rim but how about wider tires on a narrow rim? Will I get less rolling resistance? Specifically asking about 25mm GP4000 on ultegra 6800 wheels. I guess I've been spoiled as I've always had wide rims and tires since I started cycling 2 years ago. Picked up a set of ultegras and debating what tire size to go with. Can I still run a lower PSI if I run 25mm on the ultegras? 145lbs and currently running Boyd Carbon 44 clinchers with 25mm GP4000s at 85 and 90.

TimothyH

Aerodynamics are best when the width of the tire matches the width of the rim closely.

All things being equal (same pressure, wheel, rider, bike, riding conditions, brand/model tire, etc.) however, a 25mm tire will have less rolling resistance than the equivalent 23mm tire.

I put brand new 23mm Vittoria Rubino Pro III Slick tires on wheels with 17.2mm inside width. I then put the 25mm version of the same make/model tire on the same wheels and it felt noticeably easier to pedal and ride. I felt the difference as soon as I started to pedal.

You should be able to lower the pressure a little bit when going from 23 to 25 but that is something you will have to determine for yourself. The width of the rim won't affect this.


-Tim-

rms13

Here is an interesting read:

THE RIGHT TYRE WIDTH ON THE RIGHT RIM WIDTH - Engineerstalk : Engineerstalk

Their tests show that 23mm tire on 25mm rim is more aero than 23mm tire on 19mm rim but 25mm tire on 25 rim is less aero than the 23mm tire on 19mm rim. They also found that tire width has a lot more influence on rolling resistance and comfort than rim width. You get 15% increase in air volume going from 23 to 25mm tire on 17mm rim and only 2.2% increase going from 17mm to 19mm rim with 25mm tire.

In the real world, I have ridden 23mm tires on narrow rims, 25-28mm on narrow rim, 23 and 25 on 25mm rim and 28-40mm on wider rim and I feel like 25-28mm tire gives me the best ride on road regardless of rim width

mrtrinh

wow great info thank you!

chaadster

Handling is also a factor, and a wide tire on a narrow rim can exhibit sidewall flex, allowing the rim to shift across the contact patch, giving a sloppy feel. I hate it; the worst offenders I ever had were Michelin Pro Optimum 25c on Velocity Aerohead rims, which were 14mm internal, I believe. Those felt imprecise and uncertain.

aubiecat

I run 25mm GP4000s on Ultegra 6800 wheels and I like the combination. I just did some mountain riding the last two weekends with steep curvy descents and the performance was as good as I can ask for, even with running 95psi in the rear and 85psi in the front.

mrtrinh

If you don't mind me asking how much do you weigh? Any issues mounting the tires? 6800 wheels are a PITA.

aubiecat

I weight 174 lbs. I had no trouble getting the tires onto the wheels and I do it without tools. The thing about mounting tires on Ultegra wheels and all other wheels for that matter is to take your time. Keep the bead of the rest of the tire in the deep part or middle of the rim. That will give you just enough slack to work that last little bit over the edge of the rim. The tire will relax as you go.

jamesdak 

Hmmm, I weigh about 180 right now but will ride my GP4000s 700 x25c at 80/90 F/R up to 190 lbs. I don't have any pinch flats even on the rough chipseal roads I ride on. I run these tires on multiple bikes with wheelsets that range from around 17mm to 24mm inner width at these pressures.

Fiery

Nobody talks about the shape that the tyre takes when the rim width increases. -Mavic

Funny, tyre shape is one of the main things I see being discussed when talking about wide rims - it's right up there along with the aerodynamics in my experience. But then, Mavic not producing wide rims might be a factor in how they decide to present their research.

It is still an interesting article though. Thanks for sharing.

mooder

What a crappy test. No methodology?!?! What did they smoke? I might sound picky but this is VERY basic. The graphs are so amateur, it looks like a college work. They tested only 2 tire width? How many test have they done? How many models? Honestly, these results are very dodgy. The Crr they have for both 25 and 23 is VERY close and you can't even guess the proper value since their graph is so badly made (improper graduation & only 1 pressure compared). It really looks like it could be within the error margin that they didn't include by the way.

chaadster

Yes, me too, and that's what I was talking about when I brought up handling earlier: the "lightbulb" shape the rim and tire make when using a wide tire on a narrow bsw rim is inherently less stable than a pairing which produces sidewalls more parallel to the brakewall.

StanSeven

Even though the 25s felt easier, they weren't any faster. If you check out some of the test data, the difference is extremely small (generally an insignificant amount)

popeye

Very true and surface and rider weight also enter into the equation.

Homebrew01

Unless you are within milliseconds of placing top 3 in a time-trial, most of this stuff makes no difference. Get tires that are comfortable.

Mt. Tam

Another thing to consider is whether or not you'll have sufficient caliper clearance to take a wheel off. The Ultegra wheels have a 20.8 external width, so the 25mm's should clear in the open position. Unlike my mistake of putting Marathon+ 28's on Weinmann Dp18's with external width of 18.7. Brake pads have to come off to service a wheel.

TimothyH

I never said they were faster. I said they were easier to pedal.

To be clear, I've read the articles and looked at the data, then actually purchased two pair of tires and tried them back to back to see for myself. Vittoria Rubino Pro III Slicks in both 23mm and 25mm. Same bike, same wheels, same pressure, same tubes, same day... Tires were swapped twice just to make sure. My recommendation is to forget the articles and try two pair back to back. There is a noticeable difference in ride quality and pedal effort. That's my experience.


-Tim-

StanSeven

But easier to pedal means less resistence. You are putting out less effort to go the same speed or going faster if the effort is constant.

I think what happens is the added comfort and feel of the wider tires results in a smoother ride that people can feel in the pedal motion.

Willbird

A careful roll out test (is that the proper name ?)with gravity as the only power would show a lot more than "pedal effort" ?

v8powerage

That's what I have now 25 on mavic it rides rather well I think narrower the rim the more round the tyre will be and that's a good thing, it's very comfortable and easy to go uphill that's what matters the most for me.

Bah Humbug

Yeah HED talks about it a lot, and has for years.

Bah Humbug

It also depends on the surface - the rougher the surface (nasty chipseal) the bigger the advantage of bigger, lower-pressure tires.

wphamilton

I've got Rubino Pro II - 25's on my road bike and 23's on my single speed. At the same pressure I can't feel any difference, but at slightly lower pressure the 25's feel better. (wider rim on the SS though)

I haven't tried testing for rolling resistance, mainly because that's kind of difficult to measure for small differences.

msu2001la

I use 25mm GP4000s on Ultegra wheels. Other than being a pain in the ass to get them (or any tire) onto those wheels, they work just fine.

I tend to run them around 90-95psi. I weigh about 165lbs. I have no idea if they are more or less aero than 23's (the Ultegra wheelset isn't super aero anyways), but they are a little more forgiving and comfortable over rough roads, and I seem to get fewer flats.

gsa103

That was my problem as well. I tried 25mm tires on some older 19mm (external) width Bontrager rims. With any aggressive braking or cornering the tires wallowed so badly that I wound up inflating them to the same pressure I was running 23mm tires at.

With the modest width Shimano C24 rims, 23mm tires feel pretty good. I'm only running 75/85 psi so I don't have strong desire to go wider.