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Best tyre shape for cornering grip

This forum concerns road bike tyres.

Hello, so recently I've put on a rim with an internal width of 19mm and 25mm conti tyres which ended up measuring 30mm wide when fitted and the shape of the tyre is pretty much a 'vertical' U-shape with no bulging. 

How would this compare in terms of cornering grip to a narrower wheel (say 15mm internal) with the same tyre fitted, resulting in a more bulbous tyre cross-section? Which is better?

If you're new please join in and if you have questions pop them below and the forum regulars will answer as best we can.

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20 comments

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Argus Tuft | 4 years ago
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I have 2 sets of wheels - one 15 mm and one 17 - used on the same bike for a 30k round trip open road commute for 5 years.Average moving speed around 30ks.I run 23s on the front and 25s rear at 85psi.

On the right day if I concentrate hard I can detect a slight difference in ride quality.Not better or worse just different.

There's nothing in it.

 

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Argus Tuft | 4 years ago
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I have 2 sets of wheels - one 15 mm and one 17 - used on the same bike for a 30k round trip open road commute for 5 years.Average moving speed around 30ks.I run 23s on the front and 25s rear at 85psi.

On the right day if I concentrate hard I can detect a slight difference in ride quality.Not better or worse just different.

There's nothing in it.

 

Avatar
Argus Tuft | 4 years ago
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I have 2 sets of wheels - one 15 mm and one 17 - used on the same bike for a 30k round trip open road commute for 5 years.Average moving speed around 30ks.I run 23s on the front and 25s rear at 85psi.

On the right day if I concentrate hard I can detect a slight difference in ride quality.Not better or worse just different.

There's nothing in it.

 

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matthewn5 | 4 years ago
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Whatever anyone says, wider rims are miles more comfortable. Running a 23 on the front on 18.5 wide internal rims on two bikes now, absolutely zero problems of any description.

I'm normally quite skeptical about 'innovations', but this one works.

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susurruspeanut | 4 years ago
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madcarew, as it happens I was talking about cycling on ceilings specifically.

Jokes aside, do you have any evidence to support your theory? When you're cornering and leaning a lot, the rounder tyre will probably deform and the tyre shoulder that's nearest to the ground may end up being near 'vertical' (if we take the wheel as the point of reference), so I wonder how this comes into your theory.

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madcarew | 4 years ago
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The OP asked "What tyre shape is the best for cornering grip.?" The answer is, incontovertibly, "a round shape at correct inflation". With a round shape you have the most contact with the road at all lean angles, and the most predictable cornering as there is no 'shoulder' to lean over. and a 'round' shape is more stable (not so tall) as a 'U' shape. So, whichever tyre gives you the roundest shape at your preferred inflation is the best shaped tyre for cornering.

PS, if you have an upside down 'U' shape as described by some, you may just be cycling on the ceiling!

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CXR94Di2 | 4 years ago
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Having used my DT Swiss built wheels with 20mm internal width with 25mm Schwalbe Pro Ones in tubeless setup for several tours in Tenerife.  I can say they work and grip absolutley fine, inspire confidence for more lean.  Those who know Tenerife for riding can confirm the Volcano descents can be extremely fast with switchback bends one after the other.  At no point did I feel my tyres where squirming underneath me- due to using a wider rim .  I also made a full wet weather descent 2 weeks ago, rivers of water down the roads-again my setup felt very secure with no issues-obviously extra caution was taken.   

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BehindTheBikesheds | 4 years ago
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I've been running 32mm Specialized Borough Pro CX folders on the rear of my commuter for about 7 years, that's on an Open 4 ceramic currently and an open Pro ceramic before that, the Open 4 is particularly narrow. All up my minimum bike/bags etc + me is 113kg, often in excess of 125kg. I've been able to take the right hander at the mini roundabout 200m from home at 17/18mph amongst many thers. I've worn out two in the centre, no sidewalls issues, I've got two left incl the current one, going to go with the Jack brown Blue when they're through, I've been using the JB on the rear of my audax/tourer.winter racer which also has an Open pro, again no sidewall problems.

These aren't particularly heavy duty tyres, the Spesh is a 350g job with knobbles on the edges, very thick tread in the centre but very pliable sidewalls so if narrow rims with wider tyres was going to show up as problematic then it certainly would with my weight+ use, maybe you've been unlucky or are underinflating. 

 

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VeloUSA | 4 years ago
3 likes

Here's my experience: The bulbous (incandescent lightbulb looking) tire has weaker sidewalls. This is caused by the bulbous outward push on the sidewall. I took a downhill corner at 20+ MPH I could feel the front tire roll and losing grip which forced me to back off speed. Back home inspection verified what I felt. (Before I rode the decent, I rode thru a patch of dusty dirt so I could visually see where the tire was making contact)

Same Zipp Tagente tires mounted on 20.5 ID x 24 OD rims had no roll. Cornering speed increased 10 MPH. PSI @ 80 front and 85 rear was a little squishy so I increased PSI to 85x90. Cornering speed increased 5 MPH over the previous with solid grip.

So yeah, IMO a near vertical sidewall to brake track is spot on.

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shay cycles replied to VeloUSA | 4 years ago
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VeloUSA wrote:

Here's my experience: The bulbous (incandescent lightbulb looking) tire has weaker sidewalls. This is caused by the bulbous outward push on the sidewall. I took a downhill corner at 20+ MPH I could feel the front tire roll and losing grip which forced me to back off speed.

The problem there is almost certainlt tyre pressure rather than profile - your pressures are lower than the minimum in the tyre spec and a very long way below the max. Too low tyre pressue will always cause that kind of issue.

 

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VeloUSA replied to shay cycles | 4 years ago
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shay cycles wrote:

VeloUSA wrote:

Here's my experience: The bulbous (incandescent lightbulb looking) tire has weaker sidewalls. This is caused by the bulbous outward push on the sidewall. I took a downhill corner at 20+ MPH I could feel the front tire roll and losing grip which forced me to back off speed.

The problem there is almost certainlt tyre pressure rather than profile - your pressures are lower than the minimum in the tyre spec and a very long way below the max. Too low tyre pressue will always cause that kind of issue.

 

My bad, I should have noted the PSI with the narrow rims were 105/110, not below minimum.

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BBB | 4 years ago
1 like

Lots of throwback nonsense here. 

I run 28mm tyres on 25mm INTERNAL rims. The bike corners like on rails. 

Quite a number of road rims have internal width of about 20mm or more and 25mm tyres are a perfect match for that. Sidewalls are better supported so less pressure is possible for the same effective width. 

Don't be stuck in the ETRTO matrix world, people.

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BehindTheBikesheds replied to BBB | 4 years ago
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BBB wrote:

Lots of throwback nonsense here. 

I run 28mm tyres on 25mm INTERNAL rims. The bike corners like on rails. 

Quite a number of road rims have internal width of about 20mm or more and 25mm tyres are a perfect match for that. Sidewalls are better supported so less pressure is possible for the same effective width. 

Don't be stuck in the ETRTO matrix world, people.

You might think it corners on rails, however having a U shaped tyre as per the OPs description means that the rim is NOT suited to the tyre.
and what exactly is the 'quite a number', how many of those that are equipped with a 20mm internal bead are running 25mm clincher tyres, probably a tiny %.

We've already seen the fallacy of wider tyres are faster being exposed in real world use/real world pressures, maybe having very wide rims will save you a small % point in aero terms so that the tyre is closer to the ri width but the reality is that stretching tyres far beyond their design spec means you are getting distortions that are not good for the tyre nor good for efficiency. Or are you saying that a tyre that has a U shape is ideal?

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hawkinspeter | 4 years ago
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The amount of rubber in contact with the road is going to be mainly down to the tyre pressure which is not going to be affected by the shape. The amount of grip is going to be determined by the amount of rubber in contact and how well the rubber conforms to the road imperfections, so maybe the shape can affect how the tyre flexes but I can't see it being a big influence.

Anyone got any figures?

 

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Chris Hayes | 4 years ago
2 likes

You've opened a can of worms here my friend  1 

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BehindTheBikesheds | 4 years ago
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best tyre shape is not the one you have and frankly a 25mm tyre on a 19mm internal rim is ridiculous, just why, 15mm is more than enough, you've already found out that the rim isn't condusive to the tyre size.

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susurruspeanut replied to BehindTheBikesheds | 4 years ago
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BehindTheBikesheds wrote:

best tyre shape is not the one you have and frankly a 25mm tyre on a 19mm internal rim is ridiculous, just why, 15mm is more than enough, you've already found out that the rim isn't condusive to the tyre size.

Yes I agree, I just bought the cheapest spare wheel that was in the shop but it is just too wide for my tyre really...

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susurruspeanut replied to BehindTheBikesheds | 4 years ago
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BehindTheBikesheds wrote:

best tyre shape is not the one you have and frankly a 25mm tyre on a 19mm internal rim is ridiculous, just why, 15mm is more than enough, you've already found out that the rim isn't condusive to the tyre size.

Yes I agree, I just bought the cheapest spare wheel that was in the shop but it is just too wide for my tyre really...

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Simon E | 4 years ago
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In theory I'd suggest that it's the one that puts more rubber on the road. However, the real world difference may be insignificant.

The pressure you run may be a more significant factor and in the end, short of crash-testing each, it's probably the one that feels more secure to you.

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CXR94Di2 | 4 years ago
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Ive got 20 mm internal rims with 25mm tyres. They come out 28mm. They corner fine. I put it down to compound material and pressure. I really doubt anyone could tell the difference until point of loss of grip, but who wants to go that far to find out

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