28mm vs 25mm tires

Fzs1000n

Hi all, this may have been discussed before,,,,prob plenty, so here goes again:

I've got a Bontrager wheelset 19.5mm internal rim width. Had 25mm tires on them and was really happy with cornering ability.
Same tires on a former wheelset 16mm internal and the cornering feel was never right but these wheels with 23mm tires they were great. Tires were Schwalbe One's

Now on the Bonty's I fitted Pirellie P Zero 4S 28mm and the cornering at the limit is unstable and a huge backwards step.

I feel it's not that there' anything wrong with the Pirelli's rather the light bulb effect with running 28mm, i'm sure it's this.

I re-fitted the 25mm Schwalbe's to Bonty's 19.5 inner and even though tires well worn the handling a so much better. I feel this size match is ideal.

The extra compliance of the 28mm was nice and was the braking with more lever needed to lock the rear ,,,,but corning is paramount for me

Amy thoughts on 25 vs 28 with regards to inner rim width. I'm not hugely experienced with this topic but any comments / feedback with others experiences would be interesting.....

thanks all

Killerclown

A major benefit of running wider tyres, is the reduced pressures you can run, without pinch punctures ( if you’re not on tubeless obvs.)This comes with the payoff that a wider tyre, with a lower pressure on a rim with a smaller internal width, can roll about laterally / flop ( for want of a better term ). A lot of wheel manufacturers have moved to increased inner widths, because of this. Some of the latest Mavic offerings ( for example ) have increased the inner widths to try and alleviate any effects, when running bigger tyres.

cycleclinic

the OP rims are wide though. there is no light bulb here. The OP is not comparing the same tyres. the fact they are different widths is not relevant asa 28mm pireeli may size the same as a 25mm schwalbe one. they are different tyres so what the OP is feeling is the fact the pirelli's may not be all that.

I personaly cant stand schwalbe road tyres. The handling i think is poor. Schwalbe one tubeless in the wet are effing dangerous compared to other tyres i use. In the dry there are O.K. Same compound as on the one clincher. so it just goes to show different people experience different things.

Fzs1000n

I m measure the Schwalbe One 25 at 27.2mm at 90psi
Pirelli's are off now but visually they looked considerable larger

At the part of the contour of the tire which in contact with the road when leaning as far over as I dare the profile on the Pirelli's droped off quickly giving a smaller radius at this section

With Schwalbe One 25 on same inner 19.5 rim at this same lean angle the profile is a longer radius and feels far more secure

I guess the ultimate test will lie with same model tire in both 25 and 28mm

I would bet the 25mm on this rim has the potential for faster cornering in a controlled test,,,and from my own experience plus the simple the maths of it with regards the radius contact shape at the aprox max lean angle a road bicycle can do.

First.Aspect

Its quite a personal choice. I find 28s too large. You lose road feel. 23s can feel okay depending on brand. 25s are perfect.

As much as anything the benefit of 28s (lower pressure more comfort) is exactly the same as what gives rise to the main disadvantage. Even if you pressure them up there's just more air volume and the feel is not quite right.

This really doesn't bother some people. But it bothers me. OP should just stick with 25s. And there is nothing wrong with 23s either if that's how you like your bike to feel.

N0bodyOfTheGoat

It might be the Pirelli sizes big, just like Continental GP4000S IIs, where 700x28mm variants measure ~31mm wide on modern rims with internal rim width ~19mm+. In which case, the Pirelli or GP4000 700x25mm variant might give a less "bulb-shaped" fit.

Killerclown

NitrousOxide wrote:

It might be the Pirelli sizes big, just like Continental GP4000S IIs, where 700x28mm variants measure ~31mm wide on modern rims with internal rim width ~19mm+. In which case, the Pirelli or GP4000 700x25mm variant might give a less "bulb-shaped" fit.

I have the Pirellis on one of my bikes, they are a bit bigger than billed.

Killerclown

Are your inner tubes the correct size?

svetty

I'm not an expert on Pirelli tyres but the 4S moniker sounds as if they are all-year all-rounders and not performance tyres?

PhilipPirrip

You don't happen to be riding with 35kg in a rucksack by any chance?

nachetetm

Before discarding the Pirellis I would experiment a bit with the pressure. My experience is that different tires, even with similar widths, respond differently to the same pressure. The comments about the Pirellis is that they are very soft and comfy, so to have a sharper handling they may need a bit of extra pressure.

Fzs1000n

Killerclown wrote:

Are your inner tubes the correct size?

actually they are 23-25mm tubes. Surely with 85 psi or so this would negate the mismatch?

I did notice when pumping up the 28mm tires I could feel through the tire the tube has reached a point where it began to expand and the sidewall hadn't yet compressed but a few pumps later the gap disappeared as expected

Fzs1000n

Svetty wrote:

I'm not an expert on Pirelli tyres but the 4S moniker sounds as if they are all-year all-rounders and not performance tyres?

Sure. according to the Pirelli website the all rounder (4s) and the normal P Zero use the same compound. 4s has a deeper thread and more grooves. I can't imagine the two would be that far apart feel wise

dstev55

Definitely not the width of the rim being the issue here.

I run Vittoria Corsa G+'s on 19mm internal rim width albeit 27mm external width and have no issues with the handling at all. Used to run 25mm tyres and find the 28mm tyres to feel more safe and secure at the limit and less skittish over bumpy surfaces.

SJH76

Having run Bontrager wheels a fair bit in the past, I found the best tyres to run on them were Bontrager themselves. Both the R3 and more expensive high end R4 are exceptional tyres and are optimised to run on their own rims in the same way Mavic and Zipp do with their respective setups. They will probably have a better idea at what a 25mm or 28mm performs like on their own line too instead of 3rd party rubber.

Fzs1000n

dstev55 wrote:

Definitely not the width of the rim being the issue here.

I run Vittoria Corsa G+'s on 19mm internal rim width albeit 27mm external width and have no issues with the handling at all. Used to run 25mm tyres and find the 28mm tyres to feel more safe and secure at the limit and less skittish over bumpy surfaces.

The Schwalbe One's 25mm measure 27mm at 85psi,,,, at a guess the Pirelli 28's would measure 30mm perhaps (they looked about that much bigger before removing them) someone who's got them fitted could confirm actual witch also advising rim width

whatleytom

As mentioned different tyres size up very differently. I've measured a few recently with verniers. GP4000 25mm measure in at 28mm, whereas Corsa G+ 28mm actually measure up as 28mm. Obviously to a degree depends on your rim bed width too, but no surprise people feel GP4000s in 28mm feel too big.