Today, we hear a lot about “modern rim shape”. What’s behind this is simply wider rims. Some have succeeded in convincing cyclists that a wide rim makes a better wheel and nowadays, each brand launching a new wheel has to make sure its rims are at least 1mm wider than their competitors.

But what they have forgotten in their equation is the tyre. Nobody talks about the shape that the tyre takes when the rim width increases. Nobody talks about what is the right size tyre to put on those wide rims and everybody forgets about safety standards and norms.

So, talking about rim width alone is only doing half the job and it becomes pointless. It’s only when you look at both variables of the equation (tyre + rim) that it makes sense. Performance and safety are also at stake.


2.1 Rim Width

Rim width is measured at 2 points :

  • Outer width (A): most often measured at the brake track
  • Inner width (B): measured inbetween the rim hooks

The outer width (A) will mostly have an influence on the look of the rim, but also on the aerodynamics of the wheel-tyre system. But it has zero influence on the comfort, rolling efficiency or tyre shape.

The inner width (B) is the one that defines the tyre shape, by pinching its sidewalls. It influences the air volume and tyre width.

So, this is really the one measurement we have to look at when discussing rim width to tyre width in the respect of rolling efficiency, comfort and air volume.


2.2 Tyre Width

As we just mentioned, the width (section) of a tyre is directly linked to the rim on which it is mounted. It is also linked to the amount of air pressure.

To neutralise those variables, a norm defines how a tyre section should be measured. This norm called ETRTO (European Tyre and Rim Technical Organisation) has defined all the safety and performance parameters that a tyre and rim should respect to be compatible with one another. Although the name says “European”, this organisation’s work is the reference for all international and national norms in the bike industry (ISO, CEN and their national declination).

To measure a tyre section, ETRTO has defined:

  • The rim width on which each tyre section must be measured
  • The pressure at which it must be measured, taking into account that the casing of a brand new tyre will stretch within the first 24 hours of inflation, so the measurement should be done after those 24 hours

For example, a tyre said to be a section of 23mm should be measured on a rim of 15mm internal width at 6 bars (87 PSI) after 24 hours.
A tyre said to be a section of 28mm should be measured on a rim of 17mm internal width at 6 bars (87 PSI) after 24 hours.
Only the casing of the tyre should be measured. If the tyre has side knobs or an extra rubber layer down on its shoulder, this should not be taken into account.

But at the end of the day, it’s the manufacturer’s responsibility to indicate the right dimension of the tyre and one should always be able to rely on those indications so the tyre choice can be made safely.


3.1 How the tyre section influences the rolling resistance and the tyre pressure

To increase your speed for the same effort, the Rolling Resistance Coefficient (Crr) must be as low as possible.
Our measurement shows that the Crr decreases when the tyre pressure increases:

However, the Crr decreases when the tyre section increases. The graph bellow shows that at equal tyre pressure and rim width, the Crr gap between a 23mm and a 25mm tyre (for a given tyre) is about 0.3/1000:

So, when reading the 2nd graph in light of the 1st one, you can see that this 0.3/1000 gap is equivalent to a pressure difference of 1.5 bars / 22PSI.

In short, the Crr of a 23mm inflated at 100PSI, is the same as that of a 25mm tyre inflated at 80 PSI.
While increasing the tyre section, the rolling resistance is maintained, while hugely improving your comfort.
And if your goal is to lower your rolling resistance, you can just go for a wider tyre and keep the same riding pressure.

The same would go with even bigger tyres (28mm) but then weight and inertia will come into account and there will be a trade off between rolling resistance, low inertia and weight.


3.2 Better ride quality with both wider rims and wider tires

The “ride quality” is influenced by many factors and cannot be reduced to just one single number. It’s more a question of “feeling” and, as such, it is a personal matter and doesn’t have just one universal definition.

However, in most instances, cyclists refer to ride quality in terms of comfort and high “speed to effort” ratio.

The air volume is a good way to look at it.
More air volume means a stronger protection against snakebite, by increasing the distance of the gap between the ground and the rim edge.
As a result tyre pressure can be lowered to improve comfort and traction without increasing the chances of pinch flats.


So, how to increase the air volume? Here are few measurements:

Width Width change Air volume difference (mL) Difference
17mm rim Tyre 23–>25 144,25 15,0%
25mm tyre Rim 17 –> 19 24,04 2,2%

A 2mm increase of the tyre width alone has a much higher impact (+15%) than a 2mm increase of the rim width alone (+2.2%).
And of course, the combination leads to both air volume increases, which is even better.


3.3 Better aerodynamics with wider rims

For a long time the general thinking was that to be faster a part (let’s say a wheel) had to be narrow to reduce its frontal area. It’s true, but this doesn’t take into account real world conditions where the wind doesn’t always blow right in front of the cyclist.

With deep section rims becoming more and more popular it also became obvious that the ease of handling of such wheels had to be improved.

Based on those 2 factors research began to improve the wheel’s aerodynamic performance. Very soon, two facts became obvious:

  1. The tyre had to be part of the equation: you can spend hours developing the right wheels but as soon as you change the tyre the behaviour of the system in the wind changes dramatically.
  2. The best way to achieve amazing aerodynamic performance is to define a rim-tyre shape that is as close as possible to a NACA airfoil profile.

The widest point of such a profile is quite far from its leading edge. On a bicycle wheel, that means that the widest point of the rim-tyre combination must be below the tyre itself. In short, the rim has to be wider than the tyre.

Doing that, the trailing edge radius gets rounder to the benefit of the wheel’s stability in a crosswind.

The frontal drag (at 0° of yaw angle) becomes higher but at every other yaw angle this design lowers the drag and improves the stability of the wheel.

The graph bellow compares two 40mm wheels fitted with the same 23mm tyre. The blue curve is a 19mm wide rim, whereas the pink one is a 25mm wide rim.

The gap is 2,5 Watts in favour of the wide rim, based on our yaw angle weighted law (

But, if you use a 25mm tyre on the 25mm wide rim you’ll be back to the blue curve and even higher since the frontal area has become bigger!

So, widening the rim for aero benefits is really efficient as long as the tyre remains narrower than the rims widest point.

If you think I have a wide rim, so I can ride a wide tyre, thats true but means that youll annihilate the aero benefits of the wide rim. But maybe youre pursuing another goal, like more comfort or lower rolling resistance


Tyre width and rim width have to be made for each other.

If the tyre is too wide relative to the rim width, it will not be well supported by the rim and the ride may feel flimsy. There is also a higher chance of pinch flats.

Equally, if the tyre is too narrow relative to the rim width, it will get a flat shape that is bad for rolling efficiency and ride feel. For a MTB tyre this can result in the side knobs constantly coming in contact with the ground even in a straight line. The tyre will not deform as it is supposed to and the grip and rolling efficiency is no longer guaranteed.

But most importantly, there is a safety issue.

Some tests performed by several tyre manufacturers, including Mavic, have shown that a narrow tyre on a wide rim has a higher chance of severely coming off the rim.

Norms are setting barriers and rules to ensure rider safety. ISO 4210 refers to the ETRTO manual that provides a chart to show which combinations are possible and safe :

This chart says for a given tyre width (left column) which rim widths can be used (middle column for hookless rims, right column for regular rims).

Example of reading: a 23mm tyre can be safely mounted on traditional rims of 13mm to 16mm (internal width). On any rim wider than 16mm, it is not possible to use a 23mm tyre safely.

On the other hand, a rim that is 21mm wide internally, can only accept tyres from 35mm and above.

This is where Mavic and our Wheel-Tyre System helps the rider make the best choice. We deliver our wheels with the tyre that perfectly matches the rim in terms of performance, safety and dimensions.


  • A wider tyre and rim allow for better rolling efficiency while improving comfort
  • A wider rim improves aerodynamic performance (low drag and high stability) as long as the tyre width doesnt increase at the same time
  • Safety is a key item. Norms have defined the working parameters of tyre to rim widths and should always be respected

For safety matters always make sure your wheel and your tyre bear the ETRTO mention and that their sizes match according to the chart in this article.


  • Fascinating!

    But what do you offer at the wider outer rim dimensions to compete with the new fashion of wide section rims.

    I have Cosmic Carbone SLE and i am a big fan. However I see a lot of negative comments about you preference for narrow rim profile and I wonder why. See example below:

    “Although admirably quick in calm winds, the Cosmic Carbone’s antiquated aero profile – it was introduced back in 2008 – is also easily blown around in crosswinds, plus the tyre bed is inordinately narrow. Whereas more modern rims now come with nearly 20mm of width between the bead hooks (thus yielding better ride quality, handing, and aerodynamic performance), the Cosmic Carbone carries on with just 13mm. Unless Mavic has a dramatic redesign coming for 2016, we’d much rather see something more progressive like a HED Jet.”

    That is damning criticism but it seems from your analysis that he has a point…

    • Hopefully you love your wheels and they haven’t become more unstable since you read the Bike Radar article 
      This article is mainly about air volume and tyre / rim compatibility. In that respect, the only rim dimensions that matters, is the inner rim width, as this is the one that condition the tyre shape and air volume.
      When it comes to outer dimension, as we say in the article also, this has only an impact on aerodynamics, and mostly on crosswind stability. But also on weight, in a bad way.
      However, in 2012 and 2013, we’ve been busy designing the fastest aerodynamic wheel-tyre system on the market, the CXR family.
      In 2014 and 2015, we’ve focused our R&D resources on stepping up our Endurance and Performance wheel line, known as the Ksyrium family.
      So, you can imagine what our engineers are busy with at the moment…

  • I use a pair of R system SLR wheels on a full titanium Merlin. (yes forks as well) which gives a superb ride and performance. Can someone tell me if Rim tape is required for these wheels ?I am using 23 mm tyres at the moment but will try a pair of 25mm soon. will give an update later

    • Sweet bike and great match with the R-Sys SLR wheels ! No, rim tape is not needed on those wheels since the rim bed has no holes. Another 15g saved, and exactly where it matters most. 🙂


      • Thank you so much for your very quick reply. They are a delight to ride and I still can’t get over how much more comfortable they are to ride than my old very light wheels. I also have a pair of Elites on my old 531 Brian Rourke which is 80’s but you can’t believe how much difference it made to the performance and the comfort of the bike. They also look GREAT as well

  • Does this take tubular rims and tires into account?
    I currently use two sets of wheels (tubulars). 26mm at brake track (and widest point)/38mm deep and set two is 28mm at brake track (30mm aero width)/56mm deep.
    On the widest rim i use a 23mm tubular and there is no issue holding the tire even though erto must be high. Both these sets rides more stabile than my previous CCU which i found to be best with 22mm tubulars, but still more twitchy.
    Real world riding seems to tell me the widest and deepest of them handles more stabile than my previous shallower and less deep rims. I might be off here, but i find crosswinds and side winds to be the what affects steering and handling the most. Stability seems to be almost as important as aero for reasons of safty and holding speed!? I read as much technical as i can to get an insight of how this works, but for true riding i have nothing negative to say about any of these two sets. The widest and deepest set is my favorite to my surprise.

    •  The topic of compatibility between rim width and tyre width is only a clincher one. Tubular is not affected by this and there is no “internal width” on a tubular rim (no hooks for holding the tyre beads). Indeed, what’s important in a tubular set up is the gluing surface. If the rim is really wide, then, the gluing surface will be dictated by the tubular tyre itself, not that much the rim. Now, if the rim gets too narrow, there might be issues. But we are not aware of any tubular rim that would be that narrow nowadays.
      As far as aero is concerned, only the outside rim width matters and it should be considered relative to the tyre width. From our studies in CFD, wind tunnel and field testing, we found the optimal combination being a 23mm tyre with a 27mm rim (outside width) at its widest point that should be just below the brake track. This is the design we use on our CXR wheels. It has proven to offer super low drag and great side wind stability. Because you’re right, low drag is nothing if you can’t control the bike !
      23mm tyre and 27mm outside width is fairly easy to design on a tubular set up. But much more difficult on a clincher set up. Indeed, the inner rim width for a 23mm tyre should not exceed 16mm (safety concerns, as defined by the ETRTO). As the outside width, needs to be 27mm, this means +11mm, so each rim sidewalls must be 5.5mm thick. Which becomes a tricky and possibly heavy design… Of course, we could use 25mm tyres, but that would increase the aero drag and to maintain the same stability, the rim would need to be even wider (29mm) and the design complexity will still be the same. Not even talking here about frame clearance and brake caliper compatibility…


  • Hi, great article and well written! I’m just a little confused as to the contradicting information regarding the tyre/rim combination benefits when compared to the ETRTO table accepted combinations.

    i.e. Its mentioned at the end of the article ‘For safety matters always make sure your wheel and your tyre bear the ETRTO mention and that their sizes match according to the chart in this article’, however in the aero /yaw angle test you used a 23mm wide tyre on 25mm and 19mm wide rims, both of these combinations are deemed ‘unsafe’ by the ETRTO chart?

    For instance, according to the chart , a 28mm tire is the smallest you can safely use with a 19mm rim and a 23mm tire can only be safely used with a 13-16mm rim?

    I currently have upgraded to wider rims (17mm) and have been researching this topic a lot, according to the ETRTO chart the smallest tires I can safely use on this rim are 25mm, however I prefer using 23mm, which I have read that some cyclists have no problem with but again this contradicts the safety measure.

    I have found it very hard to find a clear answer on what exactly can be used with my new 17mm rims and would love some expert advice on what the generally accepted tolerances are outside of the ETRTO chart?

    Is using 23mm tires on a 17mm rim actually ok as it is only one ‘movement’ outside the ETRTO paraments etc? (i.e. you can safely use 23mm tires on a 16mm rim according to ETRTO)

    In general is one movement outside the ETRTO parameters accepted, or do is there actually a much wider range that can be combined outside the chart with no real ill effects re: safety?

    Thanks and I would love your insight/clarification on this topic, much appreciated.


    • Thank you for your comment.

      First, we have to differentiate inner and outer width :

      • Outer width is used on our aero chapter as this is the parameter that influences drag. So, in that chapter, when we speak about 19mm or 25mm, we refer to the outer rim width
      • Inner rim width is what defines the compatibility with the tyre and the combination with the different tyre width. And this is what the ETRTO chart is all about.

      There is no direct link between inner and outer width. In general, the outer width is about 4mm wider than the inner width. But, in some cases, it can be very different. For example, our CXR Ultimate 60C is 13mm internal and 27mm outer.

      Your reading of the ETRTO chart is correct. When using a 17mm inner rim width, the minimum tyre width allowed is 25mm. It’s the same with a 16mm inner rim width.
      This norm is about safety and guarantees 100% safety if all conditions are fulfilled. It’s been proven that using a 23mm tyre on a 16mm inner rim width can, in some conditions, lead to the tyre coming off the rim suddenly.
      As a responsible and liable company, Mavic cannot put its customer in an unsafe situation, although it might be only a very small proportion of them. So, we cannot recommend set up that are out of the ETRTO / ISO requirements.
      That said, riders can freely decide to take their chance on this…

      But keep in mind that you have many benefits in using 25mm tyres : they roll faster, provides more grip and more comfort. The only drawback is they’re about 15 grams heavier (on the case of Mavic tyres). There is an interest in using a 23mm tyre for your front wheel (if your rim allows it) for getting more aerodynamism. Here is a magnitude order: for a rim with a high of 60mm (so aero-typed), the difference related to the aerodynamism between 23mm and 25mm for a front wheel is about 2W at 40km/h. This difference is reduced at lower speeds and lower rims.

      Best Regards


      • Thanks for clarifying re: external rim width on aero test, makes perfect sense (and very obvious in hindsight on my part!)

        After reading all of the science it certainly looks to be proven that 25mm tires have a benefit over 23mm re: speed/roll faster, although I must admit after trialling 25mm and 23mm tires in similar conditions on the same stretch of road x3 times each, the 25mm tires still felt ‘sluggish’ especially during acceleration and it ‘feels’ like I am working harder at speed. This very well may all be in my head after riding 23mm tires for many years, but I would be interested to know if you have had any anecdotal evidence of riders having the same experience when transitioning from 23mm to 25mm? (Note: Without doubt the ride is more comfortable)

        To confirm, the new wheels I have purchased have a 17mm inner width and 22mm external width.

        Good to know I was on the right track re: 25mm tires are the recommended minimum for 17mm inner rim width wheels re: ETRTO. Although then I guess you need to be sure that the tires you are buying are labelled correctly which as I understand from research can be another big problem re: incorrect labelling/non-standardised measuring re: PSI etc.

        Above in your response you mention that a 25mm tire is also the minimum recommended for a 16mm inner rim width (which in turn would mean that a 23mm tire could only be used safely with a 15mm inner rim width maximum), however the ETRTO chart appears to indicate that a 23mm tire can be used safely on a 16mm inner rim width? Confirming this is correct?

        When you mention that it has been proven that a 23mm tire can come off a 16mm inner rim width, is this referring to testing done outside the ETRTO testing? (by Mavic I assume?)

        I agree that a wheel company should only recommend combinations based on safety etc. and I commend Mavic for producing an article such as this to help educate riders, after much research on the topic this is by far the best/easiest to understand summary of the topic I have read re: wheel/tire combinations. I must say I am surprised that a number of major wheel companies appear to recommend combinations far outside the ETRTO chart, including the company I purchased my wheels off who actually state on their website that a 23mm tire can used on their wheels with an inner rim width of up to 19mm(!), which while may be possible, is hardly the right way to educate riders of the risk they may be taking by doing this.

        Thanks again for taking the time to respond, it is much appreciated. This is indeed very fascinating science!


  • OK but what’s the point of testing a 23mm tyre on a 25mm wide rim if according to the ISO 4210 chart that is not recommended? It does make sense to have a smooth transition from tyre sidewall to rim sidewall, therefore usually installing tyres the same size or smaller than the external width of the wheel set… but apparently that is unsafe? I asked Veloflex and Challenge and they do not recommend to use 23-622 on a 17C rim, for instance.

    I’ve seen some companies recommend different size ratios, say, OK to use 23mm tyres on our new super wide rim. Maybe this also depends on if the wheelset has been specifically designed to work with 23mm tyres no matter how wide they are? This is a bit confusing.

    • Once again, there is confusion between inner width and outer width of the rim (please see the last comment).

      In the aero section of this article, the rim width is the external one, as this is the one that defines the transition from the rim to the tyre.
      Our CXR tubular rims are 27mm wide (internal width doesn’t apply on tubular rims) and can safely be used with 23mm tubular tyre.
      Our new Cosmic Pro Carbon are 25mm wide outside and 17mm inside and indeed, ETRTO doesn’t recommend to use them with tyre smaller than 25mm, rules that we strictly follow.
      Our CXR Ultimate 60 Clincher is 25mm outer width, but 13mm inner width. Hence, it can safely be used with 23mm tyre. And this is the configuration that provides the lowest drag and highest crosswind stability, in full safety as long as tyre fit is concerned.

      We find it hard to understand how some companies can safely recommend configurations that are out of the norm, unless their rim would only be compatible with their own tyre. This the the only way for them to eventually guarantee the match.
      But if the rim can be used with any other tyre, then it is a big risk taken by this companies as they have no way to know what kind of tyre their consumer is going to use. Hence, how to guarantee safety ?

      Norms are here for this reason : when 2 different companies / manufacturers design and manufactures 2 items that are made to fit each other, it is only if BOTH OF THEM respect the norm that the consumer safety can be guaranteed.

  • 1- Where is your methodology?

    2- When you make graphs, don’t forget to give them a name and a number. The results you got in the second one could be very well attributed to the error margin of your testing instrument. With no methodology it is very hard to attribute any validity to your results. Have you tested multiple times? What are the conditions of testing, etc.?

    3- Again graph 2, what was the pressure? That’s the kind of thing you put in the graphic title…

    To me, it looks like a college student with excel spent a couple of hours to produce this article that is far from what an engineer talk should be like.

    • Dear reader,

      We agree with you: the scientific rigor that may require a thesis or a research paper is missing in this article. But the goal of this blog is not to be an engineer’s white paper, but rather a collection of our deliberately popularized methods.

      We can actually specify methodologies and explain our measurement protocols, with the sensitivity and precision of our instruments. But the article would be 5 times longer! Many readers would not read the article to the end.

      On the other hand, we do not want to publicly disclose some elements of our methodology that we want to keep confidential. For example, the way we measure our rolling coefficients (Crr).

      Hope you understand our desire.


  • Mavic Ksyrium Pro Exalith Clincher Wheelset.
    Hello, I am looking to purchase this wheel set, belive they are 15mm internal width, I would like to put 28mm tyres on, is this possible? and how much will I loose going to the 28mm as oposed to the 25 mm they are supliled with. is it worth the 28mm loss in performance to gain comfort on longer rides? thanks. Guy

    • Hello Guy,

      28mm tyre are totally compatible with Ksyrium Pro Exalith and their 17mm rim width.
      28mm tyre can roll fast if inflated high, but that’s probably not your objective if you’re trying to achieve a better comfort.
      They are 15 to 30 grams heavier than 25, depending on brands.
      But the added comfort they bring is very noticeable in longer rides even if it’s impossible to put a number on the performance gain passed the 4th hours for instance.

      So if your objective is to improve your performance on long rides, go for it, that should easily offset the extra few grams.

      Enjoy your rides !


  • Very interesting article thanks.
    Question: I have mavic a ksyrium equipe s wheelset that I believe are 15mm internal width and was looking to upgrade the tires to 25mm is this a good setup?


    • Hello,
      On your 15C Ksyrium Equipe you can safely use tyres up to 32mm.
      But the best performance will be reached using either a 23 or a 25mm.
      So, yes, you can use a 25mm tyre in full confidence !

  • Thanks for the chart it a very helpful
    It appears the 16mm rims can take 23 to 32
    And 17mm can take 25 to 52 mm tires is there a reason why the range of the 17 mm rim is so much bigger

    • Hello Jason,
      Thanks for your comment.
      The Engineering Design Information (EDI) of ETRTO is using formulas to calculate the possible tyre section + rim width combination, and ensure safety in all conditions.
      According to those formulas, the wider the rim gets, the broader the range of possible tyre gets, linked to lower tyre pressure.
      Furthermore, there are years of experience backing up those formulas, since 17mm wide rim has been the standard for MTB rims for decades.
      Have a nice day.

  • Most of the pro’s apparently run 25mm tires on rims of an internal width of 19mm. If this is true, does this mean that what they are riding is unsafe?

    • Hello Steve,
      Indeed, most Pros have now switched to 25mm tyre width, all season long.
      However, 95% of them are riding tubular tyres and in that case, the rule for rim and clincher tyre width combination doesn’t apply.

  • Hi, I just recently bought a set of Cosmic carbon pro exalith wheels. On the specs listed it said that, you can run 23mm-28mm tires. The rims are 13mm inside, but according to the chart in this article the min rim width for 28mm should be 15mm. So, which one is it? Can I safely and efficiently run 28mm on those wheels?


  • Hi. I have a pair of 2013 R-Sys SL with internal measurement (B) of 15mm and external (A) 20mm. Can I safely run 25mm clinchers or should I rather use 23mm tyres? Would there be any benefit besides ride comfort by fitting 25mm tyres?

    Thank you in advance.
    Osman, South Africa.

    • Hi Osman,
      It is totally safe to use 25mm on your R-Sys SL.
      Doing so, you’ll benefit from better comfort and slightly better rolling efficiency. The only drawback will be the additional 10 to 20g per tyre.

  • Thank you for the comprehensive review and report.

    I am really surprised that the Hed’s Ardennes Plus should be used with 31mm+ tires according to the ETRTO’s manual.

    One thing to ask: In the 2nd graph, what are the air pressures for 23mm tire and 25mm tire? In reality, wider tires are filled with lower pressure, because the same pressure gives the uncomfortable rides.

    • Hello,

      ETRTO and ISO defines the general safety conditions in which products can be used. They have to make sure, that under no circumstances, the consumer will be at risk. In the case of wheel and tyre combination, the technical expert within those norms have identified that some combination, in some circumstances, can be unsafe.

      In this second graph, this is the same air pressure (7 bars) in order to see the influence on the Rolling resistance (Crr).
      Of course, in the real life, we recommend to put lower pressure in the wider tire (here 25mm) to have the same Crr and a better comfort.


  • Hi, I am building a new bike and width the new R-SYS SLR , may I know your thoughts if I place 28mm tires with regards to the recommended PSI, roll resistance, aero quality, weight increase? Thanks, Rory

    • Hello Rory,

      It is totally safe to use a 28mm tyre with your R-Sys SLR.

      Recommended tyre pressure will depend on your personal weight, on the type of roads you’re riding on and on your personal preference (comfort vs speed). If you weight around 75kg, are riding on reasonably nice roads and want to find the good balance between comfort and rolling efficiency, we recommend you inflate at 95 PSI.

      The rolling resistance will depend on the tyre pressure and of course on the tyre brand / model you’re using. If you use our Mavic Yksion Pro in 28mm instead of the 25mm delivered with the wheels, the rolling efficiency will be the same but with a better comfort and cornering (because you can put a lower air pressure in a 28mm tyre than in a 25mm).

      Aerodynamically, of course, a 28mm tyre having more frontal surface will not be as fast as a 25mm. But if you’re going for R-Sys SLR it’s probably because you spend most of your time in mountainous area. The aerodynamic disadvantage in the downhill should easily be offset by the confidence you’ll get from the extra grip given by the wider tyre.


      • Thank you for your reply, since a 28mm tyre has more frontal surface, will a 25mm front and 28mm back setup on a R-SYS SLR be more advantageous or it’s better to stay with a 25 mm front and back set up?

  • Thank you for your reply, since a 28mm tyre has more frontal surface, will a 25mm front and 28mm back setup on a R-SYS SLR be more advantageous or it’s better to stay with a 25 mm front and back set up?