Effect of Tyre Weight On Performance

[iainb]

Hi folks

The 25mm Marathons on my light tourer needed replacing a couple of weeks ago and, as an interim measure, I fitted a pair of part worn Vittoria Rubino Pros which I had knocking about which I've found to be excellent tyres on my more "sporty" bike. They are about half the weight of the Marathons and I'm sure that on a couple of regular rides I do that climbing is a bit easier. Is this just my imagination or does it make that much difference - I'm not bothered about "marginal Gains" as British Cycling put it but just interested as may affect my next choice of tyres. I accept that there may be a trade off re puncture protection but I've ridden Rubinos in some pretty grotty conditions and had hardly any flats (touch wood!)

Regards

Iain

[Mick F]

In a nutshell, rolling resistance.

Rubino Pro are excellent tyres. I've used them for years, and at present I'm on the slick version which are wonderful.
My other bike came with Schwalbe Durano, and they rode like riding through treacle. I changed to Continental GP and they difference was astounding.

[iainb]

thanks for the reply Mick

I've used Vittorias for years and found them to be excellent value for money - I see that Ribble are doing the "ordinary" Rubinos for under 7 quid at the moment. How do find the slicks for puncture resistance (without wishing to tempt fate for you!!)

[Mick F]

Not had a single one since fitting them.
Looking at my records, I've done just over 2,500miles.

[Brucey]

.... Is this just my imagination or does it make that much difference ...? ...

well, it isn't just the weight you know; on the rollers you would be looking at about 5W per tyre difference, which is probably good for about 0.5 mph or so. And that is assuming that the suspension losses with each tyre are about the same, which they won't be; the marathon will have a stiffer sidewall and will ride worse at any given pressure.

Not that I wish to jinx it, but it is wet weather riding which really tests puncture resistance.

cheers

[Psamathe]

...
Not that I wish to jinx it, but it is wet weather riding which really tests puncture resistance....

Out of interest, why is that ?
Thanks
Ian

[Brucey]

...
Not that I wish to jinx it, but it is wet weather riding which really tests puncture resistance....

Out of interest, why is that ?

it is I think for two reasons

1) there are fresh supplies of flints etc washed into the road and
2) water is an excellent cutting lubricant for rubber; the force required to cut or pierce rubber is many times smaller when water is present.

cheers

[sjs]

...
Not that I wish to jinx it, but it is wet weather riding which really tests puncture resistance....

Out of interest, why is that ?

it is I think for two reasons

1) there are fresh supplies of flints etc washed into the road and
2) water is an excellent cutting lubricant for rubber; the force required to cut or pierce rubber is many times smaller when water is present.

cheers

I'd have thought in addition that something likely to cause a puncture (small flint or whatever) would be likely to stick to the tyre for a bit longer before falling off when wet, hence would have more chance to do damage.

[Brucey]

except that if you ask the question

'how slowly do I need to ride on my mudguardless bike in order that I don't get wet from water thrown off the wheels?'

the answer is

'very slowly indeed'

water is thrown off the wheels very quickly, and stones are denser than water, so are more easily thrown off. If the stones 'stick better in the wet' I would have said this would be because they are actually stuck into the rubber already, perhaps due to the 'cutting lubricant effect'.

cheers

[PH]

...
Not that I wish to jinx it, but it is wet weather riding which really tests puncture resistance....

Out of interest, why is that ?
Thanks
Ian

It's because the puncture faeries hate us and like nothing more than seeing us soaked to the skin and shivering while dealing with their visits.

[sjs]

except that if you ask the question

'how slowly do I need to ride on my mudguardless bike in order that I don't get wet from water thrown off the wheels?'

the answer is

'very slowly indeed'

water is thrown off the wheels very quickly, and stones are denser than water, so are more easily thrown off. If the stones 'stick better in the wet' I would have said this would be because they are actually stuck into the rubber already, perhaps due to the 'cutting lubricant effect'.

cheers

Well no doubt you're right and the "sticking" point is negligible compared with the "cutting lubricant" one. My thought experiment was a bucket of small flints and another bucket of small flints in water. Both buckets are overturned. A lot more small flints stay in the wet bucket than the dry one even if the buckets are jiggled about a bit.

[Brucey]

fair point, and maybe there is an effect there. But the forces are very different; I also wonder if the water flying off a tyre would be a bit like rinsing the inside of the bucket out with a hosepipe.

Gravity is F = mg

and

Centripetal force is (mV^2)/r

as the tyre leaves the road both forces add to one another. You can solve for the critical 'V' on a 700C wheel (where the gravitational force is the same as the centripetal force, and a flint on top of the tyre isn't trying to fly off) and you get

V = (gr)-1/2 where g ~ 9.8m/s^2 and r ~ 0.35m and V is in m/s

V = 1.85m/s, i.e. about 4mph.

Any faster than that and you will get an increasingly mucky backside if you don't have mudguards.

If you are doing 10m/s (22mph) the centripetal force becomes about 29 times that of gravity. When I stop my bike in wet weather, the notable thing is that there is very little crud adhered to the tyre; if there is anything there, it'll most likely have been picked up as I slowed down, or it'll have been stuck in the tyre.

I have often wondered if people's experiences with punctures have to do with their average speed (as well as all the other things). At a touring speed of 6m/s (~13.5mph), the centripetal force is about 1/3rd that of someone on a brisk training ride, so crud presumably tends to stick x3 more to the tyres.

cheers

[The utility cyclist]

Centripetal is the force to keep an object in place, mud/dirt coming off a tyre would be referred to as centrifugal.

weight of the tyre/rims doesn't really have much of an effect unless you do a lot of stop start riding, the biggest effect is having the correct tyre pressures and tyre compounds, differing inner tubes (if used) also can have an effect. A bog standard 100-120g tube has a reasonably greater effect on rolling resistance than say a lightweight or a latex tube. One RR test site has it at a difference of 1.9Watts @80psi using a conti 4000SII and a 100g tube against an 80g latex. The ride should be more compliant with a latex but is probably hard to detect for the most part.

Personally I didn't like Conti 4 seasons, they are not particularly supple and I didn't find they rolled that well for a 28mm, I bagged some end of line Giant folding 28mm a couple of years ago that are completely slick and feel these are better/are a true 28mm when fitted (compared to the GP4S). Conti GP4000sII are better than the GP4S for only a couple of quid more, I have the tubular version on my carbon wheels, I could probably get better but for me they are fine for most situations, I maybe think a bit more about line on a particularly nasty strip of road..

Some folk are going to open tubulars or even tubeless which give a better ride/lower rolling resistances, Vittoria Corsa are quite popular and seem to roll well in tests and reviews though not had them.
I've had the older Rubino Pros in 23mm and they have always seemed to be a good tyre, the latest line of graphene Rubino's which replaced the pro III are supposed to be even better still.

[mercalia]

If you are doing 10m/s (22mph) the centripetal force becomes about 29 times that of gravity. When I stop my bike in wet weather, the notable thing is that there is very little crud adhered to the tyre; if there is anything there, it'll most likely have been picked up as I slowed down, or it'll have been stuck in the tyre.

I have often wondered if people's experiences with punctures have to do with their average speed (as well as all the other things). At a touring speed of 6m/s (~13.5mph), the centripetal force is about 1/3rd that of someone on a brisk training ride, so crud presumably tends to stick x3 more to the tyres.

cheers

well my speed less than 13 mph , average about 9 ( dont laugh ) and I dont get punctures.