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 Post subject: Re: Is Retro faster?
PostPosted: Tue Jul 23, 2013 5:05 pm 
King of the Skip Monkeys
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Whilst one still gets oil on ones tweeds, regardless of modernity, oh why bother, I'm off for a Pimms....

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 Post subject: Re: Is Retro faster?
PostPosted: Tue Jul 30, 2013 5:11 pm 
Retro Guru

Joined: Sun Jun 16, 2013 2:57 pm
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Location: Porto / Plymouth
I was asking myself this same question (are 90s bikes faster than 2013 bikes) just this morning. I know, intuitively (from the point of view of physics), that a 26" rigid MTB will be faster than a heavier modern MTB (26 or 29") over a smooth surface. The extra weight of the modern front or full suspension bike will simply require slightly more work by the rider to accelerate and to lift it up the vertical distance on the uphills.

The higher angular momentum (rotational energy in other words) of larger / heavier wheels of the 29ers will come into play when the bumpiness of the terrain is considered. Their higher angular momentum for a given speed means the wheels can more easily roll over obstacles.
5 minutes later I realised the above is pure fiction. Shame on me (a physicist). the 26" wheel will rotate faster (higher rev per minute) than the 29" version. All else being equal (same rim, tube, tyre, just two different sizes), a 26" and 29" wheel will have equal angular momentum when riding at the same speed.

But you don't need 29" wheels to get this effect - just built a wheel set with really heavy rims, straight gauge spokes, and fit super heavy tires and inner tubes. There are some other claimed benefits of te 29 inch wheels, but I suspect they are relatively minor. What I find interesting is that the old orthodoxy of "low rotating mass = good" has effectively been turned on its head. Overall, I think it's hard to judge where the 29" starts to give an advantage over the lighter, more responsive 26" wheels.

On a similar subject, I had a browse around a local bike shop at the mid range (800-1200 GBP) hardtails on sale, and I am astonished at how heavy they are for the price. My 96 Diamond Back Apex weighs in at about 11 kg (costing ~400 GBP in 1997), while the typical weight of a 1000 GBP hardtail seems to be slightly above 13 kg. That's a whopping 2 kg (4 lb) difference. Do any other riders notice the difference between the weight of their bike in terms of handling, speed, etc.? For sure, give the choice between the super heavy 26ers and my 11 kg retro bike, I'll choose the latter.


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 Post subject: Re: Is Retro faster?
PostPosted: Tue Jul 30, 2013 5:26 pm 
Old School Grand Master

Joined: Tue Oct 09, 2007 1:55 pm
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Location: New Forest, UK
The advantage with 29ers is that:
1 The larger diameter means that an obstacle is more easily climbed over, so less likely to stop you - think about the non-existent bump climbing ability of a skate scooter compared to a 26" wheel.
2 The longer contact patch gives lower rolling resistance and better adhesion (like tractor tyres)

I think all the angular momentum stuff is a distraction and mumbo jumbo compared to the more basic physics at play.

Much of the weight bloat has also happened to 26" bikes as the new CE spec effectively forces overbuilt frames.


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 Post subject: Re: Is Retro faster?
PostPosted: Tue Jul 30, 2013 5:29 pm 
King of the Skip Monkeys
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so, should I just put big tyres my racer?


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 Post subject: Re: Is Retro faster?
PostPosted: Tue Jul 30, 2013 7:06 pm 
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hamster wrote:
The advantage with 29ers is that:
1 The larger diameter means that an obstacle is more easily climbed over, so less likely to stop you - think about the non-existent bump climbing ability of a skate scooter compared to a 26" wheel.
2 The longer contact patch gives lower rolling resistance and better adhesion (like tractor tyres)

I think all the angular momentum stuff is a distraction and mumbo jumbo compared to the more basic physics at play.

Much of the weight bloat has also happened to 26" bikes as the new CE spec effectively forces overbuilt frames.


Interesting - thanks.

legrandefromage wrote:
so, should I just put big tyres my racer?


Go on, I dare you to do it!


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 Post subject: Re: Is Retro faster?
PostPosted: Tue Jul 30, 2013 7:31 pm 
Anglian Deputy AEC
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I have a regular ride of 28 miles in length. Covers varied terrain with long uphill sections, fast doubletrack and tricky technical singletrack. My modern bike is 15mins quicker than any of my retro steeds. I think it is down to the lower gearing for the climbs and suspension forks that let you crash through any obsticle.


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 Post subject: Re: Is Retro faster?
PostPosted: Tue Jul 30, 2013 8:10 pm 
Old School Grand Master

Joined: Tue Oct 09, 2007 1:55 pm
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Location: New Forest, UK
legrandefromage wrote:
so, should I just put big tyres my racer?

Well wider like 23c are faster than narrower due to the better contact patch, so in theory yes! The problem with fat tyres is that many do not have such efficient carcasses and so benefits are lost in the thick rubber tread and sidewalls.


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 Post subject: Re: Is Retro faster?
PostPosted: Tue Jul 30, 2013 8:26 pm 
Anglian Deputy AEC
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Location: Livin' in a dust bowl
Perhaps we should ask Neil__j. He has a rigid KHS and a custom built modern Ti framed bike. The Ti framed bikes geometry and design was based on his KHS with the addition of sus forks and disk brakes. He is a fast rider so maybe he can tell us which is quicker.


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 Post subject: Re: Is Retro faster?
PostPosted: Tue Jul 30, 2013 8:47 pm 
Gold Trader / MacRetro rider
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Joined: Thu May 06, 2010 10:05 pm
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In the real world a modern bike is indeed quicker than a retro bike over the same course.
it seems 29'ers are also quicker than 26'ers in some situations.

Still, you can utilise a retro frame with modern components/fork etc and still have a retro yet pretty competitive modern bike (I'm talking for xc use here).


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 Post subject: Re: Is Retro faster?
PostPosted: Tue Jul 30, 2013 9:51 pm 
Retro Guru

Joined: Sun Jun 16, 2013 2:57 pm
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Location: Porto / Plymouth
jimo746 wrote:
In the real world a modern bike is indeed quicker than a retro bike over the same course.


Interesting. So the added weight of modern 26ers doesn't make all that much difference, after all. Is the difference in speed down to the decent suspension forks?


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