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Trail and Enduro Bikes

Steel. A New Blueprint? 

Is steel be the best mountainbike material?

In the garden shed of a terraced street in north Bristol there’s a man fabricating steel bicycle frames. He has recently quit his job in the aerospace industry to pursue his passion. 

We like his bikes a lot, in fact his 29” Starling Murmur has been a stand out bike this year.

And so it is a bike of the West Country that has won our hearts and killed the clock recently. Who’d have thought that the material would be steel, the price far from ridiculous and the component specification of our test bike average to say the least.

The Murmur, with 29″ wheels and 145mm of Bristol travel and a skinny fork took several seconds off the apparent world class carbon 150-165mm enduro bikes on timed runs by several riders. It was silent, balanced, delivering levels of grip that have been largely forgotten since we chattered our way into what we were told was high-end carbon.

Don’t think for one minute though that the material has somehow made some magic bike, as we’ve been unimpressed with many steel full suspension bikes. What it does prove, that if done correctly steel is fast and it can be light without giving too much flex. It also asks the question, does carbon actually offer a performance advantage other than the lighter, stiffer, stronger talk that nearly everyone drags out? We talked to Starling creator Joe McEwan.

Come on then, tell me why steel feels so beautiful to ride? What’s the science?

My technical experience is in carbon fibre.  But what I believe is happening (without any quantifiable evidence) is as follows…

For a given volume of steel, it is stiffer and stronger than both aluminium and carbon fibre. When built into a bicycles you need to use smaller diameter tubes, otherwise the wall thickness would be too small or the weight would be too high. Small diameter steel tubes give a less stiff frame than you would get with the large diameter tubes used in carbon and aluminium frames.

But stiffness is not necessarily a good thing.  Marketing suggests it is, probably because its a simple measurable way to say one bike is better than another.  I believe we are so driven by marketing influence that we believe stiffness should be high, and therefore we lose confidence in a flexy bike and we therefore ride badly.

So, if you ignore marketing, and our marketing lead intuition, then you don’t necessarily need the stiffest bike. My bikes are not flexy, but they are not overly stiff either.  By luck or judgement, they seem to be about right!

Also, small diameter tubes don’t result in the big resonance boxes of aluminium and carbon bikes. To me silence is massively important to your confidence in a bike and consequently your speed.

Do you believe steel has a performance advantage over carbon or aluminium in any way?

Other than what I have mentioned before, steel tubes are tougher and more damage resistant. I had a steel Dobermann DH bike with a massive dent in the top tube. It didn’t worry me at all. Now if it were an aluminium or carbon bike, I’d be shitting myself.

But, material choice alone does not make a good bike. It’s a complicated design problem, with very little technical evidence (other than times) of what a good bike is. I’ll be damned if I know the answer!

You’re a carbon expert, give me some reasons why you didn’t use carbon to make your frame?

Firstly carbon is quite tricky to do at home. Some people do with some success, but it all looked a bit much to me. Also, having worked in aerospace for 20 years, I’ve seen a very high standard of carbon fiber manufacture. Even the tiniest imperfection could result in scrapping a multi thousand pound part.

The carbon technology used for bikes, although I’m sure it’s plenty fit for purpose, is a bit more agricultural. Sorry Santa Cruz, but the V10 cross sectioned frame from a few years ago really made me cringe.

Also steel is more forgiving for the home builder. It also allows you to quickly iterate designs. I’ve always ridden steel bikes and always loved them. I’ve had steel hardtails and a few steel DH bikes, but there was never any decent fully steel mid travel bikes. This was the gap I wanted to fill when I first went about designing mine.

How much does the carbon you work with in aerospace differ from bicycle manufacture?

See above. But waviness/porosity/tolerances are all massively small (i.e. good) in aerospace compared to bikes. But aerospace is a hugely limited by the risk associated with new materials. It’s very hard to introduce a new material or technology in aerospace, even if it has obvious benefits. You need to fully prove it hasn’t got some hidden problem that will cause a plane to crash, i.e. the industry is very safety driven. Whereas bikes can readily take advantage of new technologies and use them to their advantage.

Building a steel frame takes a lot less time than laminating a carbon bicycle? Why don’t more people use steel?

I don’t really know the answer to this, but I think large scale high quality steel frame manufacture is harder than building an aluminium frame. Especially with a full suspension frame where the complex shapes are hard to make with steel. So aluminium is the obvious starting point. Carbon may be hard to manufacture as well, but as it is seen as a high technology it can command a higher price than steel.
Is the margin of error is considerably less to with steel? 400 plus pieces of carbon, lots to go wrong?

400 pieces of carbon is actually good for carbon fibre.  An error in say the placement of one lamina only has a small impact (1/400th for example).  Whereas a steel frame with less parts mean they all need to be correct.

“If you ignore marketing, and our marketing lead intuition, then you don’t necessarily need the stiffest bike”

People talk of carbon being the stronger material, that aluminium degrades over time, where is steel in this mix?

Indeed for a simple coupon type test, aluminium and carbon fibre do have better strength and stiffness to weight ratios than steel. But the simple material properties are only a small part of what matter for a complex design solution such as a bike. But I think weight is overrated; another thing that be quantified by marketing managers to show one bike is better than another.

A frame that is 1kg heavier but rides well, will be better than a 1kg lighter frame that rides rubbish. How well a bike rides is difficult to quantify, but weight is easy. It may well make a difference in road racing or XC, but much less so for Enduro DH and even less so for having fun with your mates!

If carbon marketing is nearly always about stronger, stiffer, lighter, what would your sales pitch be?

I seem to need to think about this a lot at the moment, but I think my sales pitch is a simple/tough/silent bike that rides well.
Any shape any size right? These are made to order bikes?

The rear triangle geometry is fixed on all my frames, this affects BB drop, chainstay length, seat angle. But all front triangle geometry is within reason custom option; reach, head angle, head tube length, seat tube length.  And yes, they are made to order.

Talk us through the materials chosen (types and shapes of tubing) and why?

Main frame is Reynolds. I use a custom 853 downtube. The downtube takes a lot of load from the shock mount so I need to spec a thick strong tube here. I also needed a custom length to allow me to build modern long reach frames.

The rest of the front triangle is Reynolds 631. Plenty strong enough, but less of a bugger to work with than 853 which just destroys tools! Swingarm is Columbus tubes. They make very high quality tubes and I kinda like the aesthetics of the chainstays. The tubes are combined with various turned and lasercut parts.

But it’s the shape of the frame rather than the materials that counts right?

It’s the whole design solution…

What reasons did you choose UK manufacturer? Why not get it made in Asia?

They are made in my shed at the bottom of the garden.  Asia is a long commute! I have looked into a batch from Asia, but it’s a massive monetary commitment. But also, I now almost have a dream job; fiddling with bikes in my shed. I’m getting feedback from the design changes and iterations as I go along, some real engineering. Sending one design off to Asia would end up being more like a logistic/distribution job, I don’t want that.

Steel – better than carbon or ali – or just different?

You’re the bike tester!

Talk us through the suspension details….

Suspension set-up is the simplest I could make it. Single pivot, with a constant linear leverage ratio through the whole stroke. No need for funny progressive curves, modern shocks can do this well. A suspension tuner likes a nice simple curve to start with. The pivot is in line with the chain to give no feedback.

The pivot is also in a position to minimise anti-squat/rise. I try to keep it as close to 100% through the full stroke.  This means the suspension is affected as little as possible by rider weight shifts.  This I think is massively important in how the bike rides.  Nothing silly going on. Just up and down when it hits bumps, but try to keep it parallel to the ground as the rider moves about.

How many prototypes of each bike have you made? How can you tailor ‘feel’ within a frame? How does the R&D work with that?

I’ve built around 30 frames now. It took around three or four major iterations to get to the basic configuration of the Swoop 27.5″ bike. I then built about 10 frames for customers as prototypes at reduced cost, and about three or four for myself in that time. The changes to these were smaller, mostly improving manufacturing quality, but also some design improvements.

They’ve all ridden well, even from the very early prototypes. I fiddled with BB height a lot at first, then reach and head angle. But once I had the basic configuration sorted, I haven’t fiddled too much. The 29 Murmur seems to have hit the spot first time round. I’ve also got another singlespeed 90mm bike that seems pretty good after two prototypes.

Controlled flex and traction, surely everything cannot be learned from behind a screen?

I used Linkage program in the early days to arrange suspension configuration. And a bit of 2D CAD for lasercut and parts. But otherwise all the bike design is hand on. I still get a bit of paper out from time to time check a few things out.

How many people are involved with Starling now?

Starling Cycles is just me, but I do subcontract out some work:

  • Bear Bikes for machined parts;
  • Jamie Edwards for some marketing;
  • Steve from Cofa Engineering for helps with swingarm manufacture;
  • Warren from RPA powdercoaters;
  • Andy from 7PotCustoms for fancy paint jobs.

Where will the frame evolve to?

It will grow two thumbs to control the electronics whilst the drone hovers above lighting the scene and recording every moment.

I like the look of the new integrated dropper posts. I’ve always thought a gearbox is the right solution for an off-road bike. I’ve been in talks with NitroShox, so I’d like to give that a try. And finally I’m looking into a bit of additive manufacturing (I did a bit of this in my aerospace life), but maybe in chopped strand composite rather than metallics!

Why buy this bike?

Because you say it’s the fastest…

Comedian too….

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