The sun is out and it’s looking like great riding weather – so what are you doing sat indoors reading this? 😉
Martin contacted me last year as he was thinking of a titanium 29’er and wanted to get a second opinion on some options. Having previously used XACD he also fancied trying another supplier to see how they compared…
I’d been thinking about a big wheeled momentum machine (29’er) for a while but nothing out there was exactly what I was looking for. I wanted a non suspension-corrected, fully rigid frame that could be run as a singlespeed for winter riding, or with a 100 mm suspension fork and gears for summer use.
With the above in mind, and already having a set of rigid 445mm carbon forks, I decided to base the bottom bracket height, head tube angle and seat angle of the frame around that fork. This is were it got a little complicated and I started to play about with bikegeo (Geometry Calc) to come up with seat tube and head tube angles to suit the rigid fork and a future 100mm suspension fork. Changing the fork length by approximately 20mm changes the seat & head angle by 1 deg and the bottom bracket height by 8mm, approximately, so it was a case of finding the right compromise.
The numbers I settled on are 69.5deg head angle, 74deg seat angle and bottom bracket height of 305mm. The rest was fairly straight forward after that, 18.5″ seat tube, 44.0mm head tube, 23.5″ top tube, full zip tie cable routing, dropper seat post compatible, 68mm English threaded bottom bracket, custom sandblasted logos and 2.5″ tyre clearance. Sliding dropouts cater for different wheel axle sizes as you can swap out the lower part of the dropout, plus of course you can adjust the chain stay length to run it as a singlespeed.
I love the nerdy stuff! Sweating the details of the geometry is all part of the fun and often the hardest bit to get right, particularly if you want the frame to be as adaptable as Martin did. It’s one of the reasons I think you need to take three goes at a frame before you can really nail it – unless you’re very lucky!
The next major decision was who to build the frame? I have previous experience of buying a custom titanium frame from XCAD but their prices are getting high and Porter can be difficult to deal with so after some research I decided on Waltly Titanium. Dealing with Jenny from Waltly was a breath of fresh air compared to Porter and any changes along the way were taken care of without any trouble, although she was slightly slower in replying compared to Porter.
Construction time was just over 45 days and shipping about 3 days.
This seems to be a common experience – Waltly and Titan are much more flexible in terms of frame features they will add before you start incurring extra cost. So now the fun bit – how did it all turn out?
The quality of the tubes, welds and facing was spot on. Having now ridden it up mountain, down dale and Dalby forest I am delighted with the way it feels and rides in its single speed rigid set up. The next step is to try my 20mm longer rigid carbon fork, then a suspension fork and gears…
Martin had a bit of a head start here as he’s had experience of getting a frame made before. He had a pretty clear cut idea of what he was looking for and was aware of the challenges in designing a frame that would work in two different configurations.
I’d say he’s nailed that pretty well! The sliding dropouts in particular look very smart and give Martin the option to run a quick release or 12mm thru axle. Waltly specced a 1.2mm wall thickness on the chainstays which is fairly cautious, you could run a 0.9mm all over without compromising strength. Similarly if you wanted to shave a few grams off then double butting the three main tubes would be an option, this would reduce the thickness of the tubes to 0.7mm in the centre section.
Martin specced a 34.9mm seat tube so he could run a dropper post, if you fancy doing the same then don’t forget you could add extra cable guides as well to help keep things tidy. Maybe even a pierced seat tube for the ultimate in stealth routing!
The extra bracing tube on the left hand stays is optional too as most frames do without. It’s normally used to help counter the torque reaction from the disk brake mount on the seat stays, although in Martin’s case this is partly alleviated by the sliding dropouts which will spread the load between the seat and chainstays. Putting the brake mounts on the chainstay is another option if you’re running a more conventional frame. There are some funky designs of dropout which help with this too if you don’t fancy mounting it directly to the chainstay.
Martin’s main aim was to keep things strong and reliable though so his design choices are all sound, having a custom bike made is all about what you want at the end of the day! I’d mentioned the idea of splitting the stays to give the option of a belt drive later on but he didn’t want to introduce any potential weak points into the frame. As an alternative to splitting the frame you could use a bolt on style dropout that would let you introduce a belt drive after taking it apart.
Phew (what a scorcher) another excellent frame – thanks for sharing, Martin! Don’t forget I’m always on the look out for others, so if you’ve had a custom frame made that you’d like to show off then drop me a line via the Contact page. Now get out there in the sun and ride!