New 29+ frame help

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JohnPeopleman
Posts: 45
Joined: Sun Sep 23, 2018 3:27 am

by JohnPeopleman

I'm just after some thoughts and suggestions. I'm wanting to build a new custom frame. I have several frames from Waltly that I really love (nimble road bike, comfortable ultra-distance frame, and a gravel bike that takes up to 700X50C). The plan is now to build something in the 29+ range. I have done custom geometry on all of the other frames and want to understand the details of 29er geometry for the type of riding I plan to do.

I recently did a 7 day bikepacking trip that had some really chunky sections that were fun on 45mm tyres but would have been even more fun on some bigger rubber. So I thought I had best get around to designing this frame.

The bike will predominantly be for chunky gravel riding, bikepacking, and long days on and off-road. It will see plenty of blacktop, and all grades of gravel, rocks, sand, and mud. I'm not a MTB rider so it won't be seeing really technical single track, drop-offs, or that sort of thing. It needs to carry a load for bikepacking and extended touring but will mostly be used without. I'm trying to maximise the size of the front triangle for a full frame bag and get the water bottles onto the tubes, forks, and stays.

I have mostly decided on the componentry. It will have a wide drop bar (Spank 25, Curve Walmer etc.) with Campy 12s Hydro shifters and the rest Shimano 12X2 (yes it works, yes I'm a Campy fanboy). I'll build the wheels from some LB rims (probably i35s to suit 2.6"-3.0" tyres). It will be fully rigid hopefully using Curve's fork.

There are a few bikes that seem to fit the bill, but the geometry is all over the place compared to each other and also to how I currently understand the bikes I ride.

Curve GMX+ (https://www.curvecycling.com.au/collect ... cking-bike)
Evil Chamois Hagar (https://www.evil-bikes.com/a/bikes/chamois-hagar)
Salsa Fargo (https://salsacycles.com/bikes/fargo/2021_fargo_apex_1)

The dimensions I'm mainly concerned about are all of the important ones. I generally like longer chainstays, low bottom brackets, and a longer trail. The bike will be going fast but not necessarily technical but these frames are all quite different.
(for reference Height: 172cm/ 5'7.5", inseam: 82cm/32.25", Saddle Height: 72cm/28.25", long arms, big feet, Bike size: 52-54)

Chainstays: the GMX+ has a touring friendly 460mm, whilst the Hagar has a more common 29er chainstay length of 430mm. Given that I won't be riding too technical is the long chainstay beneficial? There's a chance I will put micro panniers of some kind for winter trips, and it will also be a 2X (38/28) which might benefit in terms of chainline and fitting the chainrings.

BB drop: GMX+ is very low at 88mm! Fargo seems quite high at 70mm. My endurance and gravel bikes have 75mm and I love how it feels being down in the bike. I've never experienced pedal strike on all the stuff I've ridden which seems to be the biggest drawback of low BBs. With bigger tyres is the lower BB going to give me the stability while not increasing the risk of pedal strike too much?

Trail: Fargo and GMX+ use 69deg HA with 51mm and 55mm offset leading to Trail of around 90mm. Hagar around 93mm. These numbers seem huge to me from a road perspective (I usually like low 60s on road) but they seem relatively quick for most of 29ers geometries I've looked at. With a short stem and bar reach (drop bars remember) is this still going to give me a relatively nimble front end?

Seat Tube: Fargo (73deg) and Hagar (73.5deg) seem like normalish numbers for pushing back and getting weight off your hands like on touring bikes but the GMX+ pushes way forward to almost 75deg (74.75deg). It seems all of the 29ers I look at seem to be even steeper. I know KOPS is a general rule/ myth and I usually use the balance method to set my setback, but doesn't being that far forward put heaps of weight on your hands? I know they've pushed out the front ends of MTBs but it seems like that's only going to make things worse. With my intended purpose would I benefit from using a more standard STA?

Top Tube Length/ Reach: Hagar (605mm) and GMX+ (610mm) seem to be way further forward of the Fargo (540mm/565mm). I assume this is down to the length of stem being used. However, when I've used bike comparison tools and looked at my gravel bike (90mm stem) vs either the GMX+ or Hagar (50mm stem) (same handlebars) they are around 35-40mm further forward with the same stack. I want a larger front triangle and bottle cages on the down tube like the GMX+ but that seems a little too far out. How do MTBs ride when you're that far forward of the BB?

After all that how does the compromised geometry below look?

Fork:
Curve expedition, 55mm offset, 430mm axle to crown

Cockpit
HT: 160mm, 69deg
Stem: 50mm

Saddle:
top tube: 605mm
Seat tube: 73.5deg, 85mm BB drop, 540mm length
Saddle height: 720mm

Rear:
Chainstay: 460mm

At the hoods, this is only slightly longer(15mm) than my current gravel bike which is quite comfortable and well within the comfort zone to stretch that little bit further forward. I could always throw a longer stem on my current gravel bike to see how it feels.
I need to consider standover as well but that can be done later.

Any help or comments are appreciated.

bikewithnoname
Posts: 1732
Joined: Tue Sep 22, 2009 1:29 pm
Location: Paris

by bikewithnoname

You won't be able to fit 29+ tyres on the Evil, it maxes out at 50mm (unless they've changed it recently) so that's a 2inch MTB tyre, nowhere near 29+

I'll let someone more techincally minded opine on the geo as my 29er experiences are on normal flat bar mtb's. Keep in mind 29+ tyres are heavy as hell, the addtional weight does affect the overall handling
"We live in an age when unnecessary things are our only necessities." Oscar Wilde

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JohnPeopleman
Posts: 45
Joined: Sun Sep 23, 2018 3:27 am

by JohnPeopleman

Thanks for the reply

I will making a custom frame so the Evil was just design inspiration. 50mm is great for almost everything I come across. My gravel bike can take that. It's the next level up of chunkyness that I want to play with next. A normal 29er would be fine but I'm more into long distance and bikepacking stuff where aggressive geometry isn't the most appropriate.
You're right about heavy tyres. Coming from a road background, I look at the mass of some of the heavier 29+ tyres and think they're closer to a road wheelset! I don't think 29+ is going to disappear but there doesn't seem to be much development. I think it's a great size for bikepacking but there are only a few tyres that really suit that ethos. Most have a lot of knobs rather than something akin to a grown up gravel tyre. I just have to accept the weight and rolling resistance hit.

JohnPeopleman
Posts: 45
Joined: Sun Sep 23, 2018 3:27 am

by JohnPeopleman

[Deleted]

jemima
Posts: 270
Joined: Fri Apr 22, 2011 12:36 am
Location: Perth

by jemima

Your long arm comment made me think of a design similar to the Wikkit framesets.
Curve Grovel ti.

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