Hi all, just want to start learning as I will have first custom bike soon.
As titled, I’m curious about how this trail thing play out.
I’m leaning towards a 50ish trail now for mostly front load, and gravitating towards 71 HTA with 60 offset…
But, I’m also curious for example how a front end with 73 HTA & 50 offset (almost identical trail would be different)
Not the exact figures, but Jan mentioned in his booked that the steeper and lower trail bike is more suited for front load, but somehow the “city bike and rear-loading touring bike” is way more fitted towards read load even though that one would have quite a low trail as well? (45 trail for 650x42)
Jan Heine has very specific tastes when it comes to handling. His book is well written and worth purchasing. But remember these are his preferences. Also remember that 99.9% of cyclists don’t ride low trail bikes.
The bike with the slacker HTA but identical trail figure with have a slightly higher flop factor. Meaning once it starts flopping to one side it’ll more quickly want to continue flopping. So if you’re carrying a heavy front load, it’ll take a tad more effort to recenter the flopping effect. Whether you’d notice the difference and whether it even matters is up for debate.
Having built myself a few and ridden many miles on BQ-style rando bikes, I’m not convinced that their handling is better than other mid-trail or high-trail bikes. But it’s not worse either. Just different.
IMO I wouldn’t lose sleep over the minor differences between the two bikes. Making sure your fit is dialed for the custom bike is a way bigger priority.
I would avoid 50ish trail with front loads. I find that either 40mm trail (Jan) or 60+ trail (Riv, 80s touring bikes) works pretty well with front load, but 45-55mm is kind of a no-man’s land where the front feels skittish. Maybe if you already have multiple bikes you can test it.
Could you please elaborate more on the differences?
And yeah, as a small rider (43-46cm sloping top tube) I dont have a lot of choices for fit: only 70-71ish HTA to move the front wheel further but that’s a can of worm I will bother everyone here with later…
Interesting, I never heard 45-55 being no man’s land but good to know! What bikes make you say so?
I think the Faran was designed around those figures (71HTA, 60 rake) and the goal was to have it handle nicely both with and without front load. I will also look to try a Wolverine locally soon which has similar numbers as well
Now that I know you’re making a very small bike, I’d be more concerned about avoiding toe overlap than the minute differences between 40mm and 45mm of trail.
While @Alex doesn’t like 45-55mm of trail, I was perfectly happy running 45mm trail with this style bike. It’s so subjective. And there’s no right or wrong answer.
Make sure you factor in the front fender when designing around toe overlap. If you haven’t done so already, consider using smaller crank arms and 26" wheels. You’re already making a fringe bike so there’s no harm using fringe components.
When you say “mostly front load” could you be more specific? There is a large difference between a rando bike with 2kg of front load in a handlebar bag and a touring bike with 7kg of front load in lowrider panniers. There is also a big difference if the load is static (mounted to the frame) vs dynamic (mounted to the fork).
There was a very early BQ article (disclaimer, I helped author it) that compared 3 Kogswell bicycles that were identical except for the fork offsets of 25mm, 40mm, and 50mm and that was tested with handlebar bag loads. There was a followup a couple of issues later testing 40mm, 30mm, and 25mm trail bikes with ~20kg front loads (simulating carrying groceries on a porteur). This work influenced my handling preferences.
At the same time my favorite commuter bike with a Bridgestone RB-T, which was very lightly built as a touring bike (it was really a better cross-bike than touring bike – and many cross bikes like the Cross-Check would have been better touring bikes). The stock geometry was 73 degree STA and 45mm fork offset. That puts the trail at 59mm. I found that the handling was greatly improved for moderate commuter-sized front loads when I had a 65mm offset fork. I liked the original handling unloaded.
I’ve also toured and ridden a lot on 72 degree STA/45mm rake bikes like the Surly LHT, Rivendell Atlantis, and Heron Touring. Those end up with a trail figure in the 62-65mm range (depending on tire size) and find them to work well with touring-sized front loads, they just require more leverage to steer and push riders towards wider bars. Wider bars have gotten popular anyway, so maybe that isn’t a big deal.
A lot of this also depends on the tires. I think low trail has a particularly bad reputation because it can feel very skittish if you ride a low-trail bike with skinny high pressure tires and no front load. I know that my first experiences with a low trail bike (a 1983 Trek 520) was terrible. Now I see that as rider error, it was 1999 and I had a heavy rear pannier, skinny 25mm high pressure tires, and 45mm of trail and the bike was awful because the front wheel could be knocked off course so easily. I stopped riding it after one crash caused by that. A decade later it became one of my favorite bikes when ridden with much wider tires and a front porteur rack.
I ride all sorts of bikes and these days I mostly commute on a 2015 mountain bike with ~90mm of trail which has been converted to a commuter and am back to the rear pannier. For fork-mounted front loads right around 40mm trail is still my preference.
I was reasonably closed to considering 26" wheel but decided to go with 650B for tires conveniences and…being safe (not wanting the biggest jump first).
Bikes would be 160-165 crank, I’m also not set on HTA (planned 70-71) nor STA (74-75.5) but toe overlap should not be a concern
Thanks for the extra info, it would be somewhere in the middle. 4-7kg on a handlebar bag i’d say. I planned to use those flexy Kaisei BQ blades so a higher mounted rack + handlebar bag.
I could max it at 5 too then shove the rest into a saddle bag if that make this handling equation easier?
For front end, I planned to achieve the low-mid trail by having a slacker HTA (71ish) then more rake (60) because I want to push the front wheel further for better COG position, with a somewhat long 430-440 CS and then such a short TT.
74-75.5 seems very steep for what looks like a rando/all-day road bike. Have you ridden bikes with that steep of a STA? In my experience that will push a lot of weight onto the rider’s upper body, but I’m also not the strongest rider. The ever-steepening STAs on mountain bikes make sense where you are mostly seated while climbing, but I don’t find that to be true on my road riding.
Doesn’t the 70 degree HTA/60mm offset make you less balanced for COG compared to 72 HTA/50mm offset? I definitely see how it gets you more toe clearance.
I can’t say that I’ve ridden a 70d/60mm bike, so I don’t have a strong opinion on how that will handle with a handlebar bag. You can always build it and report back. You might be able to emulate it using an existing bike, an angleset, and just building a custom fork (which would eventually become the fork for your new bike). That is probably what I’d do first.
the STA is probably my biggest concern now. Fitter put me on a 76HTA which is even steeper (though that was on 160mm crank vs my current 170).
I tried slacker with the current 170 and actually found it was way easier to pedal.
the slacker was headtube was to move the front wheel further out, so I’m not sure what you meant?
I will gather more info later to ask about fit but this was the final position from session 1. I intend to try move the saddle back further and seating more upright in the final session
STA is a hugely personal thing but I love a steeper angle these days, especially when combined with a taller handle bar position. I find that opens up my hips a bit for more all day comfort (really notoceable 100+ km rides). So yeah 75deg sounds great to me!
Also at your saddle height (~650mm) a degree of STA adjustments results in roughly 11mm for/aft movement at the saddle. Your drawing shows a 20mm setback post? I would design around an inline post and then if things feel too steep you can switch to a setback post to slacken things out.
The logic around a longer wheelbase makes sense and the 70deg/60mm offset combo sounds like a fun experiment and I can’t see it being a bad bike to ride. At that end of the day that’s all any bike that strays from the norm will be. An experiement. There’s only so much research you can do before you’re better of building something and giving it a go!
How did you get the 11mm? I usually use the triangle calculator tool online but seen somebody here worked with sin cos tan too (may be the same thing)
I just want to be really educated before since it will be a large investment for me and i feel like i have a narrower window of operation being a less athletic rider. The goal is to arrive at a middle ground where i can tweak position if needed and without having to use weird stems
Totally get the wanting to know more thing. We’ve all been there! But unless you know exactly what you want or have bike you already love or a fit you really trust then it’s never gonna be perfect. The faster you can get this bike going the more you learn for the next one!
When you wrote this I assumed it was about balance relative to the bottom bracket:
Pushing the front wheel out unweights the front wheel. I know why that is valuable in mountain biking. For road I assume more than half of your weight is already on the rear wheel (since the rear center is much shorter than the front center) and doing additional work to push out the front wheel is unnecessary.
For making a mule for this – look for a 2015-2018ish mountain bike. Many designs had ~74 degree STA and 68 degree HTA. You can then use an angleset and make a long (ugly) fork to model the geo that you want. These frames tend to be inexpensive, for instance I bought my USA-made 853 2014 RSD Triumph frame for $100. You can make a fork quickly and fairly cheaply. Top tube length might be an issue, but sizing down will probably get stack and reach where you want them. It’s going to be ugly, but it’s a way to try the body fit geo (relative saddle, bars, bb positions) and front end geo.
Here is an example of a similar mule built out of an older Bontrager frame by Hahn Rossman using a custom fork to get low-trail. Same idea, but you want a different geo that can be found in a different era of mountain bike frames. My friend Alistair still uses this bike as his daily rider.
Thanks Alex, I think it might have too much weight in the front wheel with the fitted picture above so I’m trying to remedy that (for now until I finalized the fit at least).
Really hard to replicated this geo (im aiming for 70-71HTA but not slacker) but I will try what I can. Or, just try out close enough bike but available in a super small size like diverge for example.
This is such a good idea and that Rossman is fantastic. XC MTB’s from that era and slightly earlier make fantastic gravel/all-road bikes. Yes they can be a bit ungainly when setup with drop bars and skinny tyres but it’s also a cheap way to try out something a bit out of the norm.
