Trail, Stack & Reach

[mstateglfr]

Originally Posted by Nomadmax

I grew up on and raced "traditional" frames from Italy and Belgium, and still ride them. They handle and ride the way I want, fast or slow, never making themselves known to me while we go down the road, climbing or sprinting. I have but one modern bike amongst my fleet of Merckxs and Guerciottis. To say that bike is the worst handling bike I've ever ridden, and that includes my 1971 Schwinn Varsity, would be a massive understatement. I only knew how to ride and race, math was never my strong suit, heck, let's be honest, it's a suit I don't even own.

I have two questions that may or may not have clear answers.

What is the trail number (in general) that won't try to flop the front wheel from left to right when out if the saddle climbing or sprinting?

Note:
The bike I'm talking about has (with 700x38)
Trail
77mm
Wheel Flop
24mm
Mechanical Trail
73mm

60mm? Is that the magic number?

I have no idea what the trail numbers are for any of my current fleet. All I know is that they do exactly what I want, and nothing I don't.

So I read your comment yesterday and saw your bike(with 43mm tires) has almost 80mm of trail. I think technically 79mm. I figured up 43mm because thats the tire size I use so I was comparing it to my gravel bike.


My gravel bike is a Fairlight Secan that has 60mm of trail with 17mm of wheel flop.
I think it is fun to ride, easy to steer, stable without hands on pavement, not sluggish steering, etc. I view it as neutral and that is a compliment. I dont want a gravel bike that is twitchy, but also dont want a gravel bike that has a ton of wheel flop and is vague in steering.

Your Lynsky GR300 with 43mm tires(to keep the comparison the same) has 79mm of trail and 25mm of wheel flop. A higher wheel flop number will make a front wheel feel like it tends to steer off its like at slow and mid speeds.



The Lynskey head tube angle is so slack that even a high offset fork will only partially fix the issue, assuming you want it to steer more like your road bikes. A 55mm offset gravel fork would still only get you to 68mm of trail and 22mm of wheel flop.

Now I am guessing on your road bikes, but if they have 73deg head tubes and 43mm fork rakes(pretty common numbers for steel road bikes from 30-45 years ago), with a 28mm tire you have 60mm of trail and 17mm of wheel flop.

^ Notice those numbers mirror my gravel bike with 43mm tires. Its a large reason why I really like how the bike feels.




Obviously I am biased and think my gravel frame is awesome, but I recognize that the 853 steel, while nice, is overbuilt due to having to be that way to pass testing. I am 220# though, so I imagine it is less of a negative for me compared to a light rider.

You mention titanium, and cool if you want to stick with that, but if you havent considered Breadwinner, maybe that would be a great option for you.
The Breadwinner B-Road is a Columbus Spirit tube bike with an Enve gravel fork. The seat tube, head tube, and top tubes are custom length, but the rest of the geometry is stock. The 72.5deg head tube angle along with 47mm fork results in 62mm of trail and 18mm of wheel flop if you use 38mm tires.
https://breadwinnercycles.com/product/b-road/#frame



Obviously there are a ton of frames out there to choose from. With gravel you often dont want too steep of a head tube angle, so a slack angle is then offset with a higher fork rake to then bring the trail down.
72.5 HTA with a 50mm fork = 59mm of trail and 17mm of wheel flop with a 38mm tire.
71.5 HTA with a 55.5mm fork(enve adventure fork) = 60mm of trail and 18mm of wheel flop with a 38mm tire.
72.5 HTA with a 47mm fork = 62mm of trail and 18mm of wheel flop with a 38mm tire.

^ just some general numbers to help show the relationship between head tube angle and fork offset.


Riding an unfun steering bike is no way to live life.

[Dave]

Saddle to bar drop can be calculated from saddle height. Stack and reach can also be calculated with TT length, frame size c-c and seat tube angle. There are online calculators that will do it.

As for trail, I've owned Colnago and Cinelli with lots of trail and LOOK with 58mm. None of them bothered me.

[OtayBW]

Geez - My DeRosa Primato has what I thought was high trail at ~65mm. It handles like that. Tom Kellogg writes that 56mm trail gives a frameset ~neutral trail for 700-C wheels.

[Dave]

Reading your first post again, I see that I have the same saddle height, so calculating a stack should be simple. Stack does not include the headset top cover height. 15mm was the most common height for a long time. Stem angle also has to be considered since -17 is no longer the most common like it was with quill stems.

I have one bike with a -17 stem and 11cm saddle to bar drop. It has a 510 stack and 30mm headset top cover for a total of 540mm. To get 4cm of saddle to bar drop, you'd need a total of 610mm of stack, so I'd plan on a -6 stem to help reduce the total stack by about 20mm. 590mm would be 575mm of frame stack and 15mm of headset top cover.

A medium Arenberg would probably work.

[Nomadmax]

Wow, thank you for the responses. I got in touch with Litespeed to see if I could arrange a test ride by driving down to TN. Not possible. At this point, it isn't really the money, it's the time. I'm not getting any younger. Ultimately, I may have to have something custom built as my last "new" road bike. I'll keep the Lynskey to beat on during gravel rides, to town for errands and make it a sacrificial lamb for winter. Let's see how Ti fairs with salt and beet juice

If this thread does nothing else, I hope it makes people stop and think about all those little numbers before buying a new bike or frame/fork. Because apparently, numbers mean stuff

[NHAero]

Here's one more thought. Not to take the place of a properly designed new bike y'unnerstand.

You could find a fork (or have one built) that fits the tire you want but not the 700x45 the bike is designed to accept, and that fork may have a shorter axle-to-crown length. Every 18mm shorter A-C steepens the HT angle one degree. Say you went from a stock fork at 395mm A-C to 383mm (Whisky 9 Road+, whcih is rated for up to 700Cx38). That adds 2/3 degree to the HTA, and with the Whisky 51mm rake the trail goes down to 64mm and flop to 20mm with a 700x30 tire. If you could find a fork with 55mm rake, these values drop to 60mm and 18mm.

Shorter A-C lowers the front end, so you may need to lift the bars back up another way (more spacers or higher stem) and it drops BB height so pedal strike might be more likely. This also depends on the crank length you run.

[spoonrobot]

I think there may be a angleset available for the Lynskey too.

[Nomadmax]

Originally Posted by NHAero

Here's one more thought. Not to take the place of a properly designed new bike y'unnerstand.

You could find a fork (or have one built) that fits the tire you want but not the 700x45 the bike is designed to accept, and that fork may have a shorter axle-to-crown length. Every 18mm shorter A-C steepens the HT angle one degree. Say you went from a stock fork at 395mm A-C to 383mm (Whisky 9 Road+, whcih is rated for up to 700Cx38). That adds 2/3 degree to the HTA, and with the Whisky 51mm rake the trail goes down to 64mm and flop to 20mm with a 700x30 tire. If you could find a fork with 55mm rake, these values drop to 60mm and 18mm.

Shorter A-C lowers the front end, so you may need to lift the bars back up another way (more spacers or higher stem) and it drops BB height so pedal strike might be more likely. This also depends on the crank length you run.

Originally Posted by spoonrobot

I think there may be a angleset available for the Lynskey too.

I'm not saying that wouldn't work, but........

I've found in my 64 times around the sun that trying to salvage any kind of "relationship" that wasn't right, always ended in disappointment, or worse. The best decisions I've ever made were when I walked away and started over.

[NHAero]

Originally Posted by Nomadmax

I'm not saying that wouldn't work, but........

I've found in my 64 times around the sun that trying to salvage any kind of "relationship" that wasn't right, always ended in disappointment, or worse. The best decisions I've ever made were when I walked away and started over.

It's what I did to my Litespeed Unicoi MTB to convert it to a dropbar “monster cross”. Shorter fork, more rake, worked out well. So it's possible, is all I'm saying, if you intend to keep the bike. I'd just sell it.

[Nomadmax]

Originally Posted by NHAero

It's what I did to my Litespeed Unicoi MTB to convert it to a dropbar “monster cross”. Shorter fork, more rake, worked out well. So it's possible, is all I'm saying, if you intend to keep the bike. I'd just sell it.

You're right, I may look into that as well.

The deeper I dig into this, the more questions I have that I can't really wrap my head around, despite reading the answers.

Trail vs Mechanical Trail. The explanation is that they are measured differently but I can't find a visual example that would help me understand. The one is measured horizontal and the other perpendicular, but where/how? More importanly, which one is more important for my purposes?

The other question is:

Head tube extensions, do they change the stack (+) and reach (-) by the same amount that they extend the head tube?

https://litespeed.com/collections/ac...tube-extenders

IE can a 30mm extender make a 55cm stack into a 58cm stack and a 36cm reach a 39cm reach?

If that's the case, do they eventually creak or otherwise cause problems?

To some of you, this is probably so simple that this may look like one of those troll threads. I assure you, I really want to know and am truly simple minded.

[Nomadmax]

Originally Posted by spoonrobot

I think there may be a angleset available for the Lynskey too.

If read this right

https://canecreek.com/product/angleset/

This would work on my frame/Adventure fork and change my 70.5 HTA to 72?

https://lynskeyperformance.com/gr300...verstock-sale/

[spoonrobot]

For bicycles mechanical trail vs. trail doesn't really matter that much. There's some strong opinions on this that matter more at the advanced/complex geometry edge cases but for most road/gravel bikes they're interchangeable as long as you remain consistent with using either in comparison between bikes.

It's also helpful to remember that trail is a driving number that is important only in that it illuminates wheelflop - which is the more succinct measurement of how a bike will handle at the front end.

A track bike with 75° HTA, and 30mm offset fork has 60mm of trail w/15mm of wheelflop.

A road bike with 73° HTA, and 41mm offset fork has 60mm of trail but has 17mm of wheelflop. This is a large change and the two bikes would have very different handling.

Wheelflop change is % based so even a <2mm change can have large effect.

Mechanical Trail: is the perpendicular distance from the front-wheel contact patch to the steering axis (described as positive when the axis is ahead of the contact patch).
Trail: is the distance with respect to the ground from the front-wheel contact patch to the steering axis (this is the more commonly used measurement).

Here is a graphic I made for you, all the references I have are otherwise for motorcycles/race cars and needlessly confusing. Hopefully this is more clear.

[Mark McM]

Originally Posted by Nomadmax

Trail vs Mechanical Trail. The explanation is that they are measured differently but I can't find a visual example that would help me understand. The one is measured horizontal and the other perpendicular, but where/how? More importanly, which one is more important for my purposes?

If you were to draw a line through the steering axis, than the distance between the point where that line through the steering axix intersects the ground and the point where the front wheel contacts the ground is the trail. Mechanical trail is the distance from the front wheel ground contact point and the steering axis, measured perpendicular to the steering axis. In the diagram below, the trail is labeled "ground trail" and the mechanical trail is labeled "real trail". For the small range of head angles on bicycles, the two will be roughly proportional, so because references to trail in bicycle geometry is the "ground trail", it's probably easiest to refer to that.

Originally Posted by Nomadmax

Head tube extensions, do they change the stack (+) and reach (-) by the same amount that they extend the head tube?

https://litespeed.com/collections/ac...tube-extenders

IE can a 30mm extender make a 55cm stack into a 58cm stack and a 36cm reach a 39cm reach?

When a head tube extender is added, stack will increase in proportion to the sine of the head angle, and reach will decrease in proportion to the cosine of the head angle. For common head angles on bikes, the stack will increase by about 95% of the extender length, and the reach will decrease by about 30% of extender length. So in your example, adding a 30mm extender to a frame with 550m stack and 360mm reach with a 30mm extender will change its effective stack to 579mm and effective reach to 351mm.

[spoonrobot]

Originally Posted by Mark McM

Just link his page next time, it's a good resource. And nobody ever understands that diagram when it's posted by itself.

https://www.peterverdone.com/wiki/in...chanical_Trail

[unterhausen]

For normal road riding, stem length has very little effect on handling*. Handlebar width does. I made the mistake of putting narrow bars on a high trail bike and the flop is just awesome getting while standing. And when I say awesome, I mean that I'm surprised it's never caused me to crash. But I do get used to it after a while if I've been riding my road bikes a lot.

*if you show me your free body diagram, I'll show you mine. Cognitive bias doesn't count as a FBD.