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help with bike geometry

Old 08-23-22, 12:55 PM
  #1  
arlobike
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help with bike geometry

I’ve been experimenting with mountain biking in the last year, after decades as a road cyclist. Since I wasn’t sure I’d take to it or what kind of rides I’d end up doing, I limited my initial investment to a used Gary Fisher Big Sur (26” hardtail) from 1997. I felt immediately at home on that bike with its stretched out, road-like position. And it works pretty well for the riding I’ve gravitated toward: mostly smooth singletrack and gravel roads with long climbs.

Now I’m considering buying a new bike to take advantage of some newer tech: 29” wheels, 1x drivetrain, better suspension fork. But I’m hung up on how different the geometry of new bikes is. I’ve mainly been looking at XC models, but a new XC bike seems more similar to a new trail bike than to this old Big Sur. I got that impression from looking at the geometry charts, and riding a range of models at my LBS. They all seemed squished and upright compared to what I’m used to.

So my question is, what are the benefits of this geometry and riding position, and should I try to stay close to what I have or let that go and embrace modern MTB design? The LBS salesman said comfort was a benefit, but I haven’t felt uncomfortable on the Big Sur. Internet searches tell me that XC bikes have become more like trail bikes because XC racing courses have become more technical. I'm not seeking out technical routes, but here are three specific situations I’m curious about:
  • I’ve been on tight switchbacks and quick curves that I could barely get around on this bike, and all newer bikes have a longer wheelbase. Will this be even more of a challenge on a newer bike?
  • It takes a lot of concentration on steep climbs to keep the rear wheel from sliding while also keeping the front wheel from lifting off the ground. Would a newer bike be more stable in this way?
  • If I’m climbing and encounter a root that’s more than a few inches high, it’s very difficult to get over without stopping (most of my falls have come from trying!). Could a newer hardtail help with this, or is this more a job for a full suspension (and/or more riding experience)?
At this point I haven’t seriously considered a full suspension. While that might open up more trail options for me, coming from a road background, a full suspension system just seems intimidating. I think I’d rather stick with trails that have minimal roots and rocks, plus gravel roads and an occasional paved section connecting them.

Sticking with the Big Sur is also an option, but I’d at least like to upgrade the fork and I haven’t found any new models that have the correct travel and brake mounts.

1997 Big Sur specs:
71 head angle
74 seat angle
161mm steerer
? stack
640mm reach (25.2”)
290mm BB height (11.4”)
38mm offset
74mm trail
1030mm wheelbase (40.6”)
560mm handlebar width

New XC bikes I've looked at have a wheelbase of around 1100mm, a reach of around 410mm and a head tube angle of around 69 degrees.

Last edited by arlobike; 08-23-22 at 03:09 PM.
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Old 08-23-22, 06:30 PM
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Over the past 25 years, mountain bike fit and geometry has become MUCH better for mountain biking. Yes, there is some unlearning of road riding habits and preferences you need to deal with, but the payoff s a much better mountain bike. Steep seat tubes, WIDE bars, short stems, long front ends, slack head angles.... it all just works really well. I stated riding n the 90's, in a bike similar to yours.

That said, as they have become better at riding off road, they are a little less good at stuff like gravel and paved roads. I mean they work fine, but not as well as more road like geo of old bikes. I find the steep STAs and the wide bars a little tiring once I am plopped down and just spinning on a not steep gravel or paved road for a bunch of miles,

But once you are on singletrack (or climbing a steep gravel road) its not even close. After riding modern geo, 20+ year old geo seems downright sketchy. I'm like "what the hell were people thinking?"

Regarding switchbacks, I don't really find them any harder. If anything they are easier. The steeper seat tube angles and the way you sit on the bike actually helps keep the front end down, which is really what a lot of getting up switchbacks comes down to, and the longer, more stable front helps going down. In my experience, these make up for any negatives from the extra length. If anything I am hitting switchbacks faster and with more confidence now.

Climbing and keeping the front/rear weight balanced is easier on modern geo, in my experience. Again, the steeper STA.

Regarding getting over roots on a climb... not sure if modern geo is going to help.

The stretched out fit you are describing started to change in the early 2000s. That road-like stretched out position is not so great when you are trying to move around the bike, throwing your weight fore/aft. And with the short wheelbase, you really NEEDED to do that. Modern geo requires a less exaggerated body movements fore/aft, while at the same time making such movement easier.
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Old 08-24-22, 09:20 AM
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Originally Posted by arlobike View Post
  • If Iím climbing and encounter a root thatís more than a few inches high, itís very difficult to get over without stopping (most of my falls have come from trying!). Could a newer hardtail help with this, or is this more a job for a full suspension (and/or more riding experience)?
At this point I havenít seriously considered a full suspension. While that might open up more trail options for me, coming from a road background, a full suspension system just seems intimidating. I think Iíd rather stick with trails that have minimal roots and rocks, plus gravel roads and an occasional paved section connecting them.

s.
Popping the front wheel up and over a big tree root (if its more than a few inches high, i call it a log - lol ) is an issue for even some of us who have been riding mountain bikes a loooong time -- i would say one of the newer 29'ers would help as the greater circumference of the wheel smooths things out a lot when rolling over larger objects compared to a 26" wheeled bike
- more riding experience is always a plus - but there times when i say - heck with it and just dismount and hop over . Im not very tall so the dropper posts common on bikes now makes a dismount a lot less of a pain than it used to be

For the use youre describing , a short travel hardtail would be right up your alley, but that said - if you have a few decades under your belt agewise, a full suspension bike can certainly enhance comfort and the latest designs do not really bob and result in energy loss like folks seem to think they do.

I remember the results of a study years back on pedalling efficiency amongst cyclists of different disciplines and it was widely though that it would be track cyclists, -- but alas, 'twas XC mountain bike racers. The smooth and efficient pedal stroke, it was supposed, was fostered by the mountain bikers consciously trying to eliminate the bob of a suspension bike
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Old 08-25-22, 02:02 PM
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I'm 5'10 and I prefer a 450 reach. Modern bikes are MUCH more capable than older ones, I have a collection of 80's-90's mountain bikes in addition to modern bikes. Modern is awesome for anything technical. Old is fine for the paved paths.

For the big sur, a Marzocchi Z2 (old style) is tough to beat. Minimal maintenance, coil & oil and seals are readily available

Last edited by eshew; 08-25-22 at 02:07 PM.
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Old 08-26-22, 01:24 AM
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Originally Posted by arlobike View Post
a head tube angle of around 69 degrees.
too steep...are you racing x/c?

https://www.pinkbike.com/news/video-...oundtable.html

Last edited by tungsten; 08-26-22 at 11:29 AM.
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Old 08-26-22, 10:39 PM
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Thanks for the replies! This info and encouragement now has me excited about a new bike rather than feeling reticent about it.

​​​
Originally Posted by tungsten View Post
too steep...are you racing x/c?
No racing, but I do love climbing and a more agile feel seems fun, so I've mainly looked at XC models. That said, one that I'm attracted to is the Cannondale Scalpel Hardtail, but its slacker 67 degree head tube angle stands out from the other XC models I've seen. I don't know if I'm ready to go that far yet! But one review (I'm not allowed to add links yet) says it has great handling and even says it can double as a gravel bike. Hardly anything is in stock anyway, so I have plenty of time to think it over and hopefully find more reviews as more bikes become available.
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Old 08-27-22, 07:58 AM
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Iím fairly old school in all things. I did hang up my mountain bikes in the late 90ís only to pick it back up a couple years ago.

Its not even comparable. What a basic XC bike can do compared to that 26er youíve got it night and day.

Wanna get crazy? Get some geometry thatís a bit slacker. My hardtail has a 65.5 head tube and the shortest chainstay they could fit. It also came with 800mm handlebars (which I trimmed a little) and a 160mm fork, thatís double what the DH forks had in the 90s.

I canít tell you how many times Iíve shocked myself that I just climbed up something 32x10-52 helps too. Or the rock gardens, berms, and launching pads Iíve gone over.

This big ol bike has no issues on tight switchbacks but the 69 degree 29er it replaced sure did.

The huge difference youíll notice is that 28-30lbs for a hardtail is pretty standard, maybe even on the light side. That includes much bigger wheels, bigger and wider tires, a dropper, and a fork that makes your old Manitou 4 look like a toy (it was). Itís one of those situations where the extra weight is almost certainly going to improve your times and definitely improve your enjoyment.

Last edited by rosefarts; 08-27-22 at 08:35 AM.
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Old 08-27-22, 10:07 AM
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Donít get too hung up on HTA numbers. Its just one aspect of a whole package.
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Old 08-27-22, 10:59 PM
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arlobike
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Originally Posted by Kapusta View Post
Donít get too hung up on HTA numbers. Its just one aspect of a whole package.
That's what I was trying to tell myself, but I do get obsessive sometimes. Thanks for the reminder.
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Old 08-29-22, 02:31 PM
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Originally Posted by arlobike View Post
I
  • If I’m climbing and encounter a root that’s more than a few inches high, it’s very difficult to get over without stopping (most of my falls have come from trying!). Could a newer hardtail help with this, or is this more a job for a full suspension (and/or more riding experience)?
A newer bike won't help. It's about skill.

Just before you are about to hit the root lift up on the front end like you are going to do a wheelie then unweight the back. The front tire will roll over very easily and the back tire will follow provided the root isn't tall enough to hit your bottom bracket. This video shows a log but the concept is the same for taller roots that are difficult to roll over.

#3 on the video.

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Old 08-30-22, 11:10 AM
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arlobike
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Originally Posted by prj71 View Post
Just before you are about to hit the root lift up on the front end like you are going to do a wheelie then unweight the back.
Thanks for the video. I've only had a problem when I'm climbing steeply and have very little forward momentum to work with, especially if I'm already struggling to keep the front wheel on the ground. I realized on a ride last weekend that when I lift or unweight my front wheel in that situation, I lose steering control and the bike quickly falls to one side. For smaller roots I found that it was actually better to put more weight forward, to make sure the front wheel stays planted, and power over it. The nice thing about being a beginner is that I learn something on almost every ride!
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Old 08-30-22, 11:33 AM
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Originally Posted by arlobike View Post
Thanks for the video. I've only had a problem when I'm climbing steeply and have very little forward momentum to work with, especially if I'm already struggling to keep the front wheel on the ground. I realized on a ride last weekend that when I lift or unweight my front wheel in that situation, I lose steering control and the bike quickly falls to one side. For smaller roots I found that it was actually better to put more weight forward, to make sure the front wheel stays planted, and power over it. The nice thing about being a beginner is that I learn something on almost every ride!
I think the trick with climbing over bigger roots (or water bars, onto ledges, or whatever) is to lift the front wheel without moving your weight back much when you lift the wheel and getting it forward again really quick.. I am trying to picture what I do exactly, but I end up with my weight pretty forward after my tire is over (or on top of) the obstacle. Then it is a matter of unweighted the rear and giving the bike a shove forward underneath you. It helps a lot if you can give a little burst of speed just before hitting it, as that lets you get your weight forward quicker after getting the front end up. Getting out of the saddle to start with helps.

D@mn, this is pretty hard to explain. Sorry if this is clear as mud.

Last edited by Kapusta; 08-30-22 at 11:36 AM.
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Old 08-30-22, 01:46 PM
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Originally Posted by prj71 View Post
A newer bike won't help. It's about skill.
I respectfully disagree. I spent the last few years on an old school hardtail giant and my new Top Fuel takes what skill I have and multiplies it due to the new geometry/features.

To the OPs question. You will likely get the most benefit from the 29 inch wheels and the modern geometry. The larger wheels go over obstacles such as the root you are describing far easier. I feel the slack head tube angle benefits me as well in the regard. May be the seat tube angle as well or more so but I don't know.

I can negotiate much tighter turns on my much larger bike and climb better as well. I have also been working on using the dropper post which is a very cool and nice feature now that I have begun figuring that out.

I guess the real question is do you want to try and improve your skills on the older style and then move to the newer style. For me its a no brainer. The new style has increased what my current skills can accomplish and I can work on my skills without having to relearn the bike.
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Old 08-30-22, 01:48 PM
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Letís not pretend that all things are equal.

In the 90ís I had a ProFlex and a Zaskar LE. I thought both were amazing.

Then I got a very basic Trek Xcaliber, from the mid 2010ís and was blown away by how much more capable it was.

Iím on a Yelli Screamy now, and itís light years beyond the Trek.

Especially for technical climbing. Iím constantly blown away at what Iím getting over and what Iím not falling off on. Itís a gigantic difference.

Skills matter but itís dishonest to run around telling someone they just need better technique. Sometimes our gear really does hold us back.
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Old 08-30-22, 02:46 PM
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Itís not dishonest in this case. I agree that modern geometry makes an enormous difference is so many ways, including technical climbing. However, I do not find it to make much difference in the specific situation that the OP is talking about.

Or maybe it does before you nail the technique. Sort of the way chainring clearance matters in log-overs before you figure out the proper way to do them.

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Old 10-26-22, 12:29 PM
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Well, after lots of research, I finally acquired a new bike and wanted to follow up with my experience with it. I settled on a Cannondale Scalpel HT 4, because it combines the light weight of a race bike with a head angle closer to a trail bike, and managed to find one in stock at a bike shop that could ship to me (my local shop said they wouldn't have one for 11 months). I did two easier test rides, then took it on a longer trail that was at the edge of my abilities on the old bike. I won't say this is multiples better or changes the way I can ride, but it makes things maybe 10-20% easier, and that was enough to allow me to complete the whole route without putting a foot down.

Specifically, the 29" wheels do indeed feel more capable over rocks and roots (and feel much faster when I ride a paved road to the trailhead). The slacker head angle and longer wheelbase also give a lot of stability, and I haven't noticed any loss of agility. In fact this seems to handle switchbacks better somehow -- I can really crank the handlebars to one side and still feel stable. The 760 mm handlebar width felt natural, although I need to dial in the position to improve the wrist angle -- but when I jumped back on the old bike for a comparison, its 560 mm handlebars suddenly felt ridiculous. I've felt the most benefit on rough or loose climbs. While the old bike would be wheelieing or spinning out, this one just churns uphill. It feels like a tank -- but a svelte, 24 pound tank. And then on smooth climbs, it goes up like a road bike. The 1x drivetrain is super convenient, and the 100 mm front travel compared to 60 mm on the old bike has been nice on rough descents. My position doesn't feel squished as I feared, it just feels natural when riding on trails.

I still have skills to work on (now that I'm riding over more stuff, my new nemesis is pedal strikes) but this does make the chunkier trails more rideable for me. Thanks for encouraging me to make the leap.
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