Does frame Geometry REALLY matter in F.S. ?

markz

markz

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Note: Not at all talking about the shocks themselves.

Question
Does the geometry of a 10,000 vs 5,000 vs 2000 vs 1000 really play a role in how a bicycle handles for casual users. Curbs, roots, potholes, lifted sidewalk slabs and asphalt (from roots), 4' diameter x 4" deep remnants of old tree wells, pathway washouts.

Background
I'm on the hunt for a new bicycle frame to build upon and looking around seems like the artsy fartsy / fancy dancy thru-axles and tapered headsets came into effect early 2000's. Expensive headset reducers help with half the problem. I can see now why Justin made that thru-axle motor, I always wondered why he put effort into that, I see why now!

Reason I ask
B.S.O.'s like CCM $400-$500 vs real bikes like Trek Session 7 frame. Which is literally what I got my eye one.

What I will be most likely doing, save my money, weld me up this beast....
http://veloelectriquequebec.forum-canada.net/t102-velo-electrique-strong-gt-s210-batterie-garantie-6-mois
which btw, that seat mount broke, its all steel, I have an ac220 welder. I will extend it out, matching Electra Townie position, beef up existing welds, and drop cash on a good rear suspension component and average fork, Suntour XCM/XCR springy fork. The neat thing with the frame, is its wide rear dropout, perfect match for a mxus 5kw and perhaps a fat conversion to a 20" or maybe 24" with no frame mods.
 
Geometry is the most important factor of a bike’s handling, and geometry has nothing to do with the cost of a bike. A very cheap bike can have the good geometry for you.

We pay the cost of a good DH bike because it is stiff and robust, made for riding fast and hitting hard. That is the reason, and also because it has top quality components.
 
Spend the money on a used DH bike. Anything new enough to have 9" hydro brakes from a decent manufacturer.
I wouldn't modify but instead look for one that has a frame shape which can hold the size battery you want.
 
Yeah I know, spend the money but then I ask myself do I really need a DH and I think with my weight I probably do, then I say to myself they cost too much money. That Strong GTS is a prime candidate for some welding! My guess is buy some tubing and copy the back half, yet make room for 5" wide tires for max cushiness, I got some mystery $10 shock that seems stiff I may give it a try, or find a coil with 800# or even double a pair of coils up, the spring calc states 1500lbs.



Grantmac said:
Spend the money on a used DH bike. Anything new enough to have 9" hydro brakes from a decent manufacturer.
I wouldn't modify but instead look for one that has a frame shape which can hold the size battery you want.
Click to expand...
 
Geometry makes a huge difference. Some important aspects are rake / trail and wheelbase, cg with respect to wheelbase and shock linkage. Whether you would notice the difference if these things were changed depends on a variety of things including skill level intelligence awareness pre-conceptions riding style and how hard you're riding.
 
Unless you are willing to work for free then building (and likely breaking then rebuilding) will be much more costly compared to just getting something that works.
Then again I live in a place where 2005-2010 DH bikes are under $500. So my decision is easy, I can't get the components for that cheap.
 
When you say frame geometry, what are you referring too? Cycling industry utilizes the term "geometry" to convey ALL aspects of a frame design so that buyers can be sure that they fit on a particlular size, and the actual frame configuration - chain stay lengths, wheelbase length, and the steering/ht angles will perform well based on the intended riding applications.

https://www.cyclingabout.com/understanding-bicycle-frame-geometry/

As flat tire indicated, unless you're a seasoned rider with specific needs for a specific application, general casual riding wont require a super detailed amount of attention to these things. Additionally, likely all of the original handling characteristics inherent in the design will be ruined by attempting to retrofit the bike with a bolt upright seating position anyway.

Remember that bicycles, even FS DH frames, were designed to position the rider as if he were actually going to power the machine with his legs, and engineers derived frame geometries from the use case.

You indicated that your weight somehow influences the choice to go full suspension. Why is that?

The other issue you need to consider - buy a used long travel downhill bike, then you have to figure out how to strap a shitton of batteries to it - this is often time more complicated than any other aspect of putting an ebike together, particularly if you want to do it well.

if you're cheap, buying a used purpose built FS bicycle creates more redneck engineering challenges to overcome to turn it into an upright floating ebike.
 
To be more precise after consideration, is the geometry of the way the rear suspension operates from bottoming out, to fully extended, and as flat_tire mentioned the linkage would be important too.

Important, but not factors of susp geo, are all the other aspects like head tube angle (effort in cornering), fork rake (faster/slower steering), fork trail (steering nimbleness), chain stay length (wheelbase, stable at speed, heel clearence), bb drop (saddle height, cntr gravity), seat tube angle, stack and reach, can get someone in the ballpark of a comfy and efficient ride.

Surely the mid-low end to mid-high end (at msrp) are close in susp geo, the high end would be shaving grams and using carbon fiber, and aero. Flipside are the B.S.O.'s (CCM, Schwinn, Infinity, Super Cycle) is all about the bottom line, and how it looks on the walmart rack for future landfill residency.

Yes I am "frugal" aka cheap, patience is key in surfing the online ads to find a good long travel d.h. f.s. bike to save the nut sack from constant daily massages. Seat posts with suspension are not able to handle my weight, and the one that can handle 350 lbs. is like a million Canucka$tan$ (350-400usd). Then not to mention the new fangled b.s. thru-axles, tapered headsets = more costs involved like buying a thru-axle wheel. The tapered headsets have $60 reducers to fit 1-1/8's.

Another important factor that was not at the forefront when I posted this question was the eye candy angle.
Yes, a shiny bike with fancy curves draws attention from the passerby smoking crack and on the hunt for his next fix. This reminds me of a bike I had my eyes on last week, a used Giant frame (no fork) with a fancy curve tube from bb to headset. Cost was $350cdn and was DH or AM, was local, tapered h.s. but normal q.r. I hummed and hawed, but it was sold within 5 days.

1a or 2 are very high on the list right now. 1a is at 75% and 2 is 25%.
1) Keep on getting nut sack massages on the rigid frame with f.s.
1a) Re-"engineer" the b.s.o. from crappy tire, with space for battery on downtube. Plan is, strengthen the known weak welds, extend wheel base, buy a fat fork, work on backhalf susp either by cutting it up to make fat fit (most likely) or copy on new steel (doubt it). I will snap some pics right now and post em up here. I have 16x1.60 rim and Shinko 16x3.0, or a 18x1.85 and need to buy a tire, so probably 18x4.0
2) New $200 Deviant rigid fat from Uncle Weiners import business, probably worse the department store B.S.O.'s
3) New department store rigid fat, $400-$500
4) Used department store rigid fat $200-$300
5) Used Norco, Trek, Rky.Mntn., Speczd frame $200-$300+
6) Same as 5 but new $1k+


View attachment 1



Here you can see the back half suspension getting acquainted with the welder and rims.
Yes, some thinking marks placed already.

 
The rear suspension has nothing to do with frame geometry, if it is set properly of course. If it is unfit for your weight and sag too low, then it is affecting geometry. It is not common that a bicycle shock is designed for a 350 lbs rider, but most spring shocks can be mod for this weight. If you want to keep the entire travel, you need a stronger spring because preload has its limits. The type of linkage is not so important, and it is often too weak to keep stiff with 350 lbs on it. In fact, the easiest tuning is with a single high pivot, like on dirt motorcycles. Your best choice would be a single pivot that is high on top of the crank, or a long shock because it is easier to find and tune a longer spring for extra weght. Avoid air shocks, for even those that can be tuned for your weight would not survive very long.
 
Going cheap..

I would look for an old Rocky Mountain RMX large size. It is easy to mod for a long shock, even motorcycle shock if you want. Very stiff and robust frame, old enough to find very cheap. There were many riding BC, 10/15 years ago. So it should be easy to find one not too far from your home. I have never seen one broken and they are simple suspension design as they get.
 
That RMX is a nice bike, I found none in BC, but in AB there is one fore sale in Edmonton for $750.

I will start off with hacking something together and seeing how it goes. Maybe a 800lb x 2.30 coil which seems to be the highest. I found a Trek Session 7 for a few hundred, tapered 1.5" headset and old skool QR rear, no fork





https://bikerumor.com/2018/02/28/suspension-tech-why-are-coil-shocks-making-a-comeback-on-trail-bikes/
Another key point is the more advanced leverage rate curves being engineered into modern mountain bike frames. With more advanced virtual pivot-style suspension designs, and even linkage-driven single pivots, bike designers are incorporating progressive leverage curves into the physical design of the frame’s kinematics.

That’s actually a really big deal, because previous generation designs relied on the shock to provide most of the bottom-out protection. Air shocks work well for that, because they are inherently more progressive as they compress.
Click to expand...
 
I prefer the RMX to the Session7, for it is a much tougher frame, the rear suspension is very easy to mod, and torque plates simple to make. Here in the east, it is hard to find one, a large especially. I have seen a few on pinkbike. Most of them are 2 inch straight steer tube, giving the most tuning options for steer angle when using a 1 1/8 steer fork and a Cane Creek angle set. Simple mod can fit a long shock, even a moto shock. Hard to beat that frame to build a bike for a heavy rider.
 
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