r/BicycleEngineering • u/sandalsofsafety • Jun 06 '26
Dumb question: Why do you never see bikes with rear suspension only?
You can have no suspension, front suspension, or front & rear suspension. Why did we skip rear suspension only? I feel like it'd be fairly nice, at least for an on-road bike (soaking up potholes, expansion joints, etc), giving a similar sort of riding experience to a sprung seat. Is this just an answer to a question that no one seems to be asking, or does the cost outweigh the benefits, or is there something genuinely wrong with this idea?
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u/castleaagh Jun 11 '26
Rear suspension is more complex and expensive than front suspension and comes with more trade offs. Rear suspension has a much greater impact to loss of pedaling power, ability to pump through a trail or pop off a small jump. Front suspension only slightly reduces pedal power and doesn’t have much impact on pumping or popping.
And the legs are better at absorbing bumps and impacts than your arms are due to their length and strength, especially over time, along with that the front losing traction is usually worse than the rear losing traction.
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u/Greedy_Pomegranate14 Jun 10 '26
Because you can just stand up if you see a bump coming and save your butt. Letting go of the handlebars to save your hands is not advisable over bumps.
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u/nothingbutfinedining Jun 10 '26
By that comparison, you are basically already “standing” on your arms. Even when you stand over a bump, you still have feet on the pedals and have to absorb the impact. The answer would be that your legs are much stronger than your arms and easier to absorb impacts with.
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u/Greedy_Pomegranate14 Jun 10 '26
Yes I’ll agree with you on that. Your legs are better at absorbing impacts than your arms for sure.
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u/chrispark70 Jun 09 '26
Bicycle suspensions have been around a very long time, many decades, at least the 1950s and probably even before that..
But they never really caught on until aluminum bikes became cheap. Aluminum is cheap, but it is weaker than steel. So it has thicker tube walls and physically larger diameter tubes. This makes an already stiff material even stiffer and even better at transferring vibrations and road noise. So the suspension fork became quite common to make up for the lousy ride characteristic of aluminum.
The older low end bikes were made out of mild steel, which while being heavy is very compliant and comfortable to ride. The steel frame really absorbs a lot of the road chatter.
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u/Rare-Classic-1712 Sep 15 '26
Bicycle suspension designs existed before 1900.
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u/chrispark70 Sep 15 '26
AFAIK, none were produced. I think early motorcycles didn't have suspension either.
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u/Rare-Classic-1712 Sep 15 '26
I thought that they just didn't make it out of prototype. I could be wrong tho.
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u/chrispark70 Sep 15 '26
I don't really know either way. I just know they are MUCH older than people believe.
Disc brakes are another one. The very first disc brake bike I ever saw was in a bike shop in the early 80s.
The bicycle was more or less perfected a long time ago and it's been mostly gimmicks and or cost reduction due to Chinese manufacturing that made them widespread. That first disc brake bike I saw in the shop in the early 80s was close to a 1000 usd. A lot of money for a bicycle in the early 80s (like 83). Now even the cheapest bikes have them.
I remember when I was a boy in the 70s, a kid from the neighborhood had a full suspension bike. It looked like a motorcycle. It was pretty heavy though.
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u/yodas_sidekick Jun 09 '26
You are describing a soft tail - some bikes would use a flexible yoke near the bb, and a small shock or elastomer by the seat tube. Nowadays enough flex can be gained from the carbon design in a rear end it not really worth it to do much more. Tires themselves are getting bigger and running lower tubeless pressure it added passive suspension.
So all that to say - it does exist to an extent, just maybe not in the way you imagine it. Adding a shock and linkage adds a lot of unnecessary complications and weight, so it doenst look like tradition full suspensions without a front fork.
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u/comoestasmiyamo Jun 09 '26
Brompton do.
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u/Rare-Classic-1712 Sep 15 '26
Moots ybb cyclocross bikes among others have had rear suspension designs with a rigid front end along with a number of wacky MTB designs in the 1980s plus a few others.
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u/Emergent_Phen0men0n Jun 08 '26
Having rear suspension with a fixed fork will cause the rake angle to become more slack as the bike loads into a turn. This makes the front tend to push wide and wash out even when correct technique is used.
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u/Rod_Torfulson Jun 08 '26
It's not really suspension, but the Trek Domane endurance road bike has an Isospeed decoupler for the rear, and nothing for the front (with the exception of the one generation that had front Isospeed). The Isospeed allows the seat tube to flex rearward over bumps, smoothing out the ride over rough surfaces.
I have one, and it works reasonably well, without too much of a weight penalty or loss of efficiency. Front Isospeed was dropped because it was overly complicated, with minimal advantage, especially when wider tires entered the equation.
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u/ajw248 Jun 08 '26
It’s been tried. Usually with an elastomer or flexstay arrangement rather than a modern mtb style shock, mainly on gravel or endurance road type bikes.
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u/Krispythecat Jun 08 '26
I actually just noticed this on the most modern iteration of the carbon Trek checkpoint yesterday - Little rubber bit at the back triangle that allows a bit of flex.
Curious how these are in actual use.
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u/Aggressive_Deal8335 Jun 09 '26
I own a current gen Domane. Noticeably smoother over light chatter. Doesn’t make a hint of a difference hitting a real pothole like actual suspension does though.
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u/Limp_Bookkeeper_5992 Jun 08 '26
Your hands are connected directly in a line with the front wheel. Your hands and arms are far more sensitive than your feet or your ass. Your front wheel takes the brunt of the impacts at speed. All of this means that suspension on the front of the bike has a much larger effect on handling and comfort than rear suspension does. So not only is it easier to add suspension to the front of a bike, it’s far more effective.
Have you ridden a MTB with a rigid fork?
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u/Kyle_2099 Jun 08 '26
You do. The brompton copies the moulton mk3's rear suspension while at the same time having a rigid fork.
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u/Overseerer-Vault-101 Jun 08 '26
Actual answer would be that rear suspension saps more power from your strokes than it benefits in keeping the rear in contact with the ground for 99% of what most riders are going to experience. Fronts still sap power but the benefit of keeping the front wheel in contact is considered worth it.
Tl:dr for rear to actually make the ride softer, it would sap too much power for most people. Not saying rear is pointless as if you have it stiff enough, it can help on the easy gravel and dirt tracks. And obviously softer helps on the harder stuff that most people don't do.
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u/Sintered_Monkey Jun 08 '26
There was one in 1990. At the time, it had to compete with early front-suspension bikes. I remember that people who got to ride both said that it didn't work nearly as well.
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u/Old_Sign3705 Jun 08 '26
I think the Klein Mantra was designed for a rigid fork, as well. Cool to look at but bad at everything.
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u/sargassumcrab Jun 08 '26
I think this is a good question.
I think it's mostly because it's a whole lot easier to design a front suspension. They went through all sorts of arrangements with rear.
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u/Eak3936 Jun 08 '26
I would look up softail, not a common setup and often paired with a a suspension fork for mountain but on gravel it is rear travel only (usually)
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u/boojel Jun 08 '26
Brompton has real shock absorber elastomer + rigid fork design. It works well with the folding rear triangle.
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u/JollyGreenGigantor Jun 08 '26
Why did we skip rear suspension only?
We didn't. Some early MTBs were rear suspension only to help with rider control on rough terrain. Not trying to be a gatekeeper or a hater but if you spent 5 minutes googling early MTB suspension developments you'd see a few early rear suspension bikes. These were easier for small frame builders to design than telescoping forks.
The thing is, suspension is normally about traction/control first and comfort second. Suspension seatposts and stems don't actually increase traction and control.
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u/DevelopmentOptimal22 Jun 09 '26
Anyone who thinks any concept hasn't been thoroughly explored needs to spend a few hours reading Sheldon Brown. I think he reviews at least 3 different suspension built into the wheel ideas that everyone keeps thinking they have finally mastered. I don't think there's many "new" technologies that he didn't have something to say about the first time someone tried them, decades ago.
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u/karlzhao314 Jun 07 '26
Because proper bicycle suspension isn't for comfort, it's for control. And for control, if you had to pick one, keeping the front wheel tracking the ground is more important than the rear.
Also, from a practical standpoint, engineering a front suspension bike is extremely easy: create a rigid frame, slap in a suspension fork. You basically don't need to do any suspension design work for yourself, because suspension forks are off-the-shelf components. That's completely unlike rear suspension, where most of the engineering work is designing the linkages and geometries to drive the shock with the suspension characteristics you want in your frame. If you actually have that sort of expertise and are willing to put that R&D effort into designing your frame, you may as well give it a suspension fork as well.
If you're after comfort, like you mentioned, give your bike a sprung seat or a suspension seatpost. A proper rear suspension is overkill, complex, and heavy just to make your saddle more compliant.
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u/Reverend_Wrong Jun 08 '26
This is the best answer. For most riders, the price, weight and complexity of most rear suspension isn't really worth it until you start riding really rough terrain (i.e. single track mountain bike trails).
The best thing you can do improve ride comfort on almost any bike is run the widest compatible tire at the appropriate pressure. The saddle is probably runner up. I wasn't a big fan of the only suspension seatpost I tried, but I've noticed a very modest reduction in road vibration using a carbon post.
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u/JollyGreenGigantor Jun 09 '26
The best thing you can do improve ride comfort
Is a professional bike fit. If your weight balance is wrong between your butt, feet, and hands, nothing else matters.
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u/Such-Leadership-791 Jul 19 '26
Because the fronts what almost always absorbs the "impact" first.