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650b Front / 26" Rear vs. 650B Front & Rear?

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michaelsnead

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Discussion starter · #1 ·
Hey Guys,

I'm asking this as a question based on the amazing benefits I've received since putting a 650b front wheel on my bike. I left the rear wheel unchanged.

I'm riding a 2007 Specialized Enduro SL Pro and I use it for classic All Mountain rides. Most of them start with extended climbs done at a “social” pace and end on a fun DH with stunts, jumps and drops along the way. Since the beginning of the year I’ve been on a mission to update my bike and have replaced the Specialized suspension with a Pushed 2011 Rockshox Monarch Plus RC3 shock and a 2011 Fox 36 Talas 160 RLC FIT fork. This is the 650b wheel I put on the bike:

ZTR Flow 650b - Pacenti Neo-Moto 650b x 2.3 - DT Swiss 240s Front 20mm Thru Axle - Magura Storm SL Rotor

I expected the enhanced "roll over" effect to aid in descents and I've been richly rewarded in expectation. However I've been surprised at how much more efficient I am on technical climbs because of the new front wheel. It's allowed me to dramatically reduce the number of times I have to lift the front wheel to clear an obstacle. Therefore I keep my butt planted on the saddle continuing to generated the meager amounts of power my old legs can produce. The net effect is I'm consistently making technical climbs that were only a dream before the wheel change.:D

It feels like the 26" rear wheel is generating more power than a larger wheel would. Since I haven't ridden a bike with 650b front and rear that is just a guess on my part. I'd appreciate it if those of you with experience on all three combinations of wheel sizes (26/26 vs. 650b/26 vs. 650b/650b) would comment regarding the issue of technical climbs. My question is for just technical climbing is the 650b/26 combination superior to the same bike with 650b wheels at both ends?

Thanks, in advance, for sharing your thoughts!

Michael:thumbsup:
 
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#3 ·
.650b in the rear balanced out the roll over characteristics but will add BB height & steepen the HA - may hurt descending if your current geometry is spot on.
 
#4 ·
Whether or not to go 650b front-only, or both ends if possible, mostly depends on whether a slacker handling geometry or higher BB with near original handling feels better to the rider.

For climbing a 650b rear adds about 35 - 50 grams (about 1.5 ounces) rim + tire + spoke weight, using the same brands/models. And raises the gearing rate 4%, about 1.4 teeth higher rate in the lowest cog.

For many, being forced into a higher gear encourages increased speed, momentum, and faster climbing.

When converting a 26" to 650b front-only, adjusting seat position slightly forward and bars 1/2 inch lower adjust most of the handling feel back to the previously familiar fit before converting.

The frame geometry returns to near original steepness adding a 650b to the rear, and raises the BB the majority of the 1/2 inch axle height difference.

I ran 650b front only for 6 months before adding a 650b rear, and both were noticeable improvements for me above granny gear climbing speeds. I mostly ride tight sometimes very rocky and eroded single track, and the added BB height with a 650b rear was a welcome improvement in nearly eliminating pedal strikes on my bike. And the original frame angles are more balanced for the faster smooth twisty sections and switchback turns, and I have a u-turn fork to raise for extra rocky and fast downhill. The 650b rear reduced rolling resistance slightly too, especially when muddy.
 
Discussion starter · #5 ·
derby said:
.....a 650b rear adds about 35 - 50 grams (about 1.5 ounces) rim + tire + spoke weight, using the same brands/models. And raises the gearing rate 4%, about 1.4 teeth higher rate in the lowest cog.....
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Hi Mr. derby,

Thanks for sharing your experience. It's interesting that you mention the weight a 650b wheel should add. That makes sense to me but in my case the 650b front wheel, using the same brand & model rim/hub, is 2 oz less than the 26" wheel I replaced. The tire on the new wheel is a Pacenti Neo-Moto 650b x 2.3 and my 26" tire is a Specialized Eskar Control 2Bliss Ready x 2.3 that is advertised as a 700 gram tire. My 26" complete wheel is 4 lbs, 2 oz and my 650b complete wheel is 4 lbs. My only guess is that the difference is in the spokes and real world weight of the tires?!?

Also thanks for quantifying the increase in gearing rate by adding the 650b rear wheel. That confirms my guess that the 26" wheel provides more torque in the granny gear.

Thanks again,

Michael:thumbsup:
 
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#6 ·
I have both size wheelsets and switch rear periodically and agree on the slight noticable torque with the 26 in back over time on longer rides with alot of climbing. But not as much as the benifit of rolling over stuff when the 650 gets up to speed. ;)
 
Discussion starter · #7 ·
JMac47 said:
I have both size wheelsets and switch rear periodically and agree on the slight noticable torque with the 26 in back over time on longer rides with alot of climbing. But not as much as the benifit of rolling over stuff when the 650 gets up to speed. ;)
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Hey Mr. JMac,

Thanks for sharing your experience and confirming my guess!

Take care,

Michael:thumbsup:
 
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#8 ·
I'm still surprised that the off road bicycle world in general still sees the same wheel size in front and rear as the norm. Dirt motorcycles have long since put this notion to rest. While some try to dismiss the correlation between dirt motors and MTBs, to anyone with a brain it should be obvious. The 2-wheeled dynamics for dirt motors and MTBs share lots of similarities. Just looking at the shared suspension principles and components between the two venues should give some insight.

While MX bikes have settled on a slightly taller rear wheel at 19", the trail, enduro, and off road models prefer the 18" wheel. A groomed MX track benefits from the taller wheel with shorter sidewall rubber for better tuning in groomed dirt, while the rockier, ledgier off road environment benefits from the taller sidewall rubber for better pinch flat protection and lower pressures. The two are very close in overall tire height.

Our MTB'ing is very much like off road/trail dirt motoring...rocks, ledges, etc. The taller front wheel/tire setup is great for carving in the turns and providing optimum rollover. It's not too tall to cut into front fork travel to a negative degree. Dirt motor folks tried a 23" front wheel for a short time and found it compromised overall handling and fork travel too much. My dirt motor has a 21/18 setup. For dirt motor wheels, they actually match the wheel size to the actual size of the rim, unlike bicycles. My entire front wheel/tire height is 27.5"...kind of ironic, right?...LOL! My rear wheel/tire is 25.5".

So...you think what does wheel/tire size on a dirt motor have to do with an MTB? A lot. The rollover and cornering dynamics are very similar. The spin-up and acceleration elements at the rear wheel are also very similar...motor or not. Huge, tall rear tires on dirt motors slow acceleration just like on an MTB. You have to make serious gearing compromises in many cases in both venues. For dirt motors it's usually better to balance the rear tire size to traction, power, and acceleration factors. Even the big, high powered, 450 enduro bikes are using tires in the 110/100/18 size range...and that's not a huge tire by any means like some of the old school setups with 130 and 140mm widths with equally large heights.

So...for dirt motors with 21/18 setups, you get the tallest front wheel/tire setup without sacrificing fork travel, and you get the tallest rear wheel/tire setup without sacrificing too much rollover quality, acceleration, traction, and travel. So...with a 650B in front and 26 in back, you get a very similar comparison.

Now...I'm mainly applying all of this to full suspension bikes. No offense to anyone who enjoys a hardtail or other, but I don't consider those bikes optimum for mountainbiking. I said "optimum". While you hear all manner of wailing and gnashing of teeth about how great a hardtail or rigid is, I think those comments are based on a personal bias and pursuit of something unique. If the trail has any decent roughness to it, the same level of rider on a high end full suspension bike will best the hardtail or rigid bike. Nothing wrong with wanting to ride what you want but don't try to defy physics in the real world. When I see dirt motors in the form of hardtails besting full suspension dirt motors in decently rough terrain, maybe I'll reconsider...LOL!:lol:

This concept of mountainbikes having a taller front wheel/tire setup over the rear should probably be the norm. But unlike dirt motors where function almost always trumps form, mountainbikes have such a wide lattitude of preference which often overcomes function.
 
#9 ·
I totally agree with TNC. I built up an Ellsworth Truth with a 650b front and a 26" rear. The handling is perfection and no ill affects to acceleration. This is in my mind the only way to set up a mountain bike. After doing this with my Truth, I built back up an old Homegrown hardtail into a 1X with a 2.25" front tire and a 1.85" rear to mimick this affect and sure enough the bike handles better. The additional grip provided by the larger tire in front is very noticable while the smaller tire out back provides crisp acceleration with no ill affects in cornering traction. It's so hard to convince people of this until they take a bike set up like this for a ride.
 
Discussion starter · #10 ·
What he said.....!

TNC said:
I'm still surprised that the off road bicycle world in general still sees the same wheel size in front and rear as the norm. Dirt motorcycles have long since put this notion to rest......This concept of mountainbikes having a taller front wheel/tire setup over the rear should probably be the norm. But unlike dirt motors where function almost always trumps form, mountainbikes have such a wide lattitude of preference which often overcomes function.
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Hey Thad,

As usual you are a fount of knowledge and wisdom!:D And I believe you've correctly identified the problem in your last sentence.

All that begs the question; what else should we steal....errr...I mean....borrow from our moto cousins?;)

On an entirely different subject I've been riding in an OHV area lately. The trail is designed for a motorcycle or a quad so the builders delighted in going straight up or down fall lines and considered rock faces to be playgrounds! Therefore you go from fun DH to granny gear climb over roots, rocks and potholes....in a heartbeat. The motos dig successive potholes that make for whoop-de-dos for us. I swear one pothole was so deep that I did a wheelie drop into it!. I can't imagine having fun riding here without an adjustable seat-post and travel adjust fork but I'm an old, out of shape wussy when it comes to having the bike optimized for the chore at hand. I guess 20 year old legs would cut down on the need for such exotic hardware but I lost those 40 years ago so I'll just have to deal.

An old grizzled desert rat bike mechanic at Poison Spider Bike Shop in Moab once commented to me that the Slickrock Trail was like doing 90 minutes of wind sprints....that's an apt description for this OHV trail as well. The bottom line though is that it was fun, technically challenging and will test your mettle.

Thanks, again, for sharing your experience and thoughts!

Michael:thumbsup:
 
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#11 ·
michael, as you may already know, that mechanic's comments are quite fitting. Slickrock was designed as a dirt motor trail and is still ridden by many dirt motor guys. You can really tell the flow on that trail was made for a motor...overall...but it's still a hoot on a bicycle.
 
#12 ·
B6 (26 in back, 650b in rear) is a great way to go, that's the setup I've got on my mid-travel FS rig and it seems to gain most of the rollover ability up front, while keeping the same low gearing and quick spin-up of the 26 in back. As has been stated many times here, the motocrossers run the larger wheel up front for some good reasons.
 
#13 ·
salimoneus said:
B6 (26 in back, 650b in rear) is a great way to go, that's the setup I've got on my mid-travel FS rig and it seems to gain most of the rollover ability up front, while keeping the same low gearing and quick spin-up of the 26 in back. As has been stated many times here, the motocrossers run the larger wheel up front for some good reasons.
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Hey sal...we need a real, official title for the 650/26'er setup. I'm thinking B-26. It was a twin engine bomber made by Martin aircraft during WWII. It was the baddest U.S. twin engine bomber of the war. It was named the Marauder. Just a thought.
 

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Discussion starter · #15 ·
TNC said:
Hey sal...we need a real, official title for the 650/26'er setup. I'm thinking B-26. It was a twin engine bomber made by Martin aircraft during WWII. It was the baddest U.S. twin engine bomber of the war. It was named the Marauder. Just a thought.
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Hey Thad,

Here another vote for the B-26! It's a clever moniker!!;)

Thanks for sharing,

Michael:thumbsup:
 
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#16 · (Edited)
I ride all three size wheels day in and day out. On single track there's very little difference in overall acceleration forces reqd between them. It balances out due to the bigger wheels maintaining momentum. My 26" tires are all big volume. Maybe it's also my xc race background.Keeping it smooth and minimizing any acceleration is part of my riding style. I've got a 96er as well. That's where difference in wheel sizes has a noticeable affect on handling.When you tip the 96er over and push it through a sweeping corner you can feel the dynamics of different wheel sizes and how it appears to slacken the head angle when a bike is tipped over.l can't feel that on my B26 where the difference in wheel diameters is only about 3/4".
The 26" wheel is better in climbs where you need it to dig in, I can see where the big wheel may also be a hindrance on steep climbs when edging over large obstacles that require instant acceleration and weight shift like large boulders or tree trunks.The sort of abuse that tends to break 29er hubs.
 
#19 ·
gvs_nz said:
I ride all three size wheels day in and day out. On single track there's very little difference in overall acceleration forces reqd between them. It balances out due to the bigger wheels maintaining momentum. My 26" tires are all big volume. Maybe it's also my xc race background.Keeping it smooth and minimizing any acceleration is part of my riding style. I've got a 96er as well. That's where difference in wheel sizes has a noticeable affect on handling.When you tip the 96er over and push it through a sweeping corner you can feel the dynamics of different wheel sizes and how it appears to slacken the head angle when a bike is tipped over.l can't feel that on my B26 where the difference in wheel diameters is only about 3/4".
The 26" wheel is better in climbs where you need it to dig in, I can see where the big wheel may also be a hindrance on steep climbs when edging over large obstacles that require instant acceleration and weight shift like large boulders or tree trunks.The sort of abuse that tends to break 29er hubs.
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I don't know...not sure I agree with the part about there being very little difference in overall acceleration force required between your 3 different wheel/tire sizes. Yes, the 29'er has great momentum, but that momentum must be started at some point, and that's acceleration. There's no way you can convince me...and I would think most who've ridden a full 29'er...that they accelerate as fast as a 26" rear wheeled bike with as much of everything else being somewhat equal. And please understand...I'm not a 29'er hater. While they don't fit me or my riding for the most part, I often recommend them for others at the shop I work at. I agree with you on the momentum advantage. I would never give up my 700c/29" wheels on my roadbike, but I don't have to constantly slow down and speed up on my roadbike like I do on my MTBs. I'm not seeing how you don't feel the acceleration difference between a 26 and 29'er on singletrack. Maybe your trails are different, and that's very possible. But if the trails are broken up with some decent technical terrain, then the wheel size matching the rider's physiology, strengths, and even preference can come into play a lot more.

And I agree with your fondness of the 69'er attributes. We built up a Maverick ML8 with a DUC32 fork with 29'er and a 26" rear. That bike was a hoot to ride. It cornered like it was on velcro. It was a bit of surprise to me, however, that when the trail got really rocky and technical, the increased wheel size did not make up for the reduced travel. I kind of thought that the hugely tall front tire would negate this. It didn't. The best solution seems to be the tallest wheel up front with the most available travel. While the 650B is incremental, it does its job without removing any fork travel.
 
#20 ·
I think he was saying his XC race trained style is to minimize accelerations. In other words to maintain very constant speed and momentum, to conserve his energy. I don't think he was comparing acceleration of wheel sizes.

I think bicycles moved away from larger front wheel long before motorcycles were invented (note my avatar, the first documented pedal driven bike), when the chain driven "safety bike" was designed. The frame centered cranks and chain rear drive moved the weight bias to the rear wheel, and larger wheels have noticeably lower rolling resistance. Bikes have long settled on same size front and rear wheels rather than a smaller front, to keep the rolling resistance and cornering traction near even front to rear.

Motorcycles, dirt bikes, have near even front wheel weight bias with the rear. And have the added problem of delivering far more acceleration power to the ground, compared to pedal driven bicycles. Although common on road motocycles, for dirt bikes a wider rear tire on the same sized wheel as front wheel would be very unbalanced for handling, so a smaller rear overall wheel size keeps the weight down and the increased rolling resistance of a smaller rear wheel is not a concern with a motor.

For Downhill, where wheel space for more rear travel is desirable and the front end is weighted more, a bigger front wheel does balance better. I think for AM and rough trail type riding there are benefits to both equal-sized or larger front wheel.

JMO
 
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