My 27.5+ bike problems (hopefully solved)

[Mr Cabletwitch]

So I just want to save some guys the troubles I'm having. I was in the market for a new bike and fell in love with the trek fuel ex8 27.5 plus, great bike rode really well on my demo rides (super tame terrain) and I thought it would be a great new bike so I bought it. First ride out I noticed the pedals were banging on rocks a lot. Fast forward a half dozen rides and I've fallen a couple times because of this. If I put the new bike next to my 29er you can see very clearly the 27.5+ tire is no where near as tall as the 29er. My plus bike is bonkers downhill but nearly impossible to pedal up a technical climb without constantly ratcheting pedals. Currently the problem is the 27.5+ bikes are all based on 29er bikes so bottom brackets are very low (even with it in the high setting), some terrain its great, northeast single track not so much. So I'm currently converting the bike to a 29er to make it rideable and I'll have a nice set of 27.5+ wheels and tires I can't see using unless its in the snow. Just a word of caution, the bike I'm pretty sure will be amazing on 29er wheels but I could have saved myself a bunch of money and skipped the 27.5 plus setup.

[p nut]

Wouldn't the BB height be the same with 29 wheels? The overall diameter is the same, or similar with 27.5 plus, so I don't know if a new wheelset would solve your issue.

[sparky33]

Bummer that the bike is not working out, but isn't the radius of a 27.5x3.0 within a couple millimeters of a 29x2.3? I calculate (http://yojimg.net/bike/web_tools/trailcalc.php) something like 372mm vs 373mm.

[Mr Cabletwitch]

Real world its not even close. If you compare a 29x2.1 its close, my 29x2.35 tires are a good inch and a half to two inches taller. If you compare specs between the 29er version and the 27.5 version its a 1.2cm difference and stock it comes with a small 29er tire. Not to mention you can run super low pressure with the plus tires which makes the BB even lower.

I'll try and grab a picture when I get home to show what a huge difference it is.

[dustyrider]

What length cranks are you running? Lots of guys are running shorter cranks these days...

[tele]

I've been running 27.5+ with 3" tires setup on my fat bike and definitely more pedal strikes than even with the regular 27.5 3.8 tires on the same terrain.

Sucks sometimes but I've been just dealing with it and trying to enjoy the speed to make up for it!

[Mr Cabletwitch]

What length cranks are you running? Lots of guys are running shorter cranks these days...

Bike came stock with 175, but I have a set of 170s arriving tomorrow, not sure how much of difference its going to make though. I'm hoping that the 170s will let me run the BB in low setting with the big 29ers cause I feel like the bike could be a little slacker. I'm pretty sure I can stuff a 29+ tire in there actually. I'm actually thinking for winter and mud a 29+ on the front and a 27.5 plus in the rear with the BB in the high setting might work well. Luckily the 29er wheels I have coming are same width as my Duroc 40s

[dustyrider]

Bike came stock with 175, but I have a set of 170s arriving tomorrow, not sure how much of difference its going to make though. I'm hoping that the 170s will let me run the BB in low setting with the big 29ers cause I feel like the bike could be a little slacker. I'm pretty sure I can stuff a 29+ tire in there actually. I'm actually thinking for winter and mud a 29+ on the front and a 27.5 plus in the rear with the BB in the high setting might work well. Luckily the 29er wheels I have coming are same width as my Duroc 40s

170 has become more common on complete bikes now, but I know guys on 165s and they're not downhilllers. Canfield brothers makes cranks down to 155, so clearly you're not the only one hitting pedals!

[Dirtdiggler]

Might try checking your rear shock psi.. As you pedal, your are probably mashing and compressing the rear shock causing the bb to drop, hence the pedal strike.. I know it sounds like nutz, but my Top Fuel is the same.

[JAGI410]

This is pretty common unfortunately, and I'm dealing with it myself. I just bought a Santa Cruz Tallboy C, with the S+ build. The stock Maxxis Rekon 2.8 tires are amazing, but they only measure 2.69" on a 40mm rim. I have room to stuff a bigger tire in it which would raise the BB a bit. What I have noticed though is that my "pedal consciousness" has improved and my skills are improving with each ride. I've had a couple rock strikes, especially when I run my flat pedals, but I believe with more time on the bike these will reduce.

29er mode testing will happen soon too, but I just love the plus tires so much!

[Mr Cabletwitch]

Might try checking your rear shock psi.. As you pedal, your are probably mashing and compressing the rear shock causing the bb to drop, hence the pedal strike.. I know it sounds like nutz, but my Top Fuel is the same.


Yeah I tried over pressurizing my shock and didn't help much, the only thing that really helped was running a little over 20psi in the tires which is a lot for a plus tire. I don't think there is a simple answer other than switching to a 29er setup. Until they design a bike around 27.5 plus tires I think this is going to be a constant problem. Although if I'm going anywhere that has a lift I guarantee I'm putting the 27.5+ tires right back on. The low BB and tires make it a fantastic downhill/flowy bike. I set a PR on one of my favorite downhill trails my first outing with the bike.

[Mr Cabletwitch]

This is pretty common unfortunately, and I'm dealing with it myself. I just bought a Santa Cruz Tallboy C, with the S+ build. The stock Maxxis Rekon 2.8 tires are amazing, but they only measure 2.69" on a 40mm rim. I have room to stuff a bigger tire in it which would raise the BB a bit. What I have noticed though is that my "pedal consciousness" has improved and my skills are improving with each ride. I've had a couple rock strikes, especially when I run my flat pedals, but I believe with more time on the bike these will reduce.

29er mode testing will happen soon too, but I just love the plus tires so much!

It's making me much more aware of pedal position and I'm getting better but some of the rocky climbs here in the northeast/mid atlantic region you just can't ratchet the pedals that much. I think its going to be one of those situations where I'll be switching wheel sets depending on where I ride, which is ok with me since I can have the best of both worlds. I'm just a bit disappointed that they are trying to say 27.5+ is the same as 29 which it just isn't.

[crownjewelwl]

i love my mojo 3 with plus tires

bb height with 2.8" tires is higher than my old ripley with 2.35"

[JAGI410]

That's frustrating indeed, because 27.5x2.8 and 27.5x3.0 are massively different, and neither is the same as a 29x2.3. If they were the same these bikes wouldn't have flip chip/mino links to adjust the geometry.

[Mr Cabletwitch]

i love my mojo 3 with plus tires

bb height with 2.8" tires is higher than my old ripley with 2.35"


That's because it seems like the ibis is designed around a 27.5" bike instead of a 29er, seems like Ibis realized that 29 does not = 27.5+ wish I could have swung one of those, it seems like an awesome bike!:beer:

[p nut]

How do the stock Chupacabra tires measure?

You are right about the sag of Plus tires. Still, the BB can be adjusted by 10mm in high setting, right? Maybe that coupled with actual 3" tires would help the issue.

[Mr Cabletwitch]

That's frustrating indeed, because 27.5x2.8 and 27.5x3.0 are massively different, and neither is the same as a 29x2.3. If they were the same these bikes wouldn't have flip chip/mino links to adjust the geometry.


How much different is a 27.5x2.8 vs 27.5x3.0? Since I'm going to have a set of 29er wheels for going fast anyway a bigger slower 27.5+ tire wouldn't bother me. The Fuel Ex8 comes with 27.5x2.8 stock

[Mr Cabletwitch]

How do the stock Chupacabra tires measure?

You are right about the sag of Plus tires. Still, the BB can be adjusted by 10mm in high setting, right? Maybe that coupled with actual 3" tires would help the issue.

It's already in the high setting. I can't imagine how bad it would be in the low setting. I haven't measured the chupacabras but I might have to check out a bigger tire. No way I'm spending for two newbies but I'd go to a bigger in the front, think that might make a difference?

[JAGI410]

The Fuel comes with chupacabras right? Those are more like a 2.6. A 3.0 like WTB Ranger will be bigger and roll just as well. Same weight I think too. Worth the experiment. Maybe even just start with the front one.

[Mr Cabletwitch]

The Fuel comes with chupacabras right? Those are more like a 2.6. A 3.0 like WTB Ranger will be bigger and roll just as well. Same weight I think too. Worth the experiment. Maybe even just start with the front one.

I had been debating this, might have to give it a try, don't really want more volume in the rear, but I could go with more in the front.

[ColonelJLloyd]

The Fuel comes with chupacabras right? Those are more like a 2.6. A 3.0 like WTB Ranger will be bigger and roll just as well. Same weight I think too. Worth the experiment. Maybe even just start with the front one.

I have a 29x3.0 Ranger on the front of my bike. It's so big. Haven't measured it since I installed it (tubeless on i45), but I believe it was 72mm.

[RudAwkning]

I've got a Salsa Woodsmoke. The BB drop is 58mm vs 30mm on your Trek. Even with 170mm cranks, I slap pedals all the time. But it's a bit more predictable as I'm running a hardtail. With suspension compression, it's hard to gauge when it'll happen. I've done everything I can to mitigate pedal strike. I started out with a Rock Shox SID 29" 100mm fork and WTB Ranger 2.8s (3.0s wouldn't fit in the SID). I converted the SID to 120mm which bought me a bit of clearance. I finally bought a boosted Yari with 130mm of travel and can now fit 3.0 Rangers.

I converted my BMC Fourstroke FS02 to plus as an experiment. I can barely squeeze 2.8 Rangers in there. I increased the travel on the Fox Float from 100mm to 110mm (the damper wouldn't let me go 120). BB drop on BMC is 40mm. Pedal strike is up due to the sag but fun factor is through the roof.

After months of riding just plus bikes, I recently took out my Retrotec 29er SS. It felt so weird.

[Idris Icabod]

I have a Santa Cruz Tallboy that I strike the pedals a lot on. My buddies ride Niners and don't have the same issue and side by side the Niner BB is way higher. I ride my Ti hardtail almost all of the time because of the issue. I crashed hard and broke ribs and clavicle by striking the pedal on the Tallboy during a night ride.

[Mr Cabletwitch]

I discovered a lot of the problem. The chupas are a joke. I got some 3.0 chronicles just now and mounted them up. Those are 29x2.4 on the left for reference. Now I see why they say 27.5 plus is close to a 29x2.2.

[JAGI410]

Big difference! Hope that helps quite a bit. Go ride and report back!

[Dirtdiggler]

I dig the headbadge...

[Mr Cabletwitch]

I dig the headbadge...



Thanks it's an EWR so it's a strange looking bike. My son decided it needed a well dressed alien. The hot dog guy adorns my full squish.

[SkyRider]

Generally if the bike is meant to convert between 29 and 275+ you loose about 1.5cm bb height. The solution from some manufacturers (pivot) is a extended lower headset cup. I would recommend looking for a compatible lower headset cup. It will change the geometry if you run 29" wheels but not in a way that would be to unpleasant.

From a mtb mechanic


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[Mr Cabletwitch]

Generally if the bike is meant to convert between 29 and 275+ you loose about 1.5cm bb height. The solution from some manufacturers (pivot) is a extended lower headset cup. I would recommend looking for a compatible lower headset cup. It will change the geometry if you run 29" wheels but not in a way that would be to unpleasant.

From a mtb mechanic


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Didn't think about an extended headset cup, that would help but I think the biggest issue was the tiny tires the bike came with, I'm pretty sure with the new bigger tires and my 170 cranks the bike will be very rideable. The trek has the chip that allows me to adjust the BB height. I'm looking forward to throwing the 29er setup on the bike and drop the BB height.

[SkyRider]

Didn't think about an extended headset cup, that would help but I think the biggest issue was the tiny tires the bike came with, I'm pretty sure with the new bigger tires and my 170 cranks the bike will be very rideable. The trek has the chip that allows me to adjust the BB height. I'm looking forward to throwing the 29er setup on the bike and drop the BB height.



Most of the bike that come through the shop I work at come on 2.8" maxxis tires. Generally rekons and ikons. The tire size is so hard to predict in the practical sense since every manufacturer uses a different rim to measure at this point and the allowed variance in size is largeish. The headset cup option, pivot uses a 16mm extension for example and I have seen similar come through on intenses and a few other frames, is a reliable option because you are correcting the geometry not the roll out of the tire. Hope this is helpful.


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[Mr Cabletwitch]

Most of the bike that come through the shop I work at come on 2.8" maxxis tires. Generally rekons and ikons. The tire size is so hard to predict in the practical sense since every manufacturer uses a different rim to measure at this point and the allowed variance in size is largeish. The headset cup option, pivot uses a 16mm extension for example and I have seen similar come through on intenses and a few other frames, is a reliable option because you are correcting the geometry not the roll out of the tire. Hope this is helpful.


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Do you know of an extended cup that will work on my 2017 trek fuel EX8 with the knock block.

[SkyRider]

Do you know of an extended cup that will work on my 2017 trek fuel EX8 with the knock block.



I can check when I get to the shop in a while.


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[Mr Cabletwitch]

I can check when I get to the shop in a while.


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Thanks, I'm thinking it will be fine the way it is but it would be good to have the option plus I think the bike could be a little slacker.

[Fatty]

Lot of machinations for a brand new bike.

[Red Tornado]

So I was under the impression that a 27.5 frame was sized correctly for the wheels; I'm gathering this is not the case with some manufacturers. I'm still on a 26" (please withhold "comments" LOL) but was considering adding a 27.5. Guess I'll need to research a little more to find one with a "27.5" frame as opposed to a 29'er frame with 27.5 wheels.
Understand how tire width & resulting height work but not really interested in running anything wider than maybe 2.5"; just don't need the extra rubber where I ride.

[Mr Cabletwitch]

So I was under the impression that a 27.5 frame was sized correctly for the wheels; I'm gathering this is not the case with some manufacturers. I'm still on a 26" (please withhold "comments" LOL) but was considering adding a 27.5. Guess I'll need to research a little more to find one with a "27.5" frame as opposed to a 29'er frame with 27.5 wheels.
Understand how tire width & resulting height work but not really interested in running anything wider than maybe 2.5"; just don't need the extra rubber where I ride.

a 27.5 bike is usually built around 27.5 wheels however a new trend of 27.5 plus wheels have come around which is a 27.5x2.8-27.5x3.0 these tires are close to the circumference of a 29er tire so they are being built around a 29er frame. A std 27.5 bike will be built for that wheel size specifically, back before 27.5 was so mainstream we used to build 27.5 bikes out of 26ers but thats not really the case anymore.

[Mr Cabletwitch]

Lot of machinations for a brand new bike.

Yeah I'm not real pleased about it, but my Local Bike shop that I got the bike from at least hooked me up with some true 27.5+ tires which would have probably fixed my issue from the beginning, but I did want to add a set of 29er wheels eventually anyway this just moved that along. At this point I feel like I'll have a very adaptable bike for the varied terrain here on the east coast.

[Mr Cabletwitch]

Ride update:

Had the bike out yesterday and it was wet, the chronicles floated well but there was a noticeable weight penalty over the stock tires, however the bigger size coupled with the shorter cranks took me from completely slamming pedals to just grazing them. If trek would have put some decent tires on this bike I'm sure most of people's complaints about a low BB would have been a non issue. I'm still looking forward to trying the 29er wheels since the heft of the plus tires makes lots of climbing tough. The chronicles are a nice tire though, they roll plenty fast and didn't pick up any mud so I'm very happy with them.

[SkyRider]

Thanks, I'm thinking it will be fine the way it is but it would be good to have the option plus I think the bike could be a little slacker.



No luck on that lower cup. Sorry about that


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[MattTuck]

This is all pretty interesting. Let me know when mountain bikes find a size standard that will last more than 5 years, and I'll consider one. :)

[ColonelJLloyd]

This is all pretty interesting. Let me know when mountain bikes find a size standard that will last more than 5 years, and I'll consider one. :)

None have gone away. What's good for a 5'2" 130lb rider often isn't as good for a 6"2" 220lb rider. Not to mention that the PNW, SoCal, southeast, northeast are all very varied in terrain.

[Mr Cabletwitch]

This is all pretty interesting. Let me know when mountain bikes find a size standard that will last more than 5 years, and I'll consider one. :)

Horses for courses, The only wheel size that has gone away is 26, so now we are down to 27.5 and 29, the difference here is width, both rim and tire, no different than you 650b vs 700c and narrow or wide rims, and narrow or wide tires.

The 27.5 plus thing is relatively new so its a matter of working out the bugs, I did the same thing when 29ers came out, just takes some time to figure things out.