[Enurjetik]

I am looking to mullet out a trail bike and would like to use the fork that will have the least impact on the bike's geometry. Don't get me wrong, I'm fine with raking out the front end and bumping up the bottom bracket. I simply want to minimize those things to the degree that I can.

The bike is a 150mm front, 140mm rear trail bike designed around 27.5 wheels. The head angle is 67 degrees and the bottom bracket is a 338mm. The frame has a flip-chip that will allow me to steepen the head angle to 67.4 degrees and raise the bottom bracket to 343mm. I would like to keep the front travel at 150mm.

So two questions for the group:

-Which non-boutique 150mm 29er boost fork has the lowest axle to crown distance? You would think that this is easy to determine, but I have seen conflicting data. As in, is it really true that A2C on a Fox 36 is significantly less than the A2C on a Fox 34 of the same travel?

-Are there any 27.5 forks that can accommodate a 29x2.6 DHF? I'm thinking "no," but figured I would throw this out to the group.

For background, my Devinci Marshall is currently mulleted with a 29x2.6 DHF up front and a 27.5x2.8 DHR out back. So no need to try to talk me out going down this route. I'm firmly committed to the mullet lifestyle!

 

[Nurse Ben]

All the 29er forks have a similar A-C, it's based on tire clearance.

Going from a 27.5 to a 29 fork increases A-C by ~10mm. If you choose a 29er fork with the least tire clearance, that will net you the shortest A-C, but at most you're talking a savings of 5mm.

A-C is the same between Fox 36 and Fox 34 in the 29 chassis. 27.5 forks will NOT fit a 29" wheel except for the older Fox 34. You can get all this information from Fox: https://www.ridefox.com/fox17/help.php?m=bike&listall=specsheets

34 27.5 -535mm
36 27.5 529mm
34 29 547mm
36 29 547mm

Best options:
Shortest 29er tire in front and tallest 27.5 tire in back
Reduce fork travel by 20mm to adjust for increase in A-C of 10mm + increased in tire radius of 10mm.

FYI: The Marshall is not a 140mm travel rear suspension, it's 115mm, 125mm if overshocked. You are running too much fork, drop it to 120mm and it'll work fine as a mullet. I own one and did this conversion a few years ago, it's well worth it.

 

[mountainbiker24]

There is some misinformation here... First of all, not every fork of similar travel and wheel size has the same axle-to-crown. It can vary relatively substantially between manufacturers and even slightly from model to model. Second, a 29er wheel has a diameter increase of almost 40mm over a 27.5, which means that there is an increase of just under 20mm to account for in axle-to-crown. Running a bigger tire in the back will decrease that distance, but I always run the bigger tire in front...

 

[Nurse Ben]

There is some misinformation here... First of all, not every fork of similar travel and wheel size has the same axle-to-crown. It can vary relatively substantially between manufacturers and even slightly from model to model. Second, a 29er wheel has a diameter increase of almost 40mm over a 27.5, which means that there is an increase of just under 20mm to account for in axle-to-crown. Running a bigger tire in the back will decrease that distance, but I always run the bigger tire in front...

No misinformation, I know what I'm talking about, it's very simple math, also easy enough to check mfg websites for this info. No one suggested running a bigger tire in back, so I'm thinking you were not reading for context...

I've run mullet, it's a trade off, you pretty much got a 20mm difference to work out, either by dropping the front end, finagling tire heights by running fat rear and skinny front, or you run with a chopper front end.

A-C varies little across 29er forks, a difference of 5mm between mfgs unless a fork is a one off like the old Fox 34 which had a lot of tire capacity.

 

[Enurjetik]

Thanks guys. I appreciate the input.

Nurse Ben - I should have been more clear in my original email. I'm already mulleting my Marshall. I'm considering doing the same with a different bike that has more travel. I'm running a 130mm 29er fork on the front of the Marshall and enjoying everything that brings to the table.

I just realized that you are the poster who overshocked a Marshall a while back. How did that work out for you in the long-term? Did you end up keeping the bike overshocked or go back to the original 2" stroke?

 

[crembz]

When I looked into it, Fox had a slightly shorter a-c than rockshox, manitou and ohlins were a fair bit taller. I went with a marzocchi Bomber and reduced the travel 10mm. Still netted a 22mm or so higher a2c but worked out well. From memory hta/sta were just under 1° slacker.

I have 2 mullets one based off a 27.5 HT frame the other a 29er fs.

 

[mountainbiker24]

No misinformation, I know what I'm talking about, it's very simple math, also easy enough to check mfg websites for this info. No one suggested running a bigger tire in back, so I'm thinking you were not reading for context...

I've run mullet, it's a trade off, you pretty much got a 20mm difference to work out, either by dropping the front end, finagling tire heights by running fat rear and skinny front, or you run with a chopper front end.

A-C varies little across 29er forks, a difference of 5mm between mfgs unless a fork is a one off like the old Fox 34 which had a lot of tire capacity.

I don't think you do know what you're talking about. There is a significant difference in a2c from manufacturer to manufacturer, and you did say running a taller (i.e. Bigger) tire in the back was the best option.

 

[crembz]

I don't think you do know what you're talking about. There is a significant difference in a2c from manufacturer to manufacturer, and you did say running a taller (i.e. Bigger) tire in the back was the best option.

Agreed, From memory Ohlins and Manitou were 20+mm higher than RS/Fox in 29er 160mm travel. RS were about 5mm higher than Fox. I didn't check Suntour or XFusion.

 

[mountainbiker24]

Suntour can be tough to find info on, but one of their forks was about 20mm taller than a comparable Rockshox. I think it was the Raidon 34 compared to a Recon RL.

 

[RS VR6]

I have both a 100mm Reba and Fox 32. From what I can remember...the Fox has a slightly longer A2C than the Reba. At bottom out...the o ring on the Fox is about 7 or 9mm from the crown. When the Reba bottoms out...the o ring is pushed all the way to the fork crown. Same with my Yari vs the Fox 34. When a Rock Shox fork bottoms out...it bottoms out. Not sure if that’s what the difference in A2C...just an observation.

 

[Nurse Ben]

Thanks guys. I appreciate the input.

Nurse Ben - I should have been more clear in my original email. I'm already mulleting my Marshall. I'm considering doing the same with a different bike that has more travel. I'm running a 130mm 29er fork on the front of the Marshall and enjoying everything that brings to the table.

I just realized that you are the poster who overshocked a Marshall a while back. How did that work out for you in the long-term? Did you end up keeping the bike overshocked or go back to the original 2" stroke?

Overshocking worked great, too a good biek and made it better, the bike has since moved to my son in laws house, he just had the CCI rebuilt, loves the bike.

Gotcha, so mulleting a different bike ...

So I'd shoot for a bike that has an adjustable geo, maybe a bike that has a short/tall lower cup option. For example, the GG Shred Dogg is 130/140mm rear travel speced with a 150mm fork and a tall lower cup.

Many folks are running their Shred with a 160mm 27.5 fork. I run a Bomber Z1 29 160mm fork as a 27.5 on my Shred. I wanted to ride 29 and 27.5, so I used a 29er fork (+10mm A-C) and swapped to a short lower cup (-10mm) to balance out the difference.

I ran my Shred as a mullet last weekend, swapped forks to a Pike 29 140mm (-10mm from my 27.5 set up), and though I didn't really dig it, it worked fine and kept the BB and geo nearly the same as my 27.5 set up.

 

[Nurse Ben]

I don't think you do know what you're talking about. There is a significant difference in a2c from manufacturer to manufacturer, and you did say running a taller (i.e. Bigger) tire in the back was the best option.

I said run a taller/bigger 27.5 tire in back to offset the difference between the two wheel sizes, for example a 27.5 x 2.8 out back and a 29 x 2.6 up front.

The whole idea of this project is to get the benefits of both tire sizes on the "ends" where it makes most sense. The 29" front end for fast rolling, increased stability, and obstacle bridging. The 27." back end for traction, tighter turning, and more agility.

 

[mountainbiker24]

I said run a taller/bigger 27.5 tire in back to offset the difference between the two wheel sizes, for example a 27.5 x 2.8 out back and a 29 x 2.6 up front.

The whole idea of this project is to get the benefits of both tire sizes on the "ends" where it makes most sense. The 29" front end for fast rolling, increased stability, and obstacle bridging. The 27." back end for traction, tighter turning, and more agility.

Oh my.. Taller/bigger generally means wider. I said I prefer to run a bigger (wider) tire in front. Also, a 29er gives better traction, all else being equal.