Long Wheelbase MTB? Why I Cut The Seat Tube On My $3400 Frame


Mountain bike sizing is a tricky subject and oftentimes riders spend way too much time analyzing bike geometry when it could be as simple as just getting a bike that feels comfortable. Here's Jeff, the owner of Worldwide Cyclery who talks about his decision to get an XL Yeti SB4.5, even though he stands at a mere 5'8" on a good day! Let's dive into his reasoning, what modifications had to be made to the frame, as well as his suggestions on sizing for your next mountain bike.

Transcription:

Hey Guys, Jeff from Worldwide Cyclery here. We get a lot of questions about bike sizing, and I personally have some strange, unorthodox views on the whole topic. So I wanted to go over the bike I’m riding now, my personal history as a rider, and some of the bikes I’ve ridden in the past.

This is my current rig (visual). It’s a 2017 Yeti 4.5. It’s a custom build. It’s a size XL, which seems ridiculous because I’m 5’8”. I’m a short guy and you might imagine I had to make a few modifications to make this thing work for my height; we’ll get into that a little bit later.

So to give you some background, I rode and raced downhill growing up, I rode motocross, I rode BMX — I’ve been on two wheels for a long time. Riding and racing downhill bikes for so long I got really used to long wheel base, stable bikes. So it’s pretty simple: The longer the wheel base is, the more stable the bike will be at speed. 

Of course there’s still some give and take; the longer the wheel base is, the bike will feel more like a limousine as opposed to a sports car. So at high speed in the rough, that long wheel base is ideal. In super-tight switchbacks or slow technical style riding however, that long wheel base is going to be kind of a hindrance for you. So there’s a lot of personal preference involved.

Originally when I started riding mountain bikes I used to like smaller bikes because I primarily came from BMX, and I liked how agile the bikes were. Then I rode downhill for so long I got really used to long wheel bases, so now when I have my typical trail bike that I use the majority of the time, I just want that downhill bike, long wheel base, super stable feel.

So as to how that evolved…I obviously rode Medium frames for quite some time because that’s more my “actual size” as they would say it. Then I tried a Large frame. I rode an Evil Following Large and I absolutely loved it. That longer wheel base was amazing and I fell in love with that. Then I hopped on a Large Yeti 4.5 and I loved that thing.

I switch bikes all the time. Being in the industry it’s easy for me to do, so probably every 6-8 months I’m changing a bike out. After I ended up selling that Large Yeti, I thought, “Okay, what am I going to do next?”

Banshee actually had this 29er called the Prime. It’s kind of an older bike, it’s aluminum, it has this insanely long wheel base, this massive chain stay, and I figured out that the way Banshees are set up they have these removable dropouts, so you can actually put the dropout from their 27.5 frame onto their 29er frame, and I think it makes it another 10-13mms longer.

The Large size Banshee Prime 29er was long to begin with, and then I put this longer chain stay on it. So then I had this monster bike that was all Batmanned out. I really enjoyed that thing, it was really fun. But the suspension platform was kind of average, and it was heavy because it was aluminum — and I had become too spoiled riding carbon bikes for so long.

So I decided I wanted to ride a Yeti again — it was just the best suspension platform. And I wanted to get back on a 4.5, that bike really suits where I ride most of the time. The majority of the time I’m riding more mellow stuff, not cross country, not like bike parks or anything, but just like general trail riding. For most of the riding I do out here, the 4.5 is just phenomenal. 

But I wanted to take it a step further than just doing a Large. I already did a Large, so I wanted to do an XL. Problem is with me  being 5’8”, an XL wasn’t going to work because there was just no way I was going to fit a 125mm dropper post with the size of the seat tube on an XL. So I thought, I’ll just cut the seat tube. Which everyone thought I was crazy to do that — and it was crazy — so I figured, let’s try it out! 

I took a carbon seat post, and took a Dremel to it and a drill. I tried different methods to cut it. I don’t wish this kind of pain on anyone. It was six hours of me sitting in the shop on a Sunday, it took forever, I had carbon dust all in my hair and on my face. The dust was all over the shop and it was a total mess. 

What took me six hours was (it probably took me about an hour to make the cut on the frame) but the five hours leading up to that I was testing and practicing. I was taking the carbon seat post and trying to figure out how I could cut it and drill the correct slots in there without the thing just exploding into a bunch of carbon flakes.  

That was a lot harder than I thought it would be. Putting a drill into it works only if it’s a tiny drill bit. If it’s a larger drill it starts pulling flakes out, and then how was I going to cut the slot vertically and have it centered nicely… it was just a lot of work. I ended up using a Dremel for pretty much the whole thing to make the cut all the way around, and then I used a tiny drill bit to drill the hole in the front. Then I used a dolphin-nosed style of a Dremel bit to drill the hole bigger, and then a Dremel to slice it all the way down. So it was mostly a Dremel. I didn’t want to use a hacksaw because a hacksaw just kept fraying the carbon, and any big drill bit would fray out the carbon as well.

So eventually I did it….I highly DON’T recommend it. I did it on a brand new frame, which was ridiculous because it was a really expensive frame. I’m sure it completely voided the warranty. I’m sure Yeti’s not very happy that I’m telling the public I did it — but it’s cool, so we are anyway!  

I was able to pull it off. I cut it down. The sizing on these Yeti’s, you can see how the stock tapers down, so this is the regular 34.9 seat post clamp; it bulges bigger. We had an Evil Wreckoning as a demo bike in the showroom. I measured that, and it had a 35 mil post in it, and the outer diameter of the seat tube happened to be the same as this part down here once it bulged out … So I thought, I’ll just use this seat post clamp. This is actually a seat post clamp from an Evil, and it’s intended for an Evil Wreckoning that has a 35.0 seat post that just happens to fit on the Yeti after you chop it off and get past this tapered part.

So it’s now the exact size of an actual Large as far as the seat tube goes, but the top tube is an XL, it’s an XL frame. I have a 32 mil stem on there, so it’s a super-short, tiny little dink of a stem. It ends up being a long-top tube but I shortened it up as much as I could with that stem. Super long wheel base because it’s the XL wheel base, and still a pretty short chain stay.

I personally love it;  it’s super fun. I mean it’s long, it’s stable, it feels like a downhill bike but it’s super lightweight. I really enjoy it, but it’s not for everyone. Sizing is one of those things that it’s very much a personal preference. It’s what you are looking to get out of a bike. Do you really care about it being agile, or do you care about it being stable? Because it’s all give and take. 

It’s just like wheel size, 27.5 vs. 29 — it’s not that one is better than the other. They’re just different, they handle differently in different situations, and bike sizing is very similar. The bikes handle differently in different situations. A lot of that is how short that top tube is — that’s gonna make it easier to pull up or harder to pull the front wheel off the ground. Also it’s important how long the wheel base is, because that’s going to make it more stable at speed, or less stable at speed but more agile in technical situations. So it all depends on what you’re looking for.     

A lot of the guys who come in here are more on the novice side of riding, so I always just recommend what the manufacturers recommend. If you’re not as far down the path as I am — I’ve ridden mountain bikes for over 10 years … let’s see, actually over 15 years now … and all different types of them. You know, whether it’s downhill bikes, BMX bikes or cross-country bikes, I’ve ridden so many different types of bikes that I’ve developed all these crazy preferences. 

But sometimes it’s not preferences; it’s just what I feel like.  Right now I kind of feel like riding an XL 29er because it’s fun and it’s what I’m craving right now. Maybe I’ll go on a different route and get on a Medium size 27.5 bike next because I’ll feel like I wanna ride that!

I always tell people, too, don’t overthink sizing too much. Because as long as your bike isn’t horribly incorrectly sized for you, and as long as you don’t feel uncomfortable riding the thing, just get a size that works for you. You want something that fits your preference, fits your riding style. So don’t think about it, just go ride your bike and have fun! I mean, that’s what mountain bikes are for! It’s funny to me that in this industry so many people think and debate about all these different options, when it’s really about just getting a good set-up — and having FUN!

Bike Sizing