Surly Endomorph Tire Review

Surly Endomorph fat tire in action…

When I first built up my Pugsley 4 years ago the only fat tire you could buy for it was the Endomorph. Fast forward to the present and there are more than half a dozen tire options for a Pugsley. That’s definitely taken some of the spotlight off the venerable Endo and folks are often talking about it like it’s time is over. I’ve spent a lot of time on Endos over the years in sand, snow and on dirt so I figured it was time for a review.

Endos is Baja…

Here’s what Surly has to say about the Endomorph tire:

“It was inevitable that Pugsley was going to need a new pair of shoes. To this point, the current offerings of high-volume, large-footprint bicycle rubber has consisted of downhill specific, or homemade, or scarce out-of-production tires designed for specific out-of-production rims. Though downhill tires are readily available, they are heavier than we need. We ultimately desire a tire that fits the following criteria: 1) The ability to crawl over and through a wide array of soft and loose surfaces and materials without packing up. 2) A size that will fit within the confines of the Pugsley frame and fork. 3) A weight less than 26 x 3.0″ downhill tires. 4) Full compatibility with 26” Large Marge rims and other wide bicycle specific rims. Our only option was to design our own tire.

The Endomorph 3.7 is the product of our effort. It’s 94mm wide (3.7″) x 740mm tall (29″) on our rims. It’s the highest-volume production bicycle tire on the market at this point. And, at 1260 grams, our 60 tpi tire weighs 300–400 grams less than lower-volume 3″-wide DH tires. Most 3″ DH tires hover around 1600 grams.

The center portion of the Endomorph’s medium durometer (60a) tread is comprised of widely spaced chevrons made up of small, low-profile knobs. Higher-profile knobs, at the outer edges of the tread, provide cornering traction and lateral stability in the loose stuff. No tread pattern is going to be perfect in every condition, but the Endomorph’s tread tends to perform quite well on a variety of surfaces. Truthfully, the casing volume has as much to do with our tire’s performance as the tread pattern does. High volume allows the use of low pressure without much risk of pinch flats. The use of low pressure allows the tire casing to spread out on the ground, providing greater traction and floatation due to the increased footprint. We’ve run our tires as low as 5 psi in deep snow, but 8-10 psi is generally low enough for most snow and sand riding. Want to ride on harder surfaces? Pump ‘em up to 15 psi, if the surface is hard, but rough….up to 28 psi, if you’re riding pavement or smooth, hard dirt. Of course, this is just a guideline. Trial and error/success is the best way to determine what pressure will best compliment your riding style, trail (or lack thereof) conditions and your weight.”

Endomorph on the back on my Pugsley…

The Endo has a square profile on 65mm Large Marge rims [also the only fat rim choice when I built my Pugs]. This gives it a lot of floatation for its size and a tractor like feeling in soft terrain. The low-profile chevron tread rolls easily, but lacks aggressive knobs for traction. To hook up with this tire you need to drop the air pressure so it flattens out as much as possible. The square profile and paddle like tread means the Endo needs some encouragement to steer and has trouble on side slopes. The minimal tread doesn’t pack up with mud easily or throw up a ton of sand.

I’m guessing that my Endos are the original 60 tpi variety because they don’t feel as stiff as the 27 tpi Surly fat tires I’ve had my hands on. Surly now sells Endos in 120 tpi [~1440g] and 27 tpi [~ 1560g]. As I noted in my Surly Nate fat tire review riders are finding large variations in tire actual weights so it’s well worth weighing any Endos you are looking at if you have a few to pick from so you get the lightest tire you can.

If you are buying new I’d recommend getting the 120 tpi version for the lighter weight and the supple carcass that will roll with a lot less resistance. However, a lot of fat bikes come stock with 27 tpi Endos and many riders opt to swap in something else right off the bat so it’s quite possible you’ll find some 27 tpi Endos cheap. If so I’d probably grab them. Fat bike tires are crazy expensive at $90-$150 each so I don’t blame anyone for wanting a deal.

Endos on the CDN GDR…

So what are Endos good for?

As you’d expect for the first and for a long time the only fat tire – the Endomorph is a generalist. I used it for all my fat biking for the first 3 years of owning my Pugsley. Riding the beaches of Baja to the snows of Alberta. We mountain biked with Endos on dirt and snow. We bikepacked with them on the CDN GDR. We used them on pavement when we had to get somewhere. And we did it all with a smile.

There are now specialist fat tires for paved riding or with knobs for aggressive trail riding. Surly came out with a tire called the Larry that has a longitudinal tread pattern for better steering control up front. So you’ll often see new fat bikers being told online that they need to dump their Endos in favour of tire X [fill in latest offering by Surly or 45 North]. I call bullshit on that advise in principle. Endos work fine for most fat riders for most conditions. I don’t think it makes any sense to tell a guy or gal who just dropped nearly $2K on a shiny fat bike that they now need to spend $300 on new rubber or else.

If your fat bike has Endos on it my advice is to ride ’em – a lot. Especially if you are new to fat bikes. They’ll be good for most of your riding and when you encounter situations that challenges them you’ll get to learn how to ride your fatty with some finesse. Those skills will be useful no matter what rubber you ride on your fat bike. You’ll also have time to figure out what fat biking means to you and what specialist rubber you want/need. As a bonus by the time to you ride your stock Endos for a season the options for fat rubber will probably change and you’ll have some new choices.

Now don’t get me wrong. I’m not saying Endos are the uber fat tire and there is no point looking at anything else. If money is no object you might as well get one of everything and always have the perfect tire for your needs that day. OTOH – don’t feel like you need to replace your Endos ASAP or you won’t be able to ride your fat bike and smile.

These days I’d use Endos for bikepacking, dry conditions MTBing, urban assault rides, sand/beach use, flattish snow missions and rides that have a lot of paved sections to deal with. Where I think they should be avoided are steep slick conditions [ie. wet techy MTBing or snow].

As with all fat tires pressure is critical. If you aren’t adjusting your tire’s pressure as you change surfaces you won’t be getting full performance out of it. My rule of thumb with Endos is any bouncing means too much pressure and squirmy hard to steer handling means to little pressure. In extreme soft conditions you’ll be down in the mid-single digits for pressure and your Endos will feel a bit odd, but that’s not a bad trade off for riding instead of walking.

Endo in the back and Larry in the front….

When Surly released their second fat tire it was the Larry shown above and it was touted as a great front tire companion to the Endo. That’s how a stock Pugsley or Salsa Mukluk are equipped these days. I’ll review the Larry in a separate post, but I thought it was worth mentioning this combo since it is found on so many bikes. Both our Pugsleys are setup like this at the moment. The Larry is a nice compliment to to Endo. The directional power of the Larry helps keep your fat bike rolling where you want it to go and the Endo’s flat profile and paddle style tread keeps it moving forward.  If your fat bike came with two Endos a Larry up front is a good upgrade and since you wear rear tires faster you’ll use up your second Endo on the back no worries.

Endos in the snow…

Keep your Endomorphs

At some point you’ll buy some specialist fat rubber and perhaps you’ll be tempted to get rid of your Endomorphs. My advice is hang on to them. They are a great general purpose tire and fat rubber is expensive so it makes sense to use your Endos when they fit the bill. I have a set of Surly Nate fat knobbys and while they kill the Endos for traction those same knobs mean they roll slow when I’m looking to cover ground. For a bikepacking trip where I want to put in 100km+ days I can assure you I don’t want to be rolling on Nates. Even for shorter rides I prefer the Endos or Endo + Larry combo over the Nates if I’m not in need of uber traction. That’s why when summer rolled around in Victoria I spooned some Endos on to the rear of both our Pugsleys.
Some folks clam Endos get better traction and steering when run with the chevrons facing to the rear when viewed from the top of the tire. I’ve tried that and not noticed any difference. It’s free so if you are in the mood to experiment it’s worth a try to see what you think.

Endo in Mexican beach sand…

Send me your Endomorphs!

If you have some Endos and don’t want ’em anymore send them to me. I hate to think there are Endos languishing in garages never to be ridden again or worse being thrown out. I’ll use ’em and when they are worn out I’ll recycle the carcass.