Wil delves into his experience of back-to-back testing 44mm & 51mm fork offsets to find out just how big of a difference it makes. Or doesn’t.
If you haven’t already checked out Part One of my online feature on reduced-offset forks then you can do so here. In that article, I spoke with several bike companies about their approach to mountain bike geometry, and how fork offset plays into that recipe.
Here we’ll be going into more detail about my experience of swapping forks around on various test bikes, including my current longterm rig, the Santa Cruz Blur.
Up until now, a lot of articles on reduced-offset forks have largely looked at its effect in mid and long travel applications. I wanted to approach this from the other end of the spectrum though, to see how different fork offsets are being utilised on XC and short-travel trail bikes.
The Santa Cruz Blur
I’ve been riding a custom-built Blur for around nine months now. The frame has been setup with a 120mm travel Fox 34 Step-Cast Factory Series fork, which is at the upper limit of what it’s designed for. You can read the full review of the beefed-up Blur here.
To begin with, I went with a 44mm fork offset, which is what Santa Cruz specs on the XC build (100mm travel fork), and on the TR build (110mm fork). Partway through testing, I swapped out the fork for exactly the same model in a 51mm offset.
Since then I’ve swapped the forks back and fourth during several back-to-back test sessions. Each fork has been setup with exactly the same settings. That means using identical air pressure, volume, rebound damping and low-speed compression settings.
During these back-to-back test sessions, I would ride exactly the same loop, with everything else on the bike (like the cockpit setup and tyre pressure) also staying the same. This was done in order to isolate the differences in offset as accurately as possible.
Gimme Them Numbers!
With the 120mm travel fork, the Blur’s head angle sits at 68.1°. After speaking with Josh Kissner from Santa Cruz Bicycles, who kindly dived into the technical drawings for us, we determined that the ground trail figure works out as follows;
- With a 44mm offset fork = 102.4mm trail
- With a 51mm offset fork = 93.9mm trail
The difference in ground trail between those two offsets works out to be 8.5mm. That equates to a not-insignificant 9% increase in ground trail when going to the shorter fork offset.
Given that trail isn’t typically listed in manufacturers’ geometry tables, those numbers may very well be meaningless to you. So for reference, here are the ground trail figures for a few comparable bikes;
- Canyon Lux SL (110mm fork, 69.5° & 44mm offset) = 90mm trail
- Specialized Epic EVO (120mm fork, 68.5° HA & 44mm offset) = 99mm trail
- Canyon Neuron (130mm fork, 67.5° HA & 51mm offset) = 99mm trail
- Scott Spark (120mm fork, 67.2° HA & 44mm offset) = 100.2mm trail
- Merida One-Twenty (130mm fork, 67.3° HA & 51mm offset) = 101.7mm trail
- Yeti SB100 (120mm fork, 67.8° HA & 44mm offset) = 102mm trail
- Trek Fuel EX (130mm fork, 67° HA & 51mm offset) = 103mm trail
- Intense Sniper Trail (120mm fork, 66.5° HA & 51mm offset) = 104mm trail
- Giant Trance 29 (130mm fork, 66.5° HA & 44mm offset) = 117mm trail
- Whyte S120 (120mm fork, 65.5° HA & 44mm offset) = 120mm trail
Relative to those bikes listed above, the Blur sits somewhere in the middle of the range when fitted with a 120mm fork and a 44mm offset. With the 51mm offset fork, its figure puts it down at the lower end.
Enough of the numbers though, let’s talk about how it actually rides eh?
On The Trail – Literally
Now I might be ruining things here a little bit, but I’ll just cut right to the chase. The difference between the 44mm and 51mm fork offset is not huge. Well, it’s certainly not as dramatic as some brands make it out to be anyway.
During back-to-back testing, I did find it easy to spot the difference. Without back-to-back testing though, it would be hard for you to easily determine what offset your fork has if you didn’t know already.
As nuanced as they might be though, there are key differences.
With the 51mm offset, the Blur is an absolute pleasure to ride along swoopy, bendy singletrack. With less ground trail, the front tyre feels lighter at the contact patch. This gives a really natural and intuitive feel to the steering.
Tight corners are dealt with easily and efficiently, and on uphill switchbacks, minimal input is required at the grips to tug the front wheel around the hairpin. In cramped sections of trail, the turning radius feels a little tighter and sharper.
I also found that it was easier to make last minute line changes with the 51mm offset. This was noticeable to me when riding on unfamiliar singletrack, where occasional tree branches and overgrown bushes would leap out to try and grab me after I’d turned a blind corner. If a small washout all of a sudden turned into a deep, pedal-catching gully, I found the responsive steering could get me out of trouble faster. Surprise obstacles were more easily avoidable.
However, this willingness to turn did mean that oversteer was more likely with the 51mm offset. The lighter steering meant that in fast, traction-limited corners I was see-sawing at the grips a little as the front wheel oscillated from entry to exit.
This was particularly noticeable at one of my local riding spots, the Harcourt MTB Park, where a very hot and dry summer has left the hardpacked trail surface incredibly dusty, sandy and loose. This makes things nerve-wrackingly drifty, even when the corners are banked in your favour. Here the 51mm offset fork felt a little fussier and less planted.
If the trail was pointing downwards, the sensation was more noticeable, and I could feel the front tyre wanting to tuck under if I wasn’t careful with weight distribution.
Once I fitted the 44mm offset fork and rode the same section, the difference was quite clear.
In long, high-speed bermed corners, the front wheel feels more sure-footed. The increased trail figure that the 44mm offset brings to the table gives a more steady and calmer approach to cornering at speed. Like other bikes I’ve ridden with reduced-offset forks, it feels like there’s just a touch more damping through the steering axis – like there’s more friction at the tyre contact patch when trying to turn the wheel.
On those same sandy, slightly loose corners at Harcourt, the 44mm offset fork felt like it was carving a more consistent arc all the way through the turn. As others have described in their assessment of reduced-offset forks, there simply feels like there’s less wiggle through the bars, and less need for micro-corrections to the steering mid-corner. The front tyre just sticks more.
With the larger amount of trail, I did feel that there may have been a slight improvement to front-end traction, though that might have simply been that the front wheel was a little closer to me. That being said, it does require you to work harder on tighter turns – that there is no denying.
With the 44mm offset, you do need to pre-empt the turns a little more. That’s because to steer the bike accurately and rapidly, you’re required to lean the bike more, rather than just turning the bars. Dropping the saddle via the Blur’s 150mm travel dropper post certainly helps in this regard, as do the wide 760mm bars and short 50mm stem. If I left the saddle at full height though, I was much more likely to understeer through sharp, flat corners.
In general, I found I had to ride a little more aggressively with the 44mm fork offset in order to get the most out of the Blur. This becomes a little more challenging as fatigue sets in on longer XC rides, where I found I was more regularly blowing out wide on flatter corners.
The flip-side to this fatigue conundrum though is that the 44mm offset is easier to pilot on the descents. There’s less concentration required, because the bike ploughs a line more confidently with less jerking of the grips as you’re rattling over loose, rocky and rubbly surfaces.
When my stamina was starting to fade deep into a highly technical ride with lots of steep descending, the 44mm offset no doubt helped to keep me tracking through the rough. Even while getting pinged around by sharp, embedded rocks, the added self-correcting force from the longer trail made it less likely for me to get kicked off line.
One question that popped up from a reader during the test period was in regards to the change in wheelbase length. The Blur ends up around 6mm longer with the 51mm offset, which in theory, should increase stability compared to the shorter front centre length with the 44mm offset.
In my experience, I can’t say I found I noticed that 6mm change in wheelbase length one way or another. Perhaps there was a touch more traction with the 44mm offset, simply due to the front wheel being a little closer to me. As for handling though, I found the change in trail to be the defining factor in how stable the bike felt as a whole. Even though the 51mm offset created a longer wheelbase, it was the 44mm offset setup that felt more stable overall.
So Which Would I Pick?
That my friends, is a most excellent question. As you’ve gathered already, each offset has its own strengths and weaknesses.
For descending down steeper and rougher trails, and riding at higher speeds in general, the 44mm offset is the better option. It offers greater stability and more reliability when letting off the brakes and descending as quickly as possible.
On tighter, twistier trails with a smoother surface, the 51mm offset provided more useful agility. The light steering feel is particularly noticeable on flatter trails and when climbing, and gave a more effortless feel on repeated alternating corners.
Personally, for the Blur with the 120mm travel fork and trail-oriented setup, my choice is the shorter 44mm offset. I think it suits the intentions of the bike well, particularly with the current 760mm wide bars and short 50mm stem.
While there are differences though, I will say that I found it possible to get used to either offset within a ride or two, and from there my riding style adapting pretty quickly. So it’s certainly not a deal breaker either way. As Dylan Howes from Trek said in Part One, changing offset is more akin to fine-tuning the front-end handling of your bike.
Speaking of, if you’re looking at switching up your fork offset, there are a couple of points worth considering. If you’re moving to a short offset fork, you will benefit from running a slightly shorter stem and slightly wider bars, which will help to increase leverage over the front wheel.
Conversely, if you’re changing up to a 51mm offset, the steering can be calmed down by doing the opposite. So a slightly longer stem and slightly narrower bars will reduce your leverage over the front wheel.
This last point was something I encountered while testing the Canyon Neuron CF – a 130mm travel 29er with a 51mm fork offset, a low trail figure of 99mm, 760mm wide bars, and a 60mm long stem. I tried a wider 800mm bar and a shorter 40mm stem for a few rides, but the high leverage cockpit setup made the steering feel too twitchy. For me, this experience highlighted the interaction that bar width and stem length have with the ground trail, and is something to consider when changing up any of those ingredients.
The Word From Santa Cruz
Following my fork offset testing on the Blur, I got in touch with Josh Kissner, a product manager at Santa Cruz Bicycles, to find out if his experience was similar to mine. “We did a fair bit of testing with the Blur and Highball with both offsets before making a decision”, explains Kissner. “Both ended up with a 44mm offset. I’d say it was a slam-dunk on the Highball, which has a bit of a steeper head angle than the Blur (0.5° static, but the sagged difference is more). It keeps the bike calm and stable. Especially since we’re putting shorter-than-traditional XC stems on these bikes, the steering gets a little quick with the 51mm offset.”
“The Blur was a bit of a harder decision”, Kissner reveals. “When ridden with a dropper, in an aggressive style, the shorter offset feels perfect. I’d say when high-posting through corners, it takes more effort to get turned though. “We had to decide if we wanted to prioritise high-speed handling or easier turning at lower speeds, which was a tough decision. In the end, we decided to err on the side of aggressive riding, as that’s our company DNA. We’d rather have a bike that feels better the harder you ride it, than the opposite.”
You might gather that it is indeed possible to ride both fork offsets on the Blur. It certainly won’t ruin the bike running a 51mm offset fork, it’ll just provide a different steering dynamic – which may or may not work in your favour.
Are Reduced-Offset Forks The Future Then?
Given the growing popularity of reduced-offset forks amongst the industry, is this something that will rise and bubble as a trend, or will all mountain bikes head in this direction in the future?
I asked that question to the various bike designers and product managers I’d spoken with for Part One of this feature.
“Realistically, we were all putting short-offset forks on 29er for the first bunch of years”, says Kissner. “I think we only switched to 51mm in 2015, along with the rest of the industry. Now instead of trying to make 29ers ride like 26in bikes, we’ve accepted that there are a lot of advantages to them NOT riding like 26in bikes. Plus, now we have 40mm stems and 170mm droppers, things that help tame big, long, stable bikes.” As mentioned previously, all of Santa Cruz’ current 29er models are now built with shorter 42/44mm offset forks.
Giant Bicycles has a similar perspective. “We think reduced offset has application to just about every 29er application, given the correct reach and other geometry figures are designed in conjunction”, responds Andrew Juskaitis. “As reach numbers continue to grow on just about all new 29er product, we probably will (spec more reduced-offset forks).”
Chris Cocalis of Pivot Cycles partially agrees. “If the handling aspects of 44mm offset fork become more universally accepted then it’s certainly possible”, responds Cocalis. “However, what every rider ultimately wants is the best riding experience possible. That doesn’t necessarily mean that because Eddie Master’s is killing it in the EWS with a 44mm offset X 170mm FOX 36 fork on his Firebird 29, that the guy or girl riding Trail 429’s on their local trails will have the same experience with a 44mm offset fork on a 130mm travel fork on that bike and in the conditions it was designed for.”
On this note, Cocalis reiterates the problem with over-focussing on one or two numbers in a geometry chart, rather than looking at the entire package. “It’s actually pretty messed up that we get so hung up on a couple of numbers that do have an effect, but in the big picture, it is just a small piece of the puzzle that needs to be considered when designing a great performing bike.”
While Vincenz Thoma of Canyon recognises what a reduced-offset fork can bring to the table (like it did with the new Strive 29er), he is also somewhat cautious of riders getting overly excited about the reduced-offset trend and plugging them into their existing bikes. “I personally don’t think it will help everybody if you just put a short offset fork in the same bike just because it’s a trend”, says Thoma. “In the end, the bike needs to feel right for a certain use and as said above”.
As far as Ian Alexander and Whyte Bikes is concerned though, the future will be one of only reduced-offset forks. “I think the advantages are pretty obvious, and critically, they are demonstrable as well”, says Alexander. “You can feel the tangible advantages which is not always the case with some trends and tech developments in the bicycle industry.”
For determining how ground trail affects a bike’s handling, testing two separate fork offsets on the one bike proved to be an invaluable method for isolating those performance differences. And while the characteristics are fairly subtle, they are present.
In my experience with the Blur, I preferred the shorter 44mm offset and the stability-boosting qualities it brought to the front end of this lightweight trail ripper. For going way too fast on the descents, and (mostly) getting away with it, the added ground trail brought a useful steadiness to the steering. And because I was able to adapt to that steering dynamic, I personally found the reduction in agility through really tight trails to be worth the tradeoff.
At the end of this experiment, I’ve learnt a lot about offset, trail and mountain bike geometry as a whole. I’m not entirely sure we’ll see all bikes moving to reduced-offset forks in the future, since there are benefits to using a longer offset in certain applications. And after all, not every mountain bike is designed to suit every rider and every type of riding.
That being said, and given the obvious influence that trail has on a bike’s handling, this is one measurement I think we’ll be paying a lot more attention to.
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