FlexFit by John Karrasch

FlexFit by John Karrasch Not your basic bike fit. I provide professional bike fitting services at Cahaba Cycles for all disciplines for cycling.

This includes road, MTB, cyclocross, and triathlon/TT positioning for improved comfort, power, and performance. I bring a unique combination of skills to the fit clinic with experience as a racer, therapist, and mechanic. I am up to date on the most current Trek Precision Fit training. My approach to fit is based on a true understanding of the rider's individual biomechanics and goals. I do my own

research and bring a wholistic method to a field increasingly filled with data. Numbers are important, but at the end of the day a good fitter is not dependent on any specific tool or technology. I assess movement, on and off the bike, to deliver a great fit for everyone from recreational riders to National Champions.

Vittoria Pe**te XC Trail 29 x 2.1 off road rolling resistance testing 📊In late 2025, introduced the XC Trail variants o...
05/22/2026

Vittoria Pe**te XC Trail 29 x 2.1 off road rolling resistance testing 📊

In late 2025, introduced the XC Trail variants of its popular XC Race tires, bringing along a totally new construction for the XC Trail tires that is also shared with the knobbier Trail lineup. Per Vittoria the Trail casing “is a durable 60-TPI nylon casing built for exploration. It resists abrasion and punctures while maintaining your connection to the trail with a mid-tier suppleness.” The 4Compound Formulation “strategically places 4 optimized compounds where they are needed for an unparalleled blend of speed, grip, and durability.”

The 29 x 2.1 Pe**te XC Trail tires I tested have a 1.7 mm sidewall thickness, so about twice the XC Race construction thickness and quite similar to the EXO+ casing from Maxxis in thickness. My set was an average of 780 grams and blew up to 52 mm wide and 49 mm tall on a 25 mm internal width Reserve carbon rim. In general, I have found it a good idea to give tires some break in miles before any racing, but even for testing…and this tends to take a bit longer when tires have a thick casing like these!

After lots of riding and testing with the Pe**te XC Trails, I can see these as a totally viable choice when you are in rougher, more flat prone areas…even moreso if you are racing in a group where you can’t see every sharp rock in the road! These are certainly not the fastest tire I have tested, but I think it’s good to keep the beefy construction in mind here as sometimes you can’t have it all! For a direct comparison, these are a similar speed everywhere to the Race King 29 x 2.0 Pure Grip and have a much thicker and durable construction.

The Pe**te XC Trails have quite a good ride feel everywhere and notably good handling on pavement when run at off road pressures. Given the thickness of these, many will find happiness with lower pressure everywhere than what your favorite calculator might suggest.

All testing my own via outdoor Chung Method/VE…PSI notes in the comments. ✅

Rene Herse Snoqualmie Pass TC Extralight 700 x 44 off road rolling resistance results 📊Per , “All-road tires don’t get a...
05/11/2026

Rene Herse Snoqualmie Pass TC Extralight 700 x 44 off road rolling resistance results 📊

Per , “All-road tires don’t get any better than this! We name our tires after the passes in the Cascade Mountains that inspire them: Snoqualmie Pass was the route of the Olympian Hiawatha express train to Seattle. Today, a trail heads up the pass, with spectacular views as you traverse the old railroad trestles. You’ll enjoy the speed and grip of the supple casing on the paved sections of the climb, and the large air volume will have you float over the rough gravel rather than grind through it.”

RH optimizes their tires for real world performance, so many will be excited to see results here in the real world for what is their most supple construction option - the Extralight. I measured the sidewalls on these at 0.40 mm thick, which is easily the thinnest of any tire I have tested. They took and held air well…actually even better than the Standard casing Oracle Ridge I tested last spring. My set weighed an average of 338 grams and had a flat bead to bead width of 111 mm, airing up to right at 44 mm wide and 41 mm tall on a 25 mm internal width rim. Tubeless setup with Orange Seal Regular, as usual.

I have tested a few other tires in the 40-45 mm size range, which gives us some interesting comparisons on smooth pavement as well as easy gravel which many will consider the RH slicks for. These were pretty quick on pavement and Cat 1 Gravel, but a bit off the pace of the absolute fastest options on both surfaces. I think this size range of all road slicks is a good one, as it allows for comfort as well as performance. I had no issues with these RH slicks, and for anyone not into the minimalist sidewall construction of the Extralight, RH has beefier options with the same compound and tread.

After recently having the chance to analyze some well done timed lap style testing, I will stick to my guns that well done Chung Method/Virtual Elevation is easier, faster, and has better repeatability and accuracy. All outdoor results here are from my own VE testing. PSI notes in comments.

Fresh build from and a fit by me to wrap up Melissa’s new Orbea Ordu… comin’ at ya Austria. 💅
05/09/2026

Fresh build from and a fit by me to wrap up Melissa’s new Orbea Ordu… comin’ at ya Austria. 💅

No doubt about it… dialed setup here on Glenn’s new Enve Fray. 🫡No gadgets, no nonsense… Full E1 Red AXS on an Fray wi...
05/07/2026

No doubt about it… dialed setup here on Glenn’s new Enve Fray. 🫡

No gadgets, no nonsense… Full E1 Red AXS on an Fray with Enve SES Aero bars, Aero stem, zero offset post, and 3.4 hoops to finish it up.

We actually based fit specs on a modified setup from his old Tarmac SL6 and it ended up perfect. 🎯

Continental Dubnital Race Rapid 29 x 2.0 off road rolling resistance results 📊Continental’s Race King (Dubnital as of 20...
04/29/2026

Continental Dubnital Race Rapid 29 x 2.0 off road rolling resistance results 📊

Continental’s Race King (Dubnital as of 2025) originated in prototoype form during 2007 as the 26 x 2.2” Race King World Cup, ridden to a UCI Wolrd Cup Overall Title by Irina Kalentieva, and released in 2008 to the public in Supersonic and World Cup editions with the Black Chili compound. It took until 2009 for the thicker Protection version to gain the high performing Black Chili compound.

2009 also brought a 29 inch Race King with Black Chili compound and eventually combined this with the Protection sidewall for a fast and durable 29 x 2.2 in 2012 (hi ) while the 29 x 2.0 variant had to settle for the slower Pure Grip construction, leaving many riders wishing for a high performance Race King in a 29 x 2.0 size. released the tire tested here at the 2026 Sea Otter Classic a couple weeks ago. For all intents and purposes, the 29 x 2.0 Continental Dubnital Race Rapid is THE tire so many have waited to see.

My set of 2.0 Dubs averaged 573 grams and aired up to 50 mm wide on 25 mm internal width Reserve carbon rims. They had a flat bead to bead width of 133 mm reflected in their height off the rim at 49 mm. I used Orange Seal Regular here for the tubeless setup again. Sidewalls are 0.98 mm thick, so very similar to the 2.2 and 2.4 Dubnitals I tested last year. These were very easy to inflate and I have really enjoyed them so far.

Speed wise, these are very fast… competitive with the Schwalbe RX PRO 700 x 50, one of my favorite tires I have tested. The 2.0 Dubnital is also remarkably fast on the smooth pavement test course. The tread has broad coverage to the outer edges, giving some promise of bonus sidewall protection. Yeah, there are faster tires in this size range but not very many! Impressive work from Conti here and big thanks to making sure I got some of these to test!

All outdoor results my own via Chung Method/VE testing. Wattages at speed are calculated from CRR values so easily scale to whatever speed you want.

Photo 10 credit to Luke Webber (cycling news)

* PSI notes in the comments*

Just wrapped up the fit on Nick’s Enve Melee. The Melee is probably not the most best bike in any single measurement but...
04/21/2026

Just wrapped up the fit on Nick’s Enve Melee.

The Melee is probably not the most best bike in any single measurement but damn these ride nice… and maybe that’s the most important of all.

Enjoy it Nick!! 🤝

Maxxis Aspen ST 32 x 2.15 off road rolling resistance results 📊 officially released the 29er Aspen ST to the public in 2...
04/16/2026

Maxxis Aspen ST 32 x 2.15 off road rolling resistance results 📊

officially released the 29er Aspen ST to the public in 2024, but it was quite clearly in use on pro bikes during the early 2020s…most often seen in 170 TPI Team Spec construction but also available in a 120 TPI + EXO TR casing. Both feature the MaxxSpeed compound and come in 2.25 and 2.40 widths. I tested the 29 x 2.25 170 TPI Team Spec tires last year and came away impressed with their speed and generous volume.

The 32” Aspen ST tested here is a much different tire than its 29” predecessor, with a new 120 TPI EXO casing and HYPR-X compound similar to their new gravel tire options. While the diameter grows 3 inches here, the width on this new model goes down a notch to 2.15 which seems directly targeted for use on larger wheel gravel bikes. Overall, a pretty exciting tire for me to get my hands on as I am a big fan of the HYPR-X Reaver gravel tire I tested from Maxxis last year. While the branding on this looks closer to the Reaver than the 32” Aspen, the tread pattern on the 32” Aspen ST is most definitely closest to that of the 29” Aspen ST.

Given the way total tire volume is calculated (a torus in shape), the volume of a 32er is quite close to that of a 29er setup with a tire 2-3 mm wider in cross section. This gives some eventual very interesting comparisons to be made regarding volume, width, and diameter…I am certainly zoomed in on this compared to the very similar volume 29 x 2.25 Aspen ST 170 I tested before.

It is easy to imagine a world where only tire volume, a supple casing, or tread pattern determines performance. My testing indicates that on- and off-road rolling resistance is influenced by many factors, inluding a benefit from increased diameter. This shows up yet again with the 32 x 2.15 Aspen ST tested here, with notably fast test results on pavement and across all gravel tracks. I have experienced better traction than the 29er Aspen STs in all scenarios which is a nice bonus to the efficiency gains.

All test results my own via Chung/VE method. PSI notes in comments. ✅

Vittoria Pe**te XC Race 32 x 2.4 off road rolling resistance results 📊I tested Vittoria’s Pe**te XC Race in the 29 x 2.4...
04/14/2026

Vittoria Pe**te XC Race 32 x 2.4 off road rolling resistance results 📊

I tested Vittoria’s Pe**te XC Race in the 29 x 2.4 size in late 2024, and followed that up in the spring of 2025 with the 29 x 2.25 size…both have proven to be quite popular for their speed on MTB and gravel courses. I have been riding a pre production (not on market yet!) set of 32 x 2.4 Pe**te XC Race tires for the last month or so and have quite an interesting set of test results. These are the same 60 TPI casing and Graphene + Silica Race Formulation compound construction as the 29s I have posted about…just 3 inches taller.

I will get right to the big news here. The 32 x 2.4 Pe**te XC Race is THE fastest tire I have ever tested on Cat 3 Rough Gravel!

We are looking at significant rolling speed improvements on all surfaces from smooth pavement to rough gravel compared to the 29 x 2.4 and 29 x 2.25 Pe**te. The results are remarkable and challenge some long held ideas about what makes tires roll fast.

As a refresher, I am using the Chung method (Virtual Elevation) for testing which is faster, easier, and more accurate than timed test runs at set power. VE calculates rolling resistance from measured inputs during a test session and matches to something that doesn’t change… the elevation profile of your test road! The CRR values are used to calculate the wattage tables per test surface, which is why they are so precise.

Precision is important, as with too broad an error range, one could go so far as to say that wheel size doesn’t matter at all. 👀

For those with a good memory, I originally tested the brown sidewall 29 x 2.4 Pe**tes, so made sure to get a fresh set of black sidewall 29 x 2.4s to redo some tests confirming the results to compare to the black sidewall 32 x 2.4 Pe**tes. I don’t usually get too worked up about what color the sidewalls are, but I wanted to make sure all details were covered.

PSI notes in the comments. ✅

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