I really like bikes.
Any sort of bike, really, and I find riding them good fun, good for my physical and mental health and good for seeing both new places and viewing familiar ones from a new perspective. I also really like thinking about new bikes that I might one day get and I’m in the thick of that at the moment in terms of considering my first ever custom build of a “do it all” adventure / light touring non-electric bike.
One of the things I’m needing to think through is the gearing of the new bike to ensure there are enough low gears to crawl up some of the massive climbs in New Zealand with camping gear and me included! I’m currently considering the Soma Wolverine v4 Type B frame that would look a little like this, but I’d not go for the drop bars:
The reason I’d go for the Type B frame is I really want to use a Rohloff Speedhub internal gear hub with a Gates carbon belt drive. I already have some experience with internal gear hubs and belt drives on my first eBike – read about this here. What I’m less familiar with is the gearing ratios I’d need and how to translate these from my existing derailleur / cassette drive trains into the 14 geared Speedhub.
Enter the Bicycle Gear Calculator website – pure brilliance.
My Existing Bike Drive Trains
- 34/50T Chain Ring
- 11 speed 11/32T Cassette
I can visualise this on the Gear Calculator here and it looks like this:
- 32T Chain Ring
- 12 speed 10/52T Cassette
I can visualise this on the Gear Calculator here and it looks like this:
With this configuration you can see the eMTB has much lower gearing and much higher jumps between the lowest gears (36T to 42T to 52T). So whilst it doesn’t have the same top end speed as a roadbike (as you’d expect) it should get you up steep climbs with far less effort.
There are many cool things about this training bike but two quite unique features:
- It can accurately simulate gradients, both climbs and descents making for very realistic riding. When riding virtual worlds in Zwift or riding courses from my Garmin Edge 530, the bike automatically goes up and down based on the gradient on the ride – cool!
- You can configure any group set you have on your bikes – in my case Shimano and SRAM. This is because there is no physical cassette on the Kickr Bike, but instead a weighted flywheel and belt drive will simulate the different gearing configurations you may choose. Up until now, I’ve always just mirrored the Shimano gearing on my Cannondale Synapse, but today I did something a bit different.
Comparing Rohloff Speedhub with SRAM 10/52 Eagle Cassette
The really clever thing about the Bicycle Gear Calculator website is that it allows you to compare two different hubs, meaning I could take the known configuration of my eMTB and compare it against a prospective Rohloff Speedhub I might get in the future with the Soma Wolverine.
Here is the comparison on the Bicycle Gear Calculator website and it looks like this, using a Rohloff Speedhub with a 46T Chain Ring and a 20T rear cog – the SRAM eMTB is at the top (unchanged) and the Rohloff Speedhub is at the bottom:
The Rohloff has 14 evenly indexed gears, and because there is 540% gear range you can see that the lowest and highest gears are ever so slightly lower and higher than the SRAM configuration – incredible! The cool thing about the Bicycle Gear Calculator website is that you can slide the Chain Ring and Cog up and down to immediately see the impact of different tooth configurations if you need lower/higher gearing ratios.
So, I’d been able to establish in theory that a Rohloff Speedhub with a 46/20 configuration would likely be geared pretty similarly to my eMTB which, believe me, absolutely flies up hills – thanks to it’s amazing motor! What I could not easily test is what it would be like riding a bike like that up real hill climbs without the motor assist. Then I had a brainwave.
Wahoo Kickr Bike + Garmin Course Routing = (Virtual) World Test
I remembered that you could change the gear ratios on the Wahoo Kickr bike and I wondered if I could accurately replicate the SRAM set up on my eMTB. To this point, I’d always run the Shimano 2 by 11 that my Cannondale was using which was 2 Chain Rings (34/50T) and 11 gear cassette (11/32T):
There was no SRAM Eagle cassette configuration in the Wahoo Kickr app, so I was going to need to rely on the custom configuration setting which meant I was going to need to find the actual number of teeth on each cog in the cassette – something I was able to track down here:
The jump from the 42t to the 50t cog equates to a 19 per cent jump, while shifting from the 42t to the 52t cog on the latest cassette increases this to a 23.8 per cent jump. Lower down the block (from the 10-42t cogs), the steps remain the same (10, 12, 14, 16, 18, 21, 24, 28, 32, 36, 42, 52t).SRAM gets one up on Shimano with new 52-tooth Eagle cassette – BikeRadar
Equipped with this information, I was able to recreate my SRAM eMTB gearing by manually entering in each cog size:
At this point, I was starting to feel pretty pleased with myself but now I needed a realistic course for riding the new gear configuration on my Wahoo Kickr Bike. I’d recently completed “The Three Sisters” on Zwift that has 3 of the 4 largest climbs in Watopia (898m elevation over 48.5km) and had done this on my standard Shimano configuration:
Whilst repeating this would have given me a better understanding of relative effort between the two gearing systems, I really wanted something a bit more real world, something that might simulate a ride I’d do if out bikepacking. I decided to create a route near me that would start in Diamond Harbour, bike around to Purau before setting off up the first climb of 434m and down into Port Levy, before climbing again, this time 671m exiting Port Levy on the way to Little River.
A total climb of 1131m in a little over 30km would definitely be a good test of the gearing setup, with the first climb being 5.06km and an average gradient of 9% and the second 7.5km with an average gradient of 8% according to Garmin’s ClimbPro calculations. I’m not the lightest rider by any stretch and on my road bike, in real life, that would be something that would be a little daunting and I’d definitely know a hard ride in the saddle was looming! On my eMTB with boost assistance it would be fine – the big unknown was how it would feel with my eMTB SRAM gearing ratios and my legs providing all the power!
In the end, honestly it was pretty easy:
You can safely ignore the downhill speeds because Garmin doesn’t account for corners or sanity, simply power + decline = speed!
So, it was not fast going up by any stretch, and I sat mostly in gears 1-5 for the climbs. Even though the averages were 8% and 9% respectively, these ranged from 6% to 20% in places. I tried to imagine whether I could have done these climbs on a bike with camping gear and I concluded I likely could have. My max heart rate was only 164bpm with an average of 141bpm which was pretty low given the 1100 total elevation and shows just how much difference the gear ratios made.
Similarly, a max power output of 328w is quite low with average of 196w shows it was hardly a strenuous ride. By comparison, here’s the Three Sisters data (less steep and less total elevation but it did have one sting in the tail going up to the Radio Tower):
Clearly, both higher max/average for power and heart rate showing it was a much harder ride than what I did today with the Garmin route and the SRAM gearing on the Wahoo Kickr Bike.
I was super pleased to realise I could virtually simulate any gearing combination on my Wahoo Kickr Bike allowing me to test various things before ever considering purchasing them. It was also interesting to learn via the Bicycle Gear Calculator that a 14 speed Rohloff Speedhub has almost identical top and bottom gear ratios to the 12 speed SRAM Eagle gearing on my eMTB if I used a 46/20 configuration with the Rohloff. Knowing I could tweak that further to go even lower if needed was reassuring, and Gates has a useful calculator on their website that allows you determine what length carbon belt you’d need to match your chain ring and cog combination.
So whilst I’m no closer to buying my dream custom build bike, I do feel like I’ve at least ridden it virtually up 1100m of climbing on local hills and would have a reasonable sense of how it would feel on those climbs. Of course, the Wahoo Kickr doesn’t take into consideration the weight of the bike (and any gear strapped to it) when determining the resistance on the inclines, but it does take my weight from Garmin to make it realistic in terms of effort/power and resultant speed up the hills.
Riding with super low gearing today did mean it was a slow ride up big hills, especially compared to my road bike, but sometimes that’s ok. Riding is meant to have different experiences and being able to ride consecutive days with big elevation climbs is important for longer, multi-day rides.
Lastly, this is all new to me – if you’ve got experience and knowledge on gearing ratios and have spotted errors in how I’ve calculated this, please do feel free to drop a note in the comments below to help me learn.