First of all, I am amateur cycling enthusiast and I don’t have much knowledge about mechanic specs regarding the bikes and additional equipment. I just want to buy the Zwift Hub setup to help me out with home training. The question is - Could you tell me please if I can pair my bike Triban RC100 including 7-speed 12-28 cassette with Zwift Hub? Or I can buy Zwift Hub with 8-speed cassette and use it without one gear (I read that distance between the cogs is the same for 7 and 8-speed cassette). I would be really grateful for your assistance.
You can install a 7 speed Hyperglide cassette with an extra spacer under it. The exact size of the extra spacer depends on the dimensions of the cassette - they are not all identical.
7 and 8 speed spacing are not the same
You should probably order the Hub with a cassette because it’s no cheaper without one.
You’ll need a Shimano lockring tool to install a cassette. To remove a cassette you’ll need the lockring tool and a chain whip. A bike shop can sort all this out for you if you take the bike and trainer to the shop.
A word of caution…
7 speed usually comes with spacing between the frame dropouts of 126mm; and 8 speed 130mm.
The Zwift Hub accommodates a minimum of 130mm.
Your Triban RC100 is aluminium. A steel frame would be sufficiently flexible to be stretched from 126 to 130mm but aluminium won’t like it. Best measure the distance between the rear dropouts. If it’s 130 the Zwift Hub will fit.
Regarding the 7/8 speed conundrum, both speeds use the same width chain. Despite what Paul says I suspect you may get away with using an 8 speed cassette with a 7 speed mech., with adjustment to the mech. limit screws. If not, then a 7 speed cassette with a 4mm spacer - readily available on Ebay.
Most of the modern 7 speed bikes do not have 126mm spacing but it’s worth checking.
The difference between Shimano 7 and 8 speed spacing is .2mm per cog. It’s close enough when cogs are adjacent but across the entire cassette it’s harder to get a good result on both ends. It’s OK if you only care about a few cogs and center your adjustment in the middle of those.
Hey, thanks for your helpful hand in this specific case and truly apologizes for the late response. I just checked everything properly and the width regarding back triangle is exactly 130 mm, but after reading some reviews and some independent experts I decided to buy Wahoo Kick Core instead of Zwift Hub. I also bought 7-speed cassette hyperglide and new bike chain with 108 cells. I tried some options regarding the spacers to use all 7 gears and actually 4,3 mm is the solution = 1,8 (available with the trainer originally) + 1,5 + 1,0. Right now everything works perfect with my Triban RC100. If anyone has a similar doubt just use mine advice for your reference. Best wishes!
I also have a Kickr Core. Used it almost daily for 2 years now and have been very pleased with it.