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Thread: Nobby newby biking questions

  1. #1
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    Nobby newby biking questions

    Okay, I'll freely admit that I'm a nobby newby cyclist and at the minute I just have zero comprehension of most of the terminology and options for my bike. I bought a Genesis (CDF 20) gravel bike in February and love it to bits but there's still so much I don't understand:

    1. I simply want to buy a spare inner tube and, despite trying to read up on it, I still have no idea which one to get. From my bike's spec I know the wheels are apparently size 700c and that the tyres are Kenda Booster 700 x 40c's. I'm guessing the 40c is something to do with the width/height of the tyre? So daft question, what size inner tube do I need? If I search on-line I get all sorts of size inner tubes thrown at me, showing a range of size which may or may not be relevant, and I just simply want to know what to get. (Yeah I appreciate I could also go into my local cycle shop and ask )

    2. A direct quote from the Genesis web site: 'The ability to run up to a 45mm rear tyre and a 50mm front tyre on the provided 700c rims increase the all-terrain ability of the CDF 20. If you want to experiment with 650b wheels, you could run up to a 44mm rear tyre and 50mm front tyre'

    Assuming the 40c tyres that I currently have means that I'm running 40mm tyres, I'm guessing that means that I can get bigger tyres? And presumably bigger front than back if I want to? And why would I want to? Extra grip, durability and/or off road ability I assume? And presumably 650b wheels are smaller circumference wheels that offer more off-road something or other? More mountain bikey performance from the wheels I assume?

    3. The absolute best gobbledegook is from a third-party review of my bike on their web site. Talking about the GRX chainset, which might be a 46/30 tooth paired with an 11-34t cassette (which I'm guessing is the range of gear cogs) it goes on to "helpfully" elaborate as follows:

    'If you want something even lower, then the GRX 400 rear mech will accept a 36-tooth sprocket which can be achieved by using a CS-HG50-10 mountain bike cassette from Shimano'. I'm not sure I understood a single word in that sentence

    Can somebody patiently explain to me wtf this all means? Thanks

  2. #2
    Senior Member Marco's Avatar
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    Quote Originally Posted by Fellbeast View Post
    Okay, I'll freely admit that I'm a nobby newby cyclist and at the minute I just have zero comprehension of most of the terminology and options for my bike. I bought a Genesis (CDF 20) gravel bike in February and love it to bits but there's still so much I don't understand:
    I will try to answer your questions in easy to understand English:

    Quote Originally Posted by Fellbeast View Post
    1. I simply want to buy a spare inner tube and, despite trying to read up on it, I still have no idea which one to get. From my bike's spec I know the wheels are apparently size 700c and that the tyres are Kenda Booster 700 x 40c's. I'm guessing the 40c is something to do with the width/height of the tyre? So daft question, what size inner tube do I need? If I search on-line I get all sorts of size inner tubes thrown at me, showing a range of size which may or may not be relevant, and I just simply want to know what to get. (Yeah I appreciate I could also go into my local cycle shop and ask )
    700c refers to the wheel size, and it is the metric equivalent of the 27 inch wheels that you probably started with as a kid. The 40c refers to the width of the tyre when inflated in mm.

    When buying an inner-tube you want to make sure that you get one that is 700c first of all. The second thing is the width of the inner-tube where there is some range, so you see sizes like 23-28 (which wouldn't be suitable for your bike). You need one that has a range like 32c-47 so it will fit tyres from 32mm to 47mm wide. thirdly there is the type of valve, which on the road is normally Presta. You can tell if you've got presta valves if you have to unscrew a little brass thingy before you can pump air in. Finally there is the length of the valve. Deep aero-section rims need long valves, but you are unlikey to have these You can either take the inner-tube out and measure it, or guestimate. NOTE: It is not a problem if your valve is longer than it needs to be, but it's a effing big problem if it's too short!

    I have posted below a screen shot taken 5 minutes ago from Chain Reaction Cycles (other shops are available) to give you some idea as to what you should be looking for. 42mm valves will work for non-aero wheel rims - if in doubt post a photo of your wheel from the side




    Quote Originally Posted by Fellbeast View Post
    2. A direct quote from the Genesis web site: 'The ability to run up to a 45mm rear tyre and a 50mm front tyre on the provided 700c rims increase the all-terrain ability of the CDF 20. If you want to experiment with 650b wheels, you could run up to a 44mm rear tyre and 50mm front tyre'

    Assuming the 40c tyres that I currently have means that I'm running 40mm tyres, I'm guessing that means that I can get bigger tyres? And presumably bigger front than back if I want to? And why would I want to? Extra grip, durability and/or off road ability I assume? And presumably 650b wheels are smaller circumference wheels that offer more off-road something or other? More mountain bikey performance from the wheels I assume?
    Because you have disc brakes, rather than brakes on the rim, you could, potentially, fit any disc wheel size smaller than what you've got. 650b is a smaller size than 700c that was used on smaller frames for short people. It is nothing like as widely available as 700c, so I wouldn't recommend going down that route. I have little off-road cycling experience, but 40mm is pretty wide. If you need something wider then you probably need a mountain bike

    Quote Originally Posted by Fellbeast View Post
    3. The absolute best gobbledegook is from a third-party review of my bike on their web site. Talking about the GRX chainset, which might be a 46/30 tooth paired with an 11-34t cassette (which I'm guessing is the range of gear cogs) it goes on to "helpfully" elaborate as follows:

    'If you want something even lower, then the GRX 400 rear mech will accept a 36-tooth sprocket which can be achieved by using a CS-HG50-10 mountain bike cassette from Shimano'. I'm not sure I understood a single word in that sentence
    On a bike like yours, and mine, the gear sizes are determined by the ratio of the cog at the front compared to the cog at the back. On your bike the biggest gear is 46 x 11 which is just over 4:1, whilst the smallest gear is 30 x 34 which is a ratio of just under 1:1

    At this point I need to get the calculator out to explain this. A gear of 30 x 34 is actually a ratio of 0.88. This means one rotation of your cranks will result in 0.88 rotations of the rear wheel. Using a 36-tooth sprocket would give a ration of 0.83

    The cassette is the whole group of sprockets (cogs) at the rear of the bike. You buy them as a set, although some of us mix our sets up to get exactly the gears we want.

    As you bought a well equipped bike, with a very good range of gears, I don't think you'll need to change what you've got - just replace it in the future when it has worn out.

    NOTE: I don't think I've mentioned this before, but it is not recommended to use the extreme gears of big front cog and big rear cog, or small front cog and small rear cog. The reason, in short, is that the angle of the chain is too high and it puts excessive wear on both the cogs and the chain
    Last edited by Marco; 07-05-2021 at 06:40 PM.

  3. #3
    Master molehill's Avatar
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    Fellbeast, welcome to my world of cycling pain, I have no idea.
    Possibly why fell running was so appealing in the old days, simply what size of PBs do I wear?

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    Master mr brightside's Avatar
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    Quick addition.

    Your rear derailleur cage size limits your cassette range. You can only go bigger on the top cog if your derailleur cage can take it.

    Marco is right about straining the chain by choosing big or small cogs at both ends. The amount of people I see turning a 53/32 up a hill is unbelievable! Dropping into the little ring is very underrated these days and highly unfashionable it seems. When you're turning a 36/16 the chain is dead straight, just how it should be for climbing.

  5. #5
    Master mr brightside's Avatar
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    A gravel bike was a good choice. Mountain bikes can bugger your back at our age, it's the seating position.

  6. #6
    Quote Originally Posted by Marco View Post

    NOTE: I don't think I've mentioned this before, but it is not recommended to use the extreme gears of big front cog and big rear cog, or small front cog and small rear cog. The reason, in short, is that the angle of the chain is too high and it puts excessive wear on both the cogs and the chain
    Fellbeast

    If you make this school boy error your chain, apart from looking like a dog's hind leg, will make horrible noises telling you that it wants to get back to being as straight as possible and thereby save you money by not stretching itself and wearing out the cogs on the cassette - leading to the replacement of both items.
    Last edited by Graham Breeze; 07-05-2021 at 08:49 PM.
    "...as dry as the Atacama desert".

  7. #7
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    Thanks everyone. Really really helpful

  8. #8
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    Iíd already clocked that using my small front cog with my smallest back cog was a daft thing to do, just by the noise. The chain definitely doesnít like it

    Itís a bit of an over simplification but I tend to use my big front cog most of the time on tarmac and the little front cog most of the time off-roading. There again on some of the climbs around here, I use the lowest combination at some point on the hill all of the time. And yep my chain is absolutely at it straightest at that point 😊

  9. #9
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    I'm guessing that a smaller rear wheel would be the equivalent of an additional larger cog on the back in terms of gearing.
    Cause tramps like us, baby we were born to run

  10. #10
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    I too have Genesis croix de fer 20 though a few years previous to yours. There's not a great deal difference in the spec though - my chainset is Shimano Tiagra and it came with Alex rims and continental CX tyres but otherwise pretty much the same.
    I've upgraded a few things. The saddle had to go - I now have a Brookes cambium. I also replaced the tyres with Schwalbe marathon 28c for road/light trail use i.e. my commute and bought another set of wheels (Mavic Askium) and fitted those with Vittoria Terrano Mix 33c for full on gravel mode.
    I also replaced the seat post with a Ritchie with 2.5 cm layback. Gives a bit more room and better position for me without changing the stem and more weight (and grip) over the rear wheel when off-road.
    Have fitted SPD pedals which obviously you need to be confident with if heading off road.
    I'm on my second bottom bracket (but it has done over 11000km) and I also had to replace the headset but that was due to an accident rather than personal choice.

    I also have a MTB and road bike so this one sits nicely in the middle. Obviously I would not entertain only having one bike but if I had to choose, then the CdeF would get the nod.

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