Tyres and Rolling Resistance
iwilldoit
Posts: 710
Hi All.
Changed my sons bike from a Giant XTC Jr 24" wheel to a Whyte 604 Compact with 27.5 wheels he's been complaining it's a lot harder for him to go up hills on, his new bike is Nobby Nics as I wanted him to have some grip instead of the std tyres which are a bit slick, the shop we bought it off swapped the tyres for us so don't have the old ones.
How much difference does it make if I put something like a Racing Ralph on the back, how much would this cut the rolling resistance down, or would it be better with a different type of tyre, but we do need some grip as well, he's just started doing XC racing and is doing well, but on the hard pack up hill sections you can see others pull away a little, mind that might also be they have been doing it for years and he's only been mountain biking is 10 months, also I suppose tyre width and weight will come into it.
Changed my sons bike from a Giant XTC Jr 24" wheel to a Whyte 604 Compact with 27.5 wheels he's been complaining it's a lot harder for him to go up hills on, his new bike is Nobby Nics as I wanted him to have some grip instead of the std tyres which are a bit slick, the shop we bought it off swapped the tyres for us so don't have the old ones.
How much difference does it make if I put something like a Racing Ralph on the back, how much would this cut the rolling resistance down, or would it be better with a different type of tyre, but we do need some grip as well, he's just started doing XC racing and is doing well, but on the hard pack up hill sections you can see others pull away a little, mind that might also be they have been doing it for years and he's only been mountain biking is 10 months, also I suppose tyre width and weight will come into it.
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Secondly, the rims and tyres almost certainly weigh more, and that mass is definitely positioned further from the axis of rotation, which leads to a much higher force needed to accelerate them around that axis.
Your son will get used to this, but it might take some time before he can exploit benefits of the bigger wheels, and learn to rely on carrying momentum, rather than relying on fast acceleration. Obviously, anything you can do to reduce the weight at the rim is going to be vastly beneficial - racing ralphs sound like a good bet (if the going is mostly firm) - depending on the particulars of the existing tyres and replacements, they could shed a good few hundred grams from the wheels (the reduction in rolling resistance would be noticable, too, but reducing the rotating weight is the major benefit). You could also try tubeless to make further savings.
I wouldn't use Nicks for XC racing on hardpack, Ralph's for hardpack, Rons if it's a bit muddier, if its dry and hard then Freds, they will all also be lighter than the Nic's (weight savings really show up on the climbs).
retired 9.6kg Carrera Kraken
The Carrera Hardtail combined thread - come on all you Carrera's!
The Sons Scott Genius RC20 build
Just looked at the gearing the Whyte is Front 42-32-22 Rear 11-34 and the Giant is Front 42-34-24 Rear 13-34.
Been trying to help him o the up hills, keep trying to tell him instead of moaning about it put the anger into the pedals and different ways of taking his mind off the slog up the hill, mind the bigger wheels come into their own on the other side of the hill, he's flying down them
I will try later seeing what the actual difference in weight there is in the two bikes.
retired 9.6kg Carrera Kraken
The Carrera Hardtail combined thread - come on all you Carrera's!
The Sons Scott Genius RC20 build
In terms of gearing that's about the same for "granny to big sprocket", even allowing for the jump in wheel size. It's probably just a case of him getting used to the size of it, how he's now sat on it and needs to deliver the power etc. It's no different from me riding my Inbred 29 and my Bandit 26, two completely different bikes that need riding with a different technique.
Road - Wilier Izoard Centaur/Cube Agree C62 Disc
Allround - Cotic Solaris
Your right Rookie my description of putting his anger into the pedals didn't come over quite right, more a case of thinking of keep going a sustainable pace, one thing I have been trying to get him to do is use his gears more and not go straight for the easiest gear straight away and have his legs going a million miles an hour.
He's done 2 races so far and done quite well a 7th in the first one but he did look a little on edge ( can't blame him, I would of been to the loo a few times before the start :oops: ) and a 5th 2 weeks a go, but did look a lot more like he wanted it.
Having recently switched to tubeless, I'm hoping the extra deformation of the tyres will help to soften the blow, allowing better control and less loss of speed through deflection.
Also bigger wheels require lower gearing to maintain the same speed on a particular gradient.