After doing much reading on the interwebs, I have still not yet been able to find the answer to one gearing related question that has been burning constantly in my brain, so I’m hoping there’s a gearing guru out there with some useful info…
Is there a difference between gear inches in their actual physical makeup? by this I mean if I’m running 2 different bikes with 2 different gear ratios, but virtually the same gear inches, why do they feel so different?
One of my bikes is 39 x 14 (73.5) & the other is 45 x 16 (74.2)… both have similar skid capacity, but the acceleration ability of the 39 x 14 seems like a massive improvement over the 45 x 16.
Acceleration from a stand still seems worlds apart, with the 39’er feeling like a porsche 911 off the lights, where the 46’er feels driving like a bedford van. Acceleration while already pedaling gives also gives a similar speed win to the 39’er.
Is it simply a question of the other components on the 39’er bike just being lighter thus giving it a better power to weight ratio? or does the size of the chainring actually make a difference to power delivery?
& if its the case that chainring size only effects gear inches, why aren’t more people riding tiny front / back combos, for the potential weight reductions?
whats the weight of the wheelset/cranks/chain on each bike? rotational weight (eg of wheels and tyres) will affect your acceleration, hence why a wheelset for climbing can be a lot lighter than a track wheelset. (or so goes my limited understanding).
im sure someone out there could give an explanation of whether having more teeth in contact with a chain will increase friction to such a degree that it would be noticed by the rider: my initial thought is that it wouldn’t matter so much. also, if weight reduction of cranks/chainrings/cogs was such an issue, then shimano 10 pitch would still be alive and kicking.
im gonna put my money on rotational weight of wheels/tyres.
Semi-related, isn’t this why they tried Dura-Ace 10 (or whatever it’s called). Supposedly it was smaller and lighter therefore quicker?
Also, in an old Bicycle Mechanics book I have from the late 70’s / early 80’s, the author talks about how different style of track riders run similar inches, but use different chain ring / cog combinations, stating that some like a smaller ring to take off quicker. I think.
Smaller sprockets wrap the chain in a tighter bend, losing more energy. So a 36x12 is less efficient than a 51x17, for the same gear ratio.
DA10 may have provided a performance benefit by reducing weight (everything else being equal), but BETAMAX was superior to VHS too.
If anyone mentions the different length of the torque arm from the chainring teeth to the BB spindle axis having a measurable effect I’ll stamp you with the BSNYC seal of disapproval.
Something “seeming” to make a difference is very different to quantifying it. In your (decklus’) case, you have two different bikes, likely with different frame materials, geometry, wheelsets, tyres, cockpit arrangements… Too many variables to assign any difference to the chainring size.
They are quite different wheelsets (but similar crank weights) on each. One runs aerospoke/b43 combo (the slow one) the other runs deep v’s at each end …
I have removed these elements from the equation though, by doing a swap of the wheelset/chainring/cog between the 2 bikes & yet the 39 x 14 combo still just felt faster regardless of wheelset used.
Only the system power to weight ratio matters, unless you’re playing shotput with the bike, and let me assure you that the bike components make little difference once you add 60 to 100 kg of rider. The rotational inertia of the drivetrain is completely insignificant given that torque is high and speed is low. So that’s not the answer.
Weight … some of you coolio’s think too much with regard to the issue of weight and it’s importance. Just reading (mostly looking at pics !!! ) Jan Heine’s excellent book The Competition Bicycle which features Eddy Merckx’s bike that he rode (and Ugo de Rosa built) to win the 1974 World Championships (and thus the Triple Crown = Giro & Td’F)).
To quote (and Jan measures and takes all this very seriously 'coz he’s German :-P) …
Always concerned about light weight, Merckx had grooves machined into the large chainring and stem (aka milling or drillium -ed). Nevertheless, with a stiff frame to withstand the immense power of the Cannibal, the bike was no lightweight, tipping the scales at 11.0kg (24.3 lbs).
From other sources and experts on Merckx’s bikes I have found out the seat post diameter for most of his frames is 27.0mm. I’ve also seen a bike used by Koichi Nakano (10 Time World Keirin Champ !!! http://www.youtube.com/watch?v=Nvruf90mqE ) that uses a 26.8mm seat post. I wish I had a $ for every newly born expert that calls anything less than 27.2mm gaspipe or heavy :roll:
Some of you focus on saving a few grams when even at the highest level it’s importance is very little. Seriously folks, the best way to improve your bicycle is to improve the rider. (end of rant)
Throwing it out there to the techy’s? Blakey? Mig? Anyone?
Could rpms have anything to do with it? ie. smaller fr cog higher rpms increased ease of take off?
I understand it sort of from a m/cycle POV but am still learning by trying different combo’s at the race track.
nb. m/cycle use small front and large rear because of the higher rpms from a motor.
I think Blakey has nailed it with the bikes other components … between material composition & geometry, the 2 could not be any more different … I have been looking to blame only the one component for the differences in acceleration but maybe I need to start faffin around with other bits, not just ratios.
Alas I dont have any scientific measures for any of this (except the highly scientific “feel” of it) … think I will do some measured sprints using my cyclo-computer/stopwatch & see if I can actually quantify my “feeling” with some scientific results
Same deal on the motorbike, you’d have the same take off and shift points with a 15x45 as you would a 16x48, both are a factor of 3. The 16 would give slightly better chain life and you might notice an anti squat effect change (only relevant when there’s a swingarm).
MiG (can’t quote for some reason) Terminal speed is higher though with the smaller sprockets.
I’ve tested this at Broadford. 180kph v’s 175kph on the GPS, flat out in 5th!
if there was a tangible benefit we would all know about it as it would trickle down from the top end of racing where absolutely minute changes can be the difference between win and lose
