Gear inch/ratio question

I remember it being his face that he did most of the breaking with.

well most people use gear inch charts for relative comparison, so it doesn't really matter.

SkullheadWilderness [quote]TheBrick(Tommy) It's not fucking 27 unless you ride a bike with fucking 27" wheels!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! FUCKING FUCK FUCK FUCK

hahahaha what's 8mm? its all scientific up to there, why not include some inaccuracy[/quote]

0.72 aprox = 17.78 mm
More like 18 mm. It is the fact that 26" is closer to 700cc wheel + 23 mm tyre and using a different wheel size as your multiplyer removes the point of using gear inches. You can not compare different g.i unless they have been properly calculated Just use gear ratios if you multiply every thing by 27 no matter what the wheel size is.

Object17 [quote]RPM 50 x 14

no brakes, it's the way forwards.. they say

Ooooh Controversial :][/quote]

sorry, I shouldn't really joke as you guys got hurt!

Don't stop joking on my account. I have a bleak sense of humour that finds it funny.

• it's a genuinely useful way of reducing tyre wear. Run into other riders to slow down.
  

TheBrick(Tommy) [quote]SkullheadWilderness [quote]TheBrick(Tommy) It's not fucking 27 unless you ride a bike with fucking 27" wheels!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! FUCKING FUCK FUCK FUCK

hahahaha what's 8mm? its all scientific up to there, why not include some inaccuracy[/quote]

0.72 aprox = 17.78 mm
More like 18 mm. It is the fact that 26" is closer to 700cc wheel + 23 mm tyre and using a different wheel size as your multiplyer removes the point of using gear inches. You can not compare different g.i unless they have been properly calculated Just use gear ratios if you multiply every thing by 27 no matter what the wheel size is.[/quote]

I'm with Tommy on this one. I've done medium gear time-trials (72" max) on 46x17, and they check your gear by rolling the bike along a complete revolution, and measuring the distance with a tape measure. So it's definitely not a 27" wheel.

I am a bit autistic spectrum though.

27" and 700c are wheel sizes.

tyre bead diameter is 630 for 27"; 622 for 700c. when you calculate gear inches mixing the 2 up, including tyre sizes, can give you rather different results. not to mention the hideous gap you get putting a 700c wheel on a frame made for 27" wheels.

Gear chart using Gear Inches

For 700 X 23 / 23-622 tyre

46t chainring:

13 93.0

14 86.3

15 80.6

16 75.6

17 71.1

18 67.2

19 63.6

20 60.4

21 57.6

22 54.9

48t chainring:

13 97.0

14 90.1

15 84.1

16 78.8

17 74.2

18 70.1

19 66.4

20 63.1

21 60.1

22 57.3

TheBrick(Tommy) Why do some people use 27 as their wheel size when they have 700c wheel and 23or 25 mm tyres? The entire point of using gear inches instead of gear ratios is so you can compare the gearing used between different bikes of different sized wheels. I know this is not as good a the gain ratio as this is dimensionless but it is a silly thing to use 27 as your multiplier as it removes the point and convince of gear inch to use as a comparison tool.

It is very simple to find your wheel size in inches.

700 cc rims are 622 mm in diameter.

Tyres are square so as 23 mm would add 23 mm at the bottom of the wheel and 23 mm at the top of the wheel so the wheel is now 622 + 23 +23 = 668 mm in diameter.

25.4 mm in one inch. (You can use google to look this up) So 668/25.4 is approximately 26.3 inches. Very simple. Now you can use gear inches for the purpose for which they where developed rather than negating their entire purpose by using such an extreme approximation.

If you are going to use an approximation use 26". For a start is is closer to the real value than 27" plus it is alway better to understate your measurement and surprise people when accurate measurement is done than to over state and disappoint.

Tell it like it is :)

wow, way to complicate things!

Use this http://software.bareknucklebrigade.com/ (launch the 'outside browser one' - less buggy).

shows you very easily everything you need to know!

46:17 for winners and heroes

i dont see the point in gear inches because every one in their right mind is riding 700x23c (ok maybe up to 25c) rear wheels, and like has been mentioned its the ratio (big number dived by little number) that gets your wheel turning.

it's gear inches for the road, ratio for off-road.
don't ever forget that

Ever.

MrSmith 46:17 for bummers and zeroes

Sorry Tommy I used 27 in my calcs all the time.. why? Coz I'm lazy and 27 is easier to remember than something else.. :P
It's not exact anyway and if you are just working out how much difference new gearing will make there's nothing wrong with using 27.
I'm gonna keep using 27.. 27.. 27... 27..... 27......... 27.
It's only a rough guide anyway, it's not like anyone here is going for a world record pursuit time or something where shit like this makes a difference.

I'm running 700c with 28s (I've got a fat arse and like the comfort!) which comes out at about 26.69"

I run 42:13 (finally took all the other gears off)

Thats about 86 gear inch...is this too high or too low....I'm confused...

86 gear inches is high
like god, jesus and all his disciples i ride 46x17 which depending on the charts you look at is 72-73 gear inches which i find perfect for london and the surrounding countryside

juliettyspaghetty I don't know how to compare gear ratios to each other. I'm rather confused.
I use 46 on the front and 16 on the back and its pretty hard to brake, and hop about and skid, without yanking quite hard on the bars.
I tried my friends yesterday and he has 48 on the front and 19 on the back, and his bike was so easy to ride. It was way more fun and I really preferred it.
So here's the question: if I want to change my bike so it rides the same as his, do I need to replace the chainwheel as well as the rear sprocket? I can't really afford to do this right now.... Or can I just replace the rear sprocket with a different one which will work in a similar way? If so, how many teeth do I need?
How do you work this stuff out?

If your friend has a 48t (front) - 19t (rear) set up it would be 66.4 gear inches (assuming he's running standard 23c tyres)

If you have a 46t (front) - 16t (rear) set up and want the same feel (66.4 gear inches) the cheapest way is to get a new 40 tooth front chainring (what you call a 'chainwheel').

The reason I suggest replacing the chainring and not the socket . . .

. . . if you were to try and get a 66.4 gear inch set up by changing the rear sprocket you would have to swap you current 16t for a 18t sprocket (this get's you near enough at 67.2 gear inches) - and as an 18t sprocket is bigger than a 16t sprocket your chain is now too short - so you need to get a new chain.

Changing the 46t chainring for a 40t (this get's you near enough at 65.7 gear inches) means the chain needs to be shortened - so you just have to remove a few links.

I am presumming a chain + sprocket is more expensive than a chainring (?)

Even if I am wrong, this should at least be a clue as to what you have to consider, but certainly no need to replace both.

Great gear calculator: http://software.bareknucklebrigade.com/rabbit.applet.html

you know you can add a few links to a chain, too.

no need to buy a new one.

anyway sprockets are cheaper than chainrings.

dumbass.

lpg you know you can add a few links to a chain, too.

No way ! - You should start a new thread, this is great news ! ;P

I assumed that anyone asking a question like the OP probably does not have a box with spare parts in like chain links.

lpg

anyway sprockets are cheaper than chainrings.

dumbass.

I was (and I made this clear for the hard of thinking) presuming the cost of a chain ring would be cheaper than a chain and sprocket, I also pointed out that of course I may be wrong on the pricing, but that's not the point, I am just highlighting the issues involved.

ha, i knew you'd get all defensive, you tit.
on a more serious note juliettyspaghetti, you might not need to add any links at all, it depends on the length of your dropouts. I used to use a 16/19 on a flipflop and didnt have a prob.

dont listen to tynan, he's a fool. his mother was a hamster and his father smelt of elderberries.

love,

lpg.

lpg ha, i knew you'd get all defensive, you tit.

Yes, that's right, you knew.

he's got , like, your number, man

nimhbus he's got , like, your number, man

:)

SkullheadWilderness Umm why is a maths thing. there's an excellent skid-spot calculator somewhere in the web, it'll let you work out how many spots different rations will give you. Seems odd numbers/prime numbers (uuuh I think) seem to give more skid spots, which is maybe why I never seem to be able to find a 17t sprocket when I'm buying.

This is a sweet little skid patch calculator widget for Mac 'eds.
I use it to aid day-dreaming of skid pirouettes at work.

http://www.apple.com/downloads/dashboard/calculate_convert/skidpatchcalculator.html