Speed help.

**DrunkenMistake** · 27th May 2011, 19:28

I have just put on a 14t front sprocket and a 42 rear sprocket, and obviously this is going to ruin my speedo, so what I want to know can someone give me some kind of calculation so I can figure out my Real speed, the bike is a VFR 400 NC30 and is cable driven speedo from the front sprocket

EDIT: As mentioned by TT
'Bike: 1991 VFR 40 NC30.
Standard gearing: 15 Front, 40 Rear.

You just need to know where on the speedo a 'true' 50km, 70km, and 100km would be right?'

**The Stranger:Me** · 27th May 2011, 19:31

Originally Posted by DrunkenMistake

And I mean I speed and I need help, I actually enjoy it

I have just put on a 14t front sprocket and a 42 rear sprocket, and obviously this is going to ruin my speedo, so what I want to know can someone give me some kind of calculation so I can figure out my Real speed, the bike is a VFR 400 NC30 and is cable driven speedo from the front sprocket

Go find a speed camera and make a series of passes at varying speeds, they'll do the rest for you.

**The Stranger:Me** · 27th May 2011, 19:34

Originally Posted by DrunkenMistake

And I mean I speed and I need help, I actually enjoy it

I have just put on a 14t front sprocket and a 42 rear sprocket, and obviously this is going to ruin my speedo, so what I want to know can someone give me some kind of calculation so I can figure out my Real speed, the bike is a VFR 400 NC30 and is cable driven speedo from the front sprocket

Or you could use this.

**tigertim20** · 27th May 2011, 19:37

Originally Posted by DrunkenMistake

And I mean I speed and I need help, I actually enjoy it

I have just put on a 14t front sprocket and a 42 rear sprocket, and obviously this is going to ruin my speedo, so what I want to know can someone give me some kind of calculation so I can figure out my Real speed, the bike is a VFR 400 NC30 and is cable driven speedo from the front sprocket

The information he left out is as follows.
Bike: 1991 VFR 40 NC30.
Standard gearing: 15 Front, 40 Rear.

You just need to know where on the speedo a 'true' 50km, 7km, and 100km would be right?

**JimO** · 27th May 2011, 20:09

Originally Posted by tigertim20

The information he left out is as follows.
Bike: 1991 VFR 40 NC30.
Standard gearing: 15 Front, 40 Rear.

You just need to know where on the speedo a 'true' 50km, 7km, and 100km would be right?

borrow a gps from someone

**DrunkenMistake** · 27th May 2011, 20:11

Originally Posted by JimO

borrow a gps from someone

Yeah that is a good idea,
I might get my Mrs to drive infront of me at 50km then see what im reading and work out the % difference.

**pete376403** · 27th May 2011, 20:12

Put a cat-eye or similar bicycle speedo on it. Would be as accurate as anything else if you install it correctlly

http://www.trademe.co.nz/Sports/Cycl...-378462903.htm

**DrunkenMistake** · 27th May 2011, 20:14

Originally Posted by pete376403

Put a cat-eye or similar bicycle speedo on it. Would be as accurate as anything else if you install it correctlly

http://www.trademe.co.nz/Sports/Cycl...-378462903.htm

Also another great Idea, ill see if anyone comes up with some kind of calculation or something like that and go from there.

**JimO** · 27th May 2011, 20:28

Originally Posted by DrunkenMistake

Yeah that is a good idea,
I might get my Mrs to drive infront of me at 50km then see what im reading and work out the % difference.

the car speedo will be out as well, probably reading high which is better than reading low if all else fails i have a tomtom you can borrow

**DrunkenMistake** · 27th May 2011, 20:31

Originally Posted by JimO

the car speedo will be out as well, probably reading high which is better than reading low if all else fails i have a tomtom you can borrow

I may get back to you on that actually wouldnt need it for much more than 5 mins, just need a reading at the likes of 50km to figure out the % then i can work out what it should be accross the board, I had my speedo indicating 120 when I took it for a blip to try it out with the new gearing, and I was most defiantly not doing 120 haha

**bogan** · 27th May 2011, 20:38

http://www.gearingcommander.com/ will tell you all you need to know

**DrunkenMistake** · 27th May 2011, 20:44

Originally Posted by bogan

http://www.gearingcommander.com/ will tell you all you need to know

Urgh ignore what was said here, i got them all wrong.

**Sable** · 27th May 2011, 21:17

Gearing has nothing whatsoever to do with your speedo reading smackhead.

**bogan** · 27th May 2011, 21:25

Originally Posted by DrunkenMistake

Yah I seem it, it said that 9635rpm i should be doing 70 in first gear.

and at 4000rpm i should be doing 29.8km in first, So ill sit at 4000 tomorrow when I go to work and see what the dial says

you may find it easier to maintain speed, and get a more accurate reading in higher gears. That is a fairly massive change, what's the new rpm going to be at 100kmhr?

Originally Posted by Sable

Gearing has nothing whatsoever to do with your speedo reading smackhead.

unless the speedo drive comes from your gearbox

then the final drive ratio has a lot to say about it