RPM vs Speed on 6 speed g/box

[Pappu1]

what does your tacho rpm read when doing 100kmph in 6th gear in a v7sti non-dccd gearbox?

[nt_a_foz]

Dont know if they have differnt ratio or not but mmy V8 Sti DCCD sits at around 2700rpm at 100km

[Guest boostin]

 nt_a_foz said:

Dont know if they have differnt ratio or not but mmy V8 Sti DCCD sits at around 2700rpm at 100km

Legacy 6 speeds sit at just over 2000rpm @ 100kph, so yeah, I would say there are different ratios. I would think V7 and V8 are the same though.

[Guest Fastfour]

I sit just below 3k at 100km/h

[Scoobydoo]

 Fastfour said:

I sit just below 3k at 100km/h

Ditto

[Pappu1]

 Scoobydoo']

[quote name='Fastfour said:

I sit just below 3k at 100km/h

/quote]

Ditto

do you both have the RA sti spec box or the normal sti spec box?

[Guest Fastfour]

Is there any difference in the later versions?

[Simon C]

I'm doing 2900RPM on a Type RA Spec C gearbox.

[Pappu1]

anyone with a non RA 6 speed able to confirm the speed/rpm?

as far as i thought, the RA box would sit at about 3000 on 6th at 100k and a sti spec one be more like 2700 or so....

thats what im wanting to confirm..

[Tony]

 pappu said:

anyone with a non RA 6 speed able to confirm the speed/rpm?

as far as i thought, the RA box would sit at about 3000 on 6th at 100k and a sti spec one be more like 2700 or so....

thats what im wanting to confirm..

As far as I knew, all the 6 speed ratios were the same for the earlier boxes whether it is an RA or not. There may be some changes to the newer versions though... and I think the STI Foresters also have longer ratios in some of the gears (read that somewhere)...

My gearbox is non RA and it sits around 2700-2800 in 6th @ 100km/h - dunno exactly, but it is definately under 3000.

Tyre size will also be a factor and will give variences eg. Brad has a 6 speed in his GC8 so he would be using smaller tyres than a GDB would - maybe 215/45.17 or 215/45/17 as opposed to 225/45/17...

[nt_a_foz]

Yeah as you say tony im running 215/45/17

[Guest Fastfour]

Ive gotta ask, but why does it matter Pappu?

[Guest boostin]

Tyre size won't affect your speedo speed but will affect road speed.

[Pappu1]

asking cos i drve a mates sti and it was doing approx 3000 at 100k on 6th gear and i distinctly remember the other one i drove was like 2700rpm..

hence was wondering if ther 6 speed boxes had 2 reversions in the v7 sti .. one being closer stacked (like the RA of the old shape) and the other having an overdrive 6th

[Scoobydoo]

I seem to remember older RA's revved slightly higher.

[Optical]

http://spda-online.ca/modules/tinycontent/rewrite/tc_28.html

all same.

any discrepancy will be tyre size

[Guest boostin]

But again, tyre size doesn't affect the speedo, only road speed. The speedo takes its feed from either the gearbox output shaft or the wheel speed sensors, and tyre size has no bearing on either of those.

[Optical]

good point

[Guest]

 Optical said:

http://spda-online.ca/modules/tinycontent/rewrite/tc_28.html

all same.

any discrepancy will be tyre size

I would think with larger tires on the car, one would need a little more foot on the pedal to make the rotation and maintain rotation seeing as a larger diameter has a greater rotational inertia, requires more energy so a little more rev’s are required to keep constant at 100kph,

just a thought Mass moment of inertia and all that stuff , be interesting if pappu could give the rim sizes of both cars

[Guest boostin]

 EGOREX']

[quote name='Optical said:

url]http://spda-online.ca/modules/tinycontent/rewrite/tc_28.html[/url]

all same.

any discrepancy will be tyre size

I would think with larger tires on the car, one would need a little more foot on the pedal to make the rotation and maintain rotation seeing as a larger diameter has a greater rotational inertia, requires more energy so a little more rev’s are required to keep constant at 100kph,

just a thought Mass moment of inertia and all that stuff , be interesting if pappu could give the rim sizes of both cars

But... tyres... speedo...?? Bah, forget it.

[Guest itsgotgo]

 nt_a_foz said:

Yeah as you say tony im running 215/45/17

215/45/17 Versus 225/45/17......only difference with these is how wide the tire is.

Now if the tyre were taller,not "wider" it would throw things out a little,turn ratio vs final gear.

If you jacked the car up and as a rough guide.......mark the tire at a given point aswell as the drive shaft.

see how many times the drive shaft turns to one full turn of the wheel.

so if the shaft turns 2.7 turns to one full turn of the wheel,it has 2.7 gears"old school" v8 gears ;D

it may have a different diff centre or lower profile of tyres.

[Guest Raynes]

Pretty much 3k in my V7 sti

[Tony]

 itsgotgo said:

215/45/17 Versus 225/45/17......only difference with these is how wide the tire is.

No its not - common sense would make you think that is correct (as I did as well), but its something to do with the percentage of sidewall versus width (I forget exactly what it is, but I am sure someone will chime in with the correct explanation on the subject...) so the actual diameters of the 2 are different.

A 225/45/17 is around 634mm diameter, where the 215/45/17 is 625mm (according to the good old "tyre size calc") but this may vary in different brands of tyre as well.

And yeah, boostin is correct about the speedo, I got sidetracked on the original question pappu was asking and was meaning that the tyre size would have an effect on ratio.

[funkytown]

correct tony.. the 40 or 45 measurement is a percentage of the flat area. thus a 225/45/17 will be taller (slightly) than a 215/45/17

[Guest itsgotgo]

ok thanks for that tony,good explanation,and an understandable one 8)

I had 215,s with standard forester rims on my car"foz" then went to 225 45 17 and had no change on speedo

or in rpm.

so my guess was if the car is doing 3k at 100kmh the diff head may have been changed