BMF
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| posted on 21/7/04 at 03:31 PM |
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How do I calculate max speed?
How do I work out the maximum speed I can expect?
I have a Vauxhall XE - 6500-700 rpm
Type 9 Box
3.62 LSD
Must be a formula somwhere!
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derf
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| posted on 21/7/04 at 03:40 PM |
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Engine rpm divided by gear ratio of highest gear divided by final drive times outside diameter of tire.
I belive that is it, I might have my multiplication and division mixed up.
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BMF
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| posted on 21/7/04 at 03:43 PM |
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Anyone know what ratio 5th gear on the type 9 is then?
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locoboy
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| posted on 21/7/04 at 03:43 PM |
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you need to know what size tyres you will be running and the gear ratio's in the type 9 box.
Its all pretty irrelevent if your building a 7 style car because you will loose the aerodynamics battle long before you attain maximum revs in top
gear with a XE lump and a type 9 box i would think.
ATB
Locoboy
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stephen_gusterson
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| posted on 21/7/04 at 04:03 PM |
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max theoretical speed = gearing. max real speed also = air resistance, rolling resistance, and the size of your balls 
There is a spread sheet about for a type 9 box that allows you to enter these parameters and get speeds for each gear (theoretical)
anyone have a copy?
atb
steve
[Edited on 21/7/04 by stephen_gusterson]
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white130d
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| posted on 21/7/04 at 04:47 PM |
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Speed in gears
I have a great spreadsheet in excel, email me or u2u and I can send it to ya, or maybe tonight I caqn post it on my webpage and you can get it there,
just remeber, my tonight is 5 hours after your tonight....
and steve is right about the last part of the equation...ball size....
David
"There's only 2 things that money can't buy, and that's true love and home grown tomatos" Guy Clark
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ned
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| posted on 21/7/04 at 05:12 PM |
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get the speed calculator off quaife's site and search the web for type 9 gear ratio's (5th is 0.87 from memory). easy.
Ned.
beware, I've got yellow skin
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Dave Ashurst
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| posted on 21/7/04 at 06:57 PM |
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Try this attached excel file (thanks to Rob Lane I think). I put in ratios for ford type 9, 5 speed. (3.656, 1.97, 1.37, 1 and 0.82 to the best
of my knowledge - also very probably thanks to Rob Lane)
You need to input your tyre diameter (in inches) and diff ratio.
Note that the given terminal velocity assumes you have enough power at the wheels to match the wind resistance!
regards
Dave
[Edited on 21/7/04 by Dave Ashurst]
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stephen_gusterson
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| posted on 21/7/04 at 08:05 PM |
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thats the one I was referring to dave!
atb
steve
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Bob C
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| posted on 21/7/04 at 10:03 PM |
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You want to use a DOS program that was free on the web called (from memory) "cartest"
You tell it all sorts of stuff about the car & it tells you all sorts of stuff about its performance & simulates laps round various tracks.
Data input includes wheel size, frontal area, drag coeff, gear ratios, diff ratio etc. etc. + you can put in your engine power curve. Google should
find it....
cheers
bob
PS simple XL gear ratio calculator probably useless - if you can reach max revs in top your gearing is well screwed!- very much a sprint/trackday
special.
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white130d
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| posted on 22/7/04 at 01:29 AM |
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Try this one
Hopefully it will work.
Sort of like Dave's only different
David
[Edited on 22/7/04 by white130d]
"There's only 2 things that money can't buy, and that's true love and home grown tomatos" Guy Clark
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BMF
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| posted on 22/7/04 at 08:13 AM |
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According to the spreadsheet using 205/50/15 tyres I should get 148 mph at 6500 rpm!!!
Scary!!!!
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ned
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| posted on 22/7/04 at 08:37 AM |
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these things only work on mechanical garing, remember nothing is taken into account for air/wind resistance, rolling resistance etc. you need a lot of
power to pull much over 120-30mph i a 7 due to aerodynamics for example.
Ned.
beware, I've got yellow skin
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stephen_gusterson
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| posted on 22/7/04 at 09:49 AM |
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every 10 year old knows that the speed of a car is related to the max figure on the speedo.
Get a 220mph marked speedo and it will be a ferrari beater!
atb
steve
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Bob C
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| posted on 22/7/04 at 11:35 AM |
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Have you lads stopped wasting time with gear calculators & tried www.cartestsoftware.com
yet? Very comprehensive & seems to give the right answers with "normal" cars. Only problem with BECs is rev limit of 10000 - I had to
multiply torques & cc's by primary reduction ratio to get sensible answers (R1 BEC with 133bhp max speed 135, 0-60 in about 4).
We could have a virtual race series round nurnbergring if you want.......
Cheers
Bob
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