Ned.
Rescued attachment IMG_2155b.jpg
can anybody tell me what is the lowest profile tyre you can get to fit a 14" wheel on an mk indy?
cheers des
quote:
Originally posted by desyboy
can anybody tell me what is the lowest profile tyre you can get to fit a 14" wheel on an mk indy?
cheers des
quote:
Originally posted by desyboy
can anybody tell me what is the lowest profile tyre you can get to fit a 14" wheel on an mk indy?
cheers des
yes if there is a tyre lower
As BritishTrident asked, why? Low profile = stiff sidewall = crap handling (in context). It may also screw your gearing and the wheels will look a bit lost in the arches Id think
195/40-14"
But on my car that currently runs 205/60 13" for example, that would take my top speed down from 125mph to 111mph!
here are some 195/45 14's on some pug 106 rallye rims to give perspective. you really don't want to do this on a seven type car.
Ned.
Rescued attachment IMG_2155b.jpg
i want to make the rolling diameter smaller so i have a faster pull away and more acceleration on the 1/4 mile strip.
The 195x40x14 are what make?
Cheers Des
say again, you want low profile tyres for 1/4 mile performance?
Now its too late at night to proove it mathematically with differentiation but you'd be better off with the big sticky tyres.
Otherwise trade your indy in for a hot rod, 5l V8 and these tyres would do the job...
Smaller rolling diameter means less traction. squishy side wall keeps more tread rubber in contact with the road.
Also you have to consider the effect of the speed your gear changes happen at.
You might want to look at using 13" wheels -- using a suitable (ie thin) rim 13" might clear your rear brakes and upright.
With 195/40 13s and the 3.92 diff you mentioned in u2u, you'll top out at around 100mph flat out, which is nowhere near enough for a standing
quarter in an R1 BEC. Ive done a few runs in mine on less than ideal tarmac and was managing a 110mph terminal speed, so you'd spend the last 2-3
seconds on the limiter losing any advantage you gained.
The gain will be minimal anyway, I used to have a 3.9 diff in mine and although it felt a bit quicker, in reality against a friend's car it was
no different, because you're just changing gear more often it gives the impression of going quicker but I guess you gain in gear but lose out
because of more gearchanges.
quote:
Originally posted by desyboy
The 195x40x14 are what make?
Cheers Des
Desyboy,
Buy some 13's! (cxr's should fit over sierra rear calipers) then buy some part worn acb10's off me - should be ideal for getting the
power down up the strip! I've got 195 or 215's which should be just the job
Ned.
The attached graph is MPH vs time for my BEC with a 3.62 diff and a 3.92 diff. The 3.92 is faster off the mark and is faster in each gear, but you
have to shift into higher gears sooner.
the 3.62 does the 1/4 mile in 12.37s at 114 MPH (predicted)
the 3.92 does the 1/4 mile in 12.33s at 112 MPH
smaller wheels and a 3.92 diff would bring the time and terminal speed down a bit more
Rescued attachment accel.JPG
This graph is less clear. It shows that the 3,92 diffed car builds up a 2.25m lead by about 85 MPH that declines to 1.7m by the 1/4 mile. In a drag
race, you'd win.
0-60 would be 2/10ths faster.
Rescued attachment accel.JPG
can anybody tell me what top speed would i get from a 3 .62 diff and 195x40x14 in a r1indy
I may be mistaken, but all the above seems to assume perfect traction......
Even on dry tarmac you probably won't get that.
So the mechanical advantage of the lower gearing at low speeds is probably only theoretical.....
Bob
It looks like ill have to load excel on to my laptop and use chris gamlins gear ratio calculator as nobody has come up with an answer to my question :
can anybody tell me what top speed would i get from a 3 .62 diff and 195x40x14 in a r1indy ?
Cheers Des
[Edited on 26/8/07 by desyboy]
Looks like your top speed will be about 109mph, which would probably mean you'll be crossing the quarter mile line in sixth gear on 195x40x14s.
Using a 15" wheel and 50 profile tyres, will mean one less gear change and you'll cross the line in fifth.
It's all about traction on the drag strip, so get some sticky tyres and drop the rear pressure to around 10psi
Phil