Date: Mon, 20 Jun 2005 17:58:11 -0700
Reply-To: Larry Chase <roadguy@ROADHAUS.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Larry Chase <roadguy@ROADHAUS.COM>
Subject: Re: Digest Number 2372
In-Reply-To: <d979p1+6mb2@eGroups.com>
Content-Type: text/plain; charset="us-ascii"
Damn it Al you sucked me in :)
OK ...
Original tires 185R14 / Dia = 25.5"
New tires 215/75R15 / Dia = 27.8 "
Differnce approx = 9.1726618705035971223021582733813%
So I guess the 9% seat of the pants estimate was pretty close.
Larry Chase
www.roadhaus.com
-----Original Message-----
From: notify@yahoogroups.com [mailto:notify@yahoogroups.com] On Behalf Of
lmfwric
Sent: Monday, June 20, 2005 1:43 PM
To: roadguy@roadhaus.com
Subject: Re: Digest Number 2372
It's a fizzix thing. If you consider that you need Y amount of
retarding force at the pavement to slow down your critter at some
desired rate R, a braking torque B is necessary to provide this
retarding force. Now the retarding force is ratio of the torque
times the rolling radius of the wheel. (lbs-ft/ft to give retarding
force in lbs). The larger the rolling radius, the less the
retarding force for a given braking torque. So if the larger brakes
provide 20% more braking torque and the increase in rolling radius
is 20% then the braking effect is the same as with the original
setup. If the increase in rolling radius is 10% then the braking
effect (retarding force) is increased by 10% with the larger brakes
and reduced by %10 if you retain the stock brakes.
Since the axles don't understand math, the same ratios apply for
acceleration. Increase the rolling radius by P% and the
acceleration will decrease by P%.
To maintain the same hillclimbing performance (vertical
acceleration) with the new wheels, you will have to modify the
powerplant to produce more torque at the axle. Changing the final
drive ratio appropriately will do this. Installing a better motor
will also do this. Combining the two will give the maximum
benefit. Say, 200+ lbs-ft across the 1500-6000 rpm range, should do
it nicely. Couple with a slight overdrive 0.77 4th and the stock
4.86 R&P and you have a nicely workable system. Changing both front
and rear R&P can net you a lower crawling gear for those who need
that.
All cost money, choose wisely.
>
> I have gone thru a similar progression.
>
> Stock Motor to a higher compression and slightly more powerful
engine (2.2L
> equilivant)
>
> Stock 14" tires and alloys to 15" SA VW Alloys and Michelin LTX
and now BGF TA
> 215/75R15 tires.
>
> Stock brakes to SA Big Brake Kit.
>
> The engine will def work harder getting the larger tire up to
speed. Acceleration
> off the line will be th most impacted .. perhaps as much as 9-10%
change
>
> Once you are tooling down the road ... all is good.
>
> The big brake kits do make a diff, a bit of a subtle diff ... but
a diff and I'd
> recomend them.
>
> Today I've had to go backwards on the engine displacement and I'm
running a weak
> stock 2.1L waterboxer.
>
> The larger / heavier tires are more of an impact ... obviously.
>
> I generally don't that people change to 15" tires unless they are
upgrading the
> engine.
>
>
> larry chase
> roadhaus.com
>
> ---
>
> Message: 2
> Date: Mon, 20 Jun 2005 04:14:29 -0000
> From: "mike_kunka" mike_kunka@y...>
> Subject: big brakes, tires and wheels worth it?
>
> I'm hoping someone who has done the sa brake upgrade and bigger
wheels and tires
> can
> answer this. If the added weight of the tires and wheels makes a
stronger motor
> feel
> stock, does it also make the bigger brakes feel like stock brakes?
I've just put a
> gowesty
> 2.4 in my van (non-camper), and was planning on going for the
brakes, 15" wheels
> and
> 215/75/14 t/a ko tires, but reading the list it sounds like maybe
they will all
> cancel each
> other out.
> thanks!
