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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
Comments: To: lmfwric <al_knoll@pacbell.net>
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!


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