Date: Wed, 22 May 2013 20:59:08 -0400
Reply-To: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject: Re: 14" to 16" Wheel Upgrade User Input Please.
In-Reply-To: <184240845.170714.1369247607109.JavaMail.root@sz0171a.emeryville.ca.mail.comcast.net>
Content-Type: text/plain; charset="utf-8"
A larger diameter tire affects braking the same as a longer handle on a wrench affects the amount of torque you can put on a fastener. Also there is more weight at the outer circumference so inertia is also an issue. Consider the radius as the length of the wrench. This also has an effect on acceleration. In effect you are changing the gear ratio. From experience my suggestion with stock engine and transmission 26.5 to 27 inch diameter is the maximum before drivability can be a problem. This is counter intuitive but while larger tire increase the distance per revolution (lower RPM at a given speed) the engine cannot make as much horsepower at the lower speed so it cannot overcome the wind resistance. Syncros and automatics are particularly sensitive to this effect. As I now have 235/55-17's on Fun Bus it is now difficult to break 75. Even accelerating from 60 to 70 takes some time. I know it doesn't help that the engine has 256K on it. Last time I put the 215/70-14 on it for comparison it can easily get to and go over 80 although the speedometer is somewhat optimistic with those tires.
Dennis
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Todd Last
Sent: Wednesday, May 22, 2013 2:33 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: 14" to 16" Wheel Upgrade User Input Please.
Could someone explain the physics of why a larger wheel would affect braking?
Is this simply because of a change in the contact patch of the tire?
Todd
'88 Westy
----- Original Message -----
From: "mark drillock" <mdrillock@COX.NET>
To: vanagon@GERRY.VANAGON.COM
Sent: Wednesday, May 22, 2013 10:14:25 AM
Subject: Re: 14" to 16" Wheel Upgrade User Input Please.
Obviously larger diameter tires affect the braking somewhat. I have 5 vans with 15" and 16" tires that are all substantially larger than stock diameter and yet I have all stock brakes. The key thing is they are all
86+ front brakes and I keep the full braking systems in good working
order. GOOD WORKING ORDER, that is the key. The rears are very important in that regard, they need service.
I did recently put a larger brake booster in one of them and that made a big difference in brake feel though it doesn't improve braking capacity.
Mark
Don Hanson wrote:
> Semi-thread jack, but
>
> what kind of effect have you wheel swappers felt on braking?
> Seems to me that increasing the diameter and rolling circumference of
> the wheels without increasing the brake's size...that would result in
> noticeable reduction in actual braking force...eh? I know the effect
> is dramatic when done the other way....increase the brake disc's
> diameter and the braking forces are enhanced...
> Curious, because Vanagons are somewhat under equipped with brakes
> from the factory
>
>
>